Arteriovenous malformations (AVMs) are abnormal, snarled tangles of blood vessels that cause multiple irregular connections between your arteries and veins. These malformations most often occur in the spinal cord and in any part of your brain or on its surface but can develop elsewhere in the body. Arteriovenous malformation (AVM) is usually present at birth. The arteries and veins in an AVM can rupture, causing bleeding into the brain or spinal cord. An abnormal connection between arteries and veins, usually in the brain or spine. An arteriovenous malformation (AVM) is a tangle of blood vessels that irregularly connects arteries and veins, disrupting blood flow and oxygen circulation. Arteries move oxygen-rich blood from the heart to the brain and other organs.