小児の中脳放射線障害―著しい神経症状を呈した脳腫瘍2例の検討

Fulminating Midbrain Irradiation Injury of Pediatric Brain Tumor

要旨　小児脳腫瘍への定位放射線治療などの適応は広がっているが，中脳放射線障害の報告は稀である。著しい神経症状を呈した2小児例を報告する。症例1は4年前に中脳水道狭窄，水頭症でシャント術，第三脳室穿孔術後の12歳男児で，径2.0 cmのtectal gliomaを認め，生検後γナイフ照射を受けた。3週間後より複視，1カ月後両側眼瞼下垂，進行性に両側動眼神経麻痺，意識障害が出現，ステロイドなど保存的治療に反応せず腫瘍の容量は約4～6倍に増大した。減圧摘出術を行い症状は消失し，早期放射線晩発障害と病理診断された。症例2は6歳女児，髄芽腫にて摘出術，シャント術後，化学療法および全脳と局所に分割照射を受けた。照射最終日，突然意識障害が出現した。MRI上，中脳びまん性変化と脳室拡大を認めた。照射線量は耐用線量以下で安全域と考えられた線量であった。小児の中脳を含む放射線治療は神経学的緊急症をきたし得るので，注意が必要である。中脳放射線障害の特異性について考察を加えた。

We report two children with post radiation midbrain damage causing severe neurological symptoms. A twelve-year-old boy with a four year history of hydrocephalus was diagnosed with tectal glioma, which endoscopic biopsy revealed to be low grade. He underwent γ knife radiation surgery （central 24 Gy/peripheral 12 Gy）. Two months later bilateral ptosis followed by total oculomotor palsy and drowsiness developed. Despite pulsed-steroid therapy the tumor size increased up to 4.6 times in volume. The tumor was totally removed and was diagnosed as an early delayed radiation reaction pathologically. His symptoms disappeared except for a slight upper gaze palsy. The second patient was a six-year-old girl with a medulloblastoma. Following total resection and a VP shunt she received conventional radiation therapy along with chemotherapy. After the final irradiation she became comatose （JCS II-2） and MRI revealed diffuse midbrain damage with acute aqueduct obstruction, which recovered in two weeks. Reports of irradiation injuries of the midbrain in childhood are rare but it should be considered as a possible cause of fulminant symptoms requiring emergency treatment. Because of midbrain anatomical complexity, midbrain radiation therapy requires great care, especially in children.

（Received : May 30, 2005）