Long-Term Nervus Intermedius Function Outcomes and Their Predictors in Patients With Vestibular Schwannoma After Microsurgery.

[BACKGROUND AND OBJECTIVES] The aim of this retrospective study was to identify predictors of long-term dysfunction of the nervus intermedius (NI) after vestibular schwannoma (VS) surgery.

[METHODS] A follow-up questionnaire was administered to patients who underwent VS resection by the retrosigmoid approach between December 2018 and May 2024. All patients were followed for at least 6 months after surgery, and a total of 439 patients were included in the final analysis. Clinical data, including tumor size, surgical outcomes, and postoperative facial nerve (FN) and hearing function, were retrospectively reviewed. Univariate and multivariate logistic regression analyses were performed to determine predictors of long-term NI dysfunction.

[RESULTS] Among the 439 patients, 216 (49.2%) reported long-term NI dysfunction, including 98 (22.3%) with taste dysfunction, 184 (41.9%) with eye dryness, and 66 (15.0%) with both symptoms. NI dysfunction was significantly associated with maximum tumor diameter (P < .001), extent of resection (P = .005), FN function at discharge (P < .001), and hearing outcomes (P = .002). Multivariate analysis identified poor FN function at discharge and unserviceable hearing as independent predictors of long-term NI dysfunction. For taste dysfunction, cystic tumor (P = .016) and poor FN function at discharge (P = .020) were significant, with both factors emerging as independent predictors. For eye dryness, significant variables included tumor size (P = .008), FN function at discharge (P < .001), and hearing outcomes (P = .023), although only poor FN function was independently predictive.

[CONCLUSION] Long-term NI dysfunction is a common and under-recognized complication after VS surgery. Poor FN function and unserviceable hearing at discharge independently predict NI dysfunction. In addition, cystic tumor type and poor FN function predict taste dysfunction, whereas poor FN function alone predicts eye dryness. These factors may aid in prognostication and guide surgical planning and postoperative counseling.