ガンマナイフ治療後にcyst formationを生じた三叉神経鞘腫の1例

Cyst Formation after Gamma Knife Radiosurgery for Trigeminal Schwannoma: A Case Report

Ⅰ．はじめに

　三叉神経鞘腫は手術による全摘出で治癒が得られるが，neuropathyによる顔面感覚障害などの術後合併症が出現する危険もある．Gamma knife radiosurgery（GKR）をはじめとする定位放射線治療の前庭神経鞘腫に対する有効性が確立され，脳幹圧迫などを伴わない小さな三叉神経鞘腫へのGKRも行われるようになってきたが，その長期的な効果，合併症についての報告は未だ少ない^5,8)．また，GKRの合併症の1つとして，脳動静脈奇形（arteriovenous malformation；AVM）における遅発性囊胞形成（delayed cyst formation）があるが^2-4,6,10,11)，脳腫瘍例では報告が少ない⁹⁾．今回，われわれは三叉神経鞘腫のGKR後，6年経過しcyst形成を生じ手術施行した例を経験したため文献的考察を含め報告する．

　Radiosurgery for small vestibular schwannomas is an established and effective treatment, and it has been used for trigeminal schwannoma recently. Delayed cyst formation is well recognized as a complication after gamma knife radiosurgery for arteriovenous malformation. We encountered a case of delayed cyst formation after gamma knife radiosurgery for trigeminal schwannoma. An 81-year-old male presented with abducens palsy and ataxia 6 years after gamma knife radiosurgery for trigeminal schwannoma. A cyst development in the posterior fossa was identified, and the brain stem was compressed by the cyst. The cyst was removed and the abducens palsy and ataxia improved within a month. Histological findings revealed variable tumor tissue in the cyst wall. Delayed cyst formation should be recognized as a complication after radiosurgery for schwannoma.