Papillary glioneuronal tumor with minigemistocytic components and increased proliferative activity.

Papillary glioneuronal tumor (PGNT) is a rare and new type of glioneuronal neoplasm of the central nervous system. It is characterized by pseudopapillary structures composed of hyalinized vessels rimmed by cuboidal glial cells and the proliferation of neuronal cells. We report a peculiar PGNT arising in the parietal lobe of a 67-year-old man, which was characterized by proliferation of minigemistocytic cells as well as typical components. The minigemistocytic cells had eccentric nuclei and plump eosinophilic cytoplasm that was filled with glial filaments. The Ki-67 labeling index was as high as 10% in the minigemistocytic areas. Recently, the presence of oligodendroglial-like component was suggested in PGNT. Considering that oligodendroglioma sometimes accompanies minigemistocytic components, the minigemistocytic cells in PGNT were suggested to be a part of oligodendroglial differentiation. Although PGNT is defined as an indolent glioneuronal tumor, the presence of minigemistocytic components with the high Ki-67 labeling index may indicate more aggressive nature.