June 8, 2012
Dear Mayo Clinic:
What causes a brain aneurysm? Are there any warning signs? How is a brain aneurysm treated?
A brain aneurysm is small round outpouching of an artery in the brain that develops due to thinning of the blood vessel wall. A brain aneurysm that bursts, or ruptures, can lead to serious medical problems. However, many aneurysms do not rupture, and some unruptured aneurysms do not require treatment.
Brain aneurysms are common. About 2 percent of the population has an unruptured brain aneurysm. That equals about 6 million people in the United States. But only about 25,000 brain aneurysms rupture each year.
Cigarette smoking and high blood pressure can increase a person's risk for having a brain aneurysm. Genetics also seems to play a role. People who have two or more members of their family with a history of a brain aneurysm have an increased risk of developing a brain aneurysm.
Most unruptured brain aneurysms don't cause symptoms. Rarely, an aneurysm will push on brain tissue or a nerve, causing pain, double vision, loss of vision, or facial weakness or numbness, or unsteadiness. Typically, though, an unruptured brain aneurysm is discovered on a computerized tomography (CT) or a magnetic resonance imaging (MRI) brain scan that is done for some unrelated reason. A specialized brain CT called a CT angiogram (CTA) or a specialized brain MRI called an MR angiogram (MRA) can be used to look at the aneurysm in more detail. A study of the brain arteries called a cerebral arteriogram may also be performed to evaluate the aneurysm.
When an unruptured aneurysm is found, the risk of the aneurysm rupturing without treatment should be weighed against the risks of treatment.
A brain aneurysm that ruptures leads to a serious type of stroke called a subarachnoid hemorrhage, which involves bleeding over the surface of the brain and into deeper parts of the brain. These strokes can quickly become life threatening if they are not treated promptly.
Several factors should be considered when assessing the possibility that a brain aneurysm may rupture and deciding about treatment. The risk of rupture is higher for larger aneurysms. Aneurysms in the front of the brain are at lower risk for rupture than those in the back. An aneurysm's appearance has an impact on the decision, too. Family medical history also needs to be considered, as does a person's age and overall health.
Small, unruptured aneurysms in the front of the brain are sometimes safely left alone, particularly in older patients and those who do not have a family history of aneurysm rupture. If the decision is made to manage the aneurysm without surgery or other intervention, periodic follow-up brain CTA or MRA is typically recommended to make sure that the aneurysm is not getting larger.
If the decision is made to treat an unruptured aneurysm, options usually include surgical clipping or endovascular coiling. During surgical clipping, a neurosurgeon goes into the brain and places a tiny metallic clip across the base of the aneurysm to stop blood from flowing into it. With endovascular coiling, a surgeon inserts a hollow plastic tube, or catheter, into an artery, usually in the groin, and threads it to the aneurysm. A tiny platinum wire is passed through the catheter and placed into the aneurysm. The wire coils up inside the aneurysm, plugs the aneurysm sac and causes blood to clot, sealing off the aneurysm from the artery.
Whether or not an unruptured brain aneurysm is treated, controlling blood pressure and quitting smoking are important ways to lower risk of aneurysm growth and rupture.
When determining how to deal with an unruptured brain aneurysm, find a health care team that includes a neurologist, neuroradiologist and neurosurgeon who have expertise in aneurysms and their treatment. With the help of these experts, patients can carefully consider their options and decide what is best for them.
— Robert D. Brown Jr., M.D., Neurology, Mayo Clinic, Rochester, Minn.