thoracic aortic aneurysm
Summary
A thoracic aortic aneurysm (TAA) is a permanent, localized dilation of the thoracic aorta (>50% increase in diameter compared to normal, typically >4.5 cm). Common causes include cystic medial degeneration, hypertension, atherosclerosis, and connective tissue disorders (Marfan, Ehlers-Danlos). Bicuspid aortic valve is a major risk factor for ascending aortic aneurysms; complications include dissection, rupture, and aortic regurgitation.
Detail
Pathophysiology: TAAs result from weakening of the aortic wall media, most commonly due to cystic medial degeneration/necrosis—loss of smooth muscle and elastic fibers with accumulation of mucoid material. Ascending aortic aneurysms are strongly associated with bicuspid aortic valve, Marfan syndrome (fibrillin-1 mutation), Loeys-Dietz syndrome, and Ehlers-Danlos syndrome (vascular type). Descending thoracic aneurysms are more often associated with atherosclerosis and hypertension. Tertiary syphilis (syphilitic aortitis) classically causes ascending aortic aneurysms due to obliterative endarteritis of the vasa vasorum, leading to medial ischemia and weakening—can produce a characteristic 'tree bark' appearance and may involve the aortic root, causing aortic regurgitation and coronary ostial stenosis.
Clinical features: Often asymptomatic and found incidentally on imaging (CXR showing widened mediastinum). Symptomatic patients may present with chest/back pain, hoarseness (recurrent laryngeal nerve compression), dysphagia (esophageal compression), or cough. Aortic root dilation can cause aortic regurgitation with a diastolic murmur.
Complications: The most feared complications are aortic dissection and rupture, both life-threatening emergencies. Risk of rupture increases significantly with aneurysm diameter (>5.5-6 cm for ascending, >6.5-7 cm for descending) and rate of growth.
Diagnosis: CT angiography or MRI/MRA is used for accurate sizing and surgical planning; echocardiography (particularly TEE) is useful for assessing the aortic root and valve.
Management: Blood pressure control (beta-blockers, ARBs particularly in Marfan syndrome) to reduce aortic wall stress; surgical repair (open replacement or endovascular repair) indicated based on size thresholds (typically >5.5 cm for degenerative aneurysms, >4.5-5 cm in Marfan syndrome or bicuspid valve with risk factors), rapid growth (>0.5 cm/year), or symptoms.
High-yield associations for boards: Marfan syndrome + aortic root aneurysm + lens dislocation; bicuspid aortic valve + ascending aortic aneurysm; tertiary syphilis + ascending aortic aneurysm + aortic regurgitation; Turner syndrome + aortic root dilation risk.
Sources
- First Aid for the USMLE Step 1
- Robbins and Cotran Pathologic Basis of Disease
- UpToDate: Thoracic Aortic Aneurysm
- Braunwald's Heart Disease
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