Posterior femoral cutaneous neuropathy in piriformis syndrome: A vascular hypothesis

Piriformis syndrome is described as a neuromuscular condition which occurs when the sciatic nerve is compressed and/or irritated by the piriformis muscle. It is characterized by acute tenderness in the buttock with sciatica-like pain radiating into the posterior aspect of the thigh, leg, and foot. The neurogenic leg and foot pain experienced with this condition is consistent with involvement of the sciatic nerve. However, the posterior thigh pain associated with piriformis syndrome is due to involvement of the posterior femoral cutaneous nerve (i.e., posterior cutaneous nerve of the thigh), which is a branch of the sacral plexus independent of the sciatic nerve. This nerve is rarely mentioned relative to piriformis syndrome even though posterior thigh pain is more prevalent in patients than leg and foot pain. In the few instances when the posterior femoral cutaneous nerve is referenced relative to piriformis syndrome the neuralgic signs associated with it are attributed to compression by piriformis. Yet, given the dramatic size difference between the sciatic and posterior femoral cutaneous nerves one would expect direct piriformis compression to impact the sciatic nerve first and produce leg/foot pain at a far greater frequency than posterior thigh pain. However, the opposite is seen in the literature, which raises the question, what underlying mechanism is responsible for this phenomenon? It is hypothesized that the prevalence of posterior femoral cutaneous nerve involvement in piriformis syndrome is due to compression of the inferior gluteal vein by a hypertrophied piriformis muscle.