Aneurysms are created when an artery wall weakens and widens. While they can occur in any artery, they are most common in the aortic (heart to the body), cerebral (brain), popliteal (at the back of the knee), mesenteric (to the intestine), and splenic (to the spleen) arteries. They may cause no symptoms until they suddenly burst-a terrifying prospect for many. Fortunately, though, most never rupture. Once ruptured, however, they are life-threatening and require emergency treatment. To spot a burst aneurysm, look for headache, pain, dizziness, confusion, vision changes, and a sense of impending doom. A sudden severe headache can indicate a leaking aneurysm, which usually ruptures later. Prompt action is needed to avoid death or brain damage.