小脳虫部原発卵黄囊腫の1例

Primary Yolk Sac Tumor in the Cerebellar Vermis. Case Report

Ⅰ．はじめに

　原発性脳腫瘍の中で胚細胞腫瘍は2.8％を占める比較的稀な疾患である¹⁶⁾．その発生部位は松果体部51.0％，鞍上部30.1％，基底核部3.3％と報告され¹¹⁾，後頭蓋窩での発生は稀である．今回，小脳虫部に原発した卵黄囊腫の1例を経験したので報告する．

　A 2-year-old boy presented with gait disturbance and limb ataxia. T1-weighted magnetic resonance (MR) imaging with gadolinium-diethylenetriaminepenta-acetic acid administration showed a heterogeneously enhanced mass lesion with a cystic component in the cerebellar vermis. The minimum apparent diffusion coefficient value of the lesion was 1.96×10^-3mm²/sec, and ¹H-MR spectroscopy showed elevated choline and lipid peaks, and decreased N-acetyl aspartate peak. The tumor was totally resected, and the histological diagnosis was yolk sac tumor. Consistent with this diagnosis, a-fetoprotein levels in the serum and cerebrospinal fluid were 7,094ng/ml and 22.3ng/ml, respectively. ¹⁸F-fluorodeoxyglucose-positron emission tomography, and thoracic, abdominal, and pelvic computed tomography showed no abnormal lesions, excluding the possibility of metastatic yolk sac tumor from an extracranial lesion. The patient received chemotherapy consisting of ifosfamide, cisplatin, and etoposide, and had not relapsed at 6 months after resection. Germ cell tumors rarely develop in the posterior fossa. This case suggests that yolk sac tumor could develop in the cerebellar vermis.