REPEAT GAMMA KNIFE SURGERY FOR REGROWTH OF VESTIBULAR SCHWANNOMAS

OBJECTIVE: Gamma knife surgery (GKS) has become established as a minimally invasive treatment modality for patients with vestibular schwannomas. Treatment failure and/or tumor regrowth, however, is occasionally encountered, and microsurgical resection is usually warranted in such cases. The role of repeat GKS in these situations is still unclear. The goal of this study was to investigate whether repeat GKS is an effective treatment for recurrent vestibular schwannomas and to assess the conservation of residual neurological function. METHODS: Between July 1992 and December 2007, 1951 patients harboring a unilateral vestibular schwannoma were treated with GKS. Of these, 48 patients (2.5%) had to undergo a subsequent intervention because of progression or regrowth of the tumor. Repeat GKS was performed in a total of 15 patients, 8 of whom had more than 2 years of follow-up and were eligible to be enrolled in the present study. The median follow-up period after repeat GKS was 64 months, and the median interval between these interventions was 46 months. The median tumor volume was 0.51 and 1.28 mL at the initial and second GKS treatments, respectively. Patients received a median prescription dose of 12.0 Gy at both interventions. RESULTS: We report no cases of failure. Six patients demonstrated a significant reduction in tumor volume. In 1 patient, the final tumor volume was less than the initial volume. The other 2 patients showed stabilization of tumor growth. Useful hearing ability was preserved in only 1 of the 3 patients who had serviceable hearing ability at the time of the second GKS. Neither aggravation of facial nerve dysfunction nor other neurological deficits secondary to GKS were observed. CONCLUSION: This is the first report to address repeat GKS for vestibular schwannomas. After long-term follow-up, repeat GKS with a low marginal dose seems to be a safe and effective treatment in selected patients harboring regrowth of small vestibular schwannomas that have previously been treated with GKS.