Abdominal aortic aneurysm: the lesion, its variants and rupture
- Lesion
Below the kidneys, plaques can weaken the aorta until it balloons. It grows silently and can burst.
What it is
Abdominal aortic aneurysm (AAA) is a permanent dilation of the infrarenal aorta, most often in older men who smoke and have atherosclerosis. Inflammation in the plaque destroys the media while synthesis cannot keep up, and the wall bulges. Most are silent; the risk of rupture rises steeply with diameter and growth rate. Variants include inflammatory AAA, IgG4-related aortitis and infected (mycotic) aneurysms.
Structure
- Gross: fusiform or saccular dilation, often filled with layered mural thrombus that can embolise to the legs.
- Microscopy: severe atherosclerosis with thin, destroyed media, loss of elastic lamellae and chronic adventitial inflammation.
- Inflammatory AAA: thick, fibrotic, adherent wall with lymphoplasmacytic infiltrate; IgG4-related forms show many IgG4-positive plasma cells.
- Mycotic aneurysm: necrotic wall infiltrated by neutrophils with bacteria.
Clinical notes
- Complications: rupture, embolism from mural thrombus, occlusion of branches (renal, mesenteric), compression of ureter or vertebrae.
- One-time ultrasound screening is offered to older male smokers in many health systems.
Test yourself
Think of the answer, then tap the question to see it.
What is the commonest location of an atherosclerotic aortic aneurysm?
The infrarenal abdominal aorta, between the renal arteries and the iliac bifurcation.
What does the lumen of a large AAA usually contain?
Laminated mural thrombus, which can embolise to the lower limbs.
What is a mycotic aneurysm?
An aneurysm caused or complicated by infection of the wall, for example from bacteremia or septic emboli (Salmonella is classic in the aorta).
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Aortic Aneurysm | MedlinePlus (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.