The aorta is the largest artery in the body, carrying oxygen-rich blood from the heart to the rest of the body. It looks like a big garden hose, extending from the heart down through the chest and abdominal region before it divides into two major blood vessels that supply each leg.
Aneurysms are abnormal bulges in the walls of vessels like the aorta, (see picture) usually caused by hardening of the arteries as cholesterol and other fatty deposits build up along the aortic wall. The most common type are called degenerative aneurysms. They happen when the tissue and muscle layer of the aorta break down, due to high blood pressure, chronic smoking, or a hereditary condition. Sometimes the wall of the aorta actually tears, causing its layers to separate, like a sheet of plywood left out in the rain. The separation causes the wall to weaken, and the aorta enlarges. This is called a dissecting aneurysm.
Aneurysms can occur anywhere along the aorta, but 75% of cases occur in the section running through the abdomen. (Most of the remaining cases occur in the chest region.) An abdominal aortic aneurysm is a weakened section in the wall of the lower portion of the aorta. If it is not treated, it can rupture and potentially be fatal to the patient. The risk of rupture increases as the aneurysm becomes larger.
AAA is most common in Caucasians, and affects men four times more frequently than women. It is most prevalent between the ages of 60 and 70.