Abstract

Neuromuscular choristoma is a rare benign tumor of the peripheral nerves. To the best of our knowledge, 21 cases have been reported to date. We describe here a 20-day-old female infant who presented with a buttock mass (4.5 x 4.1 x 3.2 cm on MRI) arising from the left sciatic nerve. Microscopically, it was characterized by an intimately disorganized mixture of nerve fibers and striated muscle fibers that were occasionally surrounded by the perineurium and separated by fibrous bands of varying thickness. In some areas, there appeared to be some cells in transitional forms between nerve fibers and muscle fibers, revealing variously positive expressions for S-100 protein in the muscular components. These findings are consistent with the hypothesis that neuroectodermal-derived Schwann cells can give rise to mature skeletal muscle. It appears that the fibrosis may be related to the degeneration of the neural components. The size of the mass on MRI has been unchanged during the 3-year follow-up period.

• Keywords: Neuromuscular choristoma;Sciatic nerve;Striated muscle fiber;Schwann cell;