Motor function of the recurrent laryngeal nerve: Sometimes motor fibers are also located in the posterior branch

Abstract

Background The function of the extralaryngeal branches of the recurrent laryngeal nerve (RLN) has yet to be described precisely. The goal of this study was to evaluate the incidence and motor function of the extralaryngeal branches of the RLN. Methods Our study group consisted of 335 consecutive patients undergoing thyroid and parathyroid operations in whom the branches of the RLNs (n = 200) were evaluated with intraoperative nerve monitoring and by measuring the distance from the point of branching of the RLN into anterior and posterior branches and the entry of the individual branches into the larynx–defined as the branching distance. Anterior and posterior branches of the RLN were assessed separately by electromyography (using a standard electromyography endotracheal tube) for adduction and by finger palpation for abduction. The RLNs were classified as having motor function only in the anterior branches (Group 1) or function both in the anterior and posterior branches (Group 2). Results There were 185 RLNs in Group 1 and 15 RLNs in Group 2, assessed by intraoperative nerve monitoring. Motor function was detected in all anterior branches of the RLN (100%) and in 8% of the posterior branches. The mean branching distance was greater in Group 2 compared with Group 1 (24.1 ± 13.6 mm, 17.3 ± 8.5 mm, respectively, P = .045). Conclusion Although the anterior branch of RLN always has motor function, the posterior branch also has motor function in about 8% of patients. The probability of detecting motor function in the posterior branch was greater among early branching RLNs, which have a greater branching distance. The surgeon should remember that posterior branches may contain motor fibers and protect these branches to avoid postoperative vocal cord dysfunction. © 2017 Elsevier B.V., All rights reserved.