A 60-year-old hypertensive smoker presents with acute-onset tearing back pain radiating to the flanks. CT aortogram reveals an abdominal aortic aneurysm (AAA) of 8 cm diameter with retroperitoneal hematoma. Prior to emergent surgery, which pathological mechanism is most responsible for AAA formation?

• A Intimal plaque rupture leading to aortic wall dissection (type B aortic dissection)
• B Destruction of medial elastin and collagen by matrix metalloproteinases (MMP-2, MMP-9) released by macrophages, with atherosclerosis-induced intimal ischemia of the media ✓
• C Adventitial inflammation (chronic periaortitis) with IgG4-positive plasma cell infiltration
• D Medial cystic necrosis (mucoid degeneration) from fibrillin-1 deficiency as in Marfan syndrome

Explanation

Abdominal aortic aneurysm pathogenesis involves: atherosclerotic plaque causing ischemia of the vasa vasorum depriving the media of nutrients, inflammatory cell (macrophage, T cell) infiltration of the aortic wall, and secretion of matrix metalloproteinases MMP-2 (gelatinase A) and MMP-9 (gelatinase B) that digest elastin and collagen in the media, weakening the wall. Smoking independently upregulates MMP-9. The infrarenal aorta is most affected due to absent vasa vasorum. Medial cystic necrosis (mucoid degeneration) causes thoracic aneurysm/dissection in Marfan syndrome (fibrillin-1/FBN1 mutation). IgG4-related aortitis causes inflammatory AAA (a distinct subset).

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.