Electrophysiologic monitoring characteristics of the non-recurrent laryngeal nerve and radiologic evaluation of concurrent vascular anomalies

Abstract Purpose The objective of this study is to characterize the electrophysiological characteristics of nonrecurrent inferior laryngeal nerves(NRILN) that have been dissected with the assistance of intraoperative neuromonitoring(IONM), along with the concomitant vascular anomalies observed in patients with NRILN. Methods A retrospective analysis was conducted on 7865 patients who underwent thyroidectomy with IONM at three tertiary referral centers. The study included 42 patients in whom an NRILN was detected. IONM data and postoperative vocal cord(VC) examination were recorded in all patients. The absence of initial vagal EMG response and/or a short(< 3.5 ms) latency period during the initial vagal stimulation, or the inability to identify the RLN within the Beahrs triangle was considered highly suspicious for the presence of an NRILN. Postoperative cross-sectional imaging was performed in 36 out of 42 patients to asses any concurrent vascular anomalies Results The prevalence of NRILN was 0.53%.An NRILN was suspected due to EMG findings in 32(76%) and the inability to identify the RLN within the Beahrs triangle in the remaining 10(24%) patients. Transient VC paralysis occurred in one(2.4%) patient. Of the 36 patients with postoperative imaging, 33(91.4%) had vascular anomalies. All of the 33 patients had aberrant right subclavian artery and 13(39.4%) had also accompanying additional vascular anomalies. Conclusions NRILN is an anatomical variation that increases the risk of nerve injury. Observation of absent EMG response and/or a short latency period during the initial vagal stimulation facilitates the detection of an NRILN at an early stage of thyroidectomy in the majority of the patients.