The Motor Fibers of the Recurrent Laryngeal Nerve Are Located in the Anterior Extralaryngeal Branch

This study aimed to establish the prevalence of extralaryngeal bifurcation of the recurrent laryngeal nerve (RLN) and investigate the location of the motor fibers to the intrinsic muscles of the larynx within the branches of the RLN. Recognition of extralaryngeal branching of the RLN is important, because inadvertent division of a branch may lead to significant vocal cord palsy despite the operator believing the nerve was preserved. Prospective operative data on branching of the RLN were collected in 579 patients undergoing thyroidectomy or open parathyroidectomy over a 3 year period and nerve integrity monitoring was utilized to document the position of the motor fibers of the last 176 RLNs. Adduction of the vocal cords was detected by the electromyography-endotracheal tube and abduction by finger palpation of muscle contraction in the posterior cricoarytenoid. A total of 838 RLN were studied (right--432, left--406). Bifurcations occurred on the right in 111 (25.7%) and left 93 (22.9%). Bilateral bifurcation occurred in 23 (8.9%) of bilaterally dissected nerves. Overall 176 RLNs in 118 patients were assessed by the nerve integrity monitoring. Of these 41 (23.3%) were bifid RLN. In all 41 (100%) cases of bifid RLN, motor fibers for both adduction and abduction of the vocal cords were located exclusively in the anterior branches of RLN, and none in the posterior branches. Extralaryngeal bifurcation of RLN is a common anatomical variant. The motor fibers of RLN are located in the anterior branch, for both adduction and abduction. Great care is therefore required following the presumed identification of the RLN to ensure there is no unidentified anterior branch.