Nerve Branch Diameter as an Indicator of Motor Function in Extralaryngeal Branches of the Recurrent Laryngeal Nerve During Thyroidectomy.

Objective: Preserving the recurrent laryngeal nerve (RLN) is a critical aspect of thyroidectomy, as its injury can significantly impair voice function. However, surgeons frequently encounter branched RLNs, which occur in 10.1%-42.9% of cases. This anatomical variation can be particularly challenging for novice surgeons, as identifying and preserving the motor branch requires precision. Methods: Of 239 patients who received bilateral axillo-breast approach robotic total thyroidectomy from December 2023 to January 2025, patients with extralaryngeal RLN branch were retrospectively evaluated using video recordings. The function of RLN branches was determined using intraoperative neuromonitoring (IONM). Branch diameter and branching distance to the laryngeal entry point (LEP) were measured on captured surgical images using ImageJ software, referencing a 1.3 mm monopolar hook tip. Sensory branches were further classified by insertion site (LEP vs. non-LEP). Results: Among 293 RLNs at risk, 31 (10.6%) showed extralaryngeal branching. Most nerves were double-branched (27/31). Motor branches were significantly thicker than sensory branches (1.47 ± 0.34 mm vs. 1.02 ± 0.28 mm, Conclusion: Branch diameter correlates with motor function in RLN branches. In the absence of IONM, thickness and branching location may help surgeons distinguish motor from sensory branches and preserve vocal function. Level of Evidence: Level 4.