Motor and sensory branching of the recurrent laryngeal nerve in thyroid surgery

Introduction: Recognition of extralaryngeal bifurcation of the recurrent laryngeal nerve (RLN) is crucial, because inadvertent intraoperative division may lead to significant morbidity. The purpose of this study was to examine the incidence of extralaryngeal bifurcation of the RLN and the distance that the initial bifurcation occurs from the cricothyroid insertion site of the RLN. We also sought to demonstrate the location of the RLN branches containing a predominance of motor fibers. Methods: This prospective study of 220 patients with data on 310 RLNs collected the type of operation, incidence of bifurcation, distance from the cricothyroid insertion point to the point of initial bifurcation, and location of the motor fibers by assessing a stimulus response on the Medtronic NIMS as they relate to the laryngeal muscles. Results: A total of 310 RLNs in 220 patients were studied. There were 133 RLNs (42.9%) that bifurcated before entering the larynx. These bifurcations occurred 51.1% on the right, 48.9% on the left, and 33.3% bilaterally. The median branching distance from the cricothyroid membrane on the right was 6.33 mm, and on the left was 6.37 mm. In all bifurcated RLNs, the motor fibers were located exclusively in the anterior branches. Conclusion: Extralaryngeal bifurcation was found in 42.9% of the RLNs in this case series. The motor fibers are located in the anterior branches. Great caution is therefore required after the presumed identification of the RLN to ensure there is no unidentified anterior branch.