Pineal parenchymal tumors: cell differentiation and prognosis.

Eleven pineal parenchymal tumors were studied using various antibodies specific to the central nervous system and cell-proliferation-related antigen MIB-1 in order to examine the divergent types of cell differentiation and also evaluate prognosis. Electron microscopy was also performed. All tumors were immunohistochemically positive to chromogranin A and alpha B crystallin, and were also highly positive to retinal S protein. Pineocytoma cells contained microtubules, intermediate filaments, glial bundles, clear-centered vesicles and synaptic apparati. Pineoblastoma cells also had microtubules and neurofilaments, but glial filaments and definite synapses were not identifiable. Pineal parenchymal tumors were considered to be of pinealocyte origin, and there was a continuous spectrum of divergent cell differentiation between pineocytoma and pineoblastoma cells. The MIB-1 labeling index correlated well with histological malignancy, neuronal differentiation evaluated immunohistochemically by both neurofilament protein and synaptophysin, and cases with seeding potentials. Although histopathological features of neuronal development were, until recently, seen as the hallmark of benign prognosis in pineal parenchymal tumors, they are now thought to be only one of the pieces of evidence that may be used for purposes of prognosis.