Malignant peripheral nerve sheath tumor arising from benign vestibular schwannoma treated by gamma knife radiosurgery after two previous surgeries: a case report with surgical and pathological observations.

Background Gamma knife radiosurgery (GKRS) is an effective treatment for vestibular schwannomas with lower morbidity and mortality. However, malignant transformation associated with GKRS, although uncommon, has been reported in recent publications. Methods We describe a case presenting with malignant peripheral nerve sheath tumor (MPNST) at 8 years after GKRS after incomplete resections. Results The tumor appeared to be a typical benign schwannoma at the surgery preceding GKRS, and rapidly enlarged after long-term control, causing progressive neurological deterioration. Operative findings showed that the tumor was composed of two different components, and histopathology distinctively demonstrated MPNST and benign schwannoma. Conclusions The coexistence of benign and malignant components might indicate that the present MPNST had arisen from the benign schwannoma by transformation in association with GKRS.