Objective: To assess the validity of intraoperative minimal stimulation threshold (MST) for predicting long-term facial function after vestibular schwannoma surgery.
Study design: Prospective blinded study.
Methods: MST after tumor dissection and postoperative clinical facial function, assessed using the House Brackmann grading system (HB), were used to predict long-term clinical facial function, recorded at least 6 months after surgery.
Results: Two hundred and nine consecutive patients fulfilled selection criteria and 184 had successful intraoperative electrophysiologic monitoring and were eligible for further study. MST of 0.05 mA had moderate accuracy for predicting good long-term facial function, with 94% sensitivity, 91% positive predictive value (PPV), 60% specificity, and 70% negative predictive value (NPV). A more relevant group of 77 patients with poor postoperative facial function (HB III-VI) were assessed for predicting good long-term function. Applying this criteria, test accuracy fell, with 83% sensitivity, 64% PPV, 60% specificity, and 75% NPV. Postoperative clinical facial function had a greater accuracy for predicting good long-term function, with 83% sensitivity, 79% PPV, 75% specificity, and 79% NPV. A model of predicted probabilities of good outcome (HB I and II) was derived from a logistic regression with two additive predictors (postoperative HB and MST). This demonstrated that for patients with postoperative HB grade V, MST aided prediction.
Conclusions: Intraoperative stimulation thresholds, when assessed against a relevant group of patients with poor postoperative facial function, had poor predictive accuracy. The severity of immediate postoperative clinical facial function was the most accurate predictor of long-term outcome. MST aided long-term prediction in a small but relevant group of patients with postoperative HB grade V facial function.