What are AVMs?

Arteriovenous malformations (AVMs) are defects of the circulatory system that are believed to arise during fetal development or soon after birth. They comprise snarled tangles of arteries and veins, disrupting the vital cycle that would normally carry oxygen-saturated blood in arteries away from the heart to the body's cells, and return oxygen-depleted blood by way of veins to the lungs and heart. An AVM directly connects arteries and veins, and thereby reduces oxygen to nervous system tissue and increases the risk of bleeding.

Arteriovenous malformations can form wherever arteries and veins exist. They occur most often without symptoms. However, AVMs that form in the brain or spinal cord can be especially problematic. Even in the absence of bleeding or significant oxygen loss, large AVMs can damage the brain or spinal cord by their presence. They can range in size from a fraction of an inch to more than 2.5 inches in diameter. The larger the lesion, the greater the amount of pressure there is on surrounding brain or spinal cord structures.

AVMs of the brain or spinal cord (neurological AVMs) affect approximately 300,000 Americans. They occur in males and females of all racial or ethnic backgrounds at roughly equal rates.

Common symptoms

Common symptoms of AVMs are seizures and headaches. Other neurological symptoms may include muscle weakness or paralysis in one part of the body or loss of coordination (ataxia). Also, AVMs can cause pain or disturbances of vision or speech. Mental confusion or hallucination is also possible. There is evidence that AVMs may also cause subtle learning or behavioral disorders during childhood.

Diagnosis of AVM is by either computed axial tomography (CT) or magnetic resonance imaging (MRI) scans. Angiography is an accurate way to get the exact location of the malformation. A thin tube is inserted in a leg artery, threaded toward the brain, and then injected with a dye. The scans reveal the AVM tangle.

Arteriovenous malformations can put veins under great pressure since there are no capillaries to slow blood flow. Over time, the AVM may rupture and cause a hemorrhage. While the risk of hemorrhage is small, the risk increases over time; treatment is usually recommended.


Advances in technique have made surgical treatment of most cases of AVM safe and effective. Surgery inside the skull may attempt to cut out or burn away the AVM with a laser. Another option for smaller AVMs is stereotactic radiosurgery, which focuses radiation on AVM blood vessels to slowly obliterate them. It may take from one to three years to remove the AVM.

A third treatment option is endovascular embolization, which is similar to an angiogram. A catheter is inserted into a leg artery and threaded through the body toward the affected arteries. A glue-like substance is injected to block key blood vessels leading to the AVM, thus reducing its size so radiosurgery or conventional surgery may treat it.

Surgery is a decision that must be made with full understanding of risks. Untreated, AVMs may lead to serious neurological deficits or death. Surgery on the central nervous system, however, has known risks as well; AVM surgery is invasive and can be quite complex.


If you are looking for more information on arteriovenous malformations or have a specific question, our information specialists are available business weekdays, Monday through Friday, toll-free at 800-539-7309 from 9am to 5pm ET.

Additionally, the Reeve Foundation maintains a fact sheet on arteriovenous malformations with additional resources from trusted Reeve Foundation sources. Check out our repository of fact sheets on hundreds of topics ranging from state resources to secondary complications of paralysis.

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This project was supported, in part, by grant number 90PRRC0002, from the U.S. Administration for Community Living, Department of Health and Human Services, Washington, D.C. 20201. Grantees undertaking projects under government sponsorship are encouraged to express freely their findings and conclusions. Points of view or opinions do not, therefore, necessarily represent official Administration for Community Living policy.