Sometimes it is a loop of the basilar artery coming up from below, sometimes it hits from the side, often it is a cerebellar artery dangling down from above. Where it hits the nerve roots tends to determine where the pain is felt in the face. Looking through a microscope and using long-handled instruments, the surgeon gently dissects away the filmy membranes that bind the artery to the nerve roots, freeing up the artery. Like a fire hose under pressure that has been freed from an obstruction, the artery will spring into a new position when released from the attachment to the nerve roots. This relieves a constant tension tending to pull the nerve roots away from the brain stem.
Some spongelike material is inserted between artery and nerve roots to act as a shock absorber.
Moving the artery effects a real cure. There is also another useful operation which, while not removing the cause, does usually stop the pains for a few years. While a thumb-width away from where the pounding artery is located, the site of destruction is effective because the nerve roots die all the way back into the brain. This does get rid of the pain but at the price of losing some of the nerve. Some patients prefer this operation as it is quickly done under local anesthesia and laughing gas, in an x-ray suite rather than an operating room.