高齢者小脳半球malignant astrocytomaの1例

An Elderly Patient with Cerebellar Malignant Astrocytoma

Ⅰ．はじめに

　小脳半球astrocytomaは原発性脳腫瘍の3.5％⁹⁾，全gliomaの8％の頻度といわれている⁴⁾．小児でしばしばみられ，小児原発性脳腫瘍の10％¹⁸⁾，小児後頭蓋窩腫瘍の25％程度の頻度である¹⁸⁾．一般に高分化型の腫瘍が多く，摘出により放射線療法なしで長期の寛解が得られ，予後は比較的良好とされている．

　一方，成人においては，原発性小脳半球astrocytomaは非常に稀な疾患で²⁾，特に70歳代，80歳代ではほとんどみられない¹⁴⁾．しかし発生した場合の組織形は，低分化型が多く，予後も一般に不良とされている^{2,8,11,12,14,17)}．今回われわれは，初回受診時に転移性脳腫瘍の診断となり，ガンマナイフにて治療したが，その2年後に囊胞性変化を来し，摘出術を行ったところ小脳malignant astrcytomaと判明した高齢者の1例を経験したので治療上の反省点を含めて報告する．

　Malignant cerebellar astrocytoma is very rare and the prognosis is extremely poor. We report herein the case of an elderly patient with malignant cerebellar astrocytoma. This 80-year-old man initially presented with dizziness and ataxia of the right hand. Metastatic cerebellar tumor was diagnosed on first admission, based on a past history of colon cancer treated by surgery and magnetic resonance imaging (MRI) findings supporting the diagnosis of metastasis. The patient underwent gamma knife surgery (20Gy) and was discharged. Follow-up after discharge was insufficient. Two years after gamma knife surgery, he returned to our hospital complaining of dizziness, headache, and right limb ataxia. MRI revealed a cystic mass in the right cerebellar hemisphere, and the lesion was removed by right suboccipital craniotomy. The tumor represented malignant astrocytoma. Optimal management of patients harboring sush difficult-to-treat tumors, including the role of gamma-knife radiosurgery, is discussed.