IMAGING OF TEMPORAL BONE

SHER-I-KASHMIR INSTITUTE OF MEDICAL SCIENCES
SOURA
Department of radiodiagnosis & imaging

Presentation by
Dr SAMEER PEER
First Year Post-Graduate student

Imaging of temporal bone
Anatomy
&
Pathology

CONTENTS
1. INTRODUCTION
2. ANATOMY OF TEMPORAL BONE
• GROSS ANATOMY
• RADIOLOGICAL ANATOMY
• EMBRYOLOGY
3. PATHOLOGY
• CONGENITALANOMALIES
• INFLAMMATORY CONDITIONS
• TRAUMA
• TUMOR AND TUMOR-LIKE CONDITIONS
4. REFERENCES AND FURTHER READING

INTRODUCTION
The Temporal bone is a complex structure with tiny bony objects such as the crura of
the stapes and canals like the vestibular aqueduct which are less than 1 mm in diameter.
These are close to the limits of resolution by imaging. Thus the best possible spatial
resolution is essential and discrimination of 24 line pairs per cm can be achieved on the
latest CT scanners.
This imaging is mostly by CT, for showing bone detail, and MRI, for the inner ear and its
central connections. Conventional angiography has been almost replaced by MR
angiography or CT angiography.
Metabolic imagaing such FDG-PET is being used to overcome the problem of
distinguishing recurrent tumor from radiation damage.
Radioisotope studies are rarely required to assess the activity of malignant otitis externa.

ANATOMY OF TEMPORAL BONE
• GROSS ANATOMY
• RADIOLOGICAL ANATOMY
• EMBRYOLOGY

GROSS ANATOMY
The temporal bones are situated at the sides and base of the skull. Each
consists of five parts, viz.,
• squama
• petrous
• Mastoid
• tympanic
• styloid process.

The Squama (squama temporalis).—The squama forms the anterior and
upper part of the bone, and is scale-like, thin, and translucent.
Mastoid Portion (pars mastoidea).—The mastoid portion forms the
posterior part of the bone.
Petrous Portion (pars petrosa [pyramis]).—The petrous portion or
pyramid is pyramidal and is wedged in at the base of the skull between the
sphenoid and occipital bone. Directed medialward, forward, and a little upward, it
presents for examination a base, an apex, three surfaces, and three angles, and
contains, in its interior, the essential parts of the organ of hearing.
Tympanic Part (pars tympanica).—The tympanic part is a curved plate of
bone lying below the squama and in front of the mastoid process.
Styloid Procéss (processus styloideus).—The styloid process is slender,
pointed, and of varying length; it projects downward and forward, from the under
surface of the temporal bone

Left temporal bone. Outer surface

Left temporal bone. Inner surface.

Coronal section of right temporal bone.

Left temporal bone. Inferior surface.

ANATOMY OF THE EAR
• External Ear
• Middle Ear
• Internal Ear ( Labyrinth)

THE EXTERNAL EAR
The auricula ( Lateral surface)

Cranial surface of cartilage of Right auricula

External and Middle ear opened from Front

Horizontal section through left ear ; upper part

THE MIDDLE EAR ( TYMPANUM)
Right Tympanic membrane

1. Tympanic membrane
2. Umbo
3. Handle of malleus
4. Lateral process
5. Anterior Tympanomalleolar fold
6. Posterior Tympanomalleolar fold
7. Pars Flaccida
8. Anterior Pouch of Troltsch
9. Posterior Pouch of Troltsch
10. Fibrocartilaginous ring
11. Petrotympanic Fissure
12. Auditory Tube
13. Iter chordae posterius
14. Iter chordae anterius
15. Fossa incudius for short crus of incus
16. Prominentia styloidea
Inner view of Tympanic membrane

View of the inner wall of the Tympanum

View from within, behind and above

Medial Wall, parts of posterior and anterior walls of right tympanum

INNER EAR (LABYRINTH)
Right Osseous Labyrinth

INTERIOR OF THE RIGHT OSSEOUS LABYRINTH

COCHLEA AND VESTIBULE AS VIEWED FROM ABOVE

SEMICIRCULAR CANAL & DUCT ( CROSS SECTION)

LONGITUDNAL SECTION THROUGH THE CHOCLEA

RADIOLOGICAL ANATOMY
PLAIN FILM
• FRONTO-OCCIPITAL 35 DEGREES CAUDAD
• SUBMENTO-VERTICAL
• MASTOID LATERAL OBLIQUE 25 DEGREES CAUDAD
• MASTOID PROFILE
• PETROUS BONE: ANTERIOR OBLIQUE (STENVER’S VIEW)

FRONTO-OCCIPITAL 35 DEGREES CAUDAD

MASTOID 25 DEGREES CAUDAD VIEW

PETROUS BONE : ANTERIOR OBLIQUE
(STENVER’S VIEW)

CT of TEMPORAL BONE
Computed tomography (CT) has revolutionized imaging of the temporal
bone. Recent advances in multisection CT scanners allow acquisition of
high-resolution volumetric data that enable image reformation in any plane.
Protocols vary with different institutions
e.g.
Axial CT images are acquired through the temporal bones. 0.625-mm axial
sections are then reprocessed and reformatted into magnified axial and
coronal images and displayed at 0.3-mm intervals with overlap. In addition
to the traditional axial and coronal views we can also perform reformation in
the Stenvers and Pöschl projections.
The Stenvers projection is the plane parallel to the long axis of the petrous
bone, and the Pöschl projection is the plane perpendicular to the long axis of
the petrous bone.

Sections through a plane 30 degrees to the baseline to limit the radiation dose to
the orbit

Axial CT images show the normal anatomy of
the temporal bone from inferior (a) to superior
(g).
IAC = internal auditory canal, ICA = internal
carotid artery, LSCC = lateral semicircular canal,
n. = nerve, PSCC = posterior semicircular canal,
SCC = superior semicircular canal.

Coronal CT images show the normal anatomy of the
temporal bone from anterior (a) to posterior (f).
ant. = anterior, LSCC = lateral semicircular canal, m. =
muscle, n. = nerve, SSCC = superior semicircular canal,
t. = tendon.

Pöschl projection
CT images in a plane perpendicular to the long axis of the petrous bone show
the normal anatomy of the temporal bone from anteromedial (a) to
posterolateral (g).
LSCC = lateral semicircular canal, n. = nerve, PSCC = posterior semicircular
canal, SSCC = superior semicircular canal.

Stenvers projection
CT images in a plane parallel to the long axis of the petrous bone show
the normal anatomy of the temporal bone from oblique anterior (a) to
oblique posterior (g).
ant. = anterior, LSCC = lateral semicircular canal, n. = nerve, PSCC =
posterior semicircular canal, SSCC = superior semicircular canal.

3-D CT of TEMPORAL BONE
• Helps in better understanding of the spatial orientation of various parts
of temporal bone
• Simplification of complex anatomy
• “Volume rendered” images can be sectioned in any plane and rotated
in space

To obtain good 3D reconstructions, it is absolutely essential to obtain the
thinnest possible overlapping slices.
0.75 mm collimation with a 0.75 mm slice thickness at 120 kVp, 200
mAs, a pitch of 0.8, and a 15 cm field of view with a matrix size of 512 x
512.
The initial data sets reconstructed at 0.1 mm intervals.
While obtaining 3D reconstructions, it is important to remember that any
amount of gantry tilt results in distortion of the reconstructed 3D image.
A zero degree gantry tilt when obtaining such images ensures no
distortion of the post-processed 3D images. Volume-rendered 3D images
can be generated from the original 2D data with different soft tissue and
bone algorithms e.g TeraRecon Aquarius Workstation v3.3

AXIAL PLANE (INFERIOR TO SUPERIOR)

sp: styloid process, smf: stylomastoid foramen, ns: nerve to stapedius, ms:
mastoid segment of the facial nerve, ct: chorda tympani, c aqueduct:
cochlear aqueduct, V aqueduct: vestibular aqueduct, PSCC: posterior
semicircular canal, pg: posterior genu, LSCC: lateral semicircular canal,
CN: cochlear nerve, IV: Inferior vestibular nerve, IAC: internal auditory
canal, ts: tympanic segment of the facial nerve, SV: superior vestibular
nerve, fc: fallopian canal of the facial nerve, ag: anterior genu, SSCC:
superior semicircular canal.

CORONAL PLANE ( ANTERIOR TO POSTERIOR)

ag: anterior genu, ts: tympanic segment of the facial nerve, fc: fallopian
canal of the facial nerve, CN: cochlear nerve, SV: superior vestibular nerve,
SSCC: superior semicircular canal, IAC: internal auditory canal, LSCC:
lateral semicircular canal, ms: mastoid segment of the facial nerve, c
aqueduct: cochlear aqueduct, smf: stylomastoid foramen, PSCC: posterior
semicircular canal, V aqueduct: vestibular aqueduct.

Volume-rendered 3D CT image of the
auditory system.

(Left image) Volume-rendered 3D CT image shows the relative positions of the
malleus, incus, oval window and the inner ear. B) (Right image) Widening the window
level reveals the stapes sitting on the oval window, thereby allowing transmission of
sound waves to the inner ear.

inner ear.
cochlea, having dissected open the overlying
bony wall of the cochlea to expose the
osseous spiral lamina.

temporal bone revealing the dissected
(cut) first portion of the facial nerve
canal and the canal for the superior
vestibular nerve.
temporal bone showing the canal for the
cochlear nerve.

Volume-rendered 3D CT image of the canal for the facial nerve as it traverses the
temporal bone. The facial nerve exits the anterosuperior aspect of the internal
auditory canal as the labyrinthine segment housed within its own bony channel,
the fallopian canal. It then makes a hairpin turn (the anterior genu) and courses as
the tympanic segment along the medial wall of the tympanic cavity below the
lateral semicircular canal. At the posterior genu, it makes another turn and heads
vertically down as the mastoid segment to exit the temporal bone at the
stylomastoid foramen. The canal for the chorda tympani, a branch of the mastoid
segment of the facial nerve, is also present.

MR IMAGING OF INNER EAR
POSITIONING
• Head first Supine
• Position the head in the head coil and immobilise with
coushions
• Give Coushins under the legs for extra comfort
• Centre the Laser beam Localizer over the glabella

SUGGESTED PROTOCOLS, PARAMETERS AND PLANNING
LOCALISER
A three plane localizer must be taken in the beginning to localise and plan the
sequences. These are low resolution T1 weighted scans
AXIAL SAGITTAL CORONAL

T2 tse AXIAL
• Plan the axial slices on the sagittal plane; angle the position block parallel to
the anterior and posterior margin of the corpus callosum.
• Slices must be sufficient to cover the whole brain from the vertex up to the
line of Foramen Magnum.
• Check the positioning block in the other two planes
• An appropriate angle must be given on coronal plane on tilted head
(perpendicular to the line of 3rd ventricle and brain stem).

PARAMETERS
• TR = 3000 – 4000 msec
• TE = 100-200 msec
• SLICE = 5mm
• FLIP = 130-150
• MATRIX = 320X320
• FOV 210-230

T2 TSE CORONAL
• Plan the coronal slices on the axial plane
• Angle the position block parallel to the line along right and left IAMS
• Check the position block in the other two planes.
• An appropriate angle must be given in the sagittal plane ( parallel to the
brain stem)
• Slices must be sufficient to cover IAMS from the posterior border of
sphenoid sinus upto the line of the fourth ventricle.

PARAMETERS
• TR = 3000-4000 msec
• TE = 110 msec
• FLIP = 130
• SLICE = 3 mm
• MATRIX = 256X256
• FOV = 150-180

3D CISS ( 3D SPACE OR 3D FIESTA) AXIAL
• Plan the axial slices on the coronal plane
• Angle the position block parallel to the line along the right and left
IAMS
• Check the positioning blocks in the other two planes.
• An appropriate angle must be given in the sagittal plane ( perpendicular
to the brain stem).
• Slices should be sufficient to cover IAMS from hippocampus to the line
of C1 vertebral body.

PARAMETERS
• TR= 12-15 msec
• TE = 6-7 msec
• SLICE = 0.8 mm
• FLIP = 80
• MATRIX = 384X320
• FOV = 210-230

T1 PRE AND POST CONTRAST SCANS FOR TUMOR EVALUATION
T1 TSE CORONAL
• Plan the coronal slices on the axial plane
• Positioning box angled parallel to the line joining the Right and left
IAMS
• Check the positioning blocks in the other 2 planes
• An appropriate angle should be given along the sagittal plane ( parallel
to the brain stem)
• The slices should be sufficient to cover the IAMS from the posterior
border of Sphenoid sinus upto the line of the fourth ventricle.

PARAMETERS
• TR = 400-500 msec
• TE = 15 msec
• FLIP = 150
• SLICE= 3mm
• MATRIX = 256X256
• FOV = 150-180

T1 TSE AXIAL
• Plan the axial slices on the coronal plane
• Angle the position block parallel to the line along the right and left
IAMS
• Check the positioning blocks in the other two planes.
• An appropriate angle must be given in the sagittal plane (
perpendicular to the brain stem).
• Slices should be sufficient to cover IAMS from hippocampus to the
line of C1 vertebral body.

PARAMETERS
TR = 400-600 msec
TE = 150 msec
SLICE = 3mm
FLIP = 90
MATRIX = 256X256
FOV= 170-180

MR CONTRAST
• GADOLINIUM-DTPA
• RECOMMENDED DOSAGE = 0.1 mmol/kg i.e. 0.2 ml/kg

MR IMAGING
Coronal T2 weighted MRI through the cochleae.

Coronal T2 weighted MRI through the vestibules.

Axial T2 weighted MRI to show the facial (VIIth cranial) and
vestibulocochlear (VIIIth cranial) nerves within the internal auditory
meatus

EMBRYOLOGY
The temporal bone is ossified from eight centers, exclusive of those for the
internal ear and the tympanic ossicles, viz., one for the squama including
the zygomatic process, one for the tympanic part, four for the petrous and
mastoid parts, and two for the styloid process.
Just before the close of fetal life the temporal bone consists of three
principal parts:
1. The squama is ossified in membrane from a single nucleus, which
appears near the root of the zygomatic process about the second month.
2. The petromastoid part is developed from four centers, which make their
appearance in the cartilaginous ear capsule about the fifth or sixth month
3. The tympanic ring is an incomplete circle, in the concavity of which is a
groove, the tympanic sulcus, for the attachment of the circumference of the
tympanic membrane. .

The three principal parts of the tempora bone at birth. 1. Outer surface of petromastoid
part. 2. Outer surface of tympanic ring. 3. Inner surface of squama.

Temporal bone at birth. Outer aspect

Temporal bone at birth. Inner aspect.

The embryologic development of the ear is a multistage and anatomically
complex process.
The outer ear structures develop from the first branchial cleft and the
first and second branchial arches during the 6th through 12th weeks of
intrauterine life.
The external auditory canal (EAC) initially develops as a solid core of
epithelium, termed the meatal plate, which migrates toward the first
pharyngeal pouch and subsequently hollows out during the 2nd through
7th months of intrauterine life.
The eustachian tube and tympanic cavity arise from the first
pharyngeal pouch between 10 and 30 weeks gestation.
The tympanic membrane is derived from three germ cell layers,
including ectoderm from the first branchial groove and mesoderm
and endoderm from the first branchial pouch.
The ossicular chain and supporting ligaments arise from the first and
second branchial arches.

The membranous portion of the inner ear arises from neuroectoderm (otic
placode) in the 4th week of gestation.
The otic placode invaginates, forming the otic pit, and subsequently forms the
otic vesicle (otocyst). The otocyst divides into the dorsal and ventral pouches
(pars superior and inferior, respectively), which are the precursors to the
utricle, semicircular canals, cochlear duct, and saccule.
The bony labyrinth (otic capsule) develops from mesenchyme around the
membranous labyrinth between 4 and 8 weeks gestation, continues to grow
between 8 and 16 weeks gestation, and ossifies by the 24th week of gestation.

Imaging findings of developing Temporal bone by Nemzek et al. AJNR september
1996
Comparison of adult and early fetal otic capsule structures on T2-weighted fast spin-echo MR images.
A, In the adult, there is high signal intensity of endolymph and perilymph in membranous cochlea, and vestibule
and semicircular canals are surrounded by signal void of dense bony otic capsule.
B, Sagittal image of fetus, gestational age 14 weeks 4 days. Basal turn of cochlea is the first structure that can be
readily identified.
C, Fetus, gestational age 15 weeks 5 days. Fluid is seen in cochlea and vestibule. Basal turn of cochlea is two thirds
of adult size. The upper turns of the membranous cochlea are now visible (arrow) as a single space. Note

Fetus, gestational age 17 weeks 4 days.
A, CT scan shows ossification in squamous portion (black arrow) and zygomatic process of the temporal bone
(white arrow). Note very early ossification of the malleus and incus.
B, T2-weighted fast spin-echo MR image shows vestibule and lateral semicircular canal before ossification.
CT scan of fetus, gestational age 18 weeks 4 days, shows earliest ossification of otic capsule. Note discontinuous
calcification around the apical turn of the cochlea (small arrows). Note interscalar septum and progressive
ossification of ossicles.

A, CT scan shows that cochlea and vestibule are reaching full adult size. There is now a
continuous shell of bone surrounding the cochlea.
B, CT scan shows short internal auditory canal. The canal for the cochlear nerve
(arrowhead) passes directly anteriorly. The labyrinthine segment of the facial nerve canal
is present. The common crus is partially encircled by bone.
T2-weighted fast spin-echo
axial (C) and sagittal (D) MR images show ossification in cochlea and vestibule as
decreased signal intensity. Endolymphatic duct is parallel to common crus.

Fetus, gestational age 18 weeks
5 days. CT scan shows progressive
ossification with thicker layer of
bone surrounding cochlea and
vestibule. Note canal for the
cochlear nerve (arrowhead) is
directed anteriorly.
CT scan (A) and T2-weighted fast spin-echo MR image (B) show tympanic
ring as horizontal structure with adjacent ossicles.

CT scans (A and B) and T2-weighted fast spin-echo MR image (C) show otic capsule structures are of adult
dimensions. Bone surrounds the lateral semicircular canal and the common crus. Ossicles are visible by
both CT and MR imaging. There is a large subarcuate space. Note all turns of the cochlea are visible on the
MR image (C).

Lateral plain radiograph of the skull shows a large subarcuate space beneath the superior semicircular canal.
The tympanic ring is an ossified horizontal structure that is separated from the squamous temporal bone.

A, Anteroposterior plain radiograph of the skull shows the horizontal tympanic
ring is isolated from the rest of the temporal bone.
B–D, On CT scans, note the tympanic ring and vestibular and cochlear
aqueducts. The stapes is now identified in the oval window. There is a large
subarcuate space.

A and B, CT scans show a thickening of bone surrounding the otic capsule and
greater definition of the modiolus. The labyrinthine segment of the facial canal
is better defined. The internal auditory canal remains short. Note the
pyramidal process, the facial nerve recess (straight arrow), and the sinus
tympani (curved arrow) on posterior wall of tympanic cavity.
On T2-weighted fast spin-echo axial (C) and sagittal (D) MR images, the
endolymphatic duct and vestibular aqueduct and all the turns of the cochlea
are identified

IMAGING OF TEMPORAL BONE PATHOLOGY

CONGENITAL MALFORMATIONS
Developmental malformations that affect the EAC and middle ear may cause
conductive hearing loss, whereas those that affect the membranous and bony
labyrinth may result in sensorineural hearing loss (SNHL).
Congenital hearing deficits can be nongenetic or genetic in origin.
Congenital hearing deficits from genetic causes may occur in isolation or in
association with various syndromes, such as the
• CHARGE (coloboma of the eye, heart anomaly, choanal atresia, retardation, genital
and ear anomalies)
• Klippel-Feil
• trisomy 21
• Goldenhar syndrome
• Crouzon syndrome.

Congenital atresia of the EAC
• Involves a spectrum of abnormalities in which the EAC fails to develop
fully.
• The resultant abnormality may be classified as osseous, membranous,
or mixed depending on the degree of development of the EAC.
• Furthermore, the atresia may be bilateral or, more commonly,
unilateral and is often associated with abnormalities of the pinna.
• The prevalence of atresia of the EAC is approximately one in 10,000

Atresia of the EAC in a 12-year-old boy with left conductive hearing loss and left
microtia. Axial CT image shows absence of the left EAC. The left middle ear cavity is
small. The right EAC is normal.

• Imaging abnormalities involving the bony labyrinth are present in
20%–40% of patients with SNHL.
• CT is currently insensitive to abnormalities of the membranous
labyrinth, which are responsible for most cases of SNHL.
• The specific timing of the insult during inner ear development
determines the resultant malformation type along a spectrum of
congenital inner ear malformations

congenital inner ear malformations
• labyrinthine (Michel) aplasia
• cochlear aplasia
• common cavity malformation
• incomplete partition type I (cystic cochleovestibular malformation)
• incomplete partition type II (classic Mondini malformation)
• cochleovestibular hypoplasia.
Historically, all abnormalities of partitioning of the cochlea were referred to as Mondini
malformation.
More recently, Sennaroglu and Saatci categorized incomplete partition of the cochlea
into two types.
In incomplete partition type I, the cochlea completely lacks partitioning and appears
as a cystic structure at CT.
In incomplete partition type II, the cochlea contains one and one-half turns, with a
normal basal turn and a cystic-appearing dilated apical portion.

Cochlear aplasia in a 4-year-old girl with profound left SNHL. Axial CT image shows
absence of the left cochlea and vestibular aqueduct. The left vestibule and lateral
semicircular canal are dysplastic.

Common cavity malformation
in a 2-year-old girl with profound
bilateral SNHL and cleft
palate.
Axial (a) and coronal (b) CT
images show confluence of a
globular left cochlea with a
globular enlarged left
vestibule and dysmorphic left
lateral and superior
semicircular canals (SCCs).
The right cochlea is absent,
and there is an enlarged
globular right vestibule with
absence of the right lateral
and posterior semicircular
canals.

Incomplete partition type I in a 5-year-old girl with profound right SNHL and mild
to moderate left SNHL with a conductive component on the left. Coronal CT image
shows a cystic-appearing cochlea bilaterally with absence of partitioning.

Incomplete partition type II in a
13-month-old boy with bilateral
mixed hearing loss.
images show
• one and one-half turns of the
cochlea AND
• cystic dilatation of the apical
turn bilaterally.
• The vestibular aqueducts are
enlarged bilaterally.

CHARGE syndrome in a 17-year-
old boy with bilateral mixed
hearing loss.
images show
• bilateral hypoplastic vestibules
and absence of the semicircular
canals.
• The bilateral cochlear nerve
fossette and IAC are also
hypoplastic. n. = nerve.

Enlarged vestibular aqueduct syndrome
• Is a relatively common cause of SNHL.
• Enlargement of the vestibular aqueduct is the most frequently seen osseous
abnormality in patients with SNHL.
• An enlarged vestibular aqueduct may be seen in isolation or in association with
other abnormalities of the inner ear.
• A commonly accepted imaging criterion for an enlarged vestibular aqueduct is a
caliber of 1.5 mm or greater in the midportion of the aqueduct.
• Enlargement of the vestibular aqueduct may also be suspected if the aqueduct is
larger in caliber than the normal lateral semicircular canal.

Enlargement of the vestibular aqueduct in a 23-year-old woman.
Axial CT image shows an enlarged right vestibular aqueduct. The left vestibular
aqueduct is of normal caliber.

Vascular abnormalities of the temporal bone may involve the ICA and its branches
or the internal jugular vein.
Both an aberrant course of the ICA and a high-riding jugular bulb may manifest
as tinnitus.
Differentiation of these entities from neoplastic or inflammatory processes with
imaging is critical in guiding appropriate clinical management .
Persistence of the stapedial artery is rare, with a prevalence of 0.48% , but its
identification is crucial if middle ear surgery is planned.
A persistent stapedial artery may be seen in association with an aberrant ICA.
At imaging, the persistent stapedial artery can be seen arising from the petrous
segment of the ICA or aberrant ICA and extending superiorly to supply the
middle meningeal artery.
Typical findings include apparent expansion of the tympanic segment of the
facial nerve and abnormal soft-tissue attenuation adjacent to the cochlear
promontory . In addition, the ipsilateral foramen spinosum is absent

Aberrant ICA. Axial CT image shows an aberrant ICA passing anterior to the cochlear
promontory through a dehiscent carotid plate.

Persistent stapedial artery in an 8-
year-old boy with microtia, moderate
right conductive hearing loss, and a
history of canaloplasty for atresia of
the EAC.
Axial (a) and coronal (b) CT images
show
a persistent stapedial artery arising from
the horizontal portion of the carotid
artery.
Abnormal soft-tissue attenuation lateral
to the cochlear promontory and
apparent expansion of the tympanic
segment of the facial nerve are seen,
findings indicative of the aberrant
vessel.
The foramen spinosum is absent on the
right.

Inflammatory Conditions
Several inflammatory conditions may affect the temporal bone.
At imaging, infectious or inflammatory processes can be described according to
the degree of involvement of the four anatomic regions:
• external ear,
• middle ear and mastoid,
• inner ear, and
• petrous apex.

External Auditory Canal
EAC cholesteatoma.—
• EAC cholesteatoma is a rare lesion with an incidenceof approximately 0.1%–
0.5%.
• Most cases are spontaneous or idiopathic, although these lesions can also
occur secondary to prior trauma, surgery, or radiation .
• Most patients are in an older age group and present with chronic dull pain
and otorrhea, most commonly unilaterally .
• Pathologically, it is characterized by local invasion of the lining squamous
epithelium of the EAC into the underlying bone, resulting in canal wall
erosions and periostitis.
• On CT images, the lesion is characterized by focal soft tissue within the EAC
(typically the inferior wall), with erosion extending into the underlying bone .
These imaging findings are nonspecific, however, and may be mimicked by
entities such as carcinoma and otitis externa

Coronal CT image of EAC cholesteatoma in a 73-year-old patient with a history of
chronic bone erosion of the EAC.
Image shows soft tissue along the inferior wall of the EAC (∗), causing bone erosion
(arrow).

Keratosis obturans.—
Keratosis obturans represents an expansile accumulation of keratin debris within the
EAC.
In contrast to EAC cholesteatomas, it occurs in younger patients and tends to be
bilateral.
Clinically, these patients have severe pain and conductive hearing loss, with otorrhea
being relatively rare.
There is an association of this entity with sinusitis and bronchiectasis
On CT images, there is diffuse widening of the EAC by an epidermal plug, which
may cause smooth scalloping of the surrounding bone, but there is no erosion or
periostitis

Coronal CT image of keratosis obturans demonstrates a soft-tissue plug in the
external canal (∗), with mild expansion of the canal but no bone erosion.

Malignant otitis externa.—
• Necrotizing or malignant otitis externa occurs most commonly in elderly
diabetic patients and other patients in immunocompromised states.
• The patients present with severe otalgia and otorrhea, and there is a high
mortality rate .
• The infection is usually caused by Pseudomonas aeruginosa.
• Clinically one sees granulation tissue in the inferior EAC at the bone-
cartilaginous junction.
• Infection can then spread via fissures of Santorini into the soft tissues beneath
the skull base, leading to skull base osteomyelitis, which can be heralded by
cranial neuropathies.

On images, soft-tissue thickening in the external canal is noted, often with
bone destruction and inflammatory changes in the mastoid.
Skull base osteomyelitis results from extension of the destructive process into
the clivus, jugular foramen, and prevertebral soft tissues .
Abscesses can develop in the epidural space, brain parenchyma, and the
prevertebral space as a complication.
MR and CT are complementary modalities for evaluation of this entity, with the
bone windows at CT showing the destructive process to greater advantage, and
MR imaging better demonstrating associated soft tissue complications.
The imaging differential diagnosis includes nasopharyngeal carcinoma with
secondary obstruction of the eustachian tube orifice causing a secondary
otomastoiditis

Images of malignant otitis externa in a 93-year-old diabetic woman.
(a) Axial CT image shows opacification of the right mastoid air cells. There are erosive changes in the petroclival
region on the right (arrows).
(b) Axial T1-weighted gadolinium-enhanced MR image in the same patient better demonstrates the prevertebral
abscess (large ∗). There is thrombosis of the inferior petrosal sinus with a filling defect within (arrow). Notice the
abnormal hypointensity in the right mastoid air cells, representing inflammatory changes (small ∗).

Middle Ear
The most common inflammatory condition affecting the temporal bone is
acute otitis media (AOM).
It usually occurs as the sequela of a viral upper respiratory infection with disruption
of the mucosal barrier that prevents bacteria in the nose and nasopharynx from
spreading to the middle ear.
The imaging findings of uncomplicated AOM are nonspecific, with partial
or total fluid-attenuation opacification of the middle ear seen at CT.
Chronic otomastoiditis typically occurs as a result of long-standing eustachian tube
dysfunction.

Imaging is typically performed in AOM when a complication is suspected.
Important complications to consider when evaluating acute otomastoiditis
include
• coalescent mastoiditis ,
• Bezold abscess,
• dural sinus thrombosis ,
• subperiosteal abscess,
• intracranial abscess and empyema ,
• meningitis,
• facial nerve involvement,
• labyrinthitis, and
• petrous apicitis.
These same complications can occasionally occur superimposed on chronic
otomastoiditis.

Coalescent mastoiditis in a 49-year-old woman. Axial (a) and coronal (b) CT
images show complete opacification of the mastoid air cells with fluid-attenuation
material and loss of internal bone septa. A large defect in the sigmoid sinus plate is
present, and there are bone defects in the tegmen mastoideum (white arrowheads
in b) and the external cortex of the mastoid bone (black arrowheads in b).

Dural sinus thrombosis. (a) Axial contrast-enhanced CT image shows a filling
defect in the left sigmoid sinus. (b) Axial nonenhanced two-dimensional time-
of-flight MR venographic image shows absent flow in the left jugular bulb and
sigmoid sinus.

Coronal contrast-enhanced CT image of Bezold abscess in a 7-year-old child
with acute ear infection.
Image shows a rim-enhancing collection below the mastoid tip compatible
with a Bezold abscess (∗∗).
Also note thrombus in the right sigmoid sinus (arrow).

CT images of petrous apicitis in a 78-year-old man with right ear infection.
(a) Axial image demonstrates opacification of the right petrous apex air cells with
soft-tissue attenuation (arrow). There is also scattered mastoid opacification. Note
normally aerated petrous apex air cells on the left. (b) Coronal image better
demonstrates destruction of the petrous bone (arrows).

Epidural abscess in a 23-year-old woman.
Axial contrast-enhanced CT (a) and coronal contrast-enhanced T1-weighted MR (b)
images show a rim-enhancing fluid collection in the left temporal epidural
space. There is adjacent enhancement of parenchyma and dura.

CHOLESTEATOMA
Both AOM and chronic otitis media can result in the development of aquired
cholesteatomas in the middle ear.
A cholesteatoma is a sac lined with ectopic stratified squamous epithelium and
filled with exfoliated keratin debris. Most cholesteatomas of the middle ear are
acquired (98%); only a minority are congenital.
Acquired cholesteatomas typically arise in the pars flaccida of the tympanic
membrane and less commonly in the pars tensa region.
Pars flaccida cholesteatomas are typically centered in the Prussak space, whereas
pars tensa cholesteatomas are typically centered in the sinus tympani or facial
recess.
All types of cholesteatomas may erode the ossicular chain, scutum, mastoid bone,
or Körner septum

Coronal CT image of a pars flaccida cholesteatoma in a 56-year-old woman with a deep
retraction pocket at clinical examination. Image demonstrates lobulated soft tissue in
Prussak space (arrowhead) and the attic (∗), displacing the ossicles medially and
eroding the scutum (arrow).

Coronal CT image of a pars tensa cholesteatoma in a 31-year-old man with left-
sided hearing loss and retraction pocket at clinical examination. Image
demonstrates a lobulated soft-tissue mass medial to the ossicles (∗), displacing the
ossicles laterally. The scutum remains sharp (arrow), in contrast to that in the
case of the pars flaccida cholesteatoma.

Axial CT image of automastoidectomy in a 51-year-old man with a history of
longstanding chronic otitis media on the left.
Image demonstrates a large cavity (∗) in the middle ear and mastoid antrum, with
nonvisualization of the ossicles. There is a small amount of residual inflammatory soft
tissue. There is no history of surgery.

MR images of cholesteatoma in a 15-year-old male
patient with a history of draining ear.
(a) Axial T2 weighted image demonstrates a
heterogeneously hyperintense lesion in the left middle
ear/mastoid (∗). (b) Axial gadoliniumenhanced T1-
weighted image demonstrates the lesion to be
nonenhancing (∗). (c) Coronal DW image demonstrates
reduced diffusivity within the lesion (arrow).

CHOLESTEROL GRANULOMA
Pneumatization of the petrous apex occurs in 9%–30% of persons . When
pneumatized, the petrous apex can become involved by middle ear infections.
A cholesterol granuloma results from a foreign-body giant cell reaction to the
deposition of cholesterol crystals in the air cells with fibrosis and vascular
proliferation.
The characteristic CT appearance of a cholesterol granuloma is an expansile
lesion with smooth margins.
MR imaging shows high signal intensity on T1-weighted images and often
high signal intensity on T2-weighted images owing to the cholesterol
crystals and methemoglobin from repeated hemorrhage

Cholesterol granuloma of the petrous apex in a 52-year-old man. Axial nonenhanced
(bone window) (a) and contrast-enhanced (brain window) (b) CT images show bony
expansion of the petrous apex by a nonenhancing mass.

Cholesterol granuloma of the petrous
apex in a 52-year-old man.
(a) Axial T1- weighted MR image shows a
hyperintense mass in the petrous
apex. (b) On an axial T2-weighted MR
image, the mass has heterogeneous
signal intensity. (c) Axial diffusion-
weighted MR image shows no diffusion
restriction in the mass.

Axial CT image of petrous apex effusion in a 36-year-old man with right-sided
sensorineural hearing loss demonstrates opacification of the pneumatized right
petrous apex (∗). It does not have expansile margins, distinguishing it from a
petrous apex mucocele or a cholesterol granuloma. The internal septations and
cortex are intact, distinguishing it from petrous apicitis.

INNER EAR
Labyrinthitis has three radiologic stages:
acute,
fibrous, and
labyrinthitis ossificans.
In the acute stage, contrast-enhanced T1-weighted MR imaging may show abnormal
enhancement of the labyrinth.
MR imaging also allows detection of cochlear obstruction in the fibrous stage, before
abnormalities are detectable with CT .
Labyrinthitis ossificans involves pathologic ossification of the bony labyrinth and
cochlea and is well-depicted with CT

Labyrinthitis ossificans in a 45-year-old
woman. (a, b) Axial (a) and coronal (b) CT
images show abnormal sclerosis of the
bony labyrinth and cochlea (*). n. in b =
nerve. (c) Axial T2-weighted MR image
shows absence of fluid signal intensity in
the left cochlea and semicircular canals.

TRAUMA
Historically, temporal bone fractures were classified into two main
categories, longitudinal and transverse, on the basis of the fracture
plane relative to the long axis of the petrous bone.
It is now generally recognized that temporal bone fractures may be
complex with mixed features of both longitudinal and transverse
fractures.
A common complication associated with temporal bone fractures is
hearing loss, which may be sensorineural, conductive, or mixed.
Other complications related to temporal bone fractures include
• facial nerve injury
• perilymphatic fistula
• vertigo
• cerebrospinal fluid leak
• meningitis, and
• acquired cholesteatoma.

Bilateral longitudinal fractures of the temporal bone in a 47-year-old man. Axial CT
images show fracture lines (fx in a) parallel to the long axis of the petrous bone.
Bilateral malleoincudal abnormalities (disruption on the left, subluxation on the
right) and hemotympanum are noted with fluid attenuation surrounding the ossicles.
Air attenuation is faintly seen within the left petrous ICA canal. Arrowheads in a = tiny
amount of intracranial air.

Transverse fracture of the left temporal bone with ossicular injury in a 39-year-old
man.
Axial (a) and coronal (b) CT images show a fracture line (fx) (arrowheads in a, arrows in
b) perpendicular to the long axis of the left petrous bone, traversing the IAC and
bony labyrinth. Malleoincudal disruption and hemotympanum are noted. Air
attenuation is seen within the cochlea.

Complex (mixed) fracture of the right temporal bone in a 16-year-old boy. Axial CT
image shows oblique, longitudinal, and transverse fracture lines (fx). The oblique
fracture traverses the middle ear cavity; there is associated malleoincudal subluxation
and hemotympanum. The transverse fracture involves the vestibule and vestibular
aqueduct. The longitudinal fracture extends through the base of the cochlea. There is
pneumovestibule and gas in the IAC.

Tumors and Tumorlike Conditions
Many types of tumors may affect the temporal bone. A temporal bone tumor may
be clinically suspected in several clinical scenarios.
Four common clinical presentations suspicious for a tumor are
(a) SNHL, tinnitus, or vertigo, which may indicate a vestibular schwannoma or
other cerebellopontine angle mass;
(b) pulsatile tinnitus or cranial neuropathy involving the jugular foramen;
(c) peripheral facial nerve dysfunction ; and
(d) a previously clinically identified tumor of the temporal bone.
There are also nonneoplastic conditions, including various otodystrophies, that
can mimic a neoplasm at imaging.

To assess a tumor in the temporal bone region, it is helpful to localize the
lesion to one of the following areas, each of which houses a unique set of
pathologic conditions:
(a) IAC/CPA,
(b) middle ear,
(c) EAC and mastoid, and
(d) petrous apex

IAC/CPA
The most common masses in this area are
• vestibular schwannomas,
• meningiomas,
• epidermoids, and
• nonvestibular posterior fossa schwannomas (such as trigeminal, facial, and
glossopharyngeal).
Less frequently seen are
• arachnoid cysts,
• lipomas,
• dermoids, and
• malignancies such as lymphoma, melanoma, and metastases.
In addition, tumors related to the petrous bone (eg, chondrosarcoma) and brain
(eg, glioma) may extend into the IAC/CPA.

Axial contrast-enhanced T1-weighted MR image of vestibular schwannoma. This 51
yearold man presented with sudden asymmetric sensorineural hearing loss on the
right. Image demonstrates an avidly enhancing tumor in the IAC extending through an
expanded porus acousticus (between arrows) into the CPA, where it forms an acute angle
with the posterior petrous ridge.

IAC schwannoma and meningioma in a 24-year-old man with neurofibromatosis type
2. (a) Axial CT image shows a partially calcified meningioma in the middle cranial fossa
with adjacent hyperostosis of the petrous apex. The ipsilateral IAC is widened from the
patient’s known vestibular schwannoma. (b) Axial gadolinium-enhanced T1-weighted
MR image shows varying degrees of relatively homogeneous enhancement of the
meningioma and bilateral vestibular schwannomas.

Facial nerve schwannoma. (a) Axial CT image shows a mass centered in the
geniculate ganglion with widening of the geniculate fossa and anterior portion of
the tympanic segment of the facial nerve (n.) canal. (b) Coronal gadolinium-
enhanced T1-weighted MR image shows homogeneous enhancement of the mass, which
extends into the middle cranial fossa. The labyrinthine segment of the facial nerve (n.)
canal also appears widened.

Axial T2-weighted MR image of epidermoid in a 40-year-old woman who presented with
left sensorineural hearing loss, pressure sensation in the head worse with exertion,
and tendency to drift to the left. Image shows an epidermoid in the CPA insinuating
around the basilar artery (white arrow) and causing mass effect on the brainstem and
cerebellum (black arrows). It does not enhance and is hyperintense on DW images

Middle Ear
When a soft-tissue mass is seen in the middle ear, a vascular structure must
be excluded. This includes
• a persistent stapedial artery,
• a laterally placed or aberrant carotid artery,
• a carotid artery aneurysm, and
• an exposed dehiscent jugular bulb.
True neoplasms include
• paraganglioma (most common);
• facial nerve lesions extending into the middle ear, such as schwannomas and
geniculate region hemangiomas,
• choristomas,
• meningiomas;
• adenomatous tumor of the mixed pattern type; and
• malignancies such as carcinomas and metastases (rare).

Coronal CT image of glomus tympanicum demonstrates a small, rounded nodule in
the middle ear abutting the cochlear promontory (arrow).
This 50-year-old woman had a history of chronic otitis media. At otoscopic examination,
a 2-mm erythematous mass was appreciated and clinically suspected to represent a
glomus tympanicum.

Glomus tympanicum tumor in a 54-
year-old man.
(a) Coronal CT image shows a soft-
tissue mass along the cochlear
promontory and
hypotympanum with
preservation of the ossicular
chain.
(b) Coronal gadolinium-enhanced
T1-weighted MR image shows that
the mass has homogeneous
enhancement.

Glomus jugulare tumor in a 36-year-
old man.
(a) Axial CT image shows bone
destruction from a mass in the
posterior petrous apex and
mastoid region near the jugular
foramen. There is soft-tissue
extension into the middle ear.
(b) Axial gadolinium-enhanced T1-
weighted MR image shows avid
enhancement of the mass.

Images of glomus jugulotympanicum. (a) Axial CT image demonstrates the moth-eaten,
permeative bone destruction around the tumor. On this image through the right temporal bone, one
can appreciate destruction of the margins of the jugular foramen (∗), the caroticojugular spine
(arrowhead), and the carotid canal (small arrow). Note the tumor extending into the middle ear
(large arrow). (b) Axial contrast-enhanced T1-weighted MR image shows the large enhancing tumor
with internal flow voids (arrows), creating the so called salt-and-pepper appearance. This patient
initially presented at age 56 years with right ear fullness, hearing loss, and audible whooshing sound
that correlated with heart beat.

EAC and Mastoid
Tumors in the EAC and mastoid region are often malignant, with squamous cell
carcinoma being by far the most common.
Patients with EAC squamous cell carcinoma frequently have a long history of
chronic ear infections.
There is aggressive bone destruction, and there may be invasion of surrounding
soft tissues including intracranial, inframastoid, middle ear, parotid, carotid,
and temporomandibular joint involvement.
Other malignancies such as basal cell carcinoma, melanoma, lymphoma, myeloma,
metastases, chondrosarcoma, and osteosarcoma occur much less frequently
Aggressive bone destruction may be seen with some benign processes and should
be considered in the differential diagnosis.
These include granulomatous diseases such as Langerhans cell histiocytosis,
tuberculosis, and Wegener granulomatosis.
Aggressive infections such as malignant otitis externa and radiation necrosis are
additional considerations.

Axial CT image of squamous cell carcinoma of the EAC with extension to the mastoid. Patient
was a 64-year-old woman with recurrent and persistent left ear infection not improved with
antibiotics; biopsy revealed the diagnosis. CT image demonstrates extensive bone destruction
involving the EAC margin and mastoid (black arrowheads), extending to the petrous apex
(large arrow). The dense otic capsule is relatively spared (white arrowhead). Abnormal soft
tissue fills the EAC, middle ear, and mastoid, extending into the posterior cranial fossa (small
arrows). The auricle is also thickened, with ulcerated margins.

Axial contrast-enhanced T1-weighted MR image of Langherhans cell histiocytosis shows solid
enhancing tissue involving the EAC and mastoid (black arrows). There is also involvement of the
middle ear (white arrow) and sigmoid sinus (arrowhead). Patient was a 2-year-old boy with otitis
media starting at 8 months of age, now with pus and bloody discharge and diffuse swelling in the
ear region. Biopsy revealed Langherhans cell histiocytosis.

Petrous Apex
True neoplasms in the petrous apex include
• chondrosarcoma,
• chordoma,
• osteosarcoma, and
• meningioma.
Myeloma, lymphoma, and metastases may also occur.
The petrous area may be secondarily involved by regional tumors such as
• trigeminal schwannoma,
• jugular paraganglioma, and
• nasopharyngeal carcinoma.
The latter is usually seen along the petrooccipital fissure, superior to the fossa of
Rosenmüller.

Axial contrast-enhanced T1-weighted MR image of petrous apex
chondrosarcoma.
Image shows the tumor mass in the petrous apex causing displacement of the
petrous carotid artery (arrow). It is hyperintense on T2-weighted images and
enhances avidly.

ELST in two patients. (a) Axial CT image shows bone destruction along the right posterior
petrous apex in the region of the vestibular aqueduct. (b) Axial T1-weighted MR image in another
patient, a 60-year-old woman, shows a mass in the posterior petrous apex. The mass is isointense
to adjacent brain tissue with peripheral high signal intensity from methemoglobin. (c) Axial
T2-weighted MR image in the same patient as in b shows that the mass has heterogeneous signal
intensity with multiple small flow voids (arrows).

Aneurysmal bone cyst. (a) Axial CT image shows an expansile bone lesion arising from
the inner table of the squamosal temporal bone with internal osseous septa. (b) On
an axial T2-weighted MR image, the lesion has mixed signal intensity with fluid-fluid
levels

Osteochondroma in a 53-year-old woman. Axial CT image shows a pedun-culated
osteochondroma (arrow) arising from the petrous apex with apparent narrowing of
the adjacent IAC.

Otospongiosis, also known as otosclerosis, is an unusual disease that affects the
otic capsule, resulting in progressive hearing loss. The disease typically affects
women more than men, with a female-to-male ratio of 2:1
In otospongiosis, the normal endochondral bone of the otic capsule is replaced
by spongy vascular irregular bone.
There are two categories of otospongiosis: fenestral and retrofenestral.
The more common fenestral type affects the lateral wall of the bony labryinth,
including the oval and round windows, promontory, and facial nerve canal.
The less common retrofenestral type primarily involves the otic capsule but
usually has fenestral involvement
OTOSPONGIOSIS

Early otospongiosis. Axial CT image shows subtle demineralization involving part of
the otic capsule and cochlea from early retrofenestral otospongiosis.

Fibrous dysplasia is an inherited disorder affecting the bones and can be
• monostotic or
• polyostotic.
The disease is characterized by inability to form mature lamellar bone owing to
disordered osteoblastic activity.
As a result, there is gradual replacement of normal bone by an abnormal proliferation of
isomorphic fibrous tissue elements intermixed with irregular trabeculae of woven bone.
This results in bone expansion, which can cause osseous narrowing of the vascular
channels and neuroforamina and structurally weakened bone.
There are three types of fibrous dysplasia, with variable appearances depending on the
proportions of fibrous tissue and osseous elements:
• pagetoid,
• sclerotic, and
• cystic
FIBROUS DYSPLASIA

Fibrous dysplasia in a 23-
year-old woman.
Axial CT image shows
expansion of the temporal
bone with a ground-glass
matrix, as seen in the pagetoid
subtype of fibrous dysplasia
(FD).
There is narrowing of the IAC
and the tympanic segment of
the facial nerve canal.
Involvement of the incus is
noted.

REFERENCES AND FURTHER READING
1.

“ANATOMY AND PHYSICS ARE THE TWO MOST
IMPORTANT PILLARS OF RADIOLOGY”

IMAGING OF TEMPORAL BONE

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