The vagus nerve, recurrent laryngeal nerve, and external branch of the superior laryngeal nerve have unique latencies allowing for intraoperative documentation of intact neural function during thyroid surgery

Abstract

Objectives/Hypothesis: To define normative amplitude and latency of vagus, recurrent laryngeal nerve (RLN), and external branch of superior laryngeal nerve (EBSLN) and to apply them to postoperative neural function documentation. To our knowledge, this is the first study to report electrophysiologic characteristics of all three nerves in a consecutive patient series. Study Design: Prospective. Methods: Quantitative analysis of evoked waveform data was performed on both sides in consecutive patients undergoing thyroid surgery by a single surgeon. Mean values, standard error of mean, and standard deviation were calculated for latency (in milliseconds) and amplitude (in microvolts) of the vagus nerves, RLN, and EBSLN. Pre- and postoperative vocal cord function was normal in all patients. Results: Normative latency analysis showed mean right and left vagal latency of 5.47 ms (±0.73) and 8.14 ms (±0.86), respectively (P < .0001). Pooled RLN latency was 3.96 ms (±0.69), and pooled EBSLN latency was 3.56 ms (±0.49), both significantly shorter than vagal latencies (P < .0001). There was no association between amplitude and latency parameters and tumor-size (> or <5 cm), body mass index (> or <25), age (> or < 50 years), gender, or degree of neural dissection. Conclusions: The unique right vagus, left vagus, and RLN latencies are characteristic of the individual nerves and allow identification (through the characteristic waveform latency) of an intact left or right vagus/RLN system. Timed recording of vagal waveform after thyroid lobectomy consequently documents intact ipsilateral vagal-RLN neural circuit and may be placed into the medical record as electrophysiologic documentation of existence of postresection complete neural integrity.