Soft Tissue Perineurioma

ABSTRACT

Perineurial cells, which normally surround the nerve fascicles within a nerve, can be distinguished from Schwann cells by their immunoreactivity for epithelial membrane antigen (EMA) and lack of reactivity for S-100 protein. Perineurioma is a form of benign peripheral nerve sheath tumor (PNST) almost exclusively composed of perineurial cells. It is often difficult to differentiate this tumor from the other benign PNSTs or ectopic meningioma by histology alone. Immunohistochemical and electron microscopic studies are helpful for differential diagnosis. We recently experienced a case of soft tissue perineurioma in a 14-year-old girl. This tumor was presented as a 5.6 cm sized subcutaneous movable mass in the elbow. The well encapsulated soft tissue tumor consisted of spindle cells which have whorling and storiform patterns within the collagenous stroma. The spindle cells were stained positive for EMA but negative for S-100 protein, chromogranin, neuron-specific enolase or Leu-7. Ultrastructurally, they possessed long cytoplasmic processes with incomplete basal lamina, primitive intercellular junction and occasional pinocytotic vesicles.