Cystic medial necrosis of the aorta is seen in Marfan syndrome and other aortopathies. The histological finding described by this term actually consists of:

• A True cystic spaces lined by endothelium within the aortic media
• B Medial calcification with central liquefaction creating cystic spaces
• C Mucoid/myxoid extracellular matrix accumulation between degenerated smooth muscle cells with elastic lamellae fragmentation — not true cysts or necrosis ✓
• D Inflammatory necrosis of the media with giant cells and fibrinoid necrosis

Explanation

Despite its name, 'cystic medial necrosis' is a misnomer — there are no true cysts and no actual necrosis. Histologically it represents: (1) pools of basophilic mucoid/myxoid ground substance (proteoglycans — heparan sulfate, hyaluronic acid) accumulating in the media between fragmented and disorganized elastic lamellae; (2) loss of smooth muscle cells (which may appear artifactually as 'cystic spaces' on routine H&E); and (3) elastic fiber fragmentation. The term was coined before modern understanding. This medionecrosis represents matrix degeneration predisposing to aortic dissection and aneurysm formation in Marfan syndrome, Loeys-Dietz syndrome, and bicuspid aortic valve-related aortopathy. Inflammatory medial necrosis occurs in giant cell arteritis (affecting the temporal artery and aorta), which is an entirely distinct condition.

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

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Written and medically reviewed by the StethoPrep medical team.