A 68-year-old male with a long history of hypertension is found at autopsy to have a 7 cm fusiform dilatation of the abdominal aorta below the renal arteries. The adventitia contains a dense inflammatory infiltrate with plasma cells and lymphocytes. Histologically, the media shows loss of smooth muscle cells and elastic laminae with replacement by fibrous tissue. The most important risk factor for development of abdominal aortic aneurysm (AAA) is:

• A Syphilitic aortitis causing medial destruction by endarteritis obliterans
• B Cystic medial degeneration as seen in Marfan syndrome
• C Atherosclerosis causing medial ischemia and destruction via plaque-related inflammation and MMP activation ✓
• D Immune complex–mediated type III hypersensitivity vasculitis

Explanation

Atherosclerosis is the dominant underlying cause of abdominal aortic aneurysm, acting via multiple mechanisms: intimal plaques impair diffusion of nutrients to the media (vasa vasorum obliteration), inflammatory cells (macrophages, T cells) recruited to plaques secrete matrix metalloproteinases (MMPs, especially MMP-2, MMP-9) that degrade medial elastin and collagen, and oxidative stress further weakens the arterial wall. Infrarenal aorta is most commonly affected due to relatively sparse vasa vasorum. Syphilitic aortitis classically affects the thoracic aorta; Marfan syndrome causes cystic medial necrosis in the ascending aorta leading to Type A aortic dissection.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.