Brain aneurysm


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


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:

  • Nausea and vomiting
  • Stiff neck
  • Blurred or double vision
  • Sensitivity to light
  • Seizure
  • A drooping eyelid
  • Loss of consciousness
  • Confusion

'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:

  • A sudden, extremely severe headache that may last several days and up to two weeks.

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:

  • Pain above and behind one eye.
  • A dilated pupil.
  • A change in vision or double vision.
  • Numbness of one side of the face.

When to see a doctor

Seek immediate medical attention if you develop a:

  • Sudden, extremely severe headache

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:

  • Older age. Brain aneurysms can occur at any age. However, they're more common in adults between ages 30 and 60.
  • Being female. Brain aneurysms are more common in women than in men.
  • Cigarette smoking. Smoking is a risk factor for brain aneurysms to form and for brain aneurysms to rupture.
  • High blood pressure. This condition can weaken arteries. Aneurysms are more likely to form and to rupture in weakened arteries.
  • Drug use, particularly using cocaine. Drug use raises blood pressure. If illicit drugs are used intravenously, it can lead to an infection. An infection can cause a mycotic aneurysm.
  • Heavy alcohol use. This also can increase blood pressure.
  • Inherited connective tissue disorders, such as Ehlers-Danlos syndrome. These disorders weaken blood vessels.
  • Polycystic kidney disease. This inherited disorder results in fluid-filled sacs in the kidneys. It also may increase blood pressure.
  • A narrow aorta, known as coarctation of the aorta. The aorta is the large blood vessel that delivers oxygen-rich blood from the heart to the body.
  • Brain arteriovenous malformation, known as AVM. In this condition, arteries and veins in the brain are tangled. This affects blood flow.
  • A family history of brain aneurysm. Your risk is higher if you have family members who have had a brain aneurysm. This is particularly true if two or more first-degree relatives — such as a parent, brother, sister or child — has had a brain aneurysm. If you have a family history, you can ask your health care provider about getting screened for a brain aneurysm.

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:

  • Having a large aneurysm.
  • Having aneurysms in certain locations.
  • Smoking cigarettes.
  • Having untreated high blood pressure.


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:

  • Re-bleeding. An aneurysm that has ruptured or has leaked is at risk of bleeding again. Re-bleeding can cause further damage to brain cells.
  • Narrowed blood vessels in the brain. After a brain aneurysm ruptures, blood vessels in the brain may contract and narrow. This is known as vasospasm. Vasospasm can cause an ischemic stroke, in which there's limited blood flow to brain cells. This may cause additional cell damage and loss.
  • A buildup of fluid within the brain, known as hydrocephalus. Most often, a ruptured brain aneurysm occurs in the space between the brain and the thin tissues covering the brain. The blood can block the movement of fluid that surrounds the brain and spinal cord. As a result, an excess of fluid puts pressure on the brain and can damage tissues.
  • Change in sodium level. Bleeding in the brain can disrupt the balance of sodium in the blood. This may occur from damage to the hypothalamus, an area near the base of the brain. A drop in blood sodium levels can lead to swelling of brain cells and permanent damage.


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:

  • CT scan. This specialized X-ray is usually the first test used to detect bleeding in the brain or another type of stroke. The test produces images that are 2D slices of the brain.

    A CT angiogram can create more-detailed images of the arteries providing blood flow in the brain. The test involves injecting dye that makes it easier to observe blood flow. It also can detect the presence of an aneurysm.

  • Lumbar puncture, known as a spinal tap. If you've had a subarachnoid hemorrhage, there will most likely be red blood cells in the fluid surrounding your brain and spine. This fluid is called cerebrospinal fluid. If you have symptoms of a ruptured aneurysm but a CT scan doesn't show evidence of bleeding, a test of your cerebrospinal fluid can help make a diagnosis.

    The procedure to draw cerebrospinal fluid from your back with a needle is called a lumbar puncture.

  • MRI. This imaging test uses a magnetic field and radio waves to create detailed images of the brain, either 2D images or 3D images. The images can show if there's bleeding in the brain.

    A type of MRI that captures images of the arteries in detail is called MR angiography. This type of MRI can detect the size, shape and location of an unruptured aneurysm.

  • Cerebral angiogram. During this procedure, a thin, flexible tube called a catheter is used. The catheter is inserted into a large artery, usually in the groin or the wrist. The catheter threads past your heart to the arteries in your brain. A special dye injected into the catheter travels to arteries throughout your brain.

    A series of X-rays can then reveal details about the conditions of your arteries and detect an aneurysm. A cerebral angiogram — also called a cerebral arteriogram — is usually used when other diagnostic tests don't provide enough information.

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:

  • A family history of brain aneurysms. Particularly if two first-degree relatives — your parents, siblings or children — have had brain aneurysms.
  • A disorder that increases your risk of developing a brain aneurysm. These disorders include polycystic kidney disease, coarctation of the aorta or Ehlers-Danlos syndrome, among others.

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:

  • The person's age and health.
  • Whether the person has other conditions.
  • The size and location of the aneurysm.
  • How much bleeding occurred.
  • How much time passed before receiving medical care.

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.

  • Pain relievers, such as acetaminophen (Tylenol, others), may be used to treat headache pain.
  • Calcium channel blockers prevent calcium from entering cells of the blood vessel walls. These medicines may lessen the risk of having symptoms from the narrowing of blood vessels, known as vasospasm. Vasospasm may be a complication of a ruptured aneurysm.

    One of these medicines, nimodipine (Nymalize), has been shown to reduce the risk of delayed brain injury caused by insufficient blood flow. This can happen after subarachnoid hemorrhage from a ruptured aneurysm.

  • Medicines to open blood vessels. A drug can be given to dilate the blood vessels. This can be given through an IV in the arm or with a catheter directly into the arteries supplying the brain. This can help prevent a stroke by allowing the blood to flow freely. Blood vessels also can be expanded using medicines known as a vasodilators.
  • Angioplasty. This is a procedure to expand a narrowed blood vessel in the brain caused by vasospasm. The procedure also can help prevent a stroke.
  • Anti-seizure medicines may be used to treat seizures related to a ruptured aneurysm. The medicines typically aren't given if a seizure hasn't occurred.
  • Ventricular or lumbar draining catheters and shunt surgery can lessen pressure on the brain from excess cerebrospinal fluid. Fluid can build up after a ruptured aneurysm. A catheter may be placed in the spaces that are filled with fluid inside the brain. Or it can be placed in the area surrounding the brain and spinal cord. The catheter drains the excess fluid into an external bag.

    Sometimes a shunt system is placed. A shunt system is a flexible silicone rubber tube and a valve that creates a drainage channel. The drainage channels starts in the brain and ends in the abdominal cavity.

  • Rehabilitative therapy. Damage to the brain from a subarachnoid hemorrhage may result in the need for physical, speech and occupational therapy to relearn skills.

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:

  • The aneurysm size, location and overall appearance of the aneurysm.
  • Your age and general health.
  • Family history of ruptured aneurysm.
  • Conditions you were born with that increase the risk of a ruptured aneurysm.

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:

  • Don't smoke cigarettes. If you smoke, talk to your health care provider. Your provider can suggest strategies or a treatment program to help you quit.
  • Control your blood pressure if you have high blood pressure.
  • Eat a healthy diet and exercise. Changes in diet and exercise can help lower blood pressure. Talk to your health care provider about changes that are appropriate for you.
  • Don't use drugs such as cocaine, methamphetamine or others. If you do use these drugs and would like to quit, talk to your provider.

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 do you know about the size, location and overall appearance of the aneurysm?
  • Do the imaging test results provide evidence of how likely it is to rupture?
  • What treatment do you recommend at this time? What are the risks of treatment?
  • If I wait, how often will I need to have follow-up tests?
  • What steps can I take to lower the risk of an aneurysm rupturing?

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:

  • Do you smoke?
  • How much alcohol do you drink?
  • Do you use recreational drugs?
  • Are you being treated for high blood pressure?
  • Do you take your medicines as prescribed by your health care provider?
  • Is there a history of brain aneurysm or brain aneurysm rupture in your family?

Content From Mayo Clinic Updated: 03/06/2023
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