Functional Outcomes of Salvage Surgery for Vestibular Schwannomas after Failed Gamma Knife Radiosurgery

OBJECTIVE: We reviewed our experience with salvage surgery following failed gamma knife radiosurgery (GKS) for vestibular schwannomas. METHODS: The study comprised 18 patients with unilateral vestibular schwannomas. The median prescribed radiation dose was 12 Gy (range, 10-12.5 Gy). Nine patients had regrowth after GKS, and 9 had regrowth after surgical resection plus GKS. The median interval between GKS and surgical resection was 26 months (range: 4-66 months). The maximum tumor diameter of all patients ranged 25-43 mm (median 35.5 mm). The tumor was removed subtotally in 2 patients and partially in the other 16 patients. The median follow-up period after surgical resection was 60 months (range: 12-144 months). RESULTS: Among the 17 patients with preoperative preserved facial nerve function (House-Brackmann [HB] grade I-III), 14 of them (82%) had an HB score of grade I at the last follow-up. There were no differences in facial nerve preservation between those with failed GKS and those with failed GKS plus surgery (78% vs. 100%, P = 0.156). At the post-salvage surgery follow-up, the residual tumor was unchanged or decreased in 15 patients (83%) and increased in 3 patients (17%). CONCLUSION: A surgical indication after GKS should be carefully considered because of the natural regression of transient tumor expansion with time, and surgical resection is limited to subtotal or partial removal for functional preservation. Careful follow-up is necessary in patients with tumor regrowth several years after GKS due to delayed radiation effects.