Long-Term Nervus Intermedius Dysfunction After Retrosigmoid Vestibular Schwannoma Resection: Incidence, Independent Predictors, and Development of a Nomogram

BACKGROUND AND OBJECTIVES: This study retrospectively analyzed long-term nervus intermedius (NI) outcomes after vestibular schwannoma (VS) resection by the retrosigmoid approach and developed a postoperative risk stratification nomogram. METHODS: We retrospectively analyzed 262 patients who underwent retrosigmoid VS resection. Candidate predictors were prespecified, with age, sex, surgical period, and follow-up duration forced into the model and the remainder selected by akaike information criterion-based stepwise logistic regression. Discrimination was internally validated by 1000-resample bootstrap, with the bootstrap-corrected area under the curve as the primary metric. RESULTS: Long-term NI dysfunction occurred in 129 patients (49.2%), including dry eye in 115 (43.9%), hypogeusia in 45 (17.2%), and both in 31 (11.8%). Independent predictors were tumor diameter (adjusted odds ratio [aOR] 1.12, 95% CI, 1.06-1.19), poor facial nerve function (aOR 7.95, 95% CI, 2.62-28.64), operation time (aOR 1.77, 95% CI, 1.26-2.56), and trigeminal hypoesthesia (aOR 2.28, 95% CI, 1.03-5.17). The nomogram achieved an apparent area under the curve of 0.895 (bootstrap-corrected 0.888), with satisfactory calibration (Hosmer-Lemeshow P = .82; Brier 0.132) and net clinical benefit across risk thresholds of approximately 0% to 80%. CONCLUSION: NI dysfunction is a common yet underrecognized complication after VS surgery. The nomogram enables early postoperative identification of high-risk patients, supporting timely initiation of lacrimal function monitoring and ophthalmic referral.