Histopathological variants of central neurocytoma: Report of 10 cases

Central neurocytoma is a rare neuronal tumor affecting young adults and usu ally located in the lateral ventricles. Postoperative prognosis is generall y good. Histologically, central neurocytoma is composed of isomorphous smal l round or ovoid cells alternating with irregularly shaped patches of fibri llary matrix similar to the neuropile, In a series of 10 cases, two central neurocytomas were histologically "atypical" at first examination. One was intra-ventricular. and the second had an intra-parenchymatous juxta-ventric ular location. Both were highly cellular with mitotic activity, and tumor n ecrosis was seen in one. Neuronal differentiation was assessed by synaptoph ysin immunoreactivity in all 10 cases and by ultrastructural examination in four, including the two "atypical " forms. Neuronal differentiation was le ss marked in these "atypical" forms, one also presenting focal GFAP immunor eactivity, The proliferative potential was determined by MIB-1 labeling ind ex and compared with clinical outcome, The eight classical central neurocyt omas had a MIB-1 labeling index < 2.3 %, whereas the two "atypical" forms h ad a MIB-1 labeling index > 5.2 % and both recurred. We think that there is a spectrum of small-cell neuronal tumors. The two ex tremes could be the central neurocytoma and the primary cerebral neuroblast oma, while the intermediate forms might be qualified as "atypical neurocyto ma". In our series, the histological and immunohistochemical criteria of bi ological aggressiveness appeared to be high mitotic activity, tumor necrosi s, loss of neuronal differentiation and high MIB-1 labelling index.