MPNST

Comments:
The diagnosis of malignant peripheral nerve sheath tumor (MPNST) is made if a fibrosarcomatous-appearing tumor : 1) obviously arises from a peripheral nerve; or 2) the tumor arises from a preexisting neurofibroma in NF1; or 3) the tumor has histologic features of a malignant Schwann cell tumor – including hyper- and hypocellular areas, irregular wavy hyperchromatic nuclei with tapered ends, whorled structures, epithelioid appearance of perivascular tumor cells, and immunohistochemical or ultrastructural evidence of Schwann cell differentiation.

In this image, the uninvolved portion of the nerve is separated from the tumor by a well-defined epineurium.