両側小脳橋角部転移性脳腫瘍の1例

A Rare Case of Metastatic Brain Tumors in the Bilateral Cerebellopontine Angles

Ⅰ．はじめに

　小脳橋角部腫瘍の多くは神経鞘腫や髄膜腫などの良性腫瘍であり，悪性腫瘍は稀である^9,15)．頻度として，75〜90%は聴神経腫瘍であり，転移性脳腫瘍は1%と低い¹⁵⁾．また，両側性に発生する場合，神経線維腫Ⅱ型に伴う神経鞘腫がほとんどである^9,15)．今回われわれは，難聴と顔面神経麻痺が急速に出現し，原発巣の診断に難渋した両側小脳橋角部への転移性脳腫瘍の1例を経験したので，文献的考察を加えて報告する．

　We encountered a rare case of metastatic brain tumors in the bilateral cerebellopontine angles. The patient was a 61-year-old man, who visited an otorhinolaryngology clinic with complaints of rapidly progressing bilateral hearing impairment and facial palsy. The patient was referred to our hospital because tumorous lesions were suspected in the bilateral cerebellopontine angles on brain magnetic resonance imaging. Regarding tumor markers, the patient's cancer antigen 19-9 and carcinoembryonic antigen levels were high, which suggested metastasis. However, no abnormal findings other than abdominal lymph node enlargement were detected on whole-body examination, and no primary lesion was identified. The tumor in the right cerebellopontine angle was excised using the lateral suboccipital approach and subjected to pathological examination. It was diagnosed as an adenocarcinoma；thus, both lesions were considered brain metastases from a malignant abdominal tumor, and radiochemotherapy was administered to the patient. Unfortunately, the patient died after 89 days of treatment, and a pathological autopsy revealed that the primary lesion was a common bile duct tumor. No dural metastasis was noted in the brain or spinal cord；however, tumors were detected in the epiarachnoid space during surgery. Metastasis to the bilateral cerebellopontine angles occurred in the same period, which was indicative of ascending metastasis through the vertebrobasilar artery. Hence, we suggest that progressive bilateral hearing impairment and facial palsy were a consequence of brain tumors that had metastasized bilaterally to the cerebellopontine angles.