MPNST : Architecture
Malignant peripheral nerve sheath tumor (MPNST) is a highly cellular neoplasm resembling fibrosarcoma and is composed of monomorphic spindle cells arranged in interlacing fascicles, palisades, and whorls. The tumor may show compact hypercellular areas alternating with hypocellular foci with myxoid stroma. Focal nuclear palisading and whorled arrangement of spindle cells suggesting tactoid differentiation may also be seen. Other less commonly seen features include hyalinized cords and nodules and proliferation of plump epithelioid tumor cells within the vessel walls. There are areas of geographic necrosis with palisading at the edges, similar to that seen in glioblastoma. Mitotic activity is increased. About 15% of cases show heterologous elements such as bone, cartilage, skeletal muscle, mucinous glands and squamous islands. MPNST with well-developed skeletal muscle elements has been labeled Malignant Triton Tumor.