Obturator Internus Muscle Endometriosis with Nerve Involvement: a Rare Clinical Presentation.

STUDY OBJECTIVE: To describe our surgical approach in a rare case of deep infiltrating endometriosis of the obturator internus muscle with obturator nerve involvement.

DESIGN: A step-by-step surgical explanation using video and literature review (Canadian Task Force Classification III).

SETTING: Endometriosis can be pelvic or rarely extrapelvic and is classically defined as the presence of endometrial glands and stroma outside the uterine cavity [1,2]. Pain along the sensitive area of the obturator nerve, thigh adduction weakness and difficulty in ambulation are extremely rare presenting symptoms [2-4].

PATIENT: We report a case of a 32-year-old patient who presented with cyclic leg pain in the inner right thigh radiating to the knee caused by a cystic endometriotic mass in the obturator internus muscle with nerve retraction. The patient provided informed consent to use the surgical video. Institutional review board approval was obtained.

INTERVENTIONS: Pelvic magnetic resonance imaging was performed and confirmed a nodular lesion of about 2.3 cm with high signal on T1WI and T2WI and without fat suppression on T2FS inside the right obturator internus muscle, suggesting an endometriotic lesion (Fig. 1). Surgical removal of the mass was performed using the laparoscopic approach. A normal pelvic cavity was found, and the retroperitoneal space was dissected. A mass located within the right obturator internus muscle, below the right iliac external vein, behind the corona mortis vein, and lateral to the right obturator nerve was identified. The whole region was inflamed, and the nerve was partially involved. Dissection was performed carefully with rupture of the tumor, releasing a chocolatelike fluid (Fig. 2), and the cyst was removed. Pathology examination was consistent with endometriosis. Patient improvement was observed, with pain relief and improved ability for right limb mobilization. No recurrence of endometriosis was found at the follow-up visit 6 months later.

MEASUREMENTS AND MAIN RESULTS: The obturator nerve is responsible for motor and sensitive innervation of the joins and internal muscles of thigh and knee as well as the innervation of skin in the internal thigh. Pain along the sensitive area of the obturator nerve at the time of menstruation, thigh adduction weakness, difficulty ambulating, or paresthesia can be presenting symptoms with the involvement of the obturator nerve [5]. Besides paresthesia, our patient presented all the symptoms. The suspected diagnosis of obturator internus muscle endometriosis with retraction of the obturator nerve was confirmed by laparoscopic surgery and pathological examination of the excised tissue. To our knowledge, only 4 cases of endometriosis involving the obturator nerve have been described (according to MEDLINE searched in January 2017) [5-8]. The laparoscopic approach provided an excellent access to the retroperitoneal space, allowing fine dissection of the obturator nerve and the surrounding structures with complete removal of the cystic mass.

CONCLUSION: We report a rare case of endometriosis with a single mass located inside the right obturator internus muscle with neuronal involvement of the obturator nerve. The fundamental role of laparoscopy was clearly demonstrated for the diagnosis and treatment of our patient.