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What Is an Aneurysm?

Joanna Jan, MDKatie E. Golden, MD
Written by Joanna Jan, MD | Reviewed by Katie E. Golden, MD
Published on December 1, 2021

Key takeaways:

  • An aneurysm is the outpouching or ballooning out of a blood vessel that occurs when the wall of the blood vessel becomes weak and stretched out.

  • Aneurysms can happen in any blood vessel. But most occur in the arteries in the brain or in the aorta​, which is the major artery that carries blood to the whole body.

  • Most aneurysms don’t cause any symptoms unless they burst or rupture. If this happens, it can lead to life-threatening bleeding.

Close-up of brain scans up on a light box.
beerkoff/iStock via Getty Images

Many people have heard about friends or relatives being diagnosed with an aneurysm. Or maybe you have been told you have one yourself. While this can seem like a scary diagnosis at first, it may help to learn more about what an aneurysm is and how it develops. 

Aneurysms usually don’t cause any symptoms unless they rupture or break. But this doesn’t always happen. Aneurysms at risk for complications can be monitored and treated, if necessary. We’ll discuss the different types of aneurysms, what causes them, and why they matter. 

What causes an aneurysm?

An aneurysm forms when the wall of a blood vessel becomes weak. This can happen for a lot of different reasons, like high blood pressure or plaque buildup in the arteries. Over time, as blood flows through the vessel, it can cause the weak area to stretch out more and more.

Aneurysms usually form in arteries, which are the thick-walled blood vessels that carry blood from the heart to the rest of the body. An aneurysm can also form in our veins, but this is much less common. Veins are the blood vessels that bring blood from the body back to the heart. 

What are the risk factors for developing an aneurysm?

There are different types of aneurysm, each with their own set of risk factors. For example, brain aneurysms are more common in women over the age of 40, while abdominal (aortic) aneurysms are more common in men over the age of 65. But some factors increase the risk of developing any aneurysm. These factors can also contribute to the growth of an existing aneurysm, increasing its risk of rupture. They include:

  • Smoking

  • High blood pressure that’s uncontrolled

  • Atherosclerosis, or calcification in the blood vessels 

  • Heavy alcohol use

  • Family history of aneurysms

  • Certain inherited conditions, like Marfan syndrome and Ehlers-Danlos syndrome 

Some of these factors are out of our control — like family history or age. But other factors are things we can change — like keeping blood pressure controlled, not smoking, and using alcohol in moderation.  

What are the different types of aneurysms?

An aneurysm can happen in any artery, but the most common locations are in the brain and in the aorta.

Brain aneurysms

These are also known as cerebral aneurysms or intracranial aneurysms. Of these, saccular aneurysms — also called berry aneurysms — are the most common type. Their name refers to their shape, because they look like a berry hanging off a vine. They are relatively common, affecting 2% to 3% of people

These can form in any artery in the brain, but most occur in the arteries at the base of the skull.

Aortic aneurysms

The aorta is the major artery that carries blood from the heart to the rest of the body. It travels through the chest (or thoracic cavity) and down into the abdomen, finally branching off into smaller arteries in our pelvis that supply blood to our legs.

There are two types of aortic aneurysms: 

1) Abdominal aortic aneurysms are more common in men over age 65. They involve the part of the aorta that’s located in the abdomen.

2) Thoracic aortic aneurysms are less common. They involve the part of the aorta located in the chest above the diaphragm. 

Why do aneurysms matter?

Aneurysms usually don’t cause any symptoms — until they start to lead to complications. The main risk of an aneurysm is that they can bleed, which can happen in two ways:

  • Artery dissection: This is when the walls of the artery separate, and blood gets in between the layers. This leads to extra blood clotting that can cause a stroke. Or it can tear the vessel completely and cause fatal internal bleeding.

  • Aneurysm burst or rupture: This is more likely in aneurysms that have grown very big or enlarged quickly over a short period of time. This can cause life-threatening bleeding and is a medical emergency.

Unruptured aneurysms are usually found when someone is getting an imaging study for something unrelated. But once an aneurysm is identified, a healthcare provider can help to determine the best way to treat it. This often depends on the size and location of the aneurysm. Sometimes this includes medications to help prevent a complication like a dissection or rupture. Other times, it can include a procedure to repair it. 

The bottom line

An aneurysm can form in any artery, but most commonly occurs in the brain, chest, or abdomen. This diagnosis can understandably cause anxiety, especially when an aneurysm is found unexpectedly during an unrelated workup. But not all aneurysms live up to their reputation of tearing or rupturing. 

You can take steps to help prevent aneurysm formation or enlargement. And these steps are generally in line with recommendations to maintain a healthy lifestyle — like not smoking, avoiding excessive alcohol use, and controlling high blood pressure.  


Brown, R. D., Jr., et al. (2014). Unruptured intracranial aneurysms: Epidemiology, natural history, management options, and familial screening. The Lancet Neurology

Centers for Disease Control and Prevention. (2019). Marfan syndrome.

View All References (6)

Gillespie, D. L., et al. (1997). Presentation and management of venous aneurysms. Journal of Vascular Surgery

Mostafazadeh, B., et al. (2008). The incidence of berry aneurysm in the Iranian population: An autopsy study. Turkish Neurosurgery

National Institute of Neurological Disorders and Stroke. (2018). Cerebral aneurysms fact sheet.

Sakalihasan, N., et al. (2005). Abdominal aortic aneurysm. The Lancet.

Salameh, M. J., et al. (2018). Thoracic aortic aneurysm. Vascular Medicine (London, England).

NIH National Library of Medicine. (2020). Ehlers-Danlos syndrome.

GoodRx Health has strict sourcing policies and relies on primary sources such as medical organizations, governmental agencies, academic institutions, and peer-reviewed scientific journals. Learn more about how we ensure our content is accurate, thorough, and unbiased by reading our editorial guidelines.

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