A cerebral aneurysm is a weakness in the wall of a blood vessel in the brain. Aneurysms can be a congenital defect or can develop later in life from conditions such as hypertensive vascular disease or atherosclerosis.
A burst or ruptured aneurysm allows blood to go into the brain. When the blood supply to part of the brain is reduced or completely blocked, a stroke may occur. The part of the brain deprived of blood dies and can no longer function.