Aneurysms & dissection
- 1. Aneurysms & dissection Rana el saeed Lecturer of pathology Faculty of medicine, Benha University
- 2. • An aneurysm is a localized abnormal dilation of a blood vessel or the heart ; it can be congenital or acquired. • true aneurysm :involves an intact attenuated arterial wall or thinned ventricular wall of the heart (e. g Atherosclerotic, syphilitic aneurysms) • false aneurysm (also called pseudo-aneurysm) is a defect in the vascular wall leading to an extravascular hematoma that freely communicates with the intravascular space (“pulsating hematoma”). E.g a ventricular rupture after myocardial infarction that is contained by a pericardial adhesion
- 3. • arterial dissection arises when blood enters the arterial wall itself, as a hematoma dissecting between its layers. • Dissections are often but not always aneurysmal • Consequences: true, false aneurysms and dissections can rupture, often with catastrophic consequences.
- 4. Aneurysms are generally classified by shape and size • Saccular aneurysms : spherical outpouchings Involves only a portion of the vessle wall vary from 5 to 20 cm in diameter and often contain thrombus. • Fusiform aneurysms involve diffuse, circumferential dilation of a long vascular segment vary in diameter (up to 20 cm) and in length can involve extensive portions of the aortic arch, abdominal aorta, or even the iliac arteries. • These types are not specific for any disease or clinical manifestations.
- 6. pathogensis • Aneurysms can occur when the structure or function of the connective tissue within the vascular wall is compromised. • weakening of vessel walls is important in both inherited and sporadic forms of aneurysms as well.
- 7. examples of inherited defects in connective tissues: • The intrinsic quality of the vascular wall connective tissue is poor: In Marfan syndrome: defective synthesis of protein fibrillin result in progressive dilation Loeys-Dietz syndrome: “aggressive” course aneurysms. defective synthesis of elastin and collagens I and III. Ehlers-Danlos syndrome: defective type III collagen synthesis scurvy : altered collagen cross-linking associated with vitamin C deficiency . an example of a nutritional basis for aneurysm formation
- 8. • The balance of collagen degradation and synthesis is altered by inflammation and associated proteases. • In particular, increased matrix metalloprotease (MMP) expression, especially by macrophages in atherosclerotic plaque or in vasculitis. • these enzymes have the capacity to degrade virtually all components of the extracellular matrix in the arterial wall (collagens, elastin, proteoglycans, laminin, fibronectin). • Decreased expression of tissue inhibitors of metalloproteases (TIMPs) can also contribute to the extracellular matrix degradation
- 9. • The vascular wall is weakened through loss of smooth muscle cells or the synthesis of noncollagenous or nonelastic extracellular matrix. Ischemia of the inner media occurs when there is atherosclerotic thickening of the intima. Decrease nutreient diffusion Systemic hypertension can also cause significant narrowing of arterioles of the vasa vasorum medial ischemia. Medial ischemia “degenerative changes” of the aorta, whereby smooth muscle cell loss scarring, inadequate extracellular matrix synthesis, and production of increasing amounts of amorphous ground substance Histologically, these changes are collectively recognized as cystic medial degeneration , which can be seen in a variety of settings, including Marfan syndrome and scurvy.
- 10. A, Cross-section of aortic media from a patient with Marfan syndrome, showing elastin fragmentation and areas devoid of elastin that resemble cystic spaces but are actually filled with proteoglycans (asterisks). B, Normal media for comparison, showing the regular layered pattern of elastic tissue. In both A and B, elastin is stained black
- 11. To sum up • The main 2 causes of aneurysms: Atherosclerosis (in Abdominal Aortic Aneurysm (AAA)) Hypertention (in ascending aortic aneurysms) • Other causes include trauma, vasculitis, congenital defects (e.g., fibromuscular dysplasia and berry aneurysms), and infections (mycotic aneurysms).
- 12. • Mycotic aneurysms can originate (1) from embolization of a septic embolus, usually as a complication of infective endocarditis (2) as an extension of an adjacent suppurative process (3) by circulating organisms directly infecting the arterial wall.
- 13. Abdominal Aortic Aneurysm (AAA) • occur more frequently in men and in smokers • rarely develop before age 50 • Atherosclerosis is a major cause • other factors contribute.
- 14. Morphology. • Grossly: Usually below the renal arteries and above the bifurcation of the aorta can be saccular or fusiform, up to 15 cm in diameter, and up to 25 cm in length. Occasionally can affect the renal and superior or inferior mesenteric arteries, either by producing direct pressure or by narrowing or occluding vessel ostia with mural thrombi.
- 15. A, External view, gross photograph of a large aortic aneurysm that ruptured (rupture site is indicated by the arrow). B, Opened view, with the location of the rupture tract indicated by a probe. The wall of the aneurysm is exceedingly thin, and the lumen is filled by a large quantity of layered but largely unorganized thrombus.
- 16. • Histologically: the intimal surface of the aneurysm shows severe complicated atherosclerosis with destruction and thinning of the underlying aortic media frequently contains a bland, laminated, poorly organized mural thrombus that may fill some or all of the dilated segment.
- 17. Two AAA variants merit special mention: • Inflammatory AAAs : characterized by dense periaortic fibrosis with abundant lymphoplasmacytic inflammation with many macrophages and often giant cells. Their cause is uncertain. • Mycotic AAAs : lesions that have become infected by a circulating microorganisms in the wall. In such cases suppuration further destroys the media, potentiating rapid dilation and rupture.
- 18. clinical consequences of AAA • Rupture into the peritoneal cavity or retroperitoneal tissues with massive, potentially fatal hemorrhage • Obstruction of a branch vessel resulting in ischemic injury of downstream tissues, for example, iliac (leg) • Embolism from atheroma or mural thrombus • compression on an adjacent structure, e.g., compression of a ureter or erosion of vertebrae • Presentation as an abdominal mass (often palpably pulsating) that simulates a tumor
- 19. prognosis • The risk of rupture is directly related to the size of the aneurysm • aneurysms of 5 cm and larger are managed aggressively, usually by surgical bypass involving prosthetic grafts • Currently, aneurysm treatment is evolving toward endoluminal approaches using stent grafts in selected patients • Timely surgery is critical; operative mortality for unruptured aneurysms is approximately 5%, whereas emergency surgery after rupture carries a mortality rate of more than 50%. • because atherosclerosis is a systemic disease, a person with AAA is also very likely to have atherosclerosis in other vascular beds and is at a significantly increased risk of IHD and stroke.
- 20. THORACIC AORTIC ANEURYSMS • most commonly associated with hypertension • other causes: Marfan and Loeys-Dietz syndromes • signs and symptoms referable to (1) encroachment on mediastinal structures (2) respiratory difficulties due to encroachment on the lungs and airways (3) difficulty in swallowing due to compression of the esophagus (4) persistent cough due to irritation of or pressure on the recurrent laryngeal nerves (5) pain caused by erosion of bone (i.e., ribs and vertebral bodies (6) cardiac disease : aortic valve dilation with valvular insufficiency or narrowing of the coronary ostia causing myocardial ischemia (7) rupture. Most patients with syphilitic aneurysms die of heart failure induced by aortic valvular incompetence.
- 21. AORTIC DISSECTION • Def: occurs when blood splays apart the laminar planes of the media to form a blood-filled channel within the aortic wall • aortic dissection may or may not be associated with aortic dilation. • Main causes: (1) men aged 40 to 60, with hypertension (2) younger patients with systemic or localized abnormalities of connective tissue affecting the aorta (e.g., Marfan syndrome). • Other causes: iatrogenic (e.g., during diagnostic catheterization), during or after pregnancy (unknown reason),rare with syphilis due fibrosis of media
- 22. Pathogenesis. • Hypertension is the major risk factor in aortic dissection. • Aortas of hypertensive patients have medial hypertrophy of the vasa vasorum degenerative changes in the aortic media and variable loss of medial smooth muscle cells. • A smaller number of dissections are related to inherited or acquired connective tissue disorders causing abnormal vascular ECM (e.g., Marfan syndrome, Ehlers-Danlos syndrome, vitamin C deficiency, copper metabolic defects). • Regardless the etiology of medial weakness, the trigger for the intimal tear and initial intramural aortic hemorrhage is not known in most cases. • intimal tear blood flow under systemic pressure dissects through the media progression of the medial hematoma.
- 23. Morphology. • In most cases, no specific underlying causal pathology is identified in the aortic wall. • The most frequent preexisting histologically detectable lesion is cystic medial degeneration • initiates with an intimal tear which is found in the ascending aorta, usually within 10 cm of the aortic valve sometimes into the iliac and femoral arteries • Such tears are typically transverse or oblique and 1 to 5 cm in length, with sharp, jagged edges.
- 24. • The dissection can extend along the aorta retrograde toward the heart as well as distally. • The dissecting hematoma spreads along the laminar planes of the aorta, usually between the middle and outer thirds. • It often ruptures out through the adventitia causing massive hemorrhage or cardiac tamponade • In some (lucky) instances, the dissecting hematoma reenters the lumen of the aorta through a second distal intimal tear forming a “double-barreled aorta” with a false channel that may be endothelialized and become chronic dissections
- 25. AORTIC DISSECTION Histologic view of the dissection demonstrating an aortic intramural hematoma (asterisk). Aortic elastic layers are black and blood is red in this section, stained with the Movat stain
- 26. Clinical Features • depend strongly on the region(s) affected • the most serious complications occur with lesions from the aortic valve to the arch. • aortic dissections are classified into two types • More common (and dangerous) proximal lesions (called type A dissections), involving either both the ascending and descending aorta or just the ascending aorta (types I and II of the DeBakey classification) • Distal lesions not involving the ascending part and usually beginning distal to the subclavian artery (called type B dissections or DeBakey type III)
- 27. Type A (proximal) involves the ascending aorta, either as part of a more extensive dissection (DeBakey I) or in isolation (DeBakey II). Type B (distal or DeBakey III) dissections arise beyond the takeoff of the great vessels. The serious complications predominantly occur in type A dissections
- 28. • The main symptoms is sudden onset of excruciating pain, beginning in the anterior chest, radiating to the back between the scapulae, and moving downward as the dissection progresses; the pain can be confused with that of myocardial infarction • The most common cause of death is rupture of the dissection outward into the pericardial, pleural, or peritoneal cavities. • Retrograde dissection into the aortic root can cause disruption of the aortic valvular apparatus.
- 29. • common clinical manifestations include cardiac tamponade, aortic insufficiency, and myocardial infarction or extension of the dissection into the great arteries of the neck or into the coronary, renal, mesenteric, or iliac arteries, causing critical vascular obstruction and associated ischemic consequences; compression of spinal arteries may cause transverse myelitis.
- 30. prognosis • In the past aortic dissection was typically fatal • the prognosis has markedly improved • Rapid diagnosis and institution of intensive antihypertensive therapy, coupled with surgical procedures involving plication of the aortic wall, permit 65% to 75% of stricken individuals to be saved.