Abstract
BackgroundA nonrecurrent laryngeal nerve (NRLN) is a rare but potentially serious anatomical variant. Although the incidence is reported to be 0.3% to 1.3%, it carries a much higher risk of palsy during thyroid surgery. The objective of this study is to investigate the usefulness of computed tomography (CT) for preoperative identification and intraoperative neuromonitoring identification (IONM) of NRLN in thyroid cancer patients.MethodsThe preoperative neck CT scans from 1,574 patients who needed thyroid surgery were examined. Absence of the brachiocephalic artery (BCA) and the presence of arteria lusoria were defined as positive with NRLN. Systematic intraoperative neuromonitoring (IONM) was also carried out for these 1,574 patients to localize and identify NRLN. A negative electromyography (EMG) response from lower vagal stimulation but a positive EMG response from the upper position indicated the occurrence of an NRLN.ResultsNine NRLN (0.57%) were intraoperatively identified out of the 1,574 patients, and no patient with a NRLN showed preoperative clinical symptoms related to NRLN. Prior to the operation, surgeons identified only seven suspected NRLN cases based on identification of arteria lusoria. But a review of CT scans revealed that all cases could be identified by vascular anomalies. All patients were successfully detected at an early stage of operation using intraoperative neuromonitoring (IONM). Postoperative vocal cord function was normal in all patients.ConclusionsCT of the neck is a reliable method for predicting NRLN before thyroid cancer surgery. However, some image features can be easily missed. Neurophysiology helps the surgeon to identify the NRLNs more precisely. Combining the two evaluation methods may decrease the incidence of nerve palsy, especially in cases of NRLN. Considering that CT is expensive, requires an X-ray, and achieves less information than ultrasound (US) concerning thyroid nodules, we suggest that applying US and IONM is more reasonable.
Highlights
A nonrecurrent laryngeal nerve (NRLN) is a rare but potentially serious anatomical variant
Some imaging characteristics of preoperative neck computed tomography (CT) suggest the presence of an NRLN, it can occur without a subclavian artery anomaly or even occur on the left side [2,9,10]
The RLN wraps around the sixth aortic arch, which forms the ligamentum arteriosum; on the right side, the distal parts of the sixth aortic arch and the fifth aortic arch disappear, and the nerve moves upward to lie beneath the fourth aortic arch, which forms the initial part of the subclavian artery
Summary
A nonrecurrent laryngeal nerve (NRLN) is a rare but potentially serious anatomical variant. The objective of this study is to investigate the usefulness of computed tomography (CT) for preoperative identification and intraoperative neuromonitoring identification (IONM) of NRLN in thyroid cancer patients. The nonrecurrent inferior laryngeal nerve (NRLN) is a rare anatomical variant. The reported incidence of nerve injury during surgery in cases of NRLN is nearly 12.9%, while in the recurrent laryngeal nerve (RLN) it is 1.8% [4]. A modification of standard thyroid surgery techniques is required, but preoperative identification of NRLN is even more crucial. In order to predict inadvertent nerve injury, intraoperative neuromonitoring (IONM) has commonly been applied in thyroid cancer operation to localize and identify RLN, but the usefulness of IONM for detecting NRLN has been described by only a few studies [5,7,8].
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