Unusual Relationship between the Piriform Muscle and Sciatic, Inferior Gluteal and Posterior Femoral Cutaneous Nerves

Piriformis muscle syndrome has been increasingly recognized as a cause of leg pain. Overuse, strain, or anatomical variations of the relationship between the nerve and the piriformis muscle are thought to be the underlying causes of the entrapment of the sciatic nerve. We report a variation not previously described which was found during a routine dissection. During routine dissection of the left gluteal region of an adult male cadaver we observed a high division of the sciatic nerve and the presence of an accessory piriformis muscle. The sciatic nerve divided beneath the piriformis muscle and the common fibular nerve passed over the accessory piriformis muscle, whereas the tibial nerve reflected anteriorly to pass between the accessory piriformis and the superior gemellus muscle. Additionally, both nerves communicated with a side branch under the inferior border of the accessory piriformis muscle and the inferior gluteal nerve originated from the fibular nerve. Anatomical variations in the relationship between the piriformis muscle and the sciatic nerve may be present in up to 17% of the population. Six different variations have been described and none of them is similar to our description. Though complete understanding of the physiopathology of the piriformis muscle syndrome remains to be elucidated, knowledge of the possible anatomical variations may be useful for its adequate diagnosis and treatment.