Evaluation of tumor expansion after stereotactic radiosurgery in patients harboring vestibular schwannomas

OBJECTIVE: Stereotactic radiosurgery has been accepted as a safe and effective treatment in patients harboring a vestibular schwannoma. However, during follow-up, tumor expansion induced by high-dose irradiation can occur. Tumor expansion is more likely to be transient, but this phenomenon causes some confusion regarding whether further treatment should be performed. Our purpose was to clarify what type of tumor expansion requires additional treatment. METHODS: Between May 1991 and December 1998, 346 patients with a vestibular schwannoma, excluding two with neurofibromatosis, were treated using gamma knife radiosurgery. Of these, serial follow-up images to evaluate tumor expansion were available for 254 patients. Tumor expansion was classified into three types: central necrosis (Type A), solid expansion (Type B), and cyst enlargement or formation (Type C). RESULTS: Forty-two patients (17%) had tumor expansion during follow-up. Seventeen patients required additional treatment and 25 did not have any treatments after gamma knife radiosurgery. Type A, B, and C expansion was found in 14, 16, and 12 patients, respectively. Of these, three Type A patients, seven Type B patients, and seven Type C patients underwent salvage treatments. All patients in whom cyst formation developed eventually required craniotomy. CONCLUSION: Although tumor expansion was more likely to be transient, additional treatments should be considered in patients who experience neurological deterioration. We strongly recommend simply waiting and obtaining frequent follow-up images until the patients experience neurological deterioration, even when tumor expansion is developing, excluding cyst formation, which tends to continue.