TEM studies of primitive neuroectodermal tumors with neuronal and glial differentiation

Abstract

The term primitive neuroectodermal tumor (PNET) was originally applied in 1973 by Hart and Earle to refer to a group of undifferentiated cerebral neoplasms in children. Since that report, few studies have utilized the transmission electron microscope (TEM) to establish the identity of the tumor cells and to clarify the propensity of the PNETs for pluripotential differentiation. Of particular interest are reports which suggest the possibility of simultaneous neuronal and glial differentiation within the same cell. It would be of significant interest to know if the propensity to divergent differentiation can be explained by a single population of neoplastic cells that have the potential to differentiate in multiple directions. We will present a small series of cases with ultrastructural evidence that some of the cells in the tumors express both neuronal and glial features.The first case is a primary cerebral neuroblastoma which was associated with a population of neoplastic glial cells. At the ultrastructural level neuroblast and glial cell populations were identified. We also recognized a population of cells which displayed a continuous basal lamina and rare, poorly developed junctional complexes. Of particular interest was yet another, smaller, population of cells which displayed both dense-core granules and microtubules typical of neuroblasts and abundant cytoplasmic filaments typical of glial cells (Figure 1). In two other cases, the astrocytic nature of the cells was confirmed at the ultrastructural level on the basis of prominent glial filaments in the cytoplasm. However, some of the astrocytes in one of the cases were invested partially by a distinct basal lamina (Figure 2), and there were dense-core granules in the cytoplasm (Figure 2, inset).