Functional Outcome of the Facial Nerve After Surgery for Vestibular Schwannoma: Prediction of Acceptable Long-Term Facial Nerve Function Based on Immediate Postoperative Facial Palsy

OBJECTIVE: To examine the relationship between immediate postoperative facial palsy and long-term facial palsy and identify a treatment strategy for vestibular schwannoma considering long-term outcomes of facial nerve function and tumor control. METHODS: Patients (N = 385) who underwent surgery in a single institution were reviewed retrospectively; 12 patients with neurofibromatosis, 6 with preoperative radiosurgery, and 14 with multiple surgeries were excluded. The generalized estimating equation method was used to show the correlation between immediate and later postoperative facial palsy and to identify the cutoff grade of immediate postoperative facial palsy. RESULTS: The tumor control rates for 1 year, 3 years, and 5 years were 88.7%, 83.9%, and 80.0%. Preservation of facial function above House-Brackmann (H-B) grades 1 and 2 was achieved in 47.9% of patients immediately post-operatively, in 50.1% after 1 month, and in 74.5% after >2 years. The immediate postoperative facial palsy grade showed a statistically significant relationship with the facial palsy grade on long-term follow-up (P < 0.001). H-B grade 3 immediate postoperative facial palsy was identified as the cutoff grade that showed the most significant relationship between the grade of immediate postoperative facial palsy and the grades above the cutoff (H-B grade 1-3) on long-term follow-up (P < 0.001). CONCLUSIONS: H-B grade of immediate postoperative facial palsy can predict facial palsy at long-term follow-up. H-B grade 3 immediate postoperative facial palsy is the lowest tolerable grade that guarantees functional improvement on long-term follow-up. Planned facial nerve preservation surgery followed by radiosurgery is thought to be optimal treatment in patients with vestibular schwannoma for both tumor control and facial nerve function.