Functional Preservation After Planned Partial Resection Followed by Gamma Knife Radiosurgery for Large Vestibular Schwannomas

OBJECTIVE: The treatment goal for vestibular schwannomas (VS) has been changed from total removal of the tumor to functional preservation with long-term tumor growth control. The small-to medium-sized VS can be treated by stereotactic radiosurgery, but large VS require surgical decompression for the relief of cerebellar dysfunction and increased intracranial pressure. We have been performing planned partial surgical resections followed by gamma knife radiosurgery (GKS) for large VS. Here, we evaluate a recent series of such cases from the standpoint of functional outcomes. METHODS: From January 2000 to May 2013, we treated 40 patients with large unilateral VS (maximum tumor diameter at least 25 mm) with planned partial tumor removal followed by GKS for functional preservation. The median maximum diameter of the tumors was 32.5 mm (range 25-52 mm). All patients underwent surgery via the retrosigmoid approach, and tumors situated on the ventral and in the internal auditory canal intentionally were not removed, thus preserving cranial nerve functions. GKS was performed 1-12 months after surgical resection (median interval 3 months). The median tumor volume at GKS was 3.3 cm(3) (range 0.4-10.4 cm(3)) and the median prescribed dose was 12 Gy (range 10-12 Gy). The median follow-up period after GKS was 65 months (18-156 months). RESULTS: At the final follow-up, facial nerve preservation (House-Brackmann grade I-II) was achieved in 38 patients (95%; House-Brackmann grade I: 92.5%, II: 2.5%). Among the 14 patients with preoperative pure tone average (PTA) less than 50 dB, 6 of them (42.9%) maintained PTA less than 50 dB at the last follow-up. Two patients improved from severe hearing loss to PTA less than 50 dB (1 patient after surgery and 1 patient one and half years after GKS). Five-and 10-year tumor growth control occurred in 86% of patients. Four patients (10%) required salvage surgery; the predictive factor was tumor volume greater than 6 cm(3) at GKS (P = 0.01). CONCLUSIONS: Planned partial removal of large VS followed by GKS achieved a high rate of facial nerve and hearing preservation. To achieve long-term tumor growth control, the tumor volume at GKS after planned partial surgical resection should be smaller than 6 cm3. Our results revealed that patients with hearing preservation postoperatively have a chance of maintaining hearing function, even though the possibility exists of deterioration by long-term follow-up after surgical intervention and GKS. Furthermore, some patients with severe hearing loss before treatment have the chance of hearing improvement, even those with large VS.