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.