Factors Affecting Facial Nerve Outcome of Vestibular Schwannoma Surgery: Unit- and Multivariate Analyses

Objective: To carry out univariate and multivariate analyses of the factors affecting the facial nerve outcome of vestibular schwannoma surgery. Study Design: Retrospective cohort study. Setting: Tertiary referral center. Patients: Total 652 patients with histologically proven sporadic unilateral vestibular schwannomas treated surgically either by the translabyrinthine or the retrosigmoid approach was included. Outcome Measures: House-Brackmann (HB) classification at 2 years postoperatively. Univariate and multivariate analyses of factors determining facial nerve outcome was performed and the incidence of aberrant regeneration producing hemifacial spasm, metallic taste, and crocodile tears were recorded. Results: The facial nerve was maintained intact in 98% of cases. For tumors less than 1.5 cm, 95% were normal, 100% satisfactory (HB grade: I-III) and 0% unsatisfactory (HB grade: IV-VI). For tumors 1.5 to 2.4 cm in size, 83% normal outcome, 99% satisfactory, and 1% unsatisfactory; in tumors 2.5 to 3.4 cm, 68% normal outcome, 96% satisfactory, and 4% unsatisfactory. Tumors sized 3.5 to 4.4 cm, normal outcome in 52%, satisfactory in 80% and unsatisfactory in 20%;whereas in tumors larger than 4.5 cm, 50% had normal outcome, 72% satisfactory, and 28% unsatisfactory. Conclusions: Tumor size and year of operation were significant predictors of facial nerve outcome. The surgical learning curve was steepest in the first 50 patients and thereafter flattened out until the last 200 patients when there was an incremental improvement.