An aortic aneurysm is a bulging section in the wall of the aorta—the large blood vessel delivering blood from the heart to the body—that has become stretched-out and thin. Where the wall of the blood vessel bulges out, it becomes weaker and may burst or rupture, causing bleeding.

Most aortic aneurysms are caused by a combination of hardening of the arteries (atherosclerosis), genetics, and aging. But a small number are caused by inflammation or infection. These are called inflammatory aneurysms.

An inflammatory aneurysm can cause complications, such as fever, weight loss, and symptoms of a chronic disease. A massive inflammatory response may affect body parts close to the aneurysm, including part of the small intestine, the ureter, or the veins to the kidney. Any of these structures can become obstructed by the inflammation.