arteriovenous malformation (AVM)
  1. An abnormal connection between arteries and veins that allows blood flow to bypass the small vessels where oxygen and tissue nutrients are exchanged. These unusual malformations may be present at birth or may result from injury or infection. They are often found in the brain and spinal cord, but may occur anywhere in the body.
  2. A tangle of dilated blood vessels that disrupts normal blood flow in the brain.