Central neurocytoma: immunohistochemical and ultrastructural study.

Eight cases of central neurocytomas were studied by immunohistochemistry and electron microscopy. Seven tumors were located in the lateral ventricles and one in the subependymal region. All but one patient had a favorable postoperative course. The tumors were composed of small uniform cells possessing amitotic round nuclei with frequent perinuclear halos, a few Homer Wright rosettes and no ganglion cells; an appearance resembling that of oligodendroglioma. Immunohistochemical studies disclosed neuron-specific enolase and Leu-7 positivity in all tumors, S-100 protein-positive cells were found in six, while glial fibrillary acidic protein--and vimentin-positive cells were confined to the blood vessels. Myelin basic protein as well as neurofilament were not detected in the tumors. Synaptophysin-positive areas were seen in one tumor. Ultrastructural examination showed distinctive neuronal tumor cells which had a cytoplasm with sparse dense-core vesicles and thin cell processes containing parallel microtubules. They were classified into three different types of tumor cells according to the extent of differentiation. The most consistent finding for histological diagnosis was the presence of typical or abortive synapses with clear and dense-core vesicles. Additionally, synaptophysin may be a specific marker for some central neurocytomas.