A brain (cerebral) aneurysm is a bulging, weak area in the wall of an artery that supplies blood to the brain. In most cases, a brain aneurysm causes no symptoms and goes unnoticed. In rare cases, the brain aneurysm ruptures, releasing blood into the skull and causing a stroke.

When a brain aneurysm ruptures, the result is called a subarachnoid hemorrhage. Depending on the severity of the hemorrhage, brain damage or death may result.

The most common location for brain aneurysms is in the network of blood vessels at the base of the brain called the circle of Willis.

What causes a brain aneurysm?

A person may inherit the tendency to form aneurysms, or aneurysms may develop because of hardening of the arteries (atherosclerosis) and aging. Some risk factors that can lead to brain aneurysms can be controlled, and others can’t. The following risk factors may increase your risk of developing an aneurysm or, if you already have an aneurysm, may increase your risk of it rupturing.

• Family history. People who have a family history of brain aneurysms are twice as likely to have an aneurysm as those who don’t.
• Previous aneurysm. About 20% of patients with brain aneurysms have more than one.
• Gender. Women are twice as likely to develop a brain aneurysm or to suffer a subarachnoid hemorrhage as men.
• Race. African Americans have twice as many subarachnoid hemorrhages as whites.
• Hypertension. The risk of subarachnoid hemorrhage is greater in people with a history of high blood pressure (hypertension).
• Smoking. In addition to being a cause of hypertension, the use of cigarettes may greatly increase the chances of a brain aneurysm rupturing.

What are the symptoms?

Most brain aneurysms cause no symptoms and may only be discovered during tests for another, usually unrelated, condition. In other cases, an unruptured aneurysm will cause problems by pressing on areas within the brain. When this happens, the person may suffer from severe headaches, blurred vision, changes in speech, and neck pain, depending on the areas of the brain that are affected and the severity of the aneurysm. If you have any of the following symptoms or notice them in someone you know, see a health professional immediately.

Symptoms of a ruptured brain aneurysm often come on suddenly. They may include:

• Sudden, severe headache (sometimes described as a “thunderclap” headache that is very different from any normal headache).
• Neck pain.
• Nausea and vomiting.
• Sensitivity to light.
• Fainting or loss of consciousness.
• Seizures.

How is a brain aneurysm diagnosed?

Because unruptured brain aneurysms often do not cause any symptoms, many are discovered in people who are being treated for a different condition.

If your health professional believes you have a brain aneurysm, you may have the following tests:

• Computed tomography (CT) scan. A CT scan can help identify bleeding in the brain.
• Computed tomography angiogram (CTA) scan. CTA is a more precise method of evaluating blood vessels than a standard CT scan. CTA uses a combination of CT scanning, special computer techniques, and contrast material (dye) injected into the blood to produce images of blood vessels.
• Magnetic resonance angiography (MRA). Similar to a CTA, MRA uses a magnetic field and pulses of radio wave energy to provide pictures of blood vessels inside the body. As with CTA and cerebral angiography, a dye is often used during MRA to make blood vessels show up more clearly.
• Cerebral angiogram. During this X-ray test, a catheter is inserted through a blood vessel in the groin or arm and moved up through the vessel into the brain. A dye is then injected into the cerebral artery. As with the above tests, the dye allows any problems in the artery, including aneurysms, to be seen on the X-ray. Although this test is more invasive and carries more risk than the above tests, it is the best way to locate small (less than 5 mm) brain aneurysms.