Arteriovenous malformation (AVM), a brain malformation, is an abnormal tangle of arteries and veins in the brain or the spinal cord (spinal arteriovenous malformation).

Normally oxygen-rich blood enters the brain through arteries, which branch into smaller arterioles and even smaller blood vessels (capillaries). The brain uses oxygen removed from the blood in the capillaries. Oxygen-depleted blood then passes into small venules and then into larger veins that drain the blood from the brain to the heart and lungs.

In a brain arteriovenous malformation, the blood passes directly from the arteries to the veins, bypassing capillaries. The arteries and veins in an AVM can rupture, causing bleeding into the brain. An arteriovenous malformation can develop anywhere in the body but occurs most often in the brain or spine. Even so, brain AVMs are rare and affect less than 1 percent of the population.


This disorder may not cause any symptoms until the AVM ruptures, resulting in bleeding in the brain (hemorrhage). In about half of all brain AVMs, hemorrhage is the first sign. In people without hemorrhage, the symptoms of a brain AVM may include:

  • Seizures,
  • Headache or pain in one area of the head,
  • Muscle weakness or numbness in one part of the body.

Or more serious neurological signs and symptoms, depending on the location of the AVM, including:

  • Vision loss,
  • Severe headache,
  • Weakness, numbness or paralysis,
  • Difficulty speaking,
  • Confusion or inability to understand others,
  • Severe unsteadiness.


The cause of brain AVM is unknown, but researchers believe most brain AVMs emerge during fetal development.

Risk factors

Anyone can be born with a brain AVM, but those being male and having a family history of AVM  may be a risk.


Complications of a brain AVM include:

  • Bleeding in the brain (hemorrhage). An AVM puts extreme pressure on the walls of the affected arteries and veins, causing them to become thin or weak. This may result in the AVM rupturing and bleeding into the brain (a hemorrhage).
  • Reduced oxygen to brain tissue. With an AVM, blood bypasses the network of capillaries and flows directly from arteries to veins. Blood rushes quickly through the altered path because it isn't slowed down by channels of smaller blood vessels.
  • Thin or weak blood vessels. An AVM puts extreme pressure on the thin and weak walls of the blood vessels. A bulge in a blood vessel wall (aneurysm) may develop and become susceptible to rupture.
  • Brain damage. As you grow, the body may recruit more arteries to supply blood to the fast-flowing AVM. As a result, some AVMs may get bigger and displace or compress portions of the brain. This may prevent protective fluids from flowing freely around the hemispheres of the brain.

If fluid builds up, it can push brain tissue up against the skull (hydrocephalus).


This is a congenital disorder which cannot be prevented.