The purely epithelioid malignant peripheral nerve sheath tumor.

The purely epithelioid malignant peripheral nerve sheath tumor (PNST) is a rare form of PNT possibly first described by McCormack et al. in 1954. This tumor type is distinguishable from the glandular PNT and PNT with differentiated neuroepithelium (medulloepithelioma and neuroepithelioma) and differs from the ordinary epithelioid PNT because of the absence of a spindle cell component typical of malignant PNSTs. The two examples of purely epithelioid malignant PNT we describe arose in the popliteal fossa from the sciatic and tibial nerves of men with no definite evidence of von Recklinghausen's neurofibromatosis. Both tumors were partly mucinous, and so closely mimicked carcinoma and a few non-neurogenic myxoid sarcomas histologically that their final classification depended upon proof of a neural origin.