Arteriovenous malformations (AVMs) are abnormal, snarled tangles of blood vessels that cause multiple irregular connections between the arteries and veins.
These malformations most often occur in the spinal cord and in any part of the brain or on its surface, but can develop elsewhere in the body.
AVMs can damage the brain and spinal cord by reducing the amount of oxygen reaching neurological tissues, bleeding into surrounding tissue (hemorrhage) that can cause stroke or brain damage, and by compressing or displacing parts of the brain or spinal cord. Many people with an AVM experience few, if any, significant symptoms, which can include headache, weakness, seizures, pain, and problems with speech, vision, or movement.
Most often AVMs are congenital, but they can appear sporadically. In some cases the AVM may be inherited, but it is more likely that other inherited conditions increase the risk of having an AVM.
The malformations tend to be discovered only incidentally, usually during treatment for an unrelated disorder or at autopsy.