Central neurocytoma with ependymoma-like glial component.

We present the first case of central neurocytoma with a component suggesting ependymal-like differentiation as an unclassified glioneuronal tumor. The patient was a 26-year-old Japanese man with a brain tumor extending from the frontal wall of the bilateral lateral ventricles to the corpus callosum. Histologically, the tumor's neuronal component consisted of small bland looking cells with fine, delicate, neuropil-like processes forming a rosette structure; its glial component consisted of tumor cells with thick processes arranged around the thinly walled vessels, resulting in a perivascular pseudo-rosette formation and indicating ependymal-like differentiation. Immunohistochemically, the cytoplasm of the tumor cells with ependymal-like features was positive for glial fibrillary acidic protein and negative for synaptophysin, while the tumor component with neuronal features showed the opposite immunohistochemical staining pattern. Most of the tumor cells were positive for Olig2, but EMA, D2-40, CD99, p53, and mutant IDH-1 (R132H) were totally negative. Its Ki-67 labeling index was less than 1 %. Histologically, this tumor was diagnosed as a central neurocytoma with an ependymoma-like glial component, and its tumor grade was estimated at grade II. The tumor location, infiltrating the corpus callosum, and histology were distinctive and might represent a peculiar subtype of glioneuronal tumor.