This is a procedure performed to correct a congenital disorder known as AVM, where there is a formation of tangled arteries and veins which can lead to seizures, internal bleeding and neurological symptoms. It is possible to have an AVM without any adverse effects, but it is considered to be better to remove the risk through surgery. AVM's can form in the spinal cord, brain, and brainstem, and are revealed using special neuroradiological scans.