An aneurysm is an abnormal weakening or ballooning-out of a vessel wall of an artery. Weakening of the blood vessel wall may be due to disease, injury or an abnormality present at birth. Some common locations for aneurysms include the aorta (the major artery leading away from the heart), the brain (called a cerebral aneurysm), leg, intestine and splenic artery (which supplies blood to the spleen).