About the condition Brain aneurysm

What is a brain aneurysm?

A cerebral or brain aneurysm is a bulge or ballooning in an artery in the brain caused by weakness in the blood vessel wall.

Untreated brain aneurysms may have risk of rupture, resulting in what’s called hemorrhagic or cerebral stroke. The annual rate of rupture is approximately 8–10 per 100,000 people, or about 30,000 people in the United States.1,2

It is slightly more common in women than men, especially those who are in their late 40s to mid-50s. However, an aneurysm may occur at any age.3

Brain aneurysms are more common than you may think.
An estimated 1 in 50 people has a brain aneurysm.1,3

Types of brain aneurysms

The types of brain aneurysms can be classified by both size and shape.4

Aneurysm size classifications


< 7 mm in diameter


7 – < 13 mm in diameter


13–25 mm in diameter


> 25 mm in diameter

Illustrated diagram of brain aneurysm

Aneurysm shape classifications

Illustration of saccular aneurysm

Saccular aneurysm

Also known as “berry” aneurysms due to their round, sac-like shape, saccular aneurysms are the most common type, accounting for 80–90% of cases.1-3

Illustration of fusiform aneurysm

Fusiform aneurysm

This aneurysm resembles an engorged blood vessel and can extend several centimeters in length. Fusiform aneurysms rarely rupture.1-3

Illustration of wide-necked aneurysm

Wide-necked aneurysm

A saccular aneurysm with a neck 4 mm wide, or twice as wide as the aneurysm is tall, is known as a wide-necked aneurysm.1,6

Symptoms of brain aneurysm

In cases of small and unchanging brain aneurysms, there can be no symptoms. However, as an aneurysm grows larger, it can put pressure on surrounding tissues and nerves, causing neurologic symptoms sometimes called mass effect.1

Symptoms of unruptured aneurysms include (but are not limited to):1

  • Sudden and severe headache often described as “the worst headache of my life”
  • Dilated pupils
  • Blurred or double vision
  • Pain above or behind the eye
  • Weakness/numbness on one side of the face
  • Difficulty speaking
  • Nausea, vomiting

If not treated, a brain aneurysm can continue to expand and eventually rupture.1

Diagram of brain aneurysm symptoms, including sensitivity to light, stiff neck, the worst headache of your life, pain behind one eye, and dizziness or blurred vision.

Talk to your doctor to decide which treatment option may be best for you. Treatment with these devices are prescribed by your physician. These treatments are not for everyone. Your physician should discuss all potential benefits and risks with you. Although many patients benefit from the use of these treatments, results may vary.

Causes of brain aneurysm: Are you at risk?

A brain aneurysm can result from a congenital defect, some inherited diseases, or other degenerative conditions, such as hypertension (high blood pressure) or atherosclerosis (fat buildup inside the arteries, often leading to heart attack or stroke). Other risk factors include cigarette smoking, cocaine use, blood vessel wall infection, and head trauma.1,3

There is no known way to prevent brain aneurysms.7

Treatment options

Flow diversion and Coiling are minimally invasive treatment options for brain aneurysms.

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Neurologic disorders (Chapter 3). In: Professional Guide to Diseases, 9th edn. Lippincott Williams & Wilkins, 2009.


Cerebral Aneurysms Fact Sheet, NINDS, Publication date May 2018. NIH Publication No. 18-NS-5506.


Vallée JN, Pierot L, Bonafé A, et al. Endovascular treatment of intracranial wide-necked aneurysms using three-dimensional coils: Predictors of immediate anatomic and clinical results. Am J Neuroradiol. 2004;25(2):298–306.


Novitzke J. The basics of brain aneurysms: A guide for patients. J Vasc Interv Neurol. 2008;1(3):89–90.


Internal Report TR-NV11534/TR-NV11121. Rev. A