Sciatic endometriosis: MR evaluation.

A 39-year-old woman (gravida 1, para 1) was referred for episodic pain in her back and left leg associated with difficulties in walking. Clinical history revealed cyclic left sciatica that had evolved for longer than 3 years. Pain began on the first day of menstruation and continued for the 5 or 6 days of menstruation and recurred during the following cycle after a pain-free period. On examination, she walked with left steppage gait. There was paralysis of the peroneal muscles of the left leg associated with hypesthesia in the L-5 area. Achilles reflex of the left foot was not present. Electromyography confirmed damage to the peroneal nerve, with slight damage to the tibial nerve. Sciatica was suspected, and pelvic MR revealed a distinct mass of approximately 2 cm in diameter in the left sciatic notch (Fig 1). The lesion was situated in the lower part of the piriform muscle, in contact with the sciatic nerve in the gluteal area. The lesion was hyperintense on the T1and T2-weighted images, partially surrounded by a thin hypointense zone (Fig 1 A, B). The lesion did not enhance after gadolinium injection (Fig 1 C). Because of the nerve symptoms and the topography of the lesion, our preoperative diagnosis was an atypical neurogenic tumor with a cystic or hemorrhagic content. Surgery revealed a purplish mass, which was situated within the piriform muscle, and extended below and outside in contact with the sciatic nerve. The whole region was inflamed. Section of the tumor released a chocolate color fluid. Preliminary examination indicated the diagnosis of endometriosis. The cyst was excised, and neurolysis of the sciatic nerve was performed. Pathology examination (Fig 2) revealed areas of typical endometrial glands surrounded by stroma and bordered by vessels with occasional foci of hemosiderin-laden macrophages typical of endometriosis.