Brain Arteriovenous Malformation (AVM)

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An arteriovenous malformation (AVM) is a group of blood vessels that are abnormally interconnected with one another. AVMs can occur throughout the body, and brain AVMs may be particularly harmful. Because of their structure, another term commonly used to describe AVM is "arteriovenous fistula."

Man with a headache
Getty Images/ Westend61


AVMs are made up of arteries and veins which are connected to each other in an abnormal manner.

Artery-to-Vein Connections

There are two main types of blood vessels: the arteries and the veins. Arteries bring oxygen-rich blood from the heart to every part of the body. As the arteries travel deeper into the tissues, they branch into thinner blood vessels, until they become tiny and narrow. This area of tiny blood vessels is known as the capillary bed, where oxygen is delivered directly to each cell in the body. Capillary beds merge together to form veins, and they get progressively larger as they exit the organs on their way to the heart and lungs, where blood is replenished with oxygen.

Abnormal Artery-to-Vein Connections

Brain AVMs are made up of arteries and veins which are connected in such a way that there is no capillary bed at all. This causes the pressure of the arteries to be transmitted directly into the veins within the AVM. This unusual flow of blood creates an area of high pressure and high turbulence that causes the AVM to become larger over time, and to affect the function of the surrounding brain tissue.

What Does It Look Like?

Brain AVMs vary in size. Some are tiny and may never cause any problems at all. Others form large and tortuous channels of arteries which pulsate strongly as they connect directly to the veins of the AVM. AVMs can be found anywhere in the brain, including the cerebral cortex, the white matter, and the brainstem.

Who Develops Brain AVMs?

Brain AVMs affect less than 1% of the population, and are present at birth, but they rarely affect more than one member of the same family. They occur roughly equally in men and women.

Symptoms can begin at any age, but it is not uncommon for people to be diagnosed after the age of 50.


An AVM may bleed or burst, causing severe symptoms of a subarachnoid hemorrhage. About half of AVMs cause their first symptoms this way. Symptoms of a ruptured AVM include sudden, severe head pain, weakness of one side of the face or body, seizures, confusion, loss of consciousness or persistent head pain.

About half of those who have an AVM experience symptoms even if the AVM does not bleed. These symptoms can include seizures, headaches, and stroke symptoms such as hemiplegia or hemiparesis.


Generally, a brain CT or a brain MRI is necessary if your healthcare provider thinks that you might have an AVM.

When bleeding has occurred in the brain, the AVM can be difficult to identify because of the presence of nearby blood. Other tests, such as cerebral angiogram, brain MRA or brain CTA specifically evaluate the blood vessel in the brain, and can help in definitively identifying an AVM.


The most common types of treatment available include surgical removal, endovascular embolization, and stereotactic radiosurgery -- all of which might be used either alone or in combination. The goal of these treatments is to lower the risk of bleeding, or re-bleeding.

An issue that is presently under intense research is whether healthcare providers should treat AVMs that are discovered before they cause bleeding. The risk of bleeding is weighed against the risk of surgery for each individual- based on factors such as overall health and ability to tolerate surgery, the location, size and shape of the AVM.


The prognosis of an AVM depends on several factors, beginning with whether the AVM is discovered before or after bleeding. More than 90% of those who bleed survive the event. In those whose AVM is discovered before bleeding, the prognosis is directly related to the AVM's size, symptoms, proximity to vital areas of the brain and whether or not the AVM is treated.

A Word From Verywell

You may have been told that you or a loved one has an AVM. If you have had a neurological deficit such as weakness due to a bleeding, you will likely need to undergo some rehabilitation as you recover. Overall, with careful follow up and treatment, your prognosis is good. Whether your AVM has bled or not, your treatment plan will include close follow up with your healthcare team as you and your healthcare providers determine whether or not surgical treatment is the right step for you.

1 Source
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  1. Mayo Clinic. Brain AVM (arteriovenous malformation). Last reviewed May 17, 2019.

Additional Reading

By Jose Vega MD, PhD
Jose Vega MD, PhD, is a board-certified neurologist and published researcher specializing in stroke.