A 55-year-old man with hypertension is found at autopsy to have a saccular aortic aneurysm at the infrarenal segment. Histology shows focal destruction of the media with loss of elastic laminae and smooth muscle, chronic inflammatory infiltrate with adventitial fibrosis. Which pathological mechanism is MOST responsible for the medial destruction?

• A Cystic medial necrosis — mucoid degeneration without inflammation, associated with Marfan syndrome
• B Giant cell arteritis causing granulomatous inflammation of the media in large vessels
• C Syphilitic endarteritis obliterans of vasa vasorum causing ischemic medial necrosis in the ascending aorta
• D Atherosclerosis plaque causing pressure necrosis of media with superimposed matrix metalloproteinase (MMP)-mediated elastin and collagen degradation ✓

Explanation

Abdominal aortic aneurysms (AAA) at the infrarenal segment develop from advanced atherosclerosis occluding vasa vasorum, causing ischemic medial damage. Additionally, macrophage-derived and smooth muscle cell-derived matrix metalloproteinases (MMP-2, MMP-9) degrade medial elastin and collagen, weakening the aortic wall. Cystic medial necrosis (without inflammation) is the mechanism in Marfan syndrome and hypertension-related ascending aortic aneurysms. Syphilitic aneurysms characteristically affect the ascending aorta and arch via vasa vasorum obliteration.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.