Pigmented primitive neuroectodermal tumor with multipotential differentiation in cerebellum (pigmented medullomyoblastoma). A case with light- and electron-microscopic, and immunohistochemical analysis.

A 5-year-old girl had a midline cerebellar primitive neuroectodermal tumor (PNET) with neuronal, astrocytic, rhabdomyoblastic and melanocytic differentiation (a variant of pigmented medullomyoblastoma). The tumor recurred following surgery and radiation therapy and the child died within 6 months. Autopsy revealed spread into cerebellar hemispheres, subarachnoidal space and brain stem. Neuronal differentiation was verified by electron microscopy and antiserum against neurofilament protein. Neoplastic astrocytes were identified by use of antisera to glial fibrillary acidic and S-100 proteins. Rhabdomyoblasts were identified by the use of antisera against skeletal muscle type 2 myosin and myoglobin, as well as by electron microscopy. This tumor is compared with 20 previously reported cases of cerebellar PNETs containing muscle, 2 of which showed a similar pattern of multipotential differentiation. The oncogenesis of these tumors is in dispute although origin of both the neuroectodermal and mesenchymal components from the neural crest (mesectodermal differentiation) is most widely accepted.