Some posterior branches of extralaryngeal recurrent laryngeal nerves have motor fibers.

OBJECTIVES/HYPOTHESIS: Anatomical variations of the recurrent laryngeal nerve (RLN), such as extralaryngeal branching, are a well-known risk factor for RLN injury during thyroid surgery. This study aimed to analyze the surgical anatomy and to investigate the existence of posterior branch motor fibers of extralaryngeal RLNs.

STUDY DESIGN: Prospective consecutive observational study.

METHODS: This was a prospective cohort study of 366 patients between January 2014 and February 2016. Operative data included the type of operation, incidence of nerve bifurcation, the distances among anatomical landmarks. The motor fibers were evaluated using neurostimulation with laryngeal palpation.

RESULTS: A total of 667 RLNs at risk were analyzed in this study, and of these 103 (14.5%) nerves were bifurcated or trifurcated before the laryngeal entry point (LEP). More extralaryngeal branched RLNs were observed on the right side than on the left (17.5% vs. 13.3%, P = .294). The mean distance of the LEP point of division was longer on the left side (16.2 ± 6.7 mm) than on the right (14.7 ± 5.9 mm, P = .132). All branched RLNs had a palpable laryngeal twitch when stimulating anterior branches. When stimulating posterior branches, 28.2%(29/103) of branched RLNs showed palpable laryngeal twitch. Overall incidence of posterior motor branch in total RLNs was 4.3% (29/667).

CONCLUSIONS: The motor fibers of the RLN are all located in the anterior branch, whereas some posterior branches have motor function. Identification of all of the branches of the RLN may be mandatory to decrease the risk of postoperative nerve injury.

LEVEL OF EVIDENCE: 4. Laryngoscope, 127:2678-2685, 2017.