Predictive Ability of Direct Electrical Stimulation on Facial Nerve Function Following Vestibular Schwannoma Surgery: A Systematic Review and Meta-analysis

Objective: Facial nerve preservation is critical in vestibular schwannoma (VS) surgery. Direct electrical stimulation (DES) is a widely used method for intraoperative localization of the facial nerve and assessment of nerve integrity. We sought to assess the predictive ability of DES parameters on facial nerve function post-VS surgery. Databases reviewed: A systematic literature search of English-language studies published from 1946 to 2019 was undertaken using EMBASE, MedLine/PubMed, and the Cochrane Central Register of Controlled Trials. Methods: Included studies involved patients undergoing VS surgery and assessed predictive ability of any DES parameter on postoperative facial function. Two authors independently reviewed studies and extracted data. Meta-analysis of diagnostic accuracy of DES parameters was used to calculate pooled sensitivities and specificities of common cutoffs. For DES parameters reported by less than four studies, outcomes were reported descriptively. Results: A MST cutoff of 0.10 mA had sensitivity of 0.76 (95% CI 0.53-0.90) and specificity 0.68 (95% CI 0.42-0.87) for facial function in the long term, and MST 0.05 mA had sensitivity 0.73 (95% CI 0.58-0.84) and specificity 0.74 (95% CI 0.59-0.85). CMAP amplitude < 500 mu V had sensitivity of 0.87 (95% CI 0.78-0.93) for poor short-term facial function. Conclusions: A CMAP amplitude response < 500 mu V is sensitive for poor short-term facial function, whereas MST values of 0.05 mA and 0.10 mA are both sensitive and specific in the long term. Other DES parameters may be able to accurately predict both short- and long-term postoperative facial function, but have been less studied.