[Cyst formation after gamma knife radiosurgery for trigeminal schwannoma: a case report]

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.