An aneurysm is a bulge or a weakening of an arterial wall. The wall may bulge in all directions, called a fusiform aneurysm, or it may form a sac, called a saccular aneurysm. It usually affects the larger blood vessels. It is rare for an aneurysm to occur in the very young or the very old.
Most aneurysms result from the development of abnormal arterial vessel walls.
They also can result from trauma or infection, but this is very rare. The highest incidence of brain aneurysms is in the age group of 40 to 60. Predisposition factors currently being studied are smoking habits, lifestyle and heredity. Aneurysms can enlarge and cause pressure, which can cause headache or visual disturbances, and then eventually the aneurysm could rupture. The rupturing of an aneurysm causes a subarachnoid hemorrhage, which is a very life threatening situation.