An aneurysm is a weak area in the wall of a blood vessel that causes the blood vessel to bulge or balloon out. When an aneurysm occurs in a blood vessel of the brain, it is called a cerebral, or intracranial, aneurysm.
Aneurysms in the brain occur when there is a weakened area in the wall of a blood vessel. An aneurysm may be present from birth (congenital). Or, it may develop later in life, such as after a blood vessel is injured.
There are many types of brain aneurysms. The most common type is called a berry aneurysm. This type can vary in size from a few millimeters to over a centimeter. Giant berry aneurysms can be bigger than 2.5 centimeters. These are more common in adults. Berry aneurysms are passed down through families more often than other types of aneurysms.
Other types of cerebral aneurysms involve widening of an entire blood vessel. Or, they may appear as a ballooning out of part of a blood vessel. Such aneurysms can occur in any blood vessel that supplies the brain. Hardening of arteries (atherosclerosis), trauma, and infection can all injure the blood vessel wall and cause cerebral aneurysms.
About 5% of people have a brain aneurysm, but only a small number of these aneurysms cause symptoms or rupture.
Risk factors include:
- Family history of cerebral aneurysms
- Medical problems such as polycystic kidney disease, coarctation of the aorta, and endocarditis
- High blood pressure, smoking, alcohol, and illegal drug use