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.