Mechanism-dependent outcomes of recurrent laryngeal nerve injury after thyroidectomy with intermittent intraoperative nerve monitoring

Purpose: This study aimed to evaluate the etiology and functional outcomes of recurrent laryngeal nerve (RLN) injury in patients with intraoperative loss of signal (LOS) verified by postoperative laryngoscopy. Materials and Methods: This retrospective cohort study analyzed 1840 patients (3159 nerves at risk (NAR)) who underwent thyroid surgery at a high-volume tertiary center between 2020 and 2025, with routine use of intermittent intraoperative nerve monitoring (I-IONM) and selective postoperative laryngoscopic assessment. Intraoperative LOS events were classified by presumed injury mechanism, and vocal cord paralysis (VCP) outcomes were evaluated at 6 months. Results: LOS verified by postoperative laryngoscopy occurred in 114 patients (6.2% per patient; 3.6% per NAR). Transient and permanent VCP rates were 4.3% and 1.7% per patient, respectively. Traction was the most frequent injury mechanism (64%), followed by compression (19.3%) and transection (11.4%). Recovery was strongly dependent on injury mechanism: 79.5% of traction-related and 72.7% of compression-related injuries resulted in transient VCP (T-VCP), whereas 92.3% of transection injuries led to permanent VCP (P-VCP). Conclusion: While I-IONM does not reliably prevent RLN injury, it provides clinically actionable information that guides intraoperative strategy and mechanism-based prognostic stratification. Integration of electrophysiologic findings with postoperative laryngoscopy supports informed decision-making and risk mitigation in contemporary thyroid surgery.