A cerebral or intracranial aneurysm is an abnormal focal dilation of an artery in the brain that results from a weakening of the inner muscular layer (the intima) of a blood vessel wall.
The vessel develops a "blister-like" dilation that can become thin and rupture without warning.
The resultant bleeding into the space around the brain is called a subarachnoid hemorrhage (SAH).
This kind of hemorrhage can lead to a stroke, coma and/or death.