Ultrastructure of primitive neuroectodermal neoplasms of the central nervous system.

The ultrastructure of one spinal and five cerebral neoplasms diagnosed by light microscopy as primitive neuroectodermal tumors supports a cell population consisting largely of poorly differentiated neuroepithelial cells. The most unique ultrastructure feature was the presence of annulate lamellae in four of the six cases. Glial cells in the neoplasm were not unequivocally of neoplastic origin and were possible reactive. There was no evidence of neuroblastic or neuronal elements, although there was frequently focal early neuroblastic differentiation by light microscopy. Although we have seen neoplasms which are clearly neuroblastic, these particular tumors are not purely neuroblastic and should not be classified as neuroblastomas.