髄上皮腫類似の病理像を呈したテント上primitive neuroectodermal tumorの1例

A Supratentorial Primitive Neuroectodermal Tumor Exhibiting Pathological Characteristics of Medulloepithelioma: A Case Report

Ⅰ．はじめに

　Primitive neuroectodermal tumor（PNET）は主に小児に発生する稀な脳腫瘍で，組織学的に未分化な腫瘍細胞の密な増殖を認める．胎生期の上衣下層に存在し，神経細胞，グリア細胞，上衣細胞へと分化するgerminal matrix cellを起源とし，しばしば腫瘍細胞はこれら3種類のうちいずれかへの分化を認める． 一方，髄上皮腫（medulloepithelioma）はPNETの範疇の1つに分類され，組織学的には腫瘍細胞が上皮様に配列し，胎生期の神経管に類似した構造を呈する．今回われわれは，髄上皮腫の病理所見に類似した上皮性の分化を伴う，PNET with epithelial differentiationの症例を経験した．組織学的に稀な症例であり，文献的考察を加え報告する．

　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.