Analysis of neuromonitoring signal loss during retroauricular versus conventional thyroidectomy

Objective: Loss of signal (LOS) during intraoperative neuromonitoring (IONM) of robotic or endoscopic thyroidectomy via a retroauricular approach (RAT) and during conventional open thyroidectomy (COT) was investigated to compare the risk of recurrent laryngeal nerve (RLN) injury between the two groups. Study Design: Original article. Methods: This is a retrospective case series study performed between May 2014 and September 2016. IONM using the NIM 3.0 system (Medtronic Xomed, Inc., Jacksonville, FL) was used for this study. Pre- and postoperative vocal cord functions were assessed using a flexible laryngoscope. LOS types noted intraoperatively and their associations with postoperative vocal cord palsy (VCP) were evaluated. LOS rate and temporary and permanent VCP rates were compared between the two groups. The surgical events associated with LOS were also documented and analyzed in this study. Results: In total, 153 patients were recruited, and 111 patients were enrolled in the RAT group; the remaining 42 patients were enrolled in the COT group. No statistically significant differences in intraoperative LOS (P = 0.812) and postoperative VCP rates (early, permanent; P = 0.259 and P = 0.577, respectively) between the two groups were observed. IONM accuracy of predicting postoperative VCP was 99.1% in our case series. Conclusion: On the basis of IONM findings, the risks of injury to RLN were similar between the two groups. Comparison of LOS was an objective method for verifying the novel RAT approach. We applied our IONM protocol and troubleshooting algorithm during RAT with acceptable accuracy, but the international standardized method of IONM is applicable and recommended for reducing false results using vagal nerve stimulation. Level of Evidence: 3b. Laryngoscope, 129:2199–2204, 2019.