Non-recurrent inferior laryngeal nerve: clinical manifestations, surgical outcomes, and literature review

Background: The most serious complication of thyroidectomy and parathyroidectomy is recurrent laryngeal nerve (RLN) injury. Recurrent laryngeal nerve is known to have many anatomical variations. The non-recurrent inferior laryngeal nerve(NRLN) is an extremely rare asymptomatic but important anatomical variation, and it is very susceptible to damage during surgery. In this study, we investigated the NRLN variation in a single-institution database. Materials and Methods: A total of 22 patients with NRLN were identified from 5,900 patients who underwent thyroidectomy or parathyroidectomy in our department between January 2009 and December 2015. Their clinical profiles were retrospectively analyzed. Results: All the 22 NRLNs were right-sided. According to Toniato's classification, 4 cases were type 1, 10 cases were type 2A, and 8 cases were type 2B. Statistical analyses showed no correlation between the incidence of NRLN and potential risk factors (gender, pathology variation, and application of intraoperative nerve monitoring). In the neurophysiological monitoring group, the mean operation time for exposure was 4.2 +/- 1.8 minutes(n=3), which was significantly shorter(p=0.0004) than that in the non-monitoring group, which was 9.7 +/- 2.1 minutes (n=19). No NRLN injury occurred in any of these 22 patients. Conclusion: Thyroid surgeons should be aware of this extremely rare anatomical variation in order to avoid laryngeal nerve damage. Intraoperative neurophysiological monitoring can effectively help to identify and preserve the NRLN.