Arteriovenous Malformation

An arteriovenous malformation (AVM) is a jumble of arteries and veins with no capillaries between them. This can happen in your brain or other areas. An AVM can cause bleeding or damage to tissues around it. Some people don’t have symptoms until an AVM starts to bleed. Treatments can remove an AVM, shrink it or stop blood from flowing through it.


An arteriovenous malformation looks like multiple blood vessels tangled together.
An arteriovenous malformation is a rare tangle of blood vessels, usually in your brain.

What is an arteriovenous malformation (AVM)?

An arteriovenous malformation (AVM) is an abnormal tangle of blood vessels that looks like a bird’s nest. The tangle is made of arteries that would normally provide blood to your brain and veins that would normally drain blood from brain tissue.

Blood moves through your body within an organized closed circuit of blood vessels. Your arteries carry oxygen-rich blood from your heart to your brain and to the rest of your body’s organs and tissues. Your veins return oxygen- and nutrient-poor blood and waste products from tissues back to your heart and lungs.

Normally, the exchange takes place in your capillaries, where the smallest blood vessel units of arteries and veins connect. If you have an AVM, the “bridge” of capillaries between your arteries and veins is missing. This causes high-flow arterial blood to connect directly to veins that aren’t used to high blood pressure. As a result, the abnormal connection between the artery and vein in an AVM can cause vessel rupture and bleeding into your brain.

Types of AVMs

The two types of AVMs are:

  • Brain arteriovenous malformations. These develop anywhere within your brain tissue or on the surface of your brain. AVMs most commonly occur in your brain, brainstem and spinal cord.
  • Peripheral arteriovenous malformations. These can form anywhere in your body’s 100,000 miles of blood vessels. They can happen on your face, arms or legs, and in tissues and organs like your heart, liver or lungs.

How common are arteriovenous malformations?

Arteriovenous malformations are rare. They’re present in about 1 in 100,000 people. Anyone can be born with an AVM. Providers mainly discover them in people from ages 20 to 40. The risk of symptoms is highest between ages 30 and 50.


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Symptoms and Causes

What are the symptoms of arteriovenous malformations?

Arteriovenous malformation symptoms may include:

You may or may not have symptoms if you have an arteriovenous malformation. Up to 15% of people with AVMs don’t have symptoms. Often, the first sign you have an AVM is after it bleeds. If you have a brain AVM and it leads to a blood vessel bleed (rupture), it can cause a stroke and brain damage. About 50% of people with a brain AVM have a brain bleed (hemorrhage) as their initial symptom.

What causes an arteriovenous malformation (AVM)?

Scientists aren’t sure what causes arteriovenous malformations. They believe that you’re born with them and that they likely develop during fetal development (they’re congenital). AVMs may be hereditary (run in families) in rare cases.


How does an arteriovenous malformation affect my body?

AVMs cause harm in the following ways:

  • Bleeding. The force of the blood flow from your arteries brings a lot of pressure to the AVM. Veins have weak walls and can’t always adjust to the pressure of blood flow. If your veins can’t handle the blood pressure, they might burst and bleed. Bleeding into surrounding tissue can cause permanent damage. Significant bleeding can result in death.
  • Pressing on body parts. An abnormal connection results in more blood in your veins. Veins can get big and press on nearby tissue. This not only prevents oxygenation, but also impacts draining through your lymphatic system.
  • Depleting tissues of needed oxygen. Because there’s no capillary bridge between arteries and veins, oxygen and nutrients don’t get to the tissue where there’s an AVM. The tissue and nerve cells at that site can die.

What are the complications of arteriovenous malformations?

Complications of brain AVMs include:

  • Brain bleed/stroke. This is the biggest risk of having an AVM. A bleed from an AVM in your brain causes a stroke, brain damage or seizures. AVMs in these enclosed areas can also press on and displace parts of your brain and spinal cord.
  • Seizures. This rush of electrical activity in your brain can lead to passing out and having muscle movements you can’t control.
  • Aneurysm. This is a balloon-like bulge in the walls of any of the blood vessels feeding into or around the AVM. They develop because of weakness in your blood vessel walls. Aneurysms develop in about 50% of all brain and spinal cord AVMs. AVM-related aneurysms can increase your risk of rupture (bleeding) and bleeding-related symptoms.
  • Brain damage that affects thinking, mental processing, memory or understanding speech.
  • Coma and death, especially from a large bleed in your brain.

Diagnosis and Tests

How is an arteriovenous malformation diagnosed?

Your healthcare provider will ask you about your symptoms and do a physical exam. They’ll sometimes listen for a bruit, which is a rapid blood flow sound they can hear in arteries and veins when there’s an AVM.

What tests will be done to diagnose an arteriovenous malformation?

Imaging tests providers use to detect arteriovenous malformations include:

Brain imaging tests for suspected brain AVMs may include:

Because many AVMs don’t cause symptoms, providers only discover some of them during an imaging test for another condition (such as injuries, vision problems or headaches) or after they bleed and cause symptoms.


Management and Treatment

How is an arteriovenous malformation treated?

Arteriovenous malformation treatment choices depend on:

  • The AVM’s type, size and location, and the anatomy of your arteries and veins.
  • Risk of AVM rupture.
  • Your symptoms.
  • Your age.
  • Your general health.

Ideally, the goal of arteriovenous malformation treatment is to reduce the chance of bleeding or make it permanently go away. There are several different ways to treat it. These treatment types include open surgery, catheter-based artery blocking, and/or focused radiation to the AVM. Any type of intervention has benefits and risks that depend your overall health and the characteristics of your AVM.

In general, treating an arteriovenous malformation as soon as possible is usually the best way to avoid serious complications.

Each person — and each person’s AVM — is unique. There aren’t any perfect decision-making tools. Your healthcare team will talk to you and your family about your situation and the best way to approach your AVM.

An AVM might be in an area where the dangers of surgery or other treatments pose a greater risk than doing nothing. If this is the case, your healthcare team may carefully monitor your AVM with imaging tests over time. If the AVM begins showing signs of change, indicating an increased risk of bleeding, your provider may consider treatment at that time.


Medications can relieve some of the symptoms of AVMs. These include:


Healthcare providers may try one or more of these approaches:

  • Surgery to remove the AVM. Surgery involves making a small cut near the AVM, sealing the surrounding arteries and veins so they don’t bleed, then removing the AVM. A surgeon redirects blood flow to normal blood vessels. Surgery is a cure for this condition. You’ll have a brain scan to make sure the surgery completely removed or destroyed the AVM. You’ll also have a short hospital stay (a few days) and undergo some short-term rehabilitation.
  • Embolization. In this procedure, a provider inserts a catheter into an artery in your groin or wrist and moves it to the location of the AVM. Once there, they release a glue-like substance, coils or another substance into the AVM, which slows or stops the blood flow through the AVM. Providers use this approach when the AVMs are large and have a lot of blood flowing through them. This way, they can remove them more easily with less risk of bleeding if they perform surgery immediately afterward. Embolization can also slow blood flow to reduce rupture if a surgeon doesn’t operate immediately.
  • Gamma Knife® radiosurgery. This approach uses highly focused beams of radiation that slowly shrink, scar and dissolve an AVM over a few years or make the AVM easier to remove with surgery. You’ll have scans from time to time to see if the AVM is shrinking.

Complications of the treatment

Complications or side effects from arteriovenous malformation treatment may include:

  • Bleeding.
  • Headache.
  • Swelling.
  • Damage to nearby tissues.
  • Muscle weakness on one side.
  • Effects on speech, hearing or vision.
  • Results that aren’t complete, don’t last or take months to reach their full effect.
  • Serious complications that can be disabling or fatal.


Can an arteriovenous malformation be prevented?

No, you can’t prevent AVMs because researchers believe they’re congenital (you’re born with them). But if you develop any of the symptoms listed in this article, see your healthcare provider right away. Responding quickly to developing symptoms is the best approach.

Outlook / Prognosis

What can I expect if I have an arteriovenous malformation (AVM)?

Each person’s AVM is a unique situation. If you’ve had surgery and a surgeon successfully removed your AVM, you’re cured of this condition.

The outcome of other AVM treatments is very good, but there are many variables, including:

  • Location.
  • Size.
  • Type of AVM.
  • Your age and general health.

Your healthcare team can best discuss your AVM and the likely expected outcome.

If you have an arteriovenous malformation and don’t get treatment, there’s a 2-4% chance per year that it’ll bleed.

Living With

When should I see my healthcare provider?

Arteriovenous malformations can happen more than once (recur) in some people. Contact your provider if you have new symptoms. Once you’ve had treatment, you’ll need follow-up appointments with your provider every three months. After the first year, you’ll only need appointments once a year.

When should I go to the ER?

Get help immediately if you experience:

  • Sudden, severe headache (“worst in my life”).
  • Seizures.
  • Weakness in your arms or legs.
  • Issues with your vision, balance, memory or attention.

These are signs of a life-threatening emergency. This could be a brain bleed.

What questions should I ask my doctor?

Questions to ask your provider include:

  • Where in my body is my AVM?
  • Which treatment is best for me?
  • How often do you need to monitor my condition if you don’t do surgery now?

Additional Common Questions

Are arteriovenous malformations dangerous?

They can be. The greatest danger is bleeding (hemorrhage). If you feel a sudden, severe headache (“worst in your life”), call 911. You might have a bleeding brain AVM. There’s a 2-4% chance of bleeding per year with for unruptured AVMs. Seventeen percent of previously ruptured AVMs burst (rupture) every year.

Do all arteriovenous malformations (AVMs) eventually bleed?

No. Some arteriovenous malformations never cause a bleed and may not even cause symptoms or any health problems your entire life. Healthcare providers only discover some AVMs during an imaging test for another reason or during an autopsy after death.

AVMs can cause health issues other than bleeds. Some AVMs that grow and become large can press on an area of tissue and cause tissue damage, nerve cell damage and other cell damage in that area. If large enough and in a vital area, the lack of capillaries between your arteries and veins can cause a lack of oxygen, nutrients and waste exchange in tissue in this area. This can lead to tissue death.

Can arteriovenous malformations (AVMs) be fatal?

Yes, they can be. How deadly or severe an arteriovenous malformation might be depends on its size and location. A massive bleed from a ruptured AVM in your brain can be fatal. However, some people have AVMs and never have any symptoms or health problems.

Does the location of pain in my head indicate the location of an arteriovenous malformation (AVM)?

Not necessarily. It may, but most often, the location you feel headache pain isn’t specific to the area of the AVM.

Does a pregnant person with arteriovenous malformations (AVMs) have an increased risk?

In some people, the changes pregnancy brings can cause AVM symptoms to appear suddenly or get worse. The increase in blood volume and blood pressure that comes with pregnancy can increase the risk of an AVM bleed.

How do arteriovenous malformations (AVMs) affect children?

AVMs can cause behavioral changes or small changes in your child’s ability to learn. These changes might happen before more obvious symptoms develop when your child is older (if symptoms develop).

Do brain bleeds from arteriovenous malformations (AVMs) always cause significant brain damage?

No. Some very small brain bleeds, called microbleeds, cause limited damage and few symptoms. But over time, many microbleeds can increase the risk of dementia and impair thinking functions.

What’s the difference between an arteriovenous malformation, aneurysm, hemangioma, cavernous malformation and fistula?

An aneurysm is a weakened, ballooned-out area in an artery. It most commonly forms at the point where two arteries branch. An aneurysm can develop as a complication of an AVM.

Hemangiomas are vascular (blood vessel) malformations you can see on your skin. They aren’t dangerous and don’t require treatment.

Cavernous malformations are a type of vascular lesion. Unlike an AVM, they contain slow-moving blood that’s usually clotted. They can leak but usually don’t bleed as severely as AVMs and often don’t cause symptoms.

A fistula is a general term for an abnormal connection of blood vessels. Arteriovenous fistulas can happen in the tissue that covers your brain and spinal cord. AVMs can happen inside your brain’s tissues. Fistulas are more commonly associated with head trauma or infection than AVMs.

A note from Cleveland Clinic

An arteriovenous malformation (AVM) is a serious medical condition, but available treatments are highly effective. Your healthcare team will talk with you about the details of your AVM — its size and location — and other factors to develop treatment options that are best for you. Don’t be afraid to ask questions if anything isn’t clear. You owe it to yourself to understand your options.

Medically Reviewed

Last reviewed on 10/27/2023.

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