Piriformis Syndrome is often caused by an abnormal functioning of a small muscle called Piriformis. The Piriformis muscle is a small, flat, muscle located in the buttocks near the top of the hip joint. It runs diagonally across the buttocks and the sciatic nerve runs vertically underneath it. However, for some people, the sciatic nerve runs straight through the Piriformis muscle. Due to this crossover between the muscle and the nerve, any dysfunction or compression of the sciatic nerve by the Piriformis muscle can cause pain. Hence Piriformis Syndrome is considered to be a peripheral neuritis (inflammation) of the sciatic nerve caused by an irritation or dysfunction of the piriformis muscle.