Arteriovenous malformations (AVM) of the brain and spinal cord are tangles of abnormal blood vessels. They can form wherever arteries and veins exist. The ones that form in the brain or spinal cord have the most serious symptoms.

Arteriovenous Malformation in the Brain
AVM brain blood vessels
Copyright © Nucleus Medical Media, Inc.

The exact cause of arteriovenous malformations is unknown.