Efficacy of Intraoperative Neuro-Monitoring to Localize the External Branch of the Superior Laryngeal Nerve

Background: This study investigated whether visual localization of the external branch of the superior laryngeal nerve (EBSLN) coincides with its localization via intraoperative neuro-monitoring (IONM) during thyroidectomy and whether its use influences the frequency of injuries. Methods: A prospective, comparative, cross-sectional, observational study was performed in 240 superior thyroid poles. The metrics were visual identification of the EBSLN and its corroboration with IONM. The frequency of EBSLN injuries was also determined. Statistical analysis was achieved via kappa and chi-square tests, as well as odds ratios (OR). Results: Of the 240 superior thyroid poles, IONM identified 234 (97.5%) EBSLN, whereas 190 (79.1%) were identified visually: OR=10.35 [CI 4.37-24.65] p<0.0001. Of the 190 EBSLN identified visually, 150 were confirmed through IONM. Indeed, their structure corresponded to an EBSLN to yield a kappa with a linear weighting value of 0.362. The standard error was 0.0467 [CI 0.2686-0.4554], indicating a fair agreement between the visual and IONM classification. Conclusion: IONM identified 97.5% of EBSLN cases. It was higher than the visual identification. There were no injuries to EBSLN identified through IONM.