Arteriovenous Malformation (AVM)
An arteriovenous malformation (AVM) is a congenital disorder 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). Fistulas in the AVM permit shunting of blood from the arterial to the venous side of the circulation without passage through a capillary system. This shunting causes low blood pressure (hypotension) in the arterial vessels feeding the AVM and neighboring areas of the brain that they normally supply with blood. If they are present AVMs typically cause problems before the age of 40. The most common symptoms of AVM include hemorrhaging (bleeding), seizures, headaches, and neurological problems such as paralysis or loss of speech, memory, or vision. The frequency of hemorrhage in various series ranges from 30-82%. AVM rupture accounts for 2% of all strokes and in death in about 50% of cases.