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What is a Brain Aneurysm?

A brain aneurysm is a bulging, weakened area in a blood vessel in the brain. This weakness in the artery wall may eventually cause the aneurysm to rupture. This leads to bleeding in the brain, which is a serious condition (called subarachnoid hemorrhage). Aneurysms are believed to form over time, as wear and tear of blood flow over a weak spot leads to an aneurysm. Many people live with small brain aneurysms that go unnoticed.

What are the risk factors for a Brain Aneurysm?

About five million people in the United States have some form of brain aneurysm. Common risk factors that contribute to having or rupturing an aneurysm are smoking and high blood pressure. Other contributors are atherosclerosis, use of illicit drugs, and alcohol consumption (especially binge drinking). One less controllable risk factor is family history of aneurysms, suggesting a yet-undiscovered genetic basis. Anyone with a family history of aneurysms (ie two first degree relatives including the patient) is recommended to undergo screening every 5 to 10 years.

Risk of rupture also depends the size and shape of the aneurysm, among many other variables. Expert and prompt evaluation, and treatment if needed, can decrease the risk of rupture.

In this video, Rose Du, MD, PhD, Director of Cerebrovascular Surgery discusses brain aneurysm risk factors, the decision of whether to treat an aneurysm, and what types of treatments are available.

What are the symptoms of a Brain Aneurysm, and how is a Brain Aneurysm diagnosed?

A small, unruptured aneurysm may produce no symptoms at all. Even with larger aneurysm, symptoms may not appear until the aneurysm ruptures. A large unruptured aneurysm may cause pupil dilation, double or blurred vision, numbness on one side of the face, or a drooping eyelid. An aneurysm that is leaking but not ruptured may cause a sudden and severe headache, but typically no other symptoms.

When a brain aneurysm ruptures, the patient typically experiences a sudden and severe headache. The patient may also have nausea, vomiting, neck stiffness, seizure, confusion, blurred vision, eye pain, dilated pupils, sensitivity to light, drooping eyelid, loss of balance or muscle weakness, speech impairment, or become unconscious. If you notice these symptoms, call 9-1-1 or go to the nearest emergency room.

Some cerebral aneurysms go undiscovered until they rupture, others are found by chance from imaging exam (such as CT, MRI, or angiography, or MR angiography) performed for another reason. These imaging tests also are performed when an aneurysm is suspected or when screening family members.

How is a Brain Aneurysm Treated?

A ruptured aneurysm requires emergency treatment to decrease the likelihood that it will bleed again. Unruptured small aneurysms have low risk of rupture and generally can be monitored regularly. But as their size increases, so does the risk. Larger aneurysms generally are recommended for treatment. Overall, there are many factors that contribute to predicting the future risk of rupture that your neurosurgeon will synthesize together and weigh against your risks of treatment.

The treatment goal for both ruptured and unruptured aneurysm is to reduce the risk of future rupture. This can be done through two ways:

  • Endovascular treatment is performed from within the blood vessel by threading a catheter through a blood vessel, up through the body guided by x-ray, to the aneurysm to provide treatment through processes known as “coiling” and “stenting.”
  • Surgical clipping is a more conventional surgery that requires a bony window in the skull (called craniotomy) to expose the aneurysm. The neurosurgeon, under a microscope, places a metal clip at the neck of the aneurysm to prevent blood flow into the aneurysm sac.

The method of treatment used depends upon the patient's age and overall health, the extent of the condition, the specific brain aneurysm symptoms, the patient's tolerance for medications, and personal preferences. Expert and prompt evaluation and treatment is critical, as a brain aneurysm rupture is fatal in 50 percent of patients and causes severe neurologic deficits in 25 percent of patients. Learn more about brain aneurysm treatment at Brigham and Women’s Hospital.

Contact the Center for Cerebrovascular Diseases

To schedule an appointment with a physician in the Brain Aneurysm Program at the Center for Cerebrovascular Diseases, please contact our Patient Coordinator at: (617) 732-6600. We see new patients with unruptured aneurysms as soon as the next business day.

If you are a physician seeking to refer a patient to the Center for Cerebrovascular Diseases, please call (617) 732-6600 or you can access our physicians’ office phone numbers. To contact one of our physicians with a question, patient referral or second opinion, you may also email:


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