Understanding an AVM

An Arteriovenous Malformation (AVM) is an abnormal connection between the arteries and veins in the brain. An AVM contains arteries that connect directly to veins without first narrowing down into much smaller blood vessels called capillaries. As a result, blood that is under high pressure is allowed to flow through thin-walled veins. This can interfere with normal blood circulation in the brain and can lead to a hemorrhage.

Most people with AVMs have no initial symptoms or problems. Instead, the AVMs are often discovered when healthcare providers treat another unrelated health concern. Sometimes the rupture of one of the blood vessels in an AVM will bring the issue to medical attention.

Facts about arteriovenous malformations

Most people with AVMs will never have any problems. If symptoms have not appeared by the time a person is 50, they probably will never appear. Women sometimes have symptoms as a result of the burden that pregnancy places on the blood vessels.

No one knows why AVMs form. Some experts believe that the risk of developing AVMs could be genetic. AVMs can form anywhere in the body. Those that form in the brain or close to the spinal cord, called neurological AVMs, are most likely to have long-term effects.

The biggest concern related to AVMs is that they will cause uncontrolled bleeding, or hemorrhage. Fewer than 4% of AVMs hemorrhage, but those that do can have severe, even fatal, effects. Death as a direct result of an AVM happens in about 1% of people with AVMs.

Sometimes, AVMs can reduce the amount of oxygen getting to the brain and spinal cord (this is sometimes called a "steal" effect, as if the blood were being "stolen" from where it should be flowing).


Symptoms of AVMs depend on where the malformation is located. These are physical symptoms:

  • Buzzing or rushing sound in the ears
  • Headache—although no specific type of headache has been identified
  • Backache
  • Seizures
  • Loss of sensation in part of the body
  • Muscle weakness
  • Changes in vision
  • Facial paralysis
  • Drooping eyelids
  • Problems speaking
  • Changes in a sense of smell
  • Problems with motion
  • Dizziness
  • Loss of consciousness
  • Complications of AVMs include:
  • Stroke
  • Numbness in part of the body
  • Problems with speech or movement
  • In children, developmental delays
  • Hydrocephalus (accumulation of spinal fluid within the brain due to pressure on the normal spinal fluid pathways)
  • Lower quality of life
  • Small risk for death from hemorrhage

When to call the healthcare provider

Some people only find out about an AVM when it bleeds. This causes stroke in some people. If you notice symptoms such seizure, numbness, vomiting, or physical weakness, go immediately to the emergency room or call 911 to get help.


Healthcare providers typically take a medical history and do a physical exam. Family and friends can describe the symptoms they saw, especially if the person with symptoms is unconscious. The final diagnosis, however, is usually made based on imaging tests that show areas of blood flow. These tests could include:

  • Cerebral angiogram
  • MRI scan and magnetic resonance angiography
  • CT scan and CT angiography
  • Vascular ultrasound


A treatment plan is developed based on the size and location of the AVM and could include:

  • Medicine for symptoms
  • Embolization (plugging off the malformed blood vessels)
  • Surgery
  • Radiation therapy


AVMs happen before birth or shortly thereafter. Because their cause is unknown, you can’t prevent them. The best approach is to respond quickly to the symptoms listed above.