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Brain aneurysm

Medically reviewed by Last updated on Mar 7, 2023.


A brain aneurysm (AN-yoo-riz-um) — also known as a cerebral aneurysm or intracranial aneurysm — is a bulge or ballooning in a blood vessel in the brain. An aneurysm often looks like a berry hanging on a stem.

Experts think brain aneurysms form and grow because blood flowing through the blood vessel puts pressure on a weak area of the vessel wall. This can increase the size of the brain aneurysm. If the brain aneurysm leaks or ruptures, it causes bleeding in the brain, known as a hemorrhagic stroke.

Most often, a ruptured brain aneurysm occurs in the space between the brain and the thin tissues covering the brain. This type of hemorrhagic stroke is called a subarachnoid hemorrhage.

Brain aneurysms are common. But most brain aneurysms aren't serious, especially if they're small. Most brain aneurysms don't rupture. They usually don't cause symptoms or cause health problems. In many cases, brain aneurysms are found during tests for other conditions.

However, a ruptured aneurysm quickly becomes life-threatening and requires medical treatment right away.

If a brain aneurysm hasn't ruptured, treatment may be appropriate in some cases. Treatment of an unruptured brain aneurysm may prevent a rupture in the future. Talk with your health care provider to make sure you understand the best options for your specific needs.

Brain aneurysm

An aneurysm is a ballooning at a weak spot in an artery wall. An aneurysm's walls can be thin enough to rupture. The illustration shows an individual with an unruptured aneurysm. The inset shows what happens when the aneurysm ruptures.


Ruptured aneurysm

A sudden, severe headache is the key symptom of a ruptured aneurysm. This headache is often described by people as the worst headache they've ever experienced.

In addition to a severe headache, symptoms of a ruptured aneurysm can include:

'Leaking' aneurysm

In some cases, an aneurysm may leak a slight amount of blood. When this happens, a more severe rupture often follows. Leaks may happen days or weeks before a rupture.

Leaking brain aneurysm symptoms may include:

Unruptured aneurysm

An unruptured brain aneurysm may not have any symptoms, especially if it's small. However, a larger unruptured aneurysm may press on brain tissues and nerves.

Symptoms of an unruptured brain aneurysm may include:

When to see a doctor

Seek immediate medical attention if you develop a:

If you're with someone who complains of a sudden, severe headache or who loses consciousness or has a seizure, call 911 or your local emergency number.


Brain aneurysms are caused by thinning artery walls. Aneurysms often form at forks or branches in arteries because those areas of the vessels are weaker. Although aneurysms can appear anywhere in the brain, they're most common in arteries at the base of the brain.

Risk factors

Several factors can contribute to weakness in an artery wall. These factors may increase the risk of a brain aneurysm or aneurysm rupture.

Some of these risk factors develop over time. But some conditions present at birth can increase the risk of developing a brain aneurysm.

Risk factors include:

Some types of aneurysms may occur after a head injury or from certain blood infections.

Risk factors for a ruptured aneurysm

There are some factors that make it more likely an aneurysm will rupture. They include:


When a brain aneurysm ruptures, the bleeding usually lasts only a few seconds. However, the blood can cause direct damage to surrounding cells and can kill brain cells. It also increases pressure inside the skull.

If the pressure becomes too high, it may disrupt the blood and oxygen supply to the brain. Loss of consciousness or even death may occur.

Complications that can develop after the rupture of an aneurysm include:


A sudden, severe headache or other symptoms that could be related to a ruptured aneurysm require testing. Tests can determine whether you've had bleeding into the space between your brain and surrounding tissues. This type of bleeding is known as subarachnoid hemorrhage. The tests also can determine if you've had another type of stroke.

You also may be given tests if you show symptoms of an unruptured brain aneurysm. These symptoms may include pain behind the eye, changes in vision or double vision.

Screening tests and procedures used to diagnose and detect brain aneurysms include:

Screening for brain aneurysms

The use of imaging tests to screen for unruptured brain aneurysms is generally not recommended unless you're at high risk. Talk to your health care provider about the potential benefit of a screening test if you have:

Most aneurysms don't rupture. And for many people, an unruptured aneurysm never causes symptoms. But if the aneurysm ruptures, several factors may affect the outcome, which is known as the prognosis. They include:

About 25% of people who experience a ruptured aneurysm die within 24 hours. Another 25% have complications that lead to death within six months.



There are two common treatment options for repairing a ruptured brain aneurysm. In some cases, these procedures may be considered to treat an unruptured aneurysm. However, the known risks may outweigh the potential benefits for people with some unruptured aneurysms.

Flow diversion

Flow diversion is a newer endovascular treatment option for treatment of a brain aneurysm. The procedure involves placing a stent in the blood vessel to divert blood flow away from the aneurysm. The stent that's placed is called a flow diverter.

With less blood flow going to the aneurysm, there's less risk of rupture. It also allows the body to heal. The stent prompts the body to grow new cells that seal the aneurysm.

Flow diversion may be particularly useful in larger aneurysms that can't be treated with other options.

A neurosurgeon or interventional neuroradiologist will likely work with your neurologist to recommend treatment. Treatment is based on the size, location and overall appearance of the brain aneurysm. They also may consider factors such as your ability to undergo a procedure.

Other treatments for ruptured aneurysms

Other methods for treating ruptured brain aneurysms are aimed at relieving symptoms and managing complications.

Treating unruptured brain aneurysms

A surgical clip, an endovascular coil or a flow diverter can be used to seal off an unruptured brain aneurysm. This can help prevent a future rupture. However, the risk of rupture is extremely low in some unruptured aneurysms. In these cases, the known risks of the procedures may outweigh the potential benefits.

A neurologist working with a neurosurgeon or interventional neuroradiologist can help you determine whether surgical or endovascular treatment is appropriate for you.

Factors to consider in making treatment recommendations include:

If you have high blood pressure, talk to your health care provider about medicine to manage the condition. If you have a brain aneurysm, proper control of blood pressure may lower the risk of rupture.

In addition, if you smoke cigarettes, talk with your care provider about strategies to stop smoking. Cigarette smoking is a risk factor for formation, growth and rupture of the aneurysm.

Lifestyle and home remedies

Lifestyle changes to lower your risk

If you have an unruptured brain aneurysm, you may lower the risk of rupture by making these lifestyle changes:

Coping and support

The Brain Aneurysm Foundation offers information on connecting with support groups in many states and in other countries, including the Mayo Clinic Brain Aneurysm Support Group.

Preparing for an appointment

Brain aneurysms are often detected after they've ruptured and become medical emergencies. However, a brain aneurysm may be detected when you've undergone head-imaging tests for another condition.

If such test results indicate you have a brain aneurysm, you'll need to discuss the results with a specialist in brain and nervous system disorders. These specialists include neurologists, neurosurgeons and neuroradiologists.

What you can do

To make the best use of your time with your health care provider, you may want to prepare a list of questions, such as:

What to expect from your doctor

Your neurologist, neurosurgeon or neuroradiologist may ask you the following questions to help determine the best course of action:

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