Brain aneurysm

At a glance

  • A brain aneurysm is a bulge in a blood vessel in the brain.
  • It often goes unnoticed.
  • But in some people it might be more likely to rupture (burst) and cause life-threatening bleeding.
  • To prevent this from happening, aneurysms can be treated with surgery.


Photo of an elderly woman sitting on a bench

A brain aneurysm is a berry-shaped bulge in an artery in or near the brain. Normally, arteries are strong and elastic, like hoses. An aneurysm develops when part of an artery wall becomes weak, stretches outward, and forms a bulge.

Aneurysms can develop in various parts in the body, for instance in the largest artery in the belly (abdominal aortic aneurysm) or an artery in the head (brain aneurysm). Brain aneurysms often form at points where the arteries that supply the brain with blood split and branch off.

Many people with a brain aneurysm will never know that they have one. But others experience symptoms – or their aneurysm is more likely to eventually rupture (burst) and cause life-threatening bleeding in the brain. Treatment can help to prevent such ruptures and relieve the symptoms.

Illustration: Brain aneurysms are often located in the middle of the brain.


Aneurysms often cause no symptoms at all. These aneurysms are called “asymptomatic.”

Symptoms can arise if an aneurysm is particularly large or located in certain parts of the brain. Such aneurysms can press against brain tissue or nerves carrying information away from the brain – for instance on the optic (eye) nerve. This can cause symptoms such as

  • headaches,
  • vision problems, and
  • eye muscle paralysis.

Less common symptoms include seizures and sensory, speech, or hearing problems.


Brain aneurysms typically develop over time because the affected part of the vessel wall becomes less elastic. This can happen as a result of

  • the normal aging process,
  • increased pressure on the wall of the blood vessel in people with high blood pressure, or
  • damage to the blood vessel due to smoking or inflammation.

Rarely, aneurysms are caused by genetic diseases such as Ehlers-Danlos syndrome, which leads to weak connective tissue and – as a result – weak blood vessel walls.

Risk factors

People with high blood pressure and people who smoke are more likely to develop brain aneurysms.

Women are at a higher risk of brain aneurysm than men – as are people who have a parent or sibling with a brain aneurysm. The risk also increases with age.

The same factors make the aneurysm more likely to eventually rupture. But this risk depends on things like the exact location and size of the aneurysm.

Prevalence and outlook

About 3 in 100 adults have a brain aneurysm. Some people have several brain aneurysms.

Most brain aneurysms don’t change, never cause any symptoms, and therefore remain unnoticed. Even if an aneurysm is discovered by chance, it doesn’t necessarily need to be treated. But knowing that you have an aneurysm can be worrying.

A brain aneurysm that grows over time can cause symptoms. Larger aneurysms are also more likely to rupture.


Aneurysms may rupture (burst). They are then called ruptured aneurysms. Ruptures result in bleeding in the brain – more specifically known as subarachnoid hemorrhage. This is a life-threatening emergency that needs to be treated as quickly as possible. Bleeding increases the pressure within the skull and damages the delicate brain tissue. A sudden, extremely severe headache is a typical symptom. Many patients say that the headache is the worst they have ever experienced. The pain often starts at the back of the head and neck. It then spreads across the entire head and down into the back.

Other typical symptoms of a bleeding aneurysm include the following:

  • Stiff neck
  • Nausea, vomiting
  • Confusion or loss of consciousness

Bleeding is the most common complication of aneurysms. The likelihood of brain aneurysms rupturing and causing bleeding depends on the above-mentioned risk factors and especially on the size of the aneurysm.

A rare further complication of brain aneurysms is the blockage of an artery in the brain: Blood clots often form inside aneurysms, but they generally don’t cause any problems. In rare cases, though, one of these blood clots moves back into the brain artery. The clot may then be carried in the bloodstream to a smaller branch of the artery, which it blocks (embolism), causing a stroke.


Many people find out by chance that they have a brain aneurysm during an examination for another medical problem.

If someone has symptoms such as headaches or vision problems, doctors may recommend doing a scan: (MRI) or (CT). Aneurysms are particularly easy to see using a technique known as digital subtraction angiography (DSA), where an x-ray is taken with and without injecting a contrast medium. A computer then calculates an image that only shows blood vessels – other structures, such as bones, can no longer be seen.

The , check-up scans, and the fear of complications can be distressing. So if someone has an aneurysm that would never have caused any symptoms or ruptured, and that aneurysm is discovered by chance, the chance discovery (“incidental ”) may cause unnecessary distress. This is known as “overdiagnosis.”


If the aneurysm isn’t causing any symptoms and isn’t particularly likely to rupture, treatment isn’t always needed. But it's often difficult to decide whether or not to have treatment because many factors play a role – such as the position of the aneurysm and your general health.

It is always worth trying to minimize the risk factors for complications – for example, by treating high blood pressure and by not smoking.

If the aneurysm is left untreated, an MRI or CT scan is done every one to three years. This scan shows whether the aneurysm has changed and the risk of bleeding in the brain has increased.

For people who have symptoms or a higher risk of complications, two main treatment options are considered:

  • Surgery ("neurosurgical clipping"): The aneurysm is clamped off with a small metal clip.
  • Endovascular coiling: Tiny coils are typically pushed through the blood vessel to the brain aneurysm. As a result, the blood in the aneurysm clots and the aneurysm is closed off.

Both methods can permanently stop blood from flowing into the aneurysm. Although they prevent the aneurysm from bursting, they are themselves associated with risks. To find out which option would be most suitable, it can help to have an in-depth talk with a doctors specializing in the treatment of brain aneurysms – a neurologist, neurosurgeon or neuroradiologist.

Backes D, Rinkel GJ, Laban KG et al. Patient- and Aneurysm-Specific Risk Factors for Intracranial Aneurysm Growth: A Systematic Review and Meta-Analysis. Stroke 2016; 47(4): 951-957.

Balik V, Yamada Y, Talari S et al. State-of-Art Surgical Treatment of Dissecting Anterior Circulation Intracranial Aneurysms. J Neurol Surg A Cent Eur Neurosurg 2017; 78(1): 67-77.

Brinjikji W, Zhu YQ, Lanzino G et al. Risk Factors for Growth of Intracranial Aneurysms: A Systematic Review and Meta-Analysis. AJNR Am J Neuroradiol 2016; 37(4): 615-620.

Deutsche Gesellschaft für Neurologie (DGN). Unrupturierte intrakranielle Aneurysmen (S1-Leitlinie). AWMF-Registernr.: 030-030. 2012.

Hacke W. Neurologie. Berlin: Springer; 2016.

Kleinloog R, de Mul N, Verweij BH et al. Risk Factors for Intracranial Aneurysm Rupture: A Systematic Review. Neurosurgery 2018; 82(4): 431-440.

Malhotra A, Wu X, Forman HP et al. Growth and Rupture Risk of Small Unruptured Intracranial Aneurysms: A Systematic Review. Ann Intern Med 2017; 167(1): 26-33.

Steiner T, Juvela S, Unterberg A et al. European Stroke Organization guidelines for the management of intracranial aneurysms and subarachnoid haemorrhage. Cerebrovasc Dis 2013; 35(2): 93-112.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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Updated on September 29, 2021

Next planned update: 2024


Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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