A 65-year-old man with a history of hypertension and atherosclerosis presents acutely with severe tearing chest/back pain radiating to the abdomen. CT shows a false lumen in the thoracic aorta. The underlying histological change predisposing to aortic dissection is:

• A Fibromuscular dysplasia — alternating stenoses and dilations in arterial wall
• B Atherosclerotic plaque with lipid core rupture
• C Granulomatous inflammation of the media as seen in Takayasu arteritis
• D Cystic medial degeneration (medial necrosis) — loss of elastic fibers and smooth muscle with accumulation of mucoid material in the media ✓

Explanation

Cystic medial degeneration (CMD), also called cystic medial necrosis or medionecrosis, is the critical predisposing histological change in aortic dissection, characterised by focal loss of medial smooth muscle cells, fragmentation and loss of elastic lamellae, and replacement by pools of mucoid ground substance (proteoglycans). This weakens the media and allows an intimal tear (usually in the proximal ascending aorta) to propagate a false lumen. CMD occurs in Marfan syndrome, Ehlers-Danlos syndrome type IV, and with aging/hypertension. Atherosclerosis is an intimal process and does not directly cause 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.