Medical Revising Authors: Benjamin C. Wedro, MD, FAAEM and Dennis Lee, MD
Medical Revising Editor: William C. Shiel, Jr, MD, FACP, FACR
An aneurysm is an area of a localized widening (dilation) of a blood vessel. (The word "aneurysm" is borrowed from the Greek "aneurysma" meaning "a widening").
An aortic aneurysm involves the aorta, one of the large arteries through which blood passes from the heart to the rest of the body. The aorta bulges at the site of the aneurysm like a weak spot on an old worn tire.
The aorta is first called the thoracic aorta as it leaves the heart, ascends, arches, and descends through the chest until it reaches the diaphragm (the partition between the thorax and abdomen). The aorta is then called the abdominal aorta after it has passed the diaphragm and continues down the abdomen. The abdominal aorta ends where it splits to form the two iliac arteries that go to the legs.
Aortic aneurysms can develop anywhere along the length of the aorta. The majority, however, are located along the abdominal aorta. Most (about 90%) of abdominal aneurysms are located below the level of the renal arteries, the vessels that leave the aorta to go to the kidneys. About two-thirds of abdominal aneurysms are not limited to just the aorta but extend from the aorta into one or both of the iliac arteries.
Most aortic aneurysms are fusiform. They are shaped like a spindle ("fusus" means spindle in Latin) with widening all around the circumference of the aorta. (Saccular aneurysms just involve a portion of the aortic wall with a localized out pocketing).
The inside walls of aneurysms are often lined with a laminated blood clot that is layered like a piece of plywood.
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