Ruptured Obturator Internus Muscle Abscess Causing Extensive Retroperitoneal Necrosis

Obturator internus muscle (OIM) abscess occurs rarely in adults. Accurate diagnosis is often hindered and delayed due to the deep location of the abscess and the nonspecific clinical features. Even of rarer occurrence is rupture of the obturator internus muscle abscess into the perirectal space and retroperitoneum causing extensive retroperitoneal necrotizing soft tissue infection. We present a case of ruptured left OIM abscess, which initially presented with clinical features, which were suspected as acute pancreatitis. Contrast-enhanced multidetector computed tomography (MDCT) of the abdomen and pelvis revealed ruptured left OIM abscess with extensive fat stranding, fluid collections, and pockets of gas throughout the perirectal space, perisigmoid space, and bilateral posterior pararenal and anterior pararenal spaces as well as thickening of bilateral anterior renal fascia, posterior renal fascia, and lateral conal fascia. These CT findings were consistent with extensive retroperitoneal necrotizing soft tissue infection secondary to ruptured left obturator internus muscle abscess. Broad-spectrum antibiotics were instituted immediately, and the patient was urgently worked up for drainage of the abscess and debridement of the necrotic material. However, the patient’s condition deteriorated quickly before the surgical interventions were performed and slipped into septic shock. Emergency resuscitative measures were unsuccessful, and unfortunately, the patient died. The case represents a rare pathology with an unusual presentation, which can be fatal if diagnosis and treatment is delayed.

Muscle Spindle Density of Lateral Rotators of the Thigh in Japanese Macaques and a Gibbon

We examined the six small lateral rotators of the hip joint, which is one of the most flexible joints and allows kinematically complex motions of the hindlimb, to elucidate the functional differentiation among these muscles and to test the hypothesis that species-specific characteristics in hindlimb use during locomotion are reflected in the muscle spindle density and in other parameters of the deep small hip joint rotators. For these purposes, we estimated the number of muscle spindles of the superior gemellus muscle (SG), inferior gemellus muscle, quadratus femoris muscle, obturator internus muscle (OI), obturator externus muscle, and piriformis muscle in three Japanese macaques and a gibbon, using 30-µm-thick serial sections throughout each muscle length after azan staining. The numbers of muscle spindles per 10,000 muscle fibers were determined to compare inter-muscle variation. The spindle density was highest in the SG and lowest in the OI in the Japanese macaques, suggesting that the SG, which is attached to the tendon of the OI, functions as a kinesiological monitor of the OI. On the other hand, SG the was missing in the gibbon, and the OI in the gibbon contained more spindles than that in the Japanese macaques. This suggests that the SG and the OI fused into one muscle in the gibbon. We postulate that the relative importance of the deep small hip rotator muscles differs between the Japanese macaques and gibbon and that the gibbon’s muscles are less differentiated in terms of the spindle density, probably because this brachiating species uses its hindlimbs less frequently.

Piriformis Syndrome and Other Nerve Entrapments of the Posterior Pelvis

Not every case of neurologically based pelvic/genital numbness/incontinence is due to cauda equina syndrome. Pelvic pain, incontinence, and sexual dysfunction can result from treatable peripheral nerve injury or entrapment affecting the pudendal nerves or impar ganglion. Learning the signs, physical exam findings, tests, and surgical options greatly expands a neurosurgeon’s range. The pudendal nerve and nerve to the obturator internus muscle arise after S2, S3, and S4 spinal nerves traverse the piriformis muscle. They exit the sciatic notch with the sciatic nerve but then re-enter the pelvis, where the pudendal nerve then gives off bladder, rectal, and genital branches.