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 - Northwestern Memorial Hospital - Chicago

Arteriovenous Malformation (AVM)

Arteriovenous malformations (AVMs) are abnormal masses of blood vessels—arteries and veins called the nidus that develop while an unborn baby is growing inside the mother’s uterus. The blood in the arteries dumps directly into the veins with no network of tiny capillaries in between, which normally occurs. Since the blood vessels that make up these masses are abnormally fragile, the malformations may bleed, leading to serious complications.

Although AVMs can occur anywhere (arms, hands, legs, feet, lungs, heart, liver and kidneys), about half of them are found in the brain, brainstem and spinal cord. Because they hemorrhage easily, AVMs can cause strokes, paralysis and the loss of speech, memory, or vision. There is about a 10 percent fatality rate associated with an AVM hemorrhage.

Incidence of AVMs

  • Brain AVMs occur in approximately 3 of every 100,000 people.

  • About 40 to 80 percent of them experience some bleeding.

  • It has been estimated that the annual risk of bleeding is about 1 to 4 percent.

  • The majority of AVMs are discovered in people ages 20 to 40.

  • Pregnancy and labor has been associated with an increased chance of AVM rupture.

  • After age 55, the risk of bleeding decreases.

Causes of AVMs


Some researchers suggest there is a genetic link for some AVMs, but no one is sure.

In utero

Some evidence indicates that the malformations develop when the unborn fetus is 45 to 60 days old.


Some information suggests that AVMs are primitive structures left over after fetal blood-circulating systems develop.

Symptoms of a Bleeding AVM

  • Headaches or seizures are typically, the first symptom of an AVM hemorrhage in the brain
    • Headaches may be focused in one specific area or it may be more general
    • Headaches may be mistaken for a migraine
    • Vomiting
  • Impaired vision
    • Decreased, double or blurred vision
  • Impaired speech or smell
  • Weakness
    • Drooping eyelids
    • Paralysis of the facial muscles
  • Mental changes
    • Confusion or irritability
    • Sleepiness, lethargy

About 25 percent of patients experience loss of vision, weakness, or mental changes, depending on the exact location of the AVM.

Last UpdateAugust 28, 2012