malformation, arteriovenous

malformation, arteriovenous A malformation of blood vessels in the brain, brainstem, or spinal cord that is characterized by a complex tangled web of abnormal arteries and veins connected by one or more fistulas (abnormal communications). Abbreviated AVM. An AVM has no capillary bed. The fistulas in the AVM permit high-speed, high-flow shunting of blood from the arterial to the venous side of the circulation. This creates low pressure in the arterial vessels feeding the AVM and neighboring areas of the brain that they normally supply with blood. If an AVM causes problems, it is usually before the person who has it reaches age 40. The most common symptoms include hemorrhaging (bleeding), seizures, headaches, and neurological problems such as paralysis or loss of speech, memory, or vision. Treatment for AVM may involve surgery or closing off the vessels of the AVM by nonsurgical means, using a catheter to deliver agents that block the blood vessels. Most people with AVMs never experience problems, but AVMs that hemorrhage can lead to serious neurological problems and sometimes death.