If I have a malformation of the willis polygon, what can happen?

Neurologist can help. The circle of willis, or willis polygon, is a ring of arteries (blood vessels carrying fresh oxygenated blood) that supply blood to the brain. Whether or not a malformation there causes problems depends on things such as where the abnormal artery is, is it too big or too small, is there still adequate blood flow through alternate arteries, etc... An angiogram can give a details of the arteries.