Delayed Facial Nerve Dysfunction Following CyberKnife® Radiosurgery for Vestibular Schwannoma

Objective: The incidence and risk factors for facial nerve dysfunction (FND) following CyberKnife((R)) therapy for vestibular schwannoma (VS) remain poorly understood. This study investigates whether differential radiation doses to vulnerable segments of the facial nerve may be associated with FND outcomes. Methods: Patients were identified who underwent CyberKnife((R)) radiosurgery for VS at a single institution. Basic demographics, tumor characteristics, and facial nerve function were collected. Total radiation doses to tumor, internal auditory canal (IAC), and labyrinthine segment of facial nerve (LSFN) were evaluated. Results: Six out of 64 patients experienced FND following CyberKnife((R)) treatment for VS (9.38%, 6/64). Patients with FND were compared to those without FND (control). Of the 64 patients, complete radiation records were obtained for 30 patients (6 FND vs. 24 control). There were no significant differences in demographic or tumor characteristics between control and FND cohorts. More severe FND (HB >= 4) had significantly larger tumors (3.74 vs. 1.27cm(3), p=0.037) with directionally decreased time to FND (3.50 vs. 33.5months, p=0.106) than patients with HB<4, respectively. There were directionally, nonsignificant differences between maximum radiation doses to the LSFN (2492.4 vs. 2557.0cGy, p=0.121) and IAC (2877.3 vs. 2895.5cGy, p=0.824) between the control and FND cohorts, respectively. Conclusions: FND may represent an underrecognized sequelae of CyberKnife((R)) radiosurgery for VS that can occur many months following treatment. Further studies are needed to elucidate the effect of differential radiation exposure to the facial nerve with FND following treatment.