Anatomical bases of superior gluteal nerve entrapment syndrome in the suprapiriformis foramen.

Observation of a 60 year-old-man with superior gluteal nerve (SGN) entrapment neuropathy in the suprapiriformis foramen encouraged us to explore, through anatomical dissection, the possible morphological etiologies of this condition. Ten SGNs in five embalmed cadavers were dissected via gluteal and pelvic access. The origin, course and distribution of the nervous trunk and its relations were studied. In most cases, the nerve fibers of the SGN arose from ventral branches of L4, L5 and S1 to constitute the nervous trunk in the pelvis, then reached the gluteal area and divided into two branches, cranial and caudal. By running through the suprapiriformis foramen with the cranial gluteal vascular pedicle, the nervous trunk was always up between the superior edge of the piriformis muscle and the greater sciatic notch; rarely some of the nerve fibers went through the muscle. Bone, muscular and vascular morphological factors liable to cause SGN entrapment syndrome, and the circumstances of discovery, were analyzed. The role of hypertrophy of the piriformis muscle, resulting in a narrow suprapiriformis foramen, was confirmed through surgery.