An Aneurysm is a bulge, or weakening, of a blood vessel. They often appear in the aorta (chest or abdominal), brain, back of the knee, intestine, or spleen. A ruptured aneurysm can cause internal bleeding, stroke, and can sometimes be fatal. Aneurysms often have no symptoms until they rupture. Treatment depends on the location, size, and condition of the aneurysm.