• Berndt Wowra, Alexander Muacevic, Anja Jess-Hempen, John-Martin Hempel, Stefanie Müller-Schunk, and Jörg-Christian Tonn.
• Gamma Knife Center Munik, and Departments of Neurosurgery and Ear, Nose, and Throat Surgery, Ludwig-Maximilians-University, Klinikum Grosshadern, Munich, Germany.
• J. Neurosurg. 2005 Jan 1; 102 (s_supplement): 114-118.

ObjectThe purpose of the study was to define the therapeutic profile of outpatient gamma knife surgery (GKS) for vestibular schwannoma (VS) by using sequential tumor volumetry to quantify changes following treatment.MethodsA total of 111 patients met the inclusion criteria. The median follow-up duration was 7 years (range 5-9.6 years). Thirty-seven patients (33%) had undergone surgery before GKS and 10 (9%) had neurofibromatosis Type 2 (NF2). The median VS volume was 1.6 cm3 (range 0.08-8.7 cm3). The actuarial 6-year tumor control rate after a single GKS treatment was 95%. Tumor swelling was observed in 43 patients (38.7%). Recurrence was significantly associated with NF2 (p < 0.003) and the reduced dose (p < 0.03) delivered to these tumors. The incidence of facial nerve neuropathy was mainly determined by surgery prior to GKS (p < 0.0001). Facial nerve radiation toxicity was mild and transient. No permanent facial nerve toxicity was observed. Trigeminal neuropathy occurred in 13 patients, and this was correlated with the VS volume (p < 0.02). The median hearing loss was -10 dB (range + 20 dB to -70 dB). The risk of hearing loss was correlated with age and transient tumor swelling (p < 0.05) but not with dose parameters or NF2.ConclusionsOutpatient GKS is feasible, effective, and safe. Its therapeutic profile compares favorably with that of microsurgery.

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