MALIGNANT PERIPHERAL-NERVE SHEATH TUMOR WITH PROMINENT INTRACYTOPLASMIC VACUOLATION - REPORT OF A CASE

A case of malignant peripheral nerve sheath tumor with uncommon featur es is reported, A mass was noted in the left thigh of a 16 year old ma n, Histologically, most areas of the tumor exhibited the typical appea rance of malignant peripheral nerve sheath tumor, but some tumor cells had rounded nuclei and cytoplasm, resembling an epithelioid pattern, It was noted that some rounded tumor cells showed prominent intracytop lasmic vacuolation, Immunohistochemically, almost all of the tumor cel ls, including the rounded and vacuolated ones, were positive for S-100 protein and vimentin, Electron microscopic study revealed well-develo ped cytoplasmic processes, intracytoplasmic intermediate-sized filamen ts, basement lamina formation and extracellular long-spacing collagens , These findings were compatible with those of Schwann cell differenti ation, Moreover, ultrastructurally, the vacuolated spaces contained a few granular materials and were derived from the dilatation of the rou gh endoplasmic reticulum, It is speculated that intracytoplasmic vacuo lation in malignant peripheral nerve sheath tumor would be caused by d egeneration of the tumor cells.