Upfront Gamma Knife surgery for facial nerve schwannomas: retrospective case series analysis and systematic review

Introduction Facial nerve schwannomas are rare tumors and account for less than 2% of intracranial neurinomas, despite being the most common tumors of the facial nerve. The optimal management is currently under debate and includes observation, microsurgical resection, radiosurgery (RS), and fractionated radiotherapy. Radiosurgery might be a valuable alternative, as a minimally invasive technique, in symptomatic patients and/or presenting tumor growth. Methods We review our series of four consecutive cases, treated with Gamma Knife surgery (GKS) between July 2010 and July 2017 in Lausanne University Hospital, Switzerland. Clinical and dosimetric parameters were assessed. Radiosurgery was performed using Leksell Gamma Knife Perfexion. We additionally performed a systematic review, which included 23 articles and 193 treated patients from the current literrature. Results The mean age at the time of the GKS was 44.25 years (median 43.5, range 34–56). Mean follow-up period was 31.8 months (median 36, range 3–60). Two cases presented with facial palsy and other two with hemifacial spasm. Pretherapeutically, House–Brackmann (HB) grade was II for one case, III for two, and VI for one. The mean gross tumor volume (GTV) was 0.406 ml (median 0.470 ml, range 0.030–0.638 ml). The mean marginal prescribed dose was 12 Gy at the mean 54% isodose line (median 50%, range 50–70). The mean prescription isodose volume (PIV) was 0.510 ml (median 0.596 ml, range 0.052–0.805 ml). The mean dose received by the cochlea was 4.2 Gy (median 4.1 Gy, range 0.1–10). One patient benefited from a staged-volume GKS. At last follow-up, tumor volume was stable in one and decreased in three cases. Facial palsy remained stable in two patients (one HB II and one HB III) and improved in two (from HB III to II and from HB VI to HB III). Regarding hemifacial spasm, both patients presenting one pretherapeutically had a decrease in its frequency and intensity after GKS. All patients kept stable Gardner–Robertson class 1 at last follow-up. Conclusion In our experience, RS and particularly GKS, using standard, yet low doses of radiation, appear to be a safe and effective therapeutic option in the management of these rare tumors. The results as from our systematic review are also encouraging with satisfactory rates of clinical stabilization and/or improvement and high rate of tumor control. Complications are infrequent and mostly transient.