Neuromuscular hamartoma of the sciatic nerve: Case report and review of the literature
This 11-year-old boy presented with a 3-year history of right buttock pain that radiated into his lower back and into his right lateral thigh. The pain was present most of the time regardless of activity such as walking or sitting. An initial workup involving magnetic resonance imaging (MRI) of the lumbar spine was unrevealing. The patient had significant atrophy of the right thigh, calf, and foot with an asymmetry in his shoe size with the right foot being three US shoe sizes smaller than the right. In December 2010, the patient presented to neurosurgical attention with progressive complaints of proximal right lower extremity pain, muscle spasms, and gait difficulty.\nThe patient's examination revealed a significant asymmetry in size as the measured circumference at the distal thigh was 53.5 cm at the left thigh versus 50.5 cm in the right thigh, 43 cm in the left calf versus 42 cm in the right calf. The length of his foot from the great toe to the heel was 27 cm in the left foot and 24 cm on the right foot. He had normal strength in the left lower extremity. His right lower extremity exhibited 5−/5 strength in the right hip flexor, 4+ in the quadriceps, 4+ in the hamstrings, 4+ in the hip abductor, 4+ in the hip adductor, 5− in the tibialis anterior, 4+ to 5− in the gastrocnemius, 5− in the extensor hallucis longus, 4+ in foot eversion, and 5− in foot inversion. He was unable to perform heel rise or toe rise on his right leg. He had slightly decreased sensation to light touch and pinprick in the posterior and medial portions of his right thigh, lateral aspect of the right leg, lateral right foot, second toe dorsally and fifth toe dorsally. The corresponding toes were noted to have nonpainful dorsal calluses []. The patient had negative straight leg raise bilaterally. Deep tendon reflexes were rated 2+ throughout except for an absent right ankle jerk reflex. Range of motion was full and symmetric in all lower extremity joints.\nIn addition, the patient exhibited tenderness to palpation in the infragluteal area in the right hamstring without radiation of pain, along with point tenderness in the region of the right knee lateral to the patella proximal to the head of the fibula. When walking, he complained of posterior thigh pain. The patient had no skin lesions overlying the right posterior thigh or elsewhere on his body, and no stigmata of neurofibromatosis. He had no scoliosis.\nMRI studies revealed a lesion at the right sciatic nerve extending 30 cm from the sciatic notch to the distal thigh. The tumor appeared hypointense on T2-weighted images, isointense-to-hypointense signal on the T1-weighted image with mild heterogeneous internal enhancement in a longitudinal orientation after administration of gadolinium contrast []. Associated muscle atrophy in the sciatic nerve distribution was also noted. MRI of the pelvis demonstrated no extension superior to the sciatic notch.\nThe patient's electromyography (EMG) showed electrodiagnostic evidence of a right sciatic neuropathy with evidence of ongoing denervation and reinnervation as demonstrated by increased insertional activity, positive sharp waves, and fibrillation potentials in the distribution of muscles innervated by the sciatic nerve.\nGiven the patient's history and the need for tissue diagnosis to elucidate treatment options, the patient initially underwent an ultrasound-guided biopsy followed by a computed tomography (CT)-guided biopsy of the mass, both of which were unsuccessful at obtaining adequate tissue for histologic diagnosis. The patient underwent an open biopsy through exposure of the sciatic nerve via a posterior gluteus maximus-splitting approach. The whole sciatic nerve appeared involved and was notably hypertrophic, firm, and bulbous []. The epineurium was thick. Neurolysis revealed no visual evidence of intervening nonneural tissue among the large and fibrous fascicles. Two fascicles were selected for biopsy. Postoperatively, the patient had no new neurological deficits, and remained stable by subjective report and by clinical examination.\nPathological examination showed the lesion to be a neuromuscular hamartoma (neuromuscular choristoma). Within the specimen, small nerve bundles and axons were seen intermixed with adjacent mature striated skeletal muscle bundles, surrounded by a dense collagenous matrix []. The skeletal muscle was noted to have small, bland, peripherally placed nuclei with mature features and no cellular atypia or atypical mitoses.\nThe specimens were embedded in paraffin and the sections were stained with hematoxylin and eosin and trichrome. A panel of immunohistochemistry stains was also performed. The S-100 and neurofilament stains showed normal nerve bundles. The Epithelial Membrane Antigen (EMA) stain was inconclusive. Desmin highlighted the hamartomatous striated muscle fibers intermingled with nerve bundles, and myogenin stain was negative for immature skeletal muscular elements.