Which feature histologically distinguishes a true aortic aneurysm from an aortic dissection?

• A True aneurysm is always atherosclerotic; dissection is always syphilitic
• B True aneurysm shows fibrinoid necrosis of the vessel wall; dissection shows inflammatory infiltrate
• C True aneurysm involves all three layers (intima, media, adventitia); dissection involves a blood-filled channel within the media ✓
• D True aneurysm involves only the intima and adventitia; dissection replaces the entire vessel wall

Explanation

A true aneurysm is a localised dilation involving all three layers of the vessel wall (intima, media, adventitia), most commonly due to atherosclerosis (infrarenal aorta) or medial degeneration. An aortic dissection is not an aneurysm — it is a tear in the intima that allows blood to dissect along the media, creating a false lumen within the media, not a simple dilation. Cystic medial necrosis (as in Marfan syndrome) predisposes to dissection.

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

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Written and medically reviewed by the StethoPrep medical team.