Brain Aneurysm


What is a brain aneurysm?

A brain aneurysm, also called a cerebral aneurysm, is a bulge in a weak area of an artery 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 farther. It’s similar to how a balloon gets thinner and is more likely to pop as it fills with air.

Brain aneurysms can occur anywhere in your brain, but most of them form in the major arteries along the base of your skull. Approximately 10% to 30% of people who have a brain aneurysm have multiple aneurysms. The majority of brain aneurysms are small and don’t cause symptoms.

An aneurysm can cause symptoms if it puts pressure on nearby nerves or brain tissue. If the aneurysm leaks or ruptures (bursts open), it causes bleeding in your brain. A ruptured brain aneurysm can be life-threatening and requires emergency medical treatment. As more time passes with a ruptured aneurysm, the likelihood of death or disability increases.

What happens when a brain aneurysm ruptures?

When it ruptures, blood spills (hemorrhages) into your surrounding brain tissue. The blood can put excess pressure on your brain tissue and make your brain swell. It usually causes a severe headache called a thunderclap headache, in addition to other symptoms.

A ruptured brain aneurysm can cause serious health problems such as:

  • Subarachnoid hemorrhage (SAH): Bleeding in the area between your brain and the thin tissues that cover and protect it (the arachnoid layer). About 90% of SAHs are due to ruptured brain aneurysms.
  • Hemorrhagic stroke: Bleeding in the space between your skull and brain.

This can result can in permanent brain damage or other complications such as:

  • Vasospasm: This happens when blood vessels get narrower or clamp down and less oxygen reaches your brain.
  • Hydrocephalus: This happens when a buildup of cerebrospinal fluid or blood around your brain puts increased pressure on it.
  • Seizures: A seizure is a temporary, uncontrolled surge of electrical activity in your brain. It can make brain damage due to a ruptured aneurysm worse.
  • Coma: A state of prolonged unconsciousness. It can last days to weeks.
  • Death: Ruptured brain aneurysms result in death in about 50% of cases.

Who do brain aneurysms affect?

Brain aneurysms can affect anyone and at any age. But they’re most likely to affect people between the ages of 30 and 60. They’re also more common in women and people assigned female at birth than in men and people assigned male at birth.

How common are brain aneurysms?

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

Symptoms and Causes

What are the symptoms of a brain aneurysm?

Brain aneurysm symptoms vary based on whether it’s unruptured or ruptured.

Symptoms of a ruptured brain aneurysm

Symptoms of a ruptured aneurysm include:

  • Thunderclap headache (sudden onset and severe, often described as “the worst headache of my life”).
  • Nausea and vomiting.
  • Stiff neck.
  • Blurred or double vision.
  • Sensitivity to light (photophobia).
  • Seizures.
  • Drooping eyelid and a dilated pupil.
  • Pain above and behind your eye.
  • Confusion.
  • Weakness and/or numbness.
  • Loss of consciousness.

Call 911 or get to the nearest emergency room as soon as possible if you have these symptoms.

When a brain aneurysm leaks a small about of blood it’s called a sentinel bleed. You may experience warning headaches (called sentinel headaches) from a tiny aneurysm leak days or weeks before a significant rupture.

Symptoms of an unruptured brain aneurysm

Most unruptured (intact) brain aneurysms don’t cause symptoms. If they become large enough, the bulge in your artery can put pressure on nearby nerves or brain tissue, causing the following symptoms:

  • Headaches.
  • Vision changes.
  • Enlarged (dilated) pupil.
  • Numbness or tingling on your head or face.
  • Pain above and behind your eye.
  • Seizures.

See a healthcare provider as soon as possible if you’re experiencing these symptoms.

What causes brain aneurysms?

Brain aneurysms develop when the walls of an artery in your brain become thin and weak. They usually form at branching points of arteries. Sometimes, you can be born with a brain aneurysm. This is typically due to an abnormality (birth defect) in an artery wall. Several other factors can contribute to the weakening of an artery.

The following inherited factors affect the health of your arteries and can increase your risk of developing a brain aneurysm:

The following conditions and situations can weaken your artery walls over time:

What causes a brain aneurysm to rupture?

The factors that contribute to the development of a brain aneurysm can also cause it to rupture (burst) and bleed.

Researchers think high blood pressure is the most common cause of a rupture. Higher blood pressure makes blood push harder against blood vessel walls. Situations that can increase blood pressure and lead to a brain aneurysm rupture include:

  • Ongoing stress or a sudden burst of anger or other strong emotion.
  • Working hard (straining) to lift, carry or push something heavy like weights or furniture.
  • Known high blood pressure that isn’t properly treated with medications.

Many factors determine whether an aneurysm is likely to burst, including:

  • Size and shape: Smaller aneurysms may be less likely to bleed than larger, irregularly shaped ones.
  • Growth: If an aneurysm has grown over time, it may be more likely to rupture.
  • Location: Aneurysms on the posterior communicating arteries (a pair of arteries in the back of your brain) and the anterior communicating artery (an artery in the front of your brain) have a higher risk of rupturing than brain aneurysms in other locations.
  • Race: People of Japanese or Finish heritage have higher risk of aneurysm rupture.
  • Older age: People older than 70 are at higher risk of aneurysm rupture.

People who have multiple brain aneurysms or who’ve had a previous aneurysm bleed are at the highest risk of a brain aneurysm rupture.

Diagnosis and Tests

How are brain aneurysms diagnosed?

Most people with an unruptured brain aneurysm don’t know they have one. A healthcare provider may find one during an imaging test of your brain, such as an MRI or CT scan that you got for a different medical reason.

If you have symptoms of a brain aneurysm, such as a severe headache, call 911 or go to the emergency room. A healthcare provider will order tests to see if a brain aneurysm has ruptured. These tests may include:

  • CT (computed tomography) scan: This is often the first imaging test a provider will order to see if blood has leaked into your brain. A CT scan uses X-rays and computers to produce images of a cross-section of your body. Providers may also use a CT angiogram (CTA), which produces more detailed images of blood flow in your brain’s arteries. CTA can show the size, location and shape of an unruptured or ruptured aneurysm.
  • MRI (magnetic resonance imaging) scan: MRI uses a large magnet, radio waves and a computer to produce detailed images of your brain. Magnetic resonance angiography (MRA) produces detailed images of your brain’s arteries and can show the size, location and shape of an aneurysm.
  • Cerebral angiography: This is a procedure in which a neurosurgeon or an interventional neuroradiologist inserts a catheter into a blood vessel in your groin or wrist. They thread it to your brain to take more accurate images of the arteries in your neck and brain. This imaging test can find blockages in arteries in your brain or neck. It also can identify weak spots in an artery, like an aneurysm. Providers use this test to determine the cause of bleeding in your brain and the exact location, size and shape of an aneurysm.
  • Cerebrospinal fluid (CSF) analysis: This test measures the substances in the fluid that surrounds and protects your brain and spinal cord (cerebrospinal fluid). A provider collects a CSF sample by performing a spinal tap (lumbar puncture). The analysis can detect bleeding around your brain.

Management and Treatment

How are brain aneurysms treated?

The main goal of brain aneurysm treatment is to stop or reduce the flow of blood into the aneurysm. A leaking or ruptured brain aneurysm requires emergency surgery. You may or may not need treatment for an unruptured aneurysm depending on your circumstances.

Your healthcare team will recommend the best treatment option(s) for you based on your vascular anatomy, aneurysm size and location and several other factors.

In general, recovery takes longer for ruptured aneurysms than for unruptured aneurysms.

Microvascular clipping for brain aneurysms

During this surgery, a neurosurgeon cuts a small opening in your skull to access the aneurysm. Using a tiny microscope and instruments, the neurosurgeon attaches a small metal clip at the base of the aneurysm to pinch it off. This blocks blood from flowing into the aneurysm. The surgery can stop a brain bleed or keep an intact aneurysm from enlarging or breaking open.

Recovery time is different for ruptured (several weeks to months) and unruptured (usually two to four weeks) aneurysms. Aneurysms that are completely clipped usually don’t bleed again (recur).

Endovascular coiling for brain aneurysm

For this procedure, a neurosurgeon or an interventional neuroradiologist inserts a catheter (a flexible tube) into a blood vessel, usually in your groin or wrist, and threads it to your brain. Through the catheter, the provider places a tiny coil of soft wire into the aneurysm.

Once the provider releases the coil into the aneurysm, it changes the blood flow pattern within the aneurysm, resulting in a clot. This clot prevents blood from entering the aneurysm, providing a seal in a similar way as a clip.

Flow diversion stents for brain aneurysm

For this procedure, a neurosurgeon or an interventional neuroradiologist inserts a catheter into a blood vessel in your groin or wrist and threads it to your brain. Through the catheter, the provider places a mesh tube in the part of the blood vessel that contains the aneurysm. The mesh encourages or diverts your blood flow away from instead of into the aneurysm.

WEB device for brain aneurysm

For this procedure, a neurosurgeon or an interventional neuroradiologist inserts a catheter into a blood vessel in your groin or wrist and threads it to your brain. Through the catheter, the provider places a metal mesh-like cube or sphere into the aneurysm. This works similar to a coil, as it provides a seal-like effect on the aneurysm, not allowing blood into it anymore to prevent it from enlarging or rupturing.

Additional treatments for a ruptured brain aneurysm

If you have a ruptured aneurysm, your healthcare team will use additional treatments to manage your symptoms and try to prevent complications. These treatments may include:

  • Antiseizure medications: These medications can help prevent seizures related to a ruptured aneurysm.
  • Calcium channel blockers: These medications can help reduce your risk of stroke due to vasospasm.
  • Shunt: This is a tube that helps drain cerebrospinal fluid (CSF) from your brain to somewhere else in your body. It can help prevent hydrocephalus.

People who have a ruptured aneurysm often need physical, speech and occupational therapy to regain function and learn new ways to function with any permanent disability.

Do I need treatment for an unruptured brain aneurysm?

If you have a small unruptured brain aneurysm that isn’t causing symptoms and you don’t have other relevant risk factors, your healthcare provider may recommend not treating it.

Instead, your provider will order regular imaging tests to monitor it for any changes or growth over time. They’ll also recommend you quit smoking (if you smoke) and make sure your blood pressure is well managed.

You’ll need to get help right away if you develop symptoms or if the aneurysm changes on follow-up imaging.

If you have symptoms, positive risk factors and/or the aneurysm is large, you and your healthcare provider will discuss the benefits, risks and alternatives of surgical and/or endovascular treatment. The decision depends on several factors, including but not limited to your:

  • Age.
  • Overall health and your medical conditions.
  • Aneurysm location, size and other characteristics.
  • Vascular anatomy.
  • Family history.
  • Risk of a rupture.
Care at Cleveland Clinic


How can I reduce my risk of developing an aneurysm?

You can’t prevent or change certain brain aneurysm risk factors, like your age or genetic conditions. But you can lower your risk of developing a brain aneurysm by:

Outlook / Prognosis

What is the prognosis for a ruptured brain aneurysm?

The prognosis (outlook) for a ruptured brain aneurysm depends on several factors, including:

  • Your age and overall health.
  • If you have preexisting neurological conditions.
  • The location of the aneurysm.
  • How much the aneurysm bled.
  • How quickly you received treatment.
  • If the treatment of the aneurysm was successful.

About 25% of people who experience a brain aneurysm rupture die within 24 hours. Around 50% of people die within three months of the rupture due to complications.

Of those who survive, about 66% experience permanent brain damage. Some people recover with little or no disability.

Can you live a long life with a brain aneurysm?

Many people who have a small unruptured brain aneurysm never develop symptoms and it doesn’t affect their health.

However, the mortality rate of ruptured brain aneurysms is very high.

Living With

When should I see my healthcare provider about a brain aneurysm?

If you have an unruptured brain aneurysm, you’ll need to see your healthcare provider regularly to monitor the size of the aneurysm and to manage any contributing risk factors, like high blood pressure.

If you’ve had a ruptured brain aneurysm, you’ll need to see your healthcare team regularly to monitor any complications and to make sure you don’t develop another aneurysm.

A note from Cleveland Clinic

A sudden, severe headache with or without stroke symptoms could be a sign of a brain aneurysm. Call 911 or go to an emergency room if you’re having these symptoms. The sooner you can get medical attention, the greater your chance of survival. If you have an unruptured brain aneurysm, talk with your healthcare provider about the risks and benefits of different treatment and management options. They’re available to help you.

Last reviewed by a Cleveland Clinic medical professional on 02/10/2023.


  • American Association of Neurological Surgeons. Cerebral Aneurysms. ( Accessed 2/10/2022.
  • American Heart Association. Types of Aneurysms. ( Accessed 2/10/2022.
  • American Stroke Association. What You Should Know About Cerebral Aneurysms. ( Accessed 2/10/2022.
  • Brain Aneurysm Foundation. Causes/Risk Factors. ( Accessed 2/10/2022.
  • Jersey AM, Foster DM. Cerebral Aneurysm. ( [Updated 2022 Jun 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Accessed 2/10/2022.
  • National Institute of Neurological Disorders and Stroke. Cerebral Aneurysms Fact Sheet. ( Accessed 2/10/2022.
  • Society of NeuroInterventional Surgery. Aneurysm. ( Accessed 2/10/2022.
  • Toth G, Cerejo R. Intracranial aneurysms: Review of current science and management. ( Vascular Medicine 2018;23(3):276-288. Accessed 2/10/2022.

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