What is a cerebral aneurysm?
A cerebral aneurysm (or brain aneurysm) is a weak spot on a blood vessel in the brain that fills with blood and bulges out, pressing on the brain and nerves.
An aneurysm can burst open (rupture), causing bleeding in or around the brain. This is called a hemorrhage. A ruptured aneurysm is a medical emergency that can cause a stroke, brain damage, coma, and even death.
But many aneurysms—especially small ones—never rupture or cause symptoms.
Doctors usually discover aneurysms that haven’t ruptured during brain scans used for other reasons. Aneurysms can happen anywhere in the brain, but most form in the major arteries along the bottom of the brain.
A doctor may treat an aneurysm with surgery, medicines, or treatments to block off or repair it. Sometimes, they decide the best immediate option is to watch the aneurysm over time.
Types of cerebral aneurysms
There are three types of cerebral aneurysms:
- Saccular aneurysm: A round, blood-filled bulge that forms on a blood vessel at the bottom of the brain. It’s the most common type of aneurysm and happens mostly in adults. It’s also called a “berry aneurysm.”
- Fusiform aneurysm: An aneurysm that bulges out all the way around a vessel instead of just a small bulge on one side.
- Mycotic aneurysm: An aneurysm that develops when an infection weakens a blood vessel in the brain.
Aneurysms are also named by size:
- Small: An aneurysm less than 10 millimeters (less than half an inch) around, or about the size of a large pencil eraser.
- Large: An aneurysm 11 to 25 millimeters (half an inch to 1 inch) in diameter, or about the width of a dime.
- Giant: An aneurysm larger than 25 millimeters (1 inch) around (larger than the width of a quarter).
Aneurysms can also be described as unruptured, ruptured, or leaking, depending on whether or not they burst or caused bleeding in the brain.
Unruptured aneurysm
Most people don’t have symptoms from an aneurysm until it becomes very large or ruptures suddenly. Large aneurysms that are getting bigger but haven’t yet ruptured may press on the brain tissue and nearby nerves. This pressure may cause:
- Pain above and behind the eye
- Numbness
- Weakness
- Paralysis (inability to move muscles) on one side of the face
- One pupil that is larger than the other
- Changes in eyesight, such as seeing double
Ruptured aneurysm
When an aneurysm ruptures (bursts), it causes a sudden, severe headache. Some people describe it as the worst headache of their life. A rupture may also cause:
A ruptured aneurysm is a medical emergency that can be fatal or cause serious health problems, including:
- Bleeding in or around the brain (hemorrhagic stroke)
- More bleeding if the aneurysm ruptures again
- Changes in salt (sodium) levels in the blood
- Spinal fluid buildup in the brain (hydrocephalus)
- Reduced blood flow to the brain (vasospasm)
- Seizures
After an aneurysm ruptures, some people develop delayed cerebral ischemia (DCI), a condition in which the brain doesn’t get enough blood. DCI can happen a few days or up to two weeks after bleeding and may cause more brain injury. People with DCI can develop stroke-like symptoms.
Researchers continue to learn more about DCI to better understand its causes and find ways to prevent it.
Leaking aneurysm
In rare cases, an aneurysm leaks a small amount of blood into the brain, leading to a “warning” headache that can happen days or weeks before a major rupture.
If you experience a sudden, severe headache, especially with any other symptoms, call 911 for immediate medical help.
Who is more likely to get a cerebral aneurysm?
Cerebral aneurysms can happen to anyone at any age. Sometimes, babies are born with an aneurysm, usually because part of a blood vessel wall didn’t form properly during pregnancy.
Risk factors for developing an aneurysm
A risk factor is a condition or behavior, like high blood pressure or smoking, that increases the likelihood of having a certain health problem compared to those who don't have the risk factor. Having a risk factor doesn't mean a person will have an aneurysm, and not having a risk factor doesn't mean they won’t.
Cerebral aneurysms are linked to many risk factors, including:
- Being female: Aneurysms are more common in women than in men. This risk also seems to increase after menopause.
- Family history: Having a parent, sibling, or child with a history of brain aneurysms can increase risk.
- Age: Aneurysms are most common in adults between ages 30 and 60.
- Several health conditions may damage, weaken, or put extra stress on blood vessels and increase the risk of an aneurysm, including high blood pressure, diabetes (fusiform aneurysms), high cholesterol, polycystic kidney disease, and having a connective tissue disorder.
- Certain lifestyle factors can increase the risk of an aneurysm, including cigarette smoking and using substances (cocaine or amphetamines).
- Less common risk factors include blood vessel infections caused by injecting drugs, head trauma and injuries, and brain tumors.
Risk factors for a brain aneurysm rupture
Not all cerebral aneurysms rupture. In addition to high blood pressure and smoking, certain risk factors affect the risk of rupture:
- Growth: Aneurysms that get bigger, even if they start small, are most likely to rupture.
- Size: In general, bigger aneurysms are more likely to rupture than smaller ones.
- Previous ruptures: If a person already had a rupture or “warning” bleed, they’re more likely to have another one.
- Location: Aneurysms in certain parts of the brain, such as toward the back of the brain, are more likely to rupture than others.
How are cerebral aneurysms diagnosed and treated?
Diagnosing cerebral aneurysms
Many cerebral aneurysms don’t cause symptoms and are only found after they rupture or when a doctor orders a brain scan for another reason.
Doctors use several tests to diagnose cerebral aneurysms and help determine the best treatment. These include:
- Computed tomography (CT) scans: Can quickly show whether there is bleeding in or around the brain. A special type of CT scan can help doctors find an aneurysm.
- Cerebral angiography: Gives a doctor very detailed images of blood vessels in the brain and may be used to confirm a diagnosis or to help plan treatment.
- Magnetic resonance imaging (MRI) scans: Creates detailed images of blood vessels in the brain and can help doctors find aneurysms, especially those that have not ruptured.
- Spinal fluid analysis: Collects cerebrospinal fluid (CSF), which cushions and protects the brain and spinal cord, to help find bleeding in or around the brain. A doctor usually collects the fluid by performing a spinal tap (also called a lumbar puncture). If blood is found, more tests may be needed to determine the cause.
Learn more about neurological diagnostic tests and procedures.
Treating cerebral aneurysms
A doctor may recommend monitoring the growth of very small, unruptured aneurysms if they’re unlikely to rupture. People with unruptured aneurysms can lower their risk of an aneurysm rupturing by managing conditions such as high blood pressure and avoiding smoking and using substances, such as cocaine.
Not all cerebral aneurysms need treatment. A doctor will consider the chance of rupture—along with a person’s age, health, and family history—when considering whether or not to treat an aneurysm.
Doctors treat aneurysms with surgery or with endovascular treatment, which uses a thin tube (catheter) to reach and treat the aneurysm from inside a blood vessel. Other therapies can help manage symptoms and prevent damage from both unruptured and ruptured aneurysms.
Surgery
Like any brain surgery, surgery for a ruptured cerebral aneurysm carries risks, such as damage to other blood vessels, stroke, infection, or bleeding.
Microvascular clipping is the main type of brain surgery that cuts off blood flow to an aneurysm. A surgeon places a tiny, metal, clothespin-like clip on the opening of the aneurysm to stop blood from flowing into it. When the aneurysm is clipped, it usually doesn’t come back.
Endovascular treatments
Doctors can treat some aneurysms by reaching them through blood vessels, without brain surgery. Two common types are:
- Coils: A doctor guides a thin tube through a blood vessel (usually in the groin) to an aneurysm and fills the aneurysm with tiny coils. These coils help block blood flow into the aneurysm and help prevent it from rupturing.
- Flow diversion: A doctor places a small mesh tube called a stent in a blood vessel (usually in the groin) to redirect blood flow away from an aneurysm. This treatment is often used for large aneurysms.
Other treatments
Other treatments for a ruptured aneurysm aim to manage symptoms and prevent or treat problems caused by the bleeding. These treatments include:
- Calcium channel-blockers, which are medicines that keep blood flowing to the brain after an aneurysm bursts open.
- A shunt (a thin tube) inserted into the brain, which can re-drain built-up spinal fluid away from the brain.
- Physical, speech, and occupational therapy, which can help people regain skills affected by an aneurysm rupture and adapt to any ongoing challenges.
What are the latest updates on cerebral aneurysms?
The National Institutes of Health (NIH), which includes NINDS, is the leading federal funder of research on the brain and nervous system, including research on cerebral aneurysms. NIH supports new and innovative research to better understand, diagnose, and treat cerebral aneurysms.
NIH-supported research projects cover a wide range of topics on cerebral aneurysms. This includes research on:
- How gene changes affect aneurysm formation
- Using computer models to predict whether and when aneurysms grow and rupture
- Finding safer and more effective ways to treat aneurysms
Genetics
Researchers are looking for genes that may increase a person’s risk for having an aneurysm. They’re also determining how gene changes can affect the formation of blood vessels and aneurysms.
Aneurysms can happen in blood vessels throughout the body, not just in the brain. Researchers have found a genetic change that increases the risk of aneurysms in both the brain and the aorta, a very long blood vessel in the body that begins in the heart.
Diagnostic tools
Many studies supported by NIH focus on improving the ways to predict, detect, and treat aneurysms, including:
- Developing computer models to predict whether an unruptured aneurysm is likely to get bigger. This could help doctors decide whether treatment is needed and how closely to watch an aneurysm that has not yet ruptured.
- Studying the common features of ruptured aneurysms to help doctors identify which aneurysms are most likely to rupture.
- Developing a new non-surgical way to monitor blood flow and better understand brain injury and stroke after bleeding around the brain caused by a ruptured aneurysm.
- Using brain scans to predict which aneurysms are most likely to rupture. This could help doctors decide when treatment is needed before an aneurysm ruptures.
- Finding ways to predict who will develop DCI, a condition in which part of the brain doesn’t get enough blood.
Aneurysm risk in women
Aneurysms and bleeding around the brain are more common in women after menopause than they are in men. Some research suggests that estrogen or hormone replacement therapy (HRT) may reduce the risk of bleeding around the brain in women after menopause. Because HRT can also increase some health risks, more research is needed to determine whether and when it might help reduce aneurysm risk in women.
Devices and medicines
Severe headaches are common after a brain aneurysm ruptures and are sometimes treated with opioids. NIH-funded researchers are studying whether a nerve-blocking treatment used for migraine could relieve this pain while reducing the need for opioids.
NIH research is trying to develop safe and effective treatments for people with aneurysms. This includes developing better devices for treating aneurysms, studying how blood flow affects whether treatments work, and testing medicines that may improve brain healing and prevent other health problems like stroke.
For more information on research about cerebral aneurysms, check NIH RePORTER, a searchable database of current and past research projects funded by NIH and other federal agencies. RePORTER also has links to publications and resources from these projects.
For research articles and summaries on cerebral aneurysms, search PubMed, which contains citations from medical journals and other sites.
How can I or my loved one improve care for people with cerebral aneurysms?
Consider participating in a clinical trial so clinicians and scientists can learn more about cerebral aneurysms and related disorders. Clinical research with human participants helps researchers learn more about a disorder and perhaps find better ways to safely detect, treat, or prevent disease.
All types of participants are needed—those who are healthy or may have an illness or disease—of all different ages, sexes, races, and ethnicities. This helps make sure that study results apply to as many people as possible, and that treatments will be safe and effective for everyone who will use them.
For information about participating in clinical research, visit the NINDS Clinical Trials site and NIH Clinical Research Trials and You. Learn about clinical trials currently looking for people with cerebral aneurysms at ClinicalTrials.gov, a searchable database of current and past clinical studies and research results.
Where can I find more information about cerebral aneurysms?
Information may be available from the following sources: