Assessment of real-time clinical facial function during vestibular schwannoma resection.

OBJECTIVES

To describe a technique for quantifying residual facial function after vestibular schwannoma surgery. The intraoperative electrophysiological results are correlated with immediate postoperative clinical facial function to assess technique validity.

STUDY DESIGN

Prospective blinded study.

METHODS

Thirty-two patients undergoing translabyrinthine resection of vestibular schwannoma were included. Compound muscle action potential (CMAP) amplitude was calculated to supramaximal stimulation of the facial nerve, proximal to vestibular schwannoma compression, at the brain stem. The procedure was repeated after tumor removal. Comparison of the two CMAP amplitudes enabled estimation of change in facial function during surgery. The data were correlated with intracranial tumor diameter and immediate postoperative clinical facial function.

RESULTS

CMAP amplitude recorded after tumor resection correlated with immediate postoperative clinical facial function (0.879, P < .01). Correlation was improved when residual facial function was calculated (0.944, P < .01). In contrast, preoperative tumor size had relatively poor correlation with immediate postoperative facial function (0.688, P < .01).

CONCLUSIONS

Comparison of electrophysiological data before and after tumor removal reduces intersubject variability resulting from intersubject variation in facial muscle morphology. Residual facial function closely correlates with immediate postoperative clinical facial function, assessed using the House-Brackmann grading system. From the data presented, the technique can inform the surgeon of current clinical facial function at any point during the dissection process.