Hybrid schwannoma/perineurioma of the spinal nerve: multifocal occurrence, and recurrence as an intraneural perineurioma.

A 63-year-old Japanese man complained of lower back pain and numbness and was diagnosed as intradural tumors at the T11/12 and L1 level. The thoracic tumor originated from the posterior nerve root, and the lumbar tumor originated from the cauda equina. Five months after surgical resection, the patient developed recurrent tumor consisting of enlargement of multiple caudal nerves. Pathologically, the primary tumors showed a nodular and lobular pattern, including spindle cells in a fascicular, whorl and storiform pattern, with variable cellularity, nuclear palisading and frequent small onion bulb structures. Mild pleomorphism was present, and there were four mitoses per 10 high power fields. Many cells showed immunoreactivity for S-100 and Sox10. There were also claudin-1-positive spindle cells, but no epithelial membrane antigen (EMA)-positive cells. The cells in onion bulb structures were positive for claudin-1 and glucose transporter 1 (GLUT-1). These findings led to a diagnosis of hybrid schwannoma/perineurioma. The features of high cellularity, pleomorphism and a Ki-67 index over 10% suggested a low-malignant nature. The recurrent tumor also showed high proliferative activity, as reflected by mitotic figures and a Ki-67 index of 20%. This is the first case of spinal nerve hybrid schwannoma/perineurioma with low malignant potential and peculiar intraneural perineurioma component.