[A supratentorial primitive neuroectodermal tumor exhibiting pathological characteristics of medulloepithelioma: a case report].

A 50-year-old female presented with headache symptoms and left hemifacial paresis. Brain computed tomography and magnetic resonance images demonstrated a right frontal lobe tumor with hemorrhage and calcification. A gross total resection was carried out. Pathologically, the tumor exhibited three kinds of structures. The first was an astrocytic area which occupied the large part of this tumor. Small, round cells, which were positive for glial fibrillary acidic protein, were randomly distributed. The second was an epithelioid area with the highest MIB-1 labeling index of the three structures. Undifferentiated tumor cells demonstrated a dense proliferation, and short spindle-shaped cells exhibited an epithelial and a partly luminal alignment that resembled the embryonal neural tube. The third was a sarcomatoid area. Long spindle-shaped cells, which were positive for vimentin, were in a bundle-like form. We diagnosed this tumor as a primitive neuroectodermal tumor (PNET) with epithelial differentiation. PNETs are rare brain tumors with a predominance in children. Histologically, undifferentiated tumor cells demonstrate dense proliferations. The tumor arises from germinal matrix cells that differentiate into neuronal, glial, and ependymal cells. Medulloepithelioma, which is classified in the PNET category, is a very rare brain tumor that usually develops in childhood. Pathological studies have demonstrated that papillary, tubular, or trabecular arrangements of neoplastic neuroepithelium mimic the embryonic neural tube predominantly. In our case, the tumor partly demonstrated epithelial differentiation, which is a feature of medulloepithelioma, not only glial and mesenchymal differentiation. This is a rare case of PNET with uncommon histological features.