Central neurocytomas are composed of a uniform population of round cells with scant cytoplasm in a fibrillary background. The nuclei have finely speckled chromatin and punctate nucleoli. A delicate vascular network of capillaries is usually present. The tumor cells show ultrastructural evidence of neural differentiation and are immunoreactive for synaptophysin, NSE, and other neural markers. Rare atypical forms have been reported with increased mitotic activity, necrosis, and cytologic atypia. The differential diagnosis generally includes intraventricular oligodendroglioma (from which they may be indistinguishable on light microscopy) and ependymomas.