An aneurysm is a bulging out of part of the wall of a blood vessel. It forms where the wall has weakened, often due to the buildup of plaque. It may also be an inherited condition or a complication of high blood pressure (hypertension).

Left untreated, aneurysms may tear or burst (a ruptured aneurysm). Ruptures are very painful events that cause massive internal bleeding and may result in permanent disability or death, depending on where the aneurysm is located. If an aneurysm bursts in the brain, it could cause a hemorrhagic stroke.