小脳に発生したpleomorphic xanthoastrocytomaの1例

A Case Report of Cerebellar Pleomorphic Xanthoastrocytoma

Ⅰ．はじめに

　Pleomorphic xanthoastrocytoma（PXA）は1979年に報告された，若年に発症する星細胞腫の一亜型でWHO gradeⅡに分類される腫瘍である．好発部位はテント上，特に側頭葉であり，その好発部位より痙攣発作やてんかんの長期経過のうちに発見されることが多い^3,7,12)．一方で小脳の発生例は現在までに16例の報告があるのみである^{1,2,4-6,8-11,14-19)}．一般に予後良好であるが，10～20％に再発あるいは悪性転化がみられるとの報告もある¹³⁾．

　今回われわれは，成人の小脳虫部に発生したPXAの1症例を経験したので，画像所見，病理所見について文献的考察を加え報告する．

　Pleomorphic xanthoastrocytoma (PXA) is a type of astrocytic neoplasm, classified as WHO gradeⅡ, which mainly occurs supratentorially, and rarely infratentorially. We report an unusual case of PXA in the cerebellar vermis.

　A 36-year-old man presented with headache and gait disturbance. Magnetic resonance imaging and computed tomography demonstrated a mass lesion with cyst in the cerebellar vermis. The patient underwent total resection. Histological examination demonstrated nuclear and cytoplasmic pleomorphism, and xanthomatous change. Immunohistochemical examination demonstrated xanthomatous cells expressing glial fibrillary acidic protein. The histological diagnosis was PXA of the cerebellar vermis. The patient did not receive radiation therapy or chemotherapy after resection, and has experienced no recurrence for 12 months.

　This case suggests that PXA should be considered in the differential diagnosis of cystic lesion in the cerebellar vermis.