An arteriovenous malformation (AVM) is an abnormal cluster of blood vessels in the brain or spine that can cause devastating neurological symptoms or even death. Normally, blood is carried to the brain through arteries and emptied through veins. Between the arteries and veins are capillaries that help decrease the pressure of the returning blood to the veins and back to the heart.
When someone has an AVM, they have no capillaries and some of their blood goes into the veins too early and under high pressure. This can cause a progression of symptoms that can lead to permanent disabilities or death.