Brain Aneurysm

Medically Reviewed By William C. Lloyd III, MD, FACS

What is a brain aneurysm?

A brain aneurysm is a bulge in an artery in the brain. It develops when an area in the muscular layer of the vessel weakens. This allows the artery wall to balloon or bubble outward. Most brain aneurysms occur at the base of the brain. Aneurysmal bleeding often collects within an area called the subarachnoid space. Aneurysms are dangerous because they can burst and bleed—or hemorrhage—into the brain. The skull is a closed compartment, so any new bleeding quickly creates dangerous pressure within the brain tissue. When an aneurysm bleeds into the subarachnoid space, it is called subarachnoid hemorrhage. A brain aneurysm may also be called a cerebral aneurysm or an intracranial aneurysm.

Brain aneurysms can range in size from about 1/8 inch in diameter to over 1 inch. People may not even know they have small aneurysms. Doctors usually find these aneurysms during imaging exams for other reasons. Large aneurysms can cause symptoms, such as vision problems and pain. Very large aneurysms are called giant aneurysms. They pose an enormous risk to health and well-being because they are difficult to treat.

Up to 6% of Americans have a brain aneurysm or will develop one during their lifetime. Most will not have symptoms or problems. However, about 3% of people with a brain aneurysm will suffer a brain bleed. This represents about 30,000 people per year. Brain aneurysms become more common with age. They are also more common in people with certain medical conditions and other risk factors.

Not all brain aneurysms require treatment. When treatment is necessary, there are a few surgical techniques doctor can use. Without treatment, some brain aneurysms can rupture. This is a medical emergency because the mortality rate is very high. Nearly half of people with a ruptured brain aneurysm do not survive. When people do survive, up to 35% have moderate to severe brain damage as a result.

Seek immediate medical care (call 911) if you or someone you are with have the following symptoms of a ruptured brain aneurysm:

What are the symptoms of a brain aneurysm?

Most brain aneurysms do not cause symptoms. Symptoms and signs of aneurysm can develop if it grows larger or ruptures.

Common symptoms of an unruptured aneurysm

Unruptured aneurysms can put pressure on nerves or brain tissue. A brain aneurysm causes symptoms as it grows and puts more pressure on these tissues. The most common symptoms of an unruptured aneurysm are:

Serious symptoms that might indicate a life-threatening condition

In some cases, brain aneurysms can rupture and be life threatening. Seek immediate medical care (call 911) if you, or someone you are with, have any of these life-threatening symptoms, including:

  • Loss of consciousness, which can range from a brief episode of drowsiness to coma

  • Nausea and vomiting

  • Paralysis, trouble speaking, or trouble understanding speech

  • Severe headache or seizures

  • Stiff neck

  • Vision problems including double vision, sensitivity to light, and dilated pupils

What causes a brain aneurysm?

Brain aneurysms develop when an area in an artery wall weakens and thins. This allows the area to stretch and bulge outward. The more it stretches, the more it weakens and risks rupturing.

Brain aneurysms usually develop where arteries branch. These branch points tend to be weak. The constant pressure of blood pumping past these branch points can eventually result in an aneurysm in people who are at risk of developing one. A common name for this type of aneurysm is a berry aneurysm because it resembles a berry on a Y-shaped branch.

What are the risk factors for a brain aneurysm?

Several factors increase the risk of developing a brain aneurysm. However, not all people with risk factors will develop a brain aneurysm. Risk factors include:

  • Age older than 40 years

  • AVMs (arteriovenous malformations)

  • Certain medical conditions including high blood pressure, atherosclerosis, diabetes, and polycystic kidney disease

  • Family history of brain aneurysm in a parent, sibling or child

  • Female gender

  • Genetic disorders that can make blood vessel walls weaker than normal

  • Lifestyle choices including excessive alcohol use, tobacco use, and illicit drug use

Reducing your risk of a brain aneurysm

Reducing your risk of a brain aneurysm relies on changing risk factors that are under your control. You may be able to lower your risk of a brain aneurysm by:

  • Limiting alcohol use to 1 to 2 drinks per day for men and 1 drink per day for women

  • Not using illicit drugs and getting help for addictions

  • Stopping smoking and other tobacco use

  • Treating and controlling chronic medical conditions, especially high blood pressure

Unfortunately, several brain aneurysm risk factors are beyond your control. Talk with your doctor about your risk of brain aneurysm. Find out if screening is an option for you. Also, have a conversation with your doctor if you are struggling to change lifestyle habits, such as smoking. Help is available.

How is a brain aneurysm treated?

Some brain aneurysms do not require treatment. It depends on the aneurysm’s size, type and location. Doctors often recommend monitoring small aneurysms that aren’t causing problems and aren’t at high risk of rupturing. This involves using cerebral angiography to periodically check the aneurysm for growth.

Treatment may be necessary if a brain aneurysm is causing symptoms or if it is large, growing rapidly, leaking blood into the layers of the artery wall, or ruptured. Treatment consists of some type of surgery to repair the aneurysm.

Treatment options for intracranial aneurysms include:

  • Microvascular clipping is open brain surgery to place a small metal clip around the base of the aneurysm. This seals off the aneurysm so it does not grow larger.

  • Endovascular coil embolization is a catheter-based procedure to insert tiny coils inside the aneurysm. This causes the aneurysm to clot off.

  • Endovascular flow diversion is also a catheter-based procedure. It involves inserting a stent-like device to reduce blood flow into the aneurysm, which stabilizes the aneurysm.

When a brain aneurysm ruptures, it is a medical emergency. It can bleed into the brain, causing a hemorrhagic stroke. It can also cause a subarachnoid hemorrhage if it bleeds into the space around the brain.

What are the potential complications of a brain aneurysm?

The main complication of a brain aneurysm is rupture with bleeding into the brain or around the brain. Both of these situations can lead to serious and permanent brain damage or death. When a brain aneurysm ruptures, about 40% of people will not survive it. For those who do survive, about 20 to 35% will have moderate to severe brain damage. This brain damage is not reversible. However, rehabilitation can improve a person’s ability to function.

Rehabilitation can include physical therapy, occupational therapy, and speech and swallowing therapy. The goal is to regain as much function as possible and learn to cope with disabilities.

Was this helpful?
  1. Cerebral Aneurysm. American Association of Neurological Surgeons.
  2. Cerebral Aneurysms Fact Sheet. National Institute of Neurological Disorders and Stroke.
  3. Fact Sheets - Alcohol Use and Your Health. Centers for Disease Control and Prevention.
  4. Vega C, Kwoon JV, Lavine SD. Intracranial Aneurysms: Current Evidence and Clinical Practice. Am Fam Physician. 2002 Aug 15;66(4):601-609.
  5. What You Should Know About Cerebral Aneurysms. American Stroke Association.
Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Aug 30
View All Brain Aneurysm Repair Articles
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.