Traction Injury of Recurrent Laryngeal Nerve During Thyroidectomy

Background: Loss of the neuromonitoring signal (LOS) during thyroidectomy signifies recurrent laryngeal nerve (RLN) injury, which is one of the common complications, especially by traction injury. Transient intraoperative LOS means spontaneous recovery of nerve function during surgery or within 6-month post-surgery. Few articles discuss intraoperative recovery time and transient LOS, and there is no consensus on the risk factors for RLN traction injury and its recovery course; thus, we wanted to determine the maximum intraoperative recovery time. Materials and methods: This retrospective study included patients who had undergone thyroidectomies at Tainan National Cheng Kung University Hospital between January 2015 and August 2018. A total of 775 patients (with 1000 nerves at risk) who underwent intermittent intraoperative neuromonitoring during thyroidectomy were included in this study. The LOS nerves were divided into 4 groups based on the LOS subtype and the intraoperative status of the recovery. The postoperative vocal cord function was determined by thyroid ultrasound and/or laryngoscope. All the patients would be followed up postoperatively in 2–3 days, 1 week, 2 weeks, and 4–6 weeks. Results: LOS occurred in 67 of 775 (8.6%) patients and in 70 of 1000 nerves at risk (7.0%). There were 2 in 70 nerves (2.9%) with LOS type 1 (segmental nerve traction injury) with intraoperative recovery (Group 1), 5 (7.1%) with LOS type 1 without intraoperative recovery (Group 2), 47 (67.1%) with LOS type 2 (global injury) with intraoperative recovery (Group 3), and 16 (22.8%) with LOS type 2 without intraoperative recovery (Group 4). All LOS type 1 (segmental nerve injury) nerves had pathologic lesions near the RLN or vagus nerve, but none had invaded the nerves (p < 0.05). The resolving time intraoperatively in the 2 patients in Group 1 was 5 min and 10 min, respectively. The resolving time intraoperatively in Group 3 was 1–20 min, and the average time was 4.8 min. In Group 2, 3 injured nerves recovered within 6 weeks postoperatively, and 2 nerves in 12 weeks. In Group 4, all the 16 injured nerves recovered within 6 weeks postoperatively. Conclusion: Applying intermittent intraoperative neuromonitoring during thyroidectomy, traction recurrent laryngeal nerve injury still happened in 7.0%. 70% of the injured nerves recovered the function intraoperatively after releasing the traction, and the longest duration of recovery is 20 min.