Selective vagus-recurrent laryngeal nerve anastomosis guided by intraoperative neuromonitoring: evidence of lateral motor fiber clustering in the vagus nerve.

Objective: Direct anastomosis (DA) is the standard approach after recurrent laryngeal nerve (RLN) transection but is often not feasible due to excessive tension. This experimental study evaluated a novel intraoperative neuromonitoring (IONM)-guided selective vagus-recurrent laryngeal nerve anastomosis (SVRA) technique and compared its immediate electrophysiologic performance with DA in a porcine thyroid surgery model. Methods: 18 transected nerves from 9 pigs were randomized to DA or SVRA (9 nerves per group). In the SVRA group, low-current IONM was used to map vagus nerve (VN) motor fibers innervating laryngeal musculature; these fibers were selectively dissected and anastomosed to the transected RLN. In the DA group, end-to-end RLN neurorrhaphy was performed under microscopy. Electromyography (EMG) amplitudes and latencies were recorded at baseline and serially up to 2 hours after anastomosis; hemodynamic parameters were monitored to assess the safety of VN manipulation. Results: VN motor fibers innervating the laryngeal muscles were predominantly localized to the lateral VN and were mostly concentrated in a single strand. After anastomosis, both techniques yielded early EMG recovery, with post-anastomotic amplitudes often exceeding 50% of baseline. A cross-innervation model (left VN to right RLN) produced immediate EMG responses approaching baseline and bilateral vocal fold activation. Moreover, when the anastomosed nerve was pulled, the EMG amplitude varied with the alteration of the relative position of the fiber components at the two severed ends. VN dissection did not cause clinically relevant changes in blood pressure or oxygen saturation, and only minor, non-significant heart rate increases were observed. Conclusion: IONM-guided SVRA enables selective recruitment of VN motor fibers for targeted RLN reconstruction while largely preserving VN trunk integrity. These findings support SVRA as a physiologically grounded and technically feasible reconstructive option that can achieve acute electrophysiological recovery when tension precludes DA during thyroid surgery-related RLN transection, although long-term functional reinnervation remains to be established.