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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 cerebral aneurysm to rupture. A ruptured aneurysm 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 Causes a Brain Aneurysm?

The causes of brain aneurysms aren't fully known, but risk increases as people age, becoming most common in women older than 40. An aneurysm could be the result of a genetic blood vessel defect or a weakening over time, especially where vessels fork near the base of the brain.

What Are Brain Aneurysm Risk Factors?

About five million people in the United States have some form of brain aneurysm. Common risk factors that may contribute to having an aneurysm include:

  • Smoking and alcohol consumption (especially binge drinking)
  • Atherosclerosis, a fatty build-up on the walls of blood vessels
  • High blood pressure
  • Injury or trauma to the head or brain
  • Use of illicit drugs
  • Family history of aneurysms, suggesting a yet-undiscovered genetic basis. Anyone with a family history of aneurysms (two first-degree relatives including the patient) is recommended to undergo screening every 5 to 10 years

What Causes a Brain Aneurysm to Rupture?

Risk of rupture increases when the blood pressure in the vessel rises. Rupture risks also depend on 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?

The symptoms of a brain aneurysm can vary based on the type. The most common symptom is headaches but may also include a range of other signs of a brain aneurysm, such as vision changes, numbness of the head, pain above or behind the eyes and neck pain.

Unruptured Brain Aneurysm Symptoms

A small, unruptured aneurysm may produce no symptoms at all. Even with a 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.

Leaking Aneurysm Symptoms

An aneurysm that is leaking but not ruptured may cause a sudden and severe headache, but typically no other symptoms. A more serious aneurysm rupture can follow soon after leaking.

Ruptured Brain Aneurysm Symptoms

When a brain aneurysm ruptures, the patient typically experiences a sudden and severe headache. The patient may also experience:

  • Nausea
  • Vomiting
  • Neck stiffness
  • Seizures
  • Confusion
  • Blurred vision
  • Eye pain
  • Dilated pupils
  • Sensitivity to light
  • Drooping eyelid
  • Loss of balance
  • Muscle weakness
  • Speech impairment
  • Loss of consciousness

If you notice these symptoms, call 9-1-1 or go to the nearest hospital emergency room.

How Is a Brain Aneurysm Diagnosed?

Many brain aneurysms go undiscovered until they rupture, but others are found through imaging exams. Early signs and symptoms can lead to a series of tests to determine a brain aneurysm diagnosis. If an aneurysm is suspected or if you have a family history of cerebral aneurysms, common tests include:

  • CT scans, a specialized X-ray can show bleeding in the brain
  • MRI, the magnetic resonance imaging creates a detailed image of the brain
  • MRA, a magnetic resonance angiography, a type of MRI that looks at blood vessels

What Is the Treatment for a Brain Aneurysm?

A ruptured aneurysm requires emergency treatment to decrease the likelihood that it will bleed again. Unruptured small aneurysms have a low risk of rupture and can be regularly monitored. But as their size increases, so does the risk. Larger aneurysms generally require treatment. Overall, many factors 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 aneurysms is to reduce the risk of future rupture. This can be done in 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 a 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 are 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.

How to prevent a Brain Aneurysm

Brain aneurysm prevention revolves around a healthy lifestyle. Changes in diet and exercise can lower blood pressure and eliminating smoking, drug use and alcohol intake can serve to stop the weakening of blood vessels.

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How Common Are Brain Aneurysms?

Up to 6% of people living in the United States have an unruptured brain aneurysm. While still rare, they do happen to up to 30,000 Americans each year. Brain aneurysms occur in both males and females and at any age, but brain aneurysms are most common in female adults between ages 40 and 60.

Placenta Increta and Percreta

Placenta increta and placenta percreta are similar to placenta accreta, but more severe.

  • Placenta increta is a condition where the placenta attaches more firmly to the uterus and becomes embedded in the organ’s muscle wall.
  • Placenta percreta is a condition where placenta attaches itself and grows through the uterus and potentially to the nearby organs (such as the bladder).

Obstetricians seek to make a specific diagnosis of accreta, increta or percreta before delivery using ultrasound and MRI imaging, but this is not always possible.

How Serious Is a Brain Aneurysm?

The seriousness of a brain aneurysm is based on if it has ruptured or not and if the aneurysm causes symptoms. Most aneurysms don't rupture or cause symptoms, but when they do rupture, they can become life-threatening and demand immediate medical attention.

During a normal delivery, the placenta detaches from the uterus during the last stage of labor. This can also be referred to as the “afterbirth.” With accreta, the placenta is tightly attached to the uterine wall and does not separate naturally during delivery. This causes several complications for the baby and mother.

Can You Live with a Brain Aneurysm?

Most people who have a brain aneurysm live normally without being aware they have one. Since many aneurysms don't cause health issues or exhibit symptoms, people can live for years without knowing they have a brain aneurysm.

Our team of maternal-fetal medicine specialists (high risk obstetricians), radiologists, surgeons, nurses, and other medical specialists provide supportive and compassionate care before, during, and after pregnancy for women who have or are at risk of having pregnancy complications. This care includes counseling, evaluation, and medical and surgical care.

Can a Brain Aneurysm Go Away?

It is rare for a brain aneurysm to go away on its own. An aneurysm can change over time, based on lifestyle changes.

What's the Difference Between a Stroke and a Brain Aneurysm?

A brain aneurysm can lead to a stroke, but not the other way around. The weakening of the blood vessel wall that occurs during an aneurysm can eventually rupture, sending blood to the brain and leading to a stroke. A stroke happens when blood flow to the brain is impeded. In an ischemic stroke, a ruptured blood vessel from an aneurysm can cause arteries to spasm and stop blood flow to a specific part of the brain.

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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