Is intraoperative neural monitoring necessary for exploration of the superior laryngeal nerve?

Background: We aimed to evaluate the contribution of intraoperative neuromonitoring to the visual and functional identification of the external branch of the superior laryngeal nerve and the effect on postoperative voice changes.

Methods: The prospective data of 221 patients (183 women, 38 men) who underwent thyroid operation with intraoperative neuromonitoring for exploration of the external branch of the superior laryngeal nerve were evaluated retrospectively. The surface endotracheal tube-based Medtronic NIM3 (Medtronic, Jacksonville, FL) intraoperative neuromonitoring device was used. The function of the external branch of the superior laryngeal nerve was evaluated by cricothyroid muscle twitch. Additionally, the contribution of the external branch of the superior laryngeal nerve to vocal cord adduction was evaluated using electromyographic records.

Results: A total of 374 (95.2%) of 393 external branch of the superior laryngeal nerves were identified; 145 (36.9%) external branch of the superior laryngeal nerves were identified visually before being stimulated with a probe, and 130 (33.1%) external branch of the superior laryngeal nerves were identified visually after being identified with a probe. Although 99 (25.2%) external branch of the superior laryngeal nerves were identified with a probe, they were not visualized. Intraoperative neuromonitoring provided meaningful contributions to visual (P = .001) and functional (P = .001) identification of the external branch of the superior laryngeal nerve. Positive electromyographic responses were recorded from 257 external branch of the superior laryngeal nerves (68.7%). After the patients with recurrent laryngeal nerve palsy were excluded, voice changes were detected in 6 (3.3%) of 184 patients with identified external branch of the superior laryngeal nerves and 3 (20%) of 15 patients in whom at least 1 external branch of the superior laryngeal nerve could not be identified with intraoperative neuromonitoring.

Conclusion: Intraoperative neuromonitoring provided an important contribution to the visual and functional identification of the external branch of the superior laryngeal nerve. Intraoperative neuromonitoring is a helpful adjunct for identifying the external branch of the superior laryngeal nerve.