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Intracranial Aneurysms

Medically reviewed by Last updated on Feb 6, 2023.

What are Intracranial Aneurysms?

Harvard Health Publishing

Arteries are tunnels that blood travels through to get from the heart to various parts of the body. An aneurysm is a bulge in an artery, similar to the bulge that appears at a weak spot of a hose, where the water pressure pushes out to create a bubble. Like the hose bubble, the area of an artery where an aneurysm appears is weak and has the potential to burst.

Aneurysms most frequently occur in the arteries that bring blood to the brain. Brain aneurysms are also known as intracranial aneurysms or berry aneurysms (because most of the time they look like little round berries). They occur in up to 6% of people. In general, most brain aneurysms are small, rarely cause symptoms and have a very low risk of rupture.

Women are more likely than men to develop brain aneurysms. A family history of aneurysm increases your risk of having one, as does being older than 50, currently smoking cigarettes, having high blood pressure, and using cocaine. About 20% of people with one brain aneurysm will have at least one more.

A number of inherited conditions also increase the chance of having an aneurysm, including:

  • Polycystic kidney disease
  • Ehlers-Danlos syndrome
  • Neurofibromatosis
  • Pseudoxanthoma elasticum
  • Hereditary hemorrhagic telangiectasia
  • Alpha1-antitrypsin deficiency
  • Coarctation of the aorta
  • Fibromuscular dysplasia
  • Pheochromocytoma
  • Klinefelter's syndrome
  • Tuberous sclerosis
  • Noonan's syndrome
  • Alpha-glucosidase deficiency

If a brain aneurysm does rupture, the consequences can be life threatening. The risk of rupture is higher with larger aneurysms. Those that are one-fourth of an inch (10 mm) or smaller are generally at low risk of rupture.


Most brain aneurysms don’t cause symptoms until they burst. When an aneurysm ruptures, it often causes bleeding in the brain, which is a medical emergency. Bleeding in the brain usually leads to a very severe headache (often described as "the worst headache of my life"). Brief loss of consciousness, nausea and vomiting, changes in vision, or neck stiffness may accompany the headache. If you experience these symptoms, call 911 or get to the emergency room as soon as possible.

A very large aneurysm may cause symptoms before it bursts, including: pain above and behind the eye; numbness, weakness, or paralysis on one side of the face; dilated pupils; and vision changes. 


There are no strict guidelines for who should be tested for the presence of a brain aneurysm. Clearly, any person who has had bleeding into the brain would be tested. Other reasons to proceed with testing include:

  • evaluation of a new, severe headache that is very different from prior headaches, especially if there is neck stiffness or confusion
  • having certain genetic diseases, such as polycystic kidney disease
  • having two or more relatives with a history of ruptured aneurysms.

Most often, a person is diagnosed with a brain aneurysm after it bursts and starts causing symptoms. Occasionally an aneurysm will be found when a test is done for a different purpose. The following procedures may be used to look for an aneurysm:

  • Magnetic resonance angiography. In this test, dye is also injected through a catheter. Then a magnetic resonance imaging (MRI) scan is done. The MRI takes many pictures of the arteries from different points of view, showing the doctor different "slices" or cross sections of the area being viewed. MRI is now the most frequently used test to diagnose and locate brain aneurysms.  
  • Cerebral angiography (also called intra-arterial digital subtraction angiography). In this test, a catheter is inserted into an artery in your leg or arm and snaked up to your brain. Contrast dye that highlights the arteries leading to the brain is injected through the catheter, and then x-ray images are taken. Cerebral angiography can show doctors exactly where an aneurysm is and how big it is.
  • Computed tomographic (CT). This machine takes multiple x-rays from different angles. It is often the first test done to evaluate a new severe headache to look for blood in or around the brain. It is not as accurate as cerebral angiography or MRI to diagnose the presence and location of an aneurysm. Sometimes contrast dye is used for CT scans.
  • Transcranial Doppler ultrasonography. For an ultrasound, a transducer, which looks like a microphone, is moved across the outside of the area of study. The transducer sends sound waves into your body and picks up the echoes of the sound waves as they bounce off internal organs and tissue. A computer transforms these echoes into an image that is displayed on a monitor.

Expected Duration

Once a brain aneurysm forms, it stays for life unless it is surgically removed or bursts.


Scientists haven’t figured out how to prevent brain aneurysms. However, you can reduce your risk of developing aneurysms by never using tobacco and keeping blood pressure in the normal range.

If you know that you have a brain aneurysm, you want to minimize the risk that the aneurysm will burst by

  • carefully controlling high blood pressure
  • avoiding tobacco
  • not using cocaine or other stimulant drugs
  • drinking alcohol in moderation, if you drink 


If an aneurysm is found before it bursts, a neurosurgeon will help you decide whether you should have it treated. Your overall health, the size of the aneurysm, and its location are all important factors in this decision. If an aneurysm has burst, treatment is definitely necessary.

The two surgical treatments for aneurysms are called microvascular clipping and occlusion. For both procedures, the patient is put under general anesthesia and a neurosurgeon temporarily removes part of the skull bone to get access to the aneurysm. In microvascular clipping, the surgeon finds the blood vessel that feeds the aneurysm and places a small, metal, clothespin-like clip on the aneurysm’s neck. That way, the aneurysm cannot get blood. The clip stays inside the patient’s brain, and the surgeon replaces the skull bone. In most cases, aneurysms do not return after microvascular clipping.

In an occlusion, the surgeon clamps off (occludes) the entire artery that leads to the aneurysm. This procedure is often performed when the aneurysm has damaged the artery. Sometimes the surgeon also does a bypass, where a small blood vessel is attached to the brain artery, rerouting the flow of blood away from the section of the damaged artery.

There is an alternative to surgery, called endovascular coiling (or coil embolization). For this procedure, the doctor inserts a catheter into an artery, usually in the groin. He or she watches on an angiogram monitor as the catheter snakes through the body to the site of the aneurysm. Coils made of platinum wire are passed through the catheter and directed into the aneurysm. The coils fill the bulge in the artery and cause a blood clot to form. This blocks blood flow into the aneurysm. There is little if any pressure inside the bulge, preventing the aneurysm from getting any larger. The advantage of this procedure is that it is not as invasive as surgery.

A neurosurgeon’s recommendation for surgery or coiling depends on the size and location of the aneurysm, whether the aneurysm has already burst, and the overall health status of the patient.

When To Call a Professional

If you experience a very severe, out-of-the-ordinary headache, call 911 or get to an emergency room. An aneurysm may have burst in your brain. Brief loss of consciousness, nausea and vomiting, changes in vision, or neck stiffness may accompany the headache.  


An unruptured aneurysm may never cause problems or symptoms. A burst aneurysm, however, may be fatal or cause serious health problems, such as:

  • bleeding in the space between the skull bone and the brain (subarachnoid hemorrhage)
  • bleeding into the brain (hemorrhagic stroke)
  • swelling of the brain causing high pressure within the skull (hydrocephalus)
  • vasospasm, which is when other blood vessels in the brain contract and limit blood flow to vital areas of the brain. Vasospasm can cause stroke and is the leading cause of disability and death following a burst aneurysm.
  • coma
  • short-term or permanent brain damage.

After an aneurysm bursts, if it is not treated, it may burst again and rebleed into the brain. Additional aneurysms, if present, also have a greater risk of rupturing in the future. 

How a person’s body reacts to a burst aneurysm depends on the age and general health of the person, other neurological conditions he or she has, the location of the aneurysm, the extent of bleeding (and rebleeding), and how long passed between the time of the rupture and treatment. 

About 40% of people whose aneurysms rupture do not survive the first 24 hours; up to another 25% die from complications within six months. Recovery from treatment may take weeks to months. Generally, people who are treated for an unruptured aneurysm recover more quickly than people whose aneurysms have burst. 

Additional Info

National Institute of Neurological Disorders and Stroke


Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.