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Hofer ct teaching manual - a systematic approach to ct reading, 2nd ed.

M
Michel Phuong

This document provides an overview of computed tomography (CT) scanning. It discusses the general principles of how CT works, including how x-rays pass through the body and are measured by detectors. It compares conventional CT, which acquires images sequentially, to spiral CT, which acquires a continuous stream of data as the patient passes through the scanner. Spiral CT can image areas more quickly and is better for assessing contrast enhancement. The document also discusses technical aspects like spatial resolution, reconstruction algorithms, and multi-detector CT systems.

Healthcare
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Matthias Hofer Second edition
Hofer ct teaching manual - a systematic approach to ct reading, 2nd ed.
4 Notes for theUser, "What you should know" Front Cover Flap I Keyto AnatomicStructures on pages 26-73, 152/153 (head / neck) Front Cover Flap Normal Anatomyof the Petrous Bone (Coronal andAxial) 46 Normal Variantsof the Cranium 50 Typical Partial Volume Phenomenaof theCranium 52 Notes for theUser, List of theCT diagrams Foreword andList of Abbreviations Physical andTechnical Fundamentals General Principles of CT Comparison of Conventional CTwith SpiralCT Spatial Resolution, Pitch Section Collimation:Resolution alongthe Z-axis Adaptive Detector Design ReconstructionAlgorithms Effects ofkV, mAs and ScanTime Three-dimensional Reconstruction Methods: Maximum Intensity Projection(MIP) Multiplanar Reconstruction(MPR) SurfaceRendering Cerebral CT, Pathologic Findings Intracranial Bleeds Cerebral Infarcts 3 Cerebral Tumors and Metastases InflammatoryProcesses Orbital Changes 6 Changes of the Facial Bones andParanasal Sinuses 7 8 NeckCT 9 Selection of theImagePlane 10 Checkiist for a SystemicApproach 11 Normal Anatomy ofthe Neck 12 13 Neck CT, Pathologic Changes Inflammatory Processes andTumors Thyroid Gland Test yourselfl 54 58 59 60 61 62 64 64 65 70 71 72 it (Axial) - Bones (Coronal) Chest CT Selection of theImage Plane 74 SystemicSequential Approach to Interpretation Checklist for Interpreting Chest CT 74 Normal Anatomy ofthe Chest 75 Test yourself! 82 Chest CT, Pathologic Changes Anatomy of thePulmonary Segments 84 HRCT ofthe Lungs:Technique, Effects, Indications 86 AnatomicVariants of theChest 88 Chest Wall Abnormal Lymph Nodes 89 Breast, BonyThorax 90 Mediastinum TumorMasses 91 Enlarged Lymph Nodes 92 Vascular Pathology 93 Heart 94 Lung Intrapulmonary Nodules 95 Bronchial Carcinoma, Malignant Lymphangiomatosis 96 Sarcoidosis,Tuberculosis,Aspergillosis 97 Pleural Changes,Asbestosis 98 Silicosis, Pulmonary Emphysema 99 Interstitial Pulmonary Fibrosis 100 Test yourselfl 100 Abdomen CT Selection of the ImagePlane 102 Systemic Sequential Approach toInterpretation Checklist for InterpretingAbdomen CT 10, NormalAnatomy oftheAbdomen 104 Normal Anatomy of the Pelvis (Male) 11, Normal Anatomy of the Pelvis (Female) 114 Back Cover FlapKey to Anatomic Structures on pages 71, 74-1 49 (thorax / abdomen) 15 18 14 16 17 21 24 25 20 26 26 19 27 32 33 41 45 Basic Rules for Reading CT Examinations Anatomic Drientation Partial Volume Effects Distinguishing Nodular from TubularStructures Densitometry DensityLevels of DifferentTIssues Documentation Using Different Window Settings Administration of Contrast Agents OralAdministrationof ContrastAgents Selection oftheAppropriate Contrast Agents Duration and Dose In avenous Injection of Contrast Agents In avenousAccess :l1ilo'o Effect of Contrast Agents ~""re . 8 Reaction to Contrast Agents andTheir Therapy - ayro;o · Crisis and itsTherapy Preparing the Patient Medical History Renal Function Hyperthyroidism Adverse Reaction to Contrast Agents Premedication OralAdministration of Contrast Agents Informing the Patient Removal of Foreign Objects Controlling Respiration ......,,,,,,,1 CT s.= ec OJ ' ImagePlane '3 _-=- ~:'O 02 toInterpretation Cranial CT
Table of Contents Abdomen CT, Pathologic Changes Spine AnatomicVariants oftheAbdomen 116 Cervical Spine (C-spine) 152 Typical Partial Volume Phenomena C-Spine, Disk Prolapse and Fractures 153 Abdominal Wall Thoracic Spine (T-spine): 15t Enlarged Lymph Nodes,Abscesses 117 Normal Findings and Fracture Subcutaneous Heparin Injections 118 Lumbar Spine (L-spine): 155 Abdominal Wall Metastases Normal Findings and Lumbar Disk Prolapse Inguinal Hernias L-spine, Fractures 156 liver L-spine,Tumors/ Metastases 157 Anatomy ofthe HepaticSegments 119 L-spine, Inflammations/ Internal Fixation 158 Examination Protocols 120 Selection ofWindow Display Lower Extremity Bolus Passageof Contrast Agents NormalAnatomyof theThigh 159 CTPortography NormalAnatomyoftheKnee 160 Hepatic Cysts 121 NormalAnatomyoftheCalf 161 Hepatic Metastases 122 NormalAnatomyoftheFoot 162 Solid Hepatic Lesions: 123 Fractures ofthe Foot 163 Hemangioma PelvisandThigh: Inflammatory Processes 166 Adenoma Knee, Fractures, ChecklistFracture Diagnosis 167 Focal NodularHyperplasia DiffuseHepatic Changes: 124 CT-guidedInterventions 168 Fatty Liver Hemochromatosis Examination Protocols for Spinal CT 169 Cirrhosis BiliarySystem Radiation Protection Pneumobilia 124 Radiation Dose / Cancer Risk 174 Cholestasis AutomatedBolusTracking (BT) 176 Gallbladder Tube Current Modulation 177 Cholecystolithiasis 124 Chronic Inflammatory Processes 125 CT-Angiography Spleen Intracranial Arteries 178 Enhancement,Splenomegaly 126 Cranial Dural VenousSinus 179 FocalSplenic Changes 127 CarotidArteries 180 Pancreas Aorta 182 Acute and Chronic Pancreatitis 128 Heart: CoronaryArteries, 184 Pancreas Neoplasms Screening for Coronary Adrenal Glands Artery Calcifications Hyperplasia,Adenomas, Metastases, Neoplasm 130 Pulmonary Vasculature (Pulmonary Emboli) 186 Kidneys Abdominal Vasculature 187 Congenital Variants 132 Iliofemoral Vasculature 188 Cysts, Hydronephrosis 133 VascularProtheses, Outlook 189 SolidTumors 134 TestYourself! 190 VascularRenal Changes 135 Urinary Bladder The Fundamentals of Interpreting CT 192 Indwelling Catheter, Diverticula, SolidLesions 136 Genital Organs Answers to Test Yourself 196 Uterus 137 Ovaries, Prostate Gland,Vas Deferens 138 Index 203 Gastrointestinal Tract Stomach 139 References Back Cover Flap Inflammatory Bowel Diseases 139 Colon 140 Key to Anatomic Structures Back Cover Flap Ileus 141 on pages 152-167 (spine / leg) Test Yourself! 141 Retroperitoneum Key to Anatomic Structures Back Cover Flap Aneurysms 142 on pages 71 ,74-149 (thorax / abdomen) VenousThromboses 143 Enlarged Lymph Nodes 144 Skeletal Changes Bony Pelvis: Normal Findings, Metastases 145 Fractures 147 Hip Dysplasia, Necrosis of the Femoral Head 148 Test Yourself! 149 5
6 Physical and Technical Fundamentals General Principles of CT Computed tomography is a special type of x-ray procedure that involves the indirect measurementof theweakening, or attenua- tion, of x-rays at numerous positions located around the patient being investigated. Basically speaking, allwe knowis • what leaves thex-ray tube, • what arrives at the detectorand • the position of thex-ray tubeand detectorforeach position. Simply stated, everything else is deduced from this information. Most CT slices are oriented vertical to the body's axis. They are usually called axial or transverse sections. For each section the x-ray tube rotates around the patient to obtain a preselected section thickness (Fig. 6.1). Most CT systems employ the continuous rotation and fan beam design: with this design, the x-ray tube and detector are rigidlycoupled and rotate continuous- ly around the scan field while x-rays are emitted and detected. Thus,thex-rays, whichhavepassed through thepatient, reach the detectors on the opposite side of thetube.The fan beam opening ranges from 40° to 60°, depending on the particular system design, and is defined bythe angle originating at the focusof the x-raytube and extending to theouter limits ofthe detectorarray. Typically, images are produced for each 360° rotation, permitting a high numberofmeasurement data to beacquired and sufficient doseto beapplied.Whilethescanis being performed, attenuation profiles, also referred to as samples or projections, are obtained. Attenuation profiles arereallynothing otherthan acollectionofthe signals obtained from allthedetector channels at a given angular position of the tube-detector unit. Modern CT systems (Fig. 6.4) acquire approximately 1400 projections over 360°, or about four projections per degree. Each attenuation profile comprises the data obtained from about 1500 detector channels, about 30 channels perdegree in case ofa 50° fan beam.While the patient table is moving continuously through the gantry, a digital radio- graph ("scanogramm" or "localizer", Fig. 6.2) is produced on which the desired sections can be planned. For a CT examination of the spine or the head, the gantry is angled to the optimal orientation (Fig. 6.3). Fig. 6.1 Table movement Fig.6.2 Angulnlion Gantry •o « ~ ...~ Fig.6.3 I Fig.6.4 " Multiple-Row Detector Spiral CT Multiple-row detector CT (MOCn is the latest scanner develop- ment. Rather than one detector row, multiple detector rows are placed oppositethe x-ray tube.Thisshortens theexamination time and improves the temporal resolution, allowing, for instance, the determinationof therate of vascular enhancement. The detector rows along the z-axis opposite the x-ray tube are unequal inwidth,with theouter rows wider than theinner rows to provide better conditions for image reconstruction affer data acquisition(see pages 9-11).
Physical and Technical Fundamentals 7 Comparison of ConventionalCT with Spiral CT In conventional CT, a series of equallyspaced images is acquired sequentially through a specific region, e.g. the abdomen or the head (Fig. 7.1).There is a short pause after each section in order toadvance the patient table tothe nextpreset position.Thesection thickness and overlap/intersection gap are selected at Iheoutset. The raw data for each image level is stored separately. The short pause between sections allows the conscious patient to breathe without causing major respiratory artifacts. However,theexaminationmaytakeseveral minutes,depending on the bodyregion and the size of the patient. Proper timingof image acquisition after Lv. contrast media is particularly important for assessing perfusion effects. CT is the technique of choice for acquiring complete 20 axial images of the body without the disadvantages of superimposed bone and / or air as seen in conventional x-ray images. Step-w ise table movement Fig. 7.1 Gantry x-ray tube Imaging volume " --.~,,- Continuous tab le movem ent Fig.7.2 /. X-ray lube ~ Rotat ion Both single-row detectorCT(SOCT) and multiple-row detector CT (MOCl) continuously acquire data of the patient while the examination table moves through the gantry. The x-ray tube describes an apparent helical path around thepatient (Fig. 7.2). If table advance is coordinated with the time required for a 360' rotation (pitch factor), data acquisition is complete and uninter- rupted. This modern technique has greatly improved CT because respiratory artifacts and inconsistencies do notaffect the single dataset asmarkedlyasinconventional CT. Thesingledataset can be used to reconstruct slices of differing thickness or at differing intervals. Even overlapping slices can be reconstructed. Data acquisition fortheabdomen takes only 1-2 minutes: two or three helices,eachabout 10to20seconds,are obtained.Thetime limit is determined by the duration a patient can hold his breath andthenecessarycoolingof thex-raytubes.Image reconstruction takes longer. An assessment of renal function following CM will requirea shortbreak toallowfor CM excretionto occur. One of the advantages of the helical technique is that lesions smallerthantheconventional thicknessofaslice canbedetected. Small liver metastases (7) will be missed if inconsistent depth of Fig.7.3a Conventional CT respiration results in them notbeing included in the section (Fig. 7.3a). The metastases would appear in overlapping reconstruc- tionsfrom thedataset of the helical technique (Fig. 7.3b). - ---- - - ------- -- -- 5 Fig.7.3b Spiral CT
8 Physical and Technical Fundamentals Spatial Resolution The reconstructed images shouldhavea high temporal resolution to separate even small structures from each other. This generally creates no problem along thex- ory-axis of the image since the selected field of view (FOV) typically encompasses 512 x 512 or morepicture elements (pixel).These pixels appear on the monitor as grey values proportionate to their attenuation (Fig. 8.1b). In reality, however, they are not squares but cubes (voxel = volume element) with their length along the body axis defined by the section thickness (Fig. 8.1 a). Fig.8.1a Fig.8.1b ~" .: / '/ r-, 1 I 'I ' i 129'" 122 J.. 50 l- 1 1,3~ 7 7';;::V <, v:r.:::v The imagequalityshouldimprovewithsmaller voxels, but thisonly applies to thespatial resolution since athinnersection lowers the signal-to-noise ratio. Another disadvantage of thinnersections is the inevitable increase in the radiation dose to the patient (see page 175). Nonetheless, smaller voxels with identical measure- ments in all three dimensions (isotropic voxels) offer a crucial Fig.8.2 MPRfrom isotropic voxels Pitch By now,several definitionsexistforthe pitch, which describes the rate of table increment per rotation in millimeter and section thickness. A slowly moving table per rotation generates a tight acquisition spiral (Fig. 8.4a). Increasing the table increment per rotation without changing section thickness or rotation speed creates interscan spaces oftheacquisition spiral (Fig.8.4b). The mostly used definition of the pitch describes the table travel (feed) per gantry rotation, expressed in millimeters, and selected collimation,alsoexpressed in millimeters. advantage: The multiplanar reconstruction (MPR) in coronal, sagittal or other planes displays the reconstructed images free of any step-like contour (Fig. 8.2). Using voxels of unequal dimen- sion (anisotropic voxels) for MPR is burdened by a serrated appearance of the reconstructed images (Fig. 8.3), which, for instance, can make it difficultto exclude afracture (Fig.148.5b). Fig. 8.3 MPR from anisotropic voxels Pitch= 1 Pitch = 2 mn ~Fig. 8.4 a b Tabletravel /rotation Pitch = Collimation
Physical and Technical Fundamentals 9 Pitch = Feed! rotation Collimation e.g.: 24mm ! rotation 16x 1.5 mm 24mm = - - = 1 24mm Sincetheunits(mm) inthe numeratoranddenominatorcancelout, the pitch is a dimensionless number. For a while, a so-called volume pitch was stated for multiple-row detector CT scanners, which relates the tablefeed to a single section rather than tothe entire array of sections along the z-axis. For the example given above, this means a volume pitch of 24 mm ! 1.5 mm = 16. However, there seems to be a trend to returning to the original definition ofthepitch. Section Collimation: Resolution Along the Z-Axis The resolution (along the body axis or z-axis) of the images can also be adapted tothe particular clinical question bythechoice of thecollimation.Sections between 5and 8 mm generallyaretotal- ly adequatefor standard examinationsof theabdomen. However, the exact localization of smallfracturefragmentsortheevaluation of subtle pulmonarychanges require thin slices between 0.5 and 2mm.What determines thesection thickness? The term collimation describes how thin or thick the acquired slices can bepreselected along the longitudinalaxisofthepatient _ x-ray tube Collimator Q" "[ >- 1, 1 I'l l" I II I I I I I / I I I J I I , I I I I I I I J I I ', I I I / : : : ~ , ::t:tl:L'I , , , I 1 ICollimator I, ! ! I , II 1 • •z-axis Fig,9.1 Wide sectioncollimation Depending on thewidthof collimator's aperture,theunitswithonly one detector row behindthe patient (single section) can generate sections withawidthof 10 mm,8 mm, 5 mm oreven1 mm.ACT examination obtained withverythin sections is also called a high resolution CT(HRCT) and, if the sections areat thesub-millimeter level, ultra high resolution CT (UHRCn .The UHRCT is used for the The new scanners give the examiner the option to select e craniocaudalextension(z-axis) ofthe region tobe examinedon e topogram as well as the rotationtime, section collimation (thin or thick sections?) and examinationtime (breath-holding intervals?). The software, e.g., "SureView®," calculates the suitable pitch, usually providing valuesbetween 0.5 and 2.0. (= z-axis),The examiner can limit thefan-like x-ray beam emitted from the x-ray tube by a collimator, whereby the collimator's aperture determineswhether the fanpassing throughthecollima- torand collected bythe detectorunits behindthepatient iseither wide(Fig.9.1)ornarrow(Fig.9.2), withthenarrowbeam allowing a better spatial resolution along the z-axis of the patient. The collimator cannot onlybe placed next tothex-ray tube, butalsoin front of the detectors, i.e., "behind" the patient as seen fromthe x-ray source. Collimator ?- _ x-raytube "(" J,t, --.. 1,,1,1...- I "." 1' " . I : I ~ , I .I 1 ,:I: I I I • I : I ~ , ': I , I , , , : I , I , I , I , , ,:, ';; ~::=::t11~~ - , ...! -....1: ! ,1.....-- I Ir c' ,ijB,. . • •z-axrs Fig.9.2Narrow sectioncollimation petrous bone with about 0.5 mm sections to detect delicate fracture lines through the cranial base or auditory ossicles in the tympanic cavity (see pages 46 - 49). For the liver, however, the examination is dominated by the contrast resolution since the question here is the detectability of hepatic metastases (here somewhat thicker sections).
10 Physical and Technical Fundamentals Adaptive Array Design A further development of the single-slice spiral technology is the introduction of the multislice technique, which has not one detector rows but several detector rows stacked perpendicular to the z-axis opposite the x-ray source. This enables the simul- taneous acquisition ofseveral sections. The detector rows are not inevitably equal in width.The adaptive array design consists ofdetectors that increase inwidth from the center to the edge of the detector ring and consequently allows various combinations of thickness and numbers of acquired sections. Adaptive detector design 4-row unit Variable section thickness ++++ ~~ 17mwl I !4 x5.0 mm 4 x2.5 mm 4x 1.0 mm 2 x8.0 mm 2 x0.5 mm ,,,, I I I I I I I I I I I I Resolutionalong the z-axis adaptable toclinical Question / Detectors / , ,, I I I ,/ ,/ , , I I I I ,:> / , , , I I I , 0 / , I I I I, I , U, , , , , I , es , '2 5 i j;j ; " I" 2 5 , u / 5 5 , z-axisco / I , - " " I ' ' ,/ , I I I ', , / , I I , / , " I I I , Fig. 10.1 Detectordesignof a4-row unit, as foundintheSiemensSensation4 Adaptive detector design 6-row unit Variable section thickness Collimator 6 x0.5 mm 6 x 3.0 mm 6 x 2.0 mm 6 x 1.0 mm z-ans ,,,, I I ,, I I 1/ J I II I I I "11' 1111 I I ' " I I I I I / Detectors / " " I /l1I1l1I -, .. I I ,,111111 ' e; / I I I 11/11111 " U, L ---:;~/.~!:;:'~/::'!!:~~~~,.':'~':;:::':JI.'__- - - __:_.i l ' . .~ .~ /3' 2, ill 11 2 3 ....~ / J J I "" " , ' I ... / " / I 1/1 J I 1 ' 1 " .. 11 11 1 1 111 11 Resolutionalong thez-axls adaptabletoclinical Question Fig. 10.2Detector design ofa6-rowunit,asfound inthe Siemens Emotion6
Physical and Technical Fundamentals 11 For instance, a 16-slice examination can be performed with 16 thin sectionsof a higher resolution (for theSiemensSensation 16, this means16 x0.75 mm) or with 16 sections oftwicethe thickness. For aniliofemoral CTA (seepage 188), it ispreferabletoacquireaiong volumealong thez-axis inasinglerun,of coursewithaselected wide collimationof 16 x 1.5mm. Adaptive detector design 16-row unit Variable section thickness 16x 1.5 mm x-ray tubeCollimator I I . ' / // / II I I Jl l 1 Detectors ' 1 1 1 11 1 1 1 1 1 ' " . I ( 11/ 1 1111 11 11 _____ /11 I ' ~ _ ~ II. ,,, ,f:/, ~~~" III/ I , ~-----A(-If;i ~A----- /~II I '/J/f/rlll' ~ ~ II ' ,'",1/1111 11 ' > 1111111 1 11l 1l1l 1 ~ o 1 1 / " /," "11111 ' " ~ f-------,1I'••' ." " "," •.••:.' f:----...(1; / , I I • '.' • " ' ' H. I / 1 5 I I f I I I I Q75 1 5 z-axis V~ / / . ' I I I I I I I ' , ' /1 1/ 1 I I IIIJIII I I I I 1 / 1 11 1,'111 1 Resolution along the z-axis adaptable toclinical question Fig.l1.1 Detectordesignof a16-rowunit,as found intheSiemens Sensation 16 The development ofthe CT hardwaredidnot endwith 16slices and fasterdataacquisitioncan already be achieved with32- and 64-row scanners.Thetrend tothinner slices is associatedwith higher patient exposure to radiation,requiring additional and alreadyintroduced measures for exposure reduction(seepages 174-177). measured data table positio n slice Fig. 11.2 Wide (360°) spiral reconstruction algorithm selecting high rnA values, increase the spatial resolution (image sharpness) byreducingslice thickness, and employ pitch toadjust the length of the spiral range as desired, all while reducing the patient's dose! Moreslices can be acquiredwithout increasingthe dose orstressing the x-ray tube. This technique is especially helpful when dataare reformatted to create other 2D views, like sagittal, oblique, coronal, or 3D views (MIP, surface shaded imaging,see pp.8 and 13). ReconstructionAlgorithm Spiral users have an additional advantage: In the spiral image reconstruction process, most of the data pointswere not actually measured in the particular slice being reconstructed (Fig. 11.2). Instead, data are acquired outside this slice (e ) and interpolated withmoreimportance,or "contibutinn",beingattached tothedata located closest to the slice (X). In other words: The data point closest to theslice receives more weight, orcounts more, in the reconstruction of an image at thedesired table position. When both liver and pancreas are included, many users prefer a reduced slice thickness from 10 mm to 3 mm to improve image sharpness. This increases, however, the noise level by approxi- mateiy 80%.Thereforeitwouldbenecessarytoemploy80%more rnA orto lengthen the scan time (this increases the mAs product) to maintain imagequality. This results in an interesting phenomenon. The patient dose (actually given in mGy) is determined by the mAs per rotation divided by thepitch,and the image dose is equal to themAs per rotationwithout considering the pitch. Iffor instance 150mAs per rotationwitha pitchof 1.5 are employed,the patient dose in mGy is linear related to 100mAs, andthe imagedose is related to 150 mAs. Thereforespiral users can improve contrast detectability by
12 Physical and Technical Fundamentals Thedataobtained atthedetectorchannel are passedon, profilefor profile,tothedetectorelectronics aselectricsignalscorresponding totheactual x-ray attenuation.Theseelectric signals are digitized and then transmitted to the image processor. At this stage, the images are reconstructed by means of the "pipeline principle", consisting of preprocessing, convolution, and back projection (Fig.12.1). Preprocessing includes all the corrections taken to prepare the measured scan data for reconstruction, e.q., correction for dark current, dose output, calibration, channel correction, beam hardening,and spacing errors.Thesecorrections are pertormed to further minimize the slight variationsinherently found inthetube anddetector components of theimagingchain. Convolution is basically the use of negative values to correct for smearing inherent to simple back projecfion. II, for instance, a cylindric water phantom is scanned and reconstructed without convolution, the edges of this phantom will be extremely blurry (Fig. 12.2a): What happens whenjusteight attenuation profiles of a small, highly absorbent cylindrical object are superimposed to create an image? Since the same part of the cylinder is measured by two overlapping projections, a star-shaped image is produced instead of what is in reality a cylinder. By introducing negative values justbeyond thepositive portion of theattenuation profiles, theedges of this cylinder can be sharply depicted (Fig, 12.2b). Back projection involves the reassigning of the convolved scan data to a 20 image matrix representing the section of thepatient that is scanned.This is pertormed profile for profile for the entire image reconstructionprocess.The image matrixcan bethought of asanalogoustoachessboard,consisting oftypically 512x512 or 1024 x 1024 picture elements, usually called "pixels". Back projection resuits in an exact density being assigned to each of thesepixels,which are then displayed asalighter ordarker shade of gray Thelighter the shade of gray,the higher thedensityofthe tissue within thepixel (e.g., bone). ~ - - - - - - - - -- - - - - - - - -- - - - - - - - -,, , -+0 -0 -0+0, , Data acquisition system Preprocessing Convolution Back projection : Image display ----------------------------- The Influence of kV When examining anatomic regions withhigher absorption (e.g., CT of thehead,shoulders,thoracic or lumbar spine, pelvis,and larger patients), it isoftenadvisable touse higher kV levelsinaddition to, or instead of, highermA values: when you choose higher kV, you are hardening the x-ray beam.Thusx-rays canpenetrate anatomic regions with higher absorption more easily. As a positive side effect, the lowerenergy components oftheradiation are reduced, whiCh is desirable since low energy x-rays are absorbed by the patient and donot contribute to the image. For imaging of infants or bolustracking, it may beadvisableto utilize kV lower than the standard setting. Tube Current [mAs] The tubecurrent,stated in milliampere-seconds [mAs], also has a significant effect onthe radiation dose deliveredto the patient.A patient with more body Width requires an increase in the tube currentto achieve an adequateimage quality. Thus, morecorpulent patients receive a larger radiationdose than,for instance,chiidren witha markedly smaller body width. Body regions with skeletal structures thatabsorborscatter radia- tion, such as shoulder and pelvts, require a higher tube current than,forinstance, theneck, aslender abdominal torso or thelegs. This relationshiphas been actively applied to radiation protection for some time now (compare with page 177).. Scan Time It is advantageous to select a scan time as short as possible, particularly in abdominal or chest studies where heart movement and peristalsis may degrade imagequality.Other CTinvestigations can also benefit fromlastscan times due todecreased probability of involuntary patient motion. Onthe other hand, it may be neces- sary to selecta longer scan time to provide sufficient dose or to enable more samples for maximal spatial resolution. Some users may also consciously choose longer scan times to lower the mA settingand thus increase the likelihood of longer x-ray tube life. Simple Back Projection vs. Convolution b Fig. 12,1 The pipelineprincipleof image reconstruction Fig. 12.2a Back projection without convolution Fig. 12.2b Back projection with convolution
Physical and Technical Fundamentals 13 3D Reconstructions 3ecause the helical or spiral technique acquires a continuous, sirlgle volume dataset for an entire body region, imaging of , actures and blood vessels has Improved markedly, Several c' erent methods of 3Dreconstruction havebecome established: aximal lntensily Projection IP is a mathematical method thatextracts hyperintense voxels , am 20 or 3D datasets [6, 7], These voxels are selected from several different angies through the dataset and then projected as a20image(Fig, 13.1),A3D impression isacquired byaltering the projectionangle insmall steps and then viewing the reconstructed images in quick succession (I.e" in cine mode).This procedure is also usedfor examining contrast-enhanced bloodvessels. Fig. 13.1 Frontal project ion 4I I I r: O rigina l dataset of axial sections Lateral projection Multiplanar Reconstruction This technique makes it possibieto reconstruct coronal and sagittal as well asoblique planes,MPR has becomea valuable tool in the diagnosis offractures and other ortho- pedic indications, For example, conventional axial sections do not always provide enough information about fractures, A good example is the undispiaced hairline frac- ture(* )without cortical discontinuitythat canbe moreeffectivelydemonstrated byMPR {Fig,13.2a), Fig.13,2a 3D Surface Shaded Display Thismethod shows the surface ofan organ ora bone that has been defined in Houns- ~eld units abovea particularthreshold value,The angleofview,aswell asthe location a a hypothetical source of light (from which the computer calculates shadowing) are crucial for obtaining optimal reconstructions.Thefractureofthe distal radius shown in e MPRin Figure 13.2a isseen clearly inthe bone surface inFigure 13.2b. Figs. 13,2a and 13.2b supplied withthekind permission ofJ, Brackins Romero, M, 0" Recklinghausen, Germany) Fig.13.2b * 3D surface shaded displays are also valuable in planning surgery as in the case ofthe traumatic injury to the spinal column seen in Figures 13.3 a,b, and c. Since the angle of view can befreely determined, the thoracic compression fracture( *) and thestateofthe intervertebral foraminacan be examined from several different angles (anterior inFig. 13.3a and lateral inFig. 13.3b),The sagittal MPR in Figure 13.3c determines whether any bonefragments have become dislocated intothespinal canal (compare withmyelography CT onpage147). Fig. 13.3c • Fig. 13,3bFig. 13.3a
14 , Basic Rules of Reading CT Examinations I Rotation Detector x-ray tube II 50 Image level 122 Fig. 14.1 Anatomic Orientation An image on the display is not only a 20 representation of anatomy, it contains information about the mean attenuation of tissue in a matrix consisting of about 512 x 51 2 elements (pixels). A section (Fig. 14.1) has a defined thickness (dS) and is composed of a matrix of cubic or cuboid units (voxels) of identical size. Thistechnical aspect isthe reason forthe partial volumeeffectsexplainedbelow.An imageis usually displayed asif the body were viewed from caudal. Thus the right side ofthepatient is on theleftsideof the image and vice versa (Fig. 14.1). For example, the liver (122) is located in the right half of the body, but appears in the left half of the image. Organs of the left side such as the stomach (129) and the spleen (133) appear on the right half of an image.Anterior aspects of the body,forexamplethe abdominal wall,are represented inthe upper parts of an image, posterior aspects such as thespine (50) are lower. With this system CTimages are moreeasily comparedwith conventional x-ray-images. Partial Volume Effects The radiologist determines the thickness of the image (dS)' 8-10 mm is usually chosen for thoracic or abdominal examina- tions, and2-5 mm for theskull, spine, orbits, or petrosal bones.A structure may therefore be included in the entire thickness of a slice (Fig. 14.2a) orinonlya partof it (Fig. 14.3a).Thegray scale valueofavoxeldependson the meanattenuationofall structures within it. If astructurehas a regularshape within a section, it will appear well defined.This is the case forthe abdominal aorta (89) andtheinferior vena cava (80) shown in Figures 14.2a, b. Partial volume effects occur when structures do not occupy the entire thickness of a slice, for example when a section includes partofavertebral body (50)and part of a disk (50e) the anatomy will bepoorly defined (Figs. 14.3a, b).This isalso trueif an organ tapers within a section as seen in Figures 14.4a, b. This is the reason for the poor definition of the renal poles or the borders of thegallbladder(126)orurinary bladder. Artifacts caused by breathing during image acquisition are dis- cussed onpage 19. anatomic level 80 /' 89 --------- -- -- -- --- ----- -- - --------- -- -- - - - - - -------- 0 V- '-..../ 50 -- -------- - - - - - --- --------- - ---------s::-?9-~--:J--------- 50 ' Fig. 14.2a Fig. 14.3a Fig. 14.4a CT image 00 Fig. 14,2b Fig.14.3b Fig.14.4b
Basic Rules of Reading CT Examinations 15 b :: -:_ ::::::::::: --- - - ------- - ---c _ c:or-106 @@ 50 31 31 a 6--0 ~® 50 31 31 tt--- b -----_Q_ - -- - - - - - -- ~@ 50 31 31 c 8980 135 -- -- - --- -- -- ---a Fig. 15.1 Distinguishing Between NodularandTubular Structures is essential to differentiate between possibly enlarqed or affected LNs and vessels or muscles which have been cut in transverse section. This may be extremely difficult in a single image oecause these structures have similar density aiues (gray tones). One should therefore always analyze adjacent cranial and caudal images and compare the structures in question to determine wnetner they arenodularswellings orcontinueas more or less tubular structures (Fig. 15.1): A lymph node (6) will appear in only one or two shoes and cannot be traced in adjacent images compareFigs. 15.1 a, b,andc).Theaorta(89)or :ne inferior cava(80),oramuscle,forexample the Iiopsoas (31), can be traced through a cranio- :audal series of images. " ere is a suspicious nodular swelling in one Cilage. it should becomeanautomatic reaction to 7.mpare adjacent levels to clarify whether it is - ;nply a vessel or muscle in cross-section. This xoceoure will also enable quick identification of :;-" partial volume effects described on the pre- JUs page. area in Fig. 15.2a). If dSis greater than the mass's diameter, for exampleasmall lesion inanunfavorableposition. it can only appear in partial volumeat anyscan level (Fig. 15.2b). -----~~ r ----------------------- ----- -IE)' ______~~1-- .... ..........__.__... ensitometry (Measurement of Density) " • is uncertain, for example, whether fluid found in the pleural ~ is apleural effusionor a hemothorax.a measurementof the :;(lid's density will clarify the differential diagnosis. The same ~: Dlies tofocal lesionsinthe parenchyma of the liver orthekidney. - : 'lever. it is notadvisable to carry out measurements of single cxels(=volumeelement,see Fig, 14.1)since such data areliable ;,: statistical fluctuations which can make the attenuation un- ·o~ble. It is moreaccuratetoposition alarger ' regionof interest" 0)/) consistingofseveral voxelsinafocal lesion,asnucture, oran ,,';)QUnt of fluid.The computer calculatesthe mean density levels :' all voxels andalso provides thestandard deviation (SO). : -e must be particularly careful not to overlook beam-hardening ' utacts (Fig. 19.2) or partial volume effects. If a mass does not e>:end through the entire thickness of a slice, measurements of :~ nsity will include the tissue next to it (Figs. 121.2 and 133.1- 33.3).The density of a mass will be measured correctly only if it : stheentirethicknessofthe slice (dS) (Fig. 15.2).Itisthenmore . "Iy that measurements will include only the mass (hatched Fig. 15.2 a b
16 Basic Rules of Reading CT Examinations Density Levels of Different Types of Tissues Modern equipment has a capacity of 4096 gray tones, which represent differentdensitylevelsin HUs.Thedensityof water was arbitrarily set at 0 HU and that of air at -1000 HU (Table 16.1a). The monitor can display a maximum of 256 gray tones. However, the human eye isable todiscriminate oniy approximately 20.Since thedensitiesof humantissues extendoverafairlynarrow range (a window) ofthe total spectrum(Table 16.1 b),itispossibletoselect awindow setting to represent the density of the tissueof interest. The mean density level of the window should be setascloseas possibletothe densitylevel ofthe tissuetobe examined.Thelung. with its highair content,isbest examinedat alow HU window set- ting (Fig. 17.1c), whereas bones require an adjustment to high levels (Fig. 17.2c). The width of the window influences the contrast oftheimages: the narrower the window,the greater the contrast sincethe20gray tones cover onlyasmall scaleof densi- ties. Table 16.1a Density of all tissues Table 16.1b Density of parenchymal organs andfluids Compact bone Lung D 500HU -900 HU -700~ 200 80 ± 10 70HU 60HU Blood 60HU 70 ", 10 60HU 65 ± 5 Spleen/muscle! Pancreas lymphoma 50HU 50HU 50HU 55 ± 5 4D HU Kidney 45 ", 5 40HU 30HU ExsudaleJeffusiOll 40 ± 10 30HU Suprarenal gland Transudate 20HU 20HU 25HU I 25 ± 5 30 ± 10 18 ~ 2 10HU Liver 17 ± 7 70HU Clotted blood 90HU Water ~ ~ O±5 Thyroid gland 80HU Parll'nChymal orgars 190HU 10Hul 50 ± 40 > 250230HU 30HU Spongy bone FaV connective tissue Air -1000 Fat I -90 ~ 10 700 100 o -100 500 300 -700 -300 -500 1000 -1 00 It is noteworthy that the density levels of almost all soft-tissue organs lie within a narrow range between 10 and 90 HUs (Table 16.1b). The only exception is the lung and, as mentioned above, this requires a special window setting (Figs. 17.1 a-c). With respect to hemorrhages, it should be taken into account that the density level of recently coagulated blood lies about 30HU above thatof freshblood.This density drops again inolder hemorrhages or liquefied thromboses. An exudate with a protein content above 30 gil cannot be readily distinguished from a transudate (protein content below 30gIl) at conventional window settings. Inaddition, the high degree of overlap between the densities of, forexample, lymphomas,spleen,muscles,and pancreasmakes it clear that it is notpossibleto deduce, fromdensity levels alone, whatsubstance or tissue is present. Finally,standarddensity values alsofluctuate betweenindividuals, depending aswellon theamount ofCM inthecirculating blood and in the organs.The latter aspect is of particularimportance forthe examination of the urogenital system, since Lv. CM is rapidly excreted by the kidney, resulting in rising density levels in the parenchyma during the scanning procedure.Thiseffect can beput to use whenjudging kidney function (see Fig. 135.1).
Basic Rules of Reading CT Examinations 17 Documentation ot Oiflerent Windows en the images have been acquired, a hard copy is printed for cocumentanon.For example: inorder toexamine the mediastinum anc the soft tissues of the thoracic wall, the window is set such ;nat muscles (13, 14, 20- 26), vessels (89, 90,92...), and fat are :learty represented in shades of gray. The soft-tissue window Fig.17.1 a) iscentered at50HU withawidth ofabout 350HU. The '"suit is a representation of density values from - 125HU (50- 350/2)up to+225HU(50 + 350/2).All tissueswithadensity lower than - 125HU, such as the lung, are represented in black. Those with density levels above +225 appear white and their internal structural features cannot bedifferentiated. If lung parenchyma isto be examined,for examplewhenscanning for nodules, the window center will be lower at about - 200HU. and the window wider (2000HU). Low-density pulmonary struc- tures (96) can be much more clearly differentiated in this so- called lungwindow (Fig.17.1c). -g. 17.1a: Soft tissuewindow • Fig. 17.1b Grayscale Hounsfieldunits (HU) • Fig. 17.1c: Lungwindow - order to achieve maximal contrast between gray and white -~tter inthebrain.it isnecessary toselect aspecial brainwindow :-=cause the density values of gray and white matter differ only : : tly. The brain window must be very narrow (80 to 100HU=> -:11 contrast) andthe center must lieclosetothe mean densityof :"rebral tissue (35HU) to demonstrate these slight differences i'ig.17.2a).Atthissetting it isofcourse impossibletoexamine the ;-ull since all structures hyperdense to 75-85 HU appear . e.Thebone window should therefore havea muchhighercen- i,"' at about +300HU,and asufficient widthofabout 1500 HU. The metastases (7) intheoccipital bone (55d)would only be visible in the appropriate bone window (Fig. 17.2c). but not in the brain window (Fi9. 17.2a). On the other hand. the brain is practically invisible inthe bonewindow; small cerebral metastases would not be detected. One must always be aware of these technical aspects. especially since hard copies are not usually printed at each windowsetting.Theexaminershould review thoroughly the images on the screen in additional windows to avoid missing important pathologic features. Examination of the liver poses special problems and is dealt withseparatelyon page120. - . 17.2a: Brain window Fi9·17.2b Fig. 17.2c: Bonewindow
18 Preparing the Patient I Medical History Prior to any CTexamination, a thorough medical history needs to beobtained whichfocusesonfactorsthat mayrepresent acontra- indication tocontrast media use orindicateanincreased likelihood of a reaction. In patients with suspected renal dysfunction base- line blood urea nitrogen and creatinine levels should be obtained (see below). It is important to note whether prior CT images are available for comparison. Information about prior surgery and radiation therapy in the anatomic region to be examined by CT is also important. Careful consideration of the pertinent radiologic findings on the current study in context with prior results and the patients clinical history allow the radiologistto render a meaning- fuldifferentialdiagnosis. Renal Function With the exception of few (such as stone protocol, fracture assessment) most CT exams require the Lv. administration of iodinated contrast agents for adequate assessmentof the clinical question at hand. Since contrast agents are excreted by the kidneys and may cause changes in renal hemodynamics and tubular toxicity [8], the physician should evaluate the patient's renal function by measuring the plasma creatinine prior to CT. If results suggest renal dysfunction, contrast agents should only be given in a very narrow range of indications [9, 10]. Furthermore, the use of low osmolality iodinated contrast is associated with a lower risk of renal toxicity and should be considered under this circumstance. Adequate patient hydration is also an important adjunct measure.Lastly,administrationof acetylcysteine informof tablets (Mucomyst ®) has shown a renoprotective effect in some studies. Diabetic patients on metformin therapy, an oral anti- hyperglycemic medication,must be given special attention [8, 9J. In these patients, contrast agents may cause lactic acidosis especially when there is coexisting renal dysfunction.Therefore it isrecommended towithholdmetforminon thedayofthe examand the following 48hoursand toreinstate therapyafter repeatserum creatinine measurement hasconfirmed stable renal function.Until recently, incases wherecontrast agentswas absolutelynecessary for a dialysis patient, the CT examination wasscheduled so that dialysisfollowed immediately. Recentreports, however, show that there is no need for urgent dialysis [11]. However, residual renal function in a dialysis patient can suffer from circulating contrast. Otherwise thereseemto be no other complications if thecontrast agentcirculates foradayortwountil thenext dialysis. Creatinine levels can be checked quickly and are inexpensive; Inordertosave time you may wantto havethe resultavailable on the requisition for the exam for immediate review by the radiolo- gist when prescribing the examprotocol. Hyperthyroidism Examining for hyperthyroidism is costly and time-consuming. Nevertheless, the referring physician must exclude hyper- thyroidism if there issuch a clinical suspicion before a CTexarnl- nation involving CONTRAST AGENTS is carried out. Laboratory parameters and possibly scintigraphy may be necessary. Inother cases,the information"noclinical evidence of hyperthyroidism" or even better, the documentation of thyroid function onthe requisi- tion is helpful. Thus, the radiologist can be sure that testing has been done. Notethatreferencevalues(Table 18.1)mayvaryfrom one laboratory to another. Check with your laboratory about commonly used units and normal ranges if these are not included on the report. The risk of thyrotoxicosis caused by the iodinated contrast agents can thus be avoided. If radioiodine therapy for hyperthyroidism orthyroidcancerisplanned,theLv.application of contrast agents could lead to a saturation of the iodine uptake systeminthethyroidgland for several weeks. Radioiodinetherapy may have to bedelayed for sometimeas a result. Table 18.1 Normal thyroid hormone levels TSH: 0.23 - 4.0 pg I ml TT3: 0.8- 1.8 ng/ ml TT4: 45-115ng /ml FT3: 3.5 - 6.0 pg I ml FT4: 8.0- 20.0pg I ml Adverse Reactions to Contrast Media Eversince nonionic contrast agents were introduced atthe end of the 1970s, adverse reactions have only rarely been encountered [12- 14]. Nevertheless, previous reactions are a pointer to an increased risk and should be elicited by taking a careful medical history.Theseverity ofany reactiontocontrast agents inthe past is of great importance. If the patients give a history of itching or hives following prior contrast administration, premedication is advisable. With a history of hypotension or cardiovascular collapse, contrast agents should not be given at all or only after thorough assessment of the clinical indication and appropriate premedication.Asageneral rule,patients whorequirepremedica- tion because of a previous reaction should be kept NPO 6 hours prior tothe examination.This reduces risk ataspiration incase of severe anaphylactic reaction requiring intubation and ventilation (for detailed information see pp. 24-25). Premedication (history of previous adverse reactions to contrast agents) In cases of mild adverse reactions, premedi- cationisaccomplishedwiththree oraldosesofPrednisone, 50mg each, taken 13,8 and 1 hour before the examination. In addition, 50mgof intramuscularantihistamine drug (e.g. Benadryl) isgiven 1 hour before the exam. Side effects such as raised intraocular pressure or urinary retention may occur. In addition, drowsiness may occur for about 8 hours following administration of these drugssodriving must beavoidedforthisperiod.Ifan outpatient CT examination is scheduled, the patient must be informed about potential drowsiness and the possibility of temporarily impaired vision; heor she should be accompanied on the way home. You will find checklists of all key words concerning medical historiesand suggestions for premedication on a practicalcard in the rearfoldout.
Preparing the Patient 19 Administrationof Contrast Agents -- " c period of fasting, liquid contrast agentsshould be drunk in =-=. oortions over a period of 30-60 minutes before the CT ~- canon starts so that the entire GIT is completely opacified. - '" cauent should therefore arrive at least 1 hour before anabo :: - -2. CT examination. Inorder tofacilitatethecorrect choice of :.. cast agent, the radiologist must be informed on the request ~: ethersurgery is planned shortly afterCT or whether there 9.1 a Fig. 19.1b is any suspicion of perforation or fistula (see also p. 20). In such cases water-soluble gastrografin would be used instead of a con- trast agent containing barium sulfate.Andfinally, where possible, CTofthe abdomen should be delayed for 3 days afteraconventio- nal barium examination has been carried out (for example:barium Iswallow, barium meal, small bowl enema, barium enema). Usual- ly, the digital projection radiograph (scanogram Fig. 19.1a,scouf . view) would show fhat residual barium inthe GITwould result in major artifacts (Fig. 19.1 b), rendering CT valueless. The sequence of diagnostic proce- dures for patients with abdomi- naldiseasesshouldthereforebe carefullyplanned. -, ing the Patient .r :~'s;andably, patients havedoubts aboutthe harmful erects of - 0 ,-ray burden involved in CT. Worriescan usually be reduced if •• •, ate diagnostic x-ray exposure fa natural background -=: ~;joo. Naturally,the patientmust havethefeelingthat heorshe s :,,~ taken seriously and his or her worries are understood, - ~' ise confidence and trust in the radiologist are threatened. Many patients are relieved to know that they can communicate withtheradiographersinthecontrol room viaanintercom andthat the examination can be interrupted or terminated at any time if thereare unexpected problems. Patients with claustrophobia may feel morecomfortable if they close their eyes during the examina- tion; the close proximityof the gantry isthen less of a problem. In very rarecases, a mildsedative may be helpful. :. iration :c': , starting the examination, the patient should be told of the need for controlled : ' 2.--ling. For conventional CT,the patient is instructed to breathebefore each new image •-::; ., 'on andthen to hold hisorher breathforafew seconds.Inthe helical technique it is . ~: -ssarv to stop breathing for about 20-30 seconds. If the patient cannot comply, • ,--'cgmatic movement will lead to image blur with a marked deterioration in image : 0 iy (Fig.19.2).Inthecaseofneck examinations,swallowing influences thequalityof the - ,,;,$morethan breathing. Fig. 19.2 val of all Metallic Objects ~:_ ally, jewelry of any kind and removable ' ,':2. prostheses must be removed before the .~~: or neck are examined in order to avoid • ' acts. In Figures 19.3a and b, the effects of : : - artifacts (3) are obvious. Only the cervical ~-:,:xal body (50)and the adjacent vessels(86) · = defined; the other structures are unre- :-:;' ·zable. For the same reasonall clothing with - ,,:2. ic hooks, buttons, or zippers should be ~- _ ed before thoracic or abdominal CTs are :" ~0l'm ed. Fig. 19.3a Fig. 19.3b
20 Administration of Contrast Agents I Oral Administrationof Contrast Agents For CT examination of the abdomen and pelvis, it is of major advantage to be ableto readily differentiatethe GITfromadjacent musclesor other organs. This can be accomplished by opacifying the intestinal lumen with an orally administered contrast agent. For example, withoutof contrast agent it is difficult to distinguish between the duodenum (130) and the head of the pancreas (131 inFig. 20.1). Equally, other parts of theintestinal tract (140)wouldalso bevery similar to neighboring structures. After an oral contrast agent, both the duodenum and the pancreas can be well delineated (Fig. 20.2a, b). In orderto acquire images of optimal quality, the patient shouldfast (be NBM) beforedrinking contrast agents. Fig.20.2a Choice of theAppropriale Contrast Agents The best coating of the mucous membranes is achieved with barium sulfate; however, this is not water soluble. This oral con- trast agent should therefore not be used if abdominal surgery involving opening ofthe bowellumen isscheduled,suchasinpar- tial resections or anastomotic sutures, or if there is any risk of injury tothe bowel. Neither shouldbarium sulfatebeused incases of a suspectedfistulaor aGITperforation.Awatersoluble contrast agent, such asgastrografin,is then employed; it can be resorbed bythebody after it spreads intothe abdominal cavity. For an optimal assessment of the stomach walls, plain water is increasingly used as a hypodense contrast agent in combination with intravenous buscopan,which relaxes the muscularis [15, 16]. If the urinary bladder has been removed and an i1ial conduit constructed, the abdomen is examined first with an intravenous contrast agent which is excreted into the urinein theconduit but notwithinthenativeintestines. If necessary,theintestines can be examined ina second scanafter oral contrast agents. Fig. 20.1 Fig.20.2b The TimeFactor To opacify the proximal parts of the GIT, a period of about 20-30 min is sufficient; the patient swallows the contrast agent inseveral small portions. However,if theentirecolon and especial- lytherectum need to beopacified with barium sulfate,a periodof at least 45-60 min is necessary in a fasting patient. Thewater- solublecontrastagent gastrografinspreadssomewhat morerapid- ly. For the peivic organs (bladder, cervix, orovary),100-200 ml of contrast agent may be given rectally to insure that tumors are clearlydifferentiated fromthe lowerintestinal tract. Dosage Toachieve completeopacificationof theentireGIT, 250-300 mlof a barium sulfate suspension are dissolved andthoroughly mixed with water (1000 ml). For adequate contrast of the entire GIT, 10-20 ml of water-soluble gastrografin(in 1000 mlof water) are enough. If only theupper part of the GIT needs to be opacified, 500 ml of either medium are sufficient.
Administration of Contrast Agents 21 enous Contrast Agents - - ease in the density of blood vessels not only demarcates --r oener from muscles and organs butalso provides informa- the rate of blood perfusion (contrast agent uptake) in :".- ically altered tissues: disturbances of the blood-brain ebordersof abscesses,ortheinhomogeneous uptake of , _ trast agents intumorlike lesions areonlyafew examples.This : -:-oo11enon is called contrast enhancement, l.e, the density is - :-e2sed bythe contrast agent and thusthe signal intensified. :~J.' nding uponthequestion being asked,an unenhanced(plain) - shouldbeobtainedbeforeinjectingthe contrast agents intra- _ - !y. Vascular grafts, inflammatoryprocessesin bone,aswell ;;; acscesswalls are moreeasilydiagnosed if unennanced images ~- : ~ comparedwithcontrast-enhanced images.Thesame holds - _~ 'or ocal liver lesions examined using conventional CT tech- - : _~. I helical CTisavailable,aseries ofliver images inthe early : -- e of arterial contrast agent perfusion followed bya series in -~ : ase of venous drainage [1 7] would be obtained instead of _ eo-anced images.This procedure makes it possible to detect eo =~ small focal lesions (seep, 120). -reparing thei.v.Line - -: contrast agents are injected intravenously, and the bolus be- :.: - ~ longer and diluted as it passes through the pulmonary - -::_anon.Theinjection should thereforeideally havearapidflow ~'c of2-6 0111 1sec for achieving sufficient density enhancement :' -- e vessels [18]. A Venflon canula with a diameter of at least • : 011011 (20G), or preferably 1.2-1.4 011011 (18G-17G), is used. Checking that the canula is correctly sited in the vessel is very important. Atrial injection ofsterilesaline at a high flow rateinto the veinshould be carriedoutbefore injecting contrast agents.The absence ofsubcutaneousswelling confirms properpositioning;the fact that the vein can accommodate theintendedflow canalso be confirmed. Dosage Dosage is calculated on the basis of b.w. and according to the diagnostic question at hand: examinations of the neck or of an aorticaneurysm(for example inorder toexclude thepresenceofa dissection flap), require higher concentrations than cranial CTs. Whentolerancetocontrast agentsandoptimal vessel contrast are balanced,adosageof,forexample,1.2mllkg b.w.ataconcentra- tion of0.623 glopromidlml ingeneralprovides good results. Inflow Phenomena Thestreaming artifact of enhanced and unenhanced blood results fromashort interval between the startof injectionandtheonset of dataacqulsltlon. Since inflow is usuallyfrom oneside viatheaxil- lary, subclavian, and brachiocephalic veins (91) into the superior venacava (92),thereis an apparent filling defect withinthevena cava(Figs. 21.1 a-21.3b). Knowingabout suchinflow phenomena avoids a false positive diagnosis of venousthrombosis. Using too high concentrations of contrast agents inthis area could result in disturbing artifacts, especially with the helical technique (Fig. 23.3a). More inflow phenomena will be described on the next pages. I
22 Administration of Contrast Agents Application of Contrast Agents Flow phenomena can alsobe seen inthe inferior vena cava(80) atthe level ofthe renal veins(111).Theseveins may containblood which has afairly highconcentration ofcontrast agentsandthis blood mixes with unenhanced blood returningfrom the lower extremitiesand pelvic organs. In the early post-contrast phase the vena cava (80) caudal to the level of the renal veins is hypodense relative to the adjacent aorta(89) asin Figures 22.1 a,b. I Fig.22.1a Fig.22.1b Immediatelyabove the renal veins, thecontents ofthe inferiorvena cava may appear bilaterallyenhanced by the blood fromthekidneys whereas thecentral part is still unenhanced (Fig. 22.2a, b). If the renalveins donotempty intothe cava at the same levelor if a kidney has been removed, a unilateral enhancement may occur (Fig. 22.3a, b). Such differences in density should not be mistaken forthrom- bosis of the inferior cava (ct. Figs. 23.1 and144.1). Fig. 22.2a Fig. 22.3a Fig.22.2b Fig. 22.3b
Administration of Contrast Agents 23 Flow Phenomena If wetrace theinferior vena cava cranially towardtherightatrium, additional flow phenomena become apparent asmoreveins empty into it. The cava has spiraling eddies of inhomogeneous density (+ in Fig. 23.1) caused by mixing of the blood as described on the previous page. Moments later such inhomogeneities are no longer evident inthelumen (80) anddensityleveis are identicai to those inthe aorta (89) (Fig,23.2a, b). 8ytheway, didyounoticethe artherosclerotic plaqueinthedorsal wallof theaorta (174 in89inFig.22.3a)?Thisplaqueappearsalso in Figure 23.2a.The patient had well-developedosteophytes (64) on thevertebral bodies (50). Fig. 23.2a Details Specific for Spiral GT If data acquisition begins immediately after contrast agents have beenadministered,theconcentrationof contrast agentsinthe axil- lary, subclavian, and brachiocephalic (91) veins might be high enough tocause majorartifacts(3)inthethoracic inlet. Inimages such as in Figure 23.3, it is not possible to assess the lung or Fig. 23.3a Fig.23.1 Fig.23.2b neighboring axillary tissues.An SCTof thethoraxshould therefore beobtainedfrom caudal tocranial.Inthat way structures nearthe diaphragm are imaged first, and when cranial parts are scanned the contrast agents will have been spread after having passedthe pulmonary circulation. This trick helps avoid the artifacts (3) shown in Figure 23.3. Fig. 23.3b I
24 Administration of Contrast Agents I Adverse Reactions to Contrast Agents Adverse reactions are rare; most appear during the first 30 minutes, 70% of cases occur within the first 5 minutes after contrast injection [13]. Only high-risk patients need to be super- vised for morethan30minutes. Since suchpatientscanusuallybe recognized by taking a thorough medical history, they can be premedicated accordingiy (see p. 14). If, despiteprecautions, erythema develops afteran l.v, injection of contrast agents,perhapsalsohives,itching,nausea or vomiting,or in extreme cases even hypotension or circulatory shock or short- ness ofbreath,the countermeasuresiistedbelow must beinitiated immediately. Remember that i.v. injection of Hl - and H2-receptor antagonists does not alleviate symptoms immediately.There is a period of latency, and these antagonists are therefore primarily eftective in preventing the symptoms from worsening. Serious incidents(pulmonaryedema,circulatoryshock,convulsions)occur very rarely with the new contrast media; they require immediate intensive care. Be sure to document any incident in your report. Radiologists pertorming future examinations will be forewarned about the patient's sensitivitytocontrast agents. Urticaria Management of Acute Reactions in Adults Bronchospasm 1 Discontinue injection if notcompleted 2 No treatment needed in most cases 3 Give H,-receptorblocker; Diphenhydramine(Benadryl®) PO/ 1M/ IV 25-50mg if severe orwidely disseminated; Alpha agonist(arteriolar and venousconstriction) Epinephrine SC (1;1,000)0.1-0.3 ml = 0.1 -0.3 mg (if nocardiac contraindications) Facial or Laryngeal Edema 1 Give alpha agonist(arteriolar andvenousconstriction); Ephinephrine SC or 1M (1 ;1,000) 0.1-0.3 ml(= 0.1 -0.3 mg) or, if hypotension evident, Epinephrine (1;10,000) slowlyIV1 ml (= 0.1mg) Repeatas needed uptoa maximum of 1mg 2 Give O26-10iiters/ min (via mask) Ifnotresponsivetotherapyorif there is obvious acute laryngealedema, seek appropriateassistance (e.q., cardiopulmonary arrest responseteam) 1 Give O26-10liters/ min(via mask) Monitor; electrocardiogram, O2saturation (pulse oximeter), and blood pressure. 2 Givebeta-agonist inhalers: bronchiolardilators, suchas metaproterenol (Alupent®j, terbutaline(Brethaire®), or albuterol (proventil®,Ventolin®j 2-3 pufts; repeat prn. If unresponsive toinhalers, us SC, 1M or IV epinephrine 3 Give epinephrine SCor1M(1:1 ,000)0.1-0.3 ml (= 0.1 -0.3mg) or, if hypotension evident, Epinephrine(1:10,000) slowly IV1 ml(= 0.1mg) Repeat asneeded uptoa maximum of 1 mg Alternatively: Give aminophylline: 6 mg I kgIV in D5Wover 10-20 minutes(loading dose),then 0.4-1 mg I kgI hr, as needed (caution: hypotension) Call for assistance (e.q., cardiopulmonary arrest responseteam) forseverebronchospasm orif O2saturation < 88%persists. Hypotension with Tachycardia 1 Legs elevated 60° ormore(preferred) orTrendelenburg position 2 Monitor:electrocardiogram, pulse oximeter, blood pressure 3 Give O26-10 litersI min (via mask) 4 Rapid intravenous administrationof largevolumes of isotonic Ringer's lactate or normal saline. Ifpoorly responsive: Epinephrine(1:10,000)slowly IV1 ml (= 0.1 mg) (if nocardiac contraindications) Repeat as needed up to a maximum of 1 mg if still poorly responsive seekappropriateassistance (e.q.,cardiopulmonaryarrest response team)
Administration of Contrast Agents Management of Acute Reactions in Adults 25 Hypotensionwith Bradycardia (Vagal Reaction) 1 Monitor vital signs 2 Legs elevated 60' ormore(preferred) orTrendelenburg position 3 Secureairway:giveO26-10liters / min (viamask) 4 SecureIV access: rapidfluidreplacement with Ringer's lactate ornormal saline 5 Give atropine 0.6mg IVslowlyif patient does not respond quickly tosteps 2-4 6 Repeat atropine up toatotal doseof0.04 mg / kg (2-3 mg) inadult 7 Ensurecomplete resolution of hypotension andbradycardia priortoctschanqe Hypertension, Severe 1 Give O26-10 liters / min (viamask) 2 Monitorelectrocardiogram, pulseoximeter, blood pressure 3 Give nitroglycerine0.4-mg tablet, sublingual (may repeatx3) ortopical 2%ointment,apply 1 in.strip 4 Transfer to intensive care unit oremergency department 5 Forpheochromocytoma - phentolamine5 mg IV Iodine-provoked Hyperthyroidism Fortunately, this complication is very rare with modern non-ionic iodinated contrast agents. In patients with a medical history of yperthyroidism consider blocking the thyroid gland before l.v application of contrast agents by administering a thyrostatic drug such as sodium perchlorate. Alternatively, carbimazole can be ed to block hormone synthesis. Both treatments take approxi- ately 1 week to become fully effective. Effectiveness must be :isterminedbyrepeatingthe thyroidfunction tests. Seizures orConvulsions 1 Give O26-10liters / min (viamask) 2 Consider diazepam (ValiUm®) 5 mg (or more, as appropriate) ormidazolam (Versed®) 0.5-1 mgIV 3 If longer effect needed, obtain consultation; considerphenytoin (Dilantin®) infusion - 15-18mg/ kg at 50mg/ min 4 Careful monitoring ofvitalsignsrequired, particularly of p02 because ofriskto respiratorydepressionwith benzodiazepine administration 5 Consider using cardiopulmonary arrest responseteam for intubation if needed Pulmonary Edema 1 Elevate torso; rotating tourniquets (venous compression) 2 Give O26-10 liters/ min (viamask) 3 Givediuretics- furosemide (LaSix®) 20-40 mg IV, slowpush 4 Consider giving morphine(1 -3 mgIV) 5 Transfer to intensivecare unit oremergency department 6 Corticosteroids optional In patients with unrecognizedsubclinical hyperthyroidism,theuse of iodine containing contrast agents can unmaskthe disease or even induce thyrotoxicosis.The symptoms may include diarrhea, muscle weakness as well asfever, sweating,dehydration,anxiety and restlessness, or even tachyarrhythmia. The main problem is the long periodof latency beforethethyrotoxicosis crisisbecomes manifest. I · Some patients with hyperthyroidism orother thyroid disease (especially those who live in iodine-deficient areas) may develop iodine- orovoked delayed hyperthyroidism.This effect mayappear 4 to6 weeks after theintravascularcontrastadministrationin some ofthese catients.It canoccur after theadministration of either ionic, high-osmolality or nonionic, low-osmolalitycontrast.It is usuallysett-limt- :sd. "atients withcarcinoma ofthethyroid deserve special consideration beforethe intravascularor oral administrationofiodinatedcontrast , edia (ionic or nonionic). Uptake of 1-131 in the thyroid becomes moderately decreased to about 50% at one week after iodinated - trast injection but seemsto become normal within a few weeks.Therefore, if systemic radioactive iodine therapy is part of planned -satmen, a pretherapy diagnostic study of the patient using iodinated radiographic contrast medium (intravascular or oral) may be - traindicated; consultation withthe ordering clinician prior tocontrast administration inthese patients isrecommended."
26 Cranial CT . Manycranial CT(CCT) examinationscanbeperformedwithoutinjectionof contrast medium: For instance,thedifferential diagnosis (DO) of cerebral bleeding versus infarction in patient with sudden onsetof neurologic deficits does not require the administrationof contrast medium. However, intravenous injection of contrast medium is necessary to detect an impaired blood-brain barrier (BBB) as found in tumors, metastases or inflammations. I Selection of the ImagePlane The desired image planes parallel to the orbitomeatal line are selected on the sagittal localizer image (topogram) (Fig.26.1).This isa readily reproducible line drawnfrom the supraorbital ridge to the external auditory meatus, allowing reliable comparison with follow-up CT examinations. The posterior fossa is scanned in thin sections (2-3 mm) to minimize beam hardening artifacts, and the supratentorial brain above the pyramids in thickersections (5 mm). The images are displayed as seen from below (caudal view) and consequently are laterally reversed, i.e., the left lateral ventricle is on the right and vice versa. Only CTs obtainedfor neurosurgical planningareoftendisplayedas seen from above (right = right) since thiscranial view correspondstotheneurosurgical approach forcranial trepanation. Fig. 26.1 Systematic Interpretation Each examiner is free to find a preferred sequence for reviewing the images. This means that the examiner can choose between several acceptable approachesand is not restricted toa "oneand only" strategy. However, staying with a consistent arrangement of theimages tobeinterpretedhastheadvantagethat fewerfindings areoverlooked, especiallybythenovice.The checklist belowjust contains recommendations that can serve as good guideline for thenovice. First,thesize of theventricles andextracerebral CSFspaceshasto be evaluated to exclude a life threatening space-occupying process rightaway. Hereby,the patient'sagehasto be considered because of age-related widening of the CSFspaces.Any blurring of the grey-white matter junction as manifestation of cerebral edema should be lookedfor(see below). If a pathologicchange is suspected,the adjacent sections should beinspectedtoavoid any misinterpretationduetoa partial volumeeffect(see Fig. 29.1and Fig.52.2). Always usethe legendson thefrontcover flapforthischapter.The listednumbersapplytoall headandneckimages.Thesubsequent pages provide you with a survey of the normal anatomy, followed by normal variantsand themost frequent pathologic findings. Checklist for Reading Cranial CT Age?(becauseofthe age-related width ofthe CSFspaces I cerebral atrophy; see page 50) MedicalHistorv: • Risk factors? (Trauma -+ Chance ofintracranial bleeding) (Hypertension, diabetes, nicotine -+ Vascular stenoses, infarcts) Signsofspace-occupyinglesion: • Normalconfiguration of the-tthventricle? (posterior tothepons,see pages 28/ 29) • Normalconfiguration of the 3rdventricle? (interthalamic, narrow/ slit-like,seepage30) • Normal symmetryof the lateralventricles?(concavelateral border of theanterior horn and central ventricular region?) • Midlineshift?(signof largespace-occupying process) • Preservedbasalcistern?(e.g., quadrigeminal cistern: smiliefaceI bat manfigure, see Fig.30.1) • Cortex +-~ whitematter demarcation OK?(blurred interface = signof edema) • Widthof theextracerebral CSFOK for patient'sage? (Sylvianfissure, refer to p.50) Focal lesions: • Unenhanced:DO physiologiccalcification(choroidplexus, pineal gland/ partial volume; refer toFigures 29.3 and 30.2) versusgenuinehyperdensebleeding (DOtypes ofbleeding,seepages 54-57) • Contrast enhanced: Sign ofimpaired BBB? (caused bytumors, metastases, inflammations, ...) Osseous lesions: • Check cranial vault and baseinbonewindow forosteolytic lesionsI osseousinfiltration • Intrauma patient: Ruleout fractures(especially cranial base, midfacial bones- DO sutures)
Cranial CT Normal Anatomy 27 The scan usually begins at the base of the skull and continues upward. Since the hardcopies are orientedsuch that the sections are viewed from caudal, all structures appear as if they were lelUrightreversed(see p. t 4). The small topogram shows you the corresponding posi- tion of each image. You shouldfirstcheckfor any swellings in the soft tissues whichmayindicatetrauma to the head. Always examine the condition of the basilar artery (90) in scans close to the base of the skull andthe brainstem (107).The viewis often limited by streaks of artifacts (3) radiating from thetemporal bones (55b). When examining trauma patients. remember to use the bone window to inspect the sphenoid bone (60). the zygomatic bone(56),and the calvaria (55) for fractures. In the caudal slices you can recognize basai parts of the temporal lobe (110) and the cerebellum (104). Orbital structuresare usually viewed in another scanning plane (see pp. 33·40). In Figure27.1-3 we see only a partialslice ofthe upper parts of the globe (150),the extra- ocular muscles (47), and the oifactory bulb (142). Fig. 27.1b Fig. 27.2b Fig. 27.3b - , . 27.2a - , 27.1a - e- 27.3a
28 Cranial CT . Normal Anatomy Fig. 28.1b Fig.28.2b Fig.28.1a Fig. 28.2a As the series of slices con- tinuesdorsally.thecristagalli (1 62) and the basal parts of thefrontal lobe (111) appear. The pons/medulla (107) are often obscured by artifacts (3). The pituitary gland (146) and stalk (147) are seen between the upper border of the sphenoid sinus (73) and the clinoid process (163). Of the dural sinuses, the sig- moid sinus (103) can be readily identified. The basilar artery (90) and the superior cerebellar arlery (95a) lie anterior to the pons (107). The cerebellar tentorium (131).which liesdorsal tothe middlecerebral artery (91 b), shouldn't bemistaken forthe posterior cerebral artery (91 c) at the level depicted in Figure 29.1 a on the next page. The inferior (temporal) horns ofthe lateral ventricles (133) as well as the 4th ventricle (135)can be identi- fied in Figure 28.3. Fluid occurring in the normally air-filled mastoid cells(62) or in the frontal sinus (76) may indicate a fracture (blood) or an infection(effusion). A small portion of the roof of the orbit (*) can still beseen in Figure28.3. I Fig. 28.3a Fig.28.3b
Cranial CT Normal Anatomy 29 In Figures 28.3a and 29.1 a partial volume effects of the orbit (*) or thepetrosal bone I(**) might also be misinter- preted as fresh hemorrhages in the frontal (111) or the temporallobe (110). The cortex nextto thefrontal bone (55a) often appears hyperdense compared to adjacent brain parenchyma, but this is an artifact due to beam-hardening effects of bone. Note that the choroid plexus (1 23) in the lateral ventricle (133) is enhanced after Lv. infusionof eM. Even in plain scans it may appear hyperdense becauseofcalci- fications. You will soon have recog- nizedthat theeeTimageson thesepagesweretaken after l.v. administration of eM: the vessels of the circle of Willis are markedly enhanced. The branches (94) of the middle cerebral artery (91 b) are visible in the Sylvian fissure (1 27). Even the pericallosal artery (93). a continuation of the anterior cerebral artery (91a), can be clearly identi- fied. Nevertheless, it is often difficult to distinguish be- tweenthe opticchiasm(145) and the pituitary stalk (147) because these structures havesimilar densities.
30 Cranial CT Normal Anatomy Fig. 30.1 b Fig.30.2b Fig.30.3b Fig.30.1a Fig.30.2a Fig.30.3a In addition to the above- mentioned cerebral arteries (93, 94), the falx cerebri (130) is a hyperdense struc- ture. InFigure 30.2a youcan see the extension of the hyperdense choroid plexus (123) through the foramen of Monro, which connects the lateral ventricles (133) with the 3rd ventricle(134).Check whether the contours of the lateral ventricles aresymme- tric. A midline shift could be an indirect sign of edema. Calcifications in the pineal (148) gland and the choroid plexus (123) are a common finding in adults, and are generally without any patho- logic significance. Due to partial volume effects, the upper parts of the tentorium (131) often appear without clear margins so that it be- comes difficult to demarcate the cerebellar vermis (105) and hemispheres (104) from theoccipital lobe(112). It is particularly important to carefully inspect the internal capsule (1 21) and the basal ganglia: caudate nucleus (117), putamen (118), and globus pallidus (119) aswell as the thalamus (120). Consult the number codes in the front foldout for the other structures not specifically mentioned on these pages. I
Cranial CT Normal Anatomy 31 The position of the patient's headisnot always as straight asinour example.Even small inclinations may lead to remarkably asymmetric pictures of the ventricular system, though in reality it is perfectly normal. You may see only a partial slice of the convex contoursof thelateral ventricles (1 33). This could give you the impression that they are not well defined (Fig. 31.1a). The phenomenon must not be confused with brain edema: as long as the sulci (external SAS) are not effaced, but configured regularly, the presence of edema is rather improbable. For evaluating the width of the SAS, the patient's age is an important factor. Compare the images on pages 50 and 52 in this context. The para- ventricular and supra- ventricular white matter (143) must be checked for poorly circumscribed hypo- dense regions of edema due to cerebral infarction. As residues of older infarc- tions, cystic lesions may develop. In late stages they are well defined and show the same density as CSF (see p. 58). I
32 Cranial CT Normal Anatomy Inthe uppersections(Figs.32.1-32.3) calcifications inthecerebral falx(130) oftenappear.Youshould differentiatethis kind oflesion,which has noclinical significance,from calcified meningioma.The pre- sence of CSF-filled sulci (132) inadultsisanimportant findingwithwhichtoexclude brainedema.After athoroughevaluationof thecerebral soft-tissue window,acarefulinspection of thebonewindowshould follow. Continue to check for bone metastases orfracture lines. Only now is your evaluation of acrani- al CT reallycomplete. Test yourself! Exercise 1: Note from memory asystematic order for theevaluationofcranial CTs. Ifyou have difficulties,returnto the checklist on page 26. Note: • I • • • • • • • • Fig, 32.1a Fig. 32.2a Fig. 32.3a Fig,32.1 b Fig, 32,2b Fig. 32.3b On thefollowing pages theatlas of normal anatomy continues withscansof the orbits(axial),theface (coronal), and the petrosal bones (axialand coronal).After these you will find themost common anatomic variations,typical phenomenacaused bypartial volume effects and the most important intracranial pathologicchanges on pages 50to60.
Cranial CT Normal Anatomy of the Orbit (Axial) 33 "ig.33.1a =- . 33.1b - e - 33.1 c The face and the orbits are usually studied in thinslices (2 mm) using 2-mm collimation steps. The orientation of the scanning plane is comparable to that for CCTs(see p. 26). In the sagittal topogramthelineof referencelies paralleltothefloor of theorbit at anangle of about 15°to horizontal (Fig. 33.2). The printouts are usually presented in theview from caudal: all structures on the right side of the body appear on theleft.and vice versa. Fig.33.2 Alterations in the softstructures of the orbits and the paranasal sinuses can be readily evaluated in the soft-tissuewindow(Fig. 33.1b).Forthedetection ofatumor-related arrosionof bone or a fracture.thebone window should also bechecked (Fig. 33.1 a). The following pages therefore present each scan level in both windows.The accompanying drawing (Fig. 33.1 c) referstoboth. The number codes forall drawings arefound inthelegend inthe frontfoldout. On thelower slices of theorbits you will see parts of the maxil- lary sinus (75).thenasal cavity(77) with theconchae (166).the sphenoid sinus (73). and the mastoid cells (62) as air-filled spaces. Ifthere is fluid or asoft-tissue mass.this may indicatea fracture, an infection. or a tumor of the paranasal sinuses. For examples ofsuch diseases.see pages 58to 61 . Twoparts of the mandible appear on the left side: in addition to thecoronoid process (58).thetemporomandibular joint with the head ofthe mandible(58a) isseenonthe left.The carotidartery. however, is often difficult to discern in the carotid canal (64), whether in thesoft-tissue orbone window. In the petrous part of the temporal bone (55b), the tympanic cavity (66) and the vestibular system are visible. For a more detailed evaluation of the semicircular canals and the cochlea. images obtained with the petrous bone technique are more appropriate (pp. 44-47). CM was infused intravenously before the examination of the orbits. The branches of both the facial and angular vessels(89) as well asthebasilar artery(90)there- fore appear markedly hyperdense in the soft-tissue window (Fig. 33.1b).
34 Cranial CT Normal Anatomy of the Orbit (Axial) It is not always possibleto achieve a precise sagittal position ofthe head. Even aslighttilt (Fig. 34.1) will makethetemporal lobe (110) appear on one side. whereas on theother side themastoid cells (62) can beseen. Fig. 34.1b Fig. 34.2b Fig. 34.2aFig. 34.1a Fig. 34.1c Fig. 34.2c
Cranial CT Normal Anatomy of the Orbit (Axial) 35 Fig. 35.2b Fig. 35.2aI g. 35.1a Fig. 35.1b -~ , perience shows, it is difficult to determine the course of the internal carotid artery (85a) through the base of the skull and to :e- :;rcatethe pterygopalatinefossa (79), through which,amongother structures, thegreater palatine nerve and the nasal branches of - ~ ::erygopalatineganglion (fromCNVand CN VII) pass. Fig. 35.2c
36 Cranial CT Normal Anatomy of the Orbit (Axial) On thefloor of theorbit,theshort inferior obliquemuscle(47f) oftenseems poorly delineatedfrom the lower lid.This is duetothesimilar densities of thesestructures.Directly in front of theclinoid process/dorsumsellae (163) lies the pituitary gland (146) in its fossa,which is laterally bordered by thecarotid siphon (85a). Fig. 36.1a Fig. 36,lb Fig. 36.1c Fig, 36.2a Fig,36,2b ~ 1o-_~_"lM1I .s Fig, 36.2c
Cranial CT Normal Anatomy of the Orbit (Axial) 37 all inclinationsofthe head cause slightlyasymmetricviews ofthe globe(150) and the extraocularmuscles (47).The medial wall of e nasolacrimal duct (1 52) is often so thin that it cannot be differentiated.At firstsightthe appearance of theclinoid process (163), etweenthe pituitary stalk (147)andthe carotid siphon (85a) on the left side only, may be confusing in Figure 37.2b. Fig.37.2a19.37.1a Fig. 37.1b Fig. 37.1c
38 Cranial CT Normal Anatomy of the Orbit (Axial) After intravenous injection ofeM,the branches ofthemiddle cerebral artery (91 b) originating fromthe internal carotid artery (85a) are readily disijnguished.Thegray shadeoftheopticnerves(78) as they pass through the chiasm(145) tothe optic tracts(144), however,isverysimilarto that of thesurrounding CSF(132).Youshouldalways check onthesymmetry of theextraocularmuscles(47) intheretrobulbar fattytissue(2). Fig. 38.1 a Fig. 38.1b Fig. 38.1c Fig. 38.2a Fig. 38.2b Fig. 38.2c
Cranial CT Normal Anatomy of the Orbit (Axial) 39 -~ ; obe(150) youcan now see the hyperdenselens(150a).Noticetheobliquecourseoftheophthalmic artery(* ) crossing theoptic - , 8) in the retrobulbar fatty tissue(2). Figure 39.2b shows a slight swelling (7) ofthe rightlacrimal gland (151) compared to the - " seeFig. 40.1 b). Fig. 39.2c Fig. 39.2b Fig. 39.2a
40 Cranial CT Normal Anatomy of the Orbit (Axial) Figure 40.1 bclarifiesthatinthis casethereis indeed an inflammationortumor-likethickening (7) intheright lacrimal gland (1 51).The superior rectusmuscle (47a) appears at the roof of the orbit and immediately next to it lies the levator palpebrae muscle (46). Due to similardensities,these muscles arenot easily differentiated. Fig.40.1a Fig.40.1b Fig.40.2a Fig.40.1 c Fig.40.2c Theaxial views oftheorbits andthefaceend herewiththeappearance ofthefrontal sinus(76). Examples ofpathologic changes ofthe orbits orfractures of facial bones are found on pages 61 to 63.
Cranial CT Normal Anatomy of the Facial Skeleton (Coronal) -- - oossfbilitiesofanglingtheCf gantry arelimited.Inordertoacquire scans inthe coronal - ..e patient must therefore be positioned asshown inthe planning topogram to the ; - (Fig. 41.1). The patient should be in a prone position, with the head completely . - -cell.When examining trauma patients, any lesions of the bones or ligaments of the - ca spine must always be excluded by conventional radiography priorto eeT. ~- ;~ viewedfromanterior:theanatomic structures on thepatient's rightsideappear on : -=~ inthe imagesand conversely,asif theexaminer werefacing thepatient. 00- 100 ing for fractures, images are usually acquired in the thin-slice mode (slice and -~won, each2 mm) and viewed on bone windows. Evenfinefracture lines can then be _~ . A suspected fracture of the zygomatic arch may require additional scans in the - : ane(see p. 34). In Figure 41 .2a the inferior alveolar canal (*l inthe mandible (58) : -- ~ foramen rotundum (**l in the sphenoid bone (60) are clearly visible. As for the Abb.41.1 schapter,thecode numbersforthe drawingsare explained inthe legend inthefront - t 41 Fig. 41 .2b Fig. 41.3b
42 Cranial CT Normal Anatomy of the Facial Skeleton (Coronal) Fig. 42.1a Fig. 42.2a Fig. 42.3a Fig. 42.1b Fig.42.2b Fig. 42.3b
- !3.2a Fig. 43.1b Fig. 43.2b Fig. 43.3b 43
44 Cranial CT Normal Anatomy of the Facial Skeleton (Coronal), Fig.44.1b Fig. 44.2b Fig. 44.3b The insertions of the extraocular muscles on the globe (150) can also be clearly identified (47 a-I) inthe anterior slices.The short inferior oblique muscle(471),however,isollen seen only incoronal scanning planes,becauseit doesnotpass withthe othersmuscles through the retrobulbar fatty connective tissue.Thesameproblem occurs in axial scans of the face (compare with Fig. 36.2b and Fig. 36.2c). If a case of chronic sinusitis is suspected, it is very important to check whether thesemilunar hiatus isopen.It representsthemain channel for discharging secretions of the paranasal sinuses. In Figure 60.3 you will find examples of anatomic variations which narrow this channel andmay promote chronicsinusitis. Sometimes one discovers a congenitallyreduced pneumatization of a frontal sinus (76) or an asymmetric arrangement of other paranasal sinuses without any pathologic consequences. You should always make sure that all paranasal sinuses are filled exclusively withair. thatthey are well defined and present noair- fluid levels. Hemorrhage into the paranasalsinuses orthe detec- tion of intracranial bubblesof airmust beinterpretedas an indirect sign of a fracture - you will find examples of such fractures on page63.
Test Yourself! 45 Without doubt, you will improve your understanding ofthe subject if you tackle the gaps in your knowledge instead of skipping problemsor lookingattheanswersattheend of the book.Reterto the relevant pages only if you getstuck. : ~ - epreviouspages youhave learnedabout thenormal anatomy :-' =-;; brain,theorbits, andthe face.It may besome timeago that __ 5, died the technical basics of CT and about adequate pre- : - anon of the patient. Before going on with the anatomyof the :.=- J()(al bone, it would be good to check on and refresh your : edge of the last chapters. All exercises are numbered : :-.;.~utively, beginning withthefirstone on page32. ~ Writedown from memory thetypical windowparameters for images ofthe lungs, bones, and soft tissues. Note precisely - ;;width andcenter ofeachwindow in HUand give reasons for the differences. If you havedifficulties answering this question,go back - :.:;es 16/17to refreshyourmemory. _ ; I pleura window: Center Width Gray scale range HUto HU : : -;;window: HU to HU : :-:<ssuewindow: HU to HU II a) b) c) How would you differentiate between long structures such as vessels, nerves, or certain muscles and nodularstructures • phnodes or tumors? (You will findthe answeron p. 15.) In which vessels might you find turbulence phenomena, caused by the CM injection, that must not be mistaken for a ~..i i Ii you don't remember,check backtopp. 21-23.) What aspects should you always oe are referring your patients to a CT -,a . n which probably requires the l.v, - .s:' of CM?The same applies if you consider =c ~ ; someoneto avenogram/angiogram oran _ ::- procedures are carried outwith nonionic ::--oining iodine). MRI examinations, however, = -"";.ed out with gadolinium as the CM. (The =: ;0 questions 3 and 4 can befound on pp. _,, : -9.) - •," Whichtwotypes of oral CM doyou know?What specific aspects must you consider when administering this kind of CM .;;- : ·ng onthe clinical problem?Arethereany consequences foryourlist? :'" _, (name) Indication Special schedule
46 Cranial CT Normal Anatomy of the Temporal Bone (Coronal) In order to evaluate the organ of hearing and balance, the petrosal bone is usually examined in thin slices without overlap (2/2).To ensure optimal resolu- tion,thewholeskull isnotimaged,justtherequiredpartofthepetrosalbone.The two petrosal bones (55b) are therefore enlarged and imaged separately. Only then is it possible to differentiate small structures like the ossicles (61a-i:), cochlea (68),andthesemicircular canals(70a-i:) . Thetopogram (Fig. 46.1) indicates the coronal imaging plane.The patient must • be placed in a prone position with his or her head hyperextended. Note the pneumatization of the mastoid cells (62) and the usually thinwalls of the outer auditory canal (63b). Inflammation ofthese air-filled sinuses leadsto characte- ristic effusion and swelling ofthe mucous membranes (see Fig. 60.2a). Fig. 46.1 Fig. 46.2a Fig. 46.2b 55b ~ 5.0a...... Fig. 46.3a Fig. 46.3b
Cranial CT Normal Anatomy of the Temporal Bone (Coronal) 47 Fig. 47.1b Fig. 47.2b- :. ~7 . 2a - _ . ~ 7. 3a Fig. 47.3b
48 Cranial CT Normal Anatomy of the Temporal Bone (Axial) Test Yourself! Exercise NO.7: Analogousto coronalimages, axial images are obtained withthinslices without overlap, i.e.,2 mmthicknessand 2 mm increment and viewed on bone windows. The cerebellar hemispheres (104),thetemporal lobe (110),andthesofttissues of thegaleaare therefore barely identifiable.Apart from the ossicles (61 a--i:) and the semicircular canals (70a-c) , the internal carotid artery (64), the cochlea (68),andtheinternal (63a)and external auditory canals (63b) are visualized.The funnel-shaped depression in the posterior rim of the petrosal bone (Fig, 48,2a) represents the opening of the perilymphatic duct (** = aqueduct of the , cochlea) intothesubarachnoidspace. InFigure 49.1 a note thelocalizationofthe geniculate ganglion of the facial nerve (*) ventral to the facial canal.The topo- gram (Fig. 48.1) shows an axial plane ofsection, obtained withthepatient lying supine. Think about differential diagnoses involving effusioninthemiddle ear (66), theouter auditory canal,or themastoid cells(62) and compare your results with the cases shown on pages 60and 62to 63. Fig. 48.1 Fig. 48.2a Fig. 48.3a ~ ~ Fig. 48.2b 146 00 Fig.48.3b
Fig. 49.1b 146 ~163 Fig. 49.2b 163 ~ Fig. 49.3b 49
50 Cranial CT Normal Variants Do you remember the systematic sequence forevaluating eeT scans?If not, please go back tothe checklist on page 26ortoyour own notes on page 32. After evaluating thesoft tissuesit isessential toexamine the inner andoutereSFspaces.Thewidthofthe ventricles andthesurface SAS increasescontinuouslywith age. Fig.50.1a Fig.50.1b Since thebrainofachild (Fig. 50.1a) fillsthe cranium(55),theouter subarachnoidspace isscarcelyvisible,but withincreasing age the sulci enlarge (Fig. 50.2a) and eSF (1 32) becomes visible between cortex and calvaria. Insome patients this physiologic decrease in cortex volume is especially obvious inthefrontal lobe (111).The space between it and thefrontal bone (55a) becomes quitelarge.This so-calledfrontally emphasized brain invoiution should not be mistakenforpathologiC atrophyof the brainor congenitai microcephalus. If the eTscan inFigure 50.1a had been taken of an eiderly patient, one would have to consider diffuse cerebral edema with patholo- gically effaced gyri.Beforemaking adiagnosis of cerebral edema or brain atrophy you shouldtherefore always check on the age of the patient. Fig. 50.2a Fig. 50.2b Figure 50.2a shows anadditional variationfrom thenorm. Especially in middle-aged femalepatientsyouwill sometimes find hyperos- tosis of the frontal bone (55a) (Steward-Morel-Syndrome) without any pathologic significance. The frontal bone (55a) Is internally thickened on both sides, sometimes With an undulatinq contour. In cases ofdoubt. the bone window can help to differentiate between normal spongiosa and malignant infiltration.
Cranial CT Normal Variants An incomplete fusion of the septum pellucidum (1 33a) can, as another variation, lead to the development of a so-called cavum of the septum pellucidum. Please review the normal scans in Figures 30.2a, 30.3a, and 31.1a for comparison. Usually only the part of the septum located between the two anterior horns of the lateral ventricles (Fig. 51 .1 a) is involved, less frequently the cavum extends all the way to the posterior horns (Fig.51.2a). In the plane of Figure 51.1 , just medial ofthehead ofthe caudate nucleus (1 17), you can evaluate both foramina of Monro (141) which func- tion as arouteforthechoroid plexus (123) and the CSF from the lateral ventricles (133) to the 3rd ventricle (134). Refresh your anatomic skills by naming all other struc- tures in Figure 51 .1 and checking your results in the legend. The radiologist will rarely be confrontedwithan eye pros- thesis ( * ) after enucleation of a globe (150). In patients with a history of orbital tumor, a local relapse, t.e, in the retrobulbar space (2) has to be ruled out in check-up CT scans. The CT scan of the orbit in Figure 51.3a showed minor postoperative change with- outanyevidence of recurrent tumor. Fig.51.3b 51
52 I Cranial CT Partial Volume Effects One ofthe most important rules of CTscan interpretation is to always compare several adjacent planes (see pp. 14-15). If the head istilted even slightly during the scan procedure, one lateral ventricle (133) for example, can appear in the image plane (dS)' whereas the contralateral ventricle is still outside the plane (Fig.52.1). Oniy its roofwill appear. The computer therefore calculates a blurred, hypodense area which could be mistaken for a cerebral infarction (Fig. 52.2a). By comparing this planewith the adjacent one below it (Fig. 52.3a), the situation becomes clear, since the asymmetric contoursofthe imaged ventricles arenow obvious. Fig. 52.1 Fig. 52.3a Fig. 52.2b Fig. 52.3b This exampleillustrates the importance ofthecorrect placementof the patient's head. The exact position ofthe nose inan a.p, projec- tion is obtained by usingthegantrypositioning lights. Involuntary movements ofthe head can be kept at a minimum by soft padding. In ventilated orunconscious patientsan additional immobilization ofthe head with suitablebandings may benecessary.
Cranial CT Partial Volume Effects 53 :c, "I thefirststeps in interpreting CCTs is the inspection of the ---: tssues, Contusions with subcutaneous hematomas (8) may - : cate skull trauma (Fig. 53.1 a) and call for a careful search for - "rracranial hematoma.Many injured patients cannot beexpec- ? : :0 have their heads fixed for the duration of the CT scan, and - -, Questionof whether it isjust an asymmetric projection of the "_ base or a real hematoma can be answered by comparing OL,ccent sections (Fig. 53.2a). In this example the bones of the :- C111 base caused the hyperdense partial volume effect. Despite -~ obvious right frontal extracranial contusion, intracranial this leads toconsiderable rotation.Asymmetriccontours(* inFig. 53.1 a)of the roof ofthe orbit (55a),the sphenoidbone (60),or the petrosal bone (not asymmetric in the illustrated examplesI) are therefore frequentoccurrences and may leadto misinterpretations ofthe hyperdense bone as afresh intracranial hematoma. Fig. 53.1 b bleeding could not be confirmed. Please note the considerable beam hardening (bone) artifacts (3) overlapping the brain stem (107). Such artifacts would not appear in MR images of these levels. Fig. 53.2b
54 Cranial Pathology Intracranial Hemorrhage After havingdiscussed thatpartialvolume effectsduetoasymmetricprojections (i.e.,55b inFig.54.2b) may bemisinterpreted asacute hematomas,thischapter will pointout the characteristicsofthedifferent types ofintracranial hemorrhage. Bleeding Caused bya Contusion As a direct consequence of skull trauma,cerebralcontusion bleeding may occur (Fig. 54.1 a). An acute hemorrhage (8) appears as a hyperdense mass which may be accompanied by surrounding edema (180) and displacement of adjacent brain tissue. In anemic patients the hematoma is less dense and may therefore appear isodensetonormal brain. ~ thevascularwailisdamagedonly secondarily by hypoperfusion me- diated by edema,hemorrhage may notoccuruntil hoursor.more rarely, days after skull trauma. A eeT obtained immediately after skull trauma which does not show any pathologic changes istherefore not a good predictor since deiayed cerebral bleeding cannot be ruled out. A foilow-up scan should be obtained if the patient's condition deteriorates.After completeresorp- tion of a hematoma (Fig. 54.2a), a well-defined defect isodense with eSFremains (132). Characteristics Hyperdenseblood inthesubarachnoid spaceorthebasalcisterna instead ofhypodenseeSF Fresh hematoma:crescent-shaped, hyperdense bleeding closetothe calvariawith ipsilateral edema; hematoma isconcave toward hemisphere; may extend beyond cranial sutures Biconvex,smooth ellipsoidal inshape; close tocalvaria; does notexceed cranial sutures; usuaily hyperdense, rarelysedimented Type ofbleeding Table 54.1 Subarachnoid bleeding Subdural bleeding Epidural bleeding Fig.54.2b Fig. 54.1a Fig. 54.2a Contusion frequently leadsto an epidural. subdural, or subarach- noid hemorrhage and may leak into the ventricles (Fig. 55.1 a). Possible complications of such leakage or of a subarachnoid hemorrhagearedisturbedeSFcirculationcausedbyobstruction of the pacchionian granulations,the foramen ofMonro, orofthe 4th ventricle. An hydrocephalus with increased intracranial pressure and transtentorial herniationof the brainmay result. Epidural and subdural hematomas can also lead to major dis- placement of brain tissue and to midline shifts. Quite frequently this in turn causes obstruction of the contralateral foramen of Monro resulting in unilateral dilation of the lateral ventricle on the side opposite thebleeding (Fig. 56.3).Thecharacteristicsusefulin differential diagnosisof the various types of intracranial bleeding are listedinTable 54.1.
Cranial Pathology Intracranial Hemorrhage 55 -00'= is intraventricular extension of intracranial hemorrhage - 55.1 a), physiologic calcification of thechoroid plexus (123), " lateral (133) and3rdventricles(134),aswell asthoseofthe -='" aeandthe pineal (148), must be distinguished fromfresh, :£'Censebloodclots (8). Pleasenotetheedema (180) surroun- , -.ehemorrhage (Fig. 55.1a). - = canent has been lying supine, a horizontal fluid-fluid level ec Jy blood sedimenting in theposterior horns of the lateral ventricles may be seen (Fig. 55.2a). The patient is in danger of transtentorial herniation if the ambient cistern is effaced (Fig. 55.2b). In this case the 3rd ventricle is completely filled with clotted blood (..in Fig. 55.2a, b), and both lateral ventricles are markedly dilated. CSF has leaked into the paraventricular white mater (¢). In addition, a lower section of this patient shows subarachnoid hemorrhage intotheSAS ( in Fig. 55.2b). =, 55.1b Fig.55.2b Fig.55.3b id::aro!oC.hnoid Hemorrhage - _"ecnvehydrocephalus,ascaused bysubarachnoid hemorrhage(8 inFig.55.3a, b),may easilybeidentified because thetemporal _ 33) of thelateral ventricles appear distended. In suchcases it is important to haveacloserlook at thewidth ofthe SAS overthe - =-"- suriace: blunted cerebral gyri usually indicate a diffuse cerebral edema. In the present case though, the width of the Sylvian =(127) andthesurface SAS arenormal.Acute edema is thereforenot presenl(yet).
56 Cranial Pathology Intracranial Hemorrhage Since the surface SASs arevery narrow in younger patients, it is possible to miss asubarachnoid hemorrhage in children.The only identifiable sign may be a small hyperdense area adjacent to the falx(130).Inadultsasmall subarachnoidhemorrhagealsocauses only a minor, circumscribed areaof hyperdensity (8 in Fig. 56.1 a). At the timeofthisCTscan thebleedingwas soslight that it had not yet caused anydisplacement ofbraintissue. Subdural Hematoma Bleeding intothesubduralspace results fromcerebral contusions, damaged vessels inthepiamater, orfromtorn emissary veins.The hematoma initiallyappearsasa long, hyperdense margincloseto the skull (8 in Fig. 56.2a). In contrast to an epidural hematoma, it isusuallysomewhat irregular inshape and slightlyconcavetoward the adjacent hemisphere.This kind of bleeding is notconfined by cranial sutures and may spread along the entire convexity of the hemisphere. Subdural hematomas can also cause marked displacement of brain tissue (Fig.56.3a) and lead to disturbances in CSFcircula- tionand toincarceranonofthe brainstem inthetentorial notch. It isthereforenot as important,fortreatment purposes,todistinguish between a subhematoma or an epidural hematoma as it is to ascertainthe extent of the hemorrhage. Hematomas with the pro- pensitytoexpand,especiallyif edemaisathreat,shouldtherefore bedrained or treated surgically. Fig. 56.3bFig. 56.2bFig. 56.1b Chronic subdural hematomas (8 in Fig. 56.3a) may appear homogeneously hypodenseor show inhomogeneous density with sedimen- tation of blood.The danger involved in a small, venous bleed is the symptom-free interval and the slowonset of somnolence up tothe development of a coma.Therefore, a patient with suspected bleeding aftercranial trauma should always be kept under observation in order todetect anyclinical deterioration.
Cranial Pathology Intracranial Hemorrhage 57 Extradural Hematomas Bleedings into the extradural spaces are usually caused bydam- agetothe middle meningeal artery, and rarely by venousbleeding romthesinuses orthe pacchionian bodies. Predisposed areas are temporoparietal regions or sometimestheposterior cranial fossa, in whichcasethereis severe danger of tonsillar herniation.Arteri- al hemorrhage lifts the durafrom the innersurface ofthe cranium (55) and then appears as a biconvex, hyperdense area with a smooth border to the adjacent hemisphere.The hematoma does not extend beyond thesutures between thefrontal (55a),temporal (55b), parietal (55c), or occipital (55d) bones. In small extradural hematomas (8)thebiconvexshapeisnot distinct (Fig,57,1a),mak- ing it difficulttodifferentiate the findingfromasubdural hematoma. It is importantto distinguishbetween a closed skull fracture with an intact dura, and a compound skull fracture with the danger of secondary infection. An unequivocal sign of a compound skull fracture(Fig.57.2a) istheevidence ofintracranial air bubbles(4), whichprovethat thereisaconnectionbetweenintracranial spaces andtheparanasal sinuses ortheoutside. Itis difficulttodetermine whether the bilateral, hyperdense hematomas (8) in Figure 57.2 areextradural orsubdural. Inthis case thedistortionofthemidline was caused by the right-sided, perilesional edema (left side of Fig. 57.2a) since it was shifted toward the left (the side of the hematoma). Fig,sr.ie Test Yourself! Exercise 8: Fig. 57.2b Test Yourself! Exercise 8: Spacefor your suggested answer: .vhen looking at the imageofanother patient (Fig.57.3), you will note several pathoiogic changes.Usethefree space below the picture : note how manydifferent types of bleeding (if any) you can distinguish and what other pathology/complications you suspect. You wili < dtheanswersat fhe end ofthebook, but remember: bea good sport and don't cheat, thinkfirst!
58 Cranial Pathology Stroke Apart from cardiovascular and malignant diseases, cerebral infarctionsareamong the most frequent causes ofdeath.Athrom- busoccludes acerebral artery, whichleadstoirreversible necrosis in the area of blood supply. Vascular occlusion develops in association with atherosclerotic changes of cerebral arteries or, less frequently. as a result of arteritis.A further cause are blood clots from the left heart or thrombotic plaques from the carotid bifurcationwhichembolize into a cerebral vessel. Incaseof embolization,diffuselysituated,small,hypodensezones of infarctioninboth basal gangliaandhemispheresaretypical. Old emboli result in small, well-defined areas (180) which eventually appear isodense to the CSF (132). Such areas are called lacunal infarcts(Fig.58.1a).Adiffusepattern ofdefectscalls forcolor flow Doppler imaging orcarotidangiographyandan ecnocaroiocramto exclude atrial thrombus. Please remember that in a suspected stroke it might take up te 30 hours to distinguish clearly the accompanying edema as " hypodense lesion from unaffected brain tissue.A CT scan shoulc berepeated if the initial scandoes not show any pathologicchan- ges even though the patient is symptomatic and if symptoms de notresolve (resolutionof symptoms points to atransient ischemic attack,TIA). In case of aTIA: no abnormalitiesarevisible intheCT scan. In contrast totheTIA,the prolonged reversible ischemic neurolo- gic deficit (PRIND) is often associated with hypodense zones of edema inthe CTscan. Fig.58.1a Fig. 58.2a Fig. 58.1b Fig.58.2b If the area of infarction corre- sponds to the distribution of a cerebral artery, one should con- sider an occlusion of the corre- sponding blood vessel. In classi- cal infarctions of branches of the middle cerebral artery, ischemia will cause a hypodense area a edema ( in Fig.58.2a). Depending onthe size,the infarc- tion may havesevere mass effect and cause midline shift. Smaller areas of infarction do not usually show any significant midline shift. If the arterial walls are damaged, bleeding may occur and appear as hyperdense areas coatingthe neighboring gyri. The unenhanced follow-up CT scan in Figure 58.2b shows an additional bleed into the head of the right caudate nucleus ( ) and right putamen ( ). In this casethe infarction Is 2 weeks old and necrotic tissue has been mostly resorbed and replaced by CSF.
- = 59.3a Fig. 59.3b Whereas differential diagnosis (DD) of intracranial hemorrhage and infarction may be obtained without the use of CM, detection of cranial metastases (7) is definitely im- proved by the administration of i.v CM. Even small areas in which the blood-brain barrier is disturbed become visible (Fig. 59.1 a). Large metastases sometimes cause sur- rounding edema (180) which could be misinterpreted asinfarct-related edema on unenhanced imagesif the metastasis appears isodense tothe adjacent tissue. After l.v. CM the lesion in the left hemisphere (7) is clearlydemarcated (Fig. 5g.2a).Did you also spot the second, smaller metastasis within the right frontal lobe, which also shows some surrounding edema (180)? The differential diagnosis of brain tumors is made much easier by the injection of i.v. CM. In the unen- hanced image (Fig. 59.3a), the temporoparietalglioblastoma onthe left (7) which has acentral necrosis (181) couldhave been mistaken for cerebral infarction. The post-CM image, however, reveals the typical appearance of a glioblastoma with an irregular rim enhancement of its margin (Fig. 59.3c). Abb.59.3c 59
60 Cranial Pathology Inflammatory Processes Another example of the advantages of i.v. CM is the demonstration of inflammatory processes, since the accompanying defect in the blood- brain barrier will not show on an unenhanced image. Figure 60.1a shows hypodense edema (" ) in an unenhanced section of a patient suffering from aorticvalve endocard- itis. Contrast medium (Fig. 60.1b) confirmed the finding by enhancing the inflammatory process (+). Bacteria from the aortic valve caused this septic embolism in the leffoccipital lobe. Aretention cyst, which often appears inone oftheparanasal sinuses, shouldbe considered in the differential diagnosis of advanced inflammations. They typically have a broad base on the wall of a paranasal sinus, extend into its lumen, and havea roundish convex shape ( 1 " inFig. 60.3). Inflammation of the paranasal sinuses and of the middle ear can already be diagnosed in native imagesas effusions (8), for example in the normally air-filled mastoid cells (62). Swelling of the mucous membranes oftheexternal auditory canal (63b) is visible without the need for CM. Figure 60.2a shows bilateral otitis externa and media, which is more severe on the right side where it involves the antrum and the mastoidcells. Withprogress- ingabscess formation, an image on bone windows shouldbe obtained in ordertodetectpossible bone erosion. Such cysts areonlyof significance if they obstruct the infundibulum (0) of the maxillary sinus or the semilunar canal (@), causing an accumulation of secretions. In patients with chronic sinusitis, it istherefore important to check for an unobstructed lumen of the semilunar canal (@) or for variations which may restrict mucociliarytransport of secretoryproducts. Haller's cells ("), a pneumatized middle concha (166), and a pneumatized uncinate process (@}) are among the most frequent variations. All of these variations can obstruct the semilunar canal and cause chronic, relapsing sinusitis. Fig.60.2b @ Fig. 60.3 Fig.60.2a
Fig. 61.1b You have already seen pathologic changes in the lacrimal gland (pp. 39/40) and the CT morphology of an eye prosthesis (p.51). Every mass within the orbitshould, of course, be diagnosed early and treated effec- tively because of the possibly severe consequences to vision. In order not to miss tumorinvasion into thewalls of the orbit, bone windows should also be obtained. In Figure 61 .1a thereis a hemangioma (7) withinthe retrobulbar fat (2), which is not ne- cessarily an indication for operation because of its benign character. In thiscase it causesa minor proptosis. EndocrineOphthalmopathy Minimal discrete changes can be missed duringthe reporting of a CT scan: endocrine ophthalmopathy often appears as part of Graves' disease and can, in its early stage, only be diagnosed on the basisof a thickening of the external ocular muscles, e.g. the inferior rectus muscle(47b in Figs.61.za, 61.3a). Myositisshould be consideredinthe differential diagnosis. " this early sign is not detected, the disease of the orbital tissue, which is most probably an autoimmune disease, may progress in the absence of therapeutic intervention. Therefore, you should always examine the symmetry of the external ocular muscles (47) when looking at an orbital CTscan. Therewill etten be atypical tempo- ral pattern of involvement. The first finding is an increase inthe volume of the inferiorrectus muscle (47b). Thedisease will continueand affect themedial rectus muscie (47cl,the superior rectus muscle (47a), and finally all the other external ocular muscles. 61
62 Cranial Pathology Facial Skeleton and Sinuses Incontrast to benign retention cysts (p.60), malignanttumors ofthe paranasal sinuses often lead to destruction of the facial bones and may invade the orbit, the nasal cavity (77), or even the cranial fossa. It is therefore useful to examine both the softtissue and bone windows.Forplanning aresection,different CT planesmight benecessary.Thefollowingexample shows atumor of theparanasal sinuses (7)inanaxial (Fig. 62.1 a)and acoronal view (Fig.62.2a).Originatingfromthemucousmembranes ofthe right maxillarysinus(75),the tumorhas infiltratedthenasal cavity (77) and the ethmoid cells. Fig. 62.1 a Fig. 62.1b Fig. 62.2b
-g.63.4a Fig. 63.1b Fig. 63.2b Fig. 63.3b Fig. 63.4b The most common reason for doing a coronal CTscan is, apart from determining the extent of chronic sinusitis,thediagnosisof fractures: in fractures of the orbital floor (Figs. 63.1a, 63.2a) any accompanying herniation of retrobulbar fat (2) or the inferior rectus muscle (47b) into the fracture site (* ) or even into the subjacent maxillary sinus (75) should be determined preopera- tively. Diagnosis of the fracture in Figure 63.2a is easier because there are dislocated bone frag- ments. In addition. it is important to detect indirect signs of frac- ture. such as very fine, step-like contours of the bones and secondary bleeding (8) into the nasal cavity (77) or the frontal (76) and maxillary sinuses (75). Another important question is whether or not the head of the mandible (58a in Fig. 63.3a) is fractured or the maxillary bone (57) has been fractured and displaced (*) from the sphenoid (50) bone (Fig. 63.4a). In this case, severe bleeding (8) re- quired intubation (182) and a nasogastric tube (182). Fractures of the facial skull (Le Fort[33]) IYill Straight across the maxiliary bones and the maxil- lary sinuses(Guerin'sfracture) IYP~ Across the zygomatic process of the maxilla, into the orbit, and through the frontal process of the maxilla to the contralateral side; maxillary sinus not involved IYI!.U!! Involving the lateral wall of the orbit and the frontal process of the maxilla to the contralateral side;ethmoid cells and zygomatic arch usually involved, sometimes also affectingthe baseof the skull. 63
64 Cervical CT Whenever there is no contraindication, CT examinations of the neck are carried out afteri.v. administration of CM. Malignant and inflammatory processescan bedepicted moreaccuratelywiththe aid of CM. Adequate enhancement of cervical vessels requires higherdoses ofCMthan,forexample, inCTs of the head. Inspiral CT, the injection of CM must be precisely timed to the acquisition of data. There are specific recommendations and suggested schemes forCMinjection atthe end of themanual. Selection of the Image Plane Inan analogousmanner to head CT, a sagittal planning topogram (scanogram) at lower resolution is obtained first. The transverse (axial) levels andgantry angulation aredeterminedfrom this topo- gram (Fig,64.1).Usually sections of the neck are obtained usinga 4-5 mm thickness.The axial images areobtained and printed as viewed from caudallyso the right lobe ofthe thyroid is imaged to the left of thetrachea,the left lobetothe right. Images should be obtained with a small-scan field-of-view to optimize detail in smaller structures in the neck. As the thoracic inlet is approached during the scanning, the scanfield-of-view is increased to include possible abnormalities in theclavicular fossa and the axilla. Artifacts caused by dental prostheses (3) usuallyobscure surrounding structures (*) in only one or two levels (Fig. 64.2a). It may be necessary to carry out a second acquisition at anotherangle (Fig. 64.2b) to reveal areas hidden by artifact (* ). Fig.64.1 Fig. 64.2a Fig.64.2b Systematic Sequence for Readings We have already recommended a systematic approachwithwhichto read CTscans ofthe head (see p. 26). For cervical CTs there is also no 'one and only' approach. The checklist presented here was deveioped through experience and isjust one ofmany options forthe beginner. Eachexaminer is free tosetup hisorher own checklist and strategy. During neck imaging,separatehardcopies at bone windows are rarely printed owing to cost. The radiologist must remember to check images at bone windows on the screen for fractures or lytic lesions. Checklist for Reading Cervical CT Images -+ Symmetry of neck musculature? -+ Condition and clarityof fat? -+ Normal perfusion of vessels? -+ Thrombosesor atheroscleroticstenoses? -+ Symmetryand definitionofsalivary glands? -+ Thyroid parenchyma homogeneousandwithout nodules? -+ Anyfocal pathologic enhancement with CM? -+ Narrowing of the tracheallumen? -+ Assessment of lymph nodes? Number and size? -+ Cervicalvertebraeexamined in bone window? -+ Vertebral canal patent or narrowed?
Cervical CT Normal Anatomy 65 - -eradiologist quickly reachesthelimits of CTresolution (perhaps ;..so of his/her anatomic knowledge) when trying to identify all of -9 different neck muscles.We havethereforereducedtheamount :' detail in the accompanying drawings so that smaller muscles ;;8 grouped.Singlemuscles have littleclinical relevance and thus - elegendstotheseimagesrefertocombinedmusclegroups,e.g. :;-e scalene muscles, the erector spinae muscles. Readers who ant more anatomic detail should consult the relevant literature :5,31] :ervical images usuallybegin at thebaseof theskull andcontinue :audallytothethoracic inlet. Thecranialsections (Figs.65.1-65.3) neretore include the maxillary sinus (75). the nasal cavity (77), and thepharynx(176). Dorsalto thepharynx liethelongus capitis and longuscervicismuscles (26), which extendcaudally. Lateral to the mandible (58). beginning in Figure 65.2a. the parotid gland (1 53) issituatednexttothelarge cervical vesselsand vagusnerve (also p. 64). In front of the pons/medulla oblongata (107), the vertebral arteries (88) join to form the basilarartery (90). Thespreadof inflammatory processes withinthecervicalconnec- tivetissue spacesis restricted withincompartmentsdefined bythe cervical fascia [30].The differentlayers of the cervical fascia are explained on the following page (Fig. 66.4). - . 65.1b Fig. 65.2b Fig. 65.3b
66 Cervical CT Normal Anatomy Fig. 66.3b Compartments of the Neck If infections or inflammatory processes originate in the suprasternal (0) or pre- tracheal spaces between the superficial fascia (* ) and the dorsal layer of the pretracheal fascia (**), they cannot spread into the mediastinum because both fascias insert intothe sternum(56 inFig.66.4).Atthelevelof theparotidgland there is a similarbarrier consisting of the sagittal septum which splits a retropharyngeal from a parapharyngeal space. Inflammations originating furtherdorsal, between the pretracheal (* * ) and theprevertebral (*** ) fascias, can spread caudally into the mediastinum. . Fig. 66.2b Further caudally the following cervical muscles become visible beneath the trape- ziusmuscle(23): medial liethe semispinalis capitis (28) and longissimus capitis muscles (27), and more laterally the spleniuscapitis muscle (25). The parotid gland (153) is situated cranial and posterior to the sub- mandibular gland (154) next tothemandible (58). The pharynx (176) is surrounded by Waldeyer'sringof tonsillartissue (1 57,156). Note that the carotid bulb is situated be- tween Figures 67.4a and 68.2a; it is the point at which the common carotid artery (85) bifurcates into internal (85a) and exter- nal(85b) carotid branches. Underthe tongue (155) the floor of the mouth is organized in layers. From cranial to caudal are: the genioglossus muscle (33), further laterally thegeniohyoid muscle (34),andthe anterior belly of the digastric muscle (31). The thin superficial muscleis the platysma (48). Fig. 66.1b
Fig.67.4b t==t¥=-::;'J=fL- Fig.66.1 - r---71+ -+t- Fig. 66.2 7"--7"-CH--I+- Fig. 66.3 H--H-"~'--"::'_....".+-++-H- f ig. 67.1 "-I+--H-++- Hg. 67.2 -t+++-++- Fig.67.3 -';H-,Lf---++- Fig.67.4 8 Fig. 67.5 67
68 Cervical CT Normal Anatomy The bifurcation of the common carotid artery (85) is an area of predilection for atherosclerotic plaques (Fig. 68.1 a)which may be complicated by thrombus deposition (* ). Notethe positions of the cricoid (167) and arytenoid cartilages (168) at the rima glottidis (178). In these normal individuals, eMenhances the density not only of the internal (86a), the external (86b), and the anterior jugular veins (86c), but also of the vertebral artery (88) in the transverse foramina of the cervical vertebrae. Always check for degenerative changes at the margins of the bodies of cervical vertebrae (50)orforherniated discswhichmight narrowthe spinal canal containing the cervical cord (54). On either side of the trachea (81) lie the two lobes of the thyroid gland (83), which shouldhaveasmoothoutlineand havehomogeneousparenchyma (Fig. 68.3a). Fig. 68.1a Fig. 68.2a Fig. 68.3a Fig. 68.3b
Cervical CT Normal Anatomy 69 I I I I Fig.68.1 -t+--+''+..... Fig.68.2 -++---++ ----, Fig.68.3 -+t==+=h~~'~~=t=~Fig.69.1 - Fig.69.2 -++----+---+I---'-- --+--.....,;---+- -H Fig. 69.3 -++------+---fl,,.--'----:------fl---+--H Fig. 69,lb Fig.69.2b se of its iodine content, the thyroid gland (83) appears hyperdense compared - surroundingmuscles both beforeand, even moreso,after theadministrationof eM "'";5. 69.1-69.3). Beginners occasionally mistake the esophagus (82), dorsal to the '-ea (81), for swollen lymph nodes or a tumor. In case of doubt, comparison with srsections is helpful: usuallya small, hypodense area indicatesair in the lumen of _. esophaqus in an adjacent section. As a rule, the cervicothoracic junction is 7 ~ -ned withthearms elevatedtominimize artifactsdue tobones.Themusclesofthe I girdleas well astheshoulder joints thereforeappear in unfamiliar positions. -'c 'allowing chapter deals with neck pathology and includes a short "Test Yourself"; -d; es and drawings of normal anatomy extending further caudallyare continued on - :~ 74. - . 69.3a
Cervical Pathology Inflammatory Processes and Tumors 70 Enlarged cervical LNs (Fig.70.1a) appear conspicuously asisola- ted nodular masses (6) thatcannot befollowed into adjacent levels (seep.15).Large lymphomas(7) orconglomerateLN masses (Fig. 70.1a) often developcentral necrosis (181). It is sometimes diffi- cult to distinguish them from abscesses with central necrosis (181) asshown,for example, inFigure70.2a.Abscesses typically infiltrate the surrounding adipose tissue with a streaky pattern of edema (180) so that structures such asarteries, veins, or nerves (on the leftsideoftheneckinFig.70.2a) becomedifficult toiden- tify. In immune-suppressed patients. abscesses can become remarkably large. Compare the scans in Figures 70.3a (unen- hanced)and 70.3b (enhanced):after injection ofCM,the outer wall of the abscess (*) as well as the central septa have become enhanced.Theseappearances aresosimilar to large hematomas or necrotic tumors that a differential diagnosis may be difficult without adetailed clinical history. Notealso the atherosclerotic plaques orthromboses inthe lumen of thecarotid artery (85) asinFigure70.1a. I Fig.70.1b Fig.70.2b Fig. 70.3b (enhanced)
Cervical Pathology Thyroid Gland 71 - - carenchvrna of the thyroid gland (83) should appear sharply srcatedand have an homogeneous pattern in CT scans. The =; e transverse diameter of each lobe is 1- 3 em, 1- 2 em _- , Iyand 4- 7 em in craniocaudal direction.The total volume - ~ yroid gland varies between 20and 25 ml.If thethyroidis enlarged,check for tracheal compressionorstenosis (81) andthe caudal border ofthe goitershould be determined. A benign struma (83) may extend into retrosternal regions and laterally displace supra-aorticvessels (85,87,88) (Fig. 71.2). Fig.71.1b Fig. 71.4b (181) appear. The tracheal walls (81 ) are compressed and may become infiltrated. After partial resection of a struma (Fig. 71.4), some thyroid tissue (83) may still beseen close tothetrachea. In this case the left internal jugularvein was also removed and the lumen of the right one (86a) is therefore larger than normal. Fig. 71.3bt. 1.2b --E oarenchyrnal structure of a thyroid carcinoma (7) appears -: "ilOgeneous, and the contours are not easily distinguished tr: eremaining normai parenchyma (83) (Fig 71.1 a). sc anced stages ofcarcinoma (Fig. 71.3), cervicalvessels and -- esarecompletelysurrounded bytumor,and areas of necrosis
Test Yourself! 72 Before continuing tothe next chapters, these exercises give youan opportunity to check your knowledge. The questions become increasingly difficult as yougoalong: the firstquestionshould pose no problems, whereas the last ones of each chapter will bea real challenge. Make the most of this opportunity for self-assessment and take it in good grace if you find you missed something. In our experience these littletests will help youtoremember better what you have learned. It is muchmoreeffective tolook upeach gapinyour knowledge as it occurs thantoskipaproblem and turn directlytothe answer.You should thereforeonly turn to the answers at the back of the book when you havesolved eachproblembyyourself.That way you will notsee answersto questions you haven't tackled yet. It will keep you in suspense! . . . . Which window setting (window center and windowwidth in HU) would you select for an optimal brain CT? Why? Before beginningthe examination, what gantry angle do you choose for your slices in the planning topogram and what section thickness and section increments do you use?Whydid youchoose these settings? tBDIiI What doyou rememberabout the criteriawith whichto distinguish the fourtypes ofintracranial hemorrhage?Withwhich kindsof hemorrhageareyou familiar? How can youdifferentiate betweenthem inCT morphology?What complicationsor consequences must you particularly watchoutfor (consult pp. 54-57 for help)? Type of hemorrhage: Characteristics: • • • • IDIilIiI How can you recognize asubarachnoid hemorrhage in children? ~ Imaginethe anatomyofthe cerebral basal gangliaandthendraw atransversesectionat thelevel of the internalcapsule. Compare yoursketch with Figures 30,2a and 30,2b.Repeatthisexercise occasionallyuntil youcandoit withease. I tDDD Examine Figure 72,1 carefully. The patient was involved in a car accident. Do not settle for the most obvious feature; look for other variations or abnormalities. What do you suspect? ~ Figure72,2 contains an unusualvariation; can you find it?After havinq noted it, look again to see whether you have really discovered all pathologic features.
0DlIliI The eeT in Figure 73.1 is of a 43-year- old patient. Make a note of your tenta- tive diagnosis and how youwould pro- ceed. Glili!I!Ii2t Is there any feature in this orbital scan (Fig. 73.3) that would not be con- sidered a normal finding? Note your observations below. Don't give up too quickly! Fig. 73.1 Fig. 73.3 Test Yourself! tm:mmI Do you recognize anything unusual in Figure73.2?Isthere a pathologic abnor- mality?Or is it simp- lyan artifact or even a normal finding? GDEI A confused patient, from a home for the elderly, with sus- pected intracranial bleeding is brought in for a eeT. How many fresh hemor- rhages (Fig. 73.4) doyou see? Whatis your differential dia- gnosis? Which of them is the most probable diagnosis? Which additional information could alsobe helpful? Fig. 73.2 Fig. 73.4 73
74 Thoracic CT After havingdiscussed normal anatomy ofcaudal cervical sections (p. 67), normal thoracic anatomy is presented. Fromthis page on, youwillfindthenumbercodes forthe drawings intherearfoldout. Selectionof Image Plane Asarule,thesectionsofthe thoraxare chosen inthetransverse or axial plane at thicknesses and steps of 8 to 10 mm. Sections 10mm thickwill overlap by 1 mm,for example, whenthe patient table is advanced in 8-mm steps. A small topogram (Fig. 75.1) accompanying eachsheet ofimages showsthepositionof the sec- tions relative to the major anatomic structures of the region. In order not to miss anypathologic changeswithin the lung (review p. 13), it has become accepted practice to make a hard copy of both soft-tissue and lung windows or to provide a CD with the image data. Each image can therefore beviewed at twodifferent window settings.Again thelarge number of imagesnecessitates a systematictechniqueforevaluationsoasnot towastetimelooking randomly back and forth between them. Systematic Sequencefor Readings Thebeginner often forgets tocheckthesoftlissues ofthethoracic wall because theexaminationof themediastinumandthe lungsis automatically considered more important. These tissues should therefore be evaluated first. Common sitesof abnormality are the breasts and fat in the axilla (2).After this-also using soft-tissue windows- the mediastinum is checkedforpathologic masses.The easiest approach is to orient yourself relative to the arch of the aorta (89b), which can be recognized even by the inexperienced (Fig,77.3). Fromthispoint cranially, themajor branches are iden- tified toexclude pathologic masses inthe uppermediastinumnext to the brachiocephalic trunk (88), the left common carotid artery (85), the subclavian artery (87), as well as the brachiocephalic veins (91),superior venacava (92),trachea (81),ormoredorsally, theesophagus(82).Caudally,themost common sites for enlarged LNs are: at the aortopulmonary window, directly below the bifur- cation ofthetrachea (81a), inthe perihilar tissue, posteriorto the crura ofthediaphragm (= retrocrural) nexttothedescendingaorta (89c).The presence ofafewLNs smaller than 1.5 cm indiameter intheaortopulmonary window maybeconsidered normal [19,41]. Anteriortotheaortic arch (89b) LNs of normal sizeare rarely seen in the CT. The evaluation of the soft-tissue window is complete when the heart (any coronary sclerosis, dilations?) and the lung hila(vesselswell defined andnotlobulatedorenlarged) have been checked. Onlynow shouldthe radiologist turn tothe lung or pleu- ralwindow. Since thepleural window is very wide,themarrow of the spinal coiumn aswell asthe parenchyma of the lung can be examined. It is therefore possible to evaluate bone structure in addition to the pulmonary vasculature. When examining the lung vessels, look for a gradual reduction in their diameter as you proceed from the hilum to the periphery. Pulmonary oligemiaisnormal onlyalongthe margins ofthelobes and intheperiphery. It isessential todifferentiatebetween cross-sectioned vessels and solid masses by comparing adjacent levels (ct. p. 15). Moreor lessspherical solid masses may indicate intrapulmonarymetastases.Thecheck- list will help you readthoracic CTs systematically. The simultaneous presentation of two window set- tings inonehard copy (boththe lung andthesoft-tissue window)has notproved practical because pathologic abnormalities whichhave densitylevels between the twowouldbeoverlooked. Consult thelungchapteron pages 84ff.forscansinthelung window. Checklist for Thorax Readings, 1, On the soft-tissue window: • soft tissues,especially: - axillary LNs - breast (malignant lesions?) • mediastinum infour regions: - from the aorticarch cranially (LNs?,thymoma I struma?) - hilar region (configuration andsize ofvessels, lobulatedand enlarged?) - heartandcoronary arteries(scterosisj) - fourtypical sites of predilection for LNs: • anterior toaorticarch (normal:almost none or < 6mm) • intheaortopulmonarywindow (normal: < 4LNs< 15 mm) • subcarinal (normal: < 10mm; DO:esophagus) • nexttodescendingaorta (normal:< 10mm; DO:azygos) 2, On the lung window: • Parenchymaofthelung: - normal branching pattern and caliber ofvessels? - vascular oligemiaonlyat interlobarfissures?bullae? - anysuspicious iung foci?inflammatoryinfiltrates? • Pleura: - plaques, calcification,pleural fluid,pneumothorax? • Bones (vertebrae, scapula, ribs): - normal structureof marrow? - degenerative osteophytes? - focal lyticor scleroticprocesses? - stenoses of thespinai canal?
Artifacts (3)will beobservedat thelevel ofthe thoracicinlet if eM ispresent inthesubclavian vein(87) at the timeof dataacquisition (cf. Fig. 23.3).The parenchyma ofthethyroidgland (83) should appear homogeneous and clearly defined from the surrounding fat (2). Asymmetryinthe diameter of thejuguiarvein(86) isseen quiteoften andhas nopathoiogic significance. Orthogonally sectioned branches of the axillary (93) and iateral thoracic (95) vesselsmust be distinguishedfromaxillary LNs. Ifthearms areelevated.thesupraspinatus muscle(19)lies medialtothespine of the scapula(53b) and theinfraspinatus muscie(20). Usuallythepectoralismajor(26a) andminor(26b)muscles are separated byathinlayer offat. Fig. 75.2 ;:jJ;j:~~t3~~I=I=~~3:ljFig. 75.3 --: Fig. 75.4 74 Fig. 75.1 75 Fig. 75.2a Fig. 75.2b Fig. 75.3b Fig. 75.4b
76 Thoracic GT Normal Anatomy Thoracic CTs are also viewed from caudally.The left lung (84) appears on the right side of the image and vice versa. Beginning at the aortic arch (B9b in Fig. 77.2),thelayout oftheaortic arch vesselsshould be thoroughlyfamiliar toyou.Atthesectionin Figure 76.1 ,the left subclavianartery (87) is seen most posteriorly and can be followed incranial direction intheimages on page75. Infront ofthe sub- clavian artery liethe leftcommon carotid artery (85) and the brachiocephalictrunk(88).Moretothe right andanteriorlyare the bracnio- cephalic veins(91),which formthesuperior venacava (92) at the levelsof Figures 76.3to 77.1 . In thefat of the axilla (2), normal LNs (6)are often recognizable by their typical indented shape:the hilum contains fat.At adifferent angle,the hypodense hilum will appear in the center of an oval. Healthy LNs are well defined and should not exceed 1em in diameter in this location (Figs. 76.1 and 76.3). Fig. 76.1a Fig. 76.2a Fig. 76.3a Fig. 76.2b Fig. 76.3b
Fig. 77.la The azygos vein (104) lies dorsal to the trachea (81) next to the esophagus (82). Directly above the right main bronchus, it arches anteriorly into the superior vena cava (92 in Fig. 77.2). Be sure not to confuse the paravertebral azygos vein (104), the hemiazygos vein (105) or accessory hemiazygos (105a) with paraaortic LNs (Figs. 77.3 and 76.3). 77 Fig. 77.2a Fig. 77.2b Fig. 77.3a Fig. 77.3b
78 Thoracic GT Normal Anatomy I Immediately caudal to thearch of the aorta (89b) is situated the pulmonarytrunk (90), which divides intotheright(90a)and left (90b) pulmonary arteries (Fig. 78.2). At the level of Figures 78.1 and 78.2, there is the aortopulmonary window, a site of predilection for mediastinal LNs (6).Alsocheck for enlarged LNs or malignant masses in thesubcarinal position between the two main bronchi (81 b) close to the pulmonary vessels (96) (Fig. 78.3). Near the internal thoracic (mammary) vessels (94) lies theregional lymphatic drainage ofthemedial parts ofthebreasts,whereas thelymphatic drainage ofthe lateral portions ofthe breasts is primarily totheaxillary nodes. Fig. 78.2a Fig. 78.3b Fig. 78.1a Fig. 78.3a
Iheglandulartissue (73)inthefat of the breasts oftheanteriorthoracicwall iseasily oifferentiated from skintumorsbecauseof thesymmetry (Figs.79.1 and 79.2).The main coronary arteries (77) are also distinguishable in the epicardial fat (2) (Fig. 79.3). Developa clear mental picture of the positionsof theazygos vein (104) and ;;Ieesophagus (82)next tothe descending aorta (89c) so thatyou will later be able ;0 recognizeany pathologic LNs close to these structures. Fig. 79.1b Fig. 79.2b Fig. 78.1 ~~~~i~~~~~~~Fig. 78.2 Fig. 78.3 Fig. 79.1 Fig. 79.2 Fig. 79.3 79 Fig. 79.3a Fig. 79.3b
80 Thoracic CT Normal Anatomy The leftatrium (74c) is themost posterior chamber of the heart, whereas the outlet of theleft ventricle (74d)and the ascending aorta (89a) lie inthecenter oftheheart.The right atrium (74a) lies on theright lateral side and the right ventricle (74b)anteriorly behindthe sternum (56). Only the larger central branches ofthe pulmonary vessels (96) can be seen on the soft-tissue window.The smaller, more peripheral lung vessels are better judged on the lung window (notshown here). Note the junction between the hemiazygos vein (105) and the azygos vein (104), which must not be confused with a paravertebral lymphoma (Fig. 80.2). Fig. 80.1 a Fig. 80.2a Fig. 80.3a Fig. 80.2b Fig. 80.3b
Fig. B1.3b 81
82 Thoracic CT Normal Anatomy Theinferior vena cava (80) isseen more caudally (Figs. 82.1 and 82.2), and finallythe diaphragm(30) appears togetherwiththeupper partsofthe liver (122). Many radiologistswho suspect the presence ofa bronchial carcinoma (BG) obtain images tothe caudal edgea the liver (seep. 83) because a BCoften metastasizesto the liver and the adrenal giands. The caliber of lung vessels near the periphery ofthe diaphragmissosmall that they are not visibleon the soft-tissue window, as inthepresentimages.Thepatternofthepulmonary vasculatureshouldthereforebeexamined on the lung windows, which include the negativedensity values of the Hounsfield scale. Only after thisstep has been carriedout istheevaluationofa chest CTcomplete. Fig. B2.1a Fig. 82.2a Test Yourself! Exercise 1g: Fig. 82.2b Writedowna concise but completesequenceof all criteria forinterpreting athoracic CT. Then compareyour notes withthe checklist on page 74 and repeat this exercise from time totime until you remembereverycriterion. 1) Soft-tissue window: soft-tissues, especially:
84 Thoracic CT High-Resolution CT - Normal Anatomy Segments ofthe Lung It isespeciallyimportant to be able to identifythe segmentsofthe lungs in CTimages if bronchioscopy isplanned forbiopsyor to remove a foreign body.The rightlung has 10 segments. Intheleftlung, theapical andposterior upper lobe segments have a common bronchus andthere is no 7th segment (paracardiac [medialbasal] segment ofthe lower lobe). Fig.84.1 Bronchial tree,viewfrom anterior The parenchyma next to the interlobular tissures (- -) appears avascular. The borders of the segments (.•••••••.) are usually not visible in sections of normal thickness and can only be identified by the branches of the pulmonary veins (96) which pass along these bor- ders. 1 apical 2 posterior 3 anterior 4 lateral (superiorlingula) 5 medial (Inferior lingula) 6 superior/apical 7 paracardiac/medial basal 8 anterior basal 9 lateral basal 10 posterior basal Lower lobe Upper lobe Middle lobe 9 "I :'--_- 1/2 3 4 (?0,'I=:'--- 5 1 2 3 - -1AI 6 4 Fig.84.2a Fig. 84.4a 1.... _
- •.85.3a 85
86 Thoracic GT High-Resolution GT - Pathology I High-Resolution Technique HRCTstands for high-resolutioncomputed tomography using thin sections and a high spatial resolution reconstruction algorithm. Even conventional CT scanners can acquire images of narrower slice thickness than the standard 5-8 mm.The image acquisition parameters can be adjusted on the console to a thickness of 1-2 mmif necessary. In the SCTtechnique, thinner sections can also be computed at a pitchfactor of 1:1 after acquisition(see alsop.169). However, it is not usually worth reconstructing slicesof less than 1 mm thick- ness becausethe lowsignal-to-noise ratio reduces image quality. HRCT is therefore not the method of choice for routine chest examination because radiation dosage is much higher if more sections are acquired. Longer examinationtimes and higher hard- copy filmcost ("slice pollution") arealsoarguments against using HRCT.Onlystructures withnaturallyhighlevelsof contrast suchas areas surrounding bonewill be well demonstrated. High-Resolution Effects on Image Quality Figure 86.1 shows a conventional scan of a pulmonary lesion (7) surrounded by a zone of edema or an infiltrate (185). At a dS setting of 10 mm this zonecloseiyresem- bles the poorly ventilated area at the back of the posterior lobe (178) HRCT distinguishes these areas of increased density more clearly (Fig. 86.2) because voxel averaging does not have any appreciable effect (see also p. 14). The DD includes bronchial carci- noma, metastasisofbreast cancer resulting in lymphangitis caret- nomatosa, and atypical pneumo- nia. These images show ararecompli- cation after catheterization of the right heart.The catheter was posi- tioned too peripherallyand caused hemorrhage (173) into adjacent parts of the lung. Follow-up 3weeks latershowed completerecovery. Fig. 86.1a Fig. 86.2a Fig. 86.2b
Thoracic CT High-Resolution CT - Pathology 87 : "of the many advantages of the HRCT technique is that older ~ tissue can be distinguished from acute inflammation, for pie in immune-suppressed patients or bone marrow reel- : o-ts.Older scar tissue (1 86) is always well defined (Fig. 87.1), -ereas fresh infiltrates aresurrounded bya zone of edematous ue (185) asinFigure87.2.HRCT isoften the onlymethod with - htodeterminewhether chemotherapyshould be continued in : fmphoma patient who is in the aplastic phase on therapy or whether chemotherapy must be discontinued because of fungal pneumonia. Fresh infiltrates (178) can sometimes be seen next to older scar tissue (186) (Fig. 87.3). Because the slicesare extremely thin, the horizontal interlobular fissure (*) may appear as a bizarre ring or crescentic (Figs. 87.1 and87.2). I Fig. 87.3b ~-------...., =- .87.1a =- .87.1b ',/lor areas of collapse, which are usually found close to the pleura posteriorly in the lung, must be differentiated from flat sections :' fissures (178 in Fig. 87.1). In doubtful cases, it may be helpful to repeat a scan in the prone position. Areas of collapse and poor ontilation may then disappear or be seen anteriorly. Pulmonary abnormalities due to an infiltrate or to a pneumoconiosis would be hanged.
88 Thoracic CT Anatomic Variants Amongthemanyanatomic variations ofthe thorax,an atypicai course oftheazygos vein (140) is relatively common.It can pass from the posterior mediastinum through theright apical lobe tothesuperior vena cava (92). Itislocated within afold ofthe pleura and therefore separates theazygoslobe fromtheremainderof theright upper lobe.This variation isusually discovered incidentallyonaconventional chest X-ray ( ~ in Fig. 88.1) and has noclinical significance. Figures 88.2 to 88.4 show theanomalous pathofthe vessel as it appearsin CT images. Atypical positionsor branchingoftheaortic arch(89) vesselsare rarer.Anexampleistheright subclavian artery, known asthe "Arteria lusoria," which can resemble a lesion in the upper mediastinum. Notethatnormal breast tissue,surrounded by fat(2), mayhaveveryirregularcontours(72in Fig. 88.4). When using lung windows, you should not only look for solid round lesions and inflammatoryinfiltrates, but also recognize anythinning or evenabsence of lungvessels. Fig.88.1 However, attenuation of vessels is not always a sign of emphyse- ma. Asymmetry in the broncnovascular pattern develops after a part of the lung has been resected. Inthe patient imaged in Figu- re 88.5, the left upper lobe had been removed and the remaining lungtissue hascompensated andfilledtheentireleftthoracic cavi- ty (right half of the image). There are fewer lung vessels per unit volume andanipsilateral shift of themediastinum.Thesechanges are accompanied by a slight elevation of the diaphragm. At the timeof this follow-upCT,the patient was healthy and had neither emphysema nor recurrent tumor. Fig.88,5
Thoracic Pathology Thorax Wall 89 ordingtothesequence inthe checklist onpage74,one should turn to soft-tissue windows in order to examine the soft es of the chestwall. Most abnormalities will be located inthe aeand inthe femalebreast. - aerations inLymph Nodes al axillary LNs (6) are usually oval and less than 1 em in - - " sion.Theyoften have ahypodensecenter or arehorseshoe- --;er metastaticLNs(7)areusuallypoorlydefinedanddifficultto · erentiate from surrounding fat (2). They often have central - eas of necrosis (1 81),sothat the differentialdiagnosisofan abs- .;SS with central liquefaction must be considered (Fig. 89.3). If lary lymph node metastases have been treated operatively or " radiotherapy,thedate and treatmentshould be noted onthe shapedas inFigure 89.1,afeatureknown asthe "hilumfatsign." The architecture of a normal LN is characterized by vessels enteringthe hilum,whichcontainshypodense fat. Many abnormal LNs have lost their normal contours and are rounder or irregular. Such LNs all appear solid and lack the hilum fat sign, as seen in those in the left axillain Figure 89.2. For direct comparison, two lymph nodesontheotherside inthe same image are normal. referral sheet for follow-up CT. Postoperative healing processes and scarring (186)changethe morphology of LNs (Fig. 89.4), so theyresembleabnormal nodes(see above).Againthelack of clini- cal information makes diagnosis unnecessarily difficult for the radiologist.
90 Thoracic Pathology Thorax Wall identificationof recurrent tumor.Thediagnosis of recurrent tumor ismade more difficult byfibrosisafter radiation,postoperative scar tissue,and the absence of surrounding fat. Special attention must therefore be paidtotheregional LNs (ct.pp.74,89) and the bones. so that metastases (7) in the vertebrae (50) (Fig. 90.2) are not overlooked.The bonewindow must beexamined insuchcases. Fig.90.3c Thoracic Skeleton Osteolysis within the thoracic skeleton is not uncommon and is usuallyduetoeither metastases ora plasmacell tumor. In Figure 90.3,ametastasis(7) fromathyroid carcinoma hasdestroyedpart ofthe left clavicle(52).Osteolysiscan,however,also becaused by an enchondroma or an eosinophilic granuloma, for example of a rib. In addition to destructive processes (cf. Fig. 22.3), degenera- tive processes involving sclerosis and osteophyte formation of bonemust be differentiatedfrom osteoscleroticmetastases,which aretypical of,for example, prostatecarcinoma (cf. p. 145). Breast The normal parenchyma (72) of the female breast has very irregularcontours and slender, finger-like extensions into the sur- rounding fat (2) (cf. Fig. 88.4). Bizarre shapes can often be seen (Fig. 90.1).Advanced stages ofbreast cancer (7) have asolid.irre- gular appearance (Fig. 90.1). The malignant tissue crosses the fascial planes or infiltrates the thoracic wall, depending on size. Baseline CTafter mastectomy (Fig. 90.2) should help in the early Fig.90.3b
Thoracic Pathology Mediastinum 91 - ~ e being able to detect lesions and lymphadenopathy, you ~...s' know the normal anatomy. If you are a preclinical studenf, shouldfirstly study normal sectional anatomy. Itis inyourown ests to work through the following pages only when you are ~cientl y familiar with the previouschapters. rs , :.= ign increase in fat (2) due to cortisonetherapy is occasion- observed in the anterior mediastinum (Fig. 91 .1). Indoubtful -.ses. densitometryishelpful inthe DO (cf. p. 15). Inthis example, - ; average density within the region of interest (RDI), which is - uoned in possible fatty tissue, is -89.3HU with a standard -,,91,l a -;.91.2a , gnant thickening of the walls of the esophagus must be ~~[entiated from gastric conduitsfollowing esophageal surgery - g. 91.2). Possible enlargement of LNs (6) next to the stomach -29) must be excluded by follow-up CTs. Occasionally post- eranve metalclips cause artifacts (*), which makeassessment -.a mediastinummore difficult. Following esophageal resection, .s01the colon (..) may become drawn up into the anterior - ".: astinum (Fig. 91.3). Comparison with adjacent sections c y shows that this structure is notan emphysematous bulla, _ ' S atubular organ containinga lumen. deviation of about 20HU(ct. Table 16.1).As a rule. thesize 01 an ROI inem' (AR) isalso provided (Fig.91.1).The DO ofsuchamass would includeretrostemal goiter and thymoma. In children and young adults, the density of the thymus is about +45HU.As aresult of involution,the density of the organdecreases withage from the third decade onward until it has dropped to the densitytypical 01fat (- 90 HU).The leftlobe ofthe thymus is often larger than the rightand can reachthe aortopulmonary window.A lobe should notbe thicker than 1.3 em inadults; uptothe age of 20, 1.8em is considered normal. Fig. 91.1b Fig.91.2b Fig. 91.3
92 Thoracic Pathology Mediastinum Enlarged Lymph Nodes Normal LNs areoften found at the level of the aortopulmonarywindow.They are mainly oval or irregular, less than 10mm across [1 9], and sharply delineated from mediastinal fat (2). LNs (6) in thisarea are notusually considered suspicious until they exceed 1.5 cm in diameter.The demonstrationofa"hilum fat sign" (ct. p. 89) is not Obligatory, butdoes suggest a benign nature (Fig. 92.1). Fig.92.1a Fig. 92.1b Normal size (diameter) of thoracic l Ns [19, 41]: If more than three LNs are seen inthe aortopulmonary window or if a single LN is abnormally enlarged, the DD includes not only a metastasis from a bronchial carcinoma, but also a lymphoma (Fig.92.2). Enlarged mediastinal, and especiallyhilar, LNs are also characte- ristic of sarcoidosis (Boeck's disease) (6 in Fig. 92.3). In Figure 92.2, there are intrapulmonary metastases (7) as well. Did you notice them? Other sites of predilection for abnormal LNs are anteriorto the aortic arch, beneath the bifurcation of the trachea (subcarinal), and the para-aortic and retrocrural regions. • anterior mediastinum • aortopulmonarywindow • hilar • subcarinal • para-aortic < 6 mm < 15 mm < 10 mm < 10 mm < 7mm
Thoracic Pathology Mediastinum lar Pathologies phenomenaof CMinjectedthrough an armvein(ct. p.21 )and anomalous vessels(cf.p.88)inthemediastinumhavealreadybeen .ssed. Incompletely mixed CMmust be distinguished fromapossible thrombus (173) inthelumenof the brachiocephalic vein (91). - athrombuscanadhereto acentral venous catheter(182 in Fig.93.1). 93 " , 93.1a - - 0 osclerotic plaques(174) inthe aorta(89) are oftenaccompa- -.;-: by thromboticdeposits(173 inFig.93.3).Theypromoteaortic , ;-gation and dilation and can ultimately lead to an aneurysm -,1). Dilation of the thoracic aorta is considered to be an ,; rysmif thelumeniswider than 4em.Recordingthe measure- - ,;-;s of distancesandsizes (Fig. 93.2) makes it easier toassess !r progressive dilation infollow-up CTs. It is important to check a yinvolvement ofthe branchesofthe great vessels or forthe issecting Aneurysms of theAorta according to de Bakey [20]) Type r (approx. 50%) Ascendingaorta; may extendto abdominal bifurcation TypeII (approx. 15%) Only ascending aorta, extendingto brachiocephalic trunk IypeIII (approx. 25%) Tornintima distal to leftsubclavian artery Fig. 93.1b presence of a dissection flap (172 in Fig. 93.4). Three types of dissection can be diagnosed according to the extent of the dissection flap(seede Bakey [20]). Atrue aneurysmwith a diameterof more than 6 em. with a more saccular than fusiform shape or with an eccentric lumen. has a higher incidence of rupture.The consequences of rupture include amediastinal hematoma,ahemothorax,or pericardial tamponade.
94 Thoracic Pathology Mediastinum Pulmonary Embolism Ifalarge embolus has detached from athrombusinadeep vein of the leg, it will be visible as ahypodense area (" ) within thein- volved pulmonary artery oncontrast-enhanced images (Fig.94.1). After large pulmonary emboli,the affected segmentsorlobes ( ' ) usually become poorlyventilated and atelectasis occurs.The pu- monaryvessels become attenuated,whichcanbedemonstrated in conventional x-rays.The CT-angiographic detection of pulmonary emboli isdescribed onpage 186 in more detail. Heart Youhavealready familiarized yourself withthe normal anatomyof the heart on pages 79 to 81. Dilation resulting from valvular in- competence or from cardiomyopathies, as well as intracardiac filling defects can be recognized in CT images. If CM has been injected, it is possible to detect atrialthrombus or a thrombosed ventricularaneurysm.TheimageinFigure 94.2illustrates acase of global cardiac failure with markedly dilated atria (* *) and incidental thoracicvertebral degenerative osteophytes(" ). Pericardial effusions mayoccur withviral infections, uremia,the collagen vasculardiseases,aheartattack,ortuberculosis,among other causes. Apericardialeffusion (8) appearsasabroad rimoflow-density fluid(between 10 and 40 HU) surroundingtheheart (Fig. 94.3). Only fresh blood would have a higher level of density. Massive effusions as seen in Figure94.3 not only compress theadjacent lungs (178), but alsocompromise heart function. Fig.94.3a Effusions may leadtopericardial fibrosisor calcification (" " ), whichinturn causes constrictive pericarditis(Fig. 94.4).Notethat insuchcases the vena cava,the azygos vein.oreven the atriamay be markedly dilated as asign ofcardiac insufficiency. Atherosclerosisofthecoronaryarteries causescalcificationthat is well demonstrated by thin, hyperdense lines in the epicardial fat. At present, however, a complete assessment of the degree of stenosis requires angiography.
Thoracic Pathology Lung 95 '"xal lntrapulmonary lesions -~ n multiple lung metastases are faradvanced, the lesions can "'" berecognized inthe topogram (Fig. 95.1a). Depending upon - age and vascularization of the metastases, they appear as c=rical nodulesof varying sizes (Fig. 95.1 b).The more irregular " contoursofthelesions (for example,stellateor spiculated),the -;.95.1a more likely they areto be malignant.If, however, they aresolitary and have central calcification (likea popcorn), orperipheral calci- fication, the lesions are most likely to be a benign hamartoma or granuloma. Fig. 95.1b Fig. 95.2c vesselscutincross-section.Small metastases locatedclose tothe hilum are much moredifficult to distinguishfromvessels. Insuch cases, the detailed analysis of high-resolution scans (HRCn may bethebest method. Fig. 95.2b- ~ . 95.2a : - onary metastases are notvisible inconventional x-raysunless -e are largerthan 5or6 mmindiameter. InCTimages,however, - : can be detected at 1 to 2 mm in diameter. If metastases are :u:ed inthe periphery, it iseasy todifferentiatethem from blood --" correct choice of image display(window) is essential: Small :u lesions (7) of the lung (84) do not appear on soft-tissue -'ows(Fig.95.2a) or may be mistaken fornormal vessels(96). _-g windows (Fig. 95.2c) should alwaysbe used forexamining -; parenchyma. In the case below (Fig. 95.3a), the multiple small metastases (7) close to the pleura would have been over- looked if lung windows had not been used (Fig. 95.3c). These examples demonstrate the importance of viewing each image on long andsntt-tissuewindows. =e- 95.3a Fig.95.3b Fig. 95.3c
96 Thoracic Pathology Lung As aresult ot changes inthebehavior of smokers,theincidence of bronchial carcinomas (BC), especially among women and young people, has increased. In addition to the histologic diagnosis and grading of carcinoma, the location of the lesion is an important prognostic factor:a BG ofconsiderablesize (7) intheperipheryof the lung (Fig. 96.1) will almost certainly be visible on a con- ventional chest x-ray. More advanced BGs located centrally are usuallynotoperableand mayobstruct thebronchiallumen,result- ing in distal collapse (178). Figure 96.2 illustrates an advanced case in which the tumor has areas of central necrosis (181) ana thelung is surrounded bya pleural effusion (8). Fig. 96.1 a Fig.96.2a Fig. 96.2b Lymphangitiscarcinomatosa(7 in Fig.96.3)spreads from the hilum orthe visceral pleuraintothe interstitialtissueofthelung bywayof the lymphatic vessels. Obstructionofthesevessels bycancer cells leadsto lymphatic congestion (185).At first,the upper lobes remain clear. but as the disease progresses these also become infiltrated. The larger lymphatics and LNs gradually become infiltrated by metastatic disease. Fig. 96.3a Fig. 96.3b
Thoracic Pathology Lung 97 Fig. 97.2bFig. 97.2a ...Fig. 97.1a ,, ------------- idosis '" changes of sarcoidosis - ' :k's disease) must be -,-gntiated from multiple ---;ases inthelung:epithe- ;ranulomas usually infil- ~ the hilar lymph nodes (6) "orally (Fig, 97.1) and then ,3d within the perivascular e and along the Iympha- o the periphery of the ultiple small pulmonary :- es and various degrees of -'3 itial fibrosis may be ssent,Largegranulomas (7), seen in Figure 97,2, may :11ble intrapulmonary me- ases. - . erculosis , arqer masscavitates (181), the DDwill include, forexample, a bronchial carcinoma with centralnecrosis or cavitary tuberculosis, - , re 97.3 illustrates the latter in an atypical location in an HIV+, immune-compromised patient. Note also the emphysematous - '-ges in thetissueatthe peripheryof thelesion(176). rgillus - _~finfection with Aspergillus may occur within a pre-existing 7f in immune-compromised patients. The spores of A. fumi- 5are commoninplant material andsoil.Oftenthecavityisnot Jletely filled withtheaspergillusball sothat a smallcrescent , - can be recognized (" in Fig. 97.4).Aspergillosis may also -- to allergic bronchial asthma or provoke exogenous allergic ~D1itis . Fig. 97.4
98 Thoracic Pathology Lung Pleura Massive pleural effusions(8), asseen in the case illustrated in Figure 98.1 , compress thelung(84)and may cause largeareas of atelectasis (178) affect- ing individual segments or even an entirelobe.Effusions appear ascollec- tions of homogeneous fluid of near- water densitywithin the pleural spaces. Effusions usually accompany infec- tions, lung congestion due to right heartfailure, as well as venous conges- Fig. 98.1a tion due to mesothelioma and peri- pheral bronchial carcinoma. Pleural drainage by the insertion of a catheter (182) is indicated if atelecta- sis (178) affects large portions of the lung (Fig. 98.2). In the case shown in Figure 98.2, the drainage tube was blocked by fibrin-rich fluid. The lung can only be re-inflated if the fibrin clot is cieared or the catheter is replaced. Fig. 98.2 Foreignbodiesare rarely foundinthepleural spaces (166 inFig. 98.3),but mustbe consideredafter thoracotomy (chest surgery).Images on lung windows (Fig. 98.3c) clearly show the inflammationand collapse (178)surrounding a lost swab. Asbestos-Related Lung Disease Asbestos-related lungdiseasehas afine reticulonodularpatternof increaseddensities scattered throughoutthelung tissue,especial- lyat interlobularsepta (t and ' in Fig.98.4).Typical patholo- gicfeatures inthe pleura are thickeningand plaques (186 in Fig. 98.4). Fibrosis and scar emphysema appear in later stages of the disease.Thespindle-shaped or moretriangularareas ofincreased attenuationare often difticult to distinguish from those character- istic of bronchialcarcinomas. Fig. 98.3a Fig. 98.3b Fig.98.3c
Thoracic Pathology Lung 99 costs -ole, well-defined nodulesappear infhe interstitial connective =in response to phagocytosed particles of silica. The upper lOS of the lung are most commonly affected. Signs of fibrosis, -: may progress to a honeycomb pattern, can best - and at ,( stages - be detected with HRCT (using 2-mm rather than -om slicethickness; Fig. 99.1).The finer, smaller nodules can Fig.99.3 be found scattered throughout the lung; larger opacities, which may cavitate, are located within areas of denser fibrosis (, in Fig. 99.2). Enlarged mediastinal or hilar lymph nodes (Fig. 99.3) often develop an eggshell pattern of calcification.As the disease progresses, fibrosis and scar emphysema increase (.. in Fig. 99.1). Fig. 99.2= 99.1 -- ysema "":<;'essive emphysema with accompanying bullae (176 in =J 99.4b) or bronchiectasis with associated inflammatory lnfll- '"::...0$ (178 in Fig. 99.5) are not visible on soft-tissue window images in the early stages. These infiltrates are more easily seen and detected sooner on thin section images using lung windows [25-27]. - - 99.5a Fig. 99.5b Fig. 99.4b Fig.99.5c
Thoracic Pathology Lung 100 The pathogenesis of interstitial fibrosis ofthe lung (Fig. 100.1) cannot always be established andis referred toasidiopathic pulmonary fibrosis. This is particularly truewhen it affects middle-aged women.The patternof fibrosis resembles that illustrated on the previous pages with the exception that emphysematous changes typicallybegin insuopleural regions.Rbrosisof the lung canaccompany any of thecollagenvasculardiseasesinthe advanced stages and lead tosimilarmorphologic changes.forexampleinscleroderma (Fig. 100.2) or polyarteritis nodosa (Fig. 100.3). Fig. 100.3Fig. 100.2Fig. 100.1 Test Yourself! Youshouldtrytoanswer all thequestions onthis andthefollowingpage beforeturning tothe back of thebook fortheanswerssoas not tospoil thefun oftackling each one. ~ Do you recognize any abnormalities in Figure 100.4 or is it a scan of normal anatomy?Discuss your DD. GD1IIa How would you interpret the dense area in the left lunginFigure1oo.5?Dis- cussyour DD and make a list of additional informa- tionthat you need and the steps necessary in order to be certain about the lesion. ...... Fig. 100.5 --_. ~ A62-year-oldpatient pre- sented with intense back pain and was examined by CT. What is your dia- gnosis of the changes seen in Figure 100.6? Can you classily the type ofchange and thedegree ofseverity? ~ Describe in detail the pathologic changes visible in Figure 100.7 and the steps in your DD.
Test Yourself! 101 GDmI at further diagnostic xocedures would you 'ocommend for the case ~trated inFigure101.l? Nhat do you suspect the ':sion to be? What other :tJangesdoyourecognize? Fig. 101.1 0Dl'iEt Detecting even minute changes may be decisive in order to arrive at the correct diagnosis.What do you see inFigure 101.2? ...., patient in her 2'6 ~ week of x epnancv corn- Jlained of snort- '=S5 of breath. ~ar physician ini- Jally thought it Nas because of a igh diaphragm. Two weeks later shewas examined Jy CT. Make care- ful note of all ab- normal changes you see in Figure 101.3 and the stepsin yourDO. CIDtID A56-year-oldwoman with a history of smoking pre- sented with unintended weight loss and severe attacks of coughingwhich had already lasted for 3 months. She had no pre- vious illnesses. Does Fig- ure101.4 illustratenormal anatomy, a normal vari- ant. or an abnormality? ~ Do Figures 101.5a and101.5b illustrate normalanatomy, ananomaly, or a lymphoma?Discuss your opinion.
Abdominal CT ill general, all soft-tissue organs should appear uniform and be Nell defined, exceptwhen partialvolume effects occur (cf.p.1 4)or JUringtheearlyarterial phase of CM enhancement inahelicalscan cf. pp.120 and 126). Structures suchasblood vessels and bowel oops should be clearly defined in intra-abdominal fat. The same appliestothefat in muscles. "oorly definedconnective-tissuespacesmay indicateedemaor an nflammatory or malignant infiltrafion. If the anatomy cannot be :learly resolved, additional information can begained by measu- i ngthedensity ofspecificareas orby comparingunenhanced with :M-enhanced scans(cf. pp. 15and 121 ). !,gain, the proposed checklist is not intended to be"prescriptive", xn togivean usefultoolfor the novice inorderto reducethenum- :er of missed pathologicai findings. Selection of Image Plane The sections of the abdomen are also acquired transversally (=axially).lf thetableadvance issetat 8 mmwithaslicethickness of 10 mm, there will be an overlap of 1 mm on each side of the section. In recent years, there is a trend towards thinner slices with a slicethickness between 5 and 8 mm. The small topograms on thefollowing pages (based on Fig. 103.1) clearly show the slice positions as rela- tedtotheanatomyof major structures for each series of images. Fig.103.1 103 Checklist for Abdominal Readings Systematic Sequence for Readings ;nalogous to interpreting chest CTs, we suggest you : egin with the tissues of the abdominal wall. Con- sicerabletime issaved if youconsistentlylookat them 'romcranial to caudal. For beginners a systematic in- spectionof each organ orsystem from cranial to cau- jal is recommended, so that you do not need to .oncentrate on too many structures at once. Thepro- oosecprocedureencompassestwoorthree passages mrouqnthe images.As you become experienced, you may wish to devise your own method. Experienced -eaoers are more easily able to detect all pathologic : anges in onepassagefrom cranial to caudal. : is sensibleto evaluateinternai organs that lie in the same transverse plane. The uniformity of the paren- :nyma, the size and the smooth surface of liver and sateenshould bechecked together. Thesame is true 'or the assessment of the pancreas and the adrenal ; ands: they also lie at the same level (cl. pp. .05/106). If theentire urinary system is to be exami- -ed, it saves time to inspect the reproductive organs ' "d bladder in the lesser pelvis before lookingat the :ranial parts of the GIT, or the regional lymph nodes '00 the retroperitoneal vessels (see checklist on the -ght). =lIlally, thepresenceofsclerotic andlyticbone lesions '1d the state of the spinal canal should be checked c'. p.155). Abdominal wall: liver and spleen: Gallbladder: Pancreas,adrenals: Kidneys, ureter, and bladder Reproductiveorgans: GIT: Retroperitoneum: Bone window: (especially periumbilical and inguinal regions) hernias, enlarged lymph nodes? homogeneous parenchyma without focal lesions? well-defined surfaces? well-defined,thin wall?calculi? well-defined,size normal? symmetric excretion ofeM? obstruction,atrophy,bladder wall smooth and thin? uniform prostateof normal size? spermatic cord, uterus, and ovaries? well defined?normal thicknessofwalls? stenoses or dilations? vessels: aneurysms? thromboses? enlarged lymphnodes? mesenteric (normally< 10mm) retrocrural (normally< 7 mm) para-aortic (normally< 7 mm) parailiacal (normally< 12mm) parainguinal (normally< 18mm) lumbar spine and pelvis: degenerative lesions? fractures? focal scleroticorlyticlesions? spinal stenoses?
104 Abdominal CT Normal Anatomy Theimages of theabdominal organs includethecostodiaphragmatic recesses ofthe lungs (84), which extend quite farcaudally, lateral- ly,and dorsally. Liver (122) and spleen (133) parenchymausually appear homogeneous withoutfocal lesions in thevenousphase ofCM enhancement: branches oftheportal vein (102) and the falciform ligament (1 24)canbe distinguished.Inorder to assess thegastricwall (129a),the stomach (129) can be filled with water, which acts as a low-density CM, after an Lv. injection of Buscopan.The diaphragm (30) between thethoracic and abdominal cavities has an attenuationsimilar totheparenchymaof the liver and spleen and cantherefore notbe differentiated from these organs if itsthindome is sectioned obliquely. Fig.l04.3b Fig.l04.1a Fig.l04.2a Fig. l04.3a
Fig. l05.2b 105 Theright adrenal gland usuallylies cranialtotheupper pole ollhe kidney (135), whe- reasthe left adrenal gland lies ventral to the upper poleofthe kidney. Consequentiy, thetwoadrenal glands(134) are seen on the same sections. Note the position ofthe Jiaphragm(30) betweenthelung (84) and the inferiorvena cava (80). Thevesselson e lesser curvature of the stomach (109) and the gastric walls (1 29a) are usually flell defined and clearlydemarcated inthesurrounding fatandconnective tissue (2).
106 Abdominal CT Normal Anatomy Typically the pancreas (131) has well-defined parenchyma with an irregular outline. The head and uncinate process of the pancreas extendquitefar caudally (down to Fig. 107.2).The left adrenal gland (1 34)is often v-snaoed,whereas the right adrenal gland may look likeanarroworacomma.Notetheoriginoftheceliac trunk (97) and theSMA (1 06)from the abdominal aorta(89).Enlargedlymphnodes may frequentlybefound inthisvicinity.InFigure 106.3,thecontrast-enhancing effect of anarterial bolusof CM becomes evident.At this point, the SMA (106) has enhanced morethan theaccompanyingvein (107),which does not contain any CMyet.Within moments (Fig. 107.1),the bolus of CMhas also opacified thesuperior mesenteric vein (107). Fig.l06.1 a Fig. l 06.1b Fig. l06.2a Fig.l06.3a Fig.l06.3b
-ookfor arterial calcifications inthe originsof therenal arteries (110) atthelevelof the ~nal veins (111).Theleft renalvein does notalways pass between the aorta (89) and -9 SMA(106) totheinferiorvena cava (80),as itdoesinFigure107,1.Anatomicvaria- znsarenot unusual(ct. p.11 6).Benigncysts(1 69)frequently occurintherenal pelvis 136)next tothe ureter(137) orintherenalparenchyma (135)(Figs,107.2and107.3). 3uchcysts donotenhance after eMinjection (cl. p.133). 107 Fig.107.1b Fig.107.2b- . , 107.2a Fig. 107.3b
108 Abdominal CT Normal Anatomy Closetothe gallbladder (126),you can sometimes see partialvolume effects (Fig. 108.1) of the adjacent colon (143/144),thewalls of which (1 52) should normally bethinandwell defined incontrast tothe root ofthesmall bowel mesentery (as inFig. 108.3).The duode- num (130) canonly bedistinguishedfrom the other intestinal loops (140) on the basis ofits position.Atthis level,youshouldalsocheck the kidneys (135) for smooth margins and possible parenchymal scarring. The presence of fat makes it easier to identify the rectus abdominis muscle(29) aswell asthe obliquemuscles ofthe abdominal wall (28a-c). Fig.l08.2a Fig.l08.3a Fig,108,lb Fig.l08.2b Fig.l08.3b
Abdominal CT Normal Anatomy 109 Fig. 109.1b Fig.109.2b Fig. 109.3b- . 109.3a tethe typicalpositionof the proximal partsoftheureters(137),medial totheinferior :des ofthe kidneys (135) and anteriortothe psoas muscle (31 a). In Figures109.2 - id109.3,the luminaof bothuretersappear hyperdense becauseeMisbeingexcret- ec in the urine. Partsof the renal fascia (5) can beidentified in Figures 109.2 and 109.3. Haustrations caused bythe semilunarfolds (haustral folds) (149) are typical -, mecolon (142- 144inthefigures below).
110 Abdominal CT Normal Anatomy InFigure 110.1 . the branching pattern ofthesuperior mesenteric vessels (108) whichsupply the small bowel (140) can beseen.Atthe bifurcation ofthe aorta (89) (usually at L4 vertebral body, Fig. 110.2), thecommon iliac arteries (113) areanteriortothe corresponding veins (116).The two ureters (137) are located more laterally in front of the psoas muscles (31 a). Along with the iliac bones (58) the gluteus medius muscles (35a) appear and sometimes containcalcified intramuscular injections sites (cf. Fig. 117.3). Fig. 110.2a Fig. 110.3a Fig. 110.2b Fig. 110.3b
Fig. 111.2b 111 Fig. 111.1b - order to exclude the presence of an abdominal hernia you should check for a -Jrmal width of the linea alba (47) between the rectus abdominis muscles (29). ~re caudally(Fig.111 .3)there is asite of predilectionfor enlarged LNs atthedivi- : on of the iliac vessels into external artery/vein (11 5/118). which pass anteriorly, ;old internal arteryivein (114/117), which are located more posteriorly.The transi- ;;00 from thelumbar spine (50) tothe sacrum (62) lies atthis level. - _. 111.3a Fig.111.3b
112 In the following images, the ureters (137) pass posteriorly to approach the lateral aspects of the base of the bladder (138). Within the bladder, differences in the con- centration of excreted eM in the urine can be recognized asfluid-fluid levels of diff- erent densities (Figs. 112.3 and 113.1). On the next page, a male pelvis is shown, demonstrating the prostate (153), seminal vesicle (1 54), spermatic cord (1 55), and root of penis (156). Note in particular the internal obturator muscles (41a) and the levator ani muscles (42) lateral to the anal canal (146a); images ofthe female pelvis onpages 114/ 115 werenot obtained as far caudally asin themale. Fig. 112.1 Fig. 112.2 Fi9'112'3~~~~~~~~~~~~Fig.113.1 Fig. 113.2 Fig. 113.3 Fig.112.3b Fig. 112.1a Fig. 112.3a
Abdominal CT Pelvic Anatomy (Male) 113 q g. 113.4a Fig. 113.4b
114 Inthefemale pelvis, thesize and position of the uterus (158) relativetothe urinary bladder can vary considerably from patientto patient. Theuterus mayliecranial or lateral to the bladder (Figs. 114.1-115.1). The cervix and the vagina are situated between thebladder (138) andtherectum(146),whereas theovaries (159) liemore laterally. Depending on age and thephase of the menstrual cycle, ovarianfollicles might be misinterpreted as cystic lesions (cl. o. 133). Fig. 114.1a Fig. 114.2a Fig. 114.3a
· Abdominal CT Pelvic Anatomy (Female) 115 Fig. 115.1b Fig. 115.2b :'ee intra-abdominal tluid (ascites or hemorrhage) may occur in the rectouterine pouch between rectum and uterus, aswell as in the esicouterine space. In the inguinal region, lymph nodes (6)can be upto 2 cm in diameter and be normal (Figs. 115.2and 115.3).The sue ofnormalabdominal lymph nodes does not usually exceed 1 cm. It is not possibleto examine the hipjoints on soft-tissue windows Fig. 115.3); the heads of thefemurs (66a) in the acetabular fossae (59/61) can best be analyzed on bone windows (notshown here). 'oJ assessment of bone windowscompletes the examinationof theabdominal and pelvic images. Fig. 115.3a Fig. 115.3b
116 Abdominal Pathology Variants Anatomic Variations For thebeginner, it is important to be familiar with the most common anatomic variations which may lead to misinterpretations of CT images. Insome patients,the contours ofthe right lobeof the liver (122) may appear scal- loped by impressions of the diaphragm (30) which could be mistaken for liver lesions (Fig. 116.1). The walls ofan empty stomach (129) arethickand may suggest amalignant lesion (129a). Fig. 116.1a Fig. 116.1b Ultrasound may mistake an anomalous left renal vein (111) for a retro- aorticLN. Usuallytheleft renal vein passes be- tween the SMA (106) and the aorta (89). However, the vein may be retroaortic and pass between the aorta and the spinal column (50) to the inferiorvena cava (80) (Figs. 116.2 - 116.4). Duplication of the left renal vein with preaortic and retroaortic components can also occur. Characteristic Partial Volume Effects If the wallofone organindents that of another,cross-sectional images will make it look asif one organwere withinthe other. For example,the sigmoidcolon (145)mayappear"within"the urinary bladder (138) (Fig. 116.5a). By comparing adjacent sections (Figs.116.5a and c),it is easyto recognize that only parts of both organs have been imaged. In a similarmanner, the right colic flexure (142) may appear to be "within" the gallbladder (126) (Fig.116.6). Fig. 116.6a Fig. 116.6b
Abdominal Pathology Abdominal Wall 117 lymph Node Hyperplasia ?athologic lesions of theabdominal wall occur most frequently in theinguinal region.l ymph nodehyperplasiawithnodesupto2em dimension should notbeconsidered abnormal.l argeconglom- erate masses of lNs (+) arefoundin non-Hodgkin's lymphoma (Fig. 117.1)and less frequently in Hodgkin's disease. An inguinal hematoma (173) caused by hemorrhagefrom afemo- ral artery puncturesite aftercoronary angiography should becon- sidered (Fig, 117,2) in the DO. Abscesses Intramuscular injection sitesinthe gluteal region resulting in sub- cutaneous fat (2) necrosis or postinflammatory residue (..) typically are well-defined, hyperdense, partially calcified lesions (Fig. 117,3). An abscess may spread from the gluteal muscles to the pelvis through the ischiorectalfossa.After diffuse infiltration(1 78)ofthe gluteal muscles (35) withsurrounding edema (185 inFig. 117.4), quefaction (181) may occur and. depending on the localization andsize, theabscess can involve thesciatic nerve (Fig.117.5).
118 Abdominal Pathology Abdominal Wall The CT in Figure 118.1 shows subcutaneous lesions, resulting from heparin injections (173) or small hematomas that may mimic cutaneous metastases (7) or malignant melanomas (Fig. 118.2). Larger metastases tend to invade the muscles of the abdominal wall (29) and often have hypodense, central necrosis (181). Enhancementafter intravenous CM may also point to malignancy or a florid inflammatoryprocess.Ifthe degree ofCM enhancementisuncertain, a regionof interest for densitometricanalysisis placedinthe lesion ona pre-CMand compared witha post-CM (Fi9. 118.2). Metastases inthe abdominal wall may not be evident until they become infected and develop into an abscess (1 81), which was cathe- terizedand drained inthe case illustrated (182 inFig. 118.3).The second metastasis(7),justbeneaththe rightabdominal wall (28),was notrecognized at firstbecausethe patient's symptoms were attributed to the adjacent abscess.
Abdominal Pathology Liver 119 III Fig. 119.1 II caudate lobe lateral segment, cranial part lateral segment, caudal part quadrate lobe(a:cranial, b:caudal) anterior segment.caudal part posteriorsegment, caudal part posterior segment, cranial part anterior segment, cranial part I II III IV V VI VII VIII Left lobe Right lobe Segments of the liver t a liver biopsy or radiotherapy is planned, it is helpful to know in which segment a focal lesion is situated. The liver is horizontally subdivided (blue line in Fig. 119.1 ) by the main branches of the portal vein (102) into a cranial and caudal part. The main hepatic veins (103) mark the oorders ofthesegments inthe cranial part(Fig. 119.2).The border between e left and right lobes is not marked bythe falciform ligament (124), butby eplane between the middle hepatic veinand gallbladder (126) fossa. =-g. 119.4 Fig. 119.5
120 Abdominal Pathology Liver Choice of Window In conventional (nonhelical) CT, the unenhanced liver (122) is imagedonaspecial liver windowwidth (Fig.120.1a)setbetween 120 and 140 HU. Normal liver parenchyma can be more clearly distinguished from lesions on narrow-window-width images because they provide high image contrast. If there is no fatty infiltration of the liver (which would reduce attenuation), intra- hepatic vessels (103) appear as hypodense structures.Incases of fatty infiltration, the veins may appear isodense or even hyper- dense on unenhanced images. The post-contrast agents CT images are viewedusingawindow widthofapproximately350HU; this smootnes thegray scale contrast (Fig. 120.1c). Fig. 120.1a Fig. 120.1b Fig. 120.1c Passage of a Bolus of Contrast Agents Inathree-phasehelicalacquisition ofearlyarterial, portalvenous, andlatevenousphasesof contrast agentsenhancement, anunen- hanced study is not necessary [17, 18]. Hypervascular lesions become muchmoreclearlydefinedintheearlyarterial phase(Fig. CT Portography The chancesofdemonstratingthetrueextentof liver lesions(e.g. metastases) are greatly improved if contrast agents are injected directly into the SMA or the splenic artery and images are then acquired in the portal venous phase [17,21). Since theprincipal blood supplyfor most metastases and tumors comes from thehe- 120.2a) than in the late venous phase. Inthe late venous (equili- brium) phase(Fig. 120.2b),thedensitylevels ofthe arterial, portal venous,andvenous systemsarepractically identical. patic artery,these lesionswill appear hypodensewithinthehyper- densenormal parenchyma that has enhancedwithcontrast agents (Fig. 120.3a). Inthe same patient, the early arterial phase image (Fig. 120.3b) showsthat withoutcontrast agentsportography,the extent ofthemetastaseswouldhave beengreatlyunderestimated.
· Abdominal Pathology Liver Hepatic Cysts Hepatic cysts (169) containing serous fluid aresharply defined, thin-walled, homogeneous lesionswith densityvalues close to those of later (Fig. 121.1). Partial volume effectsmay cause poor delineation from adjacent hepatic parenchyma (122) if the cysts are small. If in doubt, a ROI should be positioned within thecyst fordensity measurement (Fig, 121.2a). It is important to ensuretheROI is correctly placed in thecenter of the cyst, well away fromthecyst walls (cf. pp. 15 and 133).In small cysts,forexamplethe poorlydefined lesion in Figure 121 .2b,the average density measurement was toohigh, because adjacent liver parenchyma was included in thecalculation. atethatbenign cysts do notshowany significant enhancement after i.v CM. -iydatid (Echinococcus granulosus) cystshave a very characteristic multiloculated appearance, often with radially arranged septations oetween different cysts (169 in Fig. 121.3). It may prove difficult to differentiate between collapsed, dead cysts and other intrahepatic esions.The right lobeof the liver is most frequently affected,sometimes the leftlobeor thespleen (133) become involved,asshown in Figure 121.3. The density of the cyst 'Iuid is usually between 10 and 40 HU JI1 an unenhanced image. Partial or complete wall calcification is frequent anc the outer membrane may enhance Hith CM. The DD includes infections Hith E. alveolaris (not shown) and occaslonally hepatocellular carcinoma at is poorly defined with irregular satellitelesions. 121
122 Abdominal Pathology Liver LiverMetastases Multiple focal lesionswithintheliver suggest metastases.Common sites of origin are the colon, stomach, lung, breast, kidneys, and uterus.The morphology andvascularitydiffer betweenthetypes of livermetastases.An enhanced helical scan isthereforeobtained in Fig.122.1a Hypo- and hypervascularmetastases share the hypodense (dark) appearance in the venous phasebecauseofrapidwash-outof contrast material. If spiral CT is not avai- lable, it is helpful to compare unenhanced images (Fig. 122.2) with enhanced images (Fig. 122.3). In the example on the right, number and size of the hepatic lesions (7) would have been underestimated on the enhanced images. It is easily comprehen- sible that individual small metastases can escape detection if unenhanced images are passed over. To increase the contrast inthe hepatic parenchyma (122), a narrow win- dow setting should always be used when viewing these unenhanced images (see page 11 7).This might even bring out small metastases (7) (Fig. 122.2). These small liver metastases (7) differfrom small cysts by exhibitinq an indistinct margin and a higherdensity after intravenous injection of contrast medium (Fig. 122.4) indicative of enhancement. The average density values were55and 71HU,respectively(Fig. 122.4). In case of diagnostic doubt and for referenceat follow-up during therapy, it is useful to compare the CT images with ultrasound findings.Apart from thetypical hypoechoic halo, metastases have varied ultrasound appearances, just as in CT images [23]. The ultrasound diagnosis may be difficult, especially when calcifica- tionin metastases leads toacoustic shadowing. Even thoughthey are quite rare, slowly enlarging mucinous metastases (i.e. those from colon carcinomas) may become very calcified (" in Fig. 122.5). both the venous phase (Fig. 118.1a) and the early arterial phase (Fig. 118.1 c). Inthis manner,smallerlesions (7) become well de- finedandhepatic veins (103) will notbe mistakenformetastases.
Abdominal Pathology Liver 123 Solid Hepatic Lesions A hemangioma is the most common benign hepatic lesion. In unenhanced images small hemangioma are well-delined homo- geneous areas 01 decreased attenuation. After injection of CM, enhancement typically begins in the periphery and progresses towardthe centerofthe hemangioma (Fig. 123.1 a),reminiscent of theclosing of an optic diaphragm. In dynamic bolus-enhanced CT sequences, enhancement progresses centripetally. Following Fig.123.1a Hepaticadenoma (" )occurs most frequently inwomenbetween theages of 20and 60years who havealonghistoryof taking oral contraceptives.An adenoma originates in hepatocytesandmay be solitary or multiple.The adenoma is usually isodense, sometimes ypervascular (Fig. 123.2), and may be accompanied by hypo- denseinfarction,central necrosis.and/orspontaneoushyperdense emorrhage. Surgical excision is recommended due to the oossibility of acute hemorrhage and malignant degeneration. By administration of a CM bolus, a series of CT images is acquired every few seconds at the same location. Accumulation of CM within the cavities of the hemangioma (,, ) leads to homo- geneous enhancement in the late venous phase(Fig. 123.1b). In large hemangiomas, this might take several minutes or be in- homogeneous. Fig. 123.1b contrast, focal nodularhyperplasia(FNH) does not show any ten- dency of malignant degeneration, and lesions of this kind contain biliaryducts. On unenhanced images, FNH appearsashypodense, sometimes isodense, but well-defined lesions. After Lv. CM, FNH oftendemonstratesan irregulariyshaped, hypodense central area (*) representing its central blood supply; however this feature is seeninonly 50%of all FNH(Fig.123.3). Fig.123.2 Fig.123.3 Fig.123.4 -iepatocellular carcinoma(HCC) oftenoccurs inpatients whohave along history of hepatic cirrhosis and is seen most often in men over the age of40 years. In one-third of all cases, HCCis solitary although multifocal lesions are notrare. Thromboses in the bran- cnesof the portal veincaused by tumor invasion intothe lumenof tnevessel may beseen in one-third of cases.The CT appearance HCC (Fig.123.4)isextremelyvariable. Onunenhancedimages, .,CC usually appears hypodense or isodense; CM may show diffuse or rim enhancement and central necrosis. When there is alsocirrhosis, it may be difficult to definetheborder of an HCC. Secondary lymphoma should be considered in the DO because it may infiltrate the liver parenchyma and may be the cause of dif- fusehepatomegaly. Ofcourse,this does not mean that everycase of hepatomegalyisdue toalymphoma.Non-Hodgkin'slymphomas resembleHCCbecause oftheirsimilaritiesinvascularityandnodu- largrowth.
124 Abdominal Pathology Liver DiffuseHepatic lesions In fattychanges ofthe liver,thedensity of the unenhanced paren- chyma, which is normally about 65 HU, may reduce so that it is either isodenseoreven hypodense withregard totheblood vessels (Fig. 124.1; cf. also p. 120). In hemochromatosis (Fig. 124.2), the accumulation of iron leads to increased attenuation above 90 HU and mayreach asmuchas140HU.lnthese cases, the naturalcon- trastbetween parenchyma and vessels is even greater. Cirrhosis (Fig. 124.3), resulting from chronic liver damage, has a diffuse nodularappearance andusuallygives the organ an irregular,lumpy contour. Fig. 124.1 Fig. 124.2 Fig. 124.3 If it is not possible to treat the cause of cholestasis surgically, inserting a stent (182 in Fig. 124.6) may decompress an obstructed biliaryduct(1 28). I Abdominal Pathology Gallbladder Biliary Tract After surgical choledochoenteric anastomosis, sphincterotomy, or endoscopic retrograde cholangiopancreatography (ERCP), hypo- dense gas (+) is usually present within the intrahepatic bile ducts (Fig. 124.4). These causes of biliary gas must be differen- tiatedfrom gas-forming anaerobic bacteria within an abscess. Dilatation of theintrahepatic biliary tract (128) is called cholesta- sis(Fig.124.5).It may result from gallstones,amalignant obstruc-
Abdominal Pathology Gallbladder "he size and shape of the gallbladder vary depending on when the patient last ate food. A hydrops of the gallbladder should only be : iagnosed if there isvery marked dilatation,that is if the diameterexceeds 5 cm in several transverse planes.The attenuation of bile is usually just greater than thatof water (0 HU) but mayincreasetoupto 25HU if the bileis highly concentrated [4]. Cholecystolithiasis tones (167) withinthegallbladder (126) may show different patterns ofcaicification (Fig. 125.1).Cup-shaped and ring-likecalcifications canbe seen instones containing cholesterol and bilirubin (Fig.125.2).If stones obstructgallbladder drainage orinflammationhascaused stenosis, sludge may form resulting in increased attenuation and sedimentation of bile (Fig. 125.3). Common duct stones should be diagnosed usingthin-section CTbecause smallerstones might be missed in standard thickness sections. 125 Fig. 125.2b Fig. 125.3b Chronic Inflammatory l esions Cholecystolithiasis can lead to chronicinflammation, resulting inastone-filled,shrunken gallbladder, acute cholecystitis,or an empyema ofthe gallbladder (recognized by an irregularlythickened wall) (' , in Fig. 125.4). There is an increased risk ot malignant change with chronic inflammatory processes [24]. Thedevelopmentofa porcelain gallbladder (Fig. 125.5) with an egg-shell-likepatternof cal- cification(174) may be a premalignant lesion. Fig. 125.4 Fig. 125.5a Fig.125.5b
126 Abdominal Pathology Spleen Contrast Enhancement Before reading further, try to define a characteristic feature of the spleen by looking at Figure 126.1 a.The normal splenic parenchyma (133) has an attenuation ofapproximately45HUonunenhanced images.The attenuation ofthe spleen will only appear homogeneous in an unenhanced image or in the late venousphase of an enhanced study (Fig. 126.1c). In the early arterial phase (Fig. 126.1 a), it will enhance heterogeneously and appear patchy or marbled, a pattern representing itstrabeculararchitecture.This pattern should not be misinterpreted as an abnormality. Note also the uneven distribution of eM within the inferior vena cava (80) and the two (!) hepatic metastases (7) in the same image (Fig. 126.1 a). Did you spot the areas of near-water attenuation representing perisplenic/perihepatic ascites(8)? J, 122 J' / .•.. ~ ~ . / ~l~Rg.1m1a Rg.1m1b Rg.1m1c Thesplenicartery (99) istypicallyelongated and tortuous sothatit may be imaged inseveral consecutive slices. Inelderly patients, it is common to see atherosclerotic plaques (174 in Fig. 126.2). Occasionally, a homogeneous splenunculus [accessory spleen '], well demonstrated in the surrounding fat, may be seen at the hiium orthe inferior pole of the spleen (Fig. 126.3). Differentiating betweena splenunculus and an abnormally enlarged LN may be difficult. Fig. 126.2a Splenomegaly Diffuse enlargementof the spleen(Fig. 127.1) may be caused by several conditions: portal hypertension, leukemia/lymphoma, myelofibrosis and hemolytic anemia, or by various storage diseases. Assessment of splenic size is made difficult by individual variations in shape. Marked splenomegaly iseasiiyrecognized, butinborderlinecases of splenomega- ly and for follow-up one should know the normai range of splenic size. Inthe transverse plane,the length of the spleen ( I ) should measure no more than 10 cm (dotted line) and its width (d, atright angletothedotted line) should notexceed 5 cm (Fig. 126.4). In ultrasound, the spleen is not measured in a transverse plane but in an obliqu~ plane parallel tothe intercostal space.Inthis plane, theupperlimitofnormalis 11cmfor the long axis [28]. The craniocaudal dimension of the spleen should not exceed 15 cm, so that at a slice thickness of 1 cm it should not be visible on more than 15 sections. Splenomegaly is diagnosed if at least two ofthese three parametersare exceeded. Fig. 126.4
· Abdominal Pathology Spleen 127 !.s splenomegaly develops, the typical normal :rescentic shape is lost (Fig. 127.1). Gross splenorneqaly. which may be caused by chronic mphocytic leukemia, acts as a space-occupying nass and displaces adjacent organs. In Figure 127.1, the left kidney is compressed ( "'). If the :loodsupplycannot keeppacewithsplenicgrowth, ntarctions( ,,) may result. Theseappearas hypo- cense areas that do not enhance with CM (Fig. 127.2). -ocal Splenic lesions Splenic cysts sharethe samecharacteristicsofhepatic cysts (cf. p.121). Metastases inthespleen (7)are rareand difficulttodistinguish ~om cysts. Inthe case illustrated in Figure 127.3,the diagnosis of splenic metastases was relatively easy becausethere were hepatic -slons and malignant ascites (8). If there are multifocal lesions with inhomogeneous CM enhancement, a diagnosis of focal splenic mphoma or splenic candidiasis should be considered. Ascites (8) may accompany candidiasis, as shown in Figure 127.4. Splenic mphoma is usually characterized by diffuse infiltration andthespleen mayappear normal. Ineexaminationof the spleen(133) afterabluntthoracic orabdominal trauma mustbemeticulous.Lacerations ofthe parenchyma(181) ;;Jay leadto hematomas (8) beneath thecapsule, and delayed rupture of the capsue may cause massive hemorrhage into the abdomi- Clal cavity (Fig. 127.5). =ig. 127.3b - ·e remnants of smaller hematomas may xesent as subcapsular ( ~ ) or parenchy- -al ( t )calcifications (Fig. 127.6). seotanens within splenic cystic lesions '1g. 127.7) are strongly suggestive of ,:ninococcosis, and appearquitesimilar to - e in the liver. In most cases the liver is 'so affected (cf. p121 ).
128 Abdominal Pathology Pancreas Acute andChronic Pancreatitis Acute pancreatitis may present as edematous interstitial pancreatitis (Fig. 128.1). Hypodense penpancreatic fluid (exudate) (8) and edemaoftheconnectivetissue (185) are frequentfindings. CTshows blurring of thepancreaticcontours;thenormally lobular pattern of thepancreas is effaced (Figs. 128.1 and 128.2). Inhemorrhagic necrotizing pancreatitis (Fig.128.2),the extent of necrosis isaprognos- ticfeature. Chronic pancreatitis progresses either slowly and progressively or inrecurrentepisodes.The twomost common causes of chronic pan- creatitis are alcohol abuse and cholelithiasis Typicalfindingsinchronic pancrea- titis are fibrosis and multifocalcal- cifications (174), irregular dilata- tion of the pancreatic duct (132), and sometimes the formation of pseudocysts (169) within, or next to,the pancreas (131 ) (Figs. 128.3 and128.4). Thedisease may lead to pancreaticatrophyas alatefeature. The possibility that pancreatic car- cinoma develops in association with chronic calcific pancreatitis is presently being discussed. Pancreatic Neoplasms Most pancreatic carcinomas (7)are located within the head ofthe pancreas (131).As a result, evensmall tumors may cause cholestasis by obstructing the common bile duct (127) (Fig. 128.5). Pancreatic carcinomas tend to metastasizevery early to theliver and the re- gionalLNs.Incase ofdoubt, ERCP shouldbe carried out toimagethe pancreatic and common bileducts. Isletcell tumors,75%ofwhich arefunctional, are located within the body ofthe pancreas.The Zollinger-Ellison syndrome (Fig. 128.6) iscaused by agastrin-secreting tumor ("). Otherneoplasms associated with the pancreas are insulinomas, glucagonomas, and serotonin-producing masses. '4iIIIIIItr; "'"~ . rl Jr. . ......
130 Abdominal Pathology Adrenal Glands The normal position and shape of the adrenal glands has been describedonpages 105to106.The maximumlengths ofthe adre- nal glands range between 2.1 and 2.7em, theright adrenal often being somewhat longer than the left. The thickness of the limbs should notexceed 5to8 mminthe transverse plane.Afusiformor nodularthickening (7) is likelyto be abnormal in CT,and is usually indicative ofhyperplasia oran adenomaof the adrenal gland (134 in Fig. 130.1). Typically, the adrenals can beclearly differentiated from adjacent tat, the diaphragm (30), the kidney (1 35),the liver (122),and theinferior vena cava (80). Fig. 130.2bFig. 130.1b The following conditions may be dignosed according to the spe- cific hormonal excess: congenital adrenal cortical hyperplasia (androgens), Conn's syndrome (aldosterone), and Cushing's syndrome (cortisone). An upper pole renal cyst (Fig. 130.2) or a renal angiomyolipoma (cl.Fig, 134.4) must beincluded intheDO. Attenuation values forbenigncysts (169) shouldlieclose tothose for water (= -1 HU in the present case) (Fig. 130.2). (Compare withcysts on p. 133.) In cases of heterogeneous enlargement of the adrenal gland or infiltration of adjacent organs, a metastasis or a carcinoma (Fig. 130.3) must be suspected. Since bronchogenic carcinomas often metastasize to the liver andtheacrenals,staging chest CT studies for lung cancer should be extended to include the caudal margin of the liver and the adrenals.Tumors of the paravertebral sympathetic trunks, which are located close tothe adrenal glands, may also be detected, but they are rare. The MRI images in Figures 130.4a and 130.4b show a neuroblastoma ("j in the sagittal (a)and coronal (b)planes. Fig. 130.3 Fig. 130.4a Fig. 130.4b
, , Abdominal Pathology Adrenal Glands 131 .vhenever doubt exists whether an enlarged adrenal gland repre- sents a benign process, densitometry (see pages 121 and 131) withdetermination oftheenhancement patternshouldbe consid- ered: benignadenomas of the adrenal glandshow atendencyofa considerably more rapid wash-out of the contrast enhancement than malignant lesions, such as metastases and adrenal gland carcinomas (Fig. 131.1).This method requires anadditional scan at the level ofthe adrenal glandsafter 3, 10, or30minutes. 1 100 80 60 40 20 Dens ity (HU) 79±1 8 67±20 64±22 86±14 66±13 59±12 32±17 Time Unenhanced 30 sec. 60 sec. 90 sec. 3 min. 10 min. 30 min. I g.131.1 Rapid wash-out of contrast medium in benign adrenal glands adenomas (blue) in comparison with non-adenomas (gray) Jalignant tumors of the adrenal gland tend to have a prolonged contrast enhancement. This difference can be applied to the differential diagnosis. The dynamic enhancement pattern in the adrenal glands has been extensively investigated in numerous studies, which revealed further differences in absolute and rela- tive wash-out of the peak contrast enhancement. This wash-out pattern, however, shows a certain overlap between the tumor types, and thereforethe assessment has been proven useful only whenapplying thefollowingparameters [42]: Densitometry in theDDof space-occupying lesions of theadrenal glands Unenhanced: 10min.after injection of contrast medium: 30min.afterinjection of contrast medium: < 11HU < 45 HU < 35HU => => => Adenoma Adenoma Adenoma =Or these three values, the range of the histograms or so-called oox-whisker plots of Fig. 131.1 does not overlap for both tumor 'ipes, and a benign tumor of the adrenal glands can be safely assumed if the measured density values fall below these values. In all other cases, a benign adenoma cannot be assumed with acceptabledegree ofsensitivityand specificityand further evalua- tion is recommended.
132 Abdominal Pathology Kidney /' CongenitalVariations The attenuation of the renal parenchyma (135) on unenhanced images is approximately 30 HU.The kidneys occasionally develop to different sizes. If the outlines are smooth and the parenchymal thickness is not irregular, it is likely to represent unilateral renal hypoplasia(Fig.132.1).Thesmallerkidney neednotbe abnormal. A kidney may have an atypical orientation as in Figure 132.2. However, if akidney lies inthe iliacfossa (Fig.132.3).thisdoes not indicate an ectopic location,butarenaltransplant (135). The organ isconnectedtotheiliacvessels(113/116) and theurinary bladder (1 38). Fig.132.2b Marked differences in size, asin Figure 132.2, may indicate partial or complete renal duplication onone side. Thepositionsand number of renal arteries may vary considerably (110 in Fig. 132.1b).The renalarteries must be examined carefully for evidence ofstenosis as acause of renal hypertension.The ureter (137 ..) can be present asa partial or complete duplexureter (Fig. 132.4). In complete renal duplication, therenal pelvis is also duplicated. Occasionally, the low-density fat in the hilum (* in Fig. 132.5b) is only poorly demarcatedfrom the renal parenchyma (135) owing toabeam-hardening artifact or partial volume averaging (Fig. 132.5a).This gives theincorrect impression ofa renal tumor. Comparison with an immediately adjacent section (Fig. 132.5c) demonstratesthat only hilar fat was present. The actual tumor inthis particularexample(7) is situated atthe posterior margin of therightlobeofthe liver (122). Fig. 132.5a Fig.132.5c
Abdominal Pathology Kidney 133 Cysts "enal cysts are frequent incidental findings in adults and may be located anywhere in the parenchyma. They may be exophytic or parapelvic, in which case they can resemble a hydronephrosis. 3enigncysts containaserous,usually clear liquidwithanattenua- eon of between - 5 and +15 HU. They do not enhance with CM becausethey are avascular. The attenuation measurement may be inaccurate if there are partial volume averaging artifacts due to slice thickness (Fig. 133.1 : - 25HU) orto eccentric positioning of theROI (Fig. 133.2: - 22HU) (cf. pp. 15and 121).Only thecorrect positioningof the ROIinthecenterof thecyst (0 inFig.133.3) will provideanaccurate average of 10 HU. In rare cases, hemorrhage into benign cysts will result in hyperdense values on unenhanced images. The attenuation values will not change on post-contrast images. iIlcreased density or calcificationsin a mass may indicate past renal tuberculosis, current Echinococcusinfestation(hydatiddisease),or acystic renal cell carcinoma. Thedifference between pre- and post-contrast images also provides information on renal function: after approximately 30seconds the well-perfused renal cortex is the first partofthekidney toaccumulatethe CM (cf. Figs. 133.2 and 133.3). After another 30to60seconds the CM isexcreted intothemoredistaltubules leadingtoenhancement of themedulla.Theresult is homo- geneous enhancement ofthe renal parenchyma (cf. Fig. 133.1). Fig.133.1 Fig. 133.2 Fig. 133.3 The appearances of multiple renal cysts in children with congenital autosomal recessive polycystic kidney disease are dramatically different from those ofthe occasional cysts found inadults,which are generally incidentalfindings. Polycystic kidney diseaseinthe adult 169 inFig.133.4) is autosomal dominantand associated withmultiple cysts ofthe liver, the bileducts and, morerarely,with cysts inthe pancreas orwith abdominal orcerebral aneurysms. Fig. 133.4a Fig. 133.5 Hydronephrosis "arapelvic cysts may beconfusedwithgrade 1 hydronephrosis (Fig. 133.5),whichischaracterized intheunenhanced image byadilated renal pelvis and ureter. In grade 2 hydronephrosis, the renal calyces become poorly defined. When parenchymal atrophy ensues, the ydronephrosis is categorized as grade 3 (see p. 134). Since no CM had been given tothe patient in Figure 133.5,thehyperdense lest- )f ( If ) in therightkidney mustbe a renal calculus. -orthe diagnosis of nephrolithiasis alone, CT should beavoidedbecauseof undue radiation exposure(ref. p.174ff.).Sonography isthe ethod of choice fornephrolithiasis as well ashydronephrosis.
134 Abdominal Pathology Kidney Hydronephrosis, which causes dilatation of the ureter (137) and the renal pelvis (1 36), impairs renal function (Fig. 134.1). In this image, the left renal parenchyma (135) shows delayed and reduced CM enhancement as compared withthe normal right kidney. Chronicgrade 3hydronephrosis reduces the parenchyma to a narrow rim of tissue (Fig. 134.2), resulting finally in atrophy and a non-functioning kidney. In cases of doubt, iden- tifying the dilated ureter(" in Fig.134.2b) can resolve theDD between a parapelvic cyst and hydronephrosis. CM accumula- tes in a dilated renalpelvis, but not in acyst. Fig. 134.2a Fig. 134.2b Solid Tumors Enhancement with CMoften helps to distinguish between partial volume averaging of benign renal cysts and hypodense renal tumors, since CT morphology alone does notprovide sufficientinformation about the etiology ofa lesion.This isespeciallyso whena mass(* ) is poorly defined within the parenchyma (Fig. 134.3).Inhomogeneous enhancement, infiltration of adjacent structures, and invasion of the pelvisortherenal vein arecriteriaof malignancy. Fig.134.3 Fig. 134.4 Fig. 134.5 However,whenamassconsistsnot onlyof solid, inhomogeneous areas, but alsocontains fat,anangiomyolipoma (7)must be considered (Figs.134.4 and134.5).These benignhamartomascontainfat,atypical musclefibers,and bloodvessels.Thevessel wallsare abnormal, and thecomplicationofintratumoral orretroperitoneal hemorrhage may occur (notdepicted here).
, Abdominal Pathology Kidney 135 ~fter extracorporealshock-wavelithotripsy(ESWl),renal injuriesmay rarelyoccurthatleadtosmall hematomasorextravasation ofurine "am the ureter. If there is hematuria or persisting pain after ESWl , it is essential to obtain delayed images. Urine leaking into the ';troperitoneal spaces (+ inFigs.135.2a through 135.2c)wouldnot beopacifiedinimages obtainedbeforethe kidneyhasexcretedCM. Fig.135.1a 4g. 135.2a Fig.135.2b contoursat thekidney(135) appear blurred,anddependingon the extent of hemorrhage, hyperdense fresh hematoma (8) can be detected in the retroperitoneal spaces. in this case, enhanced images (Figs.135.1c and135.1b) showthat the renal parenchy- Fig. 135.1c Fig. 135.2c =""nal infarctions (180) usuallyhaveatrian- " arshapeon CTimages corresponding to -, vascular architecture at the kidney I g.135.3).The broad base abuts thecap- , e and the triangle gradually tapers . 'lardthe pelvis (1 36).Atypical feature is -e lack ofenhancement after i.v. CMinthe ;' ~y perfusion phaseand inthe lateexcre- phase. Embolisms usually originate in -e left heart, or in the aorta in cases of =- erosclerosis (174 in Fig. 135.3) or '-.eurysms (ct. p. 142). , mere is a low attenuation filling defect 73) in the lumen of the renal vein (111) rt sr a CM injection, the presence of bland r-ombus (Fig. 135.4) or tumor thrombus -JITl a renal carcinoma extending into -~ inferior vena cava (80) must be con- scered.
Diverticula Diverticulasituated attheperi- phery of the bladder can easily be distinguished from ovarian cysts byusing CM(Fig. 136.3). The "jet phenomenon" is often seen in the posterior basal recess of the bladder and is caused by peristalsis in the ureters. They inject spurts of CM-opacified urine into the bladder, which is filled with hypodenseurine (Fig. 136.4). 136 Abdominal Pathology Urinary Bladder Catheters The walls of the urinary bladder are best examined if the bladder is distended. If a urinary catheter (182) is in place at thetime of CT (Fig.136.1),sterilewater canbe instilledas a low-density CM. Focal ordiffuse wall thickeningof atrabeculatedbladder, associatedwith prostatic hyperplasia, will be demonstrated clearly. If a ureter (137) has been stented (182) for strictures or retroperitoneal tumors. the distal end of the JJ stent may be visible in thebladder lumen (138) (bilateral JJ stents in Fig. 136.2). Fig. 136.3 Fig. 136.4 Solid Tumors Bladder wall tumors (7), which become visible after intravenous or intravesical CM, have characteristic, irregular margins that do not enhance with CM (Fig. 136.5). Tumors must not be confused with intravesicular blood clots that may occur following transurethral resection oftheprostate. It is importanttodetermine the precise size at thetumor and towhat extent adjacentorgans(e.g., cervix, uter- us,orrectum)havebeen infiltrated (.. in Fig.136.6). Fig. 136.5a Fig. 136.5b Fig. 136.6
Abdominal Pathology Urinary Bladder , the bladder has been resected because of carcinoma, a urinary reservoir (* ) can be constructed using a loop of small bowel eumconduit) which has been isolated from the Gil Urine is excretedfromthe reservoir into a urostomy bag (.. in Fig. 137.1 b). J Figure 137.2 a colostomy ( ) isalsoseen (ct. p. 140). 137 :;g. 137.1a Fig. 137.1b Fig. 137.2 I Abdominal Pathology Reproductive Organs erus =nreign bodies in the uterine cavity (158), e.g. an intrauterine :ootraceptive device (166), are not always as clearly visible in a transverse image as in Figure 137.3. Calcifications (174) are a :naracteristic feature of benign uterine myomas. Nevertheless it can be difficult to distinguish multiple myomas from acarcinoma - . 137.3b of the uterus (7 in Fig. 137.4). If theadjacentwalls of thebladder (138) ortherectum (146)areinfiltrated,the tumor ismost likelyto be malignant (Fig. 137.5). Central necrosis (181) occurs in both kinds of tumors and is usually indicative of a rapidly growing, malignant tumor (Fig. 137.4). Fig. 137.5b
138 Abdominal Pathology Reproductive Organs Ovaries The most commonovarian lesionsare thin-walled follicular cysts (1 69)that containaclearfluid withadensityequivalent tothat ofwater, which is below 15HU(Fig. 138.1). Density measurements, however, are unreliable in small cysts (cf. p. 133). These cannot be clearly differentiatedfrom mucinouscystsorhemorrhagic cysts.Thislattertype of cystmay be caused byendometriosis. Sometimescystsreach considerable sizes (Fig.138.2) with consequent mass effect. Fig.138.3b The malignant nature of solid ovarian tu- morscan be suspected if thereare the fol- lowinggeneralcriteriaused forothertumors: 1) ill-defined margins; 2) infiltrationof adjacent structures; 3) enlarged regional LNs; and 4) inhomogeneousenhancement withCM. Peritoneal carcinomatosis (Fig. 138.3) frequently occurs in advanced ovarian carcinoma, and is characterized by the appearance of multiple fine nodules and edema (185) in the greater omentum, the root of the mesenteric, and the abdominal wall,and byascites (8). Fig. 138.3a Prostate, Vas Deferens High-densitycalcification representingpostinflammatoryresidueisoftenencountered following prostatitis(Fig.138.4).Calcificationsare also occasionally seeninthe vas deferens(Fig. 138.5).Carcinomaof theprostate isonlydetectableinadvancedstages (Fig.138.6)when the bladder wall orthe adjacent ischiorectal fossa fat is infiltrated.If a prostate carcinoma is suspected, allimages should be carefully viewed on bonewindowsfor sclerotic metastases (seep. 145). Fig,138.4 Fig. 138.5 Fig.138.6
Abdominal Pathology Gastrointestinal Tract 139 of diffusewall thickening (Fig. 134.2), theDDshould also include lymphoma, leiomyoma, or leiomyosarkoma of the stomach. It is vital to look forbubbles of intraperitoneal gas ( " inFig. 139.3), which is evidence of a small perforation possibly occuring with ulcersoradvanced ulcerating carcinomas. wall (140) and also leadto muralthickening (Fig. 139.6).TheDD should inciude ischemia if the abnormality is limited to segments in the territoryof the mesenteric vessels, e.g., in the wallsof the colon (152), as a result of advanced atheroscierosis (174), or an embolus (Fig.139.7).Youshouldtherefore check thatthe mesen- teric vessels (108) and the walls ofthe intestine enhance homo- geneously after l.v. CM. Fig.139.6b=9,139.5 Stomach espite the advantages of using water as a hypodense CM for :naging the stomach after intravenous Buscopan [15, 16], small unorsmayescape detection during conventional CTs. Endoscopy - d endosonography should be employed tocomplement CT. arked focal wall thickening, which occurs in carcinoma of the iornacn, is usually easily recognized (.. in Fig. 139.1). In cases flammation of the Intestines ",e entire small and large bowel must be examined for wall " . keningorinfiltrationof thesurroundingfatas perthecheckiist _ page81. Bothulcerativecolitis(Fig.139.4) andCrohn's disease I g.139.5) are characterized bythickening ofthe affected bowel call ( t )so that several layers ofthe wall may become visible. =ssernlnatedintravascularcoagulopathy (DIC) or over-anticoagula- n with warfarin may cause diffuse hemorrhage (8) inthe bowel
140 Abdominal Pathology Gastrointestinal Tract Colon Elderly patients frequently have diverticular disease (168) of the descending colon (144) and sigmoid colon (145 in Fig. 140.1). The condition is more significant if acute diverticulitis has developed (Fig. 140.2), which is characterized by ill-defined colonic walls and edematous infiltration of thesurrounding mesenteric fat ( inFig. 140.2). Fig. 140.1a Fig. 140.1b Fig. 140.2 Malignant thickening of thecolonic wall (152 in Fig. 140.3) is not always easily distinguished from thatfound in colitis(cf.p.139):in both conditions there is stranding of the pericolic fat. The liver shouldalways bechecked formetastases if thecause ofthecolo- nic abnormality is uncertain. Atemporary colostomy(170 in Fig. 140.4) may benecessary if a Fig. 140.4b left hemicolectomyorsigmoid colectomy waspertormed because of pertorated diverticulitis or carcinoma. The colostomy is perma- nent if the rectum was excised. A potential complication of a colostomy can be seen in Figure 140.5:there is an abscessinthe abdominalwall (181).Acarcinoidlesion ofthesmall bowel ( in Fig. 140.6) may simulate acarcinomaofthe colon. Fig. 140.6
Abdominal Pathology Gastrointestinal Tract 141 eus -odzontal air-fluidlevels ( .... )and atonic,dilated bowel loops 140) are typical features of ileus. Ifdilatation is recognized inthe :opogram(Fig. 141 .1),orin anoverview oftheabdomen, an ileus - ust be suspected. If only the small intestine (Fig. 141.2) is valved, the most likely cause isa mechanical obstruction dueto adhesions.A gallstone may cause obstruction ofthe small bowel (gallstone ileus).This follows cholecystitis withtheformation of a cholecystoenteral fistula and the passage of a gallstone into the bowel. The gallstone may obstruct the narrower caliber of the distal ileum(167 in Fig. 141.3). Fig. 141.3Fig. 141.2 -rethere anysuspicious findings other than the colic ileusin Figure •~1.4? Doestheimage remindyouof othersinthemanual?Makethe sf of the figures by returning to previous chapters, covering the ""xl, and identifying asmany structures aspossible.You will improve our learning efficiency by reviewing the images and diagrams and ..singthe legends to make sure you gotit right. 'echanical obstruction of the colon leads to similar air- fluid levels , ddilatation ( .... inFig. 141.4).Whenlookingforthecause ofan eus, the enfirecolon must be examined forobstructing or constrict- ' g tumorsorfocal inflammation. Test Yourself! Exercise 29: Spacefornotesandcompletingthe exercise:
142 Retroperitoneal Pathology Aneurysms Ectasia or aneurysms of the abdominal aorta (89) are usually the resultofatheroscleroticdisease(174) whichleadstomuralthrom- bosis (173 in Fig. 142.1).An aneurysm of the abdominal aorta is present if the diameter of the patent lumen has reached 3 cmor the outer diameter of the vessel measures more than 4 cm (Fig. 142.2). Surgical intervention in asymptomatic patients is usually consideredwhen the dilatation has reached a diameter of 5 cm. The general condition of the patient and therate at which dilatation isprogressing must be considered.If thepatent lumenis central and issurrounded by mural thrombosis(173inFig.142.2), the riskof rupture and consequent hemorrhage is reduced. Fig. 142,3a Fig. 142.3b Fig. 142.2a Fig.142.2b Fig. 142.1a The risk of rupture is greater if the patent lumen is eccentric( in Fig. 142.4) orif the cross-sectional shape ofthe vessel is very irregular.Dilatation inexcess of6 cmdiameteralso has ahighrisk of rupture. Surgical pianning requires the determination of whether, and towhat degree, the renai, mesenteric (97), and iliac (113) arteries are involved by the aneurysm (Fig. 142.3). Sudden painmay accompany ruptureordissection,which can extend from the thoracic to the abdominal aorta (cf. p. 93). Dynamic CM- enhanced CTwill show thedissection flap (172in Fig. 142.5). Fig. 142.4 Fig. 142.5a
Retroperitoneal Pathology 143 lenous Thromboses 011 cases of thrombosis ina vein of the lower extremity ( ), venography • es not always clearly show whether or not the thrombus extends into =elvic veins (Figs. 143.1a and 143.1 b).The CM. which is injected into a superficial veinof the foot.isoftendilutedtosuch adegreethat it becomes ; icult toassessthelumen of the femoral/iliac veins(" inFig.143.1 c). - suchcases. it is necessary to perform a CTwith l.v. CM. Fig. 143.2b Fig. 143.2d Thelumenofavein containing a "'esh thrombus (,,) is general- . at least twice aslarge as nor- ""al (Fig. 143.2a). The segment :ootainingthe thrombus is either ,;]iformly hypodense compared Mlhtheaccompanying artery, or : shows a hypodense filling :efect. representing the throm- : us itself. In the case illustrated Fig. 143.2a :n theright,thethrombus exten- :ed through the left common ;;ac vein (, ) to the caudal seqrnent of theinferior venacava Fig. 143.2b), where it can be ",en as a hypodense area ( t ) serroundedby contrast-enhanced, "0I'ling blood (Fig. 143.2c). CT ;icesmust be continued cranial- J until the inferior vena cava no ;/lger showsany signsofthrom- Fig. 143.2c .us ( in Fig. 143.2d). --e injection of CM into a superficial foot vein opacifies satis- " ;torily onlythe ipsilateral leg, soit may beadvisabletoinject CM , stemicallythroughanarmvein inorder toexaminebothsides of - e pelvic venous system. If one side has become occluded, ~ aterals may develop ( ) via the prepubic network of veins (Figs. 143.3a and 143.3b). Such collaterals are known as a "Palmashunt",andthese can alsobe surgicallycreatedif athrom- bus in a deeper vein resists dissolution.You should be careful not to mistake an inguinal LNwith physiologically hypodense hilarfat ("hilar fat sign" " inFig. 143.3c)forapartiallythrombosed vein. I
144 Retroperitoneal Pathology In order to avoid pulmonary embolism in cases of thrombosis (173) of the inferiorvenacava (80inFig. 144.2),the patient must be immobilized until the thrombus has either become endo- thelialized orhas responded totherapy and dissolved. Occasionally, marked collateral circulation develops via the lumbar veins (121). Depending upon the individual patient and thesize of the thrombus,the vessel may be surgically explored and throm- bectomy performed. If thromboses are recurrent, an arterio-venous shunt may be indicated in order to avoid relapse. Thesuccess ofaparticulartherapymay also be checked with venography or color-Doppler ultrasound. Fig,144.1b Fig.144.4 Fig.144.5b Fig.144.3 Fig.144.5a Conglomerate LN masses (6/7) surrounding the aorta (89) and its major branches such as the celiac trunk (97) are a typical finding in cases of non-Hodgkin lymphoma (Fig. 144,5). EnlargedLymph Nodes Thedensityof LNsisapproximately50HU,whichcorrespondstothat of muscle.LNswithdiametersbelow 1cmaregenerallyconsidered normal. Sizes between 1.0 and 1.5 cm are considered borderline, and those that exceed 1.5 cm are abnormally enlarged. Sites of predilection for enlargedLNsarethe retrocrural, mesenteric ( ), interaortico-caval (,),and para-aorticspaces (cf. p. 103). Figure144.3illustrates thecase of a patient with chronic lymphatic leukemia. It isessential tobe familiarwiththe major paths of lymphatic drainage. The drainage of the gonads, for example, is directlyto LNs at renal hilar level. LN metastases ( " in Fig. 144,4) from a testicular tumor will be found in para-aortic nodes around therenal vessels but notin the iliac nodes, as would be ex- pected with primarycarcinomas of the urinary bladder, uterus, or prostate.
Skeletal Pathology Pelvic Bones 145 a 28 35b • • 62 (Fig. 145.3a) only after they have reached considerable size. can be much more accurately detected on bone windows (Fig. 145.3c). This case shows a metastatic disease of the right ilium (58) that has destroyedthetrabeculaeandmuch of thecor- tex. The erosion extends to the sacroiliacjoint. See thefollowing pagesforfurther imagesof thispatient. .ormal Anatomy --eimportanceof examining bonewindows during abdominal CTshasalready been stressedon page103.Themarrowspaceoftheiliac - es (58) and the sacrum (62) is normally homogeneous. and the surfaces of the sacroiliac joints should be smooth and regular I g.145.1). tastases :- erotic bone metastases (7), for example from a carcinoma of -e prostate, are not always as evident as in Figure 145.2a and -.ay vary insize and degree ofcalcification. Even small and poorly :~'in ed metastases should not be overlooked ( in Fig. 145.2b). -'eycannot routinely be recognized on soft-tissuewindows. _- c metastases (7), whichcan be seen on soft-tissue windows =:. 145.3a Fig. 145.3b Fig. 145.30
146 Skeletal Pathology Pelvic Bones The mechanical integrity of a bone is suspect if any process involves its structure. Adjacent joint involvement must also be determined.MPRs (see p. 13) at various angles,forexample sagit- tal or coronal, provide additional information. If necessary, 3D reconstructions canalsobeperformed. In the case shown on the previous page (see Fig. 145.3), the .--- question of stability is easily answered: the coronal MPR (Fig.146.1a) shows thatthe trabeculae ofthe rightiliac bone have been completely destroyed for approximately 10 cm ( ). The lesion extends from the acetabulumtothe mid-point of the sacro- iliac joint and has also destroyed much of the cortex. In several areas, the cortex is disrupted (+ ). If you compare the bilateral sagittal reconstructions(Figs.146.1 b and 1c),it iseasy tosee that there isacute riskof fracture. Fig. 146.1a Fig. 146.1b The 3Dreconstruction of this pelvis (Fig. 146.2) does not add any more information, because it shows only the cortical disruption ( " ) as seenfrom the lateral perspective. The degree to which the trabeculae and marrow have been destroyed cannot be seen in this reconstruction because the attenuation level was set to detect the cortical bone, and the deeper trabeculae arethereforecovered. Fig. 146.2 'tJ' •
Skeletal Anatomy Pelvic Bones 147 -orjointssuch asthe hip joint, it maybehelpful to makean MPR inthe obliqueplane (Figs.147.3).The angle ofreconstructionis shown .Il Fig. 147.3a. Be careful not to mistaketheacetabularsuture( ,,) withthe real ischialfracture (')1 35b Fig. 147.1bFig. 147.1a Fig. 147.2a f ractures 30newindows should of course ce used for the detection of . actures: hairline fractures and minimal dislocations cannot usually be recognized on soft- tissuewindows. ; is also essential to give infor- nanon on the precise fracture s' e and position of possible . agmentsfor preoperative plan- ~ing . ln thecase ontheright,the zacture (187) of the femoral -ead (66a) is seen both in the axial plane (Fig. 147.1) and in me sagittal reconstruction (Fig. 147.2) (ct. p. 13), Fig. 147.3a Fig, 147.3b b Fig. 147.3c 66 58 ~---~ -notner exampleofafracturethatmay bemistakenforasutureis lustrated in Figure 147.4.The sutures (,,) are bilaterally sym- metric,thefractures arenot. nthis case, several fragments ofbone ( .. .. )are seenatthe right iliopubic junction, butthe rightacetabulum isintact. Note also measymmetry in the Imagewhichis caused bydifferences in the evels of the femoral heads. The patient had left acetabular :ysplasia (cf.figures onp 148). Fig. 147.4
148 Skeletal Pathology Pelvic Bones Fragments are not always as obviously displaced nor is the fracture gap ( ) as wide as in the case illustrated in Figure 148.1. Look for fine breaks ( ) and discrete irregularities (..) in the cortical outline in order not to miss a fracture or a small fragment (Fig. 148.2). Fig. 148.1 Femoral Head Necrosisand Dysplasia of the HipJoint A fracture through the femoral head or even direct trauma to the hip joint may interrupt the blood supply to the head via the acetabular artery (see alsoFigures 147.1 and 147.2). Necrosisof the head makes it appear poorly defined ( ) as seen in Figure 148.3a and causes shortening of the leg.An image obtained 2cm Fig. 148.3a Fig. 148.2 more craniallyshows thatapseudoarthosishasdeveloped inasso- ciation with the right acetabular dysplasia (Fig. 148.3b). A 3Dreconstruction gives anoverview,butdoesnot provideasmuch detail as a series of coronal MPRs (Fig. 148.5b with orientation in Fig. 148.5a). Fig. 148.3b MPRs are often used for diagnostic purposes and in planning surgery of complexfractures. They contribute valuable additional information to the conventional axial images. SCTproduces parti- cularlyaccurate MPRimagesbecausedisruptivestepartitacts can be avoided if the patient is ableto cooperate by holding his or her breath. 3D reconstructions. such as the one in Figure 142.4, yield impressiveimages, butarehelpfulonlyforspecificproblemssuch as plastic surgery. The amount of time and cost necessarytoacquire and reconstruct 3D images are in most cases also very high.
Test Yourself! "ne images and questionson this pagewill againhelp youto check on how muchyou have understood; the questions become contin- ually more difficult to answer. It you alwaysremember the basic rules of CT reading, youwill avoid jumping to thewrong conclusions. J<Jn't look uptheanswers too soonI 149 ~ Ihat abnormalitycanyou dentify in Figure 149.1? ameasmanybloodves- selsas youcan! ~ Identify as many organs and blood vessels aspos- sible in Figure 149.2. Look for any abnormali- ties. ~ What anatomic variation or abnormality do you recognizeinFigure 149.3? Be sureyouhaven't miss- ed anything. ~ "Doyousmoke?"What abnormalities did you find in Figure149.4? I mrmmaiseasy to recognizethe hepatic lesion in Figure 149.5.Whatis your DO? emmID Often abnormalities are not limited to one organ. What do yourrecognize in Figure149.6?
Test Yourself! 150 Thefollowing questions may seem tricky, but you should be able toanswer most ofthem if you goby the "rules ofthe book." ~ Describe the hepatic le- sion in Figure 150.1. What steps did you take to arrive at your differen- tial diagnosis? How would you proceed to verify it? ~ Are thechanges in Figure 150.2 "normal," or do yoususpect that they are patho- logic findings? I omf:!lEI Whichofthe twoimagelevelsontheright wouldyou select for performing densitometric measurements of thekidney lesion? Why? ~ A patient is admitted for staging of a malignant melanoma(Figure 150.4). How far advanced is the lesion? What else would you do to obtain more information? ~ Atraumapatient couldnot be scanned in the prone position.What doyousus- pect in Figure 150.5, and what would you doto ob- tain more information?
~ ! problem for those oho alreadyhavesome ine(Figure 151.1). "'()W longdid ittakeyou R find two pathologic -terat ons and diag- -use themaccurately? Test Yourself! ~ Do you see anything abnormal in Figure 151.2? If so, what would you call it (the small figure indicates a structure filled with liquid)? 151 ~ !, least three differential : agnosesshouldbecon- - deredfor Figure 151.3. Which one is the most «ely? ~ In Figure151.4, thereare alsoseveral possibilities to explain the obvious alter- ation.Are you able to find all possible lesions in an imageof this kind? I ~ at doyou sus- cect isthecasein I gure 151.5? Hhat additional . formationdo u need? ~ This image (Figure 151.6) may contain several puzzles. Again, list the most likely diagnoses and thenask yourself what further information youneed.
152 Skeletal Pathology Cervical Spine (4 :< 2mm The occipital condyles at the base of the skull articulate with the first vertebra, the atlas (50a), which is the only vertebra to lack a body. The dens (50b) of the axis protrudes upward intotheatlas and isheldinplacebythe transverse iigament (*) (Figs. 152.1 and 152.2). This iigament may be torn bya whiplash injuryduring road tra~accidents. The width of the space ( ~) between the anterior arch of the atlas (* * in Figs. 152,1 and 152.2) and thedens is also measured, as in conventional x-ray images (Fig. 152.3). Inadultsitshould not exceed 2mm; inchildren, 4mm.The vertebral arterypasses through thetransverse foramen (88). Fig. 152.1 Fig. 152.2 Fig. 152.3 The images below show normal anatomyattheleveloftheatlas(Fig. 152.4) and the body oftheaxis (Fig. 152.5). The cartilageof an intervertebral disc (50e in Fig. 152.6) will appear more homogeneous and hypodensethan thetypical pattern oftrabeculae. Fig. 152.6bFig. 152.5bFig. 152.4b
Skeletal Pathology Cervical Spine 153 Cervical Disc Protrusion Adisc protrusion (prolaps ofthe nucleuspulposus) isdemonstrat- edoptimallyinCTsectionsafter myelography(CM intheSAS). The spinal cord is virtually isodense to CSF in unenhanced images, making it difficult todefine thecontoursof thecord. After amyelo- gram, the CSF (132) will appear hyperdense to the cord (54) as well as to adisc. - disc prolapse will beseen evenmore clearlyinanMR image. The 32gittal T,-weighted image in Figure 153.3a shows the extent of : otrusions at twodiskspaces.Thediskprotrudes intothe hyper- ~rvical Spine Fractures - 's especially important to look forfractures of the cervical spine _ or torn ligaments after trauma (ref. p. 152) so that damage to -e cord is avoided if thepatient needs to be moved or transport- Normally, the CSF uniformly surrounds the cervical cord (Fig.153.1).Adiscprolapse (7).protruding intotheCSFspace can be seen because it is hypodense to the opacified CSF. The gap between thecord (54) andvertebral body (50) is filled in.Didyou recognize the pyriform fossa (172), the hyoid bone (1 59), the thyroid cartilage (1 69), and thecricoid cartilage (167)7 intenseCSF space (..)infront ofthecord.Theaxial T,-weighted image (Fig. 153.3b) shows that the prolapse extends to the left and has caused stenosisoftheintervertebral foramen ( ). ed. Figures 153.4a through c show a coronal MPR in which the right occipital condyle (160) is fractured (188) but thedens (50b) is still in normal position. Fig. 153.4b Fig. 153.4c
154 Skeletal Pathology Thoracic Spine The thoracic vertebrae articulate witheach other attheirsuperior and inferior articularfacets (SOd) and withtheribs (51) at the inferior and superior costal facets and thetransverse processes (SOl). Figure 154.1 shows a normal thoracic image: the contours of thecorti- cal boneare smoothandthetrabeculaehavea homogeneous pattern. Fig. 154.1a Fig. 154.1b Fig. 154.2a Fig. 154.2b Fig. 154.3a Fig. 154.3b Fractures of the Thoracic Spine Displaced fragments are identified by virtue of the fracture lines (187) and are best seen on bone windows. In Figure 154.2, both the transverse process (SOl) and thecorrespondingrib (51) are fractured. In complex fracture dislocations (Figs. 154.3), torsion orshearing may causecompression orcomplete dislocati- on of the spineas a whole (Figs. 154.3a, e). The axial image in Figure 154.3ashows two vertebrae ( ,,) at one level; the topo- gram in154.3bindicatesthe position ofthesagittalMPRshownin Figure 154.3e. The MPRgives a moreprecise pictureof thefrac- ture and the fragments than the oblique anterior and oblique posterior3Dviews in Figures154.3cand d.
Skeletal Pathology Lumbar Spine 155 -·e transverse processes (50!) of the lumbar vertebrae are xcastonany called costal processes.Lumbar vertebrae havemuch - ger bodies(50) than thoracic vertebrae, and the angle of their ctervertebraljoints(50d)issmaller.Lumbarspinous processesdo -0 extend as far caudally as the thoracic ones. Images of the -oonal lumbar spine usually show well-defined cortical bone and homogeneous trabeculae. At the level of a disk (Fig. 155.2), the hypodense cartilage (50e) may seem irregularly surrounded by bone: this is an oblique partial volume effect inwhich parts of an adjacent body (50) are included withthe disk.The ligamentaIlava (*) extend from one lamina to the next and can sometimes be seen behind the cord (Fig. 155.1 a). I 31 50 50e 0 22 ~ _ 22 9g,155.1b Fig. 155.2b Fig. 155.3b )egenerative change of the vertebrae can be seen in the facet joints (50d) (Fig. 155.3). There is increased subchondral sclerosis .., ,,) indicativeof arthrosis ofthe joint. .urnbar Disk Prolapse -s with cervical disk protrusions (see p. 153), it is important to : tabllshwhether the nucleus pulposus hasprotruded through the rosterior longitudinal ligament. This ligament is applied to the : terior borders of the vertebral bodies and disks. Disk material - t has penetrated the posterior longitudinal ligament and .ecome detached from the disk is referred to as a sequestration **). This can narrow the spinal canal or a lateral recess (Fig. •55.4). Thesestructuresarenot well demonstrated on soft-tissue win-dows(Fig.155.4a) because of their high density,but are dearty seen on bone windows (Fig. 155.4b). A T2-weighted MR image (Fig. 155.5) shows theextent of the prolapse: the abnormal disk (+) is thinner,isdesiccated(shows alowersignallevel [darker]), and the extruded material ( ,,) impin- ges onthetheca.
156 Skeletal Pathology Lumbar Spine Fractures Inconventional x-ravs, it isoften difficult tosee thefracture ofa lumbar transverse process (501) if the fragment is notor only minimal- lydislocated (187).InCTsections, however,afracture can be clearlydemonstrated (Fig.156.1). Figure 156.2 illustratesacase in which the spinous process (50c) was fractured.An arthrosis may develop if afracture has involved ajoint (Fig. 156.3).Therearefractures of boththesuperior and the inferior articularprocesses (50d). <, I ~~50C/ V~ 187- - 187 , ,""~~'t)~ 22 6 22 b .- Fig. 156.1b Fig. 156.2b Fig. 156.3b Older fractures donot show awell-defined fracture line (1 87).Increasedsclerosis and new bone often efface thefracturelineorapseud- arthrosis may develop. Inthe case shown inFigure 156.4,the fractured pedicle has developed a pseudarthosis. Inconventional x-rays, increased sclerosis following afracture is often difficultto differentiatefrom that resultingfromdegenerativedisease. Fig. 156.4a Fig. 156.4b
Skeletal Pathology Lumbar Spine 157 -umors and Metastases at all bone lesions originate within the bone. Malignant tumors of paravertebral tissues can also 'Vadethe bones. =igure 157.1 shows an osteolytic lesion (,, ) in the body of a lumbar vertebra in a patient with :arcinoma of the cervix. On soft-tissue windows (Fig. 157.2), there is a paravertebral metastasis (7) A't1ich has surrounded the bifurcation ofthe common iliac artery (114/5)and has infiltrated theright anterolateral aspect ofthe vertebral body. DRs in the coronai (Figs. 157.3a and b) and sagittal (Figs. 157.4a and b) planes show the extent towhichthe bone has been eroded "nd that there is risk of fracture.As in Figure146.2. the3Dreconstructions (Figs. 157.5a and b) clearly show thelesion from anterior ' -d lateral perspectives, butnotthe degreetowhichthe interior trabeculaehave been destroyed. I
158 Skeletal Pathology Lumbar Spine I Infection Abscesses inthe paravertebral soft tissues or infectiveor inflam- matory arthritides (1 81)inthe smalljoints ofthe spine may leadto diskitis which ultimately destroys the intervertebral disk (Fig. 158.1). An advanced abscess canbe detectedon soft-tissue win- dows (Fig. 158.1a) asanarea ofheterogeneous density surroun- Fig. 158.1a Methodsof Stabilization If therapeutic measures such as chemo- therapy, antibiotics, and/or surgery have been effective in the treatment of a me- tastasis or infection, it is possible to stabi- lize the spine by inserting bone prosthetic material(Fig. 158.2a, b). The choice of material depends upon the size ofthedefect and upon other individual factors. In follow-up examinations, these materials may cause considerable image artifacts because of their high relative density. Fig. 158.2a Space for additional notes: ded by a hyperdense enhancing rim representing reactive hyper- perfusion. On bone windows(Fig. 158.1c),onlysmall remnantsof bone belongingtothevertebral bodyare present andsome are dis- placed. Fig. 158.2b
Lower Extremity Normal Anatomy of the Thigh 159 iheanterior muscles of thethigh includethe sartorius muscle(38), andthe four componentsofthe quadriceps muscle(39).The most anterior istherectusfemoris (39a),and lateraltothisisthevastus .ateralis (39b).The vastusintermedius (39c) and vastusmedialis (39d) form the anterolateral borders of the adductor canal. This contains the superficial femoral artery and vein (119/120). The adductor muscles comprise the superficially located gracilis muscle (38a) and the adductor longus (44a), brevis (44b), and magnus (44c) muscles. Thepectineus muscle (37) isonly seen in memost caudal images ofthe pelvis. =jg. 159.3a The posterior muscles ofthe thigh extend thehipjoint and flex the knee joint.The groupconsists of the long and short heads of the biceps femoris muscle (188) and the semitendinosus (38b) and semimembranosus muscles (38c). In the proximal third of the thigh (Fig.159.1),thehypointense tendon ofthe biceps muscleis adjacent to the sciatic nerve (162). In the distal third of the thigh (Fig. 159,3),themedial poplitealnerve (162a),whichsupplies the dorsal muscles, can be seen separate from the lateral popliteal nerve (162b). Note the close relationship of the profundafemoris artery and vein (119a/120a)tothe femur (66) and thesuperficial posi-tion of the long saphenous vein (211a). Fig.159,lb Fig.159.2b Fig.159.3b
160 Lower Extremity Normal Anatomy of the Knee The popliteal artery (209) and vein (21 0), formed cranial to the joint line, are demonstrated at the level of the patella (191) In the fossa between the femoral condyles (66d)(Fig. 160.1).Thetibial nerve (162a) lies directly posterior tothevein,whereasthefibular (peroneal) nerve (1 62b) lies more laterally.Themedial (202a)and lateral (202b)heads of thegastrocnemiusmuscle and the plantar- is muscle (203a) can be seen posterior to the femoral condyles. The longsaphenous vein (211 a) lies medially inthesubcutaneous fat covering the sartorius muscle (38), and the biceps femoris muscle (188) lies laterally. On the section just caudal to thepatella (Fig. 160.2), the patellar tendon (1 91c) can be identified, posterior to which is the infrapa- tellar fat pad (2). Between the femoral condyles lie the cruciate ligaments (191b).Transversesections such as thesearefrequent- ly combined with coronal and sagittal MPRs (seealso the images ofafractureon p. 167). Fig. 160.1c Fig. 160.2c
Lower Extremity Normal Anatomy of the Lower Leg 161 Themusclesofthelowerlegare separated into four compartments uythe interosseus membranebetweenthe tibia(189) and the fibula (190) and by the lateral and posterior intermuscular septa Figs. 161.1 to161.3). Theanterior compartment containsthetibia- tis anterior muscle (199), the extensor hallucis longus muscle (200a) andthedigitorum longusmuscle (200b) next to the anteri- ortibial vessels(21 2). Thelateral compartment containstheperoneuslongus (201 a)and orevls (201 b) muscles next to theperonealvessels (214). In slen- cerindividuals who have no fat between the muscles, these ves- sels and the peroneal nerve are only poorlydefined (Fig. 161.2). The flexor muscles can be separated intoa superficial and a deep group. The superficial group encompasses the gastrocnemius muscle with medial (202a) and lateral (202b) heads, the soleus muscle (203), and the plantaris muscle (203a). The deep group includes the tibialis posterior (205), the flexor natlucis longus (206a), and the flexor digitorum longus muscles (206b). These musclesareparticularlywell defined inthedistal thirdof the lower leg (Fig. 161.3).Thetibilalis posterior vessels (213) andthetibial nerve (162a) pass between thetwoflexorgroups. Fig. 161.1b Fig. 161.2b Fig. 161.3b
162 , Lower Extremity Normal Anatomy of the Foot Fig. 162.1b The following three pages show the normal anatomy of thefoot onthe bonewindow. You will find the numbers to the legends inthe back fold- out. The image series beginsin a plane throughthetalus (192) just distal to the talocrural joint.Figure 162.1 shows the distal end of the fibula or lateral malleolus (190a) as well as the upper partof the calcaneous (193). In Figure 162.2,thesustentaculumtali (193a) of the caicaneous is Fig. 162.1 a seen. Compare these images of a normal foot with the images of fractures on pages 164 and 165. The Achilles tendon (215), which arises from both the soleus (203) and the gastro- cnemius (202) muscles, is seen posteriorly on these images. More distally,additional meta- tarsal bones are seen: the navicular bone (194) has begun to appear in Figure 162.2. but its joint with the talus is better assessed in Figure 162.3. The articular surfaces are normallysmooth and the synovial space be- tweenthebones is ofuniform width. I Fig. 162.3a Fig. 162.3b
Lower Extremity Normal Anatomy of the Foot 163 The cuboid bone (195) is seen on the lateral margin of the foot, between the calcaneus (193) and the navicular (194). The lateral (196c). intermediate (196b), andmedial (196a) cuneiform bones lie anterior to the navicular(Fig. 163.1). The transition to the meta- tarsal bones (197) is not always well defined, because the plane of the tarsometa- tarsal joints is at an oblique angle to the sections (partial volume effects (Fig. 163.2). Thejoints can bemoreclear- ly assessed in mulliplanar reconstructions that take this obliquity into account (cf. Fig, 164.1 ). The lumbrical and quadratus plantae muscles and the short flexor muscles of the foot (208) are seen just below the arch of the meta- tarsal bones. These muscles Iareonly poorly defined in CT images (Fig. 163.3). - .163.3a Fig. 163.3b
164 Lower Extremity Normal Anatomy of the Foot Multiplanar reconstructions are very valuable for visual- izing fractures of the foot. Thelateraldigital radiograph in Figure 164.1 a Indicates theangleof theimageplane, parallel tothelong axisof the foot,seen inFigure 164.1 b.Thisreconstructed image extends from the lateral (190a) and medial (189a) malleoli (at the loweredge of the image) throughthe talus (192) and the navicular (1 94) to the three cuneiform bones (196a-c). Two of the metatarsal bones (1 97) are included in the section. Note thatthe surfaces of the joints are smoothand evenly spaced. Thesagittal image in Figure 164.2b was reconstruc- ted slightly more laterally (see position in 164.2a) so that the cuboid bone (1 95) is included. The short flexor muscles (208) and the plantar ligaments are seen below the archof the foot. The Achilles tendon Fig. 164.1b (21 5) isseen posteriorly. Fig. 164.1c I Fig. 164.2a Fig. 164.2b Fig. 164.2c Diagnosis of Fractures Typical signs ofafracture canbe seen intheoriginal axial plane (Fig. 164.3a): irregularities inthecortical outline( ), displaced frag- ments ( ) and a fracture line ( ) in the calcaneous. The MPR in the coronal plane (indicated in Fig. 164.3b) shows that not only is the calcaneous ( l )fractured,butthereis ahairline fractureof the talus (..) involvingtheanklejoint (Fig. 164.3c).
Lower Extremity Pathology Fractures of the Foot 165 Fractures of the foot may initiallyescapedetectioninconventional x-rays if thereis nomajordisplacement of bone fragments. If the foot remains painful, a follow-up x-ray may show the fracture because fine hairline fractures can be seen when filled with hemorrhage. As an alternative, CT would show discrete fracture lines (1 87),as forexample ofthe talus (192) in Figure165.1. In chronic fractures, the displaced fragment (*) has usually be- come rounded off (Fig. 165.2). Inthis example. it is obvious that therewereactually twofragments because asecond fracture line ( '" ) is seen nexttothe main one (187). It is often difficultto treat comminuted fractures ofthecalcaneus (193), incurred for example during a fall (Fig. 165.3), because therearemanysmalldisplaced fragments.Astabilereconstruction of the arch of the foot may not be possible, resulting in a long period of sick leave. - . 165.1b Fig. 165.2b Fig. 165.3b
166 Lower Extremity Pathology Pelvis and Upper Leg Infections Theassessment of fractures oflongbones is generallythedomain of conventional radiology. But CT examinations are helpful for locating displaced fragments andin the preoperative planning of comminuted fractures. Infections, however, are more accurately imaged by CT than by conventional radiographs because bone destruction is more readily seen on bone windows (Fig. 166. 1c) and soft-tissue involvement (178) is documented on soft-tissue windows (Fig. 166.1a).This patient had septic arthritis ofthe left Fig. 166.1c hip jointwithinvolvement ofthe acetabulum(60)andfemoral head (66a). I The abscess appears more clearly after contrast enhancement (cf. Figs.166.2a and 166.2c).The increased vascularityof thewall and the fluid within the abscess (181) are well demarcated from surrounding fat (2).Adjacent muscles (38, 39, 44) are nolonger individually definedbecause ofedema (compare with the rightleg). Gas (4) has been produced and is loculated in the adjacent tis- sues. Fig. 166.2c
Lower Extremity Pathology Knee Joint 167 Fractures .afracture involves the knee joint, it isparticularly important toreducethe fragmentsaccuratelytoavoid jointsurfaceincongruities that might lead to arthosis. In the case below, axial sections clearly show the lateral displacement of a large fragment ( ,, ) of the tibia Figs.167.1aand 167.1b).Thecoronal MPR(Fig. 167.2b.with level shownin 167.2a) illustrateshow muchofthetibial plateauis affected. Fig. 167.1b Fig. 167.2b Fig. 167.3b "he3Dreconstructionseenfromaposterolateral projection(Fig. 167.3a) isnotveryhelpful,buttheview fromcranial (Fig.167.3b) gives ; good impression ofthe tibial plateau and fracture line becausethefemoral condyles have beenexcluded. Checklist Skeletal System: Fracture Diagnosis ..... Step-off ordiscontinuityof the cortex (evidenceof fracture)? ..... Articular involvementof afracture(risk ofsecondarydegenerativechanges)? ..... Stabilityon weight-bearing? Spine: e.g.•3-column model accordingto Denis (C-spine);A-B-Cclassificationaccording toMagerl (T-spine) ..... Simplefracture orcomminutedfracture,extent of displacementof thefracturefragments (surgical planning)? ..... Age of thefracture? • Acute => ragged and sharply demarcatedfractureclefts • Old => sclerotic rim,callus formation Riskof pseudoarthrosis with persistent fracture cleft? ..... Traumatic or pathologic fracture (underlyingbonetumor)?
Interventional CT 168 Itis not always possibletodeterminethenatureof alesionfrom CT appearanceand densitometryalone. In these cases, needlebiopsies may be carriedout underultrasound or CT guidance.The patient'splateletcount and coagulation st~'us mustbe checked and Informed consent obtained. InFigure 161.1 ,amassinthe caudate lobe (*) of the liver (122) is being biopsied. The close proximity of the hepatic arteryand portal vein(98/102) andinferiorvena cava (80) leaveonlya narrow path fortheneedletoapproach fromthe right side (Fig. 168.1a).First- ly the section on which the lesion appears largest is determined. The skin is cleaned and anesthetized with local anaestheic. Fig. 168.1a Fig. 168.1b Theneedle isthen inserted through the liver parenchyma toward the lesion. Slight changes inanglemay be neces- sary (Figs.168.1b, 168.1c, and168.1d). Distances can also be calculated duringtheprocedure,as seeninFigure 168.1b. After biopsy has been com- pleted, an Image is acquired to detect any hemorrhage. If a pneumothorax occurred following lung biopsy,expira- tory images of thethorax are acquired to check foratension pneumothorax. Fig. 168.1c Fig. 168.1d Ifthere isa retroperitoneal lesion close to the spinal column, a biopsy may be carried out In the prone position. The orientation inFigure168.2 istherefore unusualand one must be careful notto confuse left with right, but the proce- dure is identical. After selectionoftheoptimal level (lar- gest diameter of the lesion), and after skincleaning and local anesthesia, the needle is inserted (Fig. 168.2b) and the biopsy taken. The material should be promptly prepared for cytology and histology. The sizeand extent ofacutaneousfis- tula can often be more clearly assess- edIf CM isinstilledthroughatube(Fig. 168.3). In this example, the hip had become infected and an abscess filled thejoint after prosthetic surgery. Fig. 168.2b Fig. 168.3b Fig. 168.2a Fig. 168.3a
Skull: Bleeding ? Metastases? Fracture ? Mid-facial bones: Coronal, fracture ? Axial Axial to coronal reconstruction Petmus bone: C1 and C2 multiple trauma: Extremities (fracture?): Neck: Thyroid carcinoma ? Staqing of the pulmonary apex Thorax!abdomen: Staging ? Liver arterial + thorax Liver portovenous + pelvis Gynecologic + other tumors of the lesser pelvis Vena cava: Thrombosis Pulmonary embolism: Lung: Soft tissue window Pulmonary window Liver series: hemangioma ? (dynamic at the same level) Adrenal glands: Tumor ? Unenhanced Arterial Portovenous Late venous Perfusion: Head· unenhanced IV eM-concentration 300 ·370 Bone: Densitcmetrv t-solne Dental: Infratentorial: 3 / 3 / - Supratentorial: 8/ 8/ - 2/3 / 1 2 / 3 /2 2 / 3 /1 1 / 1,5/ 0,5 2 / 2/2 2/2/ 1,5 5 /5 /5 517,5 / 4 8 / 12 / 8 5/8/5 8 / 12/8 2 / 4 /2 5 / 8/5 8/ 0/ - 5 /~ 5 /4 5 / ~5 /4 5 / ~ 5/ 4 5/~ 5/ 4 Basis 3 / 3 /- Neurocran.8 /8 / - 10/0 / - 10 / 0 / - 1 / 1,5 /0 ,5 1,5 1,5 1,5 1,5 1,5 1,5 1,6 1,5 2 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 0,8 0,8 0,8 0,8 0,8 0,8 0,8 1,0 0,8 0,8 0,8 0,8 1,5 0,8 130 130 130 130 130 130 130 130 130 130 130 110 130 130 130 130 130 130 130 130 130 130 11 0 80 130 260 260 260 80 80 80 135 170 70 100 140 140 140 140 100 110 140 120 140 140 140 260 106 81 90 H 30 H 30 H 30 H 70 H 70 H 80 8 50 B 80 B 50 B40 B 40 B40 B40 B 40 B40 B 40 840 840 B 40 B40 H 30 H 30 S 80 H 70 caudocranial caudoc ranial cra niocaudal craniocaudal craniocaudal craniocaudal craniocaudal cra niocaudal craniocaudal cran iocaudal cra niccaudal craniocaudal craniocaudal caudocranial craniocaudal caudocranial caudocranial craniocaudal cramocaudal 250 / 40 90 / 35 1500 / 450 1500 /450 1500 /450 and 350 140 1500 /450 350 / 40 1500 /450 350 /450 1500 / 450 350 /40 2000 / · 300 350 / 40 350 / 40 350 /40 350/40 350/ 40 2000 /·300 350 /40 2000 / -300 350 /40 350 /40 250 / 40 + 90 /35 350/40 350/ 40 1500 / 450 60 / 1,5 70/2,0 120 / 3,0 - 5,0 100 / 2,5 120 / 2,5 2x 50ml bipedal 120 / 3,0 - 4,0 100 / 2,0 130 /2,0 80·100 /2 ,0 40 /8 60 25 - 40 8T post 90 60 90 - 100 8T A.asc. BT arterial: BT Venous: about 90 ~g ~~ g Pol ('D . < n ~ ~ O- 3. g (i3 C3 o- =r .... CJ) 3 ('D ~ ~ - S'WCD _ (3CDC.~c. S ~~ · co ~ .:<l ro"Q s:g ~. c. S- a II ~ 0- 8 Ci5 :-" ~ st en ~c..n C3 CO cr o CJ) CJ) CJ) ~ 0- ~ o~ a 8g :E~. enc.(O~ o <n W n :::J c.. -;-aC") ~ o :::J-< ..... -o ~ c. c: C'D 0 - (3 ~ ~. .-+ W .-+ ;::;: C'D C'D sa. !a Pol g z.(Ocr~roCJ) w :::Jc. n .-+ ~ -· n w _ $~§3'~Q (3 ~~rg~.-+c. _ ... ~ .....0 -Cc: ~ s· o 0 Co ~ 9: ~ 3 ~r cr~g:3=: co :::J :::J ~ g ~~~?- $" Q.) en 0 CJ) r::::... _ . c: .-+ C3 ro C'D .-+ 2 .-+ _ 3 CJ) (") ro s s ~. s st :::J en C3 :::J C'D c.m=-· <n g3~Sg. 'Eg~ <=.- o -· W CJ)(O~.c- CJ) ro r:::: _ l:: ...... en ro ::0 C'D -.....J 5 ' _ . .::: en 0(0 CJ) - . __ _ CJ) ... • C'D~-os. ("')oa~ ;-i (i3 s, e: -lc.c.~ ~~~ II :::r - w CD C3 0 C" en (") Co @§!g < '" <_ . c. C'D • §:-oa o o PJ _ . CJ) ~ ... 0 C'D CJ) Q.) ~ (") o 3 ~ g -~Q)c. .-+ ro (") CI:l =r ... .c _C'D CJ) c: . -0 PJ Vi· :::;:: ~ :g as., _ 0 3 -c ~ ... C'D 0 :E ~ c:D ..... ;:::::;:o ... =r =r ~ en CD I I ..... en c.o
170 Examination Protocols for 4-slice Spiral CT o co in ci o N ro. ~ t « o.D E "», roc o E 'S 0.. "' '"x .,. o _LD--. C') I- N I- t.hcoo coCJ"-' CJ- o co co oi x -e ro st « '"E o .c c. E ~ ,..j 0.. Z roc eo o I I "' "'"'- . I I 0 '" 0 6 '" "' o '"' 00 0 NN N 0 0 0000 0 lQlfL()lO l!) ...... -- ---0 0 00 0 OOLOL() If) 00 (')(") ('I) N N 00 a 0 CJ) Q) 0) Q) D "c c "'0: '§I "c ::::> x x .,..,. '0, c .2 vi 'w e.D iL o c-i o o "' "'ci Ci x X N .,. co "'- 0 0 0 0 0 0 N sc -sr o '" 00000 0 L()1.[) «:tmm "::l" I I I :)::J (IJ ro roroc c c e e e0 0 0 o 0 0 o N x x .,. .,. o co ro roc c e eo 0 . 0 0 00 0 00 NN(O(O lt) I I I I I '" '" '"'" '" '"o 0 ci f- (/] '"-eo Feed / rotation o so o "' Collimation ( e.g. 4 x 2,5 =10) m '"I I 0 0 0 0 O<OO l() MC'JC')(J 0000 "'i" "<t "::!" C') I I I I co co io "::l"OO "::l" OO "::l"~CJ (Jv N C') 6.... LO 00 0 0 0 Cl(jClCJ (J .... .,..- .... .... .... co ....... ro x x x x x 7 CJ"'1" N '<j" If)ll)lf)l() lt) I!) l!) t-- t-- t--I'- r-- I'- I"- 0000 ci 0 cl Thepitchwas caiculated accordingto theformula: Pitch = = Sequential data acquisition = Tablefeed per rotation = Section collimation = Section thickness =Reconstruction interval =Contrast medium =CM volume/ time =Delay afterthe beginning of the CM injection =Automatic bolustracking = Pitch =Tube voltage = Tubecurrent = Kernel, edgealgorithm = Sinusthrombosis = Multiplanar reconstruction = Maximum intensity projection = Renaltransplant = Hepatocellular carcinoma For the application of the contrast medium ("GM"), the amount in ml of a concentration of 300-350 g iodine/ml and the flow rateofthe injector ("flow") in ml/second is stated. In addition, the term "delay" states in seconds when the gantry begins its data acquisitionafter thebeginning of theinjectionof con- trast medium.Theterm"BT" refers tobolustracking, anautomated softwareprogram.For instance,an ROI is placed over the descending aorta, and when the intravascular density exceeds a preselected level (e.q., thebolusof contrast medium is arriving), data acquisition begins automatically (see page 176). In modern units, the examiner selects thecraniocaudal span of the body region to be examined, the desired examinationtime,the rotationspeed,and thesection collimation. The scanner then optimizes table feed and pitch on its own. Thesearethe examination protocolsfora 4-slice spi- ral CT, established for the Siemens Sensation 4. For clinical questions not suitable for spiral technique in our experience, the expression "seq." is listed instead of the table feed per rotation ("feed/rot."). The collimation ("coiL") must be selected by the examinerinadvance,whileinmultislice scannersthe reconstructed effective section thickness ("ST") can be selected later. The reconstruction interval ("RI") statesthe distance between thesectionsforthe sub- sequent reconstruction from the three-dimensional data set. The term kernel refers to the edge algo- rithmof the manufacturer: H= Head, U = Uitrahigh, B = body. Seq. Feed/rot. Coli. ST RI CM Flow Delay BT Pitch kV mAs Kern ST MPR MIP RTP HCC
Chest - Bronchial carcinoma Arterial 4x5 7 30 1,5 7 0,5 120 90 B 30 350/ 50 80-100 / 3,0 Liver BCI 7 7 B 60 2000/ -300 Abdomen NPL, lymphoma Arterial 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 200 /40 25-30 100-120 / 3,0 Venous 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 350 / 50 50-75 Stomach: Hydro CT Arterial 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 350 / 50 25-30 1100-120 / 3,0 I(stomach filled with H?O Venous 4 x 2 5 5 12 5 1 25 5 05 120 155 B 30 350/ 50 50-75 Pancreas/k idn eys 1NPL Unenhanced 4 x 5 7 25 1,25 7 0,5 120 155 B30 350/50 Arterial 4 x 1 3 4 1 3 0,5 120 165 B 30 350/ 50 I I 30-40 1100-120 / 3,0 Venous 4 x 2 5 5 12,5 1 25 5 05 120 155 B 30 350 /50 IBT Adrenal glands 1Adenoma Unenhanced 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 350 /50 Arterial 4 x l 3 4 1 3 0,5 120 165 B 30 350/50 I I 30-40 1100-120/ 3,0 After 3 min 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 350/ 50 (BT) Optional After 10 min 4 x 2 5 5 12 5 1 25 5 05 120 155 B 30 350/ 50 3-phase liver 1Hemangioma, HCC Unenhanced 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 350 / 50 Arterial 4 xl 3 4 1 3 0,5 120 165 B 30 250 / 40 25-30 1100-120 / 3,0 Venous + 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 350 / 50 (BT) ocnonatoetvis Chest-abdomen INPL, lymphoma Arterial 4x5 7 25 1,25 7 0,5 120 155 B 30 350/ 50 25-30 I 120 / 3,0 Venous 4x 5 7 25 1,25 7 0,5 120 155 B 30 350 / 50 (BT) Lunq 7 7 B 70 2000/ -500 Pelvis IVascular state (RTP) Unenhanced 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 DVT Venous 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B30 100 (BT 140 / 3,0 Heart Triaaer 4 x 1 1 25 1 5 038 0 8 05 120 400 B 30 350 /50 MPR/MIP 120 / 30 CTAngio Cranial vessels Arterial 4 x 1 1,25 5 1,25 1 0,5 140 90 H 10 110 /35 MIPNRT 18 (BT) 75 /3,0 Cervical vessels Arterial 4 x 1 1,5 5,5 1,38 1 0,5 120 100 B 20 350/ 50 MIPNRT 15 (BT) 110 / 3,5 Abdominal. vessels Arterial 4 x 1 1,25 6 1,5 1 0,5 120 130 B 20 350 / 50 MIPNRT 20-25 100-120/ 3,0 Iliofemoral vessels Arterial 4 x 2,5 3 15 1,5 1,5 0,5 120 130 B 20 350 / 50 MIPN RT 25-30 150 / 2,5-3,0 C sp ine Fracture Unenhanced 4 x l 2 5,5 1,38 2 0,75 120 150 B 70 3000 / 600 MPR L spine Fracture Unenhanced 4 xl 2 2,5 0,6 2 0,75 120 330 B 20 3000/ 600 MPR Myelo-CT Unenhanced 4 x l 2 2,5 0,6 2 0,75 120 330 B 20 3000 /600 Only for MPR 1,25 1 B 20 3000/ 600 1 Saaittal Aorta IDissection Arterial 4 x 2,5 3 15 1,5 1,5 0,5 120 130 B30 350 / 50 I Coronal 120 (BT) 1120-140 / 3,0 Aneurysm - - Han d/Feet IFracture - Unenhanced 2 x 0,5 0,5 1 1 0,3 0,75 120 100 U 90 3000/ 600 I Coronal/ Detail diagnosis sagittal Knee IBone Unenhanced 4 x l 1,25 4 1 1 0,75 120 90 B 60 3000/ 600 Soh tissues 5 5 B 30 350 / 50 Dental Before implantation Unenhanced 4 x 1 1 2,7 0,68 0,8 0,75 120 70 H 60 3000 I 600 IDertal evaluation Bone 4 x 2,5 10 Sea. 0,5 80 125 S 80 1800 I 500 .L Bone oensn Perfusion Bleeding lnfratentortal 4 x 1 4 Seq. 4 0,75 120 300 H 40 110 / 35 Supratentorial 2x8 8 Seq. 8 0,75 120 260 H 40 80/ 35 Stroke Arterial 2x5 10 Multiscan 10 1 80 250 H 30 120 / 35 I Perfusion stare I 4 I 80 / 5,0 ~ -...... -...J ......
...... ""I'V "'tJ o~ :Z:::C s:~ cn~3;:11l:" ""'CI t= c." n:g Cl)("')"T1C/) cn cn----j _ .... ~ ("') -I - ""CI ..... m 1> < ::+ -I m Q ::: - ....j 0 g CD 2 12. ffi o 3 ("')"'tJ "'tJ::c 3tn n m:E == c.-P :::::l W:r =.'g ::r -e ~::::l- ~ II ~ (") 0 ~ n ..., zr e- " _-1 3o ~ ~ mo Q,l - ....... ~ £ ~ ~Q:I _ Ol _. cr; "'T1 g II II 11 II II II II II II II II II II II II 11 II II cn ~ g ~ ~ ~~ ~~~~A22~~ ~ onn~ ~~~~ rn~ _~ ~ ~ ~ ~.0l=-5·~crcr~Sro~ ~§~~ ~~~ - :::r ~ - a 0l0lm~.=~~rn m:::ro3n~ <~ o~~roc ~~ ~o Ol o -(")3~ _nc ~ OQ) ::::lOO_ro =ro ~ g n~g c~~~~g ~ -.~Ea ~ ~::::lm~ ~ w eng Q ~~::::l~.~ og ag n~'~~3 ~ ~ a Q~ ~~ X::::l ~ ~~ ~ ..., g ro ~ m gg~ ~ ~ ~ ~ ~3·~ a _ ~ - ::::l ...,Ql mmO Ol Eoro-·-· O::::l...,a o- Il ~ n;:;' ~ 8 ~. 5 CJ) ::l cr 3 c 3 ::. ~ ~ ...., Ql ..., ~ _ 0 Ql _ . :::::l cn 0 ....... co CD ::::l cn o' sa. Q,l w :::r ~ g a. q~ ~ ~~' & ::::l~B ~~ ro ;5 ~ 3 ~::::I Q5 g s. CD' en 3 ~ :::::l S' - ~ 3 00 w 0 I.C co _ . CD =:::::l 0 g::::l n - '" '" Infralentorial 16xO,75 Supratentorial 16x 1,5 lnfratentorial 16 xO,751 4 1 5 1 0,42 1 4 I 0,75 1 120 1 260 1 H 40 1 110 / 35 1 1 60 1 50 /2,0 IVenous vessels (SVT) Supratentorial 16 x 1,5 Sku ll: ST I I 35 Orbita [Tumor 16 xO,751 4 5 0,42 4 0,75 120 100 H 30 250 /50 1 45 1 75 /2,0 1 0,7 H 30 250 /50 Coronal Fracture I 116 xo,75 2 5 0,42 2 0,75 120 100 H 60 3000 / 600 1 07 H 60 3000 / 600 ICoronal Paranasal Sinusitis, nasal pOIYPoSiSl 116 XO,75 4 5 0,42 4 0,75 120 80 H 40 1500 /50 sinuses Onlv for coronal MPR 1 07 H 60 1500 /50 Coronal Facial bones Tumor 16 xO,75 3 5 0,42 3 0,75 120 100 H 30 350 /50 ,I 45 I 75 /2,0 Fracture 1 07 H 60 3000 /600 Coronal Petrous bone IFracture 16 x O,75 0,75 5 0,42 0,5 1 120 120 U 90 3000 /600 Coronal OnIv for film documentation 1 1 U 90 3000 /600 Neck Lymphoma, tumor 16 x 1,5 5 24 1 5 0,75 120 150 B 30 250 /50 1 1 45 1 100 / 3,0 Chest Fibrosis, fungi IUnenhanCedl 16 X1,5 5 30 1,25 5 0,5 120 100 B 40 350 /50 HR 16 xO,75 1 13,5 1,1 3 0,7 0,75 120 90 B 80 2000 / -soolcoronai 5 5 B 30 350 / 50 NPL, lymphoma I Arterial 116x 1,5 6 30 1,25 6 0,5 120 100 B 40 350 /50 1 125-301 80 /2,0 (BT) Pulmonary emboli 1 Arterial 116 xO,751 5 15 1 1 ,25 I 0~7 I 0,5 I 120 I 100 IB 30 I 350 / 50 Ic oronall20-25 I100-120 / 1 Sagittal (BT) 3,5
80 Delay CM I flow [sec) [ml/ml/sec] Recon- struct. RI Sec I Voltage Current Kern Window [mm) rotation (kV) (mAs) with CM Coli ST Feed I Pitch [mm] [mm] rotation IndicationsOrgan Bronchial carcinoma Arterial 16x 1,5 6 30 1,25 6 0,5 120 100 840 350 /50 8C) : Luna window 6 6 870 2000 /-500 NPL, lymphoma Arterial 16 x O,7, 5 12 1 5 0,5 120 140 830 200/40 20-25 1 100-120 / 3,5 Venous 16 x l ,S 5 24 1 5 0,5 120 120 830 350 /50 Coronal 50-75 Stomach: Hydra CT Arterial 16 x 0,7 5 12 1 3 0,5 120 140 830 350150 25-30 1 100-120 /3,5 I(stomach filledwith H 01 Venous 16 x O7 3 12 1 3 05 120 140 830 350 /50 50-75 Pancreas! INPL Unenhanced 16 x 1,5 5 24 1 5 0,5 120 120 8 30 350 /50 kidneys Arterial 16xO ,75 5 12 1 5 0,5 120 140 830 350 / 50 1 Coronal 1 20-25 1 100-120 /3,5 I ~ Venous 16 x 1 5 5 24 1 5 05 120 120 8 30 350 / 50 50-75 Adrena/ glands 1Adenoma Uncnhanced 16 x 1,5 5 24 1 5 0,5 120 120 8 30 350 / 50 Arterial 16xO,75 1 12 1 0,7 0,5 120 140 8 30 350 /50 1 Coronal 1 30-40 I 100-120 / 3,0 After 3 min 16 x 1,5 3 24 1 3 0,5 120 120 8 30 350 /50 (BT) Optional After 10 min 16 x 1 5 5 24 1 5 05 120 120 B 30 350 / 50 3·phase liver IHemangioma, HCC Unenhanced 16 x l ,S 5 24 1 5 0,5 120 120 B 30 350 / 50 Arterial 16 x O,75 5 12 1 5 0,5 120 140 B 30 250 / 40 1 Caranal 120+25 I 100-120 13,5 Venous+ 16 x l ,S 5 24 1 5 0,5 120 120 8 30 350 /50 50-75 ootional oelvis Chest-AbdomenINPL, lymphoma Arterial 16 xl ,S 5 24 1 5 0,5 120 140 B30 350 /50 1 1 25 - 30 1 120 / 3,0 Venous 16 x 1,5 5 24 1 5 0,5 120 140 B30 350 /50 (BT) Luna 7 7 8 70 2000 / -500 Pelvis 1Vascular state (RTP) Unenhanced 16 x O,75 5 24 1 5 0,5 120 140 B30 350 / 50 DVT Venous 16 xl ,S 3 12 1 3 0,5 120 140 B 30 350 /50 10018T' 120 13,0 IHeart Triaaer 16xO,75 1 34 029 0 7 042 120 550 8 30 350 /50 MPRIMIP 100 130 ICT Angio Cranial vessels Arterial 16 x O,75 1 15 1,25 0,7 0,5 140 100 H 2O 110 / 35 MIPNRT 18 (BTl 75 /3,5 Cervical vessels Arterial 16 x O,75 1 12 1 0,7 0,5 120 120 830 350 150 MIPIVRT 15 (8T) 1001 4,0 Abdominal vessels Arterial 16 x O,75 1 15 1,25 0,7 0,5 120 130 830 350 /50 MIPIVRT 20-25 1DO-l20I3,Ch3,5 Pelvic-leg vessels Arterial 16 x l ,S 2 24 1 1,5 0,5 120 130 830 350 /50 MIPIVRT 25-30 150 / 3,0-3,5 IC spine 1 Fracture Arterial 16xO ,75 1 12 1 0,7 075 120 150 870 3000 /600 MPR ILspine IFracture Unenhanced 16 x O,75 1 6 0,5 0,7 0,75 120 330 860 3000 /600 MPR Myela-CT Unenhanced 16 x O,75 3 6 0,5 3 0,75 120 330 860 3000 1600 Only far MPR Unenhanced 1 0,7 8 60 3000 /600 MPR IA orta 1Dissection 16 x 1,5 2 21 0,88 1 0,5 120 130 830 350/50 MPRIMIP 120 (BT) I 120 / 3,0 Aneurysm Arterial VRT Hand!Feet I Fracture - 1Unenhanced 116 xo,75/0,75 I 6,8 10,57 1 0,5 I 0,75 I 120 1 120 I U 90 13000/ 6001 MPR IDetail diagnosis IKnee IBone Unenhanced 16~-1 - -13~5- -f~f3 -OY- O,75 120 120 B 60 3000T 600 1 MPR Soft tissues 5 5 8 30 350 /50 Dental Before implantation Unenhanced 16 x 0,7E 0,75 6 0,5 0,5 0,75 120 80 H 60 3000 / 600 108nl1l1ovalualiJI1 Bone 2 x 5,0 10 Sea. 0,5 80 125 S80 1800 / 500180nedens!!) Perfu sion 81eeding Infratentorial 16 x 0,7E 4 5,1 0,43 4 1 120 260 H 40 11 0 / 35 Supratentorial 16 X1,5 8 10,2 0,42 8 1 120 260 H 40 80 /35 Strake I Arterial 16 x i.s 12 Multiscan 1 1 80 209 H 30 120 I 35 IPertusion state I 4 I 40 /8,0 ~ •...... -...J W
174 Radiation Dose/Cancer Risk The physical radiation dose 0 (energy absorbed per unit mass) is expressed in Gray (Gy), used for anytype of radiation and also in the radiation therapy of malignant tumors. It has to be distin- guished from the equivalence dose H expressed in Sievert (Sv), which represents the physical radiation dose multiplied by a pro- portionalityfactor thatconsiders theunique radiation sensitivity of a particular tissue: Epithelium, mucosa of the respiratory and gastrointestinal tract and other tissues with a high rate of cell division (e.g., blood forming cells of the bone marrow) are more sensitive toionizing radiation than tissue withdormantcell division. An even better comparison of the biologiceffect can be achieved with the effective dose E, which is the sum of the doses de- livered to the individual organ.This effective dose, which weighs the relativeinherent sensitivities, is also expressed in Sievert (Sv) orMillisievert (mSv). , Furthermore, the patient's age at the time of radiation exposure must be included in a rational assessment of the radiation risk since the latency period of a radiation-induced tumor can be rat- her long (decades).Table 174,1 lists therisk coefficientsof diffe- rentorgansfollowing a low-doseexposure to the entirebody. ,Tab. 174.1 Age-dependency of cancermortalitycaused by ionizingradiation Estimated risk factorsin (% / Sv) for men/ women (italics) Age at exposure Total Leukemia Lung/Respiratory MDT 5 years 12,8/ 15,3 1,1 /0,8 0.2/ 0,5 3,6/ 6,6 15 years 11 ,4/ /5,7 1,1 /0,7 0,5/ 0,7 3,7 / 6,5 25years 9,2/11,8 0,4 / 0,3 1,2/ 1,3 3,9/ 6,8 45 years 6,0/ 5,4 1,1 / 0,7 3,5/ 2,8 0,2/ 0,7 65 years 4,8 / 3,9 1,9 / 1,5 2,7/ 1,7 0,1 / 0,5 85 years 1,1 /0,9 1,0/0,7 0,2/ 0,1 - / 0,04 Mean 7,7/ 8,1 1,1 / 0,8 1,9 / 1,5 1,7 /2,9 Chest Others 1,3 7,8/ 6,3 3,0 6,1/ 4,8 0,5 3,7/ 2,9 0,2 1,2/ 1,0 0,1 / 0,2 -/ - 0,7 3,0/ 2,2 effektive annual dose %of annual exposure This implies that the risk of radiation-induced malignancies markedly decreases with increasing age at the time of exposure. But not onlythe patient's age, butalso theamount of theindividu- al dose and the length ofthetime intervals playa decisive role.As a rule of thumb, the lower the individual dose and the longer the intervalsbetween several radiationexposures, thelower the riskof a subsequently induced neoplasm. Among other factors, this depends on the capability of the cellular nuclei to repair DNA breaks with thehelp of repair enzymes as long asthe reparative capacity is not exceeded by high individual doses. Evidence even Radiation Source exists that protective effects predominate in the low-dose range through activation of protective cell factors (DNA reparase and others). For a better assessment of the risk associated with the medicalapplication of ionizing radiation, it is revealing toconsider thedaily exposure from natural background radiation: The major component of the natural radiation exposure comes from radon,a noble gas, which gets intotheair through thebuildingmaterials of houses and apartments. Using a strictly theoretical calculation, radon and its decay productsmay induce5 to10% ofallbronchial carcinomas. In contrast, medical application of ionizing radiation "only" induces less than 1.5%of all malignancies. I Inhalation ofradon inapartments Terrestric radiation Cosmic radiation Incorporation of radioactive isotopes Subtotal of natural radiation exposure Applicationofionizing radiation inmedicine AccidentoftheChernobyl nuclear reactor (Europe) Fall-out from nuclear weapon tests Operation ofnuclearreactors Occupational radiationexposure Subtotal of man-made radiationexposure Total annual radiation exposure in the Federal Republic of Germany - 1,4 - 0,4 - 0,3 - 0,3 - 2,4 mSv - 1,5 - 0,02 - 0,01 - 0,01 - 0,01 - 1,8 mSv - 4,2 mSv 33,3 % 9,5 % 7,1 % 7,1 % 57,0% 35,7% 0,5 % 0,2% 0,2 % 0,2% 43,0% 100,0% The average annual radia- tion exposure of about 2.4 mSv has to be put in perspective with the man- made radiation exposure of 1.8 mSv (Table174.2). Tab.174.2 Relativecontributionof several radiationsources tothetotalannual exposure (Europe).
Radiation Dose/Dose Reduction 175 Ingeneral,"hard" x-rays usedforconvenfional radiography of the chest are scatteredand absorbedlessinhumantissue than "soft" x-rays used for mammography. The scatter radiation also con- tributes tothe absorption and consequentlyto the riskassociated with a particular examination. Because of the tissue-dependent variabilityoftherisk factorsandthe different characteristics ofthe various modalities used in diagnostic radiology, the organ doses arequite diverse (Table 175.1). Examination Conventional radiology,chest Conventional radiology,skull Radiology, C-spine Radiology,T-spine Radiology, L-spine DSAofthe heart DSAofthe kidneys Fluoroscopy, UGI series Fluoroscopy, BE Cranial CT ChestCT Abdomen CT Organ / tissue Lung,breast Red bone marrow Thyroid gland Breast, lung Red bonemarrow Lung Red bone marrow Red bonemarrow Red bone marrow Red bone marrow Lung,chest Red bone marrow Organ dose 0,3 mSv 4,0mSv 4,5mSv 14,0 mSv 1,0 mSv 20,0mSv 30,0 mSv 17,0 mSv 3,0 mSv 5,0mSv 20,0mSv 10,0 mSv Effective dose E 0,2mSv 0,2 mSv 2,0mSv 5,0 mSv 0,4mSv 10,0 mSv 10,0 mSv 6,0 mSv 3,0 mSv 2,0 mSv 10,0 mSv 7,0 mSv Tab.175.1 Radiation dose of different radiographic examinations. Together with arteriography andfluoroscopy. CT is responsible for a rather high radiation exposurein diagnostic radiology. Multiply- ingthe individualvalues withthenumberof thedifferent examina- tions performed annually revealsthat CT is responsible for about a third of the collective total dose.The different CT examinations deliver thefollowing average radiation doses(Table 175.2). Type of spiralCT Emotion 1 row Emotion 2 rows Emotion 6 rows Sensation 10rows Sensation 16rows Head 4,2/ 4,5 mSv 4,2/ 4,5 mSv 4,4/ 4,7 mSv 4,6/ 4,8 mSv 4,5/4,8 mSv Chest 3,9/ 5.0 mSv 2,6/ 3,3 mSv 3,2/ 4,1 mSv 3,0/ 3,8 mSv 2,8/3,6 mSv Abdomen/ 3,7/ 8,8 mSv 3,7 / 5,6 mSv 6,3/ 9,6 mSv 6,0/ 9,0 mSv 6,5/ 10,0 mSv pelvis Tab. 175.2 Comparisonofdoses in millisievert (mSv)for different CTunitsofSiemens Medical Systems.Valuesformen / women (italics). This does not consider the effects of the section thickness (see page 9-11): As a rule of thumb, the thinner the section thickness the higher the radiation dose(Table 175.3). The radiation exposure is slightly higher in units with compact geometryand shorter focusdistance (Emotion 6). I Preselected Somatomplus 4 Somatom Volume Zoom Emotion collimation 4 row 6 row1 row 4 x5,0 mm 4,5 4,6 6,8 4 x2,5mm 4,3(3mm) 5,1 7,2 4 x1,0mm 4,9 6,1 8,4 Tab,175,3 Dosis increase per 100 mAsforthin section collimation. Sensation 16 row 4,2 (1,5 mm) 4,7 (0,75 mm)
176 Radiation Dose/Dose Reduction in CT Comparison with air traveling is often used in public health discussions: On a long, high altitude transatlantic flight, cosmic rays cause a not irrelevant additional exposure. On a flight from Europe to the West Coast of the U.S.A., this can easily be in the rangeof certain CT examinations. Other calculations ofthecancer risk compare conventional chest radiography with cigarette smoking:A single chest radiograph is believed to have the same cancer risk as smoking sevencigarettes.It shouldbe kept inmind, however, that all mathematically models include several aspects andcofactorsthat are elusive to exact statisticallycalculations. While these comparisons put into perspective an excessive concern ofthe potential riskof medical radiographic examinations, Automatic Bolus Tracking (BT) For CT, several techniques are availablefor reducing the radiation dose to the patient. Especially CT requiring optimal contrast enhancementinthe vessels,e.g.,above allCTangiography,should be performed withautomatic bolus tracking toavoidunnecessary duplications because of inadequate intravascular contrast en- hancement. This softwaresolution offers the examiner the possi- bilityto place a region of interest (ROI) ( t:2 )just before orat the beginning of the target region, e.g., the lumen of the descending aorta(Fig. 176.1a).After selecting acertain thresholdvalue for the they should not be misused to belittle the radiation risk. To avoid unnecessary risks to the general population, it has become established policytoavoid dispensable radiation exposureincon- ventional radiology and CT,and totake advantage of any possible reduction ofradiation exposure to patients. It is for the same reason that pulsed fluoroscopy has replaced continuous fluoroscopy for upper GI series, enteroclysis and barium enema: The examiner selects between several pulse sequences with 1, 2, 4, and 8 images per second. The resultant dose reduction is considerable.The next pages describe solutions suitablefordose reduction that areespeciallyapplicableforCT. density of the aorta, e.g., 100 HU, the unit measures the density automatically at the preselected site every second after the be- ginning of the intravenous injection of contrast medium, usually throughthe cubital vein. Data acquisition (the actual scanning process) begins assoon as the density in the aortic lumen exceeds the threshold value, i.e., exactly when the bolus of the contrast medium has reached the selected target region after passage through the pulmonary circulation (Fig. 176.1 b). Density [HU] 100 --- - - - - - --------- - 80 60 50 40 20 o Start t [sec] Fig. 176,1 b Automaticdelay of dataacquisition until arrival of theCMbolus atthetarget region. I Fig. 176.1 a Positionof ROI, e.g., over thedescending aorta. Inaddition,the amountofcontrast medium needed toachieve the same contrast enhancement can be reduced: sterile physiologic NaCI solution is injected from a second syringe of the injection pump (see front cover flap) at the same flow rate immediately following the injection of contrast medium in order to push the contrast medium fasterand at a higher concentration throughthe brachial veins toward the heart and through the pulmonary circu- lation. Taking Advantageof thePitch By usingafaster table feed toincreasethepitch,afewsingle-slice CT units can reduce the effective patient dose by spreading the spiral ofdata acquisition (see Fig. 8.4). The software of the multislice technology uses a compensatory mechanism that automatically increases the tube current when- ever the examiner increases the pitch- effectively delivering the same totaldose forthe examination. For a 16-slice CT,the exami- nercanselect the craniocaudal spanof the z-axis, thecollimation and scan time for the desired volume - and the software deter- mines the optimal table feed or, respectively, pitch, and the tube current.
Dose Reduction 177 Reduced Tube Current for ThinPatients and Children Asarule of thumb, thenoisedoublesforeachS-cmincreaseinthe patient's diameter. Dose and noise are exponentially related: Doubling the dose reduces the noise only by a factor of 1.4. To penetrate thin patients and children for a satisfactory image, a markedly lower radiation dose is adequate. In older units lacking instantradiation measurements at the level of the detectors and modulation of the tube current (see below), the dose can be re- duced by loweringthepreselected tubecurrent (mAs). Automatic Tube Current Modulation The idea underlying this feature of the combined applications to reduceexposure(CARE) isas simpleasit is effective: it isbased on the assumption thatthe cross-sections of most body regions are oval ratherthan circular.With the patient supine, theAP diameter ( t ) ofthechest,abdomen,and pelvisis definitelyshorter than the transverse diameter ( - ). Consequently, the tube current is higher in lateral angulation than in anterior or posterior angulation (Fig. 177.1). Aftereach semi-circulation, e.g., every lS0 degrees, the same dosis is needed since the additive attenuation of the x-ravs is directionally neutral (Fig. 177.2). It isthe essence ofthe automatedmodulation thatthe tubecurrent measurestheattenua- tion profileforeachtube angulation and calculatesthe correspon- ding minimal dose still adequatetoachieve an optimalimageafter F' 1771Ig. . an additional l SD-degree angulation.As a result, thetube current is modulated with a l SD-degree delay. Plotting the tube current along the time axis displays a curve reminiscent ofa sinuscurve with theamplitudes tending todecrease from the shouldertothelegs (Fig.177.3) andwith maximaat the level oftheshoulder and pelvis. - Tube current f [mAs] Effects of automatic tubecurrentmodulation Body region Skull Shoulder region Chest Abdomen Pelvis Extremities II NV Scandirection Dose reduction 14- 26 % 22-56 % 19-27 % 11 - 24 % 21-30 % 33- 41 % v v v - - - Fig. 177.3 In addition, the life expectancy of the x-ray tube is extended and image artifacts induced by the arms placed along the patient's body,asfrequently found intraumaand ICU patients,arereduced. f f r-. r-; i-Gv r-. c?, ~ r 'CJ v v v V V Fig. 177.2 -, Compared with units delivering the same image quality without tube current modulation, the dose-reducing potential ot this techniqueisimpressive,withthe highestreduction coinciding with areas of considerable radiation absorption, e.g., at the shoulder and pelvis (Table177.1). Tab.177.1
178 CT Angiography Bringing out the information contained in images of CT anqio- graphy requires a review using different perspectives (MIP = maximum intensity projection), different reconstruction planes (MPR = multiplanar reconstruction) or a tbree-dirnensional visualization (VRT = volume rendering technique). All these reo construction images used to bedegraded by the resolutionof 0.5 mm per pixel length in the transverse plane (xy-plane) and a markedly higher resolution along thebody axis (z-axls), resulting in an anisotropic voxel (see page 8) with different lengths. The advances of the multidetector CT(MOCT) with the introduction of the ts-sucetechnologyintheyear 2001 permittheinclusionof an adequately large body volume with almost isotropic voxels in the sub-millimeter range with justifiable scan times. The following pages present recommended examination protocols for different vascularregions including several representative images. IntracranialArteries The individual axial sections are usually supplemented with displays using MIP and, e.g., sagittal MPR as well asVRT (see above).Agooddiagnosticevaluation ofthecerebral arteries canbe achieved with thin overlapping section reconstructions using a section thickness of 1.0 to 1.25 mmand a reconstruction interval (RI)of 0.6to 0.8 mm. To achieve a highvascularcontrast, thedataacquisition has to be exactly timedto encompass the firstpassage of contrast medium through the circle of Willis with a start- delay of 20 seconds, if possible beforecontrast medium has reachedthevenoussinus.If bolus tracking(BT)is notavailable,atest bolus should be injected to determine theindividual circulation time.The following exami- nation protocols can serve as guides for thevisualization of the circle ofWillis: CT system Call. ST Feed Pitch RI Sec.! Volt. Current Kernel Window Delay CM [mm] [mm] I Rot. [mm] Rot. [KV] [mAs] [W/C] [sec] [ml/ ml/sec) 1 row 4 rows 16rows 1 1,0 2 4x l 1,25 5 16xO,75 1,0 15 2,0 1,25 1,25 0,5 1,0 0,7 0,8 0,5 0,5 11 0 120 120 120 H30 250/ 40 18 - 22 120 / 3,0 90 H10 110 / 35 18 /BT 75/ 3,0 100 H20 110/ 35 18/ BT 75/ 3,5 Thesubsequently reconstructed individual sectionscandisplay the vessels asseenfrom below withtransverse MIP(Fig, 178.1b),fromthefront withcoronal MIP (Fig, 178.1c) or from thesidewithsagittal MIP (Fig.179.1a).Thefirst two planes clearlyshow themajor branches of theanterior (91 a) and middle (91 b) cerebral arteries. Figure 178.1 d shows a 3D VRT of another patient with an aneurysm ( ") arisingfrom theanterior communicating artery.Thejunctionofbothvertebral arteries(88) toformthe basal artery (90) and posterior cerebral arteries (91c) is clearlyidentified. Furthermore, the branchesof theanterior circulation are identifiable: branches of the medialcerebral artery (91 b)andthe pericallosal arteries (93). Fig. 178.1 a Fig.178.1b Fig. 178.1c Fig. 178.1d
CT Angiography Venous Sinus To visualize the venous channels,the FOV has to be extended tothe sagittal cranial vault (Fig. 179.1a) and the startdelay increased to about 100 seconds. Craniocaudal sections are recommended for bothtypes of CTA (arterial and venous cerebral vessels).The sagittal plane (Fig. 179.1b) preferably shows contrast inthevein of Galen (100) andvenous channels (101 a. 102a). C1 system Call. 51 Feed Pitch RI Sec.! Vall Current Kernel Window Delay CM [mm] [mm] I Rot. [mm] Rot. [KV] [mAs] [W/C] [sec] [mil mllsec] 179 4 rows 4 x1 1,25 5 1,0 - 1,5 0,8 0,5 120 90 soft 110/35 100 120 /3 ,0 Fig.179.1a Fig. 179.1b
180 CT Angiography Carotid Arteries Important criteriafor stenotic processes ofthecarotidarteries are the exact determination oftheseverityof the stenosis. It isfor this reason that the examination is carried out with thin sections, for instance, 4 x 1 mm or 16 x 0.75mm, allowing direct planimetric quantificationof the stenosiswithadequate accuracy on individu- alaxial sections. Furthermore, thesagittal and coronal MIP(0.7- 1.0 mm RI with 50% sectional overlapping)shows no major step deformity (see page8). Thebestreconstruction withmaximal contrast ofthecarotidartery is achieved with minimal contrast in the jugular vein. Therefore, theuseof abolustracking program isstronglyadvised.Ifapreced- ing Dopplerexamination suggests avascular process at thebifur- cation, transverse images in caudocranial direction are recom- mended. For processes near the cranial base, a craniocaudal direction can be superior. VRToften proves helpfultogetoriented (Figs. 180.1 d, e). I CT system Coli. 5T Feed Piteh RI sec.! VotL Current Kernel W/ C Delay CM [mm] [mm] / Rot. [mm] Rot. [KV] [mAs] [HU] [sec] [ml/ mJlsee] 1 row 4 rows 16rows 2,0 4 xl l,5 16x O,75 1,0 4,0 2 1,0 5,5 1,38 1,0 12,0 1 0,7 0,8 110 0,5 120 0,5 120 120 B30 350/50 12 -1 5 100 / 3,0 100 B20 350/ 50 15 /BT 110 / 3,5 120 B30 350I 50 15I BT 100 I 4,0 Fig. 180,la Fig. 180.1 b Fig. 180.1e Figure 180.1 shows the lateral topogram (a)for positioning of the FOVas well as lateral (b) and anterior (c) images of an MIPand an imageinVRT (d),showing normal findings. Incontrast, Figure 180.2 shows images ofsagittal MIP and VTRthatrevealtwo indentations of thevascularcontrast column at the typical sitefor acarotidstenosis:TheleftACI(85a) shows ashort segment ofasevereluminal nar- rowingjust distal tothe bifurcation ( " ) after a preceding bulbar stenosis( ~ ) of theACC(85) at theoriginoftheACE(85b). Fig. 180.1d Fig. 180.2a Fig. 180.2b
182 CT Angiography I Aorta The CT angiography of the aorta must above all exclude aneurysms, isthmus stenoses and possible dissection, and if present, visualize their extent. Automatic bolus tracking (BT: ROI placed over the aorta) is advisable, especially in patients with cardiacdiseaseswho have variablepulmonarycirculationtimesof contrast medium. Imaging in caudocranial direction can minimize the respiration-induced motion artifacts that primarily affect the regions close to the diaphragm since involuntary respiratory excursionsaremore likely attheendof the examination. Further- more, caudocranial imaging avoids the initial venous inflow of contrast medium through the subclavian and brachiocephalic veins and anysuperimposition onthesupra-aorticarteries. CT system Call. ST Feed Pitch RI SecJ Volt. Current Kernel WI C Delay CM [mm] [mm] I Rot. [mm] Rot. [KV] [mAs] [HU] [sec.] [mIl ml/sec] 1 row unenhanced 8,0 12,0 1,5 8,0 0,8 1 row CM 3,0 6,0 2,0 I,D 0,8 4 rows 4x 2,5 3,0 15,5 1,5 1,5 0,5 16rows 16xl,5 2,0 21 ,0 0,9 1,0 0,5 110 110 120 120 80 100 130 130 B30 B30 B20 B30 350/ 40 350/50 350/50 350/50 BT BT 201BT 120 /3,0 130/3,0 120 /3,0 As reconstruction images, MIPand MPR (Figs.182.2, 182.3) often allowan exact quantification of the vascular pathology as survey imagesinVRT(Fig 182.4).asseenhereas anexampleof aninfra- renalaneurysm of the abdominal aorta:The aneurysmaldilatation (171) begins immediately distal to the renal arteries (110) and spares boththe superior mesenteric artery (106) and iliac arteries (113). For planning any vascular surgery, it is crucial to know any involvement of visceral and peripheral arteries and any possible associated dissection. Furthermore. thelevelofthe aortic originof the artery of Adamkiewicz, which supplies the thoracospinal transition of thespinal cord,must beconsidered foraneurysmsof the descendingthoracic aorta. Fig. 182.1 a b Fig.182.2 Fig.182.3 Fig. 182.4
CT Angiography 183 Frequently,acinemodereview ofthecoronal orsagittal MPR ima- geson asecond monitor canbehelpful foraquickand convincing determinationof the extent ofa pathologic finding,asshown here inacase of thrombosis withinan abdominal aortic aneurysm.The cine mode of the coronal MPR images reveals not only an infra- renal thrombus (173) along the left lateral wall (Fig. 183.1) but also a secondthrombus further cranial alongtheright lateral wall at thelevel of the origin of theright renal artery (110) (Fig. 183.1). which is still pertused (Fig. 183.3). The individual axial sections (Figs. 183.4, 5) allow a planimetric quantification of the stenosis,andthesagittal MPR(Fig. 183.6)aclear separation from the origin of theanterior mesenteric artery (106). Fig. 183.1 Fig.183.2 Fig. 183.3 Of course, the benefit of the three-dimensional visualization by means of VRT also depends on the viewing angle. While viewing from an angle (Fig 183.7) can underestimate the extent of the thrombus and easily mistake it for a soft plaque, the extent is much better appreciated if seen from different viewing angles Fig.183.4 Fig. 183.5 Fig. 183.6 (Figs. 183.8 and183.9). Thefinal images illustrate theeffect ofa careful elimination of interfering superimposed osseous struc- tures. Becauseof its highdensity,thelumbar spinedominates the initial image (Fig. 183.8). and the vascularfindingsareonly fully appreciated after subtractionof the lumbar spine (Fig. 183.9). Fig. 183.7 Fig.183.8 Fig. 183.9
184 CT Angiography (Heart) Coronary Arteries Visualizing the coronary arteries represents a special challenge since thecardiac contractions requireshort scan times and exact timing. For a cardiac rate exceeding 70 beats per minute, a pre- medication witha beta blockershould beconsidered unless con- traindicated in view of other clinical findings. Even the shortest rotation timesavailable(0.42seconds fora 16-slice CTat thetime of the publication ofthisbook)require additional EKG triggering.To achieve adiagnosticimagequality,thewidthofthe FOV should be reduced to the cardiac size and the craniocaudal acquisition should beginjust above thetracheal bifurcation and extent to the diaphragm (Fig. 184.1). Oblique MIPs parallel tothe main branch oftheleft coronaryartery aswell asspecial projections of the RIVA and RCA (right coronary artery) and 3D views are obtained. The application of contrast medium should be biphasic with an initial bolus of 40 ml at a flow rate of 4 mils and, after a pause of 10 seconds, a second bolus of 80 ml at a flow rate of 2 mils. Bolus tracking should be used with the ROI over theascending aorta. CT system Coli. ST Feed Pitch RI Sec.! Volt. Current Kernel WIC Delay CM [mm] [mm] I Rot. [mm] Rot. [KV] [mAs] [HU] [sec.] [ml I rnl/sec] 4 rows 16rows 4 x1,0 16xO,75 1,5 0,37 3,6 0,3 0,5 0,5 0,5 0,42 120 250- 400 B20 500I 80 BT 120 400 heart 450I 60 BT 120 I 2-4 120/2-4 Thefollowing images compare aCT (Fig. 184.2a) of the leftcoro- nary artery (77a), including circumflex branch (77C) and RIVA (77b), with coronary angiography taken as gold standard (Fig. 184.2b). Figures 184.3a and 184.3b showthe same com- parisonforthe right coronary artery (77d). Fig. 184.1 89a /77a Fig. 184.2a Fig. 184.2b Fig. 184.4 Fig. 184.3a Fig. 184.3b
CT Angiography (Heart) Screening for Coronary ArteryCalcifications Compared with angiographic imaging of the coronary arteries illustrated on the preceding pages, a slightly thicker section can be selected when screening the coronary arteries for calcifications. Administration of contrast medium is not necessary, and the unen- hanced imagesareobtained incraniocaudal direction. CT system Coli. ST Feed Pitch RI SecJ Volt. Current Kernel WI C [mm) [mm) I Rot. [mm) Rot. [KY] [mAs) [HUj 185 4 rows 16 rows 4 x 2,5 3 16 x l ,S 3 1,5 0,37 3,6 0,3 0,5 0,5 0,5 0,42 120 120 133 130 heartmedium heart 370 /50 450/ 60 89a 90 , 0 Fig.185.1 Fig.185.2 Fig. 185.3 Quantification of coronary calcifications(174) isbestcarried out on adedicated separatework station but canalso be doneon a normal work station after postprocessing (Fig. 185.1-3). In this case. however, the unenhanced images are used to obtain,for instance,the Agatston score[43,44),whichcorrelates withthe risk of coronaryartery disease. Agatston Score Clinical Relevance Recommended Therapy o (negative,no identifiablecalcific plaques) 1- 10 (minimal identifiable calcific plaque burden) 11 - 100 (definite. at least mildcalcific plaque burden) 101 - 400 (definite,at least moderate calcificplaque burden) > 400 (extensive calcificplaque burden) Negative predictivevalue for coronary artery disease90 - 95% Stenosis unlikely Coronary arterydisease possible Coronary artery disease with stenosis possible Highprobability forcoronary arterydisease withstenosis possible None General guidelines forprevention Further evaluation indicated Instituterisktactor moditication and specificcardiac therapy Stress EKG is indicated - depending on outcome followed bycoronary angiogram Useful suggestionsand recommendations torconducnno screeningfor coronaryarterycalcificationscan befound inthe followingorigi- nal articles: [43] Kopp AF, OhnesorgeB, Becker Cet al: Reproducibilityand accuracyofcoronary calciummeasurements with multi-detector row versuselectron-beam-CT. Radiology (2002) 225: 113-119 [44] Rumberer JA, Brundage BH, Rader DJ et al: Electron beam CT coronary calcium scanning. Review and guidelines foruse in asymptomatic persons. Mayo Clin Proceed(1999)74:243-252 [45] JanowitzWR, Agatston AS,ViamonteM:Comparison ofserial quantitative evaluationofcalcified coronary artery plaque byultra- fast computedtomography in personswithand without obstructive coronaryarterydisease.AmJ Cardiol (1991 )68: 1-6 [46J Haberl R,BeckerA,LeberAetal:Correlationofcoronary calcification andangiographicallydocumentedstenoses inpatientswith suspectedCAD: resultsof 1764patients.JAm Coli Cardiol (2001)37:451 -457
186 CT Angiography Pulmonary Vasculature (Pulmonary Emboli) FOV and volume to be scanned are marked on the topogram (Fig. 186.1), beginning from just above the aortic arch. to visua- lize primarilythecentral hilar vessels andthe heartwiththe right atrium (a possiblesourceof emboli). Lateral and apical regions of the lung are dispensable. The total acquisition time should not exceed 15secondsinorder tocompletetheexaminationduringa single breath holdwithout artifacts.The images arebest obtained from caudal tocranial,to havethemotion-sensitive areas close to the diaphragm already completed duringtheendphase andtomini- mizetheartifacts caused bythevenousinflowofcontrast medium through brachiocephalic veins and superior vena cava. Exact timing with bolus tracking (8T, ROI over the pulmonary outflow tract)isstronglyadvised.Thereconstructedsections shouldnotbe less than 3 mm inwidth.Thesectionsfor the MIP should be close to1.0mm toavoid overlooking smallsubtle pulmonary emboli. CT system Coli. ST Feed Pitch RI Sec.! Voll Current Kernel WI C Delay CM [mm] [mm] I Rol [mrn] Rol [KV] [mAs] [HU] [sec.] [mil ml/sec] 4 rows 16rows 4 xl ,0 1-3 16xO,75 1-3 6,0 1,5 15,0 1,25 0,5 0,5 0,5 120 0,5 120 140 8 20 420/60 16 / 8T 120 / 4,0 130 8 30 450 /60 16 / 8T 120 /4 ,0 Fig.186.3 Thevascular lumina contrast well withthe pulmonary tissue(Figs. 186.2 - 186.5)and extend all theway to the periphery.Acute pulmonary emboli (Figs. 186.6 and 186.7) cause intravascular defects representing thrombi (173), located in this case in the rightpulmonaryartery(90a). Fig. 186.1 Fig. 186.2 Fig. 186.4 Fig. 186.5 Fig. 186.6 Fig.186.7
CT Angiography 187 Abdominal Vessels Most pathologic vascular processes are located close to the cen- terat theoriginof majorvascular branches,allowing theFOV tobe confined to the central two thirds of the abdominal space on the topogram (Fig.187.1).The origins of the vessels arising fromthe abdominal aorta are visualized on axial sections and on MIPand MPR images.Ifalargervolumeneeds tobe acquired onthez-axis, a four-slice CT needs a collimation of 4 x 2.5 mm to achieve an acceptableacquisition time duringone breath hold. In contrast, a suspected renal artery stenosis requires a reduction of the acqui- sition volume to the renal region. To achieve an adequate visua- lization ofpossiblestenosesinthinrenal arteries,the examination should be performedwith thin sections of, for instance,4 x 1 mm and with an RI of only 0.5 mm. Since the individual circulationtimes oftenvary, afixed delayof the injection of contrast medium is notrecommended, and the useof a test bolus or bolus tracking is suggested instead. The ROI to register the increase in density (arrival of the contrast medium = commencement of the measurement) is best placed over the lumenof thedescendingaorta(see page 176). CT system Coli. ST Feed Pitch RI Sec.! Voli. Current Kernel WI C Delay CM [mm) [mm) I Rol. [mm) Rol. [KV] [mAs) [HU) [sec.) [mil ml/sec) 1 row 4 rows 16rows 3,0 4x l ,0 1,25 16xO,751 ,0 6,0 6,0 15,0 2,0 1,5 1,25 1,5 1,0 0,7 0,8 0,5 0,5 110 120 120 100 130 130 B30 350/ 50 20/ BT B20 350/ 50 20/ BT B30 350 / 50 20/ BT 120/ 3,0 110/ 3,0 110/ 3,5 Fig. 187.1 Fig. 187.2 Fig. 187.3 The FOV is placed over the central abdominal space (Fig. 187.1). Normally, the visceral branches of the abdominal aorta show a good luminalcontrast without filling defects. includingthe branches of the mesenterial vesselsasshown in Figures187.2 and 187.3. Incase of an occlusion of the superior mesenteric artery (106). the interrupted vascular lumen (..) and the collateral vessels ( ~ ) are easily recognized onVRT and MIPimages (Figs. 187.4-6). Fig. 187.4 Fig. 187.5 Fig.187.6
188 CT Angiography Iliofemoral Vessels For CTangiography oftheiliofemoral vessels,thepatient isplaced feetfirst on the table.The length ofthe relevant bodyregion along the z-axis is critical (Fig. 188.2), and thereforeit isgenerally pre- ferred to use a wide collimation of 4 x 2.5 mm or 16 x 1.5 mm (insteadof4 x 1 mm or16 x0.75mm),which allows afaster table feed. Narrow overlapping reconstructions should guarantee the quality ofthe final images. Problems can arise with the timing of the injection of contrast medium, especiallywith unilateral high-degree stenosesbecause of the slow flow (see below) in the peripheral vessels 01 the affected side. If bolus tracking (B1)is used,the ROI is placed over the descending thoracic aorta or abdominal aorta to register the increase in thecontrast medium-induced density (see page176). Already VRT images allow a good overview from the aortic bifurcation totheanklein most cases (Fig. 188.1). , CT system Call. ST Feed Pitch RI Sec.! Volt Current Kernel WIC Delay CM [mm) [mm) I Rot [mm) Rot. [KV) [mAs) [HU) [sec.) [mil mllsec) 4 rows 16rows 4 x2,5 16x1,5 3,0 15,0 2,0 24,0 1,5 1,0 1,5 1,5 0,5 0,5 120 120 130 130 B20 350 I 50 251BT 150 I 3,0 B30 350 I 50 251BT 150 I 3,5 Fig, 188.1 Fig. 188.2 Fig. 188.3 Fig. 188.4 a 4b Incases of peripheral arterial occlusive disease, both arteriosclerotic plaques (174) and luminal narrowing with impaired flow distally (Fig. 188.4a) are clearly recognized incomparison witha normal post-stenotic flow inthetibioperoneal vessels (Fig. 188.4b). In high- degree peripheral arterial occlusive disease examined with a table feed of > 3 ern/sec, the flow can be so much delayed that the craniocaudal acquisition leaves thebolus behind.
CT Angiography 189 Vascular Prothesis CT angiography is also suitable to follow implanted stents or vascular prostheses (182) that interfere with the assessment of mural calcifications becauseof acousticshadowing (Fig.189.1 '3) incolorduplexsonography images. ;1"'89 98 1./97 ~ ~ / 99 .-:-, / ~. ~t. )L'"'lL - ..... ,..,...,~~ , A;~1 10 ~ 135 . 1061:f . '. 135 ,,,, ' 1 Fig. 189.1 Fig.189.2 Fig.189.3 Outlook CT angiography undergoes rapid technical changes and its ad- vancement can beexpected toescalate dueto morechip capacity and increasing computer power. It is foreseeable that separate work station with user-friendly software and partially automated programs will shorten reconstructions using VRTfurther. Genera- Fig.189.4 Fig.189.5a ting images of thedescendingaorta (Fig.189.4) or majorthoracic vessels (Fig. 189.5) withVRTand MIP asillustrated herewill be- comeever more effortless.Thisrepresentsachallenge fortheuser to stay abreast with the technical developmentsand to keep the departmental protocolsof the variousCTA applicationsuptodate. Fig.189.5b
190 Test Youself ! Tests 47to49: Thefollowing threeimages containseveral pathologicfindings,some obvious andothers rather subtle. Good luckwhentackling thetests! The answerscan be found on page 202 below. Fig. 190.1 Fig. 190.2 Fig. 190.3
APrimer of CT Evaluation 192 Occasionally,thebeginner faces thequestion todecidewhether a finding represents a true lesion orjustan artifact. Acontralateral comparison or a comparison with adjacent cranial or caudal sections can often be helpful. Furthermore, uncertainty arises when describing a lesion without familiarity with the appropriate vocabulary.This primer aims to remedy these problems. A General Approach to an Abnormality of theCTMorphology: Where? Location, lateralization,relative position tootherorgans/vessels Size? Size (diameterin [mm,em]; important, e.g.,monitoring of therapy) Density? Relativeto its surrounding: isodense (equal density); hyperdense(denser); or hypodense (less dense) Structure? Homogenous(e.g., fluids) orheterogenous / septate/ geographic Shape? Tubular(vessels, muscles, ...j ornodular (tumor, lymph nodes)? Reticular (resembling a net),striate ofdiffuse? Demarcation? Sharply marginated (more likely benign) or indistinctly marginated (infiltration into thesurrounding, e.g.,inflammation, malignancy) Caution: Partialvolume effect can mimic an indistinct margin! Perfusion? No, peripheral, homogenous or heterogenouscontrast enhancement Expansion? Space-occupying effectnot invariablyto beequalled with malignancy: e.g., large benign cystscandisplace adjacent vessels B Useful Terms, in Alphabetic Order [eo Application, Possible Significance) CM Defect Defect Bolus CT Band-likedensity [«> lung, connectivetissue: post-inflammatory, scar) Measuring ofdensity (¢ differential diagnosis) Uniform, neither focal nornodular; e.g., liver: hypodense ¢ hepaticsteatosis (fatty liver) hyperdense ¢ hemochromatosis Typicalcalcification pattern ofbenign hamartomas [e> lung) Calcification patternof perihilar lymphnodes ( lung ¢ silicosis; porcelaingallbiadder) Increased densitydue to accumulation ofcontrast medium Pertusion pattern(homogenous, timelyor delayed) Intravascular locationofthrombi {eo aortic aneurysm) Phenomenon (¢ sedimentedhematoma)orair-fluid levels [eo paralytic iieusor intestinal obstruction) Corticalstep deformity, displacement, number of fragments, stability, articularsurface? Diffuse, slight increasedensity seen in perifocal edema [eo fat, lung) Confined perifocal edema (¢ around inflammatory toci and metastases) Blood-containing[eo large infarcts, e.g.,cerebral) Benign criterionfor lymph nodes (¢ nodal index) Typical for vascular rarefaction inthe lung [eo emphysema) High resolution computed tomography (thin sections) [eo lung; also for MPRand3D) Denserthanthesurroundingtissue (bright -e-fresn cerebral bleedingorcalcification) Dumbbell-like Densitometry Diffuse Enhancement Dense band Eggshell-shaped Fractures Enhancement pattern Excentric Fluid Levels Halo Hemorrhagic Hilarfat Honeycombing Ground glass density Hyperdense HRCT Air inclusions Ampullary Bullae Capping Clubbing Cavity Central Demarcation Crescentic ¢ Infectionwithgas-forming bacteria ¢ compound fracture Dilatation ofthe renal pelvis (¢ physiologicvariant orobstructive uropathy) Articularinvolvement Evaluation offractures [ec- riskOf degenerativeosteoarmntis) Dynamicexamination, often without table movement to assess the contrast enhancement pattern Lung [ee- pulmonary emphysema) Periventricular abnormalityin thewhite matter [eo transependymaldiffusionofCNS; sign of SAE) Intrapulmonary hollowspace(¢ tuberculosis) Inthecenter of a lesionor close to thehilumof parenchymafous organs e.g.,ofa limbof theadrenal gland (¢ adenoma,metastases) Contrast medium, given orally,rectallyor intravenously Location ofintravascularthrombi (eo acrnc aneurysm) Courseof fracture JinesEvaluation withadditional MPH [ee- surgical planning) Typical configuration, e.g., subdural hematoma or perihepatic effusion I ascites Pathologic phenomenon inopacified vessels / urinary collecting system In opacified vessels[eo thrombus), in urinary bladder(¢ tumor, bloodclot) Depending on the vascularization, lesions become visible onlyafter administration ofcontrast medium Concentric I
A Primer of CT Evaluation 193 Circular around a lesion (edematousl one) Topographic descriptionofanintrapulmonary lesion Alongthe periphery, in contrast to central Ratioof table feedper rotationand section thickness [ee- spiraltechnique, see p.8 / 9) Pictureelement (imageformation, see p. 14) Intravascular [eo arteriosclerosis), pleura-based [ee- asbestosis) ~ scalloped, cauliflower-like (¢ hilar lymph nodes of the lung, e.g., Boeck'sdisease) Typicalpattern of benigncalcifications [ee- lung) Favoredtermfor "1don't know what is means" c::> chronic pancreatitis Can induce artifacts along vessels (¢ aortic aneurysm) Less vessels per pulmonaryvolume (¢ emphysema, SIP lobectomy) Lacking in malignant tumorsor advanced inflammations (nolonger respecting natural borders => infiltration) Convex projection intotheparanasal sinus, homogenous Net-like pattern (¢ fibrosis of the pulmonary interstitium) Preferredposterior paravertebral lymph node station Internal herniationof brainstem dueto increased intracranial pressure [ec- quadrigeminal andambient cisterns) Regionof interest (¢ densitometry) Focal space-occupying lesion (only intrapulmonic) Peripheral contrastenhancement [ec- glioblastoma) Preferred siteforcertain changes [«> lymphnodes, metastases) Thickened bile [eo cholestasls,cholecystitis) Tumor of unknownnature(ubiqurtously applicable) Biconvex configuration (¢ aortic aneurysm; epidural hematoma) Acquisition of a 3Ddata setwithcontinuoustable feed andany section reconstruction, see p. 7 Hypodense star-likefigure[ec- fNH ot theliver) Septation [eoechinacaccal cyst) Short tube of various materials to stent vessels, ureter or common bileduct bonyCortex(eo fracture diagnosis) Non-descriptivetermof a lesion. try to use more precise term Preferred lymph nodestation Symmetric andtimely renal enhancement and excretion of contrast medium =normal Wedge-shaped [eotypical infarctpattern, scarresidue) Renalvein or vena cava [eo renal tumor) Normal configuration of the pulmonary hila Volumeelement (image formation, seepage l A) Triangular configuration [ec- typical infarct pattern, scar residue) Risk of herniation Triangular Retrocrural Reticular Perifocal Perihilar Peripheral Pitch Popcorn Process Pseudocysts Pulsation Pixel Ptaque Polycyclic ROI Round lesion Scalloped enhancement Siteof predilection Stellar Stellate Stent Respecting soft-tissue planes Retentioncyst SpiralCT Rarefaction Tumor extension Vascular configuration Voxel Wedge-shaped Stepdeformity Structure Sludge Space-occupying process Spindle-shaped Subcarinal TImely Central, hypodense or homogenous liquefaction Longitudinal-transversediameter ratio (characterizationof lymphnodes) Nodular configuration (¢ lymphnodes, tumors, adenomas), miliary < granular < fine-nodular < large-nodular< confluent (¢ pulmonary interstitium) Surface ofcerebral gyri[eo cerebral edema, DO: child)or pancreas outline(¢ acute pancreatitis) Destructionof bony matrix [eo metastases, multiple myeloma) Osseousapposition(<> degenerative), less frequent dueto sclerotic metastases Effect of partial volume (causesapparentindistinctness) Parenchymal per1usion pattern in thespleen during the ea~y arterial phase Hyperperfusion Hypodense Indentation Imbibition Induration Infiltration Indistinct Indistinct margin Isodense Jet effect LN lymphangiomatosis Intramural lacuna MPR Iris effect Inflow effect Multislice Mural thickness Necrosis Nodalindex Enhancement (e::> inflammation, hypervascular tumor) Less densethanthesurrounding (dark ¢ fluid,fat,air) Striatetodiffuse enhancement (¢ fatty fissue: scar, inflammation) Blunt convex bUlging I displacement of adjacent structures (¢ tumors) Outline of a lesion (see marginal indistinctness) Causedby inflammatoryandtumorous infiltration of thesurrounding tissue(caution: DOpartial volume effect) Thickenedfibroustissue(e-scar,pulmonaryfibrosis) Perifocal extension of aninflammatory or malignantprocess Incomplete mixingof contrast medium, canmimic intravascular thrombi Located inthewallof ahollowviscus (¢ gas, tumor) Centripetal enhancement [ee- hepatic hemangiomas) As denseas ... (= isointense) Inflow of opacified urine fromthe ureter intotheurinary bladder Lacunar defect [eo latestage after cerebral infarct, isointensewith CSF) Lymph node (tor size see checklists, ¢ hilar fat) Groundglass-density (¢ pulmonary parenchyma, breast carcinoma) Multiplanar reconstructionof various image planes (sagittal, coronal ¢ diagnostic evaluation of e.g. fractures) Multiphasetechnique Data acquisitionduring early arterial, portovenous or late venous passageof the contrast medium bolus(¢ spiral CTof the liver) New multislice technique consisting of simultaneousacquisitionsof several sections in spiral mode Single or multiple layers (wall of a hollow viscus: ¢ ischemia, inflammation) Narrowed parenchymal ¢ Renal atrophy (degenerative, hydronephrosis) rim Nodular Osteolytic Partial volumeeffect Obliterated Osteoproliferative Patchy
194 B A Primer of CT Evaluation Practical Terms, Organ-related I The following list contains helpful terms, which are used for interpreting CT examinations of a particular organ. Terms locating the findings are followedbyterms describing typical morphologic changes, which are incorporated with possible conclusions and subseouent organ-related pecu- liarities. Thelist does notclaim tobecomplete (this would make it far too convoluted), but should helpthe reader to look up some of the most frequent organ-related terms quickly. Skull, intracranial Locational descriptions • Supra· ! infratentorial • Frontal I temporal I parietal I occipital • SingularI multiple • White matterI cortical Typical morphology ¢ possible diagnoses • Midlinedisplacement, obliterated cisterns, effacedsulci, narrow subarachnoidspaceor small ventricles; Obliterated white matter I cortex intertace eo:> increased intracranial pressure; possible herniation • Capping ¢ Transependymal diffusion of advanced increased ventricular CSFpressure • Intracranial air inclusions ¢ Compound fractureof thecranial vault or cranial base • Cystic homogeneous hypodense ¢ Hygroma / arachnoidal cyst • Hyperdense, biconvex/ crescentic space- occupying process along the internal table of cranial vault ¢ epidural I subdural hematoma • Hyperdenseextracerebral CSFspace ¢ Subarachnoidal hemorrhage • Hypodensewhitematter lesions ¢ Infarcts, embolic residues • CSHsodense lacunardefect ¢ Infarct residue • Peripheral scalloped enhancement ¢ Typical tor glioblastoma • Subtle roundingof thetemporalhom Early increase in CSFpressure • Ventricular enlargement ¢ Internal hydrocephalus ¢ increased CSF pressure ! Notable lindings • Immediatetherapeutic intervention with pendingherniation ! Paranasal sinuses Locational descriptions • Frontal sinus,ethmoid sinus, sphenoid sinus, maxillary sinus • Semilunar canal (important drainageduct) Typical morphology ¢ possiblediagnoses • Round, broad-based, convex homogeneous space-occupyinglesion ¢ retention cyst Notable findings • Normal variants: Haller'scells, pneumatic nasal conchae oruncinateprocess • Riskof visual loss with orbital fracture • Fracture classification offacialbones according to Le Fort (see page 63) Orbit Locational descriptions • Orbital floor, orbital roof, medial and lateral orbitalwall, retrobulbar Typical morphology ¢ possible diagnoses • Thickened extraocular muscles ¢ Endocrineophthalmopathy, Myositis Nofable findings • Riskof visionlosswithfractures of theorbital floorsolely throughcicatricial pull ontheorbital fattytissue Neck Locational descriptions • Nuchal, submandibular, prevertebral, paratra- cneal, parapharyngeal, epiglottic, subglottic, neurovascular bundle, intra- / suprahyoidal Typicalmorphology ¢ possible diagnoses • Heterogenous internal structure, possibly with intrathyroidal calcifications ¢ nodularstruma • Multipleovoid lesions along theneurovascular bundle ¢ lymph nodes Chest Locational descriptions • Peripheral = subpleuralI central = perinilar: • Basal / apical, segmental / lobular; Name segment! Typical morphology ¢ possible diagnoses • Polycyclic bulky hila ¢ Boeck's disease; hilarnodal metastases • Multiple, only indistinctlyoutlined nodules ¢ pulmonarymetastases / granulomas • Sharplyoutlined, striatedensity Without perifocaledema ¢ fibrotic edema • Perifocal groundglass-like density in HRCT ¢ Acute inflammatoryprocess • Irregular nodularthickened interlobar septae withfine-reticular thickening <> l ymphangiomatosis • Bullae withvascular rarefaction,honey combing ¢ emphysema • CaVity with layered groundglass density below air pocket ¢ aspergilloma • Fusiform thickeningalong interlobar space -e- encapsulateo pleural effusion • Apical pleuralthickening, cavities, hilar lymph nodes ¢ tuberculosis • Popcorn-likeor club-likecalcifications ¢ benign hamartomas, post-inflammatory residues Notabte findings • Normal variant oftheazygous lobe • HRCTwiththinner sections (do you remember fhe rational? Referto p.86-87) • Don't forget the pulmonarywindow Liver LocationaJ descriplions • Subdiaphragmatic, subcapsular, perihilar, name thesegment (not only the lobe), periportal, diNuseI focalI multifocal, parahepatic Typicalmorphology ¢ possible diagnoses • Diffusehypodensity withresultant hyperdense vessels (unenhanced) ¢ fattyliver (hepatic steatosis) • Diffusehyperintensity ¢ hemochromatosis • Homogeneous-hypodense, round sharply marginatedroundlesion withoutenhancement ¢ benign cysts • Focal roundlesion with enhancement ¢ metastases; abscess • Roundlesion with central hypodense stellar figure ¢ FNH • Cameral cysts withstellateseptations ¢ echinococcus(splenic involvement?) • Hypodense cannulated, but irregularly branching ¢ cholestasis • "intraparenchymal" hypodenseair pockets ¢ pneumobilia; SIP biliointestinal anastomosis Notabte findings • Multiphase spiral CT: early arterial, portal and latevenousfor improved detectionof focal lesions • Dynamic bolusCT Without tablefeed ¢ iriseffect in hemangiomas • Portography CTafter preceding catheter- placementintosplenicor mesenteric artery
A Primer of CT Evaluation 195 The checklists represent the third part of this primer. They are not repeated here. They can be foundasinserts or onthefollowing pages: Region Page Skull 26 Neck 64 Chest 74 Abdomen 103 Skeleton 167 Vessels I retroperitoneum Locationa/ descriptions • Para-aortal, paracaval, interaortocaval, prevertebral, retrocrural, mesenteric, para-iliac, inguinal, cervical Typical morphology '" possible diagnoses • Dilated aortic lumen with different times of opacificationand detection of a septum ¢ dissectedaneurysm • Beticulnnodular thickeningof theperitoneum with nodular projections andascites ¢ peritoneal carcinomatosis • Endoluminal hypodense defects ¢ thrombi; caution: DOinflow effect (refer to pp.21 - 23,73) Bone I Skeleton Locational descriptions • Cortical,subchondral,juxta-articular, metaphyseal, diaphyseal, epiphyseal, intra- and extraspinal Typical morphology ¢ possible diagnoses • Step-deformityof thecortex, corticalbreak, fractureline¢ fracture • Articular involvement ¢ risk of secondary degenerativeosteoarthritis • Focal hypodensity of thespongiosa with absent trabeculae ¢ pathologic bonemarrow infiltration Nolable findings • Evaluation of stability, MPR, 3Dreconstruction, myelo-CT ofthespine I Checklists c Notable lindings • Densitometry of cystic changesfor comparison with unenhancedsections • Evaluationof excretion: symmetric, timely? Dilated ureteral lumen? GastrointestinalTract Typicalmorphology '" possiblediagnoses • Generalized diffuse wall thickening ¢ lymphoma; ischemia; ulcerative colitis • Segmental wallthickening ¢ Crohn's disease • Air-fluidlevels withinlumen and dilatation ¢ intestinal atonyto ileus • Free air in theabdomen ¢ perforation • Intramuralair ¢ suspiciousfor necrotic intestinal wall(ischemic or inflammatory); caution: DO diverticulum! Nolable findings • Selectionof suitable oral contrast medium (refer to p. 19) Genital Organs Locaffonal ttescriptions • Parametrial, intramural,submucosal, endometrial, ischial fossa,pelvic wall, periprostatic Typicalmorphology ¢ possiblediagnoses • Hypodense,water-isodense space-occupying lesion in thescrotum ¢ hydrocele, varicocele • Nodularthickeningof the myometrium <> benign myomas, but also small uterine cancers • Growth beyond organ outline, infiltration of rectal and bladder wall ¢ suspicious for malignancy Nolabie findings • Thin sectionsthrough the lesser pelvis, rectal administrationof contrastmedium Urinary Bladder Locaffonal descripuons • lntra-, extra-, paravesical, bladder floor, bladder roof, trigonum Typical morphology", possibie diagnoses • Diffuse wall thickening ¢ cystitis,trabeculated bladder; edemafollowing radiation • Focal wall thickening,polypoid projecting into the lumen ¢ suspiciousfor malignancy Nolable Ilndings • Jeteffect, diverticulum, catheter balloon; indwelling catheter fa beclamped betore examination! Gallbladder Typical morphology ", possible diagnoses • Multi-layered edematous wall thickening with perifocal "ascites" ¢ acute cholecystitis • Intraluminal wall-based thickening with calcification¢ polyp • Intraluminal sedimentationphenomenon ¢ sludge • Eggshel l ~l i ke peripheral calcification ¢ Porcelain gallbladder, precancerosis Pancreas Loeat/analdescriptions • Head, body,tail, peripancreatic fatty tissue, uncinate process Typical morphology '" possibie diagnoses • Diffuseenlargementwith obliteratedoutlineand exudate pathways ¢ acute pancreatitis • Atrophic organ, dilated ducts, calcificationsand pseudocysts ¢ chronic pancreatitis Spleen iocstionst descriptions • SUbdiaphragmatic, subcapsular, perihilar, perisplenic Typical morphology '" possible diagnoses • Leopard-like marblepattern duringthe early arterial phase of enhancement ¢ physiologic • Wedge-shaped perfusion defect ¢ infarct • Perisplenic round lesion, isodensewith splenic parenchyma ¢ accessory spleen; LN Kidneys Locational descriptions • Parapelvic, medullary, parenchymal, cortical, subcapsular,arising, polar, perirenal, uni- / bilateral, lateralization Typical morphology", possible diagnoses • Homogenous-hypodense, round, sharply demarcatedspace-occupyinglesion without contrastenhancement ¢ benigncyst • Hypodense clubbingof thecollecting system ¢ obstruction; ampullary renal pelvis, parapelvic cyst • Irregular wallthickeningot thecystwifh contrast enhancement ¢ suspiciousfor malignancy • Thinning oftheparenchymal rim, generalized decrease in size ¢ renal atrophy • Heterogenous space-occupyinglesion extendingbeyondtheorgan outline ¢ renal cellcarcinoma • Hypodensewedge-shaped periusiondefect -e-renal infarct
196 Solutions to Test Yourself! The exercises and solutions have been numbered consecutively. Some of the exercises have several different correct solutions. If the exercises can be solved simplyby referring tothe chapters in the book, I have indicated where you will find the necessary information. Solution to exercise1(p.32): After you have completed the exercises, compare your scoreand results withthose of yourcolleagues.Thescore on theright gives youan impression of the degree of difficulty. Enjoythe challenge! 9 Points You will find the sequence for interpreting CCTs on page 26. Each stepgives you '12 point with 3 extra points for the correct sequence, which addsupto 9. Solution to exercise 2(p.45): Lung/pleural window Bone window Soft-tissue window Solution to exercise 3 (p.45): Levei - 200 HU +300 HU + 50HU Width 2000 HU 1500 HU 350 HU Gray scale -1 200to + 800 HU - 450 to +1050 HU - 125to+ 225 HU 9 Points 3 3 3 10Points a) Bariumsulfate Routineforabdominal/pelvicCT if thereare no contraindications b) Gastrografin Watersoluble, but expensive; if perforation ileusorfistulas aresuspected; prior tosurgery Nooral CM shortlyafter surgery foran ileal conduit! Solution to exercise4 (p. 45): 30minbeforeCTofupper abdomen 60 minbeforefullabdominal CT 20min beforeCT ofupperabdomen 45min before fullabdominal CT 4 4 6 Points a) b) c) Renal failure (creatinine, possibly creatinine clearance,functionfollowing kidney transplant ornephrectomy) Hyperthyroidism(clinical signs? if yes,hormone status, possiblythyroidultrasoundand scintigraphy) AllergytoCM(has CM-containing iodine already been injected? Are thereanyknown previous allergic reactions?) 2 2 2 Solution to exercise 5 (p. 45): Tubular andnodular structures can be differentiatedbycomparing aseries of images. Solutionto exercise 6 (p.45): 2 Points 3 Points Vessels inwhich beam-hardening artifacts occurbecause ofCM infloware the superior vena cava,infertor vena cava,and the subclavian vein. Solutionto exercise7 (p. 48): 3 Points Fractures, inflammatory processes, and tumorsor metastases can cause swelling of mucous membranes and retention of fluidsin the mastoid sinuses and middle ear; these are normallyfilled withair. Solution to exercise 8 (p.57): 18Points This image requirescareful study.Youwill discoverseveral types of intracranial hemorrhageandthecomplicationsresulting from them. • Bruising of theleft frontoparietal soft tissues (extracranial, indicativeoftrauma tothe head) 1 • Subdural hematoma over the right hemisphere extending tooccipital levels(hyperdense) 2 • Edema intheright frontopartetal areas, possiblyaccompanied by an epidural hematoma 2 • Signsofsubarachnoid bleeding inseveral sulci inparietal areas on the right,adjacent tothefalx 2 • Thehematoma has penetrated intothe right lateral ventricle, which is practicallyobliterated 4 • Choroid plexus intheleftlateral ventricleappears normal 1 • Thereis a midlineshift toward theleft, and edema surroundstheperiventricular white matter on the right 2 • Raised intracranial pressure(obstructed ventricle) and herniation ofthebrain (edema) can beexpected 4
Solutions to Test Yourself! Solution toexercise 9 (p. 72): Gray and whitematter appear well defined on narrow brain windows. Level Width Gray scale + 35HU 80HU - 5 HU to + 75HU CCTsectionsare normallyoriented parallel totheorbitomeatalline, so that Initial and follow-up studies can be preciselycompared. 2-mm sectionsat 4-mmincrements are acquiredthroughthe petrosal bone, then thickness and tablemovementare set at 8mm. Solution toexercise 10(p.72): 9 Points 3 2 2 2 16Points 197 Intracerebral hemorrhage Subarachnoidhemorrhage Subdural hemorrhage Epidural hemorrhage Complications inearlyphases hyperdense, often with hypodense peripheral edema hyperdense bloodinstead of hypodense CSFinthesulciand cisterns hyperdense crescentic area close tothecalvaria, concave toward thecortex, not limited bycranial sutures hyperdense, biconvex areaclose tothe calvaria, smoothtowardthecortex, always limitedby cranial sutures hemorrhage intoaventricle, CSFflow isobstructed, edema, danger ofherniation 2 2 4 4 4 Solution toexercise 11 (p. 72): 2 Points Subarachnoidhemorrhage inchildren may bevisible onlynext tothe falxor inthelateral (Sylvian) fissure. Solution toexercise 12(p. 72): Practicemakes perfect! Solution toexercise 13(p. 72): 10Points 4 Points Fractureofthe rightfrontalbone andabsent right frontalsinus (thelatterisacongenital variation, not ahemorrhage,as indicatedbythe osseoustrabecuiae) Solution toexercise 14(p. 72): 8 Points This was adifficult question. In the left internal jugular vein there isunusual sedimentation ofthe CM due toslow blood flow.The asym- metry ofthe jugularveins is not asign of thrombosis. Aleft cervical abscessmakes the neck musclesappear poorly defined. Solution toexercise 15(p.73): 4 Points In this patientthe surface subarachnoid spaces are clearlytoo narrow and theventricles distended.These signsindicatethatCSFdrain- age is reduced or blocked and thereis imminent danger ofbrain herniation. There is generalized brain edema.Aneurosurgeon should be consulted about insertingan intraventricular shunt. Solution toexercise 16(p. 73): 3 Points Itispossibletomistakethesubarachnoidhemorrhagearoundthe leftfrontallobe as an artifact. Theleft frontal cortex isoutlined by blood. Ifyoudidnotsee anyabnormality, return tothe chapter about thehead. Solution toexercise 17(p. 73): You have ofcoursetakenthe hintabout notgiving up too soon; the right medial rectus muscle (47c) is thickened. It is the second muscle to become involved inendocrine ophthalmopathy. Ifyoucannot remember which muscleisaffected first, return topage 61 . I
198 Solutions to Test Yourself! Solution to exercise 18(p.73): Part of the question was misleading. but thiswas intentional, and Ihopeyoutakeit in the right spirit. No fresh intracranial bleeding can be seen in this image (Fig. 73.4 is the same as Fig. 198.1).The abnormality in the lett frontal lobe is an area of reduced attenuation representing an earlier hemorrhage (180) which has now reached the resorption phase (4 points). The extracranial swelling and bruising in the lett frontoparietal area (1 point) is also 2 weeks old. In order to determine the nature of the hyperdense foci, particularly on the right side, you should of course ask to see adjacent images (4 points). The next caudal section (Fig. 198.2) shows that these foci are formed by the orbital roofs (*), the sphenoidbone(60), and the petrosal bone (* * ) (1 point for each). These partial volume effects were discussedon page 53.If you misinterpre- tedtheminthe question,takeitasawarn- ingand youwillbeless likelytomake this mistakeagain. Fig.198.2a Solution to exercise 19(p. 82): Compare your checklistforCCT withthe one on page 74. As inexercise 1,each itemisworth 'J, point andthecorrectsequence is worth 3 points. Fig. 198.2b 12Points 13Points 4 PointsII There is an area of lowattenuation due to incomplete CM filling inthe azygos vein, rnost likely becauseof athrombosis(2 points).The esophagus is notwell defined.There are hypodense lines crossing the pulmonarytrunkand rightpulmonary artery which are artifacts because they extend beyondthelumen ofthevessels(2 points). I Solution to exercise 21 (p. 100): Did yousuggest doingbronchioscopy orbiopsy inorder toknow moreaboutthe "Iesion"?Then you mustrevisit the basic rules of CT interpretation. But if you remembered to look first of all atthe other images intheseries, as forexam- plethe one on theright,youwillhave seenthat the "Iesion" belongs tothe sterno- clavicularjoint( '" ). This is another example of a partial volume effect. There is degenerative change inthisjoint, butnopulmonary lesionorinflammation. Abb.198.3
Solution to exercise 22(p.100): The cause of sudden back pain in this patient was the dissection (172) of the aortic aneurysm (1 point). At this level, both the ascending (89a) and the descending (89c) aorta (1 point each) show a dissection flap. It is a de Bakey type I dissection (1 point). Solutions to Test Yourself! Solution to exercise 23(p.100): Thisisa caseofbronchial carcinoma (the bronchial obstruction is not seen at this level).There isatelectasisoftheentireleft lung (84) (2 points) and an effusion (8) fillsthepleural spaces (2 points). Didyou detect themetastatic mediastinal LN(6)? (2 points) Solution to exercise 24(p. 101): The most obvious abnormality is the bronchial carcinoma (7) in the left lung. The right lung shows emphysematous bullae (176). CT-guided biopsy of the tumor should bepossiblewithout causing a pneumothorax because it has a broad pleural base (2 points). 199 Solution to exercise 25(p. 101): Thesmall metalclip(183) isa hint that the stomach has been surgically transposed into the mediastinum. The thick-walled structure with the irregular lumen isapartof the stomach (129), not an esophageal tumor. At the moment of data acquisition the stomach was contracting and is therefore notas easily identifiedas inFi9ure 91.2. Solution to exercise27(p. 101): You are alreadyfamiliar with this tragic case of bronchial carcinomainayoung pregnant woman (thus no CM enhancement, see Fig. 98.2). The anteriorlocuteofthemalignant effusion(3points) had caused the right lung to collapse (2 points) and was theretore drained. After the tibrin clot had been removed from the catheter the lung was reinflated and the mother's life was pro- longeduntil thebirthofher healthychild. Didyou noticethe metastaticLNinthe rightaxilla? (1 point) Perhaps the first thing you noticed was the irregular contour of the diaphragm (30) (1 point), but this is a normal finding. The patient was a smoker and had complained of weight loss. You should first ask for lung windows inordertocheck for metastases (7) or primary bronchial carcinoma (5 points). When a chest is examined, it should become your standard procedure to use bothsoft-tissue and lung windows (Fig.199.5a). Solution to exercise 28(p. 101): These two images show an aberrant branch of the aortic arch: The subclavian artery passes posteriortothe trachea and theesophagustowardthe right side of thebody.Youmayrememberthat this anatomic variationwasmentioned, butnot shown,onpage 120. 4 Points II I
Solutions to Test Yourself! Solution to exercise 29(p. 141): 200 ---In addition to the air-fluid levels in the dilated bowel (2 points) associated with an ileus, you should have seen the dilated right ureter anterior tothe psoasmuscle(2 points).Thecorrect diagnosisisthereforeileusandhydronephrosis.Youmayrecognizethisparticularcase as thesameoneshown in Figure 134.2a,ata slightly morecranial level. You shouldhave seenthe adenoma(134) inthe right adrenal gland (2 points). For'j, point each you should be ableto nameten other organs. Consult the number legends if you are uncertain. Solution to exercise 30(p. 149): Solution to exercise 31 (p. 149): 7 Points Solution to exercise 32(p. 149): 4 Points Solution to exercise 33(p.149): 3 Points Thisisindeed acase of situs inversus(2points).Youwillalsohave noticed that the attenuation of the liver (122) is abnormally low: fattyliver(2points). The question itself will have drawn your attention to the athero- scleroticplaques (174) inthecommon iliac arteries (113) (1 point). Theleft one is part ofanaorticaneurysm (2points). 5 PointsSolution to exercise 35(p. 149): The two cysts (169) in the right kidney (135) are impossible to miss (1point).Buttherearealso multiple,hypodenselesionsinthe spleen (1 33), due to splenic candidiasis (3 points). You may also have considered a rare case of nodular lymphoma or melanoma metastases inthe spleen('j, point each). 6 PointsSolution to exercise 34(p.149): Hopefully you saw the fairly large, irregular metastasis (7) in the posterior segment of the liver (122) (1 point). Did you also see the smaller,moreanteriormetastasis?(3 points).TheDD mayhave includ- ed an atypicalhepatic cyst (1 point) or, for the anterior lesion, partial volumeaveraging ofthe falciform ligament (1 point). 29 I
Solutions to Test Yourself! Figure 201.1 is the section next to the one in Figure 150.1 and shows that thehypodensearea intheliver isthe gallbladder.If you suggested doing anything else, for example aspiration or biopsy, beforeseeing adjacent sections,take 3 pointsaway. Solution to exercise 37 . 150 : 201 ---You may have thoughtthat the hyperdensefoci next tothe rectum (146) representcalcified LN(6) (1 point). However,the lymphatics are so well demarcated because they are still opacified after lymphography (3 points). Did you also notice the atherosclerotic plaques (174) inthefemoral arteries (119) (1 point)? 6 PointsSolution to exercise 36(p. 150): Solution to exercise 38(p. 150): 3 Points You will achieve the most accurate densitometry of a cyst if you select a section without any partial volume effects from renal paren- chyma as in Figure 150.3b (1 point). Resultsof measurements inFigure 150.3a would betoohigh (2points). Sincethisverycase was discussed onpage 133,take away2 points forthe incorrect answer. 6 Points For further documentation you should ask to see bone windows (2points) and of course the adjacent sections (2 points) inorder to assess the pelvic fracture. It is also important to determine whether the acetabular fossa was involved (2 points). The fractures of the pubic bones were already visible on soft-tissue win- dows (Fig. 150.5) because the fragments were slightlydisplaced. Solution to exercise 40 . 150 :7 Points 10Points , Solution to exercise 39(p. 150): The illustrationshowed onlyone metastasis inthe right lobeofthe liver (1 point) in a case of hepatomegaly (1 point). By using tri- phasic SCT, additional metastases become visible (2 points). CT arterial portogra- phy (3 points) is moreinvasivethan SCT alone, but it demonstrated that the spleen also has metastases. Fig.201.3 """"::;....~ _ Solution to exercise 41 (p.151): Another exampleofa partialvolume effect: thesigmoidcolon was only apparently "within" the urinary bladder (4 points). The first thing you should have asked to see was adjacent sections Ifyoudetected the fresh thrombosis(1 73)intheright femoralvein (118), youget3 points. Didyou alsosee thesynovialcyst (175)on the left (3 points)? Your DD may have included a lymphoma, a femoral or inguinal hernia, or a metastasis (1 point each). If you mistook the cyst for thrombosis of the left femoral vein as well, take away 3 points!Thevein (118) lies next tothecyst. Solution to exercise 42(p. 151): 7 Points You may remem- ber that this case was discussed on page116 (seeFig. 116.5a). There's also pararectal ascites (1 point).
Solutions to Test Yourself! 202 Solution to exercise 43(p. 151): ~ You may have thought that Figure 151.4 shows a gastric pullthrough for esophageal carcinoma (1 point) or that the esophageal walls are thickened due to metastases (2 points). However, this was a case of a paraesophageal sliding hiatus hernia(3 points). If youforgot toaskfor lung windows,youwill not have seen thelarge right paramediastinal emphysematous bulla (..)(2 points). Solution to exercise 44(p. 151):~ The beam-hardening artifacts (3) due to drainage tubes (182) were a hint that this image was taken shortly after surgery (2 points). The abnormal structures containing gases (4) are surgical packs (5 points) placed to control bleeding after multiple trauma. Whenthepatient'scondition hadstabilized theywould be removed in a second operation. Your DO may have included fecal impaction in Chilaiditi's syndrome (2 points) or an abscess with gas-forming bacteria(2points). Solution to exercise 45(p. 151): 11 Points In Figure 151.5 a poorly defined tangentialsection of a diverticulumof theurinary bladdercan be seen next to therectum on the right side (*) (5points). Your DO may have includedapararectalLN(2 points).Theirregularitiesintheattenuation values of theurine are due toeM andthe'jet phenomenon' (2 points each). Figures 202.3 and202.4 are adjacent toFigure 151.5. " Astenosisof thethoracicaortaisclearlyidentified(Fig. 190.1),aswell as athrombus inthe right pulmonaryvessels(Fig. 190.2)andan infloweffect of contrast medimintothe superior venacava as differentialdiagnosisof a genuine cava thrombosis (Fig.190.3). 6 Points Fig.202.5d 4 Points Solution to exercise 47-49 (p.190): The same oldproblem!Thehyperdense (enhanced) C-shaped structure in the pancreas (131) in Figures 151.6 or 202.5isaloop ofthe splenicartery (99) (4 points). The adjacent sections (c. d, and e) show that thesplenic artery can bevery tortuous. Solution to exercise 46(p.151): •
..... g><: . Checklist forAbdominal Readings il,ilThieme " i ~ ~ I.z- ~ I *::; " -i " ~ ~ 1§ " '" '" ~ "8, ~ ~ :;; g ~ -s E g -'!!. ~ ~ g ~~ E l'i"5 " ;1: ~ 0 "C ;1: G .0 ~z 'e ~ ~~ ~~ " ~ "0 E 0 ,; ~ .~ 0 " ~ c § ·E IB~ ~ ~ !<t 0 TI 0; ;;" i .~ "5 ~ ~ " " ·0 ~ j; • E ~~ .e i ~ rn ~ · •~ "i .s~ 1§ .is ~ .s ilE :i5 E ~ '" 2 ~ f 2 ~~ g •> ~ ~ ~ e '5 J'! ::; i'" ~ g .e ~ ~ ~ S ~ 0 0 ".§ ] -" i '§! 0> 10 i i 0 E '" ~ ~ ~~ I" § :;; ~ ~ &i I E 0- j ; l' ~ oS If. " g " t t ----- - - ------ ---_... -. ··· x well defined? normal thickness of walls? stenoses ordilations? vessels: (especially periumbilical andinguinal regions) hernias, enlargedlymph nodes? homogeneous parenchymawithout focal lesions? well-defined outline? well-defined, thin wall? calculi? well-defined, size normal? symmetric excretion of eM? obstruction, atrophy, bladderwallsmooth and thin? homogeneousprostate of normal size? spermatic cord, uterus, andovaries? aneurysms? thromboses? enlargedlymph nodes? mesenteric (norma! < 10 mm) retrocrural (normal < 7 mm) para-aortic (normal < 7 mm) parailiacal (normal < 12 mm) parainquinal (normal < 18 mm) lumbar spine and pelvis: degenerative lesions? fractures? focal sclerotic or lyticlesions? spinalstenoses? Gil: Reproductiveorgans: liverand spleen: Gallbladder: Pancreas, adrenals: Kidneys, ureter andbladder: Abdominal wall: Retroperitoneum: Bone window: Excerpt from: Hofer, Matthias CT Teaching Manual ISBN 3·13-124352-X ISBN 1-58890-277-3 @};Thieme Excerptfrom: Hofer, Matthias CT TeachingManual ISBN 3-13-124352-X ISBN 1-58890-277-3 Checklist forThorax Readings 1.On the soft-tissue window: • softtissues, especially: - axillary LNs - breast (malignant lesions?) • mediastinum infour regions: - from theaortic archcranially (LNs?, thymoma/goiter?) - hilarregion(configuration and sizeof vessels, lobulatedand enlarged? - heartand coronary arteries (sclerosis?) • fourtypical sitesof predilection for LNs: • anterior to aortic arch (normal: almost noneor < 6 mm) • in theaortopulmonary window(normal: < 4 LNs < 15 mm) • subcarmal (normal: < 10 mm; DO: esophagus) • nextto descending aorta (normal: < 10 mm; DD: azygos) 2. On the lungwindow: • Parenchymaof thelung: - normal branching patternandcaliberof vessels? - vascular oligemia only at interlobar fissures? bullae? • anysuspicious lung foci?inflammatory infiltrates? • Pleura - plaques, calcification, pleural fluid, pneumothorax? • Bones(vertebrae, scapula, ribs): - normal structure of marrow? - degenerative ostenphytes? - focal lytic or sclerotic processes? - stenosesofthe spinal canal?
Checklist for Reading Cervical CT Images Checklist: Preparing thePatient These values are infended asguidelines,larger lymphnodes are notnecessarily pathological. Biconvex, smooth eltipsoidalln shape; close to calvaria; does not exceed cranial sutures; usually hyperdense, rarely sedimented Hyperdense blood in thesubarachnoid space or the basal cisterna instead of hypodens CSF Fresh hematoma: crescent, hypertense bleeding close to the calvaria with ipsilateral edema; hematoma is concave toward hemisphere; mayextend beyond cranial sutures Characteristics Subdural bleeding Type of bleeding Subarachnoid bleeding Epidural bleeding Necessary information: • What regionor regions of the body will bescanned? • What disease? since when? • Clinicalobservations • Previousoperations or radiotherapy?When? • Previous CT?Include printouts if possible. • Renal parameters: at least current creatininelevels • Thyroidparameters or statement that hyperthyroidism is notsuspected • Any known incident of hypersensitivityto CM? Forabdominal andpelvic CTs: (because eM is administered orally) • Isabdominal surgery planned? (water-soluble CM) • Istherean ileal conduit or urostomybag? (inition scan unenhanced, then enhanced scan) • Isa lesion suspected in the lesser pelvis?(rectal CM) Checklist for Referral Sheet ChecklistforReading Cranial CTs Four aspects should be considered : Renal function? (elimination of eM) • Creatinine: normal0.7 - 1.3 mg/dl == 60-130 urnol/l • Creatinineclearance:normal 100-160 m!/ min,if there is creatinine retention, 2 litersof liquid orallyafteri.v. eM will increasediuresis (special monitoringif cardiac failure) Idiosyncratic reaction to eM?(premedicationnecessary, be informedabout glaucoma, prostate hypertrophy) • Patient should receive premedication andeM onan empty stomach (reduces thechancesof aspiration in severe incidents with loss of consciousness) • If premedication is necessary befor oral eM, thepatient mustbe at the unit at least one hour before CT begins Abdominal or pelvicCT? Scheduling OK? • To applyoral CM patient must beat unit 30 minutes prior to CT • previous GITimaging procedures with oral CM?(this may cause artifacts up to 3 days later dueto residual CM) Hyperthyroidism?If problems with iodine-containingCM are suspected, fT3, fT4 andTSHshould bedetermined; possibly alsoultrasound or scintigraphy • Age of thepatient? Medical history? • Posttraumatic changes in thesoft-tissue structures: bruises I tumors? • Normal contours of Quadrigeminal and basal cisterns? (Riskof brainstemherniation) • Sizeandcontoursofventricles and CSF spaces appropriateto patient's age? • Any blockage to flowof CSF (obstructive hydrocephalus) orsigns of brain edema (=effaced sulci)? • Asymmetries: due to head position or trueasymmetry? • Plain or contrast-enhanced CT: cerebral arteries regular? (Especially afterinjectionof CM) • Calcifications in thechoroid plexus and pineal body only?(Common findings) Anyadditional hyperdense foci? • Paraventricular white matterandcortex inconspicuous andwelldefined? Any focal lesions or local edema? • Basal ganglia andinternal capsule intact? (Most common locations of cerebral infarctions) • Bramstern, pons and cerebellumnormal? • Skull checked forfracturesandmetastases in thebone window? IlJ EIlJ .-..c:: t- ~ Excerpt from: Hofer, Matthias CTTeaching Manual ISBN3-13-124352-X ISBN1·58890·277·3 < 6 mm (DO: thymus!) < 15 mm (normalfewer fhan 4 nodes) < 10 mm < 10mm (DO: esophagus') < 7 mm (DO: azygos vein') < 10mm < 12 mm (DO: ovaries!) < 18 mm Normal Diameters l!lThieme • Symmetry of neckmusculature? • Fat planes preserved and sharplydemarcated? • Normal perfusion ofvessels? • Thromboses or atherosclerotic stenoses? • Symmetry and definition ofsalivaryglands? • Thyroid parenchyma homogeneouswithout nodules? • Anyfocal pathologic enhancement with eM? • Narrowing ofthetracheal lumen? • Assessment of lymphnodes? Numberand size? • Cervicalvertebrae examined in bone window? • Vertebral canal patentor narrowed? Lymph Nodes Anterior mediastinum Aortopulmonary window Perihilar Subcarinal Paraaortic Mesenteric Parailiac Parainguinal
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Hofer ct teaching manual - a systematic approach to ct reading, 2nd ed.

  • 3. 4 Notes for theUser, "What you should know" Front Cover Flap I Keyto AnatomicStructures on pages 26-73, 152/153 (head / neck) Front Cover Flap Normal Anatomyof the Petrous Bone (Coronal andAxial) 46 Normal Variantsof the Cranium 50 Typical Partial Volume Phenomenaof theCranium 52 Notes for theUser, List of theCT diagrams Foreword andList of Abbreviations Physical andTechnical Fundamentals General Principles of CT Comparison of Conventional CTwith SpiralCT Spatial Resolution, Pitch Section Collimation:Resolution alongthe Z-axis Adaptive Detector Design ReconstructionAlgorithms Effects ofkV, mAs and ScanTime Three-dimensional Reconstruction Methods: Maximum Intensity Projection(MIP) Multiplanar Reconstruction(MPR) SurfaceRendering Cerebral CT, Pathologic Findings Intracranial Bleeds Cerebral Infarcts 3 Cerebral Tumors and Metastases InflammatoryProcesses Orbital Changes 6 Changes of the Facial Bones andParanasal Sinuses 7 8 NeckCT 9 Selection of theImagePlane 10 Checkiist for a SystemicApproach 11 Normal Anatomy ofthe Neck 12 13 Neck CT, Pathologic Changes Inflammatory Processes andTumors Thyroid Gland Test yourselfl 54 58 59 60 61 62 64 64 65 70 71 72 it (Axial) - Bones (Coronal) Chest CT Selection of theImage Plane 74 SystemicSequential Approach to Interpretation Checklist for Interpreting Chest CT 74 Normal Anatomy ofthe Chest 75 Test yourself! 82 Chest CT, Pathologic Changes Anatomy of thePulmonary Segments 84 HRCT ofthe Lungs:Technique, Effects, Indications 86 AnatomicVariants of theChest 88 Chest Wall Abnormal Lymph Nodes 89 Breast, BonyThorax 90 Mediastinum TumorMasses 91 Enlarged Lymph Nodes 92 Vascular Pathology 93 Heart 94 Lung Intrapulmonary Nodules 95 Bronchial Carcinoma, Malignant Lymphangiomatosis 96 Sarcoidosis,Tuberculosis,Aspergillosis 97 Pleural Changes,Asbestosis 98 Silicosis, Pulmonary Emphysema 99 Interstitial Pulmonary Fibrosis 100 Test yourselfl 100 Abdomen CT Selection of the ImagePlane 102 Systemic Sequential Approach toInterpretation Checklist for InterpretingAbdomen CT 10, NormalAnatomy oftheAbdomen 104 Normal Anatomy of the Pelvis (Male) 11, Normal Anatomy of the Pelvis (Female) 114 Back Cover FlapKey to Anatomic Structures on pages 71, 74-1 49 (thorax / abdomen) 15 18 14 16 17 21 24 25 20 26 26 19 27 32 33 41 45 Basic Rules for Reading CT Examinations Anatomic Drientation Partial Volume Effects Distinguishing Nodular from TubularStructures Densitometry DensityLevels of DifferentTIssues Documentation Using Different Window Settings Administration of Contrast Agents OralAdministrationof ContrastAgents Selection oftheAppropriate Contrast Agents Duration and Dose In avenous Injection of Contrast Agents In avenousAccess :l1ilo'o Effect of Contrast Agents ~""re . 8 Reaction to Contrast Agents andTheir Therapy - ayro;o · Crisis and itsTherapy Preparing the Patient Medical History Renal Function Hyperthyroidism Adverse Reaction to Contrast Agents Premedication OralAdministration of Contrast Agents Informing the Patient Removal of Foreign Objects Controlling Respiration ......,,,,,,,1 CT s.= ec OJ ' ImagePlane '3 _-=- ~:'O 02 toInterpretation Cranial CT
  • 4. Table of Contents Abdomen CT, Pathologic Changes Spine AnatomicVariants oftheAbdomen 116 Cervical Spine (C-spine) 152 Typical Partial Volume Phenomena C-Spine, Disk Prolapse and Fractures 153 Abdominal Wall Thoracic Spine (T-spine): 15t Enlarged Lymph Nodes,Abscesses 117 Normal Findings and Fracture Subcutaneous Heparin Injections 118 Lumbar Spine (L-spine): 155 Abdominal Wall Metastases Normal Findings and Lumbar Disk Prolapse Inguinal Hernias L-spine, Fractures 156 liver L-spine,Tumors/ Metastases 157 Anatomy ofthe HepaticSegments 119 L-spine, Inflammations/ Internal Fixation 158 Examination Protocols 120 Selection ofWindow Display Lower Extremity Bolus Passageof Contrast Agents NormalAnatomyof theThigh 159 CTPortography NormalAnatomyoftheKnee 160 Hepatic Cysts 121 NormalAnatomyoftheCalf 161 Hepatic Metastases 122 NormalAnatomyoftheFoot 162 Solid Hepatic Lesions: 123 Fractures ofthe Foot 163 Hemangioma PelvisandThigh: Inflammatory Processes 166 Adenoma Knee, Fractures, ChecklistFracture Diagnosis 167 Focal NodularHyperplasia DiffuseHepatic Changes: 124 CT-guidedInterventions 168 Fatty Liver Hemochromatosis Examination Protocols for Spinal CT 169 Cirrhosis BiliarySystem Radiation Protection Pneumobilia 124 Radiation Dose / Cancer Risk 174 Cholestasis AutomatedBolusTracking (BT) 176 Gallbladder Tube Current Modulation 177 Cholecystolithiasis 124 Chronic Inflammatory Processes 125 CT-Angiography Spleen Intracranial Arteries 178 Enhancement,Splenomegaly 126 Cranial Dural VenousSinus 179 FocalSplenic Changes 127 CarotidArteries 180 Pancreas Aorta 182 Acute and Chronic Pancreatitis 128 Heart: CoronaryArteries, 184 Pancreas Neoplasms Screening for Coronary Adrenal Glands Artery Calcifications Hyperplasia,Adenomas, Metastases, Neoplasm 130 Pulmonary Vasculature (Pulmonary Emboli) 186 Kidneys Abdominal Vasculature 187 Congenital Variants 132 Iliofemoral Vasculature 188 Cysts, Hydronephrosis 133 VascularProtheses, Outlook 189 SolidTumors 134 TestYourself! 190 VascularRenal Changes 135 Urinary Bladder The Fundamentals of Interpreting CT 192 Indwelling Catheter, Diverticula, SolidLesions 136 Genital Organs Answers to Test Yourself 196 Uterus 137 Ovaries, Prostate Gland,Vas Deferens 138 Index 203 Gastrointestinal Tract Stomach 139 References Back Cover Flap Inflammatory Bowel Diseases 139 Colon 140 Key to Anatomic Structures Back Cover Flap Ileus 141 on pages 152-167 (spine / leg) Test Yourself! 141 Retroperitoneum Key to Anatomic Structures Back Cover Flap Aneurysms 142 on pages 71 ,74-149 (thorax / abdomen) VenousThromboses 143 Enlarged Lymph Nodes 144 Skeletal Changes Bony Pelvis: Normal Findings, Metastases 145 Fractures 147 Hip Dysplasia, Necrosis of the Femoral Head 148 Test Yourself! 149 5
  • 5. 6 Physical and Technical Fundamentals General Principles of CT Computed tomography is a special type of x-ray procedure that involves the indirect measurementof theweakening, or attenua- tion, of x-rays at numerous positions located around the patient being investigated. Basically speaking, allwe knowis • what leaves thex-ray tube, • what arrives at the detectorand • the position of thex-ray tubeand detectorforeach position. Simply stated, everything else is deduced from this information. Most CT slices are oriented vertical to the body's axis. They are usually called axial or transverse sections. For each section the x-ray tube rotates around the patient to obtain a preselected section thickness (Fig. 6.1). Most CT systems employ the continuous rotation and fan beam design: with this design, the x-ray tube and detector are rigidlycoupled and rotate continuous- ly around the scan field while x-rays are emitted and detected. Thus,thex-rays, whichhavepassed through thepatient, reach the detectors on the opposite side of thetube.The fan beam opening ranges from 40° to 60°, depending on the particular system design, and is defined bythe angle originating at the focusof the x-raytube and extending to theouter limits ofthe detectorarray. Typically, images are produced for each 360° rotation, permitting a high numberofmeasurement data to beacquired and sufficient doseto beapplied.Whilethescanis being performed, attenuation profiles, also referred to as samples or projections, are obtained. Attenuation profiles arereallynothing otherthan acollectionofthe signals obtained from allthedetector channels at a given angular position of the tube-detector unit. Modern CT systems (Fig. 6.4) acquire approximately 1400 projections over 360°, or about four projections per degree. Each attenuation profile comprises the data obtained from about 1500 detector channels, about 30 channels perdegree in case ofa 50° fan beam.While the patient table is moving continuously through the gantry, a digital radio- graph ("scanogramm" or "localizer", Fig. 6.2) is produced on which the desired sections can be planned. For a CT examination of the spine or the head, the gantry is angled to the optimal orientation (Fig. 6.3). Fig. 6.1 Table movement Fig.6.2 Angulnlion Gantry •o « ~ ...~ Fig.6.3 I Fig.6.4 " Multiple-Row Detector Spiral CT Multiple-row detector CT (MOCn is the latest scanner develop- ment. Rather than one detector row, multiple detector rows are placed oppositethe x-ray tube.Thisshortens theexamination time and improves the temporal resolution, allowing, for instance, the determinationof therate of vascular enhancement. The detector rows along the z-axis opposite the x-ray tube are unequal inwidth,with theouter rows wider than theinner rows to provide better conditions for image reconstruction affer data acquisition(see pages 9-11).
  • 6. Physical and Technical Fundamentals 7 Comparison of ConventionalCT with Spiral CT In conventional CT, a series of equallyspaced images is acquired sequentially through a specific region, e.g. the abdomen or the head (Fig. 7.1).There is a short pause after each section in order toadvance the patient table tothe nextpreset position.Thesection thickness and overlap/intersection gap are selected at Iheoutset. The raw data for each image level is stored separately. The short pause between sections allows the conscious patient to breathe without causing major respiratory artifacts. However,theexaminationmaytakeseveral minutes,depending on the bodyregion and the size of the patient. Proper timingof image acquisition after Lv. contrast media is particularly important for assessing perfusion effects. CT is the technique of choice for acquiring complete 20 axial images of the body without the disadvantages of superimposed bone and / or air as seen in conventional x-ray images. Step-w ise table movement Fig. 7.1 Gantry x-ray tube Imaging volume " --.~,,- Continuous tab le movem ent Fig.7.2 /. X-ray lube ~ Rotat ion Both single-row detectorCT(SOCT) and multiple-row detector CT (MOCl) continuously acquire data of the patient while the examination table moves through the gantry. The x-ray tube describes an apparent helical path around thepatient (Fig. 7.2). If table advance is coordinated with the time required for a 360' rotation (pitch factor), data acquisition is complete and uninter- rupted. This modern technique has greatly improved CT because respiratory artifacts and inconsistencies do notaffect the single dataset asmarkedlyasinconventional CT. Thesingledataset can be used to reconstruct slices of differing thickness or at differing intervals. Even overlapping slices can be reconstructed. Data acquisition fortheabdomen takes only 1-2 minutes: two or three helices,eachabout 10to20seconds,are obtained.Thetime limit is determined by the duration a patient can hold his breath andthenecessarycoolingof thex-raytubes.Image reconstruction takes longer. An assessment of renal function following CM will requirea shortbreak toallowfor CM excretionto occur. One of the advantages of the helical technique is that lesions smallerthantheconventional thicknessofaslice canbedetected. Small liver metastases (7) will be missed if inconsistent depth of Fig.7.3a Conventional CT respiration results in them notbeing included in the section (Fig. 7.3a). The metastases would appear in overlapping reconstruc- tionsfrom thedataset of the helical technique (Fig. 7.3b). - ---- - - ------- -- -- 5 Fig.7.3b Spiral CT
  • 7. 8 Physical and Technical Fundamentals Spatial Resolution The reconstructed images shouldhavea high temporal resolution to separate even small structures from each other. This generally creates no problem along thex- ory-axis of the image since the selected field of view (FOV) typically encompasses 512 x 512 or morepicture elements (pixel).These pixels appear on the monitor as grey values proportionate to their attenuation (Fig. 8.1b). In reality, however, they are not squares but cubes (voxel = volume element) with their length along the body axis defined by the section thickness (Fig. 8.1 a). Fig.8.1a Fig.8.1b ~" .: / '/ r-, 1 I 'I ' i 129'" 122 J.. 50 l- 1 1,3~ 7 7';;::V <, v:r.:::v The imagequalityshouldimprovewithsmaller voxels, but thisonly applies to thespatial resolution since athinnersection lowers the signal-to-noise ratio. Another disadvantage of thinnersections is the inevitable increase in the radiation dose to the patient (see page 175). Nonetheless, smaller voxels with identical measure- ments in all three dimensions (isotropic voxels) offer a crucial Fig.8.2 MPRfrom isotropic voxels Pitch By now,several definitionsexistforthe pitch, which describes the rate of table increment per rotation in millimeter and section thickness. A slowly moving table per rotation generates a tight acquisition spiral (Fig. 8.4a). Increasing the table increment per rotation without changing section thickness or rotation speed creates interscan spaces oftheacquisition spiral (Fig.8.4b). The mostly used definition of the pitch describes the table travel (feed) per gantry rotation, expressed in millimeters, and selected collimation,alsoexpressed in millimeters. advantage: The multiplanar reconstruction (MPR) in coronal, sagittal or other planes displays the reconstructed images free of any step-like contour (Fig. 8.2). Using voxels of unequal dimen- sion (anisotropic voxels) for MPR is burdened by a serrated appearance of the reconstructed images (Fig. 8.3), which, for instance, can make it difficultto exclude afracture (Fig.148.5b). Fig. 8.3 MPR from anisotropic voxels Pitch= 1 Pitch = 2 mn ~Fig. 8.4 a b Tabletravel /rotation Pitch = Collimation
  • 8. Physical and Technical Fundamentals 9 Pitch = Feed! rotation Collimation e.g.: 24mm ! rotation 16x 1.5 mm 24mm = - - = 1 24mm Sincetheunits(mm) inthe numeratoranddenominatorcancelout, the pitch is a dimensionless number. For a while, a so-called volume pitch was stated for multiple-row detector CT scanners, which relates the tablefeed to a single section rather than tothe entire array of sections along the z-axis. For the example given above, this means a volume pitch of 24 mm ! 1.5 mm = 16. However, there seems to be a trend to returning to the original definition ofthepitch. Section Collimation: Resolution Along the Z-Axis The resolution (along the body axis or z-axis) of the images can also be adapted tothe particular clinical question bythechoice of thecollimation.Sections between 5and 8 mm generallyaretotal- ly adequatefor standard examinationsof theabdomen. However, the exact localization of smallfracturefragmentsortheevaluation of subtle pulmonarychanges require thin slices between 0.5 and 2mm.What determines thesection thickness? The term collimation describes how thin or thick the acquired slices can bepreselected along the longitudinalaxisofthepatient _ x-ray tube Collimator Q" "[ >- 1, 1 I'l l" I II I I I I I / I I I J I I , I I I I I I I J I I ', I I I / : : : ~ , ::t:tl:L'I , , , I 1 ICollimator I, ! ! I , II 1 • •z-axis Fig,9.1 Wide sectioncollimation Depending on thewidthof collimator's aperture,theunitswithonly one detector row behindthe patient (single section) can generate sections withawidthof 10 mm,8 mm, 5 mm oreven1 mm.ACT examination obtained withverythin sections is also called a high resolution CT(HRCT) and, if the sections areat thesub-millimeter level, ultra high resolution CT (UHRCn .The UHRCT is used for the The new scanners give the examiner the option to select e craniocaudalextension(z-axis) ofthe region tobe examinedon e topogram as well as the rotationtime, section collimation (thin or thick sections?) and examinationtime (breath-holding intervals?). The software, e.g., "SureView®," calculates the suitable pitch, usually providing valuesbetween 0.5 and 2.0. (= z-axis),The examiner can limit thefan-like x-ray beam emitted from the x-ray tube by a collimator, whereby the collimator's aperture determineswhether the fanpassing throughthecollima- torand collected bythe detectorunits behindthepatient iseither wide(Fig.9.1)ornarrow(Fig.9.2), withthenarrowbeam allowing a better spatial resolution along the z-axis of the patient. The collimator cannot onlybe placed next tothex-ray tube, butalsoin front of the detectors, i.e., "behind" the patient as seen fromthe x-ray source. Collimator ?- _ x-raytube "(" J,t, --.. 1,,1,1...- I "." 1' " . I : I ~ , I .I 1 ,:I: I I I • I : I ~ , ': I , I , , , : I , I , I , I , , ,:, ';; ~::=::t11~~ - , ...! -....1: ! ,1.....-- I Ir c' ,ijB,. . • •z-axrs Fig.9.2Narrow sectioncollimation petrous bone with about 0.5 mm sections to detect delicate fracture lines through the cranial base or auditory ossicles in the tympanic cavity (see pages 46 - 49). For the liver, however, the examination is dominated by the contrast resolution since the question here is the detectability of hepatic metastases (here somewhat thicker sections).
  • 9. 10 Physical and Technical Fundamentals Adaptive Array Design A further development of the single-slice spiral technology is the introduction of the multislice technique, which has not one detector rows but several detector rows stacked perpendicular to the z-axis opposite the x-ray source. This enables the simul- taneous acquisition ofseveral sections. The detector rows are not inevitably equal in width.The adaptive array design consists ofdetectors that increase inwidth from the center to the edge of the detector ring and consequently allows various combinations of thickness and numbers of acquired sections. Adaptive detector design 4-row unit Variable section thickness ++++ ~~ 17mwl I !4 x5.0 mm 4 x2.5 mm 4x 1.0 mm 2 x8.0 mm 2 x0.5 mm ,,,, I I I I I I I I I I I I Resolutionalong the z-axis adaptable toclinical Question / Detectors / , ,, I I I ,/ ,/ , , I I I I ,:> / , , , I I I , 0 / , I I I I, I , U, , , , , I , es , '2 5 i j;j ; " I" 2 5 , u / 5 5 , z-axisco / I , - " " I ' ' ,/ , I I I ', , / , I I , / , " I I I , Fig. 10.1 Detectordesignof a4-row unit, as foundintheSiemensSensation4 Adaptive detector design 6-row unit Variable section thickness Collimator 6 x0.5 mm 6 x 3.0 mm 6 x 2.0 mm 6 x 1.0 mm z-ans ,,,, I I ,, I I 1/ J I II I I I "11' 1111 I I ' " I I I I I / Detectors / " " I /l1I1l1I -, .. I I ,,111111 ' e; / I I I 11/11111 " U, L ---:;~/.~!:;:'~/::'!!:~~~~,.':'~':;:::':JI.'__- - - __:_.i l ' . .~ .~ /3' 2, ill 11 2 3 ....~ / J J I "" " , ' I ... / " / I 1/1 J I 1 ' 1 " .. 11 11 1 1 111 11 Resolutionalong thez-axls adaptabletoclinical Question Fig. 10.2Detector design ofa6-rowunit,asfound inthe Siemens Emotion6
  • 10. Physical and Technical Fundamentals 11 For instance, a 16-slice examination can be performed with 16 thin sectionsof a higher resolution (for theSiemensSensation 16, this means16 x0.75 mm) or with 16 sections oftwicethe thickness. For aniliofemoral CTA (seepage 188), it ispreferabletoacquireaiong volumealong thez-axis inasinglerun,of coursewithaselected wide collimationof 16 x 1.5mm. Adaptive detector design 16-row unit Variable section thickness 16x 1.5 mm x-ray tubeCollimator I I . ' / // / II I I Jl l 1 Detectors ' 1 1 1 11 1 1 1 1 1 ' " . I ( 11/ 1 1111 11 11 _____ /11 I ' ~ _ ~ II. ,,, ,f:/, ~~~" III/ I , ~-----A(-If;i ~A----- /~II I '/J/f/rlll' ~ ~ II ' ,'",1/1111 11 ' > 1111111 1 11l 1l1l 1 ~ o 1 1 / " /," "11111 ' " ~ f-------,1I'••' ." " "," •.••:.' f:----...(1; / , I I • '.' • " ' ' H. I / 1 5 I I f I I I I Q75 1 5 z-axis V~ / / . ' I I I I I I I ' , ' /1 1/ 1 I I IIIJIII I I I I 1 / 1 11 1,'111 1 Resolution along the z-axis adaptable toclinical question Fig.l1.1 Detectordesignof a16-rowunit,as found intheSiemens Sensation 16 The development ofthe CT hardwaredidnot endwith 16slices and fasterdataacquisitioncan already be achieved with32- and 64-row scanners.Thetrend tothinner slices is associatedwith higher patient exposure to radiation,requiring additional and alreadyintroduced measures for exposure reduction(seepages 174-177). measured data table positio n slice Fig. 11.2 Wide (360°) spiral reconstruction algorithm selecting high rnA values, increase the spatial resolution (image sharpness) byreducingslice thickness, and employ pitch toadjust the length of the spiral range as desired, all while reducing the patient's dose! Moreslices can be acquiredwithout increasingthe dose orstressing the x-ray tube. This technique is especially helpful when dataare reformatted to create other 2D views, like sagittal, oblique, coronal, or 3D views (MIP, surface shaded imaging,see pp.8 and 13). ReconstructionAlgorithm Spiral users have an additional advantage: In the spiral image reconstruction process, most of the data pointswere not actually measured in the particular slice being reconstructed (Fig. 11.2). Instead, data are acquired outside this slice (e ) and interpolated withmoreimportance,or "contibutinn",beingattached tothedata located closest to the slice (X). In other words: The data point closest to theslice receives more weight, orcounts more, in the reconstruction of an image at thedesired table position. When both liver and pancreas are included, many users prefer a reduced slice thickness from 10 mm to 3 mm to improve image sharpness. This increases, however, the noise level by approxi- mateiy 80%.Thereforeitwouldbenecessarytoemploy80%more rnA orto lengthen the scan time (this increases the mAs product) to maintain imagequality. This results in an interesting phenomenon. The patient dose (actually given in mGy) is determined by the mAs per rotation divided by thepitch,and the image dose is equal to themAs per rotationwithout considering the pitch. Iffor instance 150mAs per rotationwitha pitchof 1.5 are employed,the patient dose in mGy is linear related to 100mAs, andthe imagedose is related to 150 mAs. Thereforespiral users can improve contrast detectability by
  • 11. 12 Physical and Technical Fundamentals Thedataobtained atthedetectorchannel are passedon, profilefor profile,tothedetectorelectronics aselectricsignalscorresponding totheactual x-ray attenuation.Theseelectric signals are digitized and then transmitted to the image processor. At this stage, the images are reconstructed by means of the "pipeline principle", consisting of preprocessing, convolution, and back projection (Fig.12.1). Preprocessing includes all the corrections taken to prepare the measured scan data for reconstruction, e.q., correction for dark current, dose output, calibration, channel correction, beam hardening,and spacing errors.Thesecorrections are pertormed to further minimize the slight variationsinherently found inthetube anddetector components of theimagingchain. Convolution is basically the use of negative values to correct for smearing inherent to simple back projecfion. II, for instance, a cylindric water phantom is scanned and reconstructed without convolution, the edges of this phantom will be extremely blurry (Fig. 12.2a): What happens whenjusteight attenuation profiles of a small, highly absorbent cylindrical object are superimposed to create an image? Since the same part of the cylinder is measured by two overlapping projections, a star-shaped image is produced instead of what is in reality a cylinder. By introducing negative values justbeyond thepositive portion of theattenuation profiles, theedges of this cylinder can be sharply depicted (Fig, 12.2b). Back projection involves the reassigning of the convolved scan data to a 20 image matrix representing the section of thepatient that is scanned.This is pertormed profile for profile for the entire image reconstructionprocess.The image matrixcan bethought of asanalogoustoachessboard,consisting oftypically 512x512 or 1024 x 1024 picture elements, usually called "pixels". Back projection resuits in an exact density being assigned to each of thesepixels,which are then displayed asalighter ordarker shade of gray Thelighter the shade of gray,the higher thedensityofthe tissue within thepixel (e.g., bone). ~ - - - - - - - - -- - - - - - - - -- - - - - - - - -,, , -+0 -0 -0+0, , Data acquisition system Preprocessing Convolution Back projection : Image display ----------------------------- The Influence of kV When examining anatomic regions withhigher absorption (e.g., CT of thehead,shoulders,thoracic or lumbar spine, pelvis,and larger patients), it isoftenadvisable touse higher kV levelsinaddition to, or instead of, highermA values: when you choose higher kV, you are hardening the x-ray beam.Thusx-rays canpenetrate anatomic regions with higher absorption more easily. As a positive side effect, the lowerenergy components oftheradiation are reduced, whiCh is desirable since low energy x-rays are absorbed by the patient and donot contribute to the image. For imaging of infants or bolustracking, it may beadvisableto utilize kV lower than the standard setting. Tube Current [mAs] The tubecurrent,stated in milliampere-seconds [mAs], also has a significant effect onthe radiation dose deliveredto the patient.A patient with more body Width requires an increase in the tube currentto achieve an adequateimage quality. Thus, morecorpulent patients receive a larger radiationdose than,for instance,chiidren witha markedly smaller body width. Body regions with skeletal structures thatabsorborscatter radia- tion, such as shoulder and pelvts, require a higher tube current than,forinstance, theneck, aslender abdominal torso or thelegs. This relationshiphas been actively applied to radiation protection for some time now (compare with page 177).. Scan Time It is advantageous to select a scan time as short as possible, particularly in abdominal or chest studies where heart movement and peristalsis may degrade imagequality.Other CTinvestigations can also benefit fromlastscan times due todecreased probability of involuntary patient motion. Onthe other hand, it may be neces- sary to selecta longer scan time to provide sufficient dose or to enable more samples for maximal spatial resolution. Some users may also consciously choose longer scan times to lower the mA settingand thus increase the likelihood of longer x-ray tube life. Simple Back Projection vs. Convolution b Fig. 12,1 The pipelineprincipleof image reconstruction Fig. 12.2a Back projection without convolution Fig. 12.2b Back projection with convolution
  • 12. Physical and Technical Fundamentals 13 3D Reconstructions 3ecause the helical or spiral technique acquires a continuous, sirlgle volume dataset for an entire body region, imaging of , actures and blood vessels has Improved markedly, Several c' erent methods of 3Dreconstruction havebecome established: aximal lntensily Projection IP is a mathematical method thatextracts hyperintense voxels , am 20 or 3D datasets [6, 7], These voxels are selected from several different angies through the dataset and then projected as a20image(Fig, 13.1),A3D impression isacquired byaltering the projectionangle insmall steps and then viewing the reconstructed images in quick succession (I.e" in cine mode).This procedure is also usedfor examining contrast-enhanced bloodvessels. Fig. 13.1 Frontal project ion 4I I I r: O rigina l dataset of axial sections Lateral projection Multiplanar Reconstruction This technique makes it possibieto reconstruct coronal and sagittal as well asoblique planes,MPR has becomea valuable tool in the diagnosis offractures and other ortho- pedic indications, For example, conventional axial sections do not always provide enough information about fractures, A good example is the undispiaced hairline frac- ture(* )without cortical discontinuitythat canbe moreeffectivelydemonstrated byMPR {Fig,13.2a), Fig.13,2a 3D Surface Shaded Display Thismethod shows the surface ofan organ ora bone that has been defined in Houns- ~eld units abovea particularthreshold value,The angleofview,aswell asthe location a a hypothetical source of light (from which the computer calculates shadowing) are crucial for obtaining optimal reconstructions.Thefractureofthe distal radius shown in e MPRin Figure 13.2a isseen clearly inthe bone surface inFigure 13.2b. Figs. 13,2a and 13.2b supplied withthekind permission ofJ, Brackins Romero, M, 0" Recklinghausen, Germany) Fig.13.2b * 3D surface shaded displays are also valuable in planning surgery as in the case ofthe traumatic injury to the spinal column seen in Figures 13.3 a,b, and c. Since the angle of view can befreely determined, the thoracic compression fracture( *) and thestateofthe intervertebral foraminacan be examined from several different angles (anterior inFig. 13.3a and lateral inFig. 13.3b),The sagittal MPR in Figure 13.3c determines whether any bonefragments have become dislocated intothespinal canal (compare withmyelography CT onpage147). Fig. 13.3c • Fig. 13,3bFig. 13.3a
  • 13. 14 , Basic Rules of Reading CT Examinations I Rotation Detector x-ray tube II 50 Image level 122 Fig. 14.1 Anatomic Orientation An image on the display is not only a 20 representation of anatomy, it contains information about the mean attenuation of tissue in a matrix consisting of about 512 x 51 2 elements (pixels). A section (Fig. 14.1) has a defined thickness (dS) and is composed of a matrix of cubic or cuboid units (voxels) of identical size. Thistechnical aspect isthe reason forthe partial volumeeffectsexplainedbelow.An imageis usually displayed asif the body were viewed from caudal. Thus the right side ofthepatient is on theleftsideof the image and vice versa (Fig. 14.1). For example, the liver (122) is located in the right half of the body, but appears in the left half of the image. Organs of the left side such as the stomach (129) and the spleen (133) appear on the right half of an image.Anterior aspects of the body,forexamplethe abdominal wall,are represented inthe upper parts of an image, posterior aspects such as thespine (50) are lower. With this system CTimages are moreeasily comparedwith conventional x-ray-images. Partial Volume Effects The radiologist determines the thickness of the image (dS)' 8-10 mm is usually chosen for thoracic or abdominal examina- tions, and2-5 mm for theskull, spine, orbits, or petrosal bones.A structure may therefore be included in the entire thickness of a slice (Fig. 14.2a) orinonlya partof it (Fig. 14.3a).Thegray scale valueofavoxeldependson the meanattenuationofall structures within it. If astructurehas a regularshape within a section, it will appear well defined.This is the case forthe abdominal aorta (89) andtheinferior vena cava (80) shown in Figures 14.2a, b. Partial volume effects occur when structures do not occupy the entire thickness of a slice, for example when a section includes partofavertebral body (50)and part of a disk (50e) the anatomy will bepoorly defined (Figs. 14.3a, b).This isalso trueif an organ tapers within a section as seen in Figures 14.4a, b. This is the reason for the poor definition of the renal poles or the borders of thegallbladder(126)orurinary bladder. Artifacts caused by breathing during image acquisition are dis- cussed onpage 19. anatomic level 80 /' 89 --------- -- -- -- --- ----- -- - --------- -- -- - - - - - -------- 0 V- '-..../ 50 -- -------- - - - - - --- --------- - ---------s::-?9-~--:J--------- 50 ' Fig. 14.2a Fig. 14.3a Fig. 14.4a CT image 00 Fig. 14,2b Fig.14.3b Fig.14.4b
  • 14. Basic Rules of Reading CT Examinations 15 b :: -:_ ::::::::::: --- - - ------- - ---c _ c:or-106 @@ 50 31 31 a 6--0 ~® 50 31 31 tt--- b -----_Q_ - -- - - - - - -- ~@ 50 31 31 c 8980 135 -- -- - --- -- -- ---a Fig. 15.1 Distinguishing Between NodularandTubular Structures is essential to differentiate between possibly enlarqed or affected LNs and vessels or muscles which have been cut in transverse section. This may be extremely difficult in a single image oecause these structures have similar density aiues (gray tones). One should therefore always analyze adjacent cranial and caudal images and compare the structures in question to determine wnetner they arenodularswellings orcontinueas more or less tubular structures (Fig. 15.1): A lymph node (6) will appear in only one or two shoes and cannot be traced in adjacent images compareFigs. 15.1 a, b,andc).Theaorta(89)or :ne inferior cava(80),oramuscle,forexample the Iiopsoas (31), can be traced through a cranio- :audal series of images. " ere is a suspicious nodular swelling in one Cilage. it should becomeanautomatic reaction to 7.mpare adjacent levels to clarify whether it is - ;nply a vessel or muscle in cross-section. This xoceoure will also enable quick identification of :;-" partial volume effects described on the pre- JUs page. area in Fig. 15.2a). If dSis greater than the mass's diameter, for exampleasmall lesion inanunfavorableposition. it can only appear in partial volumeat anyscan level (Fig. 15.2b). -----~~ r ----------------------- ----- -IE)' ______~~1-- .... ..........__.__... ensitometry (Measurement of Density) " • is uncertain, for example, whether fluid found in the pleural ~ is apleural effusionor a hemothorax.a measurementof the :;(lid's density will clarify the differential diagnosis. The same ~: Dlies tofocal lesionsinthe parenchyma of the liver orthekidney. - : 'lever. it is notadvisable to carry out measurements of single cxels(=volumeelement,see Fig, 14.1)since such data areliable ;,: statistical fluctuations which can make the attenuation un- ·o~ble. It is moreaccuratetoposition alarger ' regionof interest" 0)/) consistingofseveral voxelsinafocal lesion,asnucture, oran ,,';)QUnt of fluid.The computer calculatesthe mean density levels :' all voxels andalso provides thestandard deviation (SO). : -e must be particularly careful not to overlook beam-hardening ' utacts (Fig. 19.2) or partial volume effects. If a mass does not e>:end through the entire thickness of a slice, measurements of :~ nsity will include the tissue next to it (Figs. 121.2 and 133.1- 33.3).The density of a mass will be measured correctly only if it : stheentirethicknessofthe slice (dS) (Fig. 15.2).Itisthenmore . "Iy that measurements will include only the mass (hatched Fig. 15.2 a b
  • 15. 16 Basic Rules of Reading CT Examinations Density Levels of Different Types of Tissues Modern equipment has a capacity of 4096 gray tones, which represent differentdensitylevelsin HUs.Thedensityof water was arbitrarily set at 0 HU and that of air at -1000 HU (Table 16.1a). The monitor can display a maximum of 256 gray tones. However, the human eye isable todiscriminate oniy approximately 20.Since thedensitiesof humantissues extendoverafairlynarrow range (a window) ofthe total spectrum(Table 16.1 b),itispossibletoselect awindow setting to represent the density of the tissueof interest. The mean density level of the window should be setascloseas possibletothe densitylevel ofthe tissuetobe examined.Thelung. with its highair content,isbest examinedat alow HU window set- ting (Fig. 17.1c), whereas bones require an adjustment to high levels (Fig. 17.2c). The width of the window influences the contrast oftheimages: the narrower the window,the greater the contrast sincethe20gray tones cover onlyasmall scaleof densi- ties. Table 16.1a Density of all tissues Table 16.1b Density of parenchymal organs andfluids Compact bone Lung D 500HU -900 HU -700~ 200 80 ± 10 70HU 60HU Blood 60HU 70 ", 10 60HU 65 ± 5 Spleen/muscle! Pancreas lymphoma 50HU 50HU 50HU 55 ± 5 4D HU Kidney 45 ", 5 40HU 30HU ExsudaleJeffusiOll 40 ± 10 30HU Suprarenal gland Transudate 20HU 20HU 25HU I 25 ± 5 30 ± 10 18 ~ 2 10HU Liver 17 ± 7 70HU Clotted blood 90HU Water ~ ~ O±5 Thyroid gland 80HU Parll'nChymal orgars 190HU 10Hul 50 ± 40 > 250230HU 30HU Spongy bone FaV connective tissue Air -1000 Fat I -90 ~ 10 700 100 o -100 500 300 -700 -300 -500 1000 -1 00 It is noteworthy that the density levels of almost all soft-tissue organs lie within a narrow range between 10 and 90 HUs (Table 16.1b). The only exception is the lung and, as mentioned above, this requires a special window setting (Figs. 17.1 a-c). With respect to hemorrhages, it should be taken into account that the density level of recently coagulated blood lies about 30HU above thatof freshblood.This density drops again inolder hemorrhages or liquefied thromboses. An exudate with a protein content above 30 gil cannot be readily distinguished from a transudate (protein content below 30gIl) at conventional window settings. Inaddition, the high degree of overlap between the densities of, forexample, lymphomas,spleen,muscles,and pancreasmakes it clear that it is notpossibleto deduce, fromdensity levels alone, whatsubstance or tissue is present. Finally,standarddensity values alsofluctuate betweenindividuals, depending aswellon theamount ofCM inthecirculating blood and in the organs.The latter aspect is of particularimportance forthe examination of the urogenital system, since Lv. CM is rapidly excreted by the kidney, resulting in rising density levels in the parenchyma during the scanning procedure.Thiseffect can beput to use whenjudging kidney function (see Fig. 135.1).
  • 16. Basic Rules of Reading CT Examinations 17 Documentation ot Oiflerent Windows en the images have been acquired, a hard copy is printed for cocumentanon.For example: inorder toexamine the mediastinum anc the soft tissues of the thoracic wall, the window is set such ;nat muscles (13, 14, 20- 26), vessels (89, 90,92...), and fat are :learty represented in shades of gray. The soft-tissue window Fig.17.1 a) iscentered at50HU withawidth ofabout 350HU. The '"suit is a representation of density values from - 125HU (50- 350/2)up to+225HU(50 + 350/2).All tissueswithadensity lower than - 125HU, such as the lung, are represented in black. Those with density levels above +225 appear white and their internal structural features cannot bedifferentiated. If lung parenchyma isto be examined,for examplewhenscanning for nodules, the window center will be lower at about - 200HU. and the window wider (2000HU). Low-density pulmonary struc- tures (96) can be much more clearly differentiated in this so- called lungwindow (Fig.17.1c). -g. 17.1a: Soft tissuewindow • Fig. 17.1b Grayscale Hounsfieldunits (HU) • Fig. 17.1c: Lungwindow - order to achieve maximal contrast between gray and white -~tter inthebrain.it isnecessary toselect aspecial brainwindow :-=cause the density values of gray and white matter differ only : : tly. The brain window must be very narrow (80 to 100HU=> -:11 contrast) andthe center must lieclosetothe mean densityof :"rebral tissue (35HU) to demonstrate these slight differences i'ig.17.2a).Atthissetting it isofcourse impossibletoexamine the ;-ull since all structures hyperdense to 75-85 HU appear . e.Thebone window should therefore havea muchhighercen- i,"' at about +300HU,and asufficient widthofabout 1500 HU. The metastases (7) intheoccipital bone (55d)would only be visible in the appropriate bone window (Fig. 17.2c). but not in the brain window (Fi9. 17.2a). On the other hand. the brain is practically invisible inthe bonewindow; small cerebral metastases would not be detected. One must always be aware of these technical aspects. especially since hard copies are not usually printed at each windowsetting.Theexaminershould review thoroughly the images on the screen in additional windows to avoid missing important pathologic features. Examination of the liver poses special problems and is dealt withseparatelyon page120. - . 17.2a: Brain window Fi9·17.2b Fig. 17.2c: Bonewindow
  • 17. 18 Preparing the Patient I Medical History Prior to any CTexamination, a thorough medical history needs to beobtained whichfocusesonfactorsthat mayrepresent acontra- indication tocontrast media use orindicateanincreased likelihood of a reaction. In patients with suspected renal dysfunction base- line blood urea nitrogen and creatinine levels should be obtained (see below). It is important to note whether prior CT images are available for comparison. Information about prior surgery and radiation therapy in the anatomic region to be examined by CT is also important. Careful consideration of the pertinent radiologic findings on the current study in context with prior results and the patients clinical history allow the radiologistto render a meaning- fuldifferentialdiagnosis. Renal Function With the exception of few (such as stone protocol, fracture assessment) most CT exams require the Lv. administration of iodinated contrast agents for adequate assessmentof the clinical question at hand. Since contrast agents are excreted by the kidneys and may cause changes in renal hemodynamics and tubular toxicity [8], the physician should evaluate the patient's renal function by measuring the plasma creatinine prior to CT. If results suggest renal dysfunction, contrast agents should only be given in a very narrow range of indications [9, 10]. Furthermore, the use of low osmolality iodinated contrast is associated with a lower risk of renal toxicity and should be considered under this circumstance. Adequate patient hydration is also an important adjunct measure.Lastly,administrationof acetylcysteine informof tablets (Mucomyst ®) has shown a renoprotective effect in some studies. Diabetic patients on metformin therapy, an oral anti- hyperglycemic medication,must be given special attention [8, 9J. In these patients, contrast agents may cause lactic acidosis especially when there is coexisting renal dysfunction.Therefore it isrecommended towithholdmetforminon thedayofthe examand the following 48hoursand toreinstate therapyafter repeatserum creatinine measurement hasconfirmed stable renal function.Until recently, incases wherecontrast agentswas absolutelynecessary for a dialysis patient, the CT examination wasscheduled so that dialysisfollowed immediately. Recentreports, however, show that there is no need for urgent dialysis [11]. However, residual renal function in a dialysis patient can suffer from circulating contrast. Otherwise thereseemto be no other complications if thecontrast agentcirculates foradayortwountil thenext dialysis. Creatinine levels can be checked quickly and are inexpensive; Inordertosave time you may wantto havethe resultavailable on the requisition for the exam for immediate review by the radiolo- gist when prescribing the examprotocol. Hyperthyroidism Examining for hyperthyroidism is costly and time-consuming. Nevertheless, the referring physician must exclude hyper- thyroidism if there issuch a clinical suspicion before a CTexarnl- nation involving CONTRAST AGENTS is carried out. Laboratory parameters and possibly scintigraphy may be necessary. Inother cases,the information"noclinical evidence of hyperthyroidism" or even better, the documentation of thyroid function onthe requisi- tion is helpful. Thus, the radiologist can be sure that testing has been done. Notethatreferencevalues(Table 18.1)mayvaryfrom one laboratory to another. Check with your laboratory about commonly used units and normal ranges if these are not included on the report. The risk of thyrotoxicosis caused by the iodinated contrast agents can thus be avoided. If radioiodine therapy for hyperthyroidism orthyroidcancerisplanned,theLv.application of contrast agents could lead to a saturation of the iodine uptake systeminthethyroidgland for several weeks. Radioiodinetherapy may have to bedelayed for sometimeas a result. Table 18.1 Normal thyroid hormone levels TSH: 0.23 - 4.0 pg I ml TT3: 0.8- 1.8 ng/ ml TT4: 45-115ng /ml FT3: 3.5 - 6.0 pg I ml FT4: 8.0- 20.0pg I ml Adverse Reactions to Contrast Media Eversince nonionic contrast agents were introduced atthe end of the 1970s, adverse reactions have only rarely been encountered [12- 14]. Nevertheless, previous reactions are a pointer to an increased risk and should be elicited by taking a careful medical history.Theseverity ofany reactiontocontrast agents inthe past is of great importance. If the patients give a history of itching or hives following prior contrast administration, premedication is advisable. With a history of hypotension or cardiovascular collapse, contrast agents should not be given at all or only after thorough assessment of the clinical indication and appropriate premedication.Asageneral rule,patients whorequirepremedica- tion because of a previous reaction should be kept NPO 6 hours prior tothe examination.This reduces risk ataspiration incase of severe anaphylactic reaction requiring intubation and ventilation (for detailed information see pp. 24-25). Premedication (history of previous adverse reactions to contrast agents) In cases of mild adverse reactions, premedi- cationisaccomplishedwiththree oraldosesofPrednisone, 50mg each, taken 13,8 and 1 hour before the examination. In addition, 50mgof intramuscularantihistamine drug (e.g. Benadryl) isgiven 1 hour before the exam. Side effects such as raised intraocular pressure or urinary retention may occur. In addition, drowsiness may occur for about 8 hours following administration of these drugssodriving must beavoidedforthisperiod.Ifan outpatient CT examination is scheduled, the patient must be informed about potential drowsiness and the possibility of temporarily impaired vision; heor she should be accompanied on the way home. You will find checklists of all key words concerning medical historiesand suggestions for premedication on a practicalcard in the rearfoldout.
  • 18. Preparing the Patient 19 Administrationof Contrast Agents -- " c period of fasting, liquid contrast agentsshould be drunk in =-=. oortions over a period of 30-60 minutes before the CT ~- canon starts so that the entire GIT is completely opacified. - '" cauent should therefore arrive at least 1 hour before anabo :: - -2. CT examination. Inorder tofacilitatethecorrect choice of :.. cast agent, the radiologist must be informed on the request ~: ethersurgery is planned shortly afterCT or whether there 9.1 a Fig. 19.1b is any suspicion of perforation or fistula (see also p. 20). In such cases water-soluble gastrografin would be used instead of a con- trast agent containing barium sulfate.Andfinally, where possible, CTofthe abdomen should be delayed for 3 days afteraconventio- nal barium examination has been carried out (for example:barium Iswallow, barium meal, small bowl enema, barium enema). Usual- ly, the digital projection radiograph (scanogram Fig. 19.1a,scouf . view) would show fhat residual barium inthe GITwould result in major artifacts (Fig. 19.1 b), rendering CT valueless. The sequence of diagnostic proce- dures for patients with abdomi- naldiseasesshouldthereforebe carefullyplanned. -, ing the Patient .r :~'s;andably, patients havedoubts aboutthe harmful erects of - 0 ,-ray burden involved in CT. Worriescan usually be reduced if •• •, ate diagnostic x-ray exposure fa natural background -=: ~;joo. Naturally,the patientmust havethefeelingthat heorshe s :,,~ taken seriously and his or her worries are understood, - ~' ise confidence and trust in the radiologist are threatened. Many patients are relieved to know that they can communicate withtheradiographersinthecontrol room viaanintercom andthat the examination can be interrupted or terminated at any time if thereare unexpected problems. Patients with claustrophobia may feel morecomfortable if they close their eyes during the examina- tion; the close proximityof the gantry isthen less of a problem. In very rarecases, a mildsedative may be helpful. :. iration :c': , starting the examination, the patient should be told of the need for controlled : ' 2.--ling. For conventional CT,the patient is instructed to breathebefore each new image •-::; ., 'on andthen to hold hisorher breathforafew seconds.Inthe helical technique it is . ~: -ssarv to stop breathing for about 20-30 seconds. If the patient cannot comply, • ,--'cgmatic movement will lead to image blur with a marked deterioration in image : 0 iy (Fig.19.2).Inthecaseofneck examinations,swallowing influences thequalityof the - ,,;,$morethan breathing. Fig. 19.2 val of all Metallic Objects ~:_ ally, jewelry of any kind and removable ' ,':2. prostheses must be removed before the .~~: or neck are examined in order to avoid • ' acts. In Figures 19.3a and b, the effects of : : - artifacts (3) are obvious. Only the cervical ~-:,:xal body (50)and the adjacent vessels(86) · = defined; the other structures are unre- :-:;' ·zable. For the same reasonall clothing with - ,,:2. ic hooks, buttons, or zippers should be ~- _ ed before thoracic or abdominal CTs are :" ~0l'm ed. Fig. 19.3a Fig. 19.3b
  • 19. 20 Administration of Contrast Agents I Oral Administrationof Contrast Agents For CT examination of the abdomen and pelvis, it is of major advantage to be ableto readily differentiatethe GITfromadjacent musclesor other organs. This can be accomplished by opacifying the intestinal lumen with an orally administered contrast agent. For example, withoutof contrast agent it is difficult to distinguish between the duodenum (130) and the head of the pancreas (131 inFig. 20.1). Equally, other parts of theintestinal tract (140)wouldalso bevery similar to neighboring structures. After an oral contrast agent, both the duodenum and the pancreas can be well delineated (Fig. 20.2a, b). In orderto acquire images of optimal quality, the patient shouldfast (be NBM) beforedrinking contrast agents. Fig.20.2a Choice of theAppropriale Contrast Agents The best coating of the mucous membranes is achieved with barium sulfate; however, this is not water soluble. This oral con- trast agent should therefore not be used if abdominal surgery involving opening ofthe bowellumen isscheduled,suchasinpar- tial resections or anastomotic sutures, or if there is any risk of injury tothe bowel. Neither shouldbarium sulfatebeused incases of a suspectedfistulaor aGITperforation.Awatersoluble contrast agent, such asgastrografin,is then employed; it can be resorbed bythebody after it spreads intothe abdominal cavity. For an optimal assessment of the stomach walls, plain water is increasingly used as a hypodense contrast agent in combination with intravenous buscopan,which relaxes the muscularis [15, 16]. If the urinary bladder has been removed and an i1ial conduit constructed, the abdomen is examined first with an intravenous contrast agent which is excreted into the urinein theconduit but notwithinthenativeintestines. If necessary,theintestines can be examined ina second scanafter oral contrast agents. Fig. 20.1 Fig.20.2b The TimeFactor To opacify the proximal parts of the GIT, a period of about 20-30 min is sufficient; the patient swallows the contrast agent inseveral small portions. However,if theentirecolon and especial- lytherectum need to beopacified with barium sulfate,a periodof at least 45-60 min is necessary in a fasting patient. Thewater- solublecontrastagent gastrografinspreadssomewhat morerapid- ly. For the peivic organs (bladder, cervix, orovary),100-200 ml of contrast agent may be given rectally to insure that tumors are clearlydifferentiated fromthe lowerintestinal tract. Dosage Toachieve completeopacificationof theentireGIT, 250-300 mlof a barium sulfate suspension are dissolved andthoroughly mixed with water (1000 ml). For adequate contrast of the entire GIT, 10-20 ml of water-soluble gastrografin(in 1000 mlof water) are enough. If only theupper part of the GIT needs to be opacified, 500 ml of either medium are sufficient.
  • 20. Administration of Contrast Agents 21 enous Contrast Agents - - ease in the density of blood vessels not only demarcates --r oener from muscles and organs butalso provides informa- the rate of blood perfusion (contrast agent uptake) in :".- ically altered tissues: disturbances of the blood-brain ebordersof abscesses,ortheinhomogeneous uptake of , _ trast agents intumorlike lesions areonlyafew examples.This : -:-oo11enon is called contrast enhancement, l.e, the density is - :-e2sed bythe contrast agent and thusthe signal intensified. :~J.' nding uponthequestion being asked,an unenhanced(plain) - shouldbeobtainedbeforeinjectingthe contrast agents intra- _ - !y. Vascular grafts, inflammatoryprocessesin bone,aswell ;;; acscesswalls are moreeasilydiagnosed if unennanced images ~- : ~ comparedwithcontrast-enhanced images.Thesame holds - _~ 'or ocal liver lesions examined using conventional CT tech- - : _~. I helical CTisavailable,aseries ofliver images inthe early : -- e of arterial contrast agent perfusion followed bya series in -~ : ase of venous drainage [1 7] would be obtained instead of _ eo-anced images.This procedure makes it possible to detect eo =~ small focal lesions (seep, 120). -reparing thei.v.Line - -: contrast agents are injected intravenously, and the bolus be- :.: - ~ longer and diluted as it passes through the pulmonary - -::_anon.Theinjection should thereforeideally havearapidflow ~'c of2-6 0111 1sec for achieving sufficient density enhancement :' -- e vessels [18]. A Venflon canula with a diameter of at least • : 011011 (20G), or preferably 1.2-1.4 011011 (18G-17G), is used. Checking that the canula is correctly sited in the vessel is very important. Atrial injection ofsterilesaline at a high flow rateinto the veinshould be carriedoutbefore injecting contrast agents.The absence ofsubcutaneousswelling confirms properpositioning;the fact that the vein can accommodate theintendedflow canalso be confirmed. Dosage Dosage is calculated on the basis of b.w. and according to the diagnostic question at hand: examinations of the neck or of an aorticaneurysm(for example inorder toexclude thepresenceofa dissection flap), require higher concentrations than cranial CTs. Whentolerancetocontrast agentsandoptimal vessel contrast are balanced,adosageof,forexample,1.2mllkg b.w.ataconcentra- tion of0.623 glopromidlml ingeneralprovides good results. Inflow Phenomena Thestreaming artifact of enhanced and unenhanced blood results fromashort interval between the startof injectionandtheonset of dataacqulsltlon. Since inflow is usuallyfrom oneside viatheaxil- lary, subclavian, and brachiocephalic veins (91) into the superior venacava (92),thereis an apparent filling defect withinthevena cava(Figs. 21.1 a-21.3b). Knowingabout suchinflow phenomena avoids a false positive diagnosis of venousthrombosis. Using too high concentrations of contrast agents inthis area could result in disturbing artifacts, especially with the helical technique (Fig. 23.3a). More inflow phenomena will be described on the next pages. I
  • 21. 22 Administration of Contrast Agents Application of Contrast Agents Flow phenomena can alsobe seen inthe inferior vena cava(80) atthe level ofthe renal veins(111).Theseveins may containblood which has afairly highconcentration ofcontrast agentsandthis blood mixes with unenhanced blood returningfrom the lower extremitiesand pelvic organs. In the early post-contrast phase the vena cava (80) caudal to the level of the renal veins is hypodense relative to the adjacent aorta(89) asin Figures 22.1 a,b. I Fig.22.1a Fig.22.1b Immediatelyabove the renal veins, thecontents ofthe inferiorvena cava may appear bilaterallyenhanced by the blood fromthekidneys whereas thecentral part is still unenhanced (Fig. 22.2a, b). If the renalveins donotempty intothe cava at the same levelor if a kidney has been removed, a unilateral enhancement may occur (Fig. 22.3a, b). Such differences in density should not be mistaken forthrom- bosis of the inferior cava (ct. Figs. 23.1 and144.1). Fig. 22.2a Fig. 22.3a Fig.22.2b Fig. 22.3b
  • 22. Administration of Contrast Agents 23 Flow Phenomena If wetrace theinferior vena cava cranially towardtherightatrium, additional flow phenomena become apparent asmoreveins empty into it. The cava has spiraling eddies of inhomogeneous density (+ in Fig. 23.1) caused by mixing of the blood as described on the previous page. Moments later such inhomogeneities are no longer evident inthelumen (80) anddensityleveis are identicai to those inthe aorta (89) (Fig,23.2a, b). 8ytheway, didyounoticethe artherosclerotic plaqueinthedorsal wallof theaorta (174 in89inFig.22.3a)?Thisplaqueappearsalso in Figure 23.2a.The patient had well-developedosteophytes (64) on thevertebral bodies (50). Fig. 23.2a Details Specific for Spiral GT If data acquisition begins immediately after contrast agents have beenadministered,theconcentrationof contrast agentsinthe axil- lary, subclavian, and brachiocephalic (91) veins might be high enough tocause majorartifacts(3)inthethoracic inlet. Inimages such as in Figure 23.3, it is not possible to assess the lung or Fig. 23.3a Fig.23.1 Fig.23.2b neighboring axillary tissues.An SCTof thethoraxshould therefore beobtainedfrom caudal tocranial.Inthat way structures nearthe diaphragm are imaged first, and when cranial parts are scanned the contrast agents will have been spread after having passedthe pulmonary circulation. This trick helps avoid the artifacts (3) shown in Figure 23.3. Fig. 23.3b I
  • 23. 24 Administration of Contrast Agents I Adverse Reactions to Contrast Agents Adverse reactions are rare; most appear during the first 30 minutes, 70% of cases occur within the first 5 minutes after contrast injection [13]. Only high-risk patients need to be super- vised for morethan30minutes. Since suchpatientscanusuallybe recognized by taking a thorough medical history, they can be premedicated accordingiy (see p. 14). If, despiteprecautions, erythema develops afteran l.v, injection of contrast agents,perhapsalsohives,itching,nausea or vomiting,or in extreme cases even hypotension or circulatory shock or short- ness ofbreath,the countermeasuresiistedbelow must beinitiated immediately. Remember that i.v. injection of Hl - and H2-receptor antagonists does not alleviate symptoms immediately.There is a period of latency, and these antagonists are therefore primarily eftective in preventing the symptoms from worsening. Serious incidents(pulmonaryedema,circulatoryshock,convulsions)occur very rarely with the new contrast media; they require immediate intensive care. Be sure to document any incident in your report. Radiologists pertorming future examinations will be forewarned about the patient's sensitivitytocontrast agents. Urticaria Management of Acute Reactions in Adults Bronchospasm 1 Discontinue injection if notcompleted 2 No treatment needed in most cases 3 Give H,-receptorblocker; Diphenhydramine(Benadryl®) PO/ 1M/ IV 25-50mg if severe orwidely disseminated; Alpha agonist(arteriolar and venousconstriction) Epinephrine SC (1;1,000)0.1-0.3 ml = 0.1 -0.3 mg (if nocardiac contraindications) Facial or Laryngeal Edema 1 Give alpha agonist(arteriolar andvenousconstriction); Ephinephrine SC or 1M (1 ;1,000) 0.1-0.3 ml(= 0.1 -0.3 mg) or, if hypotension evident, Epinephrine (1;10,000) slowlyIV1 ml (= 0.1mg) Repeatas needed uptoa maximum of 1mg 2 Give O26-10iiters/ min (via mask) Ifnotresponsivetotherapyorif there is obvious acute laryngealedema, seek appropriateassistance (e.q., cardiopulmonary arrest responseteam) 1 Give O26-10liters/ min(via mask) Monitor; electrocardiogram, O2saturation (pulse oximeter), and blood pressure. 2 Givebeta-agonist inhalers: bronchiolardilators, suchas metaproterenol (Alupent®j, terbutaline(Brethaire®), or albuterol (proventil®,Ventolin®j 2-3 pufts; repeat prn. If unresponsive toinhalers, us SC, 1M or IV epinephrine 3 Give epinephrine SCor1M(1:1 ,000)0.1-0.3 ml (= 0.1 -0.3mg) or, if hypotension evident, Epinephrine(1:10,000) slowly IV1 ml(= 0.1mg) Repeat asneeded uptoa maximum of 1 mg Alternatively: Give aminophylline: 6 mg I kgIV in D5Wover 10-20 minutes(loading dose),then 0.4-1 mg I kgI hr, as needed (caution: hypotension) Call for assistance (e.q., cardiopulmonary arrest responseteam) forseverebronchospasm orif O2saturation < 88%persists. Hypotension with Tachycardia 1 Legs elevated 60° ormore(preferred) orTrendelenburg position 2 Monitor:electrocardiogram, pulse oximeter, blood pressure 3 Give O26-10 litersI min (via mask) 4 Rapid intravenous administrationof largevolumes of isotonic Ringer's lactate or normal saline. Ifpoorly responsive: Epinephrine(1:10,000)slowly IV1 ml (= 0.1 mg) (if nocardiac contraindications) Repeat as needed up to a maximum of 1 mg if still poorly responsive seekappropriateassistance (e.q.,cardiopulmonaryarrest response team)
  • 24. Administration of Contrast Agents Management of Acute Reactions in Adults 25 Hypotensionwith Bradycardia (Vagal Reaction) 1 Monitor vital signs 2 Legs elevated 60' ormore(preferred) orTrendelenburg position 3 Secureairway:giveO26-10liters / min (viamask) 4 SecureIV access: rapidfluidreplacement with Ringer's lactate ornormal saline 5 Give atropine 0.6mg IVslowlyif patient does not respond quickly tosteps 2-4 6 Repeat atropine up toatotal doseof0.04 mg / kg (2-3 mg) inadult 7 Ensurecomplete resolution of hypotension andbradycardia priortoctschanqe Hypertension, Severe 1 Give O26-10 liters / min (viamask) 2 Monitorelectrocardiogram, pulseoximeter, blood pressure 3 Give nitroglycerine0.4-mg tablet, sublingual (may repeatx3) ortopical 2%ointment,apply 1 in.strip 4 Transfer to intensive care unit oremergency department 5 Forpheochromocytoma - phentolamine5 mg IV Iodine-provoked Hyperthyroidism Fortunately, this complication is very rare with modern non-ionic iodinated contrast agents. In patients with a medical history of yperthyroidism consider blocking the thyroid gland before l.v application of contrast agents by administering a thyrostatic drug such as sodium perchlorate. Alternatively, carbimazole can be ed to block hormone synthesis. Both treatments take approxi- ately 1 week to become fully effective. Effectiveness must be :isterminedbyrepeatingthe thyroidfunction tests. Seizures orConvulsions 1 Give O26-10liters / min (viamask) 2 Consider diazepam (ValiUm®) 5 mg (or more, as appropriate) ormidazolam (Versed®) 0.5-1 mgIV 3 If longer effect needed, obtain consultation; considerphenytoin (Dilantin®) infusion - 15-18mg/ kg at 50mg/ min 4 Careful monitoring ofvitalsignsrequired, particularly of p02 because ofriskto respiratorydepressionwith benzodiazepine administration 5 Consider using cardiopulmonary arrest responseteam for intubation if needed Pulmonary Edema 1 Elevate torso; rotating tourniquets (venous compression) 2 Give O26-10 liters/ min (viamask) 3 Givediuretics- furosemide (LaSix®) 20-40 mg IV, slowpush 4 Consider giving morphine(1 -3 mgIV) 5 Transfer to intensivecare unit oremergency department 6 Corticosteroids optional In patients with unrecognizedsubclinical hyperthyroidism,theuse of iodine containing contrast agents can unmaskthe disease or even induce thyrotoxicosis.The symptoms may include diarrhea, muscle weakness as well asfever, sweating,dehydration,anxiety and restlessness, or even tachyarrhythmia. The main problem is the long periodof latency beforethethyrotoxicosis crisisbecomes manifest. I · Some patients with hyperthyroidism orother thyroid disease (especially those who live in iodine-deficient areas) may develop iodine- orovoked delayed hyperthyroidism.This effect mayappear 4 to6 weeks after theintravascularcontrastadministrationin some ofthese catients.It canoccur after theadministration of either ionic, high-osmolality or nonionic, low-osmolalitycontrast.It is usuallysett-limt- :sd. "atients withcarcinoma ofthethyroid deserve special consideration beforethe intravascularor oral administrationofiodinatedcontrast , edia (ionic or nonionic). Uptake of 1-131 in the thyroid becomes moderately decreased to about 50% at one week after iodinated - trast injection but seemsto become normal within a few weeks.Therefore, if systemic radioactive iodine therapy is part of planned -satmen, a pretherapy diagnostic study of the patient using iodinated radiographic contrast medium (intravascular or oral) may be - traindicated; consultation withthe ordering clinician prior tocontrast administration inthese patients isrecommended."
  • 25. 26 Cranial CT . Manycranial CT(CCT) examinationscanbeperformedwithoutinjectionof contrast medium: For instance,thedifferential diagnosis (DO) of cerebral bleeding versus infarction in patient with sudden onsetof neurologic deficits does not require the administrationof contrast medium. However, intravenous injection of contrast medium is necessary to detect an impaired blood-brain barrier (BBB) as found in tumors, metastases or inflammations. I Selection of the ImagePlane The desired image planes parallel to the orbitomeatal line are selected on the sagittal localizer image (topogram) (Fig.26.1).This isa readily reproducible line drawnfrom the supraorbital ridge to the external auditory meatus, allowing reliable comparison with follow-up CT examinations. The posterior fossa is scanned in thin sections (2-3 mm) to minimize beam hardening artifacts, and the supratentorial brain above the pyramids in thickersections (5 mm). The images are displayed as seen from below (caudal view) and consequently are laterally reversed, i.e., the left lateral ventricle is on the right and vice versa. Only CTs obtainedfor neurosurgical planningareoftendisplayedas seen from above (right = right) since thiscranial view correspondstotheneurosurgical approach forcranial trepanation. Fig. 26.1 Systematic Interpretation Each examiner is free to find a preferred sequence for reviewing the images. This means that the examiner can choose between several acceptable approachesand is not restricted toa "oneand only" strategy. However, staying with a consistent arrangement of theimages tobeinterpretedhastheadvantagethat fewerfindings areoverlooked, especiallybythenovice.The checklist belowjust contains recommendations that can serve as good guideline for thenovice. First,thesize of theventricles andextracerebral CSFspaceshasto be evaluated to exclude a life threatening space-occupying process rightaway. Hereby,the patient'sagehasto be considered because of age-related widening of the CSFspaces.Any blurring of the grey-white matter junction as manifestation of cerebral edema should be lookedfor(see below). If a pathologicchange is suspected,the adjacent sections should beinspectedtoavoid any misinterpretationduetoa partial volumeeffect(see Fig. 29.1and Fig.52.2). Always usethe legendson thefrontcover flapforthischapter.The listednumbersapplytoall headandneckimages.Thesubsequent pages provide you with a survey of the normal anatomy, followed by normal variantsand themost frequent pathologic findings. Checklist for Reading Cranial CT Age?(becauseofthe age-related width ofthe CSFspaces I cerebral atrophy; see page 50) MedicalHistorv: • Risk factors? (Trauma -+ Chance ofintracranial bleeding) (Hypertension, diabetes, nicotine -+ Vascular stenoses, infarcts) Signsofspace-occupyinglesion: • Normalconfiguration of the-tthventricle? (posterior tothepons,see pages 28/ 29) • Normalconfiguration of the 3rdventricle? (interthalamic, narrow/ slit-like,seepage30) • Normal symmetryof the lateralventricles?(concavelateral border of theanterior horn and central ventricular region?) • Midlineshift?(signof largespace-occupying process) • Preservedbasalcistern?(e.g., quadrigeminal cistern: smiliefaceI bat manfigure, see Fig.30.1) • Cortex +-~ whitematter demarcation OK?(blurred interface = signof edema) • Widthof theextracerebral CSFOK for patient'sage? (Sylvianfissure, refer to p.50) Focal lesions: • Unenhanced:DO physiologiccalcification(choroidplexus, pineal gland/ partial volume; refer toFigures 29.3 and 30.2) versusgenuinehyperdensebleeding (DOtypes ofbleeding,seepages 54-57) • Contrast enhanced: Sign ofimpaired BBB? (caused bytumors, metastases, inflammations, ...) Osseous lesions: • Check cranial vault and baseinbonewindow forosteolytic lesionsI osseousinfiltration • Intrauma patient: Ruleout fractures(especially cranial base, midfacial bones- DO sutures)
  • 26. Cranial CT Normal Anatomy 27 The scan usually begins at the base of the skull and continues upward. Since the hardcopies are orientedsuch that the sections are viewed from caudal, all structures appear as if they were lelUrightreversed(see p. t 4). The small topogram shows you the corresponding posi- tion of each image. You shouldfirstcheckfor any swellings in the soft tissues whichmayindicatetrauma to the head. Always examine the condition of the basilar artery (90) in scans close to the base of the skull andthe brainstem (107).The viewis often limited by streaks of artifacts (3) radiating from thetemporal bones (55b). When examining trauma patients. remember to use the bone window to inspect the sphenoid bone (60). the zygomatic bone(56),and the calvaria (55) for fractures. In the caudal slices you can recognize basai parts of the temporal lobe (110) and the cerebellum (104). Orbital structuresare usually viewed in another scanning plane (see pp. 33·40). In Figure27.1-3 we see only a partialslice ofthe upper parts of the globe (150),the extra- ocular muscles (47), and the oifactory bulb (142). Fig. 27.1b Fig. 27.2b Fig. 27.3b - , . 27.2a - , 27.1a - e- 27.3a
  • 27. 28 Cranial CT . Normal Anatomy Fig. 28.1b Fig.28.2b Fig.28.1a Fig. 28.2a As the series of slices con- tinuesdorsally.thecristagalli (1 62) and the basal parts of thefrontal lobe (111) appear. The pons/medulla (107) are often obscured by artifacts (3). The pituitary gland (146) and stalk (147) are seen between the upper border of the sphenoid sinus (73) and the clinoid process (163). Of the dural sinuses, the sig- moid sinus (103) can be readily identified. The basilar artery (90) and the superior cerebellar arlery (95a) lie anterior to the pons (107). The cerebellar tentorium (131).which liesdorsal tothe middlecerebral artery (91 b), shouldn't bemistaken forthe posterior cerebral artery (91 c) at the level depicted in Figure 29.1 a on the next page. The inferior (temporal) horns ofthe lateral ventricles (133) as well as the 4th ventricle (135)can be identi- fied in Figure 28.3. Fluid occurring in the normally air-filled mastoid cells(62) or in the frontal sinus (76) may indicate a fracture (blood) or an infection(effusion). A small portion of the roof of the orbit (*) can still beseen in Figure28.3. I Fig. 28.3a Fig.28.3b
  • 28. Cranial CT Normal Anatomy 29 In Figures 28.3a and 29.1 a partial volume effects of the orbit (*) or thepetrosal bone I(**) might also be misinter- preted as fresh hemorrhages in the frontal (111) or the temporallobe (110). The cortex nextto thefrontal bone (55a) often appears hyperdense compared to adjacent brain parenchyma, but this is an artifact due to beam-hardening effects of bone. Note that the choroid plexus (1 23) in the lateral ventricle (133) is enhanced after Lv. infusionof eM. Even in plain scans it may appear hyperdense becauseofcalci- fications. You will soon have recog- nizedthat theeeTimageson thesepagesweretaken after l.v. administration of eM: the vessels of the circle of Willis are markedly enhanced. The branches (94) of the middle cerebral artery (91 b) are visible in the Sylvian fissure (1 27). Even the pericallosal artery (93). a continuation of the anterior cerebral artery (91a), can be clearly identi- fied. Nevertheless, it is often difficult to distinguish be- tweenthe opticchiasm(145) and the pituitary stalk (147) because these structures havesimilar densities.
  • 29. 30 Cranial CT Normal Anatomy Fig. 30.1 b Fig.30.2b Fig.30.3b Fig.30.1a Fig.30.2a Fig.30.3a In addition to the above- mentioned cerebral arteries (93, 94), the falx cerebri (130) is a hyperdense struc- ture. InFigure 30.2a youcan see the extension of the hyperdense choroid plexus (123) through the foramen of Monro, which connects the lateral ventricles (133) with the 3rd ventricle(134).Check whether the contours of the lateral ventricles aresymme- tric. A midline shift could be an indirect sign of edema. Calcifications in the pineal (148) gland and the choroid plexus (123) are a common finding in adults, and are generally without any patho- logic significance. Due to partial volume effects, the upper parts of the tentorium (131) often appear without clear margins so that it be- comes difficult to demarcate the cerebellar vermis (105) and hemispheres (104) from theoccipital lobe(112). It is particularly important to carefully inspect the internal capsule (1 21) and the basal ganglia: caudate nucleus (117), putamen (118), and globus pallidus (119) aswell as the thalamus (120). Consult the number codes in the front foldout for the other structures not specifically mentioned on these pages. I
  • 30. Cranial CT Normal Anatomy 31 The position of the patient's headisnot always as straight asinour example.Even small inclinations may lead to remarkably asymmetric pictures of the ventricular system, though in reality it is perfectly normal. You may see only a partial slice of the convex contoursof thelateral ventricles (1 33). This could give you the impression that they are not well defined (Fig. 31.1a). The phenomenon must not be confused with brain edema: as long as the sulci (external SAS) are not effaced, but configured regularly, the presence of edema is rather improbable. For evaluating the width of the SAS, the patient's age is an important factor. Compare the images on pages 50 and 52 in this context. The para- ventricular and supra- ventricular white matter (143) must be checked for poorly circumscribed hypo- dense regions of edema due to cerebral infarction. As residues of older infarc- tions, cystic lesions may develop. In late stages they are well defined and show the same density as CSF (see p. 58). I
  • 31. 32 Cranial CT Normal Anatomy Inthe uppersections(Figs.32.1-32.3) calcifications inthecerebral falx(130) oftenappear.Youshould differentiatethis kind oflesion,which has noclinical significance,from calcified meningioma.The pre- sence of CSF-filled sulci (132) inadultsisanimportant findingwithwhichtoexclude brainedema.After athoroughevaluationof thecerebral soft-tissue window,acarefulinspection of thebonewindowshould follow. Continue to check for bone metastases orfracture lines. Only now is your evaluation of acrani- al CT reallycomplete. Test yourself! Exercise 1: Note from memory asystematic order for theevaluationofcranial CTs. Ifyou have difficulties,returnto the checklist on page 26. Note: • I • • • • • • • • Fig, 32.1a Fig. 32.2a Fig. 32.3a Fig,32.1 b Fig, 32,2b Fig. 32.3b On thefollowing pages theatlas of normal anatomy continues withscansof the orbits(axial),theface (coronal), and the petrosal bones (axialand coronal).After these you will find themost common anatomic variations,typical phenomenacaused bypartial volume effects and the most important intracranial pathologicchanges on pages 50to60.
  • 32. Cranial CT Normal Anatomy of the Orbit (Axial) 33 "ig.33.1a =- . 33.1b - e - 33.1 c The face and the orbits are usually studied in thinslices (2 mm) using 2-mm collimation steps. The orientation of the scanning plane is comparable to that for CCTs(see p. 26). In the sagittal topogramthelineof referencelies paralleltothefloor of theorbit at anangle of about 15°to horizontal (Fig. 33.2). The printouts are usually presented in theview from caudal: all structures on the right side of the body appear on theleft.and vice versa. Fig.33.2 Alterations in the softstructures of the orbits and the paranasal sinuses can be readily evaluated in the soft-tissuewindow(Fig. 33.1b).Forthedetection ofatumor-related arrosionof bone or a fracture.thebone window should also bechecked (Fig. 33.1 a). The following pages therefore present each scan level in both windows.The accompanying drawing (Fig. 33.1 c) referstoboth. The number codes forall drawings arefound inthelegend inthe frontfoldout. On thelower slices of theorbits you will see parts of the maxil- lary sinus (75).thenasal cavity(77) with theconchae (166).the sphenoid sinus (73). and the mastoid cells (62) as air-filled spaces. Ifthere is fluid or asoft-tissue mass.this may indicatea fracture, an infection. or a tumor of the paranasal sinuses. For examples ofsuch diseases.see pages 58to 61 . Twoparts of the mandible appear on the left side: in addition to thecoronoid process (58).thetemporomandibular joint with the head ofthe mandible(58a) isseenonthe left.The carotidartery. however, is often difficult to discern in the carotid canal (64), whether in thesoft-tissue orbone window. In the petrous part of the temporal bone (55b), the tympanic cavity (66) and the vestibular system are visible. For a more detailed evaluation of the semicircular canals and the cochlea. images obtained with the petrous bone technique are more appropriate (pp. 44-47). CM was infused intravenously before the examination of the orbits. The branches of both the facial and angular vessels(89) as well asthebasilar artery(90)there- fore appear markedly hyperdense in the soft-tissue window (Fig. 33.1b).
  • 33. 34 Cranial CT Normal Anatomy of the Orbit (Axial) It is not always possibleto achieve a precise sagittal position ofthe head. Even aslighttilt (Fig. 34.1) will makethetemporal lobe (110) appear on one side. whereas on theother side themastoid cells (62) can beseen. Fig. 34.1b Fig. 34.2b Fig. 34.2aFig. 34.1a Fig. 34.1c Fig. 34.2c
  • 34. Cranial CT Normal Anatomy of the Orbit (Axial) 35 Fig. 35.2b Fig. 35.2aI g. 35.1a Fig. 35.1b -~ , perience shows, it is difficult to determine the course of the internal carotid artery (85a) through the base of the skull and to :e- :;rcatethe pterygopalatinefossa (79), through which,amongother structures, thegreater palatine nerve and the nasal branches of - ~ ::erygopalatineganglion (fromCNVand CN VII) pass. Fig. 35.2c
  • 35. 36 Cranial CT Normal Anatomy of the Orbit (Axial) On thefloor of theorbit,theshort inferior obliquemuscle(47f) oftenseems poorly delineatedfrom the lower lid.This is duetothesimilar densities of thesestructures.Directly in front of theclinoid process/dorsumsellae (163) lies the pituitary gland (146) in its fossa,which is laterally bordered by thecarotid siphon (85a). Fig. 36.1a Fig. 36,lb Fig. 36.1c Fig, 36.2a Fig,36,2b ~ 1o-_~_"lM1I .s Fig, 36.2c
  • 36. Cranial CT Normal Anatomy of the Orbit (Axial) 37 all inclinationsofthe head cause slightlyasymmetricviews ofthe globe(150) and the extraocularmuscles (47).The medial wall of e nasolacrimal duct (1 52) is often so thin that it cannot be differentiated.At firstsightthe appearance of theclinoid process (163), etweenthe pituitary stalk (147)andthe carotid siphon (85a) on the left side only, may be confusing in Figure 37.2b. Fig.37.2a19.37.1a Fig. 37.1b Fig. 37.1c
  • 37. 38 Cranial CT Normal Anatomy of the Orbit (Axial) After intravenous injection ofeM,the branches ofthemiddle cerebral artery (91 b) originating fromthe internal carotid artery (85a) are readily disijnguished.Thegray shadeoftheopticnerves(78) as they pass through the chiasm(145) tothe optic tracts(144), however,isverysimilarto that of thesurrounding CSF(132).Youshouldalways check onthesymmetry of theextraocularmuscles(47) intheretrobulbar fattytissue(2). Fig. 38.1 a Fig. 38.1b Fig. 38.1c Fig. 38.2a Fig. 38.2b Fig. 38.2c
  • 38. Cranial CT Normal Anatomy of the Orbit (Axial) 39 -~ ; obe(150) youcan now see the hyperdenselens(150a).Noticetheobliquecourseoftheophthalmic artery(* ) crossing theoptic - , 8) in the retrobulbar fatty tissue(2). Figure 39.2b shows a slight swelling (7) ofthe rightlacrimal gland (151) compared to the - " seeFig. 40.1 b). Fig. 39.2c Fig. 39.2b Fig. 39.2a
  • 39. 40 Cranial CT Normal Anatomy of the Orbit (Axial) Figure 40.1 bclarifiesthatinthis casethereis indeed an inflammationortumor-likethickening (7) intheright lacrimal gland (1 51).The superior rectusmuscle (47a) appears at the roof of the orbit and immediately next to it lies the levator palpebrae muscle (46). Due to similardensities,these muscles arenot easily differentiated. Fig.40.1a Fig.40.1b Fig.40.2a Fig.40.1 c Fig.40.2c Theaxial views oftheorbits andthefaceend herewiththeappearance ofthefrontal sinus(76). Examples ofpathologic changes ofthe orbits orfractures of facial bones are found on pages 61 to 63.
  • 40. Cranial CT Normal Anatomy of the Facial Skeleton (Coronal) -- - oossfbilitiesofanglingtheCf gantry arelimited.Inordertoacquire scans inthe coronal - ..e patient must therefore be positioned asshown inthe planning topogram to the ; - (Fig. 41.1). The patient should be in a prone position, with the head completely . - -cell.When examining trauma patients, any lesions of the bones or ligaments of the - ca spine must always be excluded by conventional radiography priorto eeT. ~- ;~ viewedfromanterior:theanatomic structures on thepatient's rightsideappear on : -=~ inthe imagesand conversely,asif theexaminer werefacing thepatient. 00- 100 ing for fractures, images are usually acquired in the thin-slice mode (slice and -~won, each2 mm) and viewed on bone windows. Evenfinefracture lines can then be _~ . A suspected fracture of the zygomatic arch may require additional scans in the - : ane(see p. 34). In Figure 41 .2a the inferior alveolar canal (*l inthe mandible (58) : -- ~ foramen rotundum (**l in the sphenoid bone (60) are clearly visible. As for the Abb.41.1 schapter,thecode numbersforthe drawingsare explained inthe legend inthefront - t 41 Fig. 41 .2b Fig. 41.3b
  • 41. 42 Cranial CT Normal Anatomy of the Facial Skeleton (Coronal) Fig. 42.1a Fig. 42.2a Fig. 42.3a Fig. 42.1b Fig.42.2b Fig. 42.3b
  • 42. - !3.2a Fig. 43.1b Fig. 43.2b Fig. 43.3b 43
  • 43. 44 Cranial CT Normal Anatomy of the Facial Skeleton (Coronal), Fig.44.1b Fig. 44.2b Fig. 44.3b The insertions of the extraocular muscles on the globe (150) can also be clearly identified (47 a-I) inthe anterior slices.The short inferior oblique muscle(471),however,isollen seen only incoronal scanning planes,becauseit doesnotpass withthe othersmuscles through the retrobulbar fatty connective tissue.Thesameproblem occurs in axial scans of the face (compare with Fig. 36.2b and Fig. 36.2c). If a case of chronic sinusitis is suspected, it is very important to check whether thesemilunar hiatus isopen.It representsthemain channel for discharging secretions of the paranasal sinuses. In Figure 60.3 you will find examples of anatomic variations which narrow this channel andmay promote chronicsinusitis. Sometimes one discovers a congenitallyreduced pneumatization of a frontal sinus (76) or an asymmetric arrangement of other paranasal sinuses without any pathologic consequences. You should always make sure that all paranasal sinuses are filled exclusively withair. thatthey are well defined and present noair- fluid levels. Hemorrhage into the paranasalsinuses orthe detec- tion of intracranial bubblesof airmust beinterpretedas an indirect sign of a fracture - you will find examples of such fractures on page63.
  • 44. Test Yourself! 45 Without doubt, you will improve your understanding ofthe subject if you tackle the gaps in your knowledge instead of skipping problemsor lookingattheanswersattheend of the book.Reterto the relevant pages only if you getstuck. : ~ - epreviouspages youhave learnedabout thenormal anatomy :-' =-;; brain,theorbits, andthe face.It may besome timeago that __ 5, died the technical basics of CT and about adequate pre- : - anon of the patient. Before going on with the anatomyof the :.=- J()(al bone, it would be good to check on and refresh your : edge of the last chapters. All exercises are numbered : :-.;.~utively, beginning withthefirstone on page32. ~ Writedown from memory thetypical windowparameters for images ofthe lungs, bones, and soft tissues. Note precisely - ;;width andcenter ofeachwindow in HUand give reasons for the differences. If you havedifficulties answering this question,go back - :.:;es 16/17to refreshyourmemory. _ ; I pleura window: Center Width Gray scale range HUto HU : : -;;window: HU to HU : :-:<ssuewindow: HU to HU II a) b) c) How would you differentiate between long structures such as vessels, nerves, or certain muscles and nodularstructures • phnodes or tumors? (You will findthe answeron p. 15.) In which vessels might you find turbulence phenomena, caused by the CM injection, that must not be mistaken for a ~..i i Ii you don't remember,check backtopp. 21-23.) What aspects should you always oe are referring your patients to a CT -,a . n which probably requires the l.v, - .s:' of CM?The same applies if you consider =c ~ ; someoneto avenogram/angiogram oran _ ::- procedures are carried outwith nonionic ::--oining iodine). MRI examinations, however, = -"";.ed out with gadolinium as the CM. (The =: ;0 questions 3 and 4 can befound on pp. _,, : -9.) - •," Whichtwotypes of oral CM doyou know?What specific aspects must you consider when administering this kind of CM .;;- : ·ng onthe clinical problem?Arethereany consequences foryourlist? :'" _, (name) Indication Special schedule
  • 45. 46 Cranial CT Normal Anatomy of the Temporal Bone (Coronal) In order to evaluate the organ of hearing and balance, the petrosal bone is usually examined in thin slices without overlap (2/2).To ensure optimal resolu- tion,thewholeskull isnotimaged,justtherequiredpartofthepetrosalbone.The two petrosal bones (55b) are therefore enlarged and imaged separately. Only then is it possible to differentiate small structures like the ossicles (61a-i:), cochlea (68),andthesemicircular canals(70a-i:) . Thetopogram (Fig. 46.1) indicates the coronal imaging plane.The patient must • be placed in a prone position with his or her head hyperextended. Note the pneumatization of the mastoid cells (62) and the usually thinwalls of the outer auditory canal (63b). Inflammation ofthese air-filled sinuses leadsto characte- ristic effusion and swelling ofthe mucous membranes (see Fig. 60.2a). Fig. 46.1 Fig. 46.2a Fig. 46.2b 55b ~ 5.0a...... Fig. 46.3a Fig. 46.3b
  • 46. Cranial CT Normal Anatomy of the Temporal Bone (Coronal) 47 Fig. 47.1b Fig. 47.2b- :. ~7 . 2a - _ . ~ 7. 3a Fig. 47.3b
  • 47. 48 Cranial CT Normal Anatomy of the Temporal Bone (Axial) Test Yourself! Exercise NO.7: Analogousto coronalimages, axial images are obtained withthinslices without overlap, i.e.,2 mmthicknessand 2 mm increment and viewed on bone windows. The cerebellar hemispheres (104),thetemporal lobe (110),andthesofttissues of thegaleaare therefore barely identifiable.Apart from the ossicles (61 a--i:) and the semicircular canals (70a-c) , the internal carotid artery (64), the cochlea (68),andtheinternal (63a)and external auditory canals (63b) are visualized.The funnel-shaped depression in the posterior rim of the petrosal bone (Fig, 48,2a) represents the opening of the perilymphatic duct (** = aqueduct of the , cochlea) intothesubarachnoidspace. InFigure 49.1 a note thelocalizationofthe geniculate ganglion of the facial nerve (*) ventral to the facial canal.The topo- gram (Fig. 48.1) shows an axial plane ofsection, obtained withthepatient lying supine. Think about differential diagnoses involving effusioninthemiddle ear (66), theouter auditory canal,or themastoid cells(62) and compare your results with the cases shown on pages 60and 62to 63. Fig. 48.1 Fig. 48.2a Fig. 48.3a ~ ~ Fig. 48.2b 146 00 Fig.48.3b
  • 49. 50 Cranial CT Normal Variants Do you remember the systematic sequence forevaluating eeT scans?If not, please go back tothe checklist on page 26ortoyour own notes on page 32. After evaluating thesoft tissuesit isessential toexamine the inner andoutereSFspaces.Thewidthofthe ventricles andthesurface SAS increasescontinuouslywith age. Fig.50.1a Fig.50.1b Since thebrainofachild (Fig. 50.1a) fillsthe cranium(55),theouter subarachnoidspace isscarcelyvisible,but withincreasing age the sulci enlarge (Fig. 50.2a) and eSF (1 32) becomes visible between cortex and calvaria. Insome patients this physiologic decrease in cortex volume is especially obvious inthefrontal lobe (111).The space between it and thefrontal bone (55a) becomes quitelarge.This so-calledfrontally emphasized brain invoiution should not be mistakenforpathologiC atrophyof the brainor congenitai microcephalus. If the eTscan inFigure 50.1a had been taken of an eiderly patient, one would have to consider diffuse cerebral edema with patholo- gically effaced gyri.Beforemaking adiagnosis of cerebral edema or brain atrophy you shouldtherefore always check on the age of the patient. Fig. 50.2a Fig. 50.2b Figure 50.2a shows anadditional variationfrom thenorm. Especially in middle-aged femalepatientsyouwill sometimes find hyperos- tosis of the frontal bone (55a) (Steward-Morel-Syndrome) without any pathologic significance. The frontal bone (55a) Is internally thickened on both sides, sometimes With an undulatinq contour. In cases ofdoubt. the bone window can help to differentiate between normal spongiosa and malignant infiltration.
  • 50. Cranial CT Normal Variants An incomplete fusion of the septum pellucidum (1 33a) can, as another variation, lead to the development of a so-called cavum of the septum pellucidum. Please review the normal scans in Figures 30.2a, 30.3a, and 31.1a for comparison. Usually only the part of the septum located between the two anterior horns of the lateral ventricles (Fig. 51 .1 a) is involved, less frequently the cavum extends all the way to the posterior horns (Fig.51.2a). In the plane of Figure 51.1 , just medial ofthehead ofthe caudate nucleus (1 17), you can evaluate both foramina of Monro (141) which func- tion as arouteforthechoroid plexus (123) and the CSF from the lateral ventricles (133) to the 3rd ventricle (134). Refresh your anatomic skills by naming all other struc- tures in Figure 51 .1 and checking your results in the legend. The radiologist will rarely be confrontedwithan eye pros- thesis ( * ) after enucleation of a globe (150). In patients with a history of orbital tumor, a local relapse, t.e, in the retrobulbar space (2) has to be ruled out in check-up CT scans. The CT scan of the orbit in Figure 51.3a showed minor postoperative change with- outanyevidence of recurrent tumor. Fig.51.3b 51
  • 51. 52 I Cranial CT Partial Volume Effects One ofthe most important rules of CTscan interpretation is to always compare several adjacent planes (see pp. 14-15). If the head istilted even slightly during the scan procedure, one lateral ventricle (133) for example, can appear in the image plane (dS)' whereas the contralateral ventricle is still outside the plane (Fig.52.1). Oniy its roofwill appear. The computer therefore calculates a blurred, hypodense area which could be mistaken for a cerebral infarction (Fig. 52.2a). By comparing this planewith the adjacent one below it (Fig. 52.3a), the situation becomes clear, since the asymmetric contoursofthe imaged ventricles arenow obvious. Fig. 52.1 Fig. 52.3a Fig. 52.2b Fig. 52.3b This exampleillustrates the importance ofthecorrect placementof the patient's head. The exact position ofthe nose inan a.p, projec- tion is obtained by usingthegantrypositioning lights. Involuntary movements ofthe head can be kept at a minimum by soft padding. In ventilated orunconscious patientsan additional immobilization ofthe head with suitablebandings may benecessary.
  • 52. Cranial CT Partial Volume Effects 53 :c, "I thefirststeps in interpreting CCTs is the inspection of the ---: tssues, Contusions with subcutaneous hematomas (8) may - : cate skull trauma (Fig. 53.1 a) and call for a careful search for - "rracranial hematoma.Many injured patients cannot beexpec- ? : :0 have their heads fixed for the duration of the CT scan, and - -, Questionof whether it isjust an asymmetric projection of the "_ base or a real hematoma can be answered by comparing OL,ccent sections (Fig. 53.2a). In this example the bones of the :- C111 base caused the hyperdense partial volume effect. Despite -~ obvious right frontal extracranial contusion, intracranial this leads toconsiderable rotation.Asymmetriccontours(* inFig. 53.1 a)of the roof ofthe orbit (55a),the sphenoidbone (60),or the petrosal bone (not asymmetric in the illustrated examplesI) are therefore frequentoccurrences and may leadto misinterpretations ofthe hyperdense bone as afresh intracranial hematoma. Fig. 53.1 b bleeding could not be confirmed. Please note the considerable beam hardening (bone) artifacts (3) overlapping the brain stem (107). Such artifacts would not appear in MR images of these levels. Fig. 53.2b
  • 53. 54 Cranial Pathology Intracranial Hemorrhage After havingdiscussed thatpartialvolume effectsduetoasymmetricprojections (i.e.,55b inFig.54.2b) may bemisinterpreted asacute hematomas,thischapter will pointout the characteristicsofthedifferent types ofintracranial hemorrhage. Bleeding Caused bya Contusion As a direct consequence of skull trauma,cerebralcontusion bleeding may occur (Fig. 54.1 a). An acute hemorrhage (8) appears as a hyperdense mass which may be accompanied by surrounding edema (180) and displacement of adjacent brain tissue. In anemic patients the hematoma is less dense and may therefore appear isodensetonormal brain. ~ thevascularwailisdamagedonly secondarily by hypoperfusion me- diated by edema,hemorrhage may notoccuruntil hoursor.more rarely, days after skull trauma. A eeT obtained immediately after skull trauma which does not show any pathologic changes istherefore not a good predictor since deiayed cerebral bleeding cannot be ruled out. A foilow-up scan should be obtained if the patient's condition deteriorates.After completeresorp- tion of a hematoma (Fig. 54.2a), a well-defined defect isodense with eSFremains (132). Characteristics Hyperdenseblood inthesubarachnoid spaceorthebasalcisterna instead ofhypodenseeSF Fresh hematoma:crescent-shaped, hyperdense bleeding closetothe calvariawith ipsilateral edema; hematoma isconcave toward hemisphere; may extend beyond cranial sutures Biconvex,smooth ellipsoidal inshape; close tocalvaria; does notexceed cranial sutures; usuaily hyperdense, rarelysedimented Type ofbleeding Table 54.1 Subarachnoid bleeding Subdural bleeding Epidural bleeding Fig.54.2b Fig. 54.1a Fig. 54.2a Contusion frequently leadsto an epidural. subdural, or subarach- noid hemorrhage and may leak into the ventricles (Fig. 55.1 a). Possible complications of such leakage or of a subarachnoid hemorrhagearedisturbedeSFcirculationcausedbyobstruction of the pacchionian granulations,the foramen ofMonro, orofthe 4th ventricle. An hydrocephalus with increased intracranial pressure and transtentorial herniationof the brainmay result. Epidural and subdural hematomas can also lead to major dis- placement of brain tissue and to midline shifts. Quite frequently this in turn causes obstruction of the contralateral foramen of Monro resulting in unilateral dilation of the lateral ventricle on the side opposite thebleeding (Fig. 56.3).Thecharacteristicsusefulin differential diagnosisof the various types of intracranial bleeding are listedinTable 54.1.
  • 54. Cranial Pathology Intracranial Hemorrhage 55 -00'= is intraventricular extension of intracranial hemorrhage - 55.1 a), physiologic calcification of thechoroid plexus (123), " lateral (133) and3rdventricles(134),aswell asthoseofthe -='" aeandthe pineal (148), must be distinguished fromfresh, :£'Censebloodclots (8). Pleasenotetheedema (180) surroun- , -.ehemorrhage (Fig. 55.1a). - = canent has been lying supine, a horizontal fluid-fluid level ec Jy blood sedimenting in theposterior horns of the lateral ventricles may be seen (Fig. 55.2a). The patient is in danger of transtentorial herniation if the ambient cistern is effaced (Fig. 55.2b). In this case the 3rd ventricle is completely filled with clotted blood (..in Fig. 55.2a, b), and both lateral ventricles are markedly dilated. CSF has leaked into the paraventricular white mater (¢). In addition, a lower section of this patient shows subarachnoid hemorrhage intotheSAS ( in Fig. 55.2b). =, 55.1b Fig.55.2b Fig.55.3b id::aro!oC.hnoid Hemorrhage - _"ecnvehydrocephalus,ascaused bysubarachnoid hemorrhage(8 inFig.55.3a, b),may easilybeidentified because thetemporal _ 33) of thelateral ventricles appear distended. In suchcases it is important to haveacloserlook at thewidth ofthe SAS overthe - =-"- suriace: blunted cerebral gyri usually indicate a diffuse cerebral edema. In the present case though, the width of the Sylvian =(127) andthesurface SAS arenormal.Acute edema is thereforenot presenl(yet).
  • 55. 56 Cranial Pathology Intracranial Hemorrhage Since the surface SASs arevery narrow in younger patients, it is possible to miss asubarachnoid hemorrhage in children.The only identifiable sign may be a small hyperdense area adjacent to the falx(130).Inadultsasmall subarachnoidhemorrhagealsocauses only a minor, circumscribed areaof hyperdensity (8 in Fig. 56.1 a). At the timeofthisCTscan thebleedingwas soslight that it had not yet caused anydisplacement ofbraintissue. Subdural Hematoma Bleeding intothesubduralspace results fromcerebral contusions, damaged vessels inthepiamater, orfromtorn emissary veins.The hematoma initiallyappearsasa long, hyperdense margincloseto the skull (8 in Fig. 56.2a). In contrast to an epidural hematoma, it isusuallysomewhat irregular inshape and slightlyconcavetoward the adjacent hemisphere.This kind of bleeding is notconfined by cranial sutures and may spread along the entire convexity of the hemisphere. Subdural hematomas can also cause marked displacement of brain tissue (Fig.56.3a) and lead to disturbances in CSFcircula- tionand toincarceranonofthe brainstem inthetentorial notch. It isthereforenot as important,fortreatment purposes,todistinguish between a subhematoma or an epidural hematoma as it is to ascertainthe extent of the hemorrhage. Hematomas with the pro- pensitytoexpand,especiallyif edemaisathreat,shouldtherefore bedrained or treated surgically. Fig. 56.3bFig. 56.2bFig. 56.1b Chronic subdural hematomas (8 in Fig. 56.3a) may appear homogeneously hypodenseor show inhomogeneous density with sedimen- tation of blood.The danger involved in a small, venous bleed is the symptom-free interval and the slowonset of somnolence up tothe development of a coma.Therefore, a patient with suspected bleeding aftercranial trauma should always be kept under observation in order todetect anyclinical deterioration.
  • 56. Cranial Pathology Intracranial Hemorrhage 57 Extradural Hematomas Bleedings into the extradural spaces are usually caused bydam- agetothe middle meningeal artery, and rarely by venousbleeding romthesinuses orthe pacchionian bodies. Predisposed areas are temporoparietal regions or sometimestheposterior cranial fossa, in whichcasethereis severe danger of tonsillar herniation.Arteri- al hemorrhage lifts the durafrom the innersurface ofthe cranium (55) and then appears as a biconvex, hyperdense area with a smooth border to the adjacent hemisphere.The hematoma does not extend beyond thesutures between thefrontal (55a),temporal (55b), parietal (55c), or occipital (55d) bones. In small extradural hematomas (8)thebiconvexshapeisnot distinct (Fig,57,1a),mak- ing it difficulttodifferentiate the findingfromasubdural hematoma. It is importantto distinguishbetween a closed skull fracture with an intact dura, and a compound skull fracture with the danger of secondary infection. An unequivocal sign of a compound skull fracture(Fig.57.2a) istheevidence ofintracranial air bubbles(4), whichprovethat thereisaconnectionbetweenintracranial spaces andtheparanasal sinuses ortheoutside. Itis difficulttodetermine whether the bilateral, hyperdense hematomas (8) in Figure 57.2 areextradural orsubdural. Inthis case thedistortionofthemidline was caused by the right-sided, perilesional edema (left side of Fig. 57.2a) since it was shifted toward the left (the side of the hematoma). Fig,sr.ie Test Yourself! Exercise 8: Fig. 57.2b Test Yourself! Exercise 8: Spacefor your suggested answer: .vhen looking at the imageofanother patient (Fig.57.3), you will note several pathoiogic changes.Usethefree space below the picture : note how manydifferent types of bleeding (if any) you can distinguish and what other pathology/complications you suspect. You wili < dtheanswersat fhe end ofthebook, but remember: bea good sport and don't cheat, thinkfirst!
  • 57. 58 Cranial Pathology Stroke Apart from cardiovascular and malignant diseases, cerebral infarctionsareamong the most frequent causes ofdeath.Athrom- busoccludes acerebral artery, whichleadstoirreversible necrosis in the area of blood supply. Vascular occlusion develops in association with atherosclerotic changes of cerebral arteries or, less frequently. as a result of arteritis.A further cause are blood clots from the left heart or thrombotic plaques from the carotid bifurcationwhichembolize into a cerebral vessel. Incaseof embolization,diffuselysituated,small,hypodensezones of infarctioninboth basal gangliaandhemispheresaretypical. Old emboli result in small, well-defined areas (180) which eventually appear isodense to the CSF (132). Such areas are called lacunal infarcts(Fig.58.1a).Adiffusepattern ofdefectscalls forcolor flow Doppler imaging orcarotidangiographyandan ecnocaroiocramto exclude atrial thrombus. Please remember that in a suspected stroke it might take up te 30 hours to distinguish clearly the accompanying edema as " hypodense lesion from unaffected brain tissue.A CT scan shoulc berepeated if the initial scandoes not show any pathologicchan- ges even though the patient is symptomatic and if symptoms de notresolve (resolutionof symptoms points to atransient ischemic attack,TIA). In case of aTIA: no abnormalitiesarevisible intheCT scan. In contrast totheTIA,the prolonged reversible ischemic neurolo- gic deficit (PRIND) is often associated with hypodense zones of edema inthe CTscan. Fig.58.1a Fig. 58.2a Fig. 58.1b Fig.58.2b If the area of infarction corre- sponds to the distribution of a cerebral artery, one should con- sider an occlusion of the corre- sponding blood vessel. In classi- cal infarctions of branches of the middle cerebral artery, ischemia will cause a hypodense area a edema ( in Fig.58.2a). Depending onthe size,the infarc- tion may havesevere mass effect and cause midline shift. Smaller areas of infarction do not usually show any significant midline shift. If the arterial walls are damaged, bleeding may occur and appear as hyperdense areas coatingthe neighboring gyri. The unenhanced follow-up CT scan in Figure 58.2b shows an additional bleed into the head of the right caudate nucleus ( ) and right putamen ( ). In this casethe infarction Is 2 weeks old and necrotic tissue has been mostly resorbed and replaced by CSF.
  • 58. - = 59.3a Fig. 59.3b Whereas differential diagnosis (DD) of intracranial hemorrhage and infarction may be obtained without the use of CM, detection of cranial metastases (7) is definitely im- proved by the administration of i.v CM. Even small areas in which the blood-brain barrier is disturbed become visible (Fig. 59.1 a). Large metastases sometimes cause sur- rounding edema (180) which could be misinterpreted asinfarct-related edema on unenhanced imagesif the metastasis appears isodense tothe adjacent tissue. After l.v. CM the lesion in the left hemisphere (7) is clearlydemarcated (Fig. 5g.2a).Did you also spot the second, smaller metastasis within the right frontal lobe, which also shows some surrounding edema (180)? The differential diagnosis of brain tumors is made much easier by the injection of i.v. CM. In the unen- hanced image (Fig. 59.3a), the temporoparietalglioblastoma onthe left (7) which has acentral necrosis (181) couldhave been mistaken for cerebral infarction. The post-CM image, however, reveals the typical appearance of a glioblastoma with an irregular rim enhancement of its margin (Fig. 59.3c). Abb.59.3c 59
  • 59. 60 Cranial Pathology Inflammatory Processes Another example of the advantages of i.v. CM is the demonstration of inflammatory processes, since the accompanying defect in the blood- brain barrier will not show on an unenhanced image. Figure 60.1a shows hypodense edema (" ) in an unenhanced section of a patient suffering from aorticvalve endocard- itis. Contrast medium (Fig. 60.1b) confirmed the finding by enhancing the inflammatory process (+). Bacteria from the aortic valve caused this septic embolism in the leffoccipital lobe. Aretention cyst, which often appears inone oftheparanasal sinuses, shouldbe considered in the differential diagnosis of advanced inflammations. They typically have a broad base on the wall of a paranasal sinus, extend into its lumen, and havea roundish convex shape ( 1 " inFig. 60.3). Inflammation of the paranasal sinuses and of the middle ear can already be diagnosed in native imagesas effusions (8), for example in the normally air-filled mastoid cells (62). Swelling of the mucous membranes oftheexternal auditory canal (63b) is visible without the need for CM. Figure 60.2a shows bilateral otitis externa and media, which is more severe on the right side where it involves the antrum and the mastoidcells. Withprogress- ingabscess formation, an image on bone windows shouldbe obtained in ordertodetectpossible bone erosion. Such cysts areonlyof significance if they obstruct the infundibulum (0) of the maxillary sinus or the semilunar canal (@), causing an accumulation of secretions. In patients with chronic sinusitis, it istherefore important to check for an unobstructed lumen of the semilunar canal (@) or for variations which may restrict mucociliarytransport of secretoryproducts. Haller's cells ("), a pneumatized middle concha (166), and a pneumatized uncinate process (@}) are among the most frequent variations. All of these variations can obstruct the semilunar canal and cause chronic, relapsing sinusitis. Fig.60.2b @ Fig. 60.3 Fig.60.2a
  • 60. Fig. 61.1b You have already seen pathologic changes in the lacrimal gland (pp. 39/40) and the CT morphology of an eye prosthesis (p.51). Every mass within the orbitshould, of course, be diagnosed early and treated effec- tively because of the possibly severe consequences to vision. In order not to miss tumorinvasion into thewalls of the orbit, bone windows should also be obtained. In Figure 61 .1a thereis a hemangioma (7) withinthe retrobulbar fat (2), which is not ne- cessarily an indication for operation because of its benign character. In thiscase it causesa minor proptosis. EndocrineOphthalmopathy Minimal discrete changes can be missed duringthe reporting of a CT scan: endocrine ophthalmopathy often appears as part of Graves' disease and can, in its early stage, only be diagnosed on the basisof a thickening of the external ocular muscles, e.g. the inferior rectus muscle(47b in Figs.61.za, 61.3a). Myositisshould be consideredinthe differential diagnosis. " this early sign is not detected, the disease of the orbital tissue, which is most probably an autoimmune disease, may progress in the absence of therapeutic intervention. Therefore, you should always examine the symmetry of the external ocular muscles (47) when looking at an orbital CTscan. Therewill etten be atypical tempo- ral pattern of involvement. The first finding is an increase inthe volume of the inferiorrectus muscle (47b). Thedisease will continueand affect themedial rectus muscie (47cl,the superior rectus muscle (47a), and finally all the other external ocular muscles. 61
  • 61. 62 Cranial Pathology Facial Skeleton and Sinuses Incontrast to benign retention cysts (p.60), malignanttumors ofthe paranasal sinuses often lead to destruction of the facial bones and may invade the orbit, the nasal cavity (77), or even the cranial fossa. It is therefore useful to examine both the softtissue and bone windows.Forplanning aresection,different CT planesmight benecessary.Thefollowingexample shows atumor of theparanasal sinuses (7)inanaxial (Fig. 62.1 a)and acoronal view (Fig.62.2a).Originatingfromthemucousmembranes ofthe right maxillarysinus(75),the tumorhas infiltratedthenasal cavity (77) and the ethmoid cells. Fig. 62.1 a Fig. 62.1b Fig. 62.2b
  • 62. -g.63.4a Fig. 63.1b Fig. 63.2b Fig. 63.3b Fig. 63.4b The most common reason for doing a coronal CTscan is, apart from determining the extent of chronic sinusitis,thediagnosisof fractures: in fractures of the orbital floor (Figs. 63.1a, 63.2a) any accompanying herniation of retrobulbar fat (2) or the inferior rectus muscle (47b) into the fracture site (* ) or even into the subjacent maxillary sinus (75) should be determined preopera- tively. Diagnosis of the fracture in Figure 63.2a is easier because there are dislocated bone frag- ments. In addition. it is important to detect indirect signs of frac- ture. such as very fine, step-like contours of the bones and secondary bleeding (8) into the nasal cavity (77) or the frontal (76) and maxillary sinuses (75). Another important question is whether or not the head of the mandible (58a in Fig. 63.3a) is fractured or the maxillary bone (57) has been fractured and displaced (*) from the sphenoid (50) bone (Fig. 63.4a). In this case, severe bleeding (8) re- quired intubation (182) and a nasogastric tube (182). Fractures of the facial skull (Le Fort[33]) IYill Straight across the maxiliary bones and the maxil- lary sinuses(Guerin'sfracture) IYP~ Across the zygomatic process of the maxilla, into the orbit, and through the frontal process of the maxilla to the contralateral side; maxillary sinus not involved IYI!.U!! Involving the lateral wall of the orbit and the frontal process of the maxilla to the contralateral side;ethmoid cells and zygomatic arch usually involved, sometimes also affectingthe baseof the skull. 63
  • 63. 64 Cervical CT Whenever there is no contraindication, CT examinations of the neck are carried out afteri.v. administration of CM. Malignant and inflammatory processescan bedepicted moreaccuratelywiththe aid of CM. Adequate enhancement of cervical vessels requires higherdoses ofCMthan,forexample, inCTs of the head. Inspiral CT, the injection of CM must be precisely timed to the acquisition of data. There are specific recommendations and suggested schemes forCMinjection atthe end of themanual. Selection of the Image Plane Inan analogousmanner to head CT, a sagittal planning topogram (scanogram) at lower resolution is obtained first. The transverse (axial) levels andgantry angulation aredeterminedfrom this topo- gram (Fig,64.1).Usually sections of the neck are obtained usinga 4-5 mm thickness.The axial images areobtained and printed as viewed from caudallyso the right lobe ofthe thyroid is imaged to the left of thetrachea,the left lobetothe right. Images should be obtained with a small-scan field-of-view to optimize detail in smaller structures in the neck. As the thoracic inlet is approached during the scanning, the scanfield-of-view is increased to include possible abnormalities in theclavicular fossa and the axilla. Artifacts caused by dental prostheses (3) usuallyobscure surrounding structures (*) in only one or two levels (Fig. 64.2a). It may be necessary to carry out a second acquisition at anotherangle (Fig. 64.2b) to reveal areas hidden by artifact (* ). Fig.64.1 Fig. 64.2a Fig.64.2b Systematic Sequence for Readings We have already recommended a systematic approachwithwhichto read CTscans ofthe head (see p. 26). For cervical CTs there is also no 'one and only' approach. The checklist presented here was deveioped through experience and isjust one ofmany options forthe beginner. Eachexaminer is free tosetup hisorher own checklist and strategy. During neck imaging,separatehardcopies at bone windows are rarely printed owing to cost. The radiologist must remember to check images at bone windows on the screen for fractures or lytic lesions. Checklist for Reading Cervical CT Images -+ Symmetry of neck musculature? -+ Condition and clarityof fat? -+ Normal perfusion of vessels? -+ Thrombosesor atheroscleroticstenoses? -+ Symmetryand definitionofsalivary glands? -+ Thyroid parenchyma homogeneousandwithout nodules? -+ Anyfocal pathologic enhancement with CM? -+ Narrowing of the tracheallumen? -+ Assessment of lymph nodes? Number and size? -+ Cervicalvertebraeexamined in bone window? -+ Vertebral canal patent or narrowed?
  • 64. Cervical CT Normal Anatomy 65 - -eradiologist quickly reachesthelimits of CTresolution (perhaps ;..so of his/her anatomic knowledge) when trying to identify all of -9 different neck muscles.We havethereforereducedtheamount :' detail in the accompanying drawings so that smaller muscles ;;8 grouped.Singlemuscles have littleclinical relevance and thus - elegendstotheseimagesrefertocombinedmusclegroups,e.g. :;-e scalene muscles, the erector spinae muscles. Readers who ant more anatomic detail should consult the relevant literature :5,31] :ervical images usuallybegin at thebaseof theskull andcontinue :audallytothethoracic inlet. Thecranialsections (Figs.65.1-65.3) neretore include the maxillary sinus (75). the nasal cavity (77), and thepharynx(176). Dorsalto thepharynx liethelongus capitis and longuscervicismuscles (26), which extendcaudally. Lateral to the mandible (58). beginning in Figure 65.2a. the parotid gland (1 53) issituatednexttothelarge cervical vesselsand vagusnerve (also p. 64). In front of the pons/medulla oblongata (107), the vertebral arteries (88) join to form the basilarartery (90). Thespreadof inflammatory processes withinthecervicalconnec- tivetissue spacesis restricted withincompartmentsdefined bythe cervical fascia [30].The differentlayers of the cervical fascia are explained on the following page (Fig. 66.4). - . 65.1b Fig. 65.2b Fig. 65.3b
  • 65. 66 Cervical CT Normal Anatomy Fig. 66.3b Compartments of the Neck If infections or inflammatory processes originate in the suprasternal (0) or pre- tracheal spaces between the superficial fascia (* ) and the dorsal layer of the pretracheal fascia (**), they cannot spread into the mediastinum because both fascias insert intothe sternum(56 inFig.66.4).Atthelevelof theparotidgland there is a similarbarrier consisting of the sagittal septum which splits a retropharyngeal from a parapharyngeal space. Inflammations originating furtherdorsal, between the pretracheal (* * ) and theprevertebral (*** ) fascias, can spread caudally into the mediastinum. . Fig. 66.2b Further caudally the following cervical muscles become visible beneath the trape- ziusmuscle(23): medial liethe semispinalis capitis (28) and longissimus capitis muscles (27), and more laterally the spleniuscapitis muscle (25). The parotid gland (153) is situated cranial and posterior to the sub- mandibular gland (154) next tothemandible (58). The pharynx (176) is surrounded by Waldeyer'sringof tonsillartissue (1 57,156). Note that the carotid bulb is situated be- tween Figures 67.4a and 68.2a; it is the point at which the common carotid artery (85) bifurcates into internal (85a) and exter- nal(85b) carotid branches. Underthe tongue (155) the floor of the mouth is organized in layers. From cranial to caudal are: the genioglossus muscle (33), further laterally thegeniohyoid muscle (34),andthe anterior belly of the digastric muscle (31). The thin superficial muscleis the platysma (48). Fig. 66.1b
  • 66. Fig.67.4b t==t¥=-::;'J=fL- Fig.66.1 - r---71+ -+t- Fig. 66.2 7"--7"-CH--I+- Fig. 66.3 H--H-"~'--"::'_....".+-++-H- f ig. 67.1 "-I+--H-++- Hg. 67.2 -t+++-++- Fig.67.3 -';H-,Lf---++- Fig.67.4 8 Fig. 67.5 67
  • 67. 68 Cervical CT Normal Anatomy The bifurcation of the common carotid artery (85) is an area of predilection for atherosclerotic plaques (Fig. 68.1 a)which may be complicated by thrombus deposition (* ). Notethe positions of the cricoid (167) and arytenoid cartilages (168) at the rima glottidis (178). In these normal individuals, eMenhances the density not only of the internal (86a), the external (86b), and the anterior jugular veins (86c), but also of the vertebral artery (88) in the transverse foramina of the cervical vertebrae. Always check for degenerative changes at the margins of the bodies of cervical vertebrae (50)orforherniated discswhichmight narrowthe spinal canal containing the cervical cord (54). On either side of the trachea (81) lie the two lobes of the thyroid gland (83), which shouldhaveasmoothoutlineand havehomogeneousparenchyma (Fig. 68.3a). Fig. 68.1a Fig. 68.2a Fig. 68.3a Fig. 68.3b
  • 68. Cervical CT Normal Anatomy 69 I I I I Fig.68.1 -t+--+''+..... Fig.68.2 -++---++ ----, Fig.68.3 -+t==+=h~~'~~=t=~Fig.69.1 - Fig.69.2 -++----+---+I---'-- --+--.....,;---+- -H Fig. 69.3 -++------+---fl,,.--'----:------fl---+--H Fig. 69,lb Fig.69.2b se of its iodine content, the thyroid gland (83) appears hyperdense compared - surroundingmuscles both beforeand, even moreso,after theadministrationof eM "'";5. 69.1-69.3). Beginners occasionally mistake the esophagus (82), dorsal to the '-ea (81), for swollen lymph nodes or a tumor. In case of doubt, comparison with srsections is helpful: usuallya small, hypodense area indicatesair in the lumen of _. esophaqus in an adjacent section. As a rule, the cervicothoracic junction is 7 ~ -ned withthearms elevatedtominimize artifactsdue tobones.Themusclesofthe I girdleas well astheshoulder joints thereforeappear in unfamiliar positions. -'c 'allowing chapter deals with neck pathology and includes a short "Test Yourself"; -d; es and drawings of normal anatomy extending further caudallyare continued on - :~ 74. - . 69.3a
  • 69. Cervical Pathology Inflammatory Processes and Tumors 70 Enlarged cervical LNs (Fig.70.1a) appear conspicuously asisola- ted nodular masses (6) thatcannot befollowed into adjacent levels (seep.15).Large lymphomas(7) orconglomerateLN masses (Fig. 70.1a) often developcentral necrosis (181). It is sometimes diffi- cult to distinguish them from abscesses with central necrosis (181) asshown,for example, inFigure70.2a.Abscesses typically infiltrate the surrounding adipose tissue with a streaky pattern of edema (180) so that structures such asarteries, veins, or nerves (on the leftsideoftheneckinFig.70.2a) becomedifficult toiden- tify. In immune-suppressed patients. abscesses can become remarkably large. Compare the scans in Figures 70.3a (unen- hanced)and 70.3b (enhanced):after injection ofCM,the outer wall of the abscess (*) as well as the central septa have become enhanced.Theseappearances aresosimilar to large hematomas or necrotic tumors that a differential diagnosis may be difficult without adetailed clinical history. Notealso the atherosclerotic plaques orthromboses inthe lumen of thecarotid artery (85) asinFigure70.1a. I Fig.70.1b Fig.70.2b Fig. 70.3b (enhanced)
  • 70. Cervical Pathology Thyroid Gland 71 - - carenchvrna of the thyroid gland (83) should appear sharply srcatedand have an homogeneous pattern in CT scans. The =; e transverse diameter of each lobe is 1- 3 em, 1- 2 em _- , Iyand 4- 7 em in craniocaudal direction.The total volume - ~ yroid gland varies between 20and 25 ml.If thethyroidis enlarged,check for tracheal compressionorstenosis (81) andthe caudal border ofthe goitershould be determined. A benign struma (83) may extend into retrosternal regions and laterally displace supra-aorticvessels (85,87,88) (Fig. 71.2). Fig.71.1b Fig. 71.4b (181) appear. The tracheal walls (81 ) are compressed and may become infiltrated. After partial resection of a struma (Fig. 71.4), some thyroid tissue (83) may still beseen close tothetrachea. In this case the left internal jugularvein was also removed and the lumen of the right one (86a) is therefore larger than normal. Fig. 71.3bt. 1.2b --E oarenchyrnal structure of a thyroid carcinoma (7) appears -: "ilOgeneous, and the contours are not easily distinguished tr: eremaining normai parenchyma (83) (Fig 71.1 a). sc anced stages ofcarcinoma (Fig. 71.3), cervicalvessels and -- esarecompletelysurrounded bytumor,and areas of necrosis
  • 71. Test Yourself! 72 Before continuing tothe next chapters, these exercises give youan opportunity to check your knowledge. The questions become increasingly difficult as yougoalong: the firstquestionshould pose no problems, whereas the last ones of each chapter will bea real challenge. Make the most of this opportunity for self-assessment and take it in good grace if you find you missed something. In our experience these littletests will help youtoremember better what you have learned. It is muchmoreeffective tolook upeach gapinyour knowledge as it occurs thantoskipaproblem and turn directlytothe answer.You should thereforeonly turn to the answers at the back of the book when you havesolved eachproblembyyourself.That way you will notsee answersto questions you haven't tackled yet. It will keep you in suspense! . . . . Which window setting (window center and windowwidth in HU) would you select for an optimal brain CT? Why? Before beginningthe examination, what gantry angle do you choose for your slices in the planning topogram and what section thickness and section increments do you use?Whydid youchoose these settings? tBDIiI What doyou rememberabout the criteriawith whichto distinguish the fourtypes ofintracranial hemorrhage?Withwhich kindsof hemorrhageareyou familiar? How can youdifferentiate betweenthem inCT morphology?What complicationsor consequences must you particularly watchoutfor (consult pp. 54-57 for help)? Type of hemorrhage: Characteristics: • • • • IDIilIiI How can you recognize asubarachnoid hemorrhage in children? ~ Imaginethe anatomyofthe cerebral basal gangliaandthendraw atransversesectionat thelevel of the internalcapsule. Compare yoursketch with Figures 30,2a and 30,2b.Repeatthisexercise occasionallyuntil youcandoit withease. I tDDD Examine Figure 72,1 carefully. The patient was involved in a car accident. Do not settle for the most obvious feature; look for other variations or abnormalities. What do you suspect? ~ Figure72,2 contains an unusualvariation; can you find it?After havinq noted it, look again to see whether you have really discovered all pathologic features.
  • 72. 0DlIliI The eeT in Figure 73.1 is of a 43-year- old patient. Make a note of your tenta- tive diagnosis and how youwould pro- ceed. Glili!I!Ii2t Is there any feature in this orbital scan (Fig. 73.3) that would not be con- sidered a normal finding? Note your observations below. Don't give up too quickly! Fig. 73.1 Fig. 73.3 Test Yourself! tm:mmI Do you recognize anything unusual in Figure73.2?Isthere a pathologic abnor- mality?Or is it simp- lyan artifact or even a normal finding? GDEI A confused patient, from a home for the elderly, with sus- pected intracranial bleeding is brought in for a eeT. How many fresh hemor- rhages (Fig. 73.4) doyou see? Whatis your differential dia- gnosis? Which of them is the most probable diagnosis? Which additional information could alsobe helpful? Fig. 73.2 Fig. 73.4 73
  • 73. 74 Thoracic CT After havingdiscussed normal anatomy ofcaudal cervical sections (p. 67), normal thoracic anatomy is presented. Fromthis page on, youwillfindthenumbercodes forthe drawings intherearfoldout. Selectionof Image Plane Asarule,thesectionsofthe thoraxare chosen inthetransverse or axial plane at thicknesses and steps of 8 to 10 mm. Sections 10mm thickwill overlap by 1 mm,for example, whenthe patient table is advanced in 8-mm steps. A small topogram (Fig. 75.1) accompanying eachsheet ofimages showsthepositionof the sec- tions relative to the major anatomic structures of the region. In order not to miss anypathologic changeswithin the lung (review p. 13), it has become accepted practice to make a hard copy of both soft-tissue and lung windows or to provide a CD with the image data. Each image can therefore beviewed at twodifferent window settings.Again thelarge number of imagesnecessitates a systematictechniqueforevaluationsoasnot towastetimelooking randomly back and forth between them. Systematic Sequencefor Readings Thebeginner often forgets tocheckthesoftlissues ofthethoracic wall because theexaminationof themediastinumandthe lungsis automatically considered more important. These tissues should therefore be evaluated first. Common sitesof abnormality are the breasts and fat in the axilla (2).After this-also using soft-tissue windows- the mediastinum is checkedforpathologic masses.The easiest approach is to orient yourself relative to the arch of the aorta (89b), which can be recognized even by the inexperienced (Fig,77.3). Fromthispoint cranially, themajor branches are iden- tified toexclude pathologic masses inthe uppermediastinumnext to the brachiocephalic trunk (88), the left common carotid artery (85), the subclavian artery (87), as well as the brachiocephalic veins (91),superior venacava (92),trachea (81),ormoredorsally, theesophagus(82).Caudally,themost common sites for enlarged LNs are: at the aortopulmonary window, directly below the bifur- cation ofthetrachea (81a), inthe perihilar tissue, posteriorto the crura ofthediaphragm (= retrocrural) nexttothedescendingaorta (89c).The presence ofafewLNs smaller than 1.5 cm indiameter intheaortopulmonary window maybeconsidered normal [19,41]. Anteriortotheaortic arch (89b) LNs of normal sizeare rarely seen in the CT. The evaluation of the soft-tissue window is complete when the heart (any coronary sclerosis, dilations?) and the lung hila(vesselswell defined andnotlobulatedorenlarged) have been checked. Onlynow shouldthe radiologist turn tothe lung or pleu- ralwindow. Since thepleural window is very wide,themarrow of the spinal coiumn aswell asthe parenchyma of the lung can be examined. It is therefore possible to evaluate bone structure in addition to the pulmonary vasculature. When examining the lung vessels, look for a gradual reduction in their diameter as you proceed from the hilum to the periphery. Pulmonary oligemiaisnormal onlyalongthe margins ofthelobes and intheperiphery. It isessential todifferentiatebetween cross-sectioned vessels and solid masses by comparing adjacent levels (ct. p. 15). Moreor lessspherical solid masses may indicate intrapulmonarymetastases.Thecheck- list will help you readthoracic CTs systematically. The simultaneous presentation of two window set- tings inonehard copy (boththe lung andthesoft-tissue window)has notproved practical because pathologic abnormalities whichhave densitylevels between the twowouldbeoverlooked. Consult thelungchapteron pages 84ff.forscansinthelung window. Checklist for Thorax Readings, 1, On the soft-tissue window: • soft tissues,especially: - axillary LNs - breast (malignant lesions?) • mediastinum infour regions: - from the aorticarch cranially (LNs?,thymoma I struma?) - hilar region (configuration andsize ofvessels, lobulatedand enlarged?) - heartandcoronary arteries(scterosisj) - fourtypical sites of predilection for LNs: • anterior toaorticarch (normal:almost none or < 6mm) • intheaortopulmonarywindow (normal: < 4LNs< 15 mm) • subcarinal (normal: < 10mm; DO:esophagus) • nexttodescendingaorta (normal:< 10mm; DO:azygos) 2, On the lung window: • Parenchymaofthelung: - normal branching pattern and caliber ofvessels? - vascular oligemiaonlyat interlobarfissures?bullae? - anysuspicious iung foci?inflammatoryinfiltrates? • Pleura: - plaques, calcification,pleural fluid,pneumothorax? • Bones (vertebrae, scapula, ribs): - normal structureof marrow? - degenerative osteophytes? - focal lyticor scleroticprocesses? - stenoses of thespinai canal?
  • 74. Artifacts (3)will beobservedat thelevel ofthe thoracicinlet if eM ispresent inthesubclavian vein(87) at the timeof dataacquisition (cf. Fig. 23.3).The parenchyma ofthethyroidgland (83) should appear homogeneous and clearly defined from the surrounding fat (2). Asymmetryinthe diameter of thejuguiarvein(86) isseen quiteoften andhas nopathoiogic significance. Orthogonally sectioned branches of the axillary (93) and iateral thoracic (95) vesselsmust be distinguishedfromaxillary LNs. Ifthearms areelevated.thesupraspinatus muscle(19)lies medialtothespine of the scapula(53b) and theinfraspinatus muscie(20). Usuallythepectoralismajor(26a) andminor(26b)muscles are separated byathinlayer offat. Fig. 75.2 ;:jJ;j:~~t3~~I=I=~~3:ljFig. 75.3 --: Fig. 75.4 74 Fig. 75.1 75 Fig. 75.2a Fig. 75.2b Fig. 75.3b Fig. 75.4b
  • 75. 76 Thoracic GT Normal Anatomy Thoracic CTs are also viewed from caudally.The left lung (84) appears on the right side of the image and vice versa. Beginning at the aortic arch (B9b in Fig. 77.2),thelayout oftheaortic arch vesselsshould be thoroughlyfamiliar toyou.Atthesectionin Figure 76.1 ,the left subclavianartery (87) is seen most posteriorly and can be followed incranial direction intheimages on page75. Infront ofthe sub- clavian artery liethe leftcommon carotid artery (85) and the brachiocephalictrunk(88).Moretothe right andanteriorlyare the bracnio- cephalic veins(91),which formthesuperior venacava (92) at the levelsof Figures 76.3to 77.1 . In thefat of the axilla (2), normal LNs (6)are often recognizable by their typical indented shape:the hilum contains fat.At adifferent angle,the hypodense hilum will appear in the center of an oval. Healthy LNs are well defined and should not exceed 1em in diameter in this location (Figs. 76.1 and 76.3). Fig. 76.1a Fig. 76.2a Fig. 76.3a Fig. 76.2b Fig. 76.3b
  • 76. Fig. 77.la The azygos vein (104) lies dorsal to the trachea (81) next to the esophagus (82). Directly above the right main bronchus, it arches anteriorly into the superior vena cava (92 in Fig. 77.2). Be sure not to confuse the paravertebral azygos vein (104), the hemiazygos vein (105) or accessory hemiazygos (105a) with paraaortic LNs (Figs. 77.3 and 76.3). 77 Fig. 77.2a Fig. 77.2b Fig. 77.3a Fig. 77.3b
  • 77. 78 Thoracic GT Normal Anatomy I Immediately caudal to thearch of the aorta (89b) is situated the pulmonarytrunk (90), which divides intotheright(90a)and left (90b) pulmonary arteries (Fig. 78.2). At the level of Figures 78.1 and 78.2, there is the aortopulmonary window, a site of predilection for mediastinal LNs (6).Alsocheck for enlarged LNs or malignant masses in thesubcarinal position between the two main bronchi (81 b) close to the pulmonary vessels (96) (Fig. 78.3). Near the internal thoracic (mammary) vessels (94) lies theregional lymphatic drainage ofthemedial parts ofthebreasts,whereas thelymphatic drainage ofthe lateral portions ofthe breasts is primarily totheaxillary nodes. Fig. 78.2a Fig. 78.3b Fig. 78.1a Fig. 78.3a
  • 78. Iheglandulartissue (73)inthefat of the breasts oftheanteriorthoracicwall iseasily oifferentiated from skintumorsbecauseof thesymmetry (Figs.79.1 and 79.2).The main coronary arteries (77) are also distinguishable in the epicardial fat (2) (Fig. 79.3). Developa clear mental picture of the positionsof theazygos vein (104) and ;;Ieesophagus (82)next tothe descending aorta (89c) so thatyou will later be able ;0 recognizeany pathologic LNs close to these structures. Fig. 79.1b Fig. 79.2b Fig. 78.1 ~~~~i~~~~~~~Fig. 78.2 Fig. 78.3 Fig. 79.1 Fig. 79.2 Fig. 79.3 79 Fig. 79.3a Fig. 79.3b
  • 79. 80 Thoracic CT Normal Anatomy The leftatrium (74c) is themost posterior chamber of the heart, whereas the outlet of theleft ventricle (74d)and the ascending aorta (89a) lie inthecenter oftheheart.The right atrium (74a) lies on theright lateral side and the right ventricle (74b)anteriorly behindthe sternum (56). Only the larger central branches ofthe pulmonary vessels (96) can be seen on the soft-tissue window.The smaller, more peripheral lung vessels are better judged on the lung window (notshown here). Note the junction between the hemiazygos vein (105) and the azygos vein (104), which must not be confused with a paravertebral lymphoma (Fig. 80.2). Fig. 80.1 a Fig. 80.2a Fig. 80.3a Fig. 80.2b Fig. 80.3b
  • 81. 82 Thoracic CT Normal Anatomy Theinferior vena cava (80) isseen more caudally (Figs. 82.1 and 82.2), and finallythe diaphragm(30) appears togetherwiththeupper partsofthe liver (122). Many radiologistswho suspect the presence ofa bronchial carcinoma (BG) obtain images tothe caudal edgea the liver (seep. 83) because a BCoften metastasizesto the liver and the adrenal giands. The caliber of lung vessels near the periphery ofthe diaphragmissosmall that they are not visibleon the soft-tissue window, as inthepresentimages.Thepatternofthepulmonary vasculatureshouldthereforebeexamined on the lung windows, which include the negativedensity values of the Hounsfield scale. Only after thisstep has been carriedout istheevaluationofa chest CTcomplete. Fig. B2.1a Fig. 82.2a Test Yourself! Exercise 1g: Fig. 82.2b Writedowna concise but completesequenceof all criteria forinterpreting athoracic CT. Then compareyour notes withthe checklist on page 74 and repeat this exercise from time totime until you remembereverycriterion. 1) Soft-tissue window: soft-tissues, especially:
  • 82. 84 Thoracic CT High-Resolution CT - Normal Anatomy Segments ofthe Lung It isespeciallyimportant to be able to identifythe segmentsofthe lungs in CTimages if bronchioscopy isplanned forbiopsyor to remove a foreign body.The rightlung has 10 segments. Intheleftlung, theapical andposterior upper lobe segments have a common bronchus andthere is no 7th segment (paracardiac [medialbasal] segment ofthe lower lobe). Fig.84.1 Bronchial tree,viewfrom anterior The parenchyma next to the interlobular tissures (- -) appears avascular. The borders of the segments (.•••••••.) are usually not visible in sections of normal thickness and can only be identified by the branches of the pulmonary veins (96) which pass along these bor- ders. 1 apical 2 posterior 3 anterior 4 lateral (superiorlingula) 5 medial (Inferior lingula) 6 superior/apical 7 paracardiac/medial basal 8 anterior basal 9 lateral basal 10 posterior basal Lower lobe Upper lobe Middle lobe 9 "I :'--_- 1/2 3 4 (?0,'I=:'--- 5 1 2 3 - -1AI 6 4 Fig.84.2a Fig. 84.4a 1.... _
  • 84. 86 Thoracic GT High-Resolution GT - Pathology I High-Resolution Technique HRCTstands for high-resolutioncomputed tomography using thin sections and a high spatial resolution reconstruction algorithm. Even conventional CT scanners can acquire images of narrower slice thickness than the standard 5-8 mm.The image acquisition parameters can be adjusted on the console to a thickness of 1-2 mmif necessary. In the SCTtechnique, thinner sections can also be computed at a pitchfactor of 1:1 after acquisition(see alsop.169). However, it is not usually worth reconstructing slicesof less than 1 mm thick- ness becausethe lowsignal-to-noise ratio reduces image quality. HRCT is therefore not the method of choice for routine chest examination because radiation dosage is much higher if more sections are acquired. Longer examinationtimes and higher hard- copy filmcost ("slice pollution") arealsoarguments against using HRCT.Onlystructures withnaturallyhighlevelsof contrast suchas areas surrounding bonewill be well demonstrated. High-Resolution Effects on Image Quality Figure 86.1 shows a conventional scan of a pulmonary lesion (7) surrounded by a zone of edema or an infiltrate (185). At a dS setting of 10 mm this zonecloseiyresem- bles the poorly ventilated area at the back of the posterior lobe (178) HRCT distinguishes these areas of increased density more clearly (Fig. 86.2) because voxel averaging does not have any appreciable effect (see also p. 14). The DD includes bronchial carci- noma, metastasisofbreast cancer resulting in lymphangitis caret- nomatosa, and atypical pneumo- nia. These images show ararecompli- cation after catheterization of the right heart.The catheter was posi- tioned too peripherallyand caused hemorrhage (173) into adjacent parts of the lung. Follow-up 3weeks latershowed completerecovery. Fig. 86.1a Fig. 86.2a Fig. 86.2b
  • 85. Thoracic CT High-Resolution CT - Pathology 87 : "of the many advantages of the HRCT technique is that older ~ tissue can be distinguished from acute inflammation, for pie in immune-suppressed patients or bone marrow reel- : o-ts.Older scar tissue (1 86) is always well defined (Fig. 87.1), -ereas fresh infiltrates aresurrounded bya zone of edematous ue (185) asinFigure87.2.HRCT isoften the onlymethod with - htodeterminewhether chemotherapyshould be continued in : fmphoma patient who is in the aplastic phase on therapy or whether chemotherapy must be discontinued because of fungal pneumonia. Fresh infiltrates (178) can sometimes be seen next to older scar tissue (186) (Fig. 87.3). Because the slicesare extremely thin, the horizontal interlobular fissure (*) may appear as a bizarre ring or crescentic (Figs. 87.1 and87.2). I Fig. 87.3b ~-------...., =- .87.1a =- .87.1b ',/lor areas of collapse, which are usually found close to the pleura posteriorly in the lung, must be differentiated from flat sections :' fissures (178 in Fig. 87.1). In doubtful cases, it may be helpful to repeat a scan in the prone position. Areas of collapse and poor ontilation may then disappear or be seen anteriorly. Pulmonary abnormalities due to an infiltrate or to a pneumoconiosis would be hanged.
  • 86. 88 Thoracic CT Anatomic Variants Amongthemanyanatomic variations ofthe thorax,an atypicai course oftheazygos vein (140) is relatively common.It can pass from the posterior mediastinum through theright apical lobe tothesuperior vena cava (92). Itislocated within afold ofthe pleura and therefore separates theazygoslobe fromtheremainderof theright upper lobe.This variation isusually discovered incidentallyonaconventional chest X-ray ( ~ in Fig. 88.1) and has noclinical significance. Figures 88.2 to 88.4 show theanomalous pathofthe vessel as it appearsin CT images. Atypical positionsor branchingoftheaortic arch(89) vesselsare rarer.Anexampleistheright subclavian artery, known asthe "Arteria lusoria," which can resemble a lesion in the upper mediastinum. Notethatnormal breast tissue,surrounded by fat(2), mayhaveveryirregularcontours(72in Fig. 88.4). When using lung windows, you should not only look for solid round lesions and inflammatoryinfiltrates, but also recognize anythinning or evenabsence of lungvessels. Fig.88.1 However, attenuation of vessels is not always a sign of emphyse- ma. Asymmetry in the broncnovascular pattern develops after a part of the lung has been resected. Inthe patient imaged in Figu- re 88.5, the left upper lobe had been removed and the remaining lungtissue hascompensated andfilledtheentireleftthoracic cavi- ty (right half of the image). There are fewer lung vessels per unit volume andanipsilateral shift of themediastinum.Thesechanges are accompanied by a slight elevation of the diaphragm. At the timeof this follow-upCT,the patient was healthy and had neither emphysema nor recurrent tumor. Fig.88,5
  • 87. Thoracic Pathology Thorax Wall 89 ordingtothesequence inthe checklist onpage74,one should turn to soft-tissue windows in order to examine the soft es of the chestwall. Most abnormalities will be located inthe aeand inthe femalebreast. - aerations inLymph Nodes al axillary LNs (6) are usually oval and less than 1 em in - - " sion.Theyoften have ahypodensecenter or arehorseshoe- --;er metastaticLNs(7)areusuallypoorlydefinedanddifficultto · erentiate from surrounding fat (2). They often have central - eas of necrosis (1 81),sothat the differentialdiagnosisofan abs- .;SS with central liquefaction must be considered (Fig. 89.3). If lary lymph node metastases have been treated operatively or " radiotherapy,thedate and treatmentshould be noted onthe shapedas inFigure 89.1,afeatureknown asthe "hilumfatsign." The architecture of a normal LN is characterized by vessels enteringthe hilum,whichcontainshypodense fat. Many abnormal LNs have lost their normal contours and are rounder or irregular. Such LNs all appear solid and lack the hilum fat sign, as seen in those in the left axillain Figure 89.2. For direct comparison, two lymph nodesontheotherside inthe same image are normal. referral sheet for follow-up CT. Postoperative healing processes and scarring (186)changethe morphology of LNs (Fig. 89.4), so theyresembleabnormal nodes(see above).Againthelack of clini- cal information makes diagnosis unnecessarily difficult for the radiologist.
  • 88. 90 Thoracic Pathology Thorax Wall identificationof recurrent tumor.Thediagnosis of recurrent tumor ismade more difficult byfibrosisafter radiation,postoperative scar tissue,and the absence of surrounding fat. Special attention must therefore be paidtotheregional LNs (ct.pp.74,89) and the bones. so that metastases (7) in the vertebrae (50) (Fig. 90.2) are not overlooked.The bonewindow must beexamined insuchcases. Fig.90.3c Thoracic Skeleton Osteolysis within the thoracic skeleton is not uncommon and is usuallyduetoeither metastases ora plasmacell tumor. In Figure 90.3,ametastasis(7) fromathyroid carcinoma hasdestroyedpart ofthe left clavicle(52).Osteolysiscan,however,also becaused by an enchondroma or an eosinophilic granuloma, for example of a rib. In addition to destructive processes (cf. Fig. 22.3), degenera- tive processes involving sclerosis and osteophyte formation of bonemust be differentiatedfrom osteoscleroticmetastases,which aretypical of,for example, prostatecarcinoma (cf. p. 145). Breast The normal parenchyma (72) of the female breast has very irregularcontours and slender, finger-like extensions into the sur- rounding fat (2) (cf. Fig. 88.4). Bizarre shapes can often be seen (Fig. 90.1).Advanced stages ofbreast cancer (7) have asolid.irre- gular appearance (Fig. 90.1). The malignant tissue crosses the fascial planes or infiltrates the thoracic wall, depending on size. Baseline CTafter mastectomy (Fig. 90.2) should help in the early Fig.90.3b
  • 89. Thoracic Pathology Mediastinum 91 - ~ e being able to detect lesions and lymphadenopathy, you ~...s' know the normal anatomy. If you are a preclinical studenf, shouldfirstly study normal sectional anatomy. Itis inyourown ests to work through the following pages only when you are ~cientl y familiar with the previouschapters. rs , :.= ign increase in fat (2) due to cortisonetherapy is occasion- observed in the anterior mediastinum (Fig. 91 .1). Indoubtful -.ses. densitometryishelpful inthe DO (cf. p. 15). Inthis example, - ; average density within the region of interest (RDI), which is - uoned in possible fatty tissue, is -89.3HU with a standard -,,91,l a -;.91.2a , gnant thickening of the walls of the esophagus must be ~~[entiated from gastric conduitsfollowing esophageal surgery - g. 91.2). Possible enlargement of LNs (6) next to the stomach -29) must be excluded by follow-up CTs. Occasionally post- eranve metalclips cause artifacts (*), which makeassessment -.a mediastinummore difficult. Following esophageal resection, .s01the colon (..) may become drawn up into the anterior - ".: astinum (Fig. 91.3). Comparison with adjacent sections c y shows that this structure is notan emphysematous bulla, _ ' S atubular organ containinga lumen. deviation of about 20HU(ct. Table 16.1).As a rule. thesize 01 an ROI inem' (AR) isalso provided (Fig.91.1).The DO ofsuchamass would includeretrostemal goiter and thymoma. In children and young adults, the density of the thymus is about +45HU.As aresult of involution,the density of the organdecreases withage from the third decade onward until it has dropped to the densitytypical 01fat (- 90 HU).The leftlobe ofthe thymus is often larger than the rightand can reachthe aortopulmonary window.A lobe should notbe thicker than 1.3 em inadults; uptothe age of 20, 1.8em is considered normal. Fig. 91.1b Fig.91.2b Fig. 91.3
  • 90. 92 Thoracic Pathology Mediastinum Enlarged Lymph Nodes Normal LNs areoften found at the level of the aortopulmonarywindow.They are mainly oval or irregular, less than 10mm across [1 9], and sharply delineated from mediastinal fat (2). LNs (6) in thisarea are notusually considered suspicious until they exceed 1.5 cm in diameter.The demonstrationofa"hilum fat sign" (ct. p. 89) is not Obligatory, butdoes suggest a benign nature (Fig. 92.1). Fig.92.1a Fig. 92.1b Normal size (diameter) of thoracic l Ns [19, 41]: If more than three LNs are seen inthe aortopulmonary window or if a single LN is abnormally enlarged, the DD includes not only a metastasis from a bronchial carcinoma, but also a lymphoma (Fig.92.2). Enlarged mediastinal, and especiallyhilar, LNs are also characte- ristic of sarcoidosis (Boeck's disease) (6 in Fig. 92.3). In Figure 92.2, there are intrapulmonary metastases (7) as well. Did you notice them? Other sites of predilection for abnormal LNs are anteriorto the aortic arch, beneath the bifurcation of the trachea (subcarinal), and the para-aortic and retrocrural regions. • anterior mediastinum • aortopulmonarywindow • hilar • subcarinal • para-aortic < 6 mm < 15 mm < 10 mm < 10 mm < 7mm
  • 91. Thoracic Pathology Mediastinum lar Pathologies phenomenaof CMinjectedthrough an armvein(ct. p.21 )and anomalous vessels(cf.p.88)inthemediastinumhavealreadybeen .ssed. Incompletely mixed CMmust be distinguished fromapossible thrombus (173) inthelumenof the brachiocephalic vein (91). - athrombuscanadhereto acentral venous catheter(182 in Fig.93.1). 93 " , 93.1a - - 0 osclerotic plaques(174) inthe aorta(89) are oftenaccompa- -.;-: by thromboticdeposits(173 inFig.93.3).Theypromoteaortic , ;-gation and dilation and can ultimately lead to an aneurysm -,1). Dilation of the thoracic aorta is considered to be an ,; rysmif thelumeniswider than 4em.Recordingthe measure- - ,;-;s of distancesandsizes (Fig. 93.2) makes it easier toassess !r progressive dilation infollow-up CTs. It is important to check a yinvolvement ofthe branchesofthe great vessels or forthe issecting Aneurysms of theAorta according to de Bakey [20]) Type r (approx. 50%) Ascendingaorta; may extendto abdominal bifurcation TypeII (approx. 15%) Only ascending aorta, extendingto brachiocephalic trunk IypeIII (approx. 25%) Tornintima distal to leftsubclavian artery Fig. 93.1b presence of a dissection flap (172 in Fig. 93.4). Three types of dissection can be diagnosed according to the extent of the dissection flap(seede Bakey [20]). Atrue aneurysmwith a diameterof more than 6 em. with a more saccular than fusiform shape or with an eccentric lumen. has a higher incidence of rupture.The consequences of rupture include amediastinal hematoma,ahemothorax,or pericardial tamponade.
  • 92. 94 Thoracic Pathology Mediastinum Pulmonary Embolism Ifalarge embolus has detached from athrombusinadeep vein of the leg, it will be visible as ahypodense area (" ) within thein- volved pulmonary artery oncontrast-enhanced images (Fig.94.1). After large pulmonary emboli,the affected segmentsorlobes ( ' ) usually become poorlyventilated and atelectasis occurs.The pu- monaryvessels become attenuated,whichcanbedemonstrated in conventional x-rays.The CT-angiographic detection of pulmonary emboli isdescribed onpage 186 in more detail. Heart Youhavealready familiarized yourself withthe normal anatomyof the heart on pages 79 to 81. Dilation resulting from valvular in- competence or from cardiomyopathies, as well as intracardiac filling defects can be recognized in CT images. If CM has been injected, it is possible to detect atrialthrombus or a thrombosed ventricularaneurysm.TheimageinFigure 94.2illustrates acase of global cardiac failure with markedly dilated atria (* *) and incidental thoracicvertebral degenerative osteophytes(" ). Pericardial effusions mayoccur withviral infections, uremia,the collagen vasculardiseases,aheartattack,ortuberculosis,among other causes. Apericardialeffusion (8) appearsasabroad rimoflow-density fluid(between 10 and 40 HU) surroundingtheheart (Fig. 94.3). Only fresh blood would have a higher level of density. Massive effusions as seen in Figure94.3 not only compress theadjacent lungs (178), but alsocompromise heart function. Fig.94.3a Effusions may leadtopericardial fibrosisor calcification (" " ), whichinturn causes constrictive pericarditis(Fig. 94.4).Notethat insuchcases the vena cava,the azygos vein.oreven the atriamay be markedly dilated as asign ofcardiac insufficiency. Atherosclerosisofthecoronaryarteries causescalcificationthat is well demonstrated by thin, hyperdense lines in the epicardial fat. At present, however, a complete assessment of the degree of stenosis requires angiography.
  • 93. Thoracic Pathology Lung 95 '"xal lntrapulmonary lesions -~ n multiple lung metastases are faradvanced, the lesions can "'" berecognized inthe topogram (Fig. 95.1a). Depending upon - age and vascularization of the metastases, they appear as c=rical nodulesof varying sizes (Fig. 95.1 b).The more irregular " contoursofthelesions (for example,stellateor spiculated),the -;.95.1a more likely they areto be malignant.If, however, they aresolitary and have central calcification (likea popcorn), orperipheral calci- fication, the lesions are most likely to be a benign hamartoma or granuloma. Fig. 95.1b Fig. 95.2c vesselscutincross-section.Small metastases locatedclose tothe hilum are much moredifficult to distinguishfromvessels. Insuch cases, the detailed analysis of high-resolution scans (HRCn may bethebest method. Fig. 95.2b- ~ . 95.2a : - onary metastases are notvisible inconventional x-raysunless -e are largerthan 5or6 mmindiameter. InCTimages,however, - : can be detected at 1 to 2 mm in diameter. If metastases are :u:ed inthe periphery, it iseasy todifferentiatethem from blood --" correct choice of image display(window) is essential: Small :u lesions (7) of the lung (84) do not appear on soft-tissue -'ows(Fig.95.2a) or may be mistaken fornormal vessels(96). _-g windows (Fig. 95.2c) should alwaysbe used forexamining -; parenchyma. In the case below (Fig. 95.3a), the multiple small metastases (7) close to the pleura would have been over- looked if lung windows had not been used (Fig. 95.3c). These examples demonstrate the importance of viewing each image on long andsntt-tissuewindows. =e- 95.3a Fig.95.3b Fig. 95.3c
  • 94. 96 Thoracic Pathology Lung As aresult ot changes inthebehavior of smokers,theincidence of bronchial carcinomas (BC), especially among women and young people, has increased. In addition to the histologic diagnosis and grading of carcinoma, the location of the lesion is an important prognostic factor:a BG ofconsiderablesize (7) intheperipheryof the lung (Fig. 96.1) will almost certainly be visible on a con- ventional chest x-ray. More advanced BGs located centrally are usuallynotoperableand mayobstruct thebronchiallumen,result- ing in distal collapse (178). Figure 96.2 illustrates an advanced case in which the tumor has areas of central necrosis (181) ana thelung is surrounded bya pleural effusion (8). Fig. 96.1 a Fig.96.2a Fig. 96.2b Lymphangitiscarcinomatosa(7 in Fig.96.3)spreads from the hilum orthe visceral pleuraintothe interstitialtissueofthelung bywayof the lymphatic vessels. Obstructionofthesevessels bycancer cells leadsto lymphatic congestion (185).At first,the upper lobes remain clear. but as the disease progresses these also become infiltrated. The larger lymphatics and LNs gradually become infiltrated by metastatic disease. Fig. 96.3a Fig. 96.3b
  • 95. Thoracic Pathology Lung 97 Fig. 97.2bFig. 97.2a ...Fig. 97.1a ,, ------------- idosis '" changes of sarcoidosis - ' :k's disease) must be -,-gntiated from multiple ---;ases inthelung:epithe- ;ranulomas usually infil- ~ the hilar lymph nodes (6) "orally (Fig, 97.1) and then ,3d within the perivascular e and along the Iympha- o the periphery of the ultiple small pulmonary :- es and various degrees of -'3 itial fibrosis may be ssent,Largegranulomas (7), seen in Figure 97,2, may :11ble intrapulmonary me- ases. - . erculosis , arqer masscavitates (181), the DDwill include, forexample, a bronchial carcinoma with centralnecrosis or cavitary tuberculosis, - , re 97.3 illustrates the latter in an atypical location in an HIV+, immune-compromised patient. Note also the emphysematous - '-ges in thetissueatthe peripheryof thelesion(176). rgillus - _~finfection with Aspergillus may occur within a pre-existing 7f in immune-compromised patients. The spores of A. fumi- 5are commoninplant material andsoil.Oftenthecavityisnot Jletely filled withtheaspergillusball sothat a smallcrescent , - can be recognized (" in Fig. 97.4).Aspergillosis may also -- to allergic bronchial asthma or provoke exogenous allergic ~D1itis . Fig. 97.4
  • 96. 98 Thoracic Pathology Lung Pleura Massive pleural effusions(8), asseen in the case illustrated in Figure 98.1 , compress thelung(84)and may cause largeareas of atelectasis (178) affect- ing individual segments or even an entirelobe.Effusions appear ascollec- tions of homogeneous fluid of near- water densitywithin the pleural spaces. Effusions usually accompany infec- tions, lung congestion due to right heartfailure, as well as venous conges- Fig. 98.1a tion due to mesothelioma and peri- pheral bronchial carcinoma. Pleural drainage by the insertion of a catheter (182) is indicated if atelecta- sis (178) affects large portions of the lung (Fig. 98.2). In the case shown in Figure 98.2, the drainage tube was blocked by fibrin-rich fluid. The lung can only be re-inflated if the fibrin clot is cieared or the catheter is replaced. Fig. 98.2 Foreignbodiesare rarely foundinthepleural spaces (166 inFig. 98.3),but mustbe consideredafter thoracotomy (chest surgery).Images on lung windows (Fig. 98.3c) clearly show the inflammationand collapse (178)surrounding a lost swab. Asbestos-Related Lung Disease Asbestos-related lungdiseasehas afine reticulonodularpatternof increaseddensities scattered throughoutthelung tissue,especial- lyat interlobularsepta (t and ' in Fig.98.4).Typical patholo- gicfeatures inthe pleura are thickeningand plaques (186 in Fig. 98.4). Fibrosis and scar emphysema appear in later stages of the disease.Thespindle-shaped or moretriangularareas ofincreased attenuationare often difticult to distinguish from those character- istic of bronchialcarcinomas. Fig. 98.3a Fig. 98.3b Fig.98.3c
  • 97. Thoracic Pathology Lung 99 costs -ole, well-defined nodulesappear infhe interstitial connective =in response to phagocytosed particles of silica. The upper lOS of the lung are most commonly affected. Signs of fibrosis, -: may progress to a honeycomb pattern, can best - and at ,( stages - be detected with HRCT (using 2-mm rather than -om slicethickness; Fig. 99.1).The finer, smaller nodules can Fig.99.3 be found scattered throughout the lung; larger opacities, which may cavitate, are located within areas of denser fibrosis (, in Fig. 99.2). Enlarged mediastinal or hilar lymph nodes (Fig. 99.3) often develop an eggshell pattern of calcification.As the disease progresses, fibrosis and scar emphysema increase (.. in Fig. 99.1). Fig. 99.2= 99.1 -- ysema "":<;'essive emphysema with accompanying bullae (176 in =J 99.4b) or bronchiectasis with associated inflammatory lnfll- '"::...0$ (178 in Fig. 99.5) are not visible on soft-tissue window images in the early stages. These infiltrates are more easily seen and detected sooner on thin section images using lung windows [25-27]. - - 99.5a Fig. 99.5b Fig. 99.4b Fig.99.5c
  • 98. Thoracic Pathology Lung 100 The pathogenesis of interstitial fibrosis ofthe lung (Fig. 100.1) cannot always be established andis referred toasidiopathic pulmonary fibrosis. This is particularly truewhen it affects middle-aged women.The patternof fibrosis resembles that illustrated on the previous pages with the exception that emphysematous changes typicallybegin insuopleural regions.Rbrosisof the lung canaccompany any of thecollagenvasculardiseasesinthe advanced stages and lead tosimilarmorphologic changes.forexampleinscleroderma (Fig. 100.2) or polyarteritis nodosa (Fig. 100.3). Fig. 100.3Fig. 100.2Fig. 100.1 Test Yourself! Youshouldtrytoanswer all thequestions onthis andthefollowingpage beforeturning tothe back of thebook fortheanswerssoas not tospoil thefun oftackling each one. ~ Do you recognize any abnormalities in Figure 100.4 or is it a scan of normal anatomy?Discuss your DD. GD1IIa How would you interpret the dense area in the left lunginFigure1oo.5?Dis- cussyour DD and make a list of additional informa- tionthat you need and the steps necessary in order to be certain about the lesion. ...... Fig. 100.5 --_. ~ A62-year-oldpatient pre- sented with intense back pain and was examined by CT. What is your dia- gnosis of the changes seen in Figure 100.6? Can you classily the type ofchange and thedegree ofseverity? ~ Describe in detail the pathologic changes visible in Figure 100.7 and the steps in your DD.
  • 99. Test Yourself! 101 GDmI at further diagnostic xocedures would you 'ocommend for the case ~trated inFigure101.l? Nhat do you suspect the ':sion to be? What other :tJangesdoyourecognize? Fig. 101.1 0Dl'iEt Detecting even minute changes may be decisive in order to arrive at the correct diagnosis.What do you see inFigure 101.2? ...., patient in her 2'6 ~ week of x epnancv corn- Jlained of snort- '=S5 of breath. ~ar physician ini- Jally thought it Nas because of a igh diaphragm. Two weeks later shewas examined Jy CT. Make care- ful note of all ab- normal changes you see in Figure 101.3 and the stepsin yourDO. CIDtID A56-year-oldwoman with a history of smoking pre- sented with unintended weight loss and severe attacks of coughingwhich had already lasted for 3 months. She had no pre- vious illnesses. Does Fig- ure101.4 illustratenormal anatomy, a normal vari- ant. or an abnormality? ~ Do Figures 101.5a and101.5b illustrate normalanatomy, ananomaly, or a lymphoma?Discuss your opinion.
  • 100. Abdominal CT ill general, all soft-tissue organs should appear uniform and be Nell defined, exceptwhen partialvolume effects occur (cf.p.1 4)or JUringtheearlyarterial phase of CM enhancement inahelicalscan cf. pp.120 and 126). Structures suchasblood vessels and bowel oops should be clearly defined in intra-abdominal fat. The same appliestothefat in muscles. "oorly definedconnective-tissuespacesmay indicateedemaor an nflammatory or malignant infiltrafion. If the anatomy cannot be :learly resolved, additional information can begained by measu- i ngthedensity ofspecificareas orby comparingunenhanced with :M-enhanced scans(cf. pp. 15and 121 ). !,gain, the proposed checklist is not intended to be"prescriptive", xn togivean usefultoolfor the novice inorderto reducethenum- :er of missed pathologicai findings. Selection of Image Plane The sections of the abdomen are also acquired transversally (=axially).lf thetableadvance issetat 8 mmwithaslicethickness of 10 mm, there will be an overlap of 1 mm on each side of the section. In recent years, there is a trend towards thinner slices with a slicethickness between 5 and 8 mm. The small topograms on thefollowing pages (based on Fig. 103.1) clearly show the slice positions as rela- tedtotheanatomyof major structures for each series of images. Fig.103.1 103 Checklist for Abdominal Readings Systematic Sequence for Readings ;nalogous to interpreting chest CTs, we suggest you : egin with the tissues of the abdominal wall. Con- sicerabletime issaved if youconsistentlylookat them 'romcranial to caudal. For beginners a systematic in- spectionof each organ orsystem from cranial to cau- jal is recommended, so that you do not need to .oncentrate on too many structures at once. Thepro- oosecprocedureencompassestwoorthree passages mrouqnthe images.As you become experienced, you may wish to devise your own method. Experienced -eaoers are more easily able to detect all pathologic : anges in onepassagefrom cranial to caudal. : is sensibleto evaluateinternai organs that lie in the same transverse plane. The uniformity of the paren- :nyma, the size and the smooth surface of liver and sateenshould bechecked together. Thesame is true 'or the assessment of the pancreas and the adrenal ; ands: they also lie at the same level (cl. pp. .05/106). If theentire urinary system is to be exami- -ed, it saves time to inspect the reproductive organs ' "d bladder in the lesser pelvis before lookingat the :ranial parts of the GIT, or the regional lymph nodes '00 the retroperitoneal vessels (see checklist on the -ght). =lIlally, thepresenceofsclerotic andlyticbone lesions '1d the state of the spinal canal should be checked c'. p.155). Abdominal wall: liver and spleen: Gallbladder: Pancreas,adrenals: Kidneys, ureter, and bladder Reproductiveorgans: GIT: Retroperitoneum: Bone window: (especially periumbilical and inguinal regions) hernias, enlarged lymph nodes? homogeneous parenchyma without focal lesions? well-defined surfaces? well-defined,thin wall?calculi? well-defined,size normal? symmetric excretion ofeM? obstruction,atrophy,bladder wall smooth and thin? uniform prostateof normal size? spermatic cord, uterus, and ovaries? well defined?normal thicknessofwalls? stenoses or dilations? vessels: aneurysms? thromboses? enlarged lymphnodes? mesenteric (normally< 10mm) retrocrural (normally< 7 mm) para-aortic (normally< 7 mm) parailiacal (normally< 12mm) parainguinal (normally< 18mm) lumbar spine and pelvis: degenerative lesions? fractures? focal scleroticorlyticlesions? spinal stenoses?
  • 101. 104 Abdominal CT Normal Anatomy Theimages of theabdominal organs includethecostodiaphragmatic recesses ofthe lungs (84), which extend quite farcaudally, lateral- ly,and dorsally. Liver (122) and spleen (133) parenchymausually appear homogeneous withoutfocal lesions in thevenousphase ofCM enhancement: branches oftheportal vein (102) and the falciform ligament (1 24)canbe distinguished.Inorder to assess thegastricwall (129a),the stomach (129) can be filled with water, which acts as a low-density CM, after an Lv. injection of Buscopan.The diaphragm (30) between thethoracic and abdominal cavities has an attenuationsimilar totheparenchymaof the liver and spleen and cantherefore notbe differentiated from these organs if itsthindome is sectioned obliquely. Fig.l04.3b Fig.l04.1a Fig.l04.2a Fig. l04.3a
  • 102. Fig. l05.2b 105 Theright adrenal gland usuallylies cranialtotheupper pole ollhe kidney (135), whe- reasthe left adrenal gland lies ventral to the upper poleofthe kidney. Consequentiy, thetwoadrenal glands(134) are seen on the same sections. Note the position ofthe Jiaphragm(30) betweenthelung (84) and the inferiorvena cava (80). Thevesselson e lesser curvature of the stomach (109) and the gastric walls (1 29a) are usually flell defined and clearlydemarcated inthesurrounding fatandconnective tissue (2).
  • 103. 106 Abdominal CT Normal Anatomy Typically the pancreas (131) has well-defined parenchyma with an irregular outline. The head and uncinate process of the pancreas extendquitefar caudally (down to Fig. 107.2).The left adrenal gland (1 34)is often v-snaoed,whereas the right adrenal gland may look likeanarroworacomma.Notetheoriginoftheceliac trunk (97) and theSMA (1 06)from the abdominal aorta(89).Enlargedlymphnodes may frequentlybefound inthisvicinity.InFigure 106.3,thecontrast-enhancing effect of anarterial bolusof CM becomes evident.At this point, the SMA (106) has enhanced morethan theaccompanyingvein (107),which does not contain any CMyet.Within moments (Fig. 107.1),the bolus of CMhas also opacified thesuperior mesenteric vein (107). Fig.l06.1 a Fig. l 06.1b Fig. l06.2a Fig.l06.3a Fig.l06.3b
  • 104. -ookfor arterial calcifications inthe originsof therenal arteries (110) atthelevelof the ~nal veins (111).Theleft renalvein does notalways pass between the aorta (89) and -9 SMA(106) totheinferiorvena cava (80),as itdoesinFigure107,1.Anatomicvaria- znsarenot unusual(ct. p.11 6).Benigncysts(1 69)frequently occurintherenal pelvis 136)next tothe ureter(137) orintherenalparenchyma (135)(Figs,107.2and107.3). 3uchcysts donotenhance after eMinjection (cl. p.133). 107 Fig.107.1b Fig.107.2b- . , 107.2a Fig. 107.3b
  • 105. 108 Abdominal CT Normal Anatomy Closetothe gallbladder (126),you can sometimes see partialvolume effects (Fig. 108.1) of the adjacent colon (143/144),thewalls of which (1 52) should normally bethinandwell defined incontrast tothe root ofthesmall bowel mesentery (as inFig. 108.3).The duode- num (130) canonly bedistinguishedfrom the other intestinal loops (140) on the basis ofits position.Atthis level,youshouldalsocheck the kidneys (135) for smooth margins and possible parenchymal scarring. The presence of fat makes it easier to identify the rectus abdominis muscle(29) aswell asthe obliquemuscles ofthe abdominal wall (28a-c). Fig.l08.2a Fig.l08.3a Fig,108,lb Fig.l08.2b Fig.l08.3b
  • 106. Abdominal CT Normal Anatomy 109 Fig. 109.1b Fig.109.2b Fig. 109.3b- . 109.3a tethe typicalpositionof the proximal partsoftheureters(137),medial totheinferior :des ofthe kidneys (135) and anteriortothe psoas muscle (31 a). In Figures109.2 - id109.3,the luminaof bothuretersappear hyperdense becauseeMisbeingexcret- ec in the urine. Partsof the renal fascia (5) can beidentified in Figures 109.2 and 109.3. Haustrations caused bythe semilunarfolds (haustral folds) (149) are typical -, mecolon (142- 144inthefigures below).
  • 107. 110 Abdominal CT Normal Anatomy InFigure 110.1 . the branching pattern ofthesuperior mesenteric vessels (108) whichsupply the small bowel (140) can beseen.Atthe bifurcation ofthe aorta (89) (usually at L4 vertebral body, Fig. 110.2), thecommon iliac arteries (113) areanteriortothe corresponding veins (116).The two ureters (137) are located more laterally in front of the psoas muscles (31 a). Along with the iliac bones (58) the gluteus medius muscles (35a) appear and sometimes containcalcified intramuscular injections sites (cf. Fig. 117.3). Fig. 110.2a Fig. 110.3a Fig. 110.2b Fig. 110.3b
  • 108. Fig. 111.2b 111 Fig. 111.1b - order to exclude the presence of an abdominal hernia you should check for a -Jrmal width of the linea alba (47) between the rectus abdominis muscles (29). ~re caudally(Fig.111 .3)there is asite of predilectionfor enlarged LNs atthedivi- : on of the iliac vessels into external artery/vein (11 5/118). which pass anteriorly, ;old internal arteryivein (114/117), which are located more posteriorly.The transi- ;;00 from thelumbar spine (50) tothe sacrum (62) lies atthis level. - _. 111.3a Fig.111.3b
  • 109. 112 In the following images, the ureters (137) pass posteriorly to approach the lateral aspects of the base of the bladder (138). Within the bladder, differences in the con- centration of excreted eM in the urine can be recognized asfluid-fluid levels of diff- erent densities (Figs. 112.3 and 113.1). On the next page, a male pelvis is shown, demonstrating the prostate (153), seminal vesicle (1 54), spermatic cord (1 55), and root of penis (156). Note in particular the internal obturator muscles (41a) and the levator ani muscles (42) lateral to the anal canal (146a); images ofthe female pelvis onpages 114/ 115 werenot obtained as far caudally asin themale. Fig. 112.1 Fig. 112.2 Fi9'112'3~~~~~~~~~~~~Fig.113.1 Fig. 113.2 Fig. 113.3 Fig.112.3b Fig. 112.1a Fig. 112.3a
  • 110. Abdominal CT Pelvic Anatomy (Male) 113 q g. 113.4a Fig. 113.4b
  • 111. 114 Inthefemale pelvis, thesize and position of the uterus (158) relativetothe urinary bladder can vary considerably from patientto patient. Theuterus mayliecranial or lateral to the bladder (Figs. 114.1-115.1). The cervix and the vagina are situated between thebladder (138) andtherectum(146),whereas theovaries (159) liemore laterally. Depending on age and thephase of the menstrual cycle, ovarianfollicles might be misinterpreted as cystic lesions (cl. o. 133). Fig. 114.1a Fig. 114.2a Fig. 114.3a
  • 112. · Abdominal CT Pelvic Anatomy (Female) 115 Fig. 115.1b Fig. 115.2b :'ee intra-abdominal tluid (ascites or hemorrhage) may occur in the rectouterine pouch between rectum and uterus, aswell as in the esicouterine space. In the inguinal region, lymph nodes (6)can be upto 2 cm in diameter and be normal (Figs. 115.2and 115.3).The sue ofnormalabdominal lymph nodes does not usually exceed 1 cm. It is not possibleto examine the hipjoints on soft-tissue windows Fig. 115.3); the heads of thefemurs (66a) in the acetabular fossae (59/61) can best be analyzed on bone windows (notshown here). 'oJ assessment of bone windowscompletes the examinationof theabdominal and pelvic images. Fig. 115.3a Fig. 115.3b
  • 113. 116 Abdominal Pathology Variants Anatomic Variations For thebeginner, it is important to be familiar with the most common anatomic variations which may lead to misinterpretations of CT images. Insome patients,the contours ofthe right lobeof the liver (122) may appear scal- loped by impressions of the diaphragm (30) which could be mistaken for liver lesions (Fig. 116.1). The walls ofan empty stomach (129) arethickand may suggest amalignant lesion (129a). Fig. 116.1a Fig. 116.1b Ultrasound may mistake an anomalous left renal vein (111) for a retro- aorticLN. Usuallytheleft renal vein passes be- tween the SMA (106) and the aorta (89). However, the vein may be retroaortic and pass between the aorta and the spinal column (50) to the inferiorvena cava (80) (Figs. 116.2 - 116.4). Duplication of the left renal vein with preaortic and retroaortic components can also occur. Characteristic Partial Volume Effects If the wallofone organindents that of another,cross-sectional images will make it look asif one organwere withinthe other. For example,the sigmoidcolon (145)mayappear"within"the urinary bladder (138) (Fig. 116.5a). By comparing adjacent sections (Figs.116.5a and c),it is easyto recognize that only parts of both organs have been imaged. In a similarmanner, the right colic flexure (142) may appear to be "within" the gallbladder (126) (Fig.116.6). Fig. 116.6a Fig. 116.6b
  • 114. Abdominal Pathology Abdominal Wall 117 lymph Node Hyperplasia ?athologic lesions of theabdominal wall occur most frequently in theinguinal region.l ymph nodehyperplasiawithnodesupto2em dimension should notbeconsidered abnormal.l argeconglom- erate masses of lNs (+) arefoundin non-Hodgkin's lymphoma (Fig. 117.1)and less frequently in Hodgkin's disease. An inguinal hematoma (173) caused by hemorrhagefrom afemo- ral artery puncturesite aftercoronary angiography should becon- sidered (Fig, 117,2) in the DO. Abscesses Intramuscular injection sitesinthe gluteal region resulting in sub- cutaneous fat (2) necrosis or postinflammatory residue (..) typically are well-defined, hyperdense, partially calcified lesions (Fig. 117,3). An abscess may spread from the gluteal muscles to the pelvis through the ischiorectalfossa.After diffuse infiltration(1 78)ofthe gluteal muscles (35) withsurrounding edema (185 inFig. 117.4), quefaction (181) may occur and. depending on the localization andsize, theabscess can involve thesciatic nerve (Fig.117.5).
  • 115. 118 Abdominal Pathology Abdominal Wall The CT in Figure 118.1 shows subcutaneous lesions, resulting from heparin injections (173) or small hematomas that may mimic cutaneous metastases (7) or malignant melanomas (Fig. 118.2). Larger metastases tend to invade the muscles of the abdominal wall (29) and often have hypodense, central necrosis (181). Enhancementafter intravenous CM may also point to malignancy or a florid inflammatoryprocess.Ifthe degree ofCM enhancementisuncertain, a regionof interest for densitometricanalysisis placedinthe lesion ona pre-CMand compared witha post-CM (Fi9. 118.2). Metastases inthe abdominal wall may not be evident until they become infected and develop into an abscess (1 81), which was cathe- terizedand drained inthe case illustrated (182 inFig. 118.3).The second metastasis(7),justbeneaththe rightabdominal wall (28),was notrecognized at firstbecausethe patient's symptoms were attributed to the adjacent abscess.
  • 116. Abdominal Pathology Liver 119 III Fig. 119.1 II caudate lobe lateral segment, cranial part lateral segment, caudal part quadrate lobe(a:cranial, b:caudal) anterior segment.caudal part posteriorsegment, caudal part posterior segment, cranial part anterior segment, cranial part I II III IV V VI VII VIII Left lobe Right lobe Segments of the liver t a liver biopsy or radiotherapy is planned, it is helpful to know in which segment a focal lesion is situated. The liver is horizontally subdivided (blue line in Fig. 119.1 ) by the main branches of the portal vein (102) into a cranial and caudal part. The main hepatic veins (103) mark the oorders ofthesegments inthe cranial part(Fig. 119.2).The border between e left and right lobes is not marked bythe falciform ligament (124), butby eplane between the middle hepatic veinand gallbladder (126) fossa. =-g. 119.4 Fig. 119.5
  • 117. 120 Abdominal Pathology Liver Choice of Window In conventional (nonhelical) CT, the unenhanced liver (122) is imagedonaspecial liver windowwidth (Fig.120.1a)setbetween 120 and 140 HU. Normal liver parenchyma can be more clearly distinguished from lesions on narrow-window-width images because they provide high image contrast. If there is no fatty infiltration of the liver (which would reduce attenuation), intra- hepatic vessels (103) appear as hypodense structures.Incases of fatty infiltration, the veins may appear isodense or even hyper- dense on unenhanced images. The post-contrast agents CT images are viewedusingawindow widthofapproximately350HU; this smootnes thegray scale contrast (Fig. 120.1c). Fig. 120.1a Fig. 120.1b Fig. 120.1c Passage of a Bolus of Contrast Agents Inathree-phasehelicalacquisition ofearlyarterial, portalvenous, andlatevenousphasesof contrast agentsenhancement, anunen- hanced study is not necessary [17, 18]. Hypervascular lesions become muchmoreclearlydefinedintheearlyarterial phase(Fig. CT Portography The chancesofdemonstratingthetrueextentof liver lesions(e.g. metastases) are greatly improved if contrast agents are injected directly into the SMA or the splenic artery and images are then acquired in the portal venous phase [17,21). Since theprincipal blood supplyfor most metastases and tumors comes from thehe- 120.2a) than in the late venous phase. Inthe late venous (equili- brium) phase(Fig. 120.2b),thedensitylevels ofthe arterial, portal venous,andvenous systemsarepractically identical. patic artery,these lesionswill appear hypodensewithinthehyper- densenormal parenchyma that has enhancedwithcontrast agents (Fig. 120.3a). Inthe same patient, the early arterial phase image (Fig. 120.3b) showsthat withoutcontrast agentsportography,the extent ofthemetastaseswouldhave beengreatlyunderestimated.
  • 118. · Abdominal Pathology Liver Hepatic Cysts Hepatic cysts (169) containing serous fluid aresharply defined, thin-walled, homogeneous lesionswith densityvalues close to those of later (Fig. 121.1). Partial volume effectsmay cause poor delineation from adjacent hepatic parenchyma (122) if the cysts are small. If in doubt, a ROI should be positioned within thecyst fordensity measurement (Fig, 121.2a). It is important to ensuretheROI is correctly placed in thecenter of the cyst, well away fromthecyst walls (cf. pp. 15 and 133).In small cysts,forexamplethe poorlydefined lesion in Figure 121 .2b,the average density measurement was toohigh, because adjacent liver parenchyma was included in thecalculation. atethatbenign cysts do notshowany significant enhancement after i.v CM. -iydatid (Echinococcus granulosus) cystshave a very characteristic multiloculated appearance, often with radially arranged septations oetween different cysts (169 in Fig. 121.3). It may prove difficult to differentiate between collapsed, dead cysts and other intrahepatic esions.The right lobeof the liver is most frequently affected,sometimes the leftlobeor thespleen (133) become involved,asshown in Figure 121.3. The density of the cyst 'Iuid is usually between 10 and 40 HU JI1 an unenhanced image. Partial or complete wall calcification is frequent anc the outer membrane may enhance Hith CM. The DD includes infections Hith E. alveolaris (not shown) and occaslonally hepatocellular carcinoma at is poorly defined with irregular satellitelesions. 121
  • 119. 122 Abdominal Pathology Liver LiverMetastases Multiple focal lesionswithintheliver suggest metastases.Common sites of origin are the colon, stomach, lung, breast, kidneys, and uterus.The morphology andvascularitydiffer betweenthetypes of livermetastases.An enhanced helical scan isthereforeobtained in Fig.122.1a Hypo- and hypervascularmetastases share the hypodense (dark) appearance in the venous phasebecauseofrapidwash-outof contrast material. If spiral CT is not avai- lable, it is helpful to compare unenhanced images (Fig. 122.2) with enhanced images (Fig. 122.3). In the example on the right, number and size of the hepatic lesions (7) would have been underestimated on the enhanced images. It is easily comprehen- sible that individual small metastases can escape detection if unenhanced images are passed over. To increase the contrast inthe hepatic parenchyma (122), a narrow win- dow setting should always be used when viewing these unenhanced images (see page 11 7).This might even bring out small metastases (7) (Fig. 122.2). These small liver metastases (7) differfrom small cysts by exhibitinq an indistinct margin and a higherdensity after intravenous injection of contrast medium (Fig. 122.4) indicative of enhancement. The average density values were55and 71HU,respectively(Fig. 122.4). In case of diagnostic doubt and for referenceat follow-up during therapy, it is useful to compare the CT images with ultrasound findings.Apart from thetypical hypoechoic halo, metastases have varied ultrasound appearances, just as in CT images [23]. The ultrasound diagnosis may be difficult, especially when calcifica- tionin metastases leads toacoustic shadowing. Even thoughthey are quite rare, slowly enlarging mucinous metastases (i.e. those from colon carcinomas) may become very calcified (" in Fig. 122.5). both the venous phase (Fig. 118.1a) and the early arterial phase (Fig. 118.1 c). Inthis manner,smallerlesions (7) become well de- finedandhepatic veins (103) will notbe mistakenformetastases.
  • 120. Abdominal Pathology Liver 123 Solid Hepatic Lesions A hemangioma is the most common benign hepatic lesion. In unenhanced images small hemangioma are well-delined homo- geneous areas 01 decreased attenuation. After injection of CM, enhancement typically begins in the periphery and progresses towardthe centerofthe hemangioma (Fig. 123.1 a),reminiscent of theclosing of an optic diaphragm. In dynamic bolus-enhanced CT sequences, enhancement progresses centripetally. Following Fig.123.1a Hepaticadenoma (" )occurs most frequently inwomenbetween theages of 20and 60years who havealonghistoryof taking oral contraceptives.An adenoma originates in hepatocytesandmay be solitary or multiple.The adenoma is usually isodense, sometimes ypervascular (Fig. 123.2), and may be accompanied by hypo- denseinfarction,central necrosis.and/orspontaneoushyperdense emorrhage. Surgical excision is recommended due to the oossibility of acute hemorrhage and malignant degeneration. By administration of a CM bolus, a series of CT images is acquired every few seconds at the same location. Accumulation of CM within the cavities of the hemangioma (,, ) leads to homo- geneous enhancement in the late venous phase(Fig. 123.1b). In large hemangiomas, this might take several minutes or be in- homogeneous. Fig. 123.1b contrast, focal nodularhyperplasia(FNH) does not show any ten- dency of malignant degeneration, and lesions of this kind contain biliaryducts. On unenhanced images, FNH appearsashypodense, sometimes isodense, but well-defined lesions. After Lv. CM, FNH oftendemonstratesan irregulariyshaped, hypodense central area (*) representing its central blood supply; however this feature is seeninonly 50%of all FNH(Fig.123.3). Fig.123.2 Fig.123.3 Fig.123.4 -iepatocellular carcinoma(HCC) oftenoccurs inpatients whohave along history of hepatic cirrhosis and is seen most often in men over the age of40 years. In one-third of all cases, HCCis solitary although multifocal lesions are notrare. Thromboses in the bran- cnesof the portal veincaused by tumor invasion intothe lumenof tnevessel may beseen in one-third of cases.The CT appearance HCC (Fig.123.4)isextremelyvariable. Onunenhancedimages, .,CC usually appears hypodense or isodense; CM may show diffuse or rim enhancement and central necrosis. When there is alsocirrhosis, it may be difficult to definetheborder of an HCC. Secondary lymphoma should be considered in the DO because it may infiltrate the liver parenchyma and may be the cause of dif- fusehepatomegaly. Ofcourse,this does not mean that everycase of hepatomegalyisdue toalymphoma.Non-Hodgkin'slymphomas resembleHCCbecause oftheirsimilaritiesinvascularityandnodu- largrowth.
  • 121. 124 Abdominal Pathology Liver DiffuseHepatic lesions In fattychanges ofthe liver,thedensity of the unenhanced paren- chyma, which is normally about 65 HU, may reduce so that it is either isodenseoreven hypodense withregard totheblood vessels (Fig. 124.1; cf. also p. 120). In hemochromatosis (Fig. 124.2), the accumulation of iron leads to increased attenuation above 90 HU and mayreach asmuchas140HU.lnthese cases, the naturalcon- trastbetween parenchyma and vessels is even greater. Cirrhosis (Fig. 124.3), resulting from chronic liver damage, has a diffuse nodularappearance andusuallygives the organ an irregular,lumpy contour. Fig. 124.1 Fig. 124.2 Fig. 124.3 If it is not possible to treat the cause of cholestasis surgically, inserting a stent (182 in Fig. 124.6) may decompress an obstructed biliaryduct(1 28). I Abdominal Pathology Gallbladder Biliary Tract After surgical choledochoenteric anastomosis, sphincterotomy, or endoscopic retrograde cholangiopancreatography (ERCP), hypo- dense gas (+) is usually present within the intrahepatic bile ducts (Fig. 124.4). These causes of biliary gas must be differen- tiatedfrom gas-forming anaerobic bacteria within an abscess. Dilatation of theintrahepatic biliary tract (128) is called cholesta- sis(Fig.124.5).It may result from gallstones,amalignant obstruc-
  • 122. Abdominal Pathology Gallbladder "he size and shape of the gallbladder vary depending on when the patient last ate food. A hydrops of the gallbladder should only be : iagnosed if there isvery marked dilatation,that is if the diameterexceeds 5 cm in several transverse planes.The attenuation of bile is usually just greater than thatof water (0 HU) but mayincreasetoupto 25HU if the bileis highly concentrated [4]. Cholecystolithiasis tones (167) withinthegallbladder (126) may show different patterns ofcaicification (Fig. 125.1).Cup-shaped and ring-likecalcifications canbe seen instones containing cholesterol and bilirubin (Fig.125.2).If stones obstructgallbladder drainage orinflammationhascaused stenosis, sludge may form resulting in increased attenuation and sedimentation of bile (Fig. 125.3). Common duct stones should be diagnosed usingthin-section CTbecause smallerstones might be missed in standard thickness sections. 125 Fig. 125.2b Fig. 125.3b Chronic Inflammatory l esions Cholecystolithiasis can lead to chronicinflammation, resulting inastone-filled,shrunken gallbladder, acute cholecystitis,or an empyema ofthe gallbladder (recognized by an irregularlythickened wall) (' , in Fig. 125.4). There is an increased risk ot malignant change with chronic inflammatory processes [24]. Thedevelopmentofa porcelain gallbladder (Fig. 125.5) with an egg-shell-likepatternof cal- cification(174) may be a premalignant lesion. Fig. 125.4 Fig. 125.5a Fig.125.5b
  • 123. 126 Abdominal Pathology Spleen Contrast Enhancement Before reading further, try to define a characteristic feature of the spleen by looking at Figure 126.1 a.The normal splenic parenchyma (133) has an attenuation ofapproximately45HUonunenhanced images.The attenuation ofthe spleen will only appear homogeneous in an unenhanced image or in the late venousphase of an enhanced study (Fig. 126.1c). In the early arterial phase (Fig. 126.1 a), it will enhance heterogeneously and appear patchy or marbled, a pattern representing itstrabeculararchitecture.This pattern should not be misinterpreted as an abnormality. Note also the uneven distribution of eM within the inferior vena cava (80) and the two (!) hepatic metastases (7) in the same image (Fig. 126.1 a). Did you spot the areas of near-water attenuation representing perisplenic/perihepatic ascites(8)? J, 122 J' / .•.. ~ ~ . / ~l~Rg.1m1a Rg.1m1b Rg.1m1c Thesplenicartery (99) istypicallyelongated and tortuous sothatit may be imaged inseveral consecutive slices. Inelderly patients, it is common to see atherosclerotic plaques (174 in Fig. 126.2). Occasionally, a homogeneous splenunculus [accessory spleen '], well demonstrated in the surrounding fat, may be seen at the hiium orthe inferior pole of the spleen (Fig. 126.3). Differentiating betweena splenunculus and an abnormally enlarged LN may be difficult. Fig. 126.2a Splenomegaly Diffuse enlargementof the spleen(Fig. 127.1) may be caused by several conditions: portal hypertension, leukemia/lymphoma, myelofibrosis and hemolytic anemia, or by various storage diseases. Assessment of splenic size is made difficult by individual variations in shape. Marked splenomegaly iseasiiyrecognized, butinborderlinecases of splenomega- ly and for follow-up one should know the normai range of splenic size. Inthe transverse plane,the length of the spleen ( I ) should measure no more than 10 cm (dotted line) and its width (d, atright angletothedotted line) should notexceed 5 cm (Fig. 126.4). In ultrasound, the spleen is not measured in a transverse plane but in an obliqu~ plane parallel tothe intercostal space.Inthis plane, theupperlimitofnormalis 11cmfor the long axis [28]. The craniocaudal dimension of the spleen should not exceed 15 cm, so that at a slice thickness of 1 cm it should not be visible on more than 15 sections. Splenomegaly is diagnosed if at least two ofthese three parametersare exceeded. Fig. 126.4
  • 124. · Abdominal Pathology Spleen 127 !.s splenomegaly develops, the typical normal :rescentic shape is lost (Fig. 127.1). Gross splenorneqaly. which may be caused by chronic mphocytic leukemia, acts as a space-occupying nass and displaces adjacent organs. In Figure 127.1, the left kidney is compressed ( "'). If the :loodsupplycannot keeppacewithsplenicgrowth, ntarctions( ,,) may result. Theseappearas hypo- cense areas that do not enhance with CM (Fig. 127.2). -ocal Splenic lesions Splenic cysts sharethe samecharacteristicsofhepatic cysts (cf. p.121). Metastases inthespleen (7)are rareand difficulttodistinguish ~om cysts. Inthe case illustrated in Figure 127.3,the diagnosis of splenic metastases was relatively easy becausethere were hepatic -slons and malignant ascites (8). If there are multifocal lesions with inhomogeneous CM enhancement, a diagnosis of focal splenic mphoma or splenic candidiasis should be considered. Ascites (8) may accompany candidiasis, as shown in Figure 127.4. Splenic mphoma is usually characterized by diffuse infiltration andthespleen mayappear normal. Ineexaminationof the spleen(133) afterabluntthoracic orabdominal trauma mustbemeticulous.Lacerations ofthe parenchyma(181) ;;Jay leadto hematomas (8) beneath thecapsule, and delayed rupture of the capsue may cause massive hemorrhage into the abdomi- Clal cavity (Fig. 127.5). =ig. 127.3b - ·e remnants of smaller hematomas may xesent as subcapsular ( ~ ) or parenchy- -al ( t )calcifications (Fig. 127.6). seotanens within splenic cystic lesions '1g. 127.7) are strongly suggestive of ,:ninococcosis, and appearquitesimilar to - e in the liver. In most cases the liver is 'so affected (cf. p121 ).
  • 125. 128 Abdominal Pathology Pancreas Acute andChronic Pancreatitis Acute pancreatitis may present as edematous interstitial pancreatitis (Fig. 128.1). Hypodense penpancreatic fluid (exudate) (8) and edemaoftheconnectivetissue (185) are frequentfindings. CTshows blurring of thepancreaticcontours;thenormally lobular pattern of thepancreas is effaced (Figs. 128.1 and 128.2). Inhemorrhagic necrotizing pancreatitis (Fig.128.2),the extent of necrosis isaprognos- ticfeature. Chronic pancreatitis progresses either slowly and progressively or inrecurrentepisodes.The twomost common causes of chronic pan- creatitis are alcohol abuse and cholelithiasis Typicalfindingsinchronic pancrea- titis are fibrosis and multifocalcal- cifications (174), irregular dilata- tion of the pancreatic duct (132), and sometimes the formation of pseudocysts (169) within, or next to,the pancreas (131 ) (Figs. 128.3 and128.4). Thedisease may lead to pancreaticatrophyas alatefeature. The possibility that pancreatic car- cinoma develops in association with chronic calcific pancreatitis is presently being discussed. Pancreatic Neoplasms Most pancreatic carcinomas (7)are located within the head ofthe pancreas (131).As a result, evensmall tumors may cause cholestasis by obstructing the common bile duct (127) (Fig. 128.5). Pancreatic carcinomas tend to metastasizevery early to theliver and the re- gionalLNs.Incase ofdoubt, ERCP shouldbe carried out toimagethe pancreatic and common bileducts. Isletcell tumors,75%ofwhich arefunctional, are located within the body ofthe pancreas.The Zollinger-Ellison syndrome (Fig. 128.6) iscaused by agastrin-secreting tumor ("). Otherneoplasms associated with the pancreas are insulinomas, glucagonomas, and serotonin-producing masses. '4iIIIIIItr; "'"~ . rl Jr. . ......
  • 126. 130 Abdominal Pathology Adrenal Glands The normal position and shape of the adrenal glands has been describedonpages 105to106.The maximumlengths ofthe adre- nal glands range between 2.1 and 2.7em, theright adrenal often being somewhat longer than the left. The thickness of the limbs should notexceed 5to8 mminthe transverse plane.Afusiformor nodularthickening (7) is likelyto be abnormal in CT,and is usually indicative ofhyperplasia oran adenomaof the adrenal gland (134 in Fig. 130.1). Typically, the adrenals can beclearly differentiated from adjacent tat, the diaphragm (30), the kidney (1 35),the liver (122),and theinferior vena cava (80). Fig. 130.2bFig. 130.1b The following conditions may be dignosed according to the spe- cific hormonal excess: congenital adrenal cortical hyperplasia (androgens), Conn's syndrome (aldosterone), and Cushing's syndrome (cortisone). An upper pole renal cyst (Fig. 130.2) or a renal angiomyolipoma (cl.Fig, 134.4) must beincluded intheDO. Attenuation values forbenigncysts (169) shouldlieclose tothose for water (= -1 HU in the present case) (Fig. 130.2). (Compare withcysts on p. 133.) In cases of heterogeneous enlargement of the adrenal gland or infiltration of adjacent organs, a metastasis or a carcinoma (Fig. 130.3) must be suspected. Since bronchogenic carcinomas often metastasize to the liver andtheacrenals,staging chest CT studies for lung cancer should be extended to include the caudal margin of the liver and the adrenals.Tumors of the paravertebral sympathetic trunks, which are located close tothe adrenal glands, may also be detected, but they are rare. The MRI images in Figures 130.4a and 130.4b show a neuroblastoma ("j in the sagittal (a)and coronal (b)planes. Fig. 130.3 Fig. 130.4a Fig. 130.4b
  • 127. , , Abdominal Pathology Adrenal Glands 131 .vhenever doubt exists whether an enlarged adrenal gland repre- sents a benign process, densitometry (see pages 121 and 131) withdetermination oftheenhancement patternshouldbe consid- ered: benignadenomas of the adrenal glandshow atendencyofa considerably more rapid wash-out of the contrast enhancement than malignant lesions, such as metastases and adrenal gland carcinomas (Fig. 131.1).This method requires anadditional scan at the level ofthe adrenal glandsafter 3, 10, or30minutes. 1 100 80 60 40 20 Dens ity (HU) 79±1 8 67±20 64±22 86±14 66±13 59±12 32±17 Time Unenhanced 30 sec. 60 sec. 90 sec. 3 min. 10 min. 30 min. I g.131.1 Rapid wash-out of contrast medium in benign adrenal glands adenomas (blue) in comparison with non-adenomas (gray) Jalignant tumors of the adrenal gland tend to have a prolonged contrast enhancement. This difference can be applied to the differential diagnosis. The dynamic enhancement pattern in the adrenal glands has been extensively investigated in numerous studies, which revealed further differences in absolute and rela- tive wash-out of the peak contrast enhancement. This wash-out pattern, however, shows a certain overlap between the tumor types, and thereforethe assessment has been proven useful only whenapplying thefollowingparameters [42]: Densitometry in theDDof space-occupying lesions of theadrenal glands Unenhanced: 10min.after injection of contrast medium: 30min.afterinjection of contrast medium: < 11HU < 45 HU < 35HU => => => Adenoma Adenoma Adenoma =Or these three values, the range of the histograms or so-called oox-whisker plots of Fig. 131.1 does not overlap for both tumor 'ipes, and a benign tumor of the adrenal glands can be safely assumed if the measured density values fall below these values. In all other cases, a benign adenoma cannot be assumed with acceptabledegree ofsensitivityand specificityand further evalua- tion is recommended.
  • 128. 132 Abdominal Pathology Kidney /' CongenitalVariations The attenuation of the renal parenchyma (135) on unenhanced images is approximately 30 HU.The kidneys occasionally develop to different sizes. If the outlines are smooth and the parenchymal thickness is not irregular, it is likely to represent unilateral renal hypoplasia(Fig.132.1).Thesmallerkidney neednotbe abnormal. A kidney may have an atypical orientation as in Figure 132.2. However, if akidney lies inthe iliacfossa (Fig.132.3).thisdoes not indicate an ectopic location,butarenaltransplant (135). The organ isconnectedtotheiliacvessels(113/116) and theurinary bladder (1 38). Fig.132.2b Marked differences in size, asin Figure 132.2, may indicate partial or complete renal duplication onone side. Thepositionsand number of renal arteries may vary considerably (110 in Fig. 132.1b).The renalarteries must be examined carefully for evidence ofstenosis as acause of renal hypertension.The ureter (137 ..) can be present asa partial or complete duplexureter (Fig. 132.4). In complete renal duplication, therenal pelvis is also duplicated. Occasionally, the low-density fat in the hilum (* in Fig. 132.5b) is only poorly demarcatedfrom the renal parenchyma (135) owing toabeam-hardening artifact or partial volume averaging (Fig. 132.5a).This gives theincorrect impression ofa renal tumor. Comparison with an immediately adjacent section (Fig. 132.5c) demonstratesthat only hilar fat was present. The actual tumor inthis particularexample(7) is situated atthe posterior margin of therightlobeofthe liver (122). Fig. 132.5a Fig.132.5c
  • 129. Abdominal Pathology Kidney 133 Cysts "enal cysts are frequent incidental findings in adults and may be located anywhere in the parenchyma. They may be exophytic or parapelvic, in which case they can resemble a hydronephrosis. 3enigncysts containaserous,usually clear liquidwithanattenua- eon of between - 5 and +15 HU. They do not enhance with CM becausethey are avascular. The attenuation measurement may be inaccurate if there are partial volume averaging artifacts due to slice thickness (Fig. 133.1 : - 25HU) orto eccentric positioning of theROI (Fig. 133.2: - 22HU) (cf. pp. 15and 121).Only thecorrect positioningof the ROIinthecenterof thecyst (0 inFig.133.3) will provideanaccurate average of 10 HU. In rare cases, hemorrhage into benign cysts will result in hyperdense values on unenhanced images. The attenuation values will not change on post-contrast images. iIlcreased density or calcificationsin a mass may indicate past renal tuberculosis, current Echinococcusinfestation(hydatiddisease),or acystic renal cell carcinoma. Thedifference between pre- and post-contrast images also provides information on renal function: after approximately 30seconds the well-perfused renal cortex is the first partofthekidney toaccumulatethe CM (cf. Figs. 133.2 and 133.3). After another 30to60seconds the CM isexcreted intothemoredistaltubules leadingtoenhancement of themedulla.Theresult is homo- geneous enhancement ofthe renal parenchyma (cf. Fig. 133.1). Fig.133.1 Fig. 133.2 Fig. 133.3 The appearances of multiple renal cysts in children with congenital autosomal recessive polycystic kidney disease are dramatically different from those ofthe occasional cysts found inadults,which are generally incidentalfindings. Polycystic kidney diseaseinthe adult 169 inFig.133.4) is autosomal dominantand associated withmultiple cysts ofthe liver, the bileducts and, morerarely,with cysts inthe pancreas orwith abdominal orcerebral aneurysms. Fig. 133.4a Fig. 133.5 Hydronephrosis "arapelvic cysts may beconfusedwithgrade 1 hydronephrosis (Fig. 133.5),whichischaracterized intheunenhanced image byadilated renal pelvis and ureter. In grade 2 hydronephrosis, the renal calyces become poorly defined. When parenchymal atrophy ensues, the ydronephrosis is categorized as grade 3 (see p. 134). Since no CM had been given tothe patient in Figure 133.5,thehyperdense lest- )f ( If ) in therightkidney mustbe a renal calculus. -orthe diagnosis of nephrolithiasis alone, CT should beavoidedbecauseof undue radiation exposure(ref. p.174ff.).Sonography isthe ethod of choice fornephrolithiasis as well ashydronephrosis.
  • 130. 134 Abdominal Pathology Kidney Hydronephrosis, which causes dilatation of the ureter (137) and the renal pelvis (1 36), impairs renal function (Fig. 134.1). In this image, the left renal parenchyma (135) shows delayed and reduced CM enhancement as compared withthe normal right kidney. Chronicgrade 3hydronephrosis reduces the parenchyma to a narrow rim of tissue (Fig. 134.2), resulting finally in atrophy and a non-functioning kidney. In cases of doubt, iden- tifying the dilated ureter(" in Fig.134.2b) can resolve theDD between a parapelvic cyst and hydronephrosis. CM accumula- tes in a dilated renalpelvis, but not in acyst. Fig. 134.2a Fig. 134.2b Solid Tumors Enhancement with CMoften helps to distinguish between partial volume averaging of benign renal cysts and hypodense renal tumors, since CT morphology alone does notprovide sufficientinformation about the etiology ofa lesion.This isespeciallyso whena mass(* ) is poorly defined within the parenchyma (Fig. 134.3).Inhomogeneous enhancement, infiltration of adjacent structures, and invasion of the pelvisortherenal vein arecriteriaof malignancy. Fig.134.3 Fig. 134.4 Fig. 134.5 However,whenamassconsistsnot onlyof solid, inhomogeneous areas, but alsocontains fat,anangiomyolipoma (7)must be considered (Figs.134.4 and134.5).These benignhamartomascontainfat,atypical musclefibers,and bloodvessels.Thevessel wallsare abnormal, and thecomplicationofintratumoral orretroperitoneal hemorrhage may occur (notdepicted here).
  • 131. , Abdominal Pathology Kidney 135 ~fter extracorporealshock-wavelithotripsy(ESWl),renal injuriesmay rarelyoccurthatleadtosmall hematomasorextravasation ofurine "am the ureter. If there is hematuria or persisting pain after ESWl , it is essential to obtain delayed images. Urine leaking into the ';troperitoneal spaces (+ inFigs.135.2a through 135.2c)wouldnot beopacifiedinimages obtainedbeforethe kidneyhasexcretedCM. Fig.135.1a 4g. 135.2a Fig.135.2b contoursat thekidney(135) appear blurred,anddependingon the extent of hemorrhage, hyperdense fresh hematoma (8) can be detected in the retroperitoneal spaces. in this case, enhanced images (Figs.135.1c and135.1b) showthat the renal parenchy- Fig. 135.1c Fig. 135.2c =""nal infarctions (180) usuallyhaveatrian- " arshapeon CTimages corresponding to -, vascular architecture at the kidney I g.135.3).The broad base abuts thecap- , e and the triangle gradually tapers . 'lardthe pelvis (1 36).Atypical feature is -e lack ofenhancement after i.v. CMinthe ;' ~y perfusion phaseand inthe lateexcre- phase. Embolisms usually originate in -e left heart, or in the aorta in cases of =- erosclerosis (174 in Fig. 135.3) or '-.eurysms (ct. p. 142). , mere is a low attenuation filling defect 73) in the lumen of the renal vein (111) rt sr a CM injection, the presence of bland r-ombus (Fig. 135.4) or tumor thrombus -JITl a renal carcinoma extending into -~ inferior vena cava (80) must be con- scered.
  • 132. Diverticula Diverticulasituated attheperi- phery of the bladder can easily be distinguished from ovarian cysts byusing CM(Fig. 136.3). The "jet phenomenon" is often seen in the posterior basal recess of the bladder and is caused by peristalsis in the ureters. They inject spurts of CM-opacified urine into the bladder, which is filled with hypodenseurine (Fig. 136.4). 136 Abdominal Pathology Urinary Bladder Catheters The walls of the urinary bladder are best examined if the bladder is distended. If a urinary catheter (182) is in place at thetime of CT (Fig.136.1),sterilewater canbe instilledas a low-density CM. Focal ordiffuse wall thickeningof atrabeculatedbladder, associatedwith prostatic hyperplasia, will be demonstrated clearly. If a ureter (137) has been stented (182) for strictures or retroperitoneal tumors. the distal end of the JJ stent may be visible in thebladder lumen (138) (bilateral JJ stents in Fig. 136.2). Fig. 136.3 Fig. 136.4 Solid Tumors Bladder wall tumors (7), which become visible after intravenous or intravesical CM, have characteristic, irregular margins that do not enhance with CM (Fig. 136.5). Tumors must not be confused with intravesicular blood clots that may occur following transurethral resection oftheprostate. It is importanttodetermine the precise size at thetumor and towhat extent adjacentorgans(e.g., cervix, uter- us,orrectum)havebeen infiltrated (.. in Fig.136.6). Fig. 136.5a Fig. 136.5b Fig. 136.6
  • 133. Abdominal Pathology Urinary Bladder , the bladder has been resected because of carcinoma, a urinary reservoir (* ) can be constructed using a loop of small bowel eumconduit) which has been isolated from the Gil Urine is excretedfromthe reservoir into a urostomy bag (.. in Fig. 137.1 b). J Figure 137.2 a colostomy ( ) isalsoseen (ct. p. 140). 137 :;g. 137.1a Fig. 137.1b Fig. 137.2 I Abdominal Pathology Reproductive Organs erus =nreign bodies in the uterine cavity (158), e.g. an intrauterine :ootraceptive device (166), are not always as clearly visible in a transverse image as in Figure 137.3. Calcifications (174) are a :naracteristic feature of benign uterine myomas. Nevertheless it can be difficult to distinguish multiple myomas from acarcinoma - . 137.3b of the uterus (7 in Fig. 137.4). If theadjacentwalls of thebladder (138) ortherectum (146)areinfiltrated,the tumor ismost likelyto be malignant (Fig. 137.5). Central necrosis (181) occurs in both kinds of tumors and is usually indicative of a rapidly growing, malignant tumor (Fig. 137.4). Fig. 137.5b
  • 134. 138 Abdominal Pathology Reproductive Organs Ovaries The most commonovarian lesionsare thin-walled follicular cysts (1 69)that containaclearfluid withadensityequivalent tothat ofwater, which is below 15HU(Fig. 138.1). Density measurements, however, are unreliable in small cysts (cf. p. 133). These cannot be clearly differentiatedfrom mucinouscystsorhemorrhagic cysts.Thislattertype of cystmay be caused byendometriosis. Sometimescystsreach considerable sizes (Fig.138.2) with consequent mass effect. Fig.138.3b The malignant nature of solid ovarian tu- morscan be suspected if thereare the fol- lowinggeneralcriteriaused forothertumors: 1) ill-defined margins; 2) infiltrationof adjacent structures; 3) enlarged regional LNs; and 4) inhomogeneousenhancement withCM. Peritoneal carcinomatosis (Fig. 138.3) frequently occurs in advanced ovarian carcinoma, and is characterized by the appearance of multiple fine nodules and edema (185) in the greater omentum, the root of the mesenteric, and the abdominal wall,and byascites (8). Fig. 138.3a Prostate, Vas Deferens High-densitycalcification representingpostinflammatoryresidueisoftenencountered following prostatitis(Fig.138.4).Calcificationsare also occasionally seeninthe vas deferens(Fig. 138.5).Carcinomaof theprostate isonlydetectableinadvancedstages (Fig.138.6)when the bladder wall orthe adjacent ischiorectal fossa fat is infiltrated.If a prostate carcinoma is suspected, allimages should be carefully viewed on bonewindowsfor sclerotic metastases (seep. 145). Fig,138.4 Fig. 138.5 Fig.138.6
  • 135. Abdominal Pathology Gastrointestinal Tract 139 of diffusewall thickening (Fig. 134.2), theDDshould also include lymphoma, leiomyoma, or leiomyosarkoma of the stomach. It is vital to look forbubbles of intraperitoneal gas ( " inFig. 139.3), which is evidence of a small perforation possibly occuring with ulcersoradvanced ulcerating carcinomas. wall (140) and also leadto muralthickening (Fig. 139.6).TheDD should inciude ischemia if the abnormality is limited to segments in the territoryof the mesenteric vessels, e.g., in the wallsof the colon (152), as a result of advanced atheroscierosis (174), or an embolus (Fig.139.7).Youshouldtherefore check thatthe mesen- teric vessels (108) and the walls ofthe intestine enhance homo- geneously after l.v. CM. Fig.139.6b=9,139.5 Stomach espite the advantages of using water as a hypodense CM for :naging the stomach after intravenous Buscopan [15, 16], small unorsmayescape detection during conventional CTs. Endoscopy - d endosonography should be employed tocomplement CT. arked focal wall thickening, which occurs in carcinoma of the iornacn, is usually easily recognized (.. in Fig. 139.1). In cases flammation of the Intestines ",e entire small and large bowel must be examined for wall " . keningorinfiltrationof thesurroundingfatas perthecheckiist _ page81. Bothulcerativecolitis(Fig.139.4) andCrohn's disease I g.139.5) are characterized bythickening ofthe affected bowel call ( t )so that several layers ofthe wall may become visible. =ssernlnatedintravascularcoagulopathy (DIC) or over-anticoagula- n with warfarin may cause diffuse hemorrhage (8) inthe bowel
  • 136. 140 Abdominal Pathology Gastrointestinal Tract Colon Elderly patients frequently have diverticular disease (168) of the descending colon (144) and sigmoid colon (145 in Fig. 140.1). The condition is more significant if acute diverticulitis has developed (Fig. 140.2), which is characterized by ill-defined colonic walls and edematous infiltration of thesurrounding mesenteric fat ( inFig. 140.2). Fig. 140.1a Fig. 140.1b Fig. 140.2 Malignant thickening of thecolonic wall (152 in Fig. 140.3) is not always easily distinguished from thatfound in colitis(cf.p.139):in both conditions there is stranding of the pericolic fat. The liver shouldalways bechecked formetastases if thecause ofthecolo- nic abnormality is uncertain. Atemporary colostomy(170 in Fig. 140.4) may benecessary if a Fig. 140.4b left hemicolectomyorsigmoid colectomy waspertormed because of pertorated diverticulitis or carcinoma. The colostomy is perma- nent if the rectum was excised. A potential complication of a colostomy can be seen in Figure 140.5:there is an abscessinthe abdominalwall (181).Acarcinoidlesion ofthesmall bowel ( in Fig. 140.6) may simulate acarcinomaofthe colon. Fig. 140.6
  • 137. Abdominal Pathology Gastrointestinal Tract 141 eus -odzontal air-fluidlevels ( .... )and atonic,dilated bowel loops 140) are typical features of ileus. Ifdilatation is recognized inthe :opogram(Fig. 141 .1),orin anoverview oftheabdomen, an ileus - ust be suspected. If only the small intestine (Fig. 141.2) is valved, the most likely cause isa mechanical obstruction dueto adhesions.A gallstone may cause obstruction ofthe small bowel (gallstone ileus).This follows cholecystitis withtheformation of a cholecystoenteral fistula and the passage of a gallstone into the bowel. The gallstone may obstruct the narrower caliber of the distal ileum(167 in Fig. 141.3). Fig. 141.3Fig. 141.2 -rethere anysuspicious findings other than the colic ileusin Figure •~1.4? Doestheimage remindyouof othersinthemanual?Makethe sf of the figures by returning to previous chapters, covering the ""xl, and identifying asmany structures aspossible.You will improve our learning efficiency by reviewing the images and diagrams and ..singthe legends to make sure you gotit right. 'echanical obstruction of the colon leads to similar air- fluid levels , ddilatation ( .... inFig. 141.4).Whenlookingforthecause ofan eus, the enfirecolon must be examined forobstructing or constrict- ' g tumorsorfocal inflammation. Test Yourself! Exercise 29: Spacefornotesandcompletingthe exercise:
  • 138. 142 Retroperitoneal Pathology Aneurysms Ectasia or aneurysms of the abdominal aorta (89) are usually the resultofatheroscleroticdisease(174) whichleadstomuralthrom- bosis (173 in Fig. 142.1).An aneurysm of the abdominal aorta is present if the diameter of the patent lumen has reached 3 cmor the outer diameter of the vessel measures more than 4 cm (Fig. 142.2). Surgical intervention in asymptomatic patients is usually consideredwhen the dilatation has reached a diameter of 5 cm. The general condition of the patient and therate at which dilatation isprogressing must be considered.If thepatent lumenis central and issurrounded by mural thrombosis(173inFig.142.2), the riskof rupture and consequent hemorrhage is reduced. Fig. 142,3a Fig. 142.3b Fig. 142.2a Fig.142.2b Fig. 142.1a The risk of rupture is greater if the patent lumen is eccentric( in Fig. 142.4) orif the cross-sectional shape ofthe vessel is very irregular.Dilatation inexcess of6 cmdiameteralso has ahighrisk of rupture. Surgical pianning requires the determination of whether, and towhat degree, the renai, mesenteric (97), and iliac (113) arteries are involved by the aneurysm (Fig. 142.3). Sudden painmay accompany ruptureordissection,which can extend from the thoracic to the abdominal aorta (cf. p. 93). Dynamic CM- enhanced CTwill show thedissection flap (172in Fig. 142.5). Fig. 142.4 Fig. 142.5a
  • 139. Retroperitoneal Pathology 143 lenous Thromboses 011 cases of thrombosis ina vein of the lower extremity ( ), venography • es not always clearly show whether or not the thrombus extends into =elvic veins (Figs. 143.1a and 143.1 b).The CM. which is injected into a superficial veinof the foot.isoftendilutedtosuch adegreethat it becomes ; icult toassessthelumen of the femoral/iliac veins(" inFig.143.1 c). - suchcases. it is necessary to perform a CTwith l.v. CM. Fig. 143.2b Fig. 143.2d Thelumenofavein containing a "'esh thrombus (,,) is general- . at least twice aslarge as nor- ""al (Fig. 143.2a). The segment :ootainingthe thrombus is either ,;]iformly hypodense compared Mlhtheaccompanying artery, or : shows a hypodense filling :efect. representing the throm- : us itself. In the case illustrated Fig. 143.2a :n theright,thethrombus exten- :ed through the left common ;;ac vein (, ) to the caudal seqrnent of theinferior venacava Fig. 143.2b), where it can be ",en as a hypodense area ( t ) serroundedby contrast-enhanced, "0I'ling blood (Fig. 143.2c). CT ;icesmust be continued cranial- J until the inferior vena cava no ;/lger showsany signsofthrom- Fig. 143.2c .us ( in Fig. 143.2d). --e injection of CM into a superficial foot vein opacifies satis- " ;torily onlythe ipsilateral leg, soit may beadvisabletoinject CM , stemicallythroughanarmvein inorder toexaminebothsides of - e pelvic venous system. If one side has become occluded, ~ aterals may develop ( ) via the prepubic network of veins (Figs. 143.3a and 143.3b). Such collaterals are known as a "Palmashunt",andthese can alsobe surgicallycreatedif athrom- bus in a deeper vein resists dissolution.You should be careful not to mistake an inguinal LNwith physiologically hypodense hilarfat ("hilar fat sign" " inFig. 143.3c)forapartiallythrombosed vein. I
  • 140. 144 Retroperitoneal Pathology In order to avoid pulmonary embolism in cases of thrombosis (173) of the inferiorvenacava (80inFig. 144.2),the patient must be immobilized until the thrombus has either become endo- thelialized orhas responded totherapy and dissolved. Occasionally, marked collateral circulation develops via the lumbar veins (121). Depending upon the individual patient and thesize of the thrombus,the vessel may be surgically explored and throm- bectomy performed. If thromboses are recurrent, an arterio-venous shunt may be indicated in order to avoid relapse. Thesuccess ofaparticulartherapymay also be checked with venography or color-Doppler ultrasound. Fig,144.1b Fig.144.4 Fig.144.5b Fig.144.3 Fig.144.5a Conglomerate LN masses (6/7) surrounding the aorta (89) and its major branches such as the celiac trunk (97) are a typical finding in cases of non-Hodgkin lymphoma (Fig. 144,5). EnlargedLymph Nodes Thedensityof LNsisapproximately50HU,whichcorrespondstothat of muscle.LNswithdiametersbelow 1cmaregenerallyconsidered normal. Sizes between 1.0 and 1.5 cm are considered borderline, and those that exceed 1.5 cm are abnormally enlarged. Sites of predilection for enlargedLNsarethe retrocrural, mesenteric ( ), interaortico-caval (,),and para-aorticspaces (cf. p. 103). Figure144.3illustrates thecase of a patient with chronic lymphatic leukemia. It isessential tobe familiarwiththe major paths of lymphatic drainage. The drainage of the gonads, for example, is directlyto LNs at renal hilar level. LN metastases ( " in Fig. 144,4) from a testicular tumor will be found in para-aortic nodes around therenal vessels but notin the iliac nodes, as would be ex- pected with primarycarcinomas of the urinary bladder, uterus, or prostate.
  • 141. Skeletal Pathology Pelvic Bones 145 a 28 35b • • 62 (Fig. 145.3a) only after they have reached considerable size. can be much more accurately detected on bone windows (Fig. 145.3c). This case shows a metastatic disease of the right ilium (58) that has destroyedthetrabeculaeandmuch of thecor- tex. The erosion extends to the sacroiliacjoint. See thefollowing pagesforfurther imagesof thispatient. .ormal Anatomy --eimportanceof examining bonewindows during abdominal CTshasalready been stressedon page103.Themarrowspaceoftheiliac - es (58) and the sacrum (62) is normally homogeneous. and the surfaces of the sacroiliac joints should be smooth and regular I g.145.1). tastases :- erotic bone metastases (7), for example from a carcinoma of -e prostate, are not always as evident as in Figure 145.2a and -.ay vary insize and degree ofcalcification. Even small and poorly :~'in ed metastases should not be overlooked ( in Fig. 145.2b). -'eycannot routinely be recognized on soft-tissuewindows. _- c metastases (7), whichcan be seen on soft-tissue windows =:. 145.3a Fig. 145.3b Fig. 145.30
  • 142. 146 Skeletal Pathology Pelvic Bones The mechanical integrity of a bone is suspect if any process involves its structure. Adjacent joint involvement must also be determined.MPRs (see p. 13) at various angles,forexample sagit- tal or coronal, provide additional information. If necessary, 3D reconstructions canalsobeperformed. In the case shown on the previous page (see Fig. 145.3), the .--- question of stability is easily answered: the coronal MPR (Fig.146.1a) shows thatthe trabeculae ofthe rightiliac bone have been completely destroyed for approximately 10 cm ( ). The lesion extends from the acetabulumtothe mid-point of the sacro- iliac joint and has also destroyed much of the cortex. In several areas, the cortex is disrupted (+ ). If you compare the bilateral sagittal reconstructions(Figs.146.1 b and 1c),it iseasy tosee that there isacute riskof fracture. Fig. 146.1a Fig. 146.1b The 3Dreconstruction of this pelvis (Fig. 146.2) does not add any more information, because it shows only the cortical disruption ( " ) as seenfrom the lateral perspective. The degree to which the trabeculae and marrow have been destroyed cannot be seen in this reconstruction because the attenuation level was set to detect the cortical bone, and the deeper trabeculae arethereforecovered. Fig. 146.2 'tJ' •
  • 143. Skeletal Anatomy Pelvic Bones 147 -orjointssuch asthe hip joint, it maybehelpful to makean MPR inthe obliqueplane (Figs.147.3).The angle ofreconstructionis shown .Il Fig. 147.3a. Be careful not to mistaketheacetabularsuture( ,,) withthe real ischialfracture (')1 35b Fig. 147.1bFig. 147.1a Fig. 147.2a f ractures 30newindows should of course ce used for the detection of . actures: hairline fractures and minimal dislocations cannot usually be recognized on soft- tissuewindows. ; is also essential to give infor- nanon on the precise fracture s' e and position of possible . agmentsfor preoperative plan- ~ing . ln thecase ontheright,the zacture (187) of the femoral -ead (66a) is seen both in the axial plane (Fig. 147.1) and in me sagittal reconstruction (Fig. 147.2) (ct. p. 13), Fig. 147.3a Fig, 147.3b b Fig. 147.3c 66 58 ~---~ -notner exampleofafracturethatmay bemistakenforasutureis lustrated in Figure 147.4.The sutures (,,) are bilaterally sym- metric,thefractures arenot. nthis case, several fragments ofbone ( .. .. )are seenatthe right iliopubic junction, butthe rightacetabulum isintact. Note also measymmetry in the Imagewhichis caused bydifferences in the evels of the femoral heads. The patient had left acetabular :ysplasia (cf.figures onp 148). Fig. 147.4
  • 144. 148 Skeletal Pathology Pelvic Bones Fragments are not always as obviously displaced nor is the fracture gap ( ) as wide as in the case illustrated in Figure 148.1. Look for fine breaks ( ) and discrete irregularities (..) in the cortical outline in order not to miss a fracture or a small fragment (Fig. 148.2). Fig. 148.1 Femoral Head Necrosisand Dysplasia of the HipJoint A fracture through the femoral head or even direct trauma to the hip joint may interrupt the blood supply to the head via the acetabular artery (see alsoFigures 147.1 and 147.2). Necrosisof the head makes it appear poorly defined ( ) as seen in Figure 148.3a and causes shortening of the leg.An image obtained 2cm Fig. 148.3a Fig. 148.2 more craniallyshows thatapseudoarthosishasdeveloped inasso- ciation with the right acetabular dysplasia (Fig. 148.3b). A 3Dreconstruction gives anoverview,butdoesnot provideasmuch detail as a series of coronal MPRs (Fig. 148.5b with orientation in Fig. 148.5a). Fig. 148.3b MPRs are often used for diagnostic purposes and in planning surgery of complexfractures. They contribute valuable additional information to the conventional axial images. SCTproduces parti- cularlyaccurate MPRimagesbecausedisruptivestepartitacts can be avoided if the patient is ableto cooperate by holding his or her breath. 3D reconstructions. such as the one in Figure 142.4, yield impressiveimages, butarehelpfulonlyforspecificproblemssuch as plastic surgery. The amount of time and cost necessarytoacquire and reconstruct 3D images are in most cases also very high.
  • 145. Test Yourself! "ne images and questionson this pagewill againhelp youto check on how muchyou have understood; the questions become contin- ually more difficult to answer. It you alwaysremember the basic rules of CT reading, youwill avoid jumping to thewrong conclusions. J<Jn't look uptheanswers too soonI 149 ~ Ihat abnormalitycanyou dentify in Figure 149.1? ameasmanybloodves- selsas youcan! ~ Identify as many organs and blood vessels aspos- sible in Figure 149.2. Look for any abnormali- ties. ~ What anatomic variation or abnormality do you recognizeinFigure 149.3? Be sureyouhaven't miss- ed anything. ~ "Doyousmoke?"What abnormalities did you find in Figure149.4? I mrmmaiseasy to recognizethe hepatic lesion in Figure 149.5.Whatis your DO? emmID Often abnormalities are not limited to one organ. What do yourrecognize in Figure149.6?
  • 146. Test Yourself! 150 Thefollowing questions may seem tricky, but you should be able toanswer most ofthem if you goby the "rules ofthe book." ~ Describe the hepatic le- sion in Figure 150.1. What steps did you take to arrive at your differen- tial diagnosis? How would you proceed to verify it? ~ Are thechanges in Figure 150.2 "normal," or do yoususpect that they are patho- logic findings? I omf:!lEI Whichofthe twoimagelevelsontheright wouldyou select for performing densitometric measurements of thekidney lesion? Why? ~ A patient is admitted for staging of a malignant melanoma(Figure 150.4). How far advanced is the lesion? What else would you do to obtain more information? ~ Atraumapatient couldnot be scanned in the prone position.What doyousus- pect in Figure 150.5, and what would you doto ob- tain more information?
  • 147. ~ ! problem for those oho alreadyhavesome ine(Figure 151.1). "'()W longdid ittakeyou R find two pathologic -terat ons and diag- -use themaccurately? Test Yourself! ~ Do you see anything abnormal in Figure 151.2? If so, what would you call it (the small figure indicates a structure filled with liquid)? 151 ~ !, least three differential : agnosesshouldbecon- - deredfor Figure 151.3. Which one is the most «ely? ~ In Figure151.4, thereare alsoseveral possibilities to explain the obvious alter- ation.Are you able to find all possible lesions in an imageof this kind? I ~ at doyou sus- cect isthecasein I gure 151.5? Hhat additional . formationdo u need? ~ This image (Figure 151.6) may contain several puzzles. Again, list the most likely diagnoses and thenask yourself what further information youneed.
  • 148. 152 Skeletal Pathology Cervical Spine (4 :< 2mm The occipital condyles at the base of the skull articulate with the first vertebra, the atlas (50a), which is the only vertebra to lack a body. The dens (50b) of the axis protrudes upward intotheatlas and isheldinplacebythe transverse iigament (*) (Figs. 152.1 and 152.2). This iigament may be torn bya whiplash injuryduring road tra~accidents. The width of the space ( ~) between the anterior arch of the atlas (* * in Figs. 152,1 and 152.2) and thedens is also measured, as in conventional x-ray images (Fig. 152.3). Inadultsitshould not exceed 2mm; inchildren, 4mm.The vertebral arterypasses through thetransverse foramen (88). Fig. 152.1 Fig. 152.2 Fig. 152.3 The images below show normal anatomyattheleveloftheatlas(Fig. 152.4) and the body oftheaxis (Fig. 152.5). The cartilageof an intervertebral disc (50e in Fig. 152.6) will appear more homogeneous and hypodensethan thetypical pattern oftrabeculae. Fig. 152.6bFig. 152.5bFig. 152.4b
  • 149. Skeletal Pathology Cervical Spine 153 Cervical Disc Protrusion Adisc protrusion (prolaps ofthe nucleuspulposus) isdemonstrat- edoptimallyinCTsectionsafter myelography(CM intheSAS). The spinal cord is virtually isodense to CSF in unenhanced images, making it difficult todefine thecontoursof thecord. After amyelo- gram, the CSF (132) will appear hyperdense to the cord (54) as well as to adisc. - disc prolapse will beseen evenmore clearlyinanMR image. The 32gittal T,-weighted image in Figure 153.3a shows the extent of : otrusions at twodiskspaces.Thediskprotrudes intothe hyper- ~rvical Spine Fractures - 's especially important to look forfractures of the cervical spine _ or torn ligaments after trauma (ref. p. 152) so that damage to -e cord is avoided if thepatient needs to be moved or transport- Normally, the CSF uniformly surrounds the cervical cord (Fig.153.1).Adiscprolapse (7).protruding intotheCSFspace can be seen because it is hypodense to the opacified CSF. The gap between thecord (54) andvertebral body (50) is filled in.Didyou recognize the pyriform fossa (172), the hyoid bone (1 59), the thyroid cartilage (1 69), and thecricoid cartilage (167)7 intenseCSF space (..)infront ofthecord.Theaxial T,-weighted image (Fig. 153.3b) shows that the prolapse extends to the left and has caused stenosisoftheintervertebral foramen ( ). ed. Figures 153.4a through c show a coronal MPR in which the right occipital condyle (160) is fractured (188) but thedens (50b) is still in normal position. Fig. 153.4b Fig. 153.4c
  • 150. 154 Skeletal Pathology Thoracic Spine The thoracic vertebrae articulate witheach other attheirsuperior and inferior articularfacets (SOd) and withtheribs (51) at the inferior and superior costal facets and thetransverse processes (SOl). Figure 154.1 shows a normal thoracic image: the contours of thecorti- cal boneare smoothandthetrabeculaehavea homogeneous pattern. Fig. 154.1a Fig. 154.1b Fig. 154.2a Fig. 154.2b Fig. 154.3a Fig. 154.3b Fractures of the Thoracic Spine Displaced fragments are identified by virtue of the fracture lines (187) and are best seen on bone windows. In Figure 154.2, both the transverse process (SOl) and thecorrespondingrib (51) are fractured. In complex fracture dislocations (Figs. 154.3), torsion orshearing may causecompression orcomplete dislocati- on of the spineas a whole (Figs. 154.3a, e). The axial image in Figure 154.3ashows two vertebrae ( ,,) at one level; the topo- gram in154.3bindicatesthe position ofthesagittalMPRshownin Figure 154.3e. The MPRgives a moreprecise pictureof thefrac- ture and the fragments than the oblique anterior and oblique posterior3Dviews in Figures154.3cand d.
  • 151. Skeletal Pathology Lumbar Spine 155 -·e transverse processes (50!) of the lumbar vertebrae are xcastonany called costal processes.Lumbar vertebrae havemuch - ger bodies(50) than thoracic vertebrae, and the angle of their ctervertebraljoints(50d)issmaller.Lumbarspinous processesdo -0 extend as far caudally as the thoracic ones. Images of the -oonal lumbar spine usually show well-defined cortical bone and homogeneous trabeculae. At the level of a disk (Fig. 155.2), the hypodense cartilage (50e) may seem irregularly surrounded by bone: this is an oblique partial volume effect inwhich parts of an adjacent body (50) are included withthe disk.The ligamentaIlava (*) extend from one lamina to the next and can sometimes be seen behind the cord (Fig. 155.1 a). I 31 50 50e 0 22 ~ _ 22 9g,155.1b Fig. 155.2b Fig. 155.3b )egenerative change of the vertebrae can be seen in the facet joints (50d) (Fig. 155.3). There is increased subchondral sclerosis .., ,,) indicativeof arthrosis ofthe joint. .urnbar Disk Prolapse -s with cervical disk protrusions (see p. 153), it is important to : tabllshwhether the nucleus pulposus hasprotruded through the rosterior longitudinal ligament. This ligament is applied to the : terior borders of the vertebral bodies and disks. Disk material - t has penetrated the posterior longitudinal ligament and .ecome detached from the disk is referred to as a sequestration **). This can narrow the spinal canal or a lateral recess (Fig. •55.4). Thesestructuresarenot well demonstrated on soft-tissue win-dows(Fig.155.4a) because of their high density,but are dearty seen on bone windows (Fig. 155.4b). A T2-weighted MR image (Fig. 155.5) shows theextent of the prolapse: the abnormal disk (+) is thinner,isdesiccated(shows alowersignallevel [darker]), and the extruded material ( ,,) impin- ges onthetheca.
  • 152. 156 Skeletal Pathology Lumbar Spine Fractures Inconventional x-ravs, it isoften difficult tosee thefracture ofa lumbar transverse process (501) if the fragment is notor only minimal- lydislocated (187).InCTsections, however,afracture can be clearlydemonstrated (Fig.156.1). Figure 156.2 illustratesacase in which the spinous process (50c) was fractured.An arthrosis may develop if afracture has involved ajoint (Fig. 156.3).Therearefractures of boththesuperior and the inferior articularprocesses (50d). <, I ~~50C/ V~ 187- - 187 , ,""~~'t)~ 22 6 22 b .- Fig. 156.1b Fig. 156.2b Fig. 156.3b Older fractures donot show awell-defined fracture line (1 87).Increasedsclerosis and new bone often efface thefracturelineorapseud- arthrosis may develop. Inthe case shown inFigure 156.4,the fractured pedicle has developed a pseudarthosis. Inconventional x-rays, increased sclerosis following afracture is often difficultto differentiatefrom that resultingfromdegenerativedisease. Fig. 156.4a Fig. 156.4b
  • 153. Skeletal Pathology Lumbar Spine 157 -umors and Metastases at all bone lesions originate within the bone. Malignant tumors of paravertebral tissues can also 'Vadethe bones. =igure 157.1 shows an osteolytic lesion (,, ) in the body of a lumbar vertebra in a patient with :arcinoma of the cervix. On soft-tissue windows (Fig. 157.2), there is a paravertebral metastasis (7) A't1ich has surrounded the bifurcation ofthe common iliac artery (114/5)and has infiltrated theright anterolateral aspect ofthe vertebral body. DRs in the coronai (Figs. 157.3a and b) and sagittal (Figs. 157.4a and b) planes show the extent towhichthe bone has been eroded "nd that there is risk of fracture.As in Figure146.2. the3Dreconstructions (Figs. 157.5a and b) clearly show thelesion from anterior ' -d lateral perspectives, butnotthe degreetowhichthe interior trabeculaehave been destroyed. I
  • 154. 158 Skeletal Pathology Lumbar Spine I Infection Abscesses inthe paravertebral soft tissues or infectiveor inflam- matory arthritides (1 81)inthe smalljoints ofthe spine may leadto diskitis which ultimately destroys the intervertebral disk (Fig. 158.1). An advanced abscess canbe detectedon soft-tissue win- dows (Fig. 158.1a) asanarea ofheterogeneous density surroun- Fig. 158.1a Methodsof Stabilization If therapeutic measures such as chemo- therapy, antibiotics, and/or surgery have been effective in the treatment of a me- tastasis or infection, it is possible to stabi- lize the spine by inserting bone prosthetic material(Fig. 158.2a, b). The choice of material depends upon the size ofthedefect and upon other individual factors. In follow-up examinations, these materials may cause considerable image artifacts because of their high relative density. Fig. 158.2a Space for additional notes: ded by a hyperdense enhancing rim representing reactive hyper- perfusion. On bone windows(Fig. 158.1c),onlysmall remnantsof bone belongingtothevertebral bodyare present andsome are dis- placed. Fig. 158.2b
  • 155. Lower Extremity Normal Anatomy of the Thigh 159 iheanterior muscles of thethigh includethe sartorius muscle(38), andthe four componentsofthe quadriceps muscle(39).The most anterior istherectusfemoris (39a),and lateraltothisisthevastus .ateralis (39b).The vastusintermedius (39c) and vastusmedialis (39d) form the anterolateral borders of the adductor canal. This contains the superficial femoral artery and vein (119/120). The adductor muscles comprise the superficially located gracilis muscle (38a) and the adductor longus (44a), brevis (44b), and magnus (44c) muscles. Thepectineus muscle (37) isonly seen in memost caudal images ofthe pelvis. =jg. 159.3a The posterior muscles ofthe thigh extend thehipjoint and flex the knee joint.The groupconsists of the long and short heads of the biceps femoris muscle (188) and the semitendinosus (38b) and semimembranosus muscles (38c). In the proximal third of the thigh (Fig.159.1),thehypointense tendon ofthe biceps muscleis adjacent to the sciatic nerve (162). In the distal third of the thigh (Fig. 159,3),themedial poplitealnerve (162a),whichsupplies the dorsal muscles, can be seen separate from the lateral popliteal nerve (162b). Note the close relationship of the profundafemoris artery and vein (119a/120a)tothe femur (66) and thesuperficial posi-tion of the long saphenous vein (211a). Fig.159,lb Fig.159.2b Fig.159.3b
  • 156. 160 Lower Extremity Normal Anatomy of the Knee The popliteal artery (209) and vein (21 0), formed cranial to the joint line, are demonstrated at the level of the patella (191) In the fossa between the femoral condyles (66d)(Fig. 160.1).Thetibial nerve (162a) lies directly posterior tothevein,whereasthefibular (peroneal) nerve (1 62b) lies more laterally.Themedial (202a)and lateral (202b)heads of thegastrocnemiusmuscle and the plantar- is muscle (203a) can be seen posterior to the femoral condyles. The longsaphenous vein (211 a) lies medially inthesubcutaneous fat covering the sartorius muscle (38), and the biceps femoris muscle (188) lies laterally. On the section just caudal to thepatella (Fig. 160.2), the patellar tendon (1 91c) can be identified, posterior to which is the infrapa- tellar fat pad (2). Between the femoral condyles lie the cruciate ligaments (191b).Transversesections such as thesearefrequent- ly combined with coronal and sagittal MPRs (seealso the images ofafractureon p. 167). Fig. 160.1c Fig. 160.2c
  • 157. Lower Extremity Normal Anatomy of the Lower Leg 161 Themusclesofthelowerlegare separated into four compartments uythe interosseus membranebetweenthe tibia(189) and the fibula (190) and by the lateral and posterior intermuscular septa Figs. 161.1 to161.3). Theanterior compartment containsthetibia- tis anterior muscle (199), the extensor hallucis longus muscle (200a) andthedigitorum longusmuscle (200b) next to the anteri- ortibial vessels(21 2). Thelateral compartment containstheperoneuslongus (201 a)and orevls (201 b) muscles next to theperonealvessels (214). In slen- cerindividuals who have no fat between the muscles, these ves- sels and the peroneal nerve are only poorlydefined (Fig. 161.2). The flexor muscles can be separated intoa superficial and a deep group. The superficial group encompasses the gastrocnemius muscle with medial (202a) and lateral (202b) heads, the soleus muscle (203), and the plantaris muscle (203a). The deep group includes the tibialis posterior (205), the flexor natlucis longus (206a), and the flexor digitorum longus muscles (206b). These musclesareparticularlywell defined inthedistal thirdof the lower leg (Fig. 161.3).Thetibilalis posterior vessels (213) andthetibial nerve (162a) pass between thetwoflexorgroups. Fig. 161.1b Fig. 161.2b Fig. 161.3b
  • 158. 162 , Lower Extremity Normal Anatomy of the Foot Fig. 162.1b The following three pages show the normal anatomy of thefoot onthe bonewindow. You will find the numbers to the legends inthe back fold- out. The image series beginsin a plane throughthetalus (192) just distal to the talocrural joint.Figure 162.1 shows the distal end of the fibula or lateral malleolus (190a) as well as the upper partof the calcaneous (193). In Figure 162.2,thesustentaculumtali (193a) of the caicaneous is Fig. 162.1 a seen. Compare these images of a normal foot with the images of fractures on pages 164 and 165. The Achilles tendon (215), which arises from both the soleus (203) and the gastro- cnemius (202) muscles, is seen posteriorly on these images. More distally,additional meta- tarsal bones are seen: the navicular bone (194) has begun to appear in Figure 162.2. but its joint with the talus is better assessed in Figure 162.3. The articular surfaces are normallysmooth and the synovial space be- tweenthebones is ofuniform width. I Fig. 162.3a Fig. 162.3b
  • 159. Lower Extremity Normal Anatomy of the Foot 163 The cuboid bone (195) is seen on the lateral margin of the foot, between the calcaneus (193) and the navicular (194). The lateral (196c). intermediate (196b), andmedial (196a) cuneiform bones lie anterior to the navicular(Fig. 163.1). The transition to the meta- tarsal bones (197) is not always well defined, because the plane of the tarsometa- tarsal joints is at an oblique angle to the sections (partial volume effects (Fig. 163.2). Thejoints can bemoreclear- ly assessed in mulliplanar reconstructions that take this obliquity into account (cf. Fig, 164.1 ). The lumbrical and quadratus plantae muscles and the short flexor muscles of the foot (208) are seen just below the arch of the meta- tarsal bones. These muscles Iareonly poorly defined in CT images (Fig. 163.3). - .163.3a Fig. 163.3b
  • 160. 164 Lower Extremity Normal Anatomy of the Foot Multiplanar reconstructions are very valuable for visual- izing fractures of the foot. Thelateraldigital radiograph in Figure 164.1 a Indicates theangleof theimageplane, parallel tothelong axisof the foot,seen inFigure 164.1 b.Thisreconstructed image extends from the lateral (190a) and medial (189a) malleoli (at the loweredge of the image) throughthe talus (192) and the navicular (1 94) to the three cuneiform bones (196a-c). Two of the metatarsal bones (1 97) are included in the section. Note thatthe surfaces of the joints are smoothand evenly spaced. Thesagittal image in Figure 164.2b was reconstruc- ted slightly more laterally (see position in 164.2a) so that the cuboid bone (1 95) is included. The short flexor muscles (208) and the plantar ligaments are seen below the archof the foot. The Achilles tendon Fig. 164.1b (21 5) isseen posteriorly. Fig. 164.1c I Fig. 164.2a Fig. 164.2b Fig. 164.2c Diagnosis of Fractures Typical signs ofafracture canbe seen intheoriginal axial plane (Fig. 164.3a): irregularities inthecortical outline( ), displaced frag- ments ( ) and a fracture line ( ) in the calcaneous. The MPR in the coronal plane (indicated in Fig. 164.3b) shows that not only is the calcaneous ( l )fractured,butthereis ahairline fractureof the talus (..) involvingtheanklejoint (Fig. 164.3c).
  • 161. Lower Extremity Pathology Fractures of the Foot 165 Fractures of the foot may initiallyescapedetectioninconventional x-rays if thereis nomajordisplacement of bone fragments. If the foot remains painful, a follow-up x-ray may show the fracture because fine hairline fractures can be seen when filled with hemorrhage. As an alternative, CT would show discrete fracture lines (1 87),as forexample ofthe talus (192) in Figure165.1. In chronic fractures, the displaced fragment (*) has usually be- come rounded off (Fig. 165.2). Inthis example. it is obvious that therewereactually twofragments because asecond fracture line ( '" ) is seen nexttothe main one (187). It is often difficultto treat comminuted fractures ofthecalcaneus (193), incurred for example during a fall (Fig. 165.3), because therearemanysmalldisplaced fragments.Astabilereconstruction of the arch of the foot may not be possible, resulting in a long period of sick leave. - . 165.1b Fig. 165.2b Fig. 165.3b
  • 162. 166 Lower Extremity Pathology Pelvis and Upper Leg Infections Theassessment of fractures oflongbones is generallythedomain of conventional radiology. But CT examinations are helpful for locating displaced fragments andin the preoperative planning of comminuted fractures. Infections, however, are more accurately imaged by CT than by conventional radiographs because bone destruction is more readily seen on bone windows (Fig. 166. 1c) and soft-tissue involvement (178) is documented on soft-tissue windows (Fig. 166.1a).This patient had septic arthritis ofthe left Fig. 166.1c hip jointwithinvolvement ofthe acetabulum(60)andfemoral head (66a). I The abscess appears more clearly after contrast enhancement (cf. Figs.166.2a and 166.2c).The increased vascularityof thewall and the fluid within the abscess (181) are well demarcated from surrounding fat (2).Adjacent muscles (38, 39, 44) are nolonger individually definedbecause ofedema (compare with the rightleg). Gas (4) has been produced and is loculated in the adjacent tis- sues. Fig. 166.2c
  • 163. Lower Extremity Pathology Knee Joint 167 Fractures .afracture involves the knee joint, it isparticularly important toreducethe fragmentsaccuratelytoavoid jointsurfaceincongruities that might lead to arthosis. In the case below, axial sections clearly show the lateral displacement of a large fragment ( ,, ) of the tibia Figs.167.1aand 167.1b).Thecoronal MPR(Fig. 167.2b.with level shownin 167.2a) illustrateshow muchofthetibial plateauis affected. Fig. 167.1b Fig. 167.2b Fig. 167.3b "he3Dreconstructionseenfromaposterolateral projection(Fig. 167.3a) isnotveryhelpful,buttheview fromcranial (Fig.167.3b) gives ; good impression ofthe tibial plateau and fracture line becausethefemoral condyles have beenexcluded. Checklist Skeletal System: Fracture Diagnosis ..... Step-off ordiscontinuityof the cortex (evidenceof fracture)? ..... Articular involvementof afracture(risk ofsecondarydegenerativechanges)? ..... Stabilityon weight-bearing? Spine: e.g.•3-column model accordingto Denis (C-spine);A-B-Cclassificationaccording toMagerl (T-spine) ..... Simplefracture orcomminutedfracture,extent of displacementof thefracturefragments (surgical planning)? ..... Age of thefracture? • Acute => ragged and sharply demarcatedfractureclefts • Old => sclerotic rim,callus formation Riskof pseudoarthrosis with persistent fracture cleft? ..... Traumatic or pathologic fracture (underlyingbonetumor)?
  • 164. Interventional CT 168 Itis not always possibletodeterminethenatureof alesionfrom CT appearanceand densitometryalone. In these cases, needlebiopsies may be carriedout underultrasound or CT guidance.The patient'splateletcount and coagulation st~'us mustbe checked and Informed consent obtained. InFigure 161.1 ,amassinthe caudate lobe (*) of the liver (122) is being biopsied. The close proximity of the hepatic arteryand portal vein(98/102) andinferiorvena cava (80) leaveonlya narrow path fortheneedletoapproach fromthe right side (Fig. 168.1a).First- ly the section on which the lesion appears largest is determined. The skin is cleaned and anesthetized with local anaestheic. Fig. 168.1a Fig. 168.1b Theneedle isthen inserted through the liver parenchyma toward the lesion. Slight changes inanglemay be neces- sary (Figs.168.1b, 168.1c, and168.1d). Distances can also be calculated duringtheprocedure,as seeninFigure 168.1b. After biopsy has been com- pleted, an Image is acquired to detect any hemorrhage. If a pneumothorax occurred following lung biopsy,expira- tory images of thethorax are acquired to check foratension pneumothorax. Fig. 168.1c Fig. 168.1d Ifthere isa retroperitoneal lesion close to the spinal column, a biopsy may be carried out In the prone position. The orientation inFigure168.2 istherefore unusualand one must be careful notto confuse left with right, but the proce- dure is identical. After selectionoftheoptimal level (lar- gest diameter of the lesion), and after skincleaning and local anesthesia, the needle is inserted (Fig. 168.2b) and the biopsy taken. The material should be promptly prepared for cytology and histology. The sizeand extent ofacutaneousfis- tula can often be more clearly assess- edIf CM isinstilledthroughatube(Fig. 168.3). In this example, the hip had become infected and an abscess filled thejoint after prosthetic surgery. Fig. 168.2b Fig. 168.3b Fig. 168.2a Fig. 168.3a
  • 165. Skull: Bleeding ? Metastases? Fracture ? Mid-facial bones: Coronal, fracture ? Axial Axial to coronal reconstruction Petmus bone: C1 and C2 multiple trauma: Extremities (fracture?): Neck: Thyroid carcinoma ? Staqing of the pulmonary apex Thorax!abdomen: Staging ? Liver arterial + thorax Liver portovenous + pelvis Gynecologic + other tumors of the lesser pelvis Vena cava: Thrombosis Pulmonary embolism: Lung: Soft tissue window Pulmonary window Liver series: hemangioma ? (dynamic at the same level) Adrenal glands: Tumor ? Unenhanced Arterial Portovenous Late venous Perfusion: Head· unenhanced IV eM-concentration 300 ·370 Bone: Densitcmetrv t-solne Dental: Infratentorial: 3 / 3 / - Supratentorial: 8/ 8/ - 2/3 / 1 2 / 3 /2 2 / 3 /1 1 / 1,5/ 0,5 2 / 2/2 2/2/ 1,5 5 /5 /5 517,5 / 4 8 / 12 / 8 5/8/5 8 / 12/8 2 / 4 /2 5 / 8/5 8/ 0/ - 5 /~ 5 /4 5 / ~5 /4 5 / ~ 5/ 4 5/~ 5/ 4 Basis 3 / 3 /- Neurocran.8 /8 / - 10/0 / - 10 / 0 / - 1 / 1,5 /0 ,5 1,5 1,5 1,5 1,5 1,5 1,5 1,6 1,5 2 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 0,8 0,8 0,8 0,8 0,8 0,8 0,8 1,0 0,8 0,8 0,8 0,8 1,5 0,8 130 130 130 130 130 130 130 130 130 130 130 110 130 130 130 130 130 130 130 130 130 130 11 0 80 130 260 260 260 80 80 80 135 170 70 100 140 140 140 140 100 110 140 120 140 140 140 260 106 81 90 H 30 H 30 H 30 H 70 H 70 H 80 8 50 B 80 B 50 B40 B 40 B40 B40 B 40 B40 B 40 840 840 B 40 B40 H 30 H 30 S 80 H 70 caudocranial caudoc ranial cra niocaudal craniocaudal craniocaudal craniocaudal craniocaudal cra niocaudal craniocaudal cran iocaudal cra niccaudal craniocaudal craniocaudal caudocranial craniocaudal caudocranial caudocranial craniocaudal cramocaudal 250 / 40 90 / 35 1500 / 450 1500 /450 1500 /450 and 350 140 1500 /450 350 / 40 1500 /450 350 /450 1500 / 450 350 /40 2000 / · 300 350 / 40 350 / 40 350 /40 350/40 350/ 40 2000 /·300 350 /40 2000 / -300 350 /40 350 /40 250 / 40 + 90 /35 350/40 350/ 40 1500 / 450 60 / 1,5 70/2,0 120 / 3,0 - 5,0 100 / 2,5 120 / 2,5 2x 50ml bipedal 120 / 3,0 - 4,0 100 / 2,0 130 /2,0 80·100 /2 ,0 40 /8 60 25 - 40 8T post 90 60 90 - 100 8T A.asc. BT arterial: BT Venous: about 90 ~g ~~ g Pol ('D . < n ~ ~ O- 3. g (i3 C3 o- =r .... CJ) 3 ('D ~ ~ - S'WCD _ (3CDC.~c. S ~~ · co ~ .:<l ro"Q s:g ~. c. S- a II ~ 0- 8 Ci5 :-" ~ st en ~c..n C3 CO cr o CJ) CJ) CJ) ~ 0- ~ o~ a 8g :E~. enc.(O~ o <n W n :::J c.. -;-aC") ~ o :::J-< ..... -o ~ c. c: C'D 0 - (3 ~ ~. .-+ W .-+ ;::;: C'D C'D sa. !a Pol g z.(Ocr~roCJ) w :::Jc. n .-+ ~ -· n w _ $~§3'~Q (3 ~~rg~.-+c. _ ... ~ .....0 -Cc: ~ s· o 0 Co ~ 9: ~ 3 ~r cr~g:3=: co :::J :::J ~ g ~~~?- $" Q.) en 0 CJ) r::::... _ . c: .-+ C3 ro C'D .-+ 2 .-+ _ 3 CJ) (") ro s s ~. s st :::J en C3 :::J C'D c.m=-· <n g3~Sg. 'Eg~ <=.- o -· W CJ)(O~.c- CJ) ro r:::: _ l:: ...... en ro ::0 C'D -.....J 5 ' _ . .::: en 0(0 CJ) - . __ _ CJ) ... • C'D~-os. ("')oa~ ;-i (i3 s, e: -lc.c.~ ~~~ II :::r - w CD C3 0 C" en (") Co @§!g < '" <_ . c. C'D • §:-oa o o PJ _ . CJ) ~ ... 0 C'D CJ) Q.) ~ (") o 3 ~ g -~Q)c. .-+ ro (") CI:l =r ... .c _C'D CJ) c: . -0 PJ Vi· :::;:: ~ :g as., _ 0 3 -c ~ ... C'D 0 :E ~ c:D ..... ;:::::;:o ... =r =r ~ en CD I I ..... en c.o
  • 166. 170 Examination Protocols for 4-slice Spiral CT o co in ci o N ro. ~ t « o.D E "», roc o E 'S 0.. "' '"x .,. o _LD--. C') I- N I- t.hcoo coCJ"-' CJ- o co co oi x -e ro st « '"E o .c c. E ~ ,..j 0.. Z roc eo o I I "' "'"'- . I I 0 '" 0 6 '" "' o '"' 00 0 NN N 0 0 0000 0 lQlfL()lO l!) ...... -- ---0 0 00 0 OOLOL() If) 00 (')(") ('I) N N 00 a 0 CJ) Q) 0) Q) D "c c "'0: '§I "c ::::> x x .,..,. '0, c .2 vi 'w e.D iL o c-i o o "' "'ci Ci x X N .,. co "'- 0 0 0 0 0 0 N sc -sr o '" 00000 0 L()1.[) «:tmm "::l" I I I :)::J (IJ ro roroc c c e e e0 0 0 o 0 0 o N x x .,. .,. o co ro roc c e eo 0 . 0 0 00 0 00 NN(O(O lt) I I I I I '" '" '"'" '" '"o 0 ci f- (/] '"-eo Feed / rotation o so o "' Collimation ( e.g. 4 x 2,5 =10) m '"I I 0 0 0 0 O<OO l() MC'JC')(J 0000 "'i" "<t "::!" C') I I I I co co io "::l"OO "::l" OO "::l"~CJ (Jv N C') 6.... LO 00 0 0 0 Cl(jClCJ (J .... .,..- .... .... .... co ....... ro x x x x x 7 CJ"'1" N '<j" If)ll)lf)l() lt) I!) l!) t-- t-- t--I'- r-- I'- I"- 0000 ci 0 cl Thepitchwas caiculated accordingto theformula: Pitch = = Sequential data acquisition = Tablefeed per rotation = Section collimation = Section thickness =Reconstruction interval =Contrast medium =CM volume/ time =Delay afterthe beginning of the CM injection =Automatic bolustracking = Pitch =Tube voltage = Tubecurrent = Kernel, edgealgorithm = Sinusthrombosis = Multiplanar reconstruction = Maximum intensity projection = Renaltransplant = Hepatocellular carcinoma For the application of the contrast medium ("GM"), the amount in ml of a concentration of 300-350 g iodine/ml and the flow rateofthe injector ("flow") in ml/second is stated. In addition, the term "delay" states in seconds when the gantry begins its data acquisitionafter thebeginning of theinjectionof con- trast medium.Theterm"BT" refers tobolustracking, anautomated softwareprogram.For instance,an ROI is placed over the descending aorta, and when the intravascular density exceeds a preselected level (e.q., thebolusof contrast medium is arriving), data acquisition begins automatically (see page 176). In modern units, the examiner selects thecraniocaudal span of the body region to be examined, the desired examinationtime,the rotationspeed,and thesection collimation. The scanner then optimizes table feed and pitch on its own. Thesearethe examination protocolsfora 4-slice spi- ral CT, established for the Siemens Sensation 4. For clinical questions not suitable for spiral technique in our experience, the expression "seq." is listed instead of the table feed per rotation ("feed/rot."). The collimation ("coiL") must be selected by the examinerinadvance,whileinmultislice scannersthe reconstructed effective section thickness ("ST") can be selected later. The reconstruction interval ("RI") statesthe distance between thesectionsforthe sub- sequent reconstruction from the three-dimensional data set. The term kernel refers to the edge algo- rithmof the manufacturer: H= Head, U = Uitrahigh, B = body. Seq. Feed/rot. Coli. ST RI CM Flow Delay BT Pitch kV mAs Kern ST MPR MIP RTP HCC
  • 167. Chest - Bronchial carcinoma Arterial 4x5 7 30 1,5 7 0,5 120 90 B 30 350/ 50 80-100 / 3,0 Liver BCI 7 7 B 60 2000/ -300 Abdomen NPL, lymphoma Arterial 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 200 /40 25-30 100-120 / 3,0 Venous 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 350 / 50 50-75 Stomach: Hydro CT Arterial 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 350 / 50 25-30 1100-120 / 3,0 I(stomach filled with H?O Venous 4 x 2 5 5 12 5 1 25 5 05 120 155 B 30 350/ 50 50-75 Pancreas/k idn eys 1NPL Unenhanced 4 x 5 7 25 1,25 7 0,5 120 155 B30 350/50 Arterial 4 x 1 3 4 1 3 0,5 120 165 B 30 350/ 50 I I 30-40 1100-120 / 3,0 Venous 4 x 2 5 5 12,5 1 25 5 05 120 155 B 30 350 /50 IBT Adrenal glands 1Adenoma Unenhanced 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 350 /50 Arterial 4 x l 3 4 1 3 0,5 120 165 B 30 350/50 I I 30-40 1100-120/ 3,0 After 3 min 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 350/ 50 (BT) Optional After 10 min 4 x 2 5 5 12 5 1 25 5 05 120 155 B 30 350/ 50 3-phase liver 1Hemangioma, HCC Unenhanced 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 350 / 50 Arterial 4 xl 3 4 1 3 0,5 120 165 B 30 250 / 40 25-30 1100-120 / 3,0 Venous + 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 350 / 50 (BT) ocnonatoetvis Chest-abdomen INPL, lymphoma Arterial 4x5 7 25 1,25 7 0,5 120 155 B 30 350/ 50 25-30 I 120 / 3,0 Venous 4x 5 7 25 1,25 7 0,5 120 155 B 30 350 / 50 (BT) Lunq 7 7 B 70 2000/ -500 Pelvis IVascular state (RTP) Unenhanced 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B 30 DVT Venous 4 x 2,5 5 12,5 1,25 5 0,5 120 155 B30 100 (BT 140 / 3,0 Heart Triaaer 4 x 1 1 25 1 5 038 0 8 05 120 400 B 30 350 /50 MPR/MIP 120 / 30 CTAngio Cranial vessels Arterial 4 x 1 1,25 5 1,25 1 0,5 140 90 H 10 110 /35 MIPNRT 18 (BT) 75 /3,0 Cervical vessels Arterial 4 x 1 1,5 5,5 1,38 1 0,5 120 100 B 20 350/ 50 MIPNRT 15 (BT) 110 / 3,5 Abdominal. vessels Arterial 4 x 1 1,25 6 1,5 1 0,5 120 130 B 20 350 / 50 MIPNRT 20-25 100-120/ 3,0 Iliofemoral vessels Arterial 4 x 2,5 3 15 1,5 1,5 0,5 120 130 B 20 350 / 50 MIPN RT 25-30 150 / 2,5-3,0 C sp ine Fracture Unenhanced 4 x l 2 5,5 1,38 2 0,75 120 150 B 70 3000 / 600 MPR L spine Fracture Unenhanced 4 xl 2 2,5 0,6 2 0,75 120 330 B 20 3000/ 600 MPR Myelo-CT Unenhanced 4 x l 2 2,5 0,6 2 0,75 120 330 B 20 3000 /600 Only for MPR 1,25 1 B 20 3000/ 600 1 Saaittal Aorta IDissection Arterial 4 x 2,5 3 15 1,5 1,5 0,5 120 130 B30 350 / 50 I Coronal 120 (BT) 1120-140 / 3,0 Aneurysm - - Han d/Feet IFracture - Unenhanced 2 x 0,5 0,5 1 1 0,3 0,75 120 100 U 90 3000/ 600 I Coronal/ Detail diagnosis sagittal Knee IBone Unenhanced 4 x l 1,25 4 1 1 0,75 120 90 B 60 3000/ 600 Soh tissues 5 5 B 30 350 / 50 Dental Before implantation Unenhanced 4 x 1 1 2,7 0,68 0,8 0,75 120 70 H 60 3000 I 600 IDertal evaluation Bone 4 x 2,5 10 Sea. 0,5 80 125 S 80 1800 I 500 .L Bone oensn Perfusion Bleeding lnfratentortal 4 x 1 4 Seq. 4 0,75 120 300 H 40 110 / 35 Supratentorial 2x8 8 Seq. 8 0,75 120 260 H 40 80/ 35 Stroke Arterial 2x5 10 Multiscan 10 1 80 250 H 30 120 / 35 I Perfusion stare I 4 I 80 / 5,0 ~ -...... -...J ......
  • 168. ...... ""I'V "'tJ o~ :Z:::C s:~ cn~3;:11l:" ""'CI t= c." n:g Cl)("')"T1C/) cn cn----j _ .... ~ ("') -I - ""CI ..... m 1> < ::+ -I m Q ::: - ....j 0 g CD 2 12. ffi o 3 ("')"'tJ "'tJ::c 3tn n m:E == c.-P :::::l W:r =.'g ::r -e ~::::l- ~ II ~ (") 0 ~ n ..., zr e- " _-1 3o ~ ~ mo Q,l - ....... ~ £ ~ ~Q:I _ Ol _. cr; "'T1 g II II 11 II II II II II II II II II II II II 11 II II cn ~ g ~ ~ ~~ ~~~~A22~~ ~ onn~ ~~~~ rn~ _~ ~ ~ ~ ~.0l=-5·~crcr~Sro~ ~§~~ ~~~ - :::r ~ - a 0l0lm~.=~~rn m:::ro3n~ <~ o~~roc ~~ ~o Ol o -(")3~ _nc ~ OQ) ::::lOO_ro =ro ~ g n~g c~~~~g ~ -.~Ea ~ ~::::lm~ ~ w eng Q ~~::::l~.~ og ag n~'~~3 ~ ~ a Q~ ~~ X::::l ~ ~~ ~ ..., g ro ~ m gg~ ~ ~ ~ ~ ~3·~ a _ ~ - ::::l ...,Ql mmO Ol Eoro-·-· O::::l...,a o- Il ~ n;:;' ~ 8 ~. 5 CJ) ::l cr 3 c 3 ::. ~ ~ ...., Ql ..., ~ _ 0 Ql _ . :::::l cn 0 ....... co CD ::::l cn o' sa. Q,l w :::r ~ g a. q~ ~ ~~' & ::::l~B ~~ ro ;5 ~ 3 ~::::I Q5 g s. CD' en 3 ~ :::::l S' - ~ 3 00 w 0 I.C co _ . CD =:::::l 0 g::::l n - '" '" Infralentorial 16xO,75 Supratentorial 16x 1,5 lnfratentorial 16 xO,751 4 1 5 1 0,42 1 4 I 0,75 1 120 1 260 1 H 40 1 110 / 35 1 1 60 1 50 /2,0 IVenous vessels (SVT) Supratentorial 16 x 1,5 Sku ll: ST I I 35 Orbita [Tumor 16 xO,751 4 5 0,42 4 0,75 120 100 H 30 250 /50 1 45 1 75 /2,0 1 0,7 H 30 250 /50 Coronal Fracture I 116 xo,75 2 5 0,42 2 0,75 120 100 H 60 3000 / 600 1 07 H 60 3000 / 600 ICoronal Paranasal Sinusitis, nasal pOIYPoSiSl 116 XO,75 4 5 0,42 4 0,75 120 80 H 40 1500 /50 sinuses Onlv for coronal MPR 1 07 H 60 1500 /50 Coronal Facial bones Tumor 16 xO,75 3 5 0,42 3 0,75 120 100 H 30 350 /50 ,I 45 I 75 /2,0 Fracture 1 07 H 60 3000 /600 Coronal Petrous bone IFracture 16 x O,75 0,75 5 0,42 0,5 1 120 120 U 90 3000 /600 Coronal OnIv for film documentation 1 1 U 90 3000 /600 Neck Lymphoma, tumor 16 x 1,5 5 24 1 5 0,75 120 150 B 30 250 /50 1 1 45 1 100 / 3,0 Chest Fibrosis, fungi IUnenhanCedl 16 X1,5 5 30 1,25 5 0,5 120 100 B 40 350 /50 HR 16 xO,75 1 13,5 1,1 3 0,7 0,75 120 90 B 80 2000 / -soolcoronai 5 5 B 30 350 / 50 NPL, lymphoma I Arterial 116x 1,5 6 30 1,25 6 0,5 120 100 B 40 350 /50 1 125-301 80 /2,0 (BT) Pulmonary emboli 1 Arterial 116 xO,751 5 15 1 1 ,25 I 0~7 I 0,5 I 120 I 100 IB 30 I 350 / 50 Ic oronall20-25 I100-120 / 1 Sagittal (BT) 3,5
  • 169. 80 Delay CM I flow [sec) [ml/ml/sec] Recon- struct. RI Sec I Voltage Current Kern Window [mm) rotation (kV) (mAs) with CM Coli ST Feed I Pitch [mm] [mm] rotation IndicationsOrgan Bronchial carcinoma Arterial 16x 1,5 6 30 1,25 6 0,5 120 100 840 350 /50 8C) : Luna window 6 6 870 2000 /-500 NPL, lymphoma Arterial 16 x O,7, 5 12 1 5 0,5 120 140 830 200/40 20-25 1 100-120 / 3,5 Venous 16 x l ,S 5 24 1 5 0,5 120 120 830 350 /50 Coronal 50-75 Stomach: Hydra CT Arterial 16 x 0,7 5 12 1 3 0,5 120 140 830 350150 25-30 1 100-120 /3,5 I(stomach filledwith H 01 Venous 16 x O7 3 12 1 3 05 120 140 830 350 /50 50-75 Pancreas! INPL Unenhanced 16 x 1,5 5 24 1 5 0,5 120 120 8 30 350 /50 kidneys Arterial 16xO ,75 5 12 1 5 0,5 120 140 830 350 / 50 1 Coronal 1 20-25 1 100-120 /3,5 I ~ Venous 16 x 1 5 5 24 1 5 05 120 120 8 30 350 / 50 50-75 Adrena/ glands 1Adenoma Uncnhanced 16 x 1,5 5 24 1 5 0,5 120 120 8 30 350 / 50 Arterial 16xO,75 1 12 1 0,7 0,5 120 140 8 30 350 /50 1 Coronal 1 30-40 I 100-120 / 3,0 After 3 min 16 x 1,5 3 24 1 3 0,5 120 120 8 30 350 /50 (BT) Optional After 10 min 16 x 1 5 5 24 1 5 05 120 120 B 30 350 / 50 3·phase liver IHemangioma, HCC Unenhanced 16 x l ,S 5 24 1 5 0,5 120 120 B 30 350 / 50 Arterial 16 x O,75 5 12 1 5 0,5 120 140 B 30 250 / 40 1 Caranal 120+25 I 100-120 13,5 Venous+ 16 x l ,S 5 24 1 5 0,5 120 120 8 30 350 /50 50-75 ootional oelvis Chest-AbdomenINPL, lymphoma Arterial 16 xl ,S 5 24 1 5 0,5 120 140 B30 350 /50 1 1 25 - 30 1 120 / 3,0 Venous 16 x 1,5 5 24 1 5 0,5 120 140 B30 350 /50 (BT) Luna 7 7 8 70 2000 / -500 Pelvis 1Vascular state (RTP) Unenhanced 16 x O,75 5 24 1 5 0,5 120 140 B30 350 / 50 DVT Venous 16 xl ,S 3 12 1 3 0,5 120 140 B 30 350 /50 10018T' 120 13,0 IHeart Triaaer 16xO,75 1 34 029 0 7 042 120 550 8 30 350 /50 MPRIMIP 100 130 ICT Angio Cranial vessels Arterial 16 x O,75 1 15 1,25 0,7 0,5 140 100 H 2O 110 / 35 MIPNRT 18 (BTl 75 /3,5 Cervical vessels Arterial 16 x O,75 1 12 1 0,7 0,5 120 120 830 350 150 MIPIVRT 15 (8T) 1001 4,0 Abdominal vessels Arterial 16 x O,75 1 15 1,25 0,7 0,5 120 130 830 350 /50 MIPIVRT 20-25 1DO-l20I3,Ch3,5 Pelvic-leg vessels Arterial 16 x l ,S 2 24 1 1,5 0,5 120 130 830 350 /50 MIPIVRT 25-30 150 / 3,0-3,5 IC spine 1 Fracture Arterial 16xO ,75 1 12 1 0,7 075 120 150 870 3000 /600 MPR ILspine IFracture Unenhanced 16 x O,75 1 6 0,5 0,7 0,75 120 330 860 3000 /600 MPR Myela-CT Unenhanced 16 x O,75 3 6 0,5 3 0,75 120 330 860 3000 1600 Only far MPR Unenhanced 1 0,7 8 60 3000 /600 MPR IA orta 1Dissection 16 x 1,5 2 21 0,88 1 0,5 120 130 830 350/50 MPRIMIP 120 (BT) I 120 / 3,0 Aneurysm Arterial VRT Hand!Feet I Fracture - 1Unenhanced 116 xo,75/0,75 I 6,8 10,57 1 0,5 I 0,75 I 120 1 120 I U 90 13000/ 6001 MPR IDetail diagnosis IKnee IBone Unenhanced 16~-1 - -13~5- -f~f3 -OY- O,75 120 120 B 60 3000T 600 1 MPR Soft tissues 5 5 8 30 350 /50 Dental Before implantation Unenhanced 16 x 0,7E 0,75 6 0,5 0,5 0,75 120 80 H 60 3000 / 600 108nl1l1ovalualiJI1 Bone 2 x 5,0 10 Sea. 0,5 80 125 S80 1800 / 500180nedens!!) Perfu sion 81eeding Infratentorial 16 x 0,7E 4 5,1 0,43 4 1 120 260 H 40 11 0 / 35 Supratentorial 16 X1,5 8 10,2 0,42 8 1 120 260 H 40 80 /35 Strake I Arterial 16 x i.s 12 Multiscan 1 1 80 209 H 30 120 I 35 IPertusion state I 4 I 40 /8,0 ~ •...... -...J W
  • 170. 174 Radiation Dose/Cancer Risk The physical radiation dose 0 (energy absorbed per unit mass) is expressed in Gray (Gy), used for anytype of radiation and also in the radiation therapy of malignant tumors. It has to be distin- guished from the equivalence dose H expressed in Sievert (Sv), which represents the physical radiation dose multiplied by a pro- portionalityfactor thatconsiders theunique radiation sensitivity of a particular tissue: Epithelium, mucosa of the respiratory and gastrointestinal tract and other tissues with a high rate of cell division (e.g., blood forming cells of the bone marrow) are more sensitive toionizing radiation than tissue withdormantcell division. An even better comparison of the biologiceffect can be achieved with the effective dose E, which is the sum of the doses de- livered to the individual organ.This effective dose, which weighs the relativeinherent sensitivities, is also expressed in Sievert (Sv) orMillisievert (mSv). , Furthermore, the patient's age at the time of radiation exposure must be included in a rational assessment of the radiation risk since the latency period of a radiation-induced tumor can be rat- her long (decades).Table 174,1 lists therisk coefficientsof diffe- rentorgansfollowing a low-doseexposure to the entirebody. ,Tab. 174.1 Age-dependency of cancermortalitycaused by ionizingradiation Estimated risk factorsin (% / Sv) for men/ women (italics) Age at exposure Total Leukemia Lung/Respiratory MDT 5 years 12,8/ 15,3 1,1 /0,8 0.2/ 0,5 3,6/ 6,6 15 years 11 ,4/ /5,7 1,1 /0,7 0,5/ 0,7 3,7 / 6,5 25years 9,2/11,8 0,4 / 0,3 1,2/ 1,3 3,9/ 6,8 45 years 6,0/ 5,4 1,1 / 0,7 3,5/ 2,8 0,2/ 0,7 65 years 4,8 / 3,9 1,9 / 1,5 2,7/ 1,7 0,1 / 0,5 85 years 1,1 /0,9 1,0/0,7 0,2/ 0,1 - / 0,04 Mean 7,7/ 8,1 1,1 / 0,8 1,9 / 1,5 1,7 /2,9 Chest Others 1,3 7,8/ 6,3 3,0 6,1/ 4,8 0,5 3,7/ 2,9 0,2 1,2/ 1,0 0,1 / 0,2 -/ - 0,7 3,0/ 2,2 effektive annual dose %of annual exposure This implies that the risk of radiation-induced malignancies markedly decreases with increasing age at the time of exposure. But not onlythe patient's age, butalso theamount of theindividu- al dose and the length ofthetime intervals playa decisive role.As a rule of thumb, the lower the individual dose and the longer the intervalsbetween several radiationexposures, thelower the riskof a subsequently induced neoplasm. Among other factors, this depends on the capability of the cellular nuclei to repair DNA breaks with thehelp of repair enzymes as long asthe reparative capacity is not exceeded by high individual doses. Evidence even Radiation Source exists that protective effects predominate in the low-dose range through activation of protective cell factors (DNA reparase and others). For a better assessment of the risk associated with the medicalapplication of ionizing radiation, it is revealing toconsider thedaily exposure from natural background radiation: The major component of the natural radiation exposure comes from radon,a noble gas, which gets intotheair through thebuildingmaterials of houses and apartments. Using a strictly theoretical calculation, radon and its decay productsmay induce5 to10% ofallbronchial carcinomas. In contrast, medical application of ionizing radiation "only" induces less than 1.5%of all malignancies. I Inhalation ofradon inapartments Terrestric radiation Cosmic radiation Incorporation of radioactive isotopes Subtotal of natural radiation exposure Applicationofionizing radiation inmedicine AccidentoftheChernobyl nuclear reactor (Europe) Fall-out from nuclear weapon tests Operation ofnuclearreactors Occupational radiationexposure Subtotal of man-made radiationexposure Total annual radiation exposure in the Federal Republic of Germany - 1,4 - 0,4 - 0,3 - 0,3 - 2,4 mSv - 1,5 - 0,02 - 0,01 - 0,01 - 0,01 - 1,8 mSv - 4,2 mSv 33,3 % 9,5 % 7,1 % 7,1 % 57,0% 35,7% 0,5 % 0,2% 0,2 % 0,2% 43,0% 100,0% The average annual radia- tion exposure of about 2.4 mSv has to be put in perspective with the man- made radiation exposure of 1.8 mSv (Table174.2). Tab.174.2 Relativecontributionof several radiationsources tothetotalannual exposure (Europe).
  • 171. Radiation Dose/Dose Reduction 175 Ingeneral,"hard" x-rays usedforconvenfional radiography of the chest are scatteredand absorbedlessinhumantissue than "soft" x-rays used for mammography. The scatter radiation also con- tributes tothe absorption and consequentlyto the riskassociated with a particular examination. Because of the tissue-dependent variabilityoftherisk factorsandthe different characteristics ofthe various modalities used in diagnostic radiology, the organ doses arequite diverse (Table 175.1). Examination Conventional radiology,chest Conventional radiology,skull Radiology, C-spine Radiology,T-spine Radiology, L-spine DSAofthe heart DSAofthe kidneys Fluoroscopy, UGI series Fluoroscopy, BE Cranial CT ChestCT Abdomen CT Organ / tissue Lung,breast Red bone marrow Thyroid gland Breast, lung Red bonemarrow Lung Red bone marrow Red bonemarrow Red bone marrow Red bone marrow Lung,chest Red bone marrow Organ dose 0,3 mSv 4,0mSv 4,5mSv 14,0 mSv 1,0 mSv 20,0mSv 30,0 mSv 17,0 mSv 3,0 mSv 5,0mSv 20,0mSv 10,0 mSv Effective dose E 0,2mSv 0,2 mSv 2,0mSv 5,0 mSv 0,4mSv 10,0 mSv 10,0 mSv 6,0 mSv 3,0 mSv 2,0 mSv 10,0 mSv 7,0 mSv Tab.175.1 Radiation dose of different radiographic examinations. Together with arteriography andfluoroscopy. CT is responsible for a rather high radiation exposurein diagnostic radiology. Multiply- ingthe individualvalues withthenumberof thedifferent examina- tions performed annually revealsthat CT is responsible for about a third of the collective total dose.The different CT examinations deliver thefollowing average radiation doses(Table 175.2). Type of spiralCT Emotion 1 row Emotion 2 rows Emotion 6 rows Sensation 10rows Sensation 16rows Head 4,2/ 4,5 mSv 4,2/ 4,5 mSv 4,4/ 4,7 mSv 4,6/ 4,8 mSv 4,5/4,8 mSv Chest 3,9/ 5.0 mSv 2,6/ 3,3 mSv 3,2/ 4,1 mSv 3,0/ 3,8 mSv 2,8/3,6 mSv Abdomen/ 3,7/ 8,8 mSv 3,7 / 5,6 mSv 6,3/ 9,6 mSv 6,0/ 9,0 mSv 6,5/ 10,0 mSv pelvis Tab. 175.2 Comparisonofdoses in millisievert (mSv)for different CTunitsofSiemens Medical Systems.Valuesformen / women (italics). This does not consider the effects of the section thickness (see page 9-11): As a rule of thumb, the thinner the section thickness the higher the radiation dose(Table 175.3). The radiation exposure is slightly higher in units with compact geometryand shorter focusdistance (Emotion 6). I Preselected Somatomplus 4 Somatom Volume Zoom Emotion collimation 4 row 6 row1 row 4 x5,0 mm 4,5 4,6 6,8 4 x2,5mm 4,3(3mm) 5,1 7,2 4 x1,0mm 4,9 6,1 8,4 Tab,175,3 Dosis increase per 100 mAsforthin section collimation. Sensation 16 row 4,2 (1,5 mm) 4,7 (0,75 mm)
  • 172. 176 Radiation Dose/Dose Reduction in CT Comparison with air traveling is often used in public health discussions: On a long, high altitude transatlantic flight, cosmic rays cause a not irrelevant additional exposure. On a flight from Europe to the West Coast of the U.S.A., this can easily be in the rangeof certain CT examinations. Other calculations ofthecancer risk compare conventional chest radiography with cigarette smoking:A single chest radiograph is believed to have the same cancer risk as smoking sevencigarettes.It shouldbe kept inmind, however, that all mathematically models include several aspects andcofactorsthat are elusive to exact statisticallycalculations. While these comparisons put into perspective an excessive concern ofthe potential riskof medical radiographic examinations, Automatic Bolus Tracking (BT) For CT, several techniques are availablefor reducing the radiation dose to the patient. Especially CT requiring optimal contrast enhancementinthe vessels,e.g.,above allCTangiography,should be performed withautomatic bolus tracking toavoidunnecessary duplications because of inadequate intravascular contrast en- hancement. This softwaresolution offers the examiner the possi- bilityto place a region of interest (ROI) ( t:2 )just before orat the beginning of the target region, e.g., the lumen of the descending aorta(Fig. 176.1a).After selecting acertain thresholdvalue for the they should not be misused to belittle the radiation risk. To avoid unnecessary risks to the general population, it has become established policytoavoid dispensable radiation exposureincon- ventional radiology and CT,and totake advantage of any possible reduction ofradiation exposure to patients. It is for the same reason that pulsed fluoroscopy has replaced continuous fluoroscopy for upper GI series, enteroclysis and barium enema: The examiner selects between several pulse sequences with 1, 2, 4, and 8 images per second. The resultant dose reduction is considerable.The next pages describe solutions suitablefordose reduction that areespeciallyapplicableforCT. density of the aorta, e.g., 100 HU, the unit measures the density automatically at the preselected site every second after the be- ginning of the intravenous injection of contrast medium, usually throughthe cubital vein. Data acquisition (the actual scanning process) begins assoon as the density in the aortic lumen exceeds the threshold value, i.e., exactly when the bolus of the contrast medium has reached the selected target region after passage through the pulmonary circulation (Fig. 176.1 b). Density [HU] 100 --- - - - - - --------- - 80 60 50 40 20 o Start t [sec] Fig. 176,1 b Automaticdelay of dataacquisition until arrival of theCMbolus atthetarget region. I Fig. 176.1 a Positionof ROI, e.g., over thedescending aorta. Inaddition,the amountofcontrast medium needed toachieve the same contrast enhancement can be reduced: sterile physiologic NaCI solution is injected from a second syringe of the injection pump (see front cover flap) at the same flow rate immediately following the injection of contrast medium in order to push the contrast medium fasterand at a higher concentration throughthe brachial veins toward the heart and through the pulmonary circu- lation. Taking Advantageof thePitch By usingafaster table feed toincreasethepitch,afewsingle-slice CT units can reduce the effective patient dose by spreading the spiral ofdata acquisition (see Fig. 8.4). The software of the multislice technology uses a compensatory mechanism that automatically increases the tube current when- ever the examiner increases the pitch- effectively delivering the same totaldose forthe examination. For a 16-slice CT,the exami- nercanselect the craniocaudal spanof the z-axis, thecollimation and scan time for the desired volume - and the software deter- mines the optimal table feed or, respectively, pitch, and the tube current.
  • 173. Dose Reduction 177 Reduced Tube Current for ThinPatients and Children Asarule of thumb, thenoisedoublesforeachS-cmincreaseinthe patient's diameter. Dose and noise are exponentially related: Doubling the dose reduces the noise only by a factor of 1.4. To penetrate thin patients and children for a satisfactory image, a markedly lower radiation dose is adequate. In older units lacking instantradiation measurements at the level of the detectors and modulation of the tube current (see below), the dose can be re- duced by loweringthepreselected tubecurrent (mAs). Automatic Tube Current Modulation The idea underlying this feature of the combined applications to reduceexposure(CARE) isas simpleasit is effective: it isbased on the assumption thatthe cross-sections of most body regions are oval ratherthan circular.With the patient supine, theAP diameter ( t ) ofthechest,abdomen,and pelvisis definitelyshorter than the transverse diameter ( - ). Consequently, the tube current is higher in lateral angulation than in anterior or posterior angulation (Fig. 177.1). Aftereach semi-circulation, e.g., every lS0 degrees, the same dosis is needed since the additive attenuation of the x-ravs is directionally neutral (Fig. 177.2). It isthe essence ofthe automatedmodulation thatthe tubecurrent measurestheattenua- tion profileforeachtube angulation and calculatesthe correspon- ding minimal dose still adequatetoachieve an optimalimageafter F' 1771Ig. . an additional l SD-degree angulation.As a result, thetube current is modulated with a l SD-degree delay. Plotting the tube current along the time axis displays a curve reminiscent ofa sinuscurve with theamplitudes tending todecrease from the shouldertothelegs (Fig.177.3) andwith maximaat the level oftheshoulder and pelvis. - Tube current f [mAs] Effects of automatic tubecurrentmodulation Body region Skull Shoulder region Chest Abdomen Pelvis Extremities II NV Scandirection Dose reduction 14- 26 % 22-56 % 19-27 % 11 - 24 % 21-30 % 33- 41 % v v v - - - Fig. 177.3 In addition, the life expectancy of the x-ray tube is extended and image artifacts induced by the arms placed along the patient's body,asfrequently found intraumaand ICU patients,arereduced. f f r-. r-; i-Gv r-. c?, ~ r 'CJ v v v V V Fig. 177.2 -, Compared with units delivering the same image quality without tube current modulation, the dose-reducing potential ot this techniqueisimpressive,withthe highestreduction coinciding with areas of considerable radiation absorption, e.g., at the shoulder and pelvis (Table177.1). Tab.177.1
  • 174. 178 CT Angiography Bringing out the information contained in images of CT anqio- graphy requires a review using different perspectives (MIP = maximum intensity projection), different reconstruction planes (MPR = multiplanar reconstruction) or a tbree-dirnensional visualization (VRT = volume rendering technique). All these reo construction images used to bedegraded by the resolutionof 0.5 mm per pixel length in the transverse plane (xy-plane) and a markedly higher resolution along thebody axis (z-axls), resulting in an anisotropic voxel (see page 8) with different lengths. The advances of the multidetector CT(MOCT) with the introduction of the ts-sucetechnologyintheyear 2001 permittheinclusionof an adequately large body volume with almost isotropic voxels in the sub-millimeter range with justifiable scan times. The following pages present recommended examination protocols for different vascularregions including several representative images. IntracranialArteries The individual axial sections are usually supplemented with displays using MIP and, e.g., sagittal MPR as well asVRT (see above).Agooddiagnosticevaluation ofthecerebral arteries canbe achieved with thin overlapping section reconstructions using a section thickness of 1.0 to 1.25 mmand a reconstruction interval (RI)of 0.6to 0.8 mm. To achieve a highvascularcontrast, thedataacquisition has to be exactly timedto encompass the firstpassage of contrast medium through the circle of Willis with a start- delay of 20 seconds, if possible beforecontrast medium has reachedthevenoussinus.If bolus tracking(BT)is notavailable,atest bolus should be injected to determine theindividual circulation time.The following exami- nation protocols can serve as guides for thevisualization of the circle ofWillis: CT system Call. ST Feed Pitch RI Sec.! Volt. Current Kernel Window Delay CM [mm] [mm] I Rot. [mm] Rot. [KV] [mAs] [W/C] [sec] [ml/ ml/sec) 1 row 4 rows 16rows 1 1,0 2 4x l 1,25 5 16xO,75 1,0 15 2,0 1,25 1,25 0,5 1,0 0,7 0,8 0,5 0,5 11 0 120 120 120 H30 250/ 40 18 - 22 120 / 3,0 90 H10 110 / 35 18 /BT 75/ 3,0 100 H20 110/ 35 18/ BT 75/ 3,5 Thesubsequently reconstructed individual sectionscandisplay the vessels asseenfrom below withtransverse MIP(Fig, 178.1b),fromthefront withcoronal MIP (Fig, 178.1c) or from thesidewithsagittal MIP (Fig.179.1a).Thefirst two planes clearlyshow themajor branches of theanterior (91 a) and middle (91 b) cerebral arteries. Figure 178.1 d shows a 3D VRT of another patient with an aneurysm ( ") arisingfrom theanterior communicating artery.Thejunctionofbothvertebral arteries(88) toformthe basal artery (90) and posterior cerebral arteries (91c) is clearlyidentified. Furthermore, the branchesof theanterior circulation are identifiable: branches of the medialcerebral artery (91 b)andthe pericallosal arteries (93). Fig. 178.1 a Fig.178.1b Fig. 178.1c Fig. 178.1d
  • 175. CT Angiography Venous Sinus To visualize the venous channels,the FOV has to be extended tothe sagittal cranial vault (Fig. 179.1a) and the startdelay increased to about 100 seconds. Craniocaudal sections are recommended for bothtypes of CTA (arterial and venous cerebral vessels).The sagittal plane (Fig. 179.1b) preferably shows contrast inthevein of Galen (100) andvenous channels (101 a. 102a). C1 system Call. 51 Feed Pitch RI Sec.! Vall Current Kernel Window Delay CM [mm] [mm] I Rot. [mm] Rot. [KV] [mAs] [W/C] [sec] [mil mllsec] 179 4 rows 4 x1 1,25 5 1,0 - 1,5 0,8 0,5 120 90 soft 110/35 100 120 /3 ,0 Fig.179.1a Fig. 179.1b
  • 176. 180 CT Angiography Carotid Arteries Important criteriafor stenotic processes ofthecarotidarteries are the exact determination oftheseverityof the stenosis. It isfor this reason that the examination is carried out with thin sections, for instance, 4 x 1 mm or 16 x 0.75mm, allowing direct planimetric quantificationof the stenosiswithadequate accuracy on individu- alaxial sections. Furthermore, thesagittal and coronal MIP(0.7- 1.0 mm RI with 50% sectional overlapping)shows no major step deformity (see page8). Thebestreconstruction withmaximal contrast ofthecarotidartery is achieved with minimal contrast in the jugular vein. Therefore, theuseof abolustracking program isstronglyadvised.Ifapreced- ing Dopplerexamination suggests avascular process at thebifur- cation, transverse images in caudocranial direction are recom- mended. For processes near the cranial base, a craniocaudal direction can be superior. VRToften proves helpfultogetoriented (Figs. 180.1 d, e). I CT system Coli. 5T Feed Piteh RI sec.! VotL Current Kernel W/ C Delay CM [mm] [mm] / Rot. [mm] Rot. [KV] [mAs] [HU] [sec] [ml/ mJlsee] 1 row 4 rows 16rows 2,0 4 xl l,5 16x O,75 1,0 4,0 2 1,0 5,5 1,38 1,0 12,0 1 0,7 0,8 110 0,5 120 0,5 120 120 B30 350/50 12 -1 5 100 / 3,0 100 B20 350/ 50 15 /BT 110 / 3,5 120 B30 350I 50 15I BT 100 I 4,0 Fig. 180,la Fig. 180.1 b Fig. 180.1e Figure 180.1 shows the lateral topogram (a)for positioning of the FOVas well as lateral (b) and anterior (c) images of an MIPand an imageinVRT (d),showing normal findings. Incontrast, Figure 180.2 shows images ofsagittal MIP and VTRthatrevealtwo indentations of thevascularcontrast column at the typical sitefor acarotidstenosis:TheleftACI(85a) shows ashort segment ofasevereluminal nar- rowingjust distal tothe bifurcation ( " ) after a preceding bulbar stenosis( ~ ) of theACC(85) at theoriginoftheACE(85b). Fig. 180.1d Fig. 180.2a Fig. 180.2b
  • 177. 182 CT Angiography I Aorta The CT angiography of the aorta must above all exclude aneurysms, isthmus stenoses and possible dissection, and if present, visualize their extent. Automatic bolus tracking (BT: ROI placed over the aorta) is advisable, especially in patients with cardiacdiseaseswho have variablepulmonarycirculationtimesof contrast medium. Imaging in caudocranial direction can minimize the respiration-induced motion artifacts that primarily affect the regions close to the diaphragm since involuntary respiratory excursionsaremore likely attheendof the examination. Further- more, caudocranial imaging avoids the initial venous inflow of contrast medium through the subclavian and brachiocephalic veins and anysuperimposition onthesupra-aorticarteries. CT system Call. ST Feed Pitch RI SecJ Volt. Current Kernel WI C Delay CM [mm] [mm] I Rot. [mm] Rot. [KV] [mAs] [HU] [sec.] [mIl ml/sec] 1 row unenhanced 8,0 12,0 1,5 8,0 0,8 1 row CM 3,0 6,0 2,0 I,D 0,8 4 rows 4x 2,5 3,0 15,5 1,5 1,5 0,5 16rows 16xl,5 2,0 21 ,0 0,9 1,0 0,5 110 110 120 120 80 100 130 130 B30 B30 B20 B30 350/ 40 350/50 350/50 350/50 BT BT 201BT 120 /3,0 130/3,0 120 /3,0 As reconstruction images, MIPand MPR (Figs.182.2, 182.3) often allowan exact quantification of the vascular pathology as survey imagesinVRT(Fig 182.4).asseenhereas anexampleof aninfra- renalaneurysm of the abdominal aorta:The aneurysmaldilatation (171) begins immediately distal to the renal arteries (110) and spares boththe superior mesenteric artery (106) and iliac arteries (113). For planning any vascular surgery, it is crucial to know any involvement of visceral and peripheral arteries and any possible associated dissection. Furthermore. thelevelofthe aortic originof the artery of Adamkiewicz, which supplies the thoracospinal transition of thespinal cord,must beconsidered foraneurysmsof the descendingthoracic aorta. Fig. 182.1 a b Fig.182.2 Fig.182.3 Fig. 182.4
  • 178. CT Angiography 183 Frequently,acinemodereview ofthecoronal orsagittal MPR ima- geson asecond monitor canbehelpful foraquickand convincing determinationof the extent ofa pathologic finding,asshown here inacase of thrombosis withinan abdominal aortic aneurysm.The cine mode of the coronal MPR images reveals not only an infra- renal thrombus (173) along the left lateral wall (Fig. 183.1) but also a secondthrombus further cranial alongtheright lateral wall at thelevel of the origin of theright renal artery (110) (Fig. 183.1). which is still pertused (Fig. 183.3). The individual axial sections (Figs. 183.4, 5) allow a planimetric quantification of the stenosis,andthesagittal MPR(Fig. 183.6)aclear separation from the origin of theanterior mesenteric artery (106). Fig. 183.1 Fig.183.2 Fig. 183.3 Of course, the benefit of the three-dimensional visualization by means of VRT also depends on the viewing angle. While viewing from an angle (Fig 183.7) can underestimate the extent of the thrombus and easily mistake it for a soft plaque, the extent is much better appreciated if seen from different viewing angles Fig.183.4 Fig. 183.5 Fig. 183.6 (Figs. 183.8 and183.9). Thefinal images illustrate theeffect ofa careful elimination of interfering superimposed osseous struc- tures. Becauseof its highdensity,thelumbar spinedominates the initial image (Fig. 183.8). and the vascularfindingsareonly fully appreciated after subtractionof the lumbar spine (Fig. 183.9). Fig. 183.7 Fig.183.8 Fig. 183.9
  • 179. 184 CT Angiography (Heart) Coronary Arteries Visualizing the coronary arteries represents a special challenge since thecardiac contractions requireshort scan times and exact timing. For a cardiac rate exceeding 70 beats per minute, a pre- medication witha beta blockershould beconsidered unless con- traindicated in view of other clinical findings. Even the shortest rotation timesavailable(0.42seconds fora 16-slice CTat thetime of the publication ofthisbook)require additional EKG triggering.To achieve adiagnosticimagequality,thewidthofthe FOV should be reduced to the cardiac size and the craniocaudal acquisition should beginjust above thetracheal bifurcation and extent to the diaphragm (Fig. 184.1). Oblique MIPs parallel tothe main branch oftheleft coronaryartery aswell asspecial projections of the RIVA and RCA (right coronary artery) and 3D views are obtained. The application of contrast medium should be biphasic with an initial bolus of 40 ml at a flow rate of 4 mils and, after a pause of 10 seconds, a second bolus of 80 ml at a flow rate of 2 mils. Bolus tracking should be used with the ROI over theascending aorta. CT system Coli. ST Feed Pitch RI Sec.! Volt. Current Kernel WIC Delay CM [mm] [mm] I Rot. [mm] Rot. [KV] [mAs] [HU] [sec.] [ml I rnl/sec] 4 rows 16rows 4 x1,0 16xO,75 1,5 0,37 3,6 0,3 0,5 0,5 0,5 0,42 120 250- 400 B20 500I 80 BT 120 400 heart 450I 60 BT 120 I 2-4 120/2-4 Thefollowing images compare aCT (Fig. 184.2a) of the leftcoro- nary artery (77a), including circumflex branch (77C) and RIVA (77b), with coronary angiography taken as gold standard (Fig. 184.2b). Figures 184.3a and 184.3b showthe same com- parisonforthe right coronary artery (77d). Fig. 184.1 89a /77a Fig. 184.2a Fig. 184.2b Fig. 184.4 Fig. 184.3a Fig. 184.3b
  • 180. CT Angiography (Heart) Screening for Coronary ArteryCalcifications Compared with angiographic imaging of the coronary arteries illustrated on the preceding pages, a slightly thicker section can be selected when screening the coronary arteries for calcifications. Administration of contrast medium is not necessary, and the unen- hanced imagesareobtained incraniocaudal direction. CT system Coli. ST Feed Pitch RI SecJ Volt. Current Kernel WI C [mm) [mm) I Rot. [mm) Rot. [KY] [mAs) [HUj 185 4 rows 16 rows 4 x 2,5 3 16 x l ,S 3 1,5 0,37 3,6 0,3 0,5 0,5 0,5 0,42 120 120 133 130 heartmedium heart 370 /50 450/ 60 89a 90 , 0 Fig.185.1 Fig.185.2 Fig. 185.3 Quantification of coronary calcifications(174) isbestcarried out on adedicated separatework station but canalso be doneon a normal work station after postprocessing (Fig. 185.1-3). In this case. however, the unenhanced images are used to obtain,for instance,the Agatston score[43,44),whichcorrelates withthe risk of coronaryartery disease. Agatston Score Clinical Relevance Recommended Therapy o (negative,no identifiablecalcific plaques) 1- 10 (minimal identifiable calcific plaque burden) 11 - 100 (definite. at least mildcalcific plaque burden) 101 - 400 (definite,at least moderate calcificplaque burden) > 400 (extensive calcificplaque burden) Negative predictivevalue for coronary artery disease90 - 95% Stenosis unlikely Coronary arterydisease possible Coronary artery disease with stenosis possible Highprobability forcoronary arterydisease withstenosis possible None General guidelines forprevention Further evaluation indicated Instituterisktactor moditication and specificcardiac therapy Stress EKG is indicated - depending on outcome followed bycoronary angiogram Useful suggestionsand recommendations torconducnno screeningfor coronaryarterycalcificationscan befound inthe followingorigi- nal articles: [43] Kopp AF, OhnesorgeB, Becker Cet al: Reproducibilityand accuracyofcoronary calciummeasurements with multi-detector row versuselectron-beam-CT. Radiology (2002) 225: 113-119 [44] Rumberer JA, Brundage BH, Rader DJ et al: Electron beam CT coronary calcium scanning. Review and guidelines foruse in asymptomatic persons. Mayo Clin Proceed(1999)74:243-252 [45] JanowitzWR, Agatston AS,ViamonteM:Comparison ofserial quantitative evaluationofcalcified coronary artery plaque byultra- fast computedtomography in personswithand without obstructive coronaryarterydisease.AmJ Cardiol (1991 )68: 1-6 [46J Haberl R,BeckerA,LeberAetal:Correlationofcoronary calcification andangiographicallydocumentedstenoses inpatientswith suspectedCAD: resultsof 1764patients.JAm Coli Cardiol (2001)37:451 -457
  • 181. 186 CT Angiography Pulmonary Vasculature (Pulmonary Emboli) FOV and volume to be scanned are marked on the topogram (Fig. 186.1), beginning from just above the aortic arch. to visua- lize primarilythecentral hilar vessels andthe heartwiththe right atrium (a possiblesourceof emboli). Lateral and apical regions of the lung are dispensable. The total acquisition time should not exceed 15secondsinorder tocompletetheexaminationduringa single breath holdwithout artifacts.The images arebest obtained from caudal tocranial,to havethemotion-sensitive areas close to the diaphragm already completed duringtheendphase andtomini- mizetheartifacts caused bythevenousinflowofcontrast medium through brachiocephalic veins and superior vena cava. Exact timing with bolus tracking (8T, ROI over the pulmonary outflow tract)isstronglyadvised.Thereconstructedsections shouldnotbe less than 3 mm inwidth.Thesectionsfor the MIP should be close to1.0mm toavoid overlooking smallsubtle pulmonary emboli. CT system Coli. ST Feed Pitch RI Sec.! Voll Current Kernel WI C Delay CM [mm] [mm] I Rol [mrn] Rol [KV] [mAs] [HU] [sec.] [mil ml/sec] 4 rows 16rows 4 xl ,0 1-3 16xO,75 1-3 6,0 1,5 15,0 1,25 0,5 0,5 0,5 120 0,5 120 140 8 20 420/60 16 / 8T 120 / 4,0 130 8 30 450 /60 16 / 8T 120 /4 ,0 Fig.186.3 Thevascular lumina contrast well withthe pulmonary tissue(Figs. 186.2 - 186.5)and extend all theway to the periphery.Acute pulmonary emboli (Figs. 186.6 and 186.7) cause intravascular defects representing thrombi (173), located in this case in the rightpulmonaryartery(90a). Fig. 186.1 Fig. 186.2 Fig. 186.4 Fig. 186.5 Fig. 186.6 Fig.186.7
  • 182. CT Angiography 187 Abdominal Vessels Most pathologic vascular processes are located close to the cen- terat theoriginof majorvascular branches,allowing theFOV tobe confined to the central two thirds of the abdominal space on the topogram (Fig.187.1).The origins of the vessels arising fromthe abdominal aorta are visualized on axial sections and on MIPand MPR images.Ifalargervolumeneeds tobe acquired onthez-axis, a four-slice CT needs a collimation of 4 x 2.5 mm to achieve an acceptableacquisition time duringone breath hold. In contrast, a suspected renal artery stenosis requires a reduction of the acqui- sition volume to the renal region. To achieve an adequate visua- lization ofpossiblestenosesinthinrenal arteries,the examination should be performedwith thin sections of, for instance,4 x 1 mm and with an RI of only 0.5 mm. Since the individual circulationtimes oftenvary, afixed delayof the injection of contrast medium is notrecommended, and the useof a test bolus or bolus tracking is suggested instead. The ROI to register the increase in density (arrival of the contrast medium = commencement of the measurement) is best placed over the lumenof thedescendingaorta(see page 176). CT system Coli. ST Feed Pitch RI Sec.! Voli. Current Kernel WI C Delay CM [mm) [mm) I Rol. [mm) Rol. [KV] [mAs) [HU) [sec.) [mil ml/sec) 1 row 4 rows 16rows 3,0 4x l ,0 1,25 16xO,751 ,0 6,0 6,0 15,0 2,0 1,5 1,25 1,5 1,0 0,7 0,8 0,5 0,5 110 120 120 100 130 130 B30 350/ 50 20/ BT B20 350/ 50 20/ BT B30 350 / 50 20/ BT 120/ 3,0 110/ 3,0 110/ 3,5 Fig. 187.1 Fig. 187.2 Fig. 187.3 The FOV is placed over the central abdominal space (Fig. 187.1). Normally, the visceral branches of the abdominal aorta show a good luminalcontrast without filling defects. includingthe branches of the mesenterial vesselsasshown in Figures187.2 and 187.3. Incase of an occlusion of the superior mesenteric artery (106). the interrupted vascular lumen (..) and the collateral vessels ( ~ ) are easily recognized onVRT and MIPimages (Figs. 187.4-6). Fig. 187.4 Fig. 187.5 Fig.187.6
  • 183. 188 CT Angiography Iliofemoral Vessels For CTangiography oftheiliofemoral vessels,thepatient isplaced feetfirst on the table.The length ofthe relevant bodyregion along the z-axis is critical (Fig. 188.2), and thereforeit isgenerally pre- ferred to use a wide collimation of 4 x 2.5 mm or 16 x 1.5 mm (insteadof4 x 1 mm or16 x0.75mm),which allows afaster table feed. Narrow overlapping reconstructions should guarantee the quality ofthe final images. Problems can arise with the timing of the injection of contrast medium, especiallywith unilateral high-degree stenosesbecause of the slow flow (see below) in the peripheral vessels 01 the affected side. If bolus tracking (B1)is used,the ROI is placed over the descending thoracic aorta or abdominal aorta to register the increase in thecontrast medium-induced density (see page176). Already VRT images allow a good overview from the aortic bifurcation totheanklein most cases (Fig. 188.1). , CT system Call. ST Feed Pitch RI Sec.! Volt Current Kernel WIC Delay CM [mm) [mm) I Rot [mm) Rot. [KV) [mAs) [HU) [sec.) [mil mllsec) 4 rows 16rows 4 x2,5 16x1,5 3,0 15,0 2,0 24,0 1,5 1,0 1,5 1,5 0,5 0,5 120 120 130 130 B20 350 I 50 251BT 150 I 3,0 B30 350 I 50 251BT 150 I 3,5 Fig, 188.1 Fig. 188.2 Fig. 188.3 Fig. 188.4 a 4b Incases of peripheral arterial occlusive disease, both arteriosclerotic plaques (174) and luminal narrowing with impaired flow distally (Fig. 188.4a) are clearly recognized incomparison witha normal post-stenotic flow inthetibioperoneal vessels (Fig. 188.4b). In high- degree peripheral arterial occlusive disease examined with a table feed of > 3 ern/sec, the flow can be so much delayed that the craniocaudal acquisition leaves thebolus behind.
  • 184. CT Angiography 189 Vascular Prothesis CT angiography is also suitable to follow implanted stents or vascular prostheses (182) that interfere with the assessment of mural calcifications becauseof acousticshadowing (Fig.189.1 '3) incolorduplexsonography images. ;1"'89 98 1./97 ~ ~ / 99 .-:-, / ~. ~t. )L'"'lL - ..... ,..,...,~~ , A;~1 10 ~ 135 . 1061:f . '. 135 ,,,, ' 1 Fig. 189.1 Fig.189.2 Fig.189.3 Outlook CT angiography undergoes rapid technical changes and its ad- vancement can beexpected toescalate dueto morechip capacity and increasing computer power. It is foreseeable that separate work station with user-friendly software and partially automated programs will shorten reconstructions using VRTfurther. Genera- Fig.189.4 Fig.189.5a ting images of thedescendingaorta (Fig.189.4) or majorthoracic vessels (Fig. 189.5) withVRTand MIP asillustrated herewill be- comeever more effortless.Thisrepresentsachallenge fortheuser to stay abreast with the technical developmentsand to keep the departmental protocolsof the variousCTA applicationsuptodate. Fig.189.5b
  • 185. 190 Test Youself ! Tests 47to49: Thefollowing threeimages containseveral pathologicfindings,some obvious andothers rather subtle. Good luckwhentackling thetests! The answerscan be found on page 202 below. Fig. 190.1 Fig. 190.2 Fig. 190.3
  • 186. APrimer of CT Evaluation 192 Occasionally,thebeginner faces thequestion todecidewhether a finding represents a true lesion orjustan artifact. Acontralateral comparison or a comparison with adjacent cranial or caudal sections can often be helpful. Furthermore, uncertainty arises when describing a lesion without familiarity with the appropriate vocabulary.This primer aims to remedy these problems. A General Approach to an Abnormality of theCTMorphology: Where? Location, lateralization,relative position tootherorgans/vessels Size? Size (diameterin [mm,em]; important, e.g.,monitoring of therapy) Density? Relativeto its surrounding: isodense (equal density); hyperdense(denser); or hypodense (less dense) Structure? Homogenous(e.g., fluids) orheterogenous / septate/ geographic Shape? Tubular(vessels, muscles, ...j ornodular (tumor, lymph nodes)? Reticular (resembling a net),striate ofdiffuse? Demarcation? Sharply marginated (more likely benign) or indistinctly marginated (infiltration into thesurrounding, e.g.,inflammation, malignancy) Caution: Partialvolume effect can mimic an indistinct margin! Perfusion? No, peripheral, homogenous or heterogenouscontrast enhancement Expansion? Space-occupying effectnot invariablyto beequalled with malignancy: e.g., large benign cystscandisplace adjacent vessels B Useful Terms, in Alphabetic Order [eo Application, Possible Significance) CM Defect Defect Bolus CT Band-likedensity [«> lung, connectivetissue: post-inflammatory, scar) Measuring ofdensity (¢ differential diagnosis) Uniform, neither focal nornodular; e.g., liver: hypodense ¢ hepaticsteatosis (fatty liver) hyperdense ¢ hemochromatosis Typicalcalcification pattern ofbenign hamartomas [e> lung) Calcification patternof perihilar lymphnodes ( lung ¢ silicosis; porcelaingallbiadder) Increased densitydue to accumulation ofcontrast medium Pertusion pattern(homogenous, timelyor delayed) Intravascular locationofthrombi {eo aortic aneurysm) Phenomenon (¢ sedimentedhematoma)orair-fluid levels [eo paralytic iieusor intestinal obstruction) Corticalstep deformity, displacement, number of fragments, stability, articularsurface? Diffuse, slight increasedensity seen in perifocal edema [eo fat, lung) Confined perifocal edema (¢ around inflammatory toci and metastases) Blood-containing[eo large infarcts, e.g.,cerebral) Benign criterionfor lymph nodes (¢ nodal index) Typical for vascular rarefaction inthe lung [eo emphysema) High resolution computed tomography (thin sections) [eo lung; also for MPRand3D) Denserthanthesurroundingtissue (bright -e-fresn cerebral bleedingorcalcification) Dumbbell-like Densitometry Diffuse Enhancement Dense band Eggshell-shaped Fractures Enhancement pattern Excentric Fluid Levels Halo Hemorrhagic Hilarfat Honeycombing Ground glass density Hyperdense HRCT Air inclusions Ampullary Bullae Capping Clubbing Cavity Central Demarcation Crescentic ¢ Infectionwithgas-forming bacteria ¢ compound fracture Dilatation ofthe renal pelvis (¢ physiologicvariant orobstructive uropathy) Articularinvolvement Evaluation offractures [ec- riskOf degenerativeosteoarmntis) Dynamicexamination, often without table movement to assess the contrast enhancement pattern Lung [ee- pulmonary emphysema) Periventricular abnormalityin thewhite matter [eo transependymaldiffusionofCNS; sign of SAE) Intrapulmonary hollowspace(¢ tuberculosis) Inthecenter of a lesionor close to thehilumof parenchymafous organs e.g.,ofa limbof theadrenal gland (¢ adenoma,metastases) Contrast medium, given orally,rectallyor intravenously Location ofintravascularthrombi (eo acrnc aneurysm) Courseof fracture JinesEvaluation withadditional MPH [ee- surgical planning) Typical configuration, e.g., subdural hematoma or perihepatic effusion I ascites Pathologic phenomenon inopacified vessels / urinary collecting system In opacified vessels[eo thrombus), in urinary bladder(¢ tumor, bloodclot) Depending on the vascularization, lesions become visible onlyafter administration ofcontrast medium Concentric I
  • 187. A Primer of CT Evaluation 193 Circular around a lesion (edematousl one) Topographic descriptionofanintrapulmonary lesion Alongthe periphery, in contrast to central Ratioof table feedper rotationand section thickness [ee- spiraltechnique, see p.8 / 9) Pictureelement (imageformation, see p. 14) Intravascular [eo arteriosclerosis), pleura-based [ee- asbestosis) ~ scalloped, cauliflower-like (¢ hilar lymph nodes of the lung, e.g., Boeck'sdisease) Typicalpattern of benigncalcifications [ee- lung) Favoredtermfor "1don't know what is means" c::> chronic pancreatitis Can induce artifacts along vessels (¢ aortic aneurysm) Less vessels per pulmonaryvolume (¢ emphysema, SIP lobectomy) Lacking in malignant tumorsor advanced inflammations (nolonger respecting natural borders => infiltration) Convex projection intotheparanasal sinus, homogenous Net-like pattern (¢ fibrosis of the pulmonary interstitium) Preferredposterior paravertebral lymph node station Internal herniationof brainstem dueto increased intracranial pressure [ec- quadrigeminal andambient cisterns) Regionof interest (¢ densitometry) Focal space-occupying lesion (only intrapulmonic) Peripheral contrastenhancement [ec- glioblastoma) Preferred siteforcertain changes [«> lymphnodes, metastases) Thickened bile [eo cholestasls,cholecystitis) Tumor of unknownnature(ubiqurtously applicable) Biconvex configuration (¢ aortic aneurysm; epidural hematoma) Acquisition of a 3Ddata setwithcontinuoustable feed andany section reconstruction, see p. 7 Hypodense star-likefigure[ec- fNH ot theliver) Septation [eoechinacaccal cyst) Short tube of various materials to stent vessels, ureter or common bileduct bonyCortex(eo fracture diagnosis) Non-descriptivetermof a lesion. try to use more precise term Preferred lymph nodestation Symmetric andtimely renal enhancement and excretion of contrast medium =normal Wedge-shaped [eotypical infarctpattern, scarresidue) Renalvein or vena cava [eo renal tumor) Normal configuration of the pulmonary hila Volumeelement (image formation, seepage l A) Triangular configuration [ec- typical infarct pattern, scar residue) Risk of herniation Triangular Retrocrural Reticular Perifocal Perihilar Peripheral Pitch Popcorn Process Pseudocysts Pulsation Pixel Ptaque Polycyclic ROI Round lesion Scalloped enhancement Siteof predilection Stellar Stellate Stent Respecting soft-tissue planes Retentioncyst SpiralCT Rarefaction Tumor extension Vascular configuration Voxel Wedge-shaped Stepdeformity Structure Sludge Space-occupying process Spindle-shaped Subcarinal TImely Central, hypodense or homogenous liquefaction Longitudinal-transversediameter ratio (characterizationof lymphnodes) Nodular configuration (¢ lymphnodes, tumors, adenomas), miliary < granular < fine-nodular < large-nodular< confluent (¢ pulmonary interstitium) Surface ofcerebral gyri[eo cerebral edema, DO: child)or pancreas outline(¢ acute pancreatitis) Destructionof bony matrix [eo metastases, multiple myeloma) Osseousapposition(<> degenerative), less frequent dueto sclerotic metastases Effect of partial volume (causesapparentindistinctness) Parenchymal per1usion pattern in thespleen during the ea~y arterial phase Hyperperfusion Hypodense Indentation Imbibition Induration Infiltration Indistinct Indistinct margin Isodense Jet effect LN lymphangiomatosis Intramural lacuna MPR Iris effect Inflow effect Multislice Mural thickness Necrosis Nodalindex Enhancement (e::> inflammation, hypervascular tumor) Less densethanthesurrounding (dark ¢ fluid,fat,air) Striatetodiffuse enhancement (¢ fatty fissue: scar, inflammation) Blunt convex bUlging I displacement of adjacent structures (¢ tumors) Outline of a lesion (see marginal indistinctness) Causedby inflammatoryandtumorous infiltration of thesurrounding tissue(caution: DOpartial volume effect) Thickenedfibroustissue(e-scar,pulmonaryfibrosis) Perifocal extension of aninflammatory or malignantprocess Incomplete mixingof contrast medium, canmimic intravascular thrombi Located inthewallof ahollowviscus (¢ gas, tumor) Centripetal enhancement [ee- hepatic hemangiomas) As denseas ... (= isointense) Inflow of opacified urine fromthe ureter intotheurinary bladder Lacunar defect [eo latestage after cerebral infarct, isointensewith CSF) Lymph node (tor size see checklists, ¢ hilar fat) Groundglass-density (¢ pulmonary parenchyma, breast carcinoma) Multiplanar reconstructionof various image planes (sagittal, coronal ¢ diagnostic evaluation of e.g. fractures) Multiphasetechnique Data acquisitionduring early arterial, portovenous or late venous passageof the contrast medium bolus(¢ spiral CTof the liver) New multislice technique consisting of simultaneousacquisitionsof several sections in spiral mode Single or multiple layers (wall of a hollow viscus: ¢ ischemia, inflammation) Narrowed parenchymal ¢ Renal atrophy (degenerative, hydronephrosis) rim Nodular Osteolytic Partial volumeeffect Obliterated Osteoproliferative Patchy
  • 188. 194 B A Primer of CT Evaluation Practical Terms, Organ-related I The following list contains helpful terms, which are used for interpreting CT examinations of a particular organ. Terms locating the findings are followedbyterms describing typical morphologic changes, which are incorporated with possible conclusions and subseouent organ-related pecu- liarities. Thelist does notclaim tobecomplete (this would make it far too convoluted), but should helpthe reader to look up some of the most frequent organ-related terms quickly. Skull, intracranial Locational descriptions • Supra· ! infratentorial • Frontal I temporal I parietal I occipital • SingularI multiple • White matterI cortical Typical morphology ¢ possible diagnoses • Midlinedisplacement, obliterated cisterns, effacedsulci, narrow subarachnoidspaceor small ventricles; Obliterated white matter I cortex intertace eo:> increased intracranial pressure; possible herniation • Capping ¢ Transependymal diffusion of advanced increased ventricular CSFpressure • Intracranial air inclusions ¢ Compound fractureof thecranial vault or cranial base • Cystic homogeneous hypodense ¢ Hygroma / arachnoidal cyst • Hyperdense, biconvex/ crescentic space- occupying process along the internal table of cranial vault ¢ epidural I subdural hematoma • Hyperdenseextracerebral CSFspace ¢ Subarachnoidal hemorrhage • Hypodensewhitematter lesions ¢ Infarcts, embolic residues • CSHsodense lacunardefect ¢ Infarct residue • Peripheral scalloped enhancement ¢ Typical tor glioblastoma • Subtle roundingof thetemporalhom Early increase in CSFpressure • Ventricular enlargement ¢ Internal hydrocephalus ¢ increased CSF pressure ! Notable lindings • Immediatetherapeutic intervention with pendingherniation ! Paranasal sinuses Locational descriptions • Frontal sinus,ethmoid sinus, sphenoid sinus, maxillary sinus • Semilunar canal (important drainageduct) Typical morphology ¢ possiblediagnoses • Round, broad-based, convex homogeneous space-occupyinglesion ¢ retention cyst Notable findings • Normal variants: Haller'scells, pneumatic nasal conchae oruncinateprocess • Riskof visual loss with orbital fracture • Fracture classification offacialbones according to Le Fort (see page 63) Orbit Locational descriptions • Orbital floor, orbital roof, medial and lateral orbitalwall, retrobulbar Typical morphology ¢ possible diagnoses • Thickened extraocular muscles ¢ Endocrineophthalmopathy, Myositis Nofable findings • Riskof visionlosswithfractures of theorbital floorsolely throughcicatricial pull ontheorbital fattytissue Neck Locational descriptions • Nuchal, submandibular, prevertebral, paratra- cneal, parapharyngeal, epiglottic, subglottic, neurovascular bundle, intra- / suprahyoidal Typicalmorphology ¢ possible diagnoses • Heterogenous internal structure, possibly with intrathyroidal calcifications ¢ nodularstruma • Multipleovoid lesions along theneurovascular bundle ¢ lymph nodes Chest Locational descriptions • Peripheral = subpleuralI central = perinilar: • Basal / apical, segmental / lobular; Name segment! Typical morphology ¢ possible diagnoses • Polycyclic bulky hila ¢ Boeck's disease; hilarnodal metastases • Multiple, only indistinctlyoutlined nodules ¢ pulmonarymetastases / granulomas • Sharplyoutlined, striatedensity Without perifocaledema ¢ fibrotic edema • Perifocal groundglass-like density in HRCT ¢ Acute inflammatoryprocess • Irregular nodularthickened interlobar septae withfine-reticular thickening <> l ymphangiomatosis • Bullae withvascular rarefaction,honey combing ¢ emphysema • CaVity with layered groundglass density below air pocket ¢ aspergilloma • Fusiform thickeningalong interlobar space -e- encapsulateo pleural effusion • Apical pleuralthickening, cavities, hilar lymph nodes ¢ tuberculosis • Popcorn-likeor club-likecalcifications ¢ benign hamartomas, post-inflammatory residues Notabte findings • Normal variant oftheazygous lobe • HRCTwiththinner sections (do you remember fhe rational? Referto p.86-87) • Don't forget the pulmonarywindow Liver LocationaJ descriplions • Subdiaphragmatic, subcapsular, perihilar, name thesegment (not only the lobe), periportal, diNuseI focalI multifocal, parahepatic Typicalmorphology ¢ possible diagnoses • Diffusehypodensity withresultant hyperdense vessels (unenhanced) ¢ fattyliver (hepatic steatosis) • Diffusehyperintensity ¢ hemochromatosis • Homogeneous-hypodense, round sharply marginatedroundlesion withoutenhancement ¢ benign cysts • Focal roundlesion with enhancement ¢ metastases; abscess • Roundlesion with central hypodense stellar figure ¢ FNH • Cameral cysts withstellateseptations ¢ echinococcus(splenic involvement?) • Hypodense cannulated, but irregularly branching ¢ cholestasis • "intraparenchymal" hypodenseair pockets ¢ pneumobilia; SIP biliointestinal anastomosis Notabte findings • Multiphase spiral CT: early arterial, portal and latevenousfor improved detectionof focal lesions • Dynamic bolusCT Without tablefeed ¢ iriseffect in hemangiomas • Portography CTafter preceding catheter- placementintosplenicor mesenteric artery
  • 189. A Primer of CT Evaluation 195 The checklists represent the third part of this primer. They are not repeated here. They can be foundasinserts or onthefollowing pages: Region Page Skull 26 Neck 64 Chest 74 Abdomen 103 Skeleton 167 Vessels I retroperitoneum Locationa/ descriptions • Para-aortal, paracaval, interaortocaval, prevertebral, retrocrural, mesenteric, para-iliac, inguinal, cervical Typical morphology '" possible diagnoses • Dilated aortic lumen with different times of opacificationand detection of a septum ¢ dissectedaneurysm • Beticulnnodular thickeningof theperitoneum with nodular projections andascites ¢ peritoneal carcinomatosis • Endoluminal hypodense defects ¢ thrombi; caution: DOinflow effect (refer to pp.21 - 23,73) Bone I Skeleton Locational descriptions • Cortical,subchondral,juxta-articular, metaphyseal, diaphyseal, epiphyseal, intra- and extraspinal Typical morphology ¢ possible diagnoses • Step-deformityof thecortex, corticalbreak, fractureline¢ fracture • Articular involvement ¢ risk of secondary degenerativeosteoarthritis • Focal hypodensity of thespongiosa with absent trabeculae ¢ pathologic bonemarrow infiltration Nolable findings • Evaluation of stability, MPR, 3Dreconstruction, myelo-CT ofthespine I Checklists c Notable lindings • Densitometry of cystic changesfor comparison with unenhancedsections • Evaluationof excretion: symmetric, timely? Dilated ureteral lumen? GastrointestinalTract Typicalmorphology '" possiblediagnoses • Generalized diffuse wall thickening ¢ lymphoma; ischemia; ulcerative colitis • Segmental wallthickening ¢ Crohn's disease • Air-fluidlevels withinlumen and dilatation ¢ intestinal atonyto ileus • Free air in theabdomen ¢ perforation • Intramuralair ¢ suspiciousfor necrotic intestinal wall(ischemic or inflammatory); caution: DO diverticulum! Nolable findings • Selectionof suitable oral contrast medium (refer to p. 19) Genital Organs Locaffonal ttescriptions • Parametrial, intramural,submucosal, endometrial, ischial fossa,pelvic wall, periprostatic Typicalmorphology ¢ possiblediagnoses • Hypodense,water-isodense space-occupying lesion in thescrotum ¢ hydrocele, varicocele • Nodularthickeningof the myometrium <> benign myomas, but also small uterine cancers • Growth beyond organ outline, infiltration of rectal and bladder wall ¢ suspicious for malignancy Nolabie findings • Thin sectionsthrough the lesser pelvis, rectal administrationof contrastmedium Urinary Bladder Locaffonal descripuons • lntra-, extra-, paravesical, bladder floor, bladder roof, trigonum Typical morphology", possibie diagnoses • Diffuse wall thickening ¢ cystitis,trabeculated bladder; edemafollowing radiation • Focal wall thickening,polypoid projecting into the lumen ¢ suspiciousfor malignancy Nolable Ilndings • Jeteffect, diverticulum, catheter balloon; indwelling catheter fa beclamped betore examination! Gallbladder Typical morphology ", possible diagnoses • Multi-layered edematous wall thickening with perifocal "ascites" ¢ acute cholecystitis • Intraluminal wall-based thickening with calcification¢ polyp • Intraluminal sedimentationphenomenon ¢ sludge • Eggshel l ~l i ke peripheral calcification ¢ Porcelain gallbladder, precancerosis Pancreas Loeat/analdescriptions • Head, body,tail, peripancreatic fatty tissue, uncinate process Typical morphology '" possibie diagnoses • Diffuseenlargementwith obliteratedoutlineand exudate pathways ¢ acute pancreatitis • Atrophic organ, dilated ducts, calcificationsand pseudocysts ¢ chronic pancreatitis Spleen iocstionst descriptions • SUbdiaphragmatic, subcapsular, perihilar, perisplenic Typical morphology '" possible diagnoses • Leopard-like marblepattern duringthe early arterial phase of enhancement ¢ physiologic • Wedge-shaped perfusion defect ¢ infarct • Perisplenic round lesion, isodensewith splenic parenchyma ¢ accessory spleen; LN Kidneys Locational descriptions • Parapelvic, medullary, parenchymal, cortical, subcapsular,arising, polar, perirenal, uni- / bilateral, lateralization Typical morphology", possible diagnoses • Homogenous-hypodense, round, sharply demarcatedspace-occupyinglesion without contrastenhancement ¢ benigncyst • Hypodense clubbingof thecollecting system ¢ obstruction; ampullary renal pelvis, parapelvic cyst • Irregular wallthickeningot thecystwifh contrast enhancement ¢ suspiciousfor malignancy • Thinning oftheparenchymal rim, generalized decrease in size ¢ renal atrophy • Heterogenous space-occupyinglesion extendingbeyondtheorgan outline ¢ renal cellcarcinoma • Hypodensewedge-shaped periusiondefect -e-renal infarct
  • 190. 196 Solutions to Test Yourself! The exercises and solutions have been numbered consecutively. Some of the exercises have several different correct solutions. If the exercises can be solved simplyby referring tothe chapters in the book, I have indicated where you will find the necessary information. Solution to exercise1(p.32): After you have completed the exercises, compare your scoreand results withthose of yourcolleagues.Thescore on theright gives youan impression of the degree of difficulty. Enjoythe challenge! 9 Points You will find the sequence for interpreting CCTs on page 26. Each stepgives you '12 point with 3 extra points for the correct sequence, which addsupto 9. Solution to exercise 2(p.45): Lung/pleural window Bone window Soft-tissue window Solution to exercise 3 (p.45): Levei - 200 HU +300 HU + 50HU Width 2000 HU 1500 HU 350 HU Gray scale -1 200to + 800 HU - 450 to +1050 HU - 125to+ 225 HU 9 Points 3 3 3 10Points a) Bariumsulfate Routineforabdominal/pelvicCT if thereare no contraindications b) Gastrografin Watersoluble, but expensive; if perforation ileusorfistulas aresuspected; prior tosurgery Nooral CM shortlyafter surgery foran ileal conduit! Solution to exercise4 (p. 45): 30minbeforeCTofupper abdomen 60 minbeforefullabdominal CT 20min beforeCT ofupperabdomen 45min before fullabdominal CT 4 4 6 Points a) b) c) Renal failure (creatinine, possibly creatinine clearance,functionfollowing kidney transplant ornephrectomy) Hyperthyroidism(clinical signs? if yes,hormone status, possiblythyroidultrasoundand scintigraphy) AllergytoCM(has CM-containing iodine already been injected? Are thereanyknown previous allergic reactions?) 2 2 2 Solution to exercise 5 (p. 45): Tubular andnodular structures can be differentiatedbycomparing aseries of images. Solutionto exercise 6 (p.45): 2 Points 3 Points Vessels inwhich beam-hardening artifacts occurbecause ofCM infloware the superior vena cava,infertor vena cava,and the subclavian vein. Solutionto exercise7 (p. 48): 3 Points Fractures, inflammatory processes, and tumorsor metastases can cause swelling of mucous membranes and retention of fluidsin the mastoid sinuses and middle ear; these are normallyfilled withair. Solution to exercise 8 (p.57): 18Points This image requirescareful study.Youwill discoverseveral types of intracranial hemorrhageandthecomplicationsresulting from them. • Bruising of theleft frontoparietal soft tissues (extracranial, indicativeoftrauma tothe head) 1 • Subdural hematoma over the right hemisphere extending tooccipital levels(hyperdense) 2 • Edema intheright frontopartetal areas, possiblyaccompanied by an epidural hematoma 2 • Signsofsubarachnoid bleeding inseveral sulci inparietal areas on the right,adjacent tothefalx 2 • Thehematoma has penetrated intothe right lateral ventricle, which is practicallyobliterated 4 • Choroid plexus intheleftlateral ventricleappears normal 1 • Thereis a midlineshift toward theleft, and edema surroundstheperiventricular white matter on the right 2 • Raised intracranial pressure(obstructed ventricle) and herniation ofthebrain (edema) can beexpected 4
  • 191. Solutions to Test Yourself! Solution toexercise 9 (p. 72): Gray and whitematter appear well defined on narrow brain windows. Level Width Gray scale + 35HU 80HU - 5 HU to + 75HU CCTsectionsare normallyoriented parallel totheorbitomeatalline, so that Initial and follow-up studies can be preciselycompared. 2-mm sectionsat 4-mmincrements are acquiredthroughthe petrosal bone, then thickness and tablemovementare set at 8mm. Solution toexercise 10(p.72): 9 Points 3 2 2 2 16Points 197 Intracerebral hemorrhage Subarachnoidhemorrhage Subdural hemorrhage Epidural hemorrhage Complications inearlyphases hyperdense, often with hypodense peripheral edema hyperdense bloodinstead of hypodense CSFinthesulciand cisterns hyperdense crescentic area close tothecalvaria, concave toward thecortex, not limited bycranial sutures hyperdense, biconvex areaclose tothe calvaria, smoothtowardthecortex, always limitedby cranial sutures hemorrhage intoaventricle, CSFflow isobstructed, edema, danger ofherniation 2 2 4 4 4 Solution toexercise 11 (p. 72): 2 Points Subarachnoidhemorrhage inchildren may bevisible onlynext tothe falxor inthelateral (Sylvian) fissure. Solution toexercise 12(p. 72): Practicemakes perfect! Solution toexercise 13(p. 72): 10Points 4 Points Fractureofthe rightfrontalbone andabsent right frontalsinus (thelatterisacongenital variation, not ahemorrhage,as indicatedbythe osseoustrabecuiae) Solution toexercise 14(p. 72): 8 Points This was adifficult question. In the left internal jugular vein there isunusual sedimentation ofthe CM due toslow blood flow.The asym- metry ofthe jugularveins is not asign of thrombosis. Aleft cervical abscessmakes the neck musclesappear poorly defined. Solution toexercise 15(p.73): 4 Points In this patientthe surface subarachnoid spaces are clearlytoo narrow and theventricles distended.These signsindicatethatCSFdrain- age is reduced or blocked and thereis imminent danger ofbrain herniation. There is generalized brain edema.Aneurosurgeon should be consulted about insertingan intraventricular shunt. Solution toexercise 16(p. 73): 3 Points Itispossibletomistakethesubarachnoidhemorrhagearoundthe leftfrontallobe as an artifact. Theleft frontal cortex isoutlined by blood. Ifyoudidnotsee anyabnormality, return tothe chapter about thehead. Solution toexercise 17(p. 73): You have ofcoursetakenthe hintabout notgiving up too soon; the right medial rectus muscle (47c) is thickened. It is the second muscle to become involved inendocrine ophthalmopathy. Ifyoucannot remember which muscleisaffected first, return topage 61 . I
  • 192. 198 Solutions to Test Yourself! Solution to exercise 18(p.73): Part of the question was misleading. but thiswas intentional, and Ihopeyoutakeit in the right spirit. No fresh intracranial bleeding can be seen in this image (Fig. 73.4 is the same as Fig. 198.1).The abnormality in the lett frontal lobe is an area of reduced attenuation representing an earlier hemorrhage (180) which has now reached the resorption phase (4 points). The extracranial swelling and bruising in the lett frontoparietal area (1 point) is also 2 weeks old. In order to determine the nature of the hyperdense foci, particularly on the right side, you should of course ask to see adjacent images (4 points). The next caudal section (Fig. 198.2) shows that these foci are formed by the orbital roofs (*), the sphenoidbone(60), and the petrosal bone (* * ) (1 point for each). These partial volume effects were discussedon page 53.If you misinterpre- tedtheminthe question,takeitasawarn- ingand youwillbeless likelytomake this mistakeagain. Fig.198.2a Solution to exercise 19(p. 82): Compare your checklistforCCT withthe one on page 74. As inexercise 1,each itemisworth 'J, point andthecorrectsequence is worth 3 points. Fig. 198.2b 12Points 13Points 4 PointsII There is an area of lowattenuation due to incomplete CM filling inthe azygos vein, rnost likely becauseof athrombosis(2 points).The esophagus is notwell defined.There are hypodense lines crossing the pulmonarytrunkand rightpulmonary artery which are artifacts because they extend beyondthelumen ofthevessels(2 points). I Solution to exercise 21 (p. 100): Did yousuggest doingbronchioscopy orbiopsy inorder toknow moreaboutthe "Iesion"?Then you mustrevisit the basic rules of CT interpretation. But if you remembered to look first of all atthe other images intheseries, as forexam- plethe one on theright,youwillhave seenthat the "Iesion" belongs tothe sterno- clavicularjoint( '" ). This is another example of a partial volume effect. There is degenerative change inthisjoint, butnopulmonary lesionorinflammation. Abb.198.3
  • 193. Solution to exercise 22(p.100): The cause of sudden back pain in this patient was the dissection (172) of the aortic aneurysm (1 point). At this level, both the ascending (89a) and the descending (89c) aorta (1 point each) show a dissection flap. It is a de Bakey type I dissection (1 point). Solutions to Test Yourself! Solution to exercise 23(p.100): Thisisa caseofbronchial carcinoma (the bronchial obstruction is not seen at this level).There isatelectasisoftheentireleft lung (84) (2 points) and an effusion (8) fillsthepleural spaces (2 points). Didyou detect themetastatic mediastinal LN(6)? (2 points) Solution to exercise 24(p. 101): The most obvious abnormality is the bronchial carcinoma (7) in the left lung. The right lung shows emphysematous bullae (176). CT-guided biopsy of the tumor should bepossiblewithout causing a pneumothorax because it has a broad pleural base (2 points). 199 Solution to exercise 25(p. 101): Thesmall metalclip(183) isa hint that the stomach has been surgically transposed into the mediastinum. The thick-walled structure with the irregular lumen isapartof the stomach (129), not an esophageal tumor. At the moment of data acquisition the stomach was contracting and is therefore notas easily identifiedas inFi9ure 91.2. Solution to exercise27(p. 101): You are alreadyfamiliar with this tragic case of bronchial carcinomainayoung pregnant woman (thus no CM enhancement, see Fig. 98.2). The anteriorlocuteofthemalignant effusion(3points) had caused the right lung to collapse (2 points) and was theretore drained. After the tibrin clot had been removed from the catheter the lung was reinflated and the mother's life was pro- longeduntil thebirthofher healthychild. Didyou noticethe metastaticLNinthe rightaxilla? (1 point) Perhaps the first thing you noticed was the irregular contour of the diaphragm (30) (1 point), but this is a normal finding. The patient was a smoker and had complained of weight loss. You should first ask for lung windows inordertocheck for metastases (7) or primary bronchial carcinoma (5 points). When a chest is examined, it should become your standard procedure to use bothsoft-tissue and lung windows (Fig.199.5a). Solution to exercise 28(p. 101): These two images show an aberrant branch of the aortic arch: The subclavian artery passes posteriortothe trachea and theesophagustowardthe right side of thebody.Youmayrememberthat this anatomic variationwasmentioned, butnot shown,onpage 120. 4 Points II I
  • 194. Solutions to Test Yourself! Solution to exercise 29(p. 141): 200 ---In addition to the air-fluid levels in the dilated bowel (2 points) associated with an ileus, you should have seen the dilated right ureter anterior tothe psoasmuscle(2 points).Thecorrect diagnosisisthereforeileusandhydronephrosis.Youmayrecognizethisparticularcase as thesameoneshown in Figure 134.2a,ata slightly morecranial level. You shouldhave seenthe adenoma(134) inthe right adrenal gland (2 points). For'j, point each you should be ableto nameten other organs. Consult the number legends if you are uncertain. Solution to exercise 30(p. 149): Solution to exercise 31 (p. 149): 7 Points Solution to exercise 32(p. 149): 4 Points Solution to exercise 33(p.149): 3 Points Thisisindeed acase of situs inversus(2points).Youwillalsohave noticed that the attenuation of the liver (122) is abnormally low: fattyliver(2points). The question itself will have drawn your attention to the athero- scleroticplaques (174) inthecommon iliac arteries (113) (1 point). Theleft one is part ofanaorticaneurysm (2points). 5 PointsSolution to exercise 35(p. 149): The two cysts (169) in the right kidney (135) are impossible to miss (1point).Buttherearealso multiple,hypodenselesionsinthe spleen (1 33), due to splenic candidiasis (3 points). You may also have considered a rare case of nodular lymphoma or melanoma metastases inthe spleen('j, point each). 6 PointsSolution to exercise 34(p.149): Hopefully you saw the fairly large, irregular metastasis (7) in the posterior segment of the liver (122) (1 point). Did you also see the smaller,moreanteriormetastasis?(3 points).TheDD mayhave includ- ed an atypicalhepatic cyst (1 point) or, for the anterior lesion, partial volumeaveraging ofthe falciform ligament (1 point). 29 I
  • 195. Solutions to Test Yourself! Figure 201.1 is the section next to the one in Figure 150.1 and shows that thehypodensearea intheliver isthe gallbladder.If you suggested doing anything else, for example aspiration or biopsy, beforeseeing adjacent sections,take 3 pointsaway. Solution to exercise 37 . 150 : 201 ---You may have thoughtthat the hyperdensefoci next tothe rectum (146) representcalcified LN(6) (1 point). However,the lymphatics are so well demarcated because they are still opacified after lymphography (3 points). Did you also notice the atherosclerotic plaques (174) inthefemoral arteries (119) (1 point)? 6 PointsSolution to exercise 36(p. 150): Solution to exercise 38(p. 150): 3 Points You will achieve the most accurate densitometry of a cyst if you select a section without any partial volume effects from renal paren- chyma as in Figure 150.3b (1 point). Resultsof measurements inFigure 150.3a would betoohigh (2points). Sincethisverycase was discussed onpage 133,take away2 points forthe incorrect answer. 6 Points For further documentation you should ask to see bone windows (2points) and of course the adjacent sections (2 points) inorder to assess the pelvic fracture. It is also important to determine whether the acetabular fossa was involved (2 points). The fractures of the pubic bones were already visible on soft-tissue win- dows (Fig. 150.5) because the fragments were slightlydisplaced. Solution to exercise 40 . 150 :7 Points 10Points , Solution to exercise 39(p. 150): The illustrationshowed onlyone metastasis inthe right lobeofthe liver (1 point) in a case of hepatomegaly (1 point). By using tri- phasic SCT, additional metastases become visible (2 points). CT arterial portogra- phy (3 points) is moreinvasivethan SCT alone, but it demonstrated that the spleen also has metastases. Fig.201.3 """"::;....~ _ Solution to exercise 41 (p.151): Another exampleofa partialvolume effect: thesigmoidcolon was only apparently "within" the urinary bladder (4 points). The first thing you should have asked to see was adjacent sections Ifyoudetected the fresh thrombosis(1 73)intheright femoralvein (118), youget3 points. Didyou alsosee thesynovialcyst (175)on the left (3 points)? Your DD may have included a lymphoma, a femoral or inguinal hernia, or a metastasis (1 point each). If you mistook the cyst for thrombosis of the left femoral vein as well, take away 3 points!Thevein (118) lies next tothecyst. Solution to exercise 42(p. 151): 7 Points You may remem- ber that this case was discussed on page116 (seeFig. 116.5a). There's also pararectal ascites (1 point).
  • 196. Solutions to Test Yourself! 202 Solution to exercise 43(p. 151): ~ You may have thought that Figure 151.4 shows a gastric pullthrough for esophageal carcinoma (1 point) or that the esophageal walls are thickened due to metastases (2 points). However, this was a case of a paraesophageal sliding hiatus hernia(3 points). If youforgot toaskfor lung windows,youwill not have seen thelarge right paramediastinal emphysematous bulla (..)(2 points). Solution to exercise 44(p. 151):~ The beam-hardening artifacts (3) due to drainage tubes (182) were a hint that this image was taken shortly after surgery (2 points). The abnormal structures containing gases (4) are surgical packs (5 points) placed to control bleeding after multiple trauma. Whenthepatient'scondition hadstabilized theywould be removed in a second operation. Your DO may have included fecal impaction in Chilaiditi's syndrome (2 points) or an abscess with gas-forming bacteria(2points). Solution to exercise 45(p. 151): 11 Points In Figure 151.5 a poorly defined tangentialsection of a diverticulumof theurinary bladdercan be seen next to therectum on the right side (*) (5points). Your DO may have includedapararectalLN(2 points).Theirregularitiesintheattenuation values of theurine are due toeM andthe'jet phenomenon' (2 points each). Figures 202.3 and202.4 are adjacent toFigure 151.5. " Astenosisof thethoracicaortaisclearlyidentified(Fig. 190.1),aswell as athrombus inthe right pulmonaryvessels(Fig. 190.2)andan infloweffect of contrast medimintothe superior venacava as differentialdiagnosisof a genuine cava thrombosis (Fig.190.3). 6 Points Fig.202.5d 4 Points Solution to exercise 47-49 (p.190): The same oldproblem!Thehyperdense (enhanced) C-shaped structure in the pancreas (131) in Figures 151.6 or 202.5isaloop ofthe splenicartery (99) (4 points). The adjacent sections (c. d, and e) show that thesplenic artery can bevery tortuous. Solution to exercise 46(p.151): •
  • 197. ..... g><: . Checklist forAbdominal Readings il,ilThieme " i ~ ~ I.z- ~ I *::; " -i " ~ ~ 1§ " '" '" ~ "8, ~ ~ :;; g ~ -s E g -'!!. ~ ~ g ~~ E l'i"5 " ;1: ~ 0 "C ;1: G .0 ~z 'e ~ ~~ ~~ " ~ "0 E 0 ,; ~ .~ 0 " ~ c § ·E IB~ ~ ~ !<t 0 TI 0; ;;" i .~ "5 ~ ~ " " ·0 ~ j; • E ~~ .e i ~ rn ~ · •~ "i .s~ 1§ .is ~ .s ilE :i5 E ~ '" 2 ~ f 2 ~~ g •> ~ ~ ~ e '5 J'! ::; i'" ~ g .e ~ ~ ~ S ~ 0 0 ".§ ] -" i '§! 0> 10 i i 0 E '" ~ ~ ~~ I" § :;; ~ ~ &i I E 0- j ; l' ~ oS If. " g " t t ----- - - ------ ---_... -. ··· x well defined? normal thickness of walls? stenoses ordilations? vessels: (especially periumbilical andinguinal regions) hernias, enlargedlymph nodes? homogeneous parenchymawithout focal lesions? well-defined outline? well-defined, thin wall? calculi? well-defined, size normal? symmetric excretion of eM? obstruction, atrophy, bladderwallsmooth and thin? homogeneousprostate of normal size? spermatic cord, uterus, andovaries? aneurysms? thromboses? enlargedlymph nodes? mesenteric (norma! < 10 mm) retrocrural (normal < 7 mm) para-aortic (normal < 7 mm) parailiacal (normal < 12 mm) parainquinal (normal < 18 mm) lumbar spine and pelvis: degenerative lesions? fractures? focal sclerotic or lyticlesions? spinalstenoses? Gil: Reproductiveorgans: liverand spleen: Gallbladder: Pancreas, adrenals: Kidneys, ureter andbladder: Abdominal wall: Retroperitoneum: Bone window: Excerpt from: Hofer, Matthias CT Teaching Manual ISBN 3·13-124352-X ISBN 1-58890-277-3 @};Thieme Excerptfrom: Hofer, Matthias CT TeachingManual ISBN 3-13-124352-X ISBN 1-58890-277-3 Checklist forThorax Readings 1.On the soft-tissue window: • softtissues, especially: - axillary LNs - breast (malignant lesions?) • mediastinum infour regions: - from theaortic archcranially (LNs?, thymoma/goiter?) - hilarregion(configuration and sizeof vessels, lobulatedand enlarged? - heartand coronary arteries (sclerosis?) • fourtypical sitesof predilection for LNs: • anterior to aortic arch (normal: almost noneor < 6 mm) • in theaortopulmonary window(normal: < 4 LNs < 15 mm) • subcarmal (normal: < 10 mm; DO: esophagus) • nextto descending aorta (normal: < 10 mm; DD: azygos) 2. On the lungwindow: • Parenchymaof thelung: - normal branching patternandcaliberof vessels? - vascular oligemia only at interlobar fissures? bullae? • anysuspicious lung foci?inflammatory infiltrates? • Pleura - plaques, calcification, pleural fluid, pneumothorax? • Bones(vertebrae, scapula, ribs): - normal structure of marrow? - degenerative ostenphytes? - focal lytic or sclerotic processes? - stenosesofthe spinal canal?
  • 198. Checklist for Reading Cervical CT Images Checklist: Preparing thePatient These values are infended asguidelines,larger lymphnodes are notnecessarily pathological. Biconvex, smooth eltipsoidalln shape; close to calvaria; does not exceed cranial sutures; usually hyperdense, rarely sedimented Hyperdense blood in thesubarachnoid space or the basal cisterna instead of hypodens CSF Fresh hematoma: crescent, hypertense bleeding close to the calvaria with ipsilateral edema; hematoma is concave toward hemisphere; mayextend beyond cranial sutures Characteristics Subdural bleeding Type of bleeding Subarachnoid bleeding Epidural bleeding Necessary information: • What regionor regions of the body will bescanned? • What disease? since when? • Clinicalobservations • Previousoperations or radiotherapy?When? • Previous CT?Include printouts if possible. • Renal parameters: at least current creatininelevels • Thyroidparameters or statement that hyperthyroidism is notsuspected • Any known incident of hypersensitivityto CM? Forabdominal andpelvic CTs: (because eM is administered orally) • Isabdominal surgery planned? (water-soluble CM) • Istherean ileal conduit or urostomybag? (inition scan unenhanced, then enhanced scan) • Isa lesion suspected in the lesser pelvis?(rectal CM) Checklist for Referral Sheet ChecklistforReading Cranial CTs Four aspects should be considered : Renal function? (elimination of eM) • Creatinine: normal0.7 - 1.3 mg/dl == 60-130 urnol/l • Creatinineclearance:normal 100-160 m!/ min,if there is creatinine retention, 2 litersof liquid orallyafteri.v. eM will increasediuresis (special monitoringif cardiac failure) Idiosyncratic reaction to eM?(premedicationnecessary, be informedabout glaucoma, prostate hypertrophy) • Patient should receive premedication andeM onan empty stomach (reduces thechancesof aspiration in severe incidents with loss of consciousness) • If premedication is necessary befor oral eM, thepatient mustbe at the unit at least one hour before CT begins Abdominal or pelvicCT? Scheduling OK? • To applyoral CM patient must beat unit 30 minutes prior to CT • previous GITimaging procedures with oral CM?(this may cause artifacts up to 3 days later dueto residual CM) Hyperthyroidism?If problems with iodine-containingCM are suspected, fT3, fT4 andTSHshould bedetermined; possibly alsoultrasound or scintigraphy • Age of thepatient? Medical history? • Posttraumatic changes in thesoft-tissue structures: bruises I tumors? • Normal contours of Quadrigeminal and basal cisterns? (Riskof brainstemherniation) • Sizeandcontoursofventricles and CSF spaces appropriateto patient's age? • Any blockage to flowof CSF (obstructive hydrocephalus) orsigns of brain edema (=effaced sulci)? • Asymmetries: due to head position or trueasymmetry? • Plain or contrast-enhanced CT: cerebral arteries regular? (Especially afterinjectionof CM) • Calcifications in thechoroid plexus and pineal body only?(Common findings) Anyadditional hyperdense foci? • Paraventricular white matterandcortex inconspicuous andwelldefined? Any focal lesions or local edema? • Basal ganglia andinternal capsule intact? (Most common locations of cerebral infarctions) • Bramstern, pons and cerebellumnormal? • Skull checked forfracturesandmetastases in thebone window? IlJ EIlJ .-..c:: t- ~ Excerpt from: Hofer, Matthias CTTeaching Manual ISBN3-13-124352-X ISBN1·58890·277·3 < 6 mm (DO: thymus!) < 15 mm (normalfewer fhan 4 nodes) < 10 mm < 10mm (DO: esophagus') < 7 mm (DO: azygos vein') < 10mm < 12 mm (DO: ovaries!) < 18 mm Normal Diameters l!lThieme • Symmetry of neckmusculature? • Fat planes preserved and sharplydemarcated? • Normal perfusion ofvessels? • Thromboses or atherosclerotic stenoses? • Symmetry and definition ofsalivaryglands? • Thyroid parenchyma homogeneouswithout nodules? • Anyfocal pathologic enhancement with eM? • Narrowing ofthetracheal lumen? • Assessment of lymphnodes? Numberand size? • Cervicalvertebrae examined in bone window? • Vertebral canal patentor narrowed? Lymph Nodes Anterior mediastinum Aortopulmonary window Perihilar Subcarinal Paraaortic Mesenteric Parailiac Parainguinal