What is a brain (cerebral) aneurysm?

A brain aneurysm is a bulge in a weak area of a blood vessel in or around your brain. The constant pressure of blood flow pushes the weakened section outward, creating a blister-like bump.

When blood rushes into this bulge, the aneurysm stretches even further. It’s similar to how a balloon gets thinner and is more likely to pop as it fills with air. If the aneurysm leaks or ruptures (bursts open), it causes bleeding in your brain. Sometimes it causes a hemorrhagic stroke, bleeding in or around the brain that can lead to brain damage and be fatal.

These aneurysms are also called cerebral aneurysms. Cerebral means in the brain.

How common are brain aneurysms?

Up to 6% of people in the U.S. have an aneurysm in their brain that isn’t bleeding (called an unruptured aneurysm). Ruptured brain aneurysms are rare. They occur in approximately 30,000 Americans a year.

Who gets brain aneurysms?

You’re more likely to develop a brain aneurysm if you:

Are aneurysms hereditary?

Among first-degree relatives, if one person has a cerebral aneurysm it would be appropriate to have the rest of the family, children or siblings, checked out after a discussion with your primary care physician. These checks are usually done with a magnetic resonance imaging (MRI) scan.

Studies suggest the link may vary between 10% and 20%. But all have shown that doctors find that relatives of aneurysm patients occasionally have an aneurysm too. That risk becomes even more likely if you or your family members have other risk factors for cerebral aneurysms.

What causes brain aneurysms?

It’s not clear why a brain aneurysm forms. Researchers believe these factors irritate and weaken blood vessels:

When do brain aneurysms develop?

Brain aneurysms can form in people as young as 30, rarely even earlier, but they’re more likely after age 40.

What causes brain aneurysms to bleed?

Researchers haven’t discovered exactly what causes an aneurysm to leak or rupture, which causes bleeding in or around the brain. But anything that increases your blood pressure can be dangerous. Higher blood pressure makes blood push harder against blood vessel walls. Things that may increase blood pressure include:

  • Ongoing stress or a sudden burst of anger or other strong emotion.
  • Working hard to lift, carry or push something heavy like weights or furniture.
  • Known high blood pressure that is not treated appropriately with medications.

Are brain aneurysms painful?

Most people who have an unruptured brain aneurysm don’t even know it’s there. It usually doesn’t cause pain or any symptoms at all.

However, many smaller (not only larger) aneurysms are actually found when investigating causes of chronic headache. Researchers don't know for sure if headaches are directly related to an unruptured aneurysm. One thought is that the swollen blood vessel is pressing into the nerves and membranes/tissues around the brain, causing the headache.

A sudden, severe headache (sometimes called “thunderclap headache”) can be a sign of a ruptured aneurysm. Rarely, you can also have a headache that lasts for days or weeks from an aneurysm that’s leaking a small amount of blood. This type of lingering headache is called a sentinel headache. It’s a warning that the aneurysm is about to burst.

What are the symptoms of an unruptured brain aneurysm?

The most common signs of an intact aneurysm are headaches. Other signs may include:

  • Vision changes.
  • Enlarged (dilated) pupil, the black part of the eye.
  • Seizures.
  • Numbness or tingling on the head or face.
  • Pain above and behind the eye.
  • Neck pain.
  • Nausea and vomiting.

What are the symptoms of a ruptured brain aneurysm?

A brain aneurysm that is leaking or has burst open is life-threatening. It requires emergency medical treatment. People with a ruptured brain aneurysm often say the headache is the worst headache of their lives. The severe headache comes on suddenly and lasts for hours to days.

Besides a severe headache, you may have some of the same symptoms of an unruptured aneurysm (see list above). You might also have:

  • Stiff neck.
  • Drowsiness or even coma.
  • Mental confusion.
  • Dizziness or problems with your balance.
  • Difficulty speaking.
  • Weakness or no feeling in an arm or leg.
  • Heart attack.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy