Brain Aneurysms

What is a brain aneurysm?

Brain aneurysms are weak areas in the wall of a blood vessel. A brain aneurysm usually forms in an artery, which is the type of blood vessel that carries oxygen-rich blood to the brain. Over time, these weak areas in the walls of arteries balloon out, causing the blood vessel wall to become even weaker as the aneurysm grows. Occasionally aneurysms can leak or rupture and cause a hemorrhagic stroke, the type of stroke that is caused by bleeding inside the brain.

Why do people develop aneurysms?

Little is known about why some people develop aneurysms while other do not. In many cases, aneurysms are inherited through heredity, but long term high blood pressure and cigarette smoking appear to predispose people to develop aneurysms, too.

About 5% of the population in the United States has at least one aneurysm in the brain, but up to 80% of those who have a brain aneurysm will never be affected by bleeding in the brain.

Brain aneurysms usually develop at locations in the blood vessels where arteries divide into branches. The following arteries in the brain are the most likely to have aneurysms:

  • The anterior communicating artery (30%)
  • The posterior communicating artery (25%)
  • The middle cerebral artery (20%)

If I have a brain aneurysm, will I feel any symptoms?

Very often, small aneurysms do not cause any symptoms unless they bleed. Sometimes, however, the growing aneurysm might push against nearby blood vessels or other structures in the brain as it grows.

A small or growing aneurysm can produce symptoms such as headaches, double vision, or pain around the eyes when you look to the sides.

How will I know if a brain aneurysm bleeds?

If a brain aneurysm bleeds, people often feel a "thunderclap headache" they might call the “worst headache of their lives,” as well as neck pain and stiffness.

An aneurysm rupture can also produce typical stroke symptoms, as a result of bleeding from the aneurysm spreading throughout the brain. When an aneurysm ruptures, the region of the brain that normally receives blood supply from the bleeding artery may suffer, causing an ischemic stroke as well as a hemorrhagic stroke.

Sometimes a brain aneurysm rupture causes collapse, loss of consciousness or seizures.

What are the risk factors for aneurysm bleeding and rupture?

When an aneurysm ruptures, it causes profuse bleeding in the brain leading to a hemorrhagic stroke. In general, aneurysms bleed during situations when blood pressure is excessively elevated.

Episodes of markedly high blood pressure can be triggered by a number of causes, including:

  • The use of illicit drugs, such as cocaine and amphetamines
  • Systemic triggers
  • Medical emergencies

Aneurysms are also more likely to bleed after they reach a size of more than 10 millimeters, or about a third of an inch. Overall, there is a small risk of bleeding from a brain aneurysm.

Sometimes, aneurysms are repaired surgically or by a neuro-interventional procedure in order to reduce the risk of bleeding. Whether or not you are a candidate for a brain aneurysm repair depends on the location and size of your aneurysm, as well as your overall health and ability to safely tolerate a procedure.

What happens after an aneurysm ruptures and bleeds?

The prognosis after an aneurysm bleed is variable, depending on the size of the bleed. A brain aneurysm rupture can be treated, but, approximately 10% of people with a ruptured aneurysm experience such profuse bleeding inside the brain that they die before ever reaching a hospital.

In general, up to 50% of people with bleeding in the brain die from the complications of the bleeding itself. There is also a very high risk of bleeding again shortly after the first aneurysm leak or rupture. Up to 4% of brain aneurysm rupture survivors can bleed again within the first 24 hours after the initial episode of bleeding.

By the end of the second week after an aneurysm bleed, brain aneurysm rupture survivors have a 15 to 20% chance of bleeding again.

After a brain aneurysm bleeds, surgery may be needed to remove the blood. But, depending on the amount of blood and the location of bleeding in the brain, surgery may not be necessary or may not be possible.


Patient- and Aneurysm-Specific Risk Factors for Intracranial Aneurysm Growth: A Systematic Review and Meta-Analysis.Backes D, Rinkel GJ, Laban KG, Algra A, Vergouwen MD, Stroke. 2016 Apr;47(4):951-7.

Edited by Heidi Moawad MD

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