Prior Surgical Resection is a Predictor of Facial Nerve Function Decrement after Radiosurgery for Vestibular Schwannomas

Purpose Gamma Knife radiosurgery (GKRS) is a common treatment modality for vestibular schwannomas (VS). Following surgical resection, GKRS can serve as adjunctive treatment for residual or recurrent tumor. However, it is poorly understood whether prior surgical resection influences the risk of facial nerve injury from GKRS. Methods An institutional database of GKRS treating adult VS was queried for patients with > 2 years of follow-up post-GKRS. Two cohorts were identified: patients with surgical resection prior to GKRS and patients receiving only GKRS. Facial nerve function was graded with the House-Brackmann (HB) scale pre-GKRS and post-GKRS until last follow-up. Results There were 31 patients in the surgery-GKRS cohort and 107 in the GKRS-only cohort. The surgery-GKRS cohort had a significantly lower median age (57.1 vs 63.6 years) and higher median tumor volume at time of GKRS (1.96 vs 0.84 cm ³ ). Facial nerve function worsened within 2 years post-GKRS in 7/31 (22.6%) of surgery-GKRS patients and 7/107 (6.5%) of GKRS-only patients. At last follow-up, facial nerve function worsened in 5/31 (16.1%) of surgery-GKRS patients and 3/107 (2.8%) of GKRS-only patients. After controlling for patient, tumor, and radiosurgical parameters, surgical resection prior to GKRS was significantly predictive of facial nerve function decrement after GKRS within 2 years and at last follow-up. Larger tumor volume was predictive of facial nerve function decrement at last follow-up. Conclusions Prior surgical resection may be an underestimated risk factor for new/worsened facial palsy following GKRS for VS, possibly due to less reserve in the nerve.