Immunohistochemical study concerning the origin of neurocytoma--a case report.

A 26-year-old woman presented with rapid tumor growth in her left frontal lobe during 9 years of observation. Operative findings revealed a massive tumor connected to gelatinous, transparent membranous tissue (MT), which extended from the paraventricular zone and continued into the lateral ventricle. Histological diagnosis was atypical neurocytoma. Immunohistochemical analyses revealed that the tumor was strongly positive for not only neural markers but also a glial marker, while the MT was positive for a neural marker. The Ki-67/MIB-1 labeling index was 9.1% in the tumor body and 0% in the MT. Musashi 1, a marker of neural stem cells, was strongly positive in both the tumor body and the MT. We speculate that the tumor growth was due to a rapid decline of the Musashi 1-positive cells to glial differentiation. These cells may be candidates for the origin of the tumor.