An aneurysm develops from a weakened or thin spot on the wall of a blood vessel. Over time, the fragile area may balloon out due to pressure changes inside of the vessel. The concern is if the “ballooning” or aneurysm gets too large, it may rupture causing blood to spill into an area of the body producing injury. Aneurysms may develop along any blood vessel in the body, but typically develop at branching points of arteries. When the aneurysm develops along the wall of a blood vessel supplying the brain it is called a cerebral aneurysm. If a brain aneurysm ruptures, the bleeding usually occurs under one of the layers or membranes of the brain called the arachnoid layer, producing a subarachnoid hemorrhage (SAH).
Incidence and Risk Factors
The exact incidence of intracranial (brain) aneurysms is unknown, but has been estimated at 1-6% of the population. Aneurysms increase in frequency with age beyond the third decade and are approximately 1.6 times more common in women. Notably, only a small percentage of aneurysms may rupture or cause symptoms. The proper identification of risk factors is essential in the management of cerebral aneurysms.
Interestingly, the majority of cerebral aneurysms are sporadic, which means they are not related to a specific disease process or inherited trait, but occur as a congenital defect resulting from an inborn abnormality of an arterial wall. High blood pressure (hypertension) and smoking are two important risk factors for the development and rupture of brain aneurysms. Other risk factors include particular diseases that may cause blood vessel abnormalities like polycystic kidney disease, connective tissue disorders, fibromuscular dysplasia, Marfan’s syndrome, collagen vascular disorders, and coarctation of the aorta (narrowing of the aorta between the upper body branches and lower body branches). In addition, some types of head or neck trauma and infections (involving the arterial wall) may cause an aneurysm to develop.
A minority of cerebral aneurysms are found within families. In regards to screening for an aneurysm, the general recommendation is screening should be considered for a particular individual if 2 or more first-degree relatives (e.g. sibling, parent or child) have cerebral aneurysms. The screening is typically performed with non-invasive imaging that may include a MR- angiogram or CT angiogram.