Nonrecurrent Laryngeal Nerve in the Era of Intraoperative Nerve Monitoring

Abstract

Nonrecurrent laryngeal nerve (non-RLN) is an anatomical variation increasing the risk of vocal cord palsy. Prediction and early identification of non-RLN may minimize such a risk of injury. This study assessed the effect of intraoperative neuromonitoring (IONM) on the detection of non-RLN. A total of 462 (236 right) nerves in 272 patients were identified and totally exposed, and all intraoperative steps of IONM were sequentially applied on the vagus nerve (VN) and RLN. Right predissection VN stimulation at a distal point did not create a sound signal in three cases (3/236; 1.27%). Proximal dissection of the right VN under IONM guidance established a proximal point, creating a positive signal. The separation point of non-RLN from VN was discovered in all three patients. Non-RLNs were exposed from separation to laryngeal entry. Positive IONM signals were obtained after resection of thyroid lobes, and postoperative period was uneventful in patients with non-RLN. Absence of distal VN signal is a precise predictor of the non-RLN. IONM-guided proximal dissection of the right VN leads to identification of the non-RLN. The prediction of non-RLN by the absence of the VN signal at an early stage of surgery may prevent or minimize the risk of nerve injury.

Two Concomitant Right Nonrecurrent Laryngeal Nerves Encountered During Thyroidectomy (Type 4 Course): Reported for the First Time

“…[7][8][9] Intraoperatively, the course of the nerve is searched in the trache0-esophageal groove after identification of the inferior thyroid artery and applying some lateral traction over it because it is closely related to the artery, failure of identification should raise the possibility of this anomaly, in such situation, some authors recommend doing an orderly dissection, starting by careful identification and mobilization of the vagus nerve before proceeding to do thyroidectomy which may enable the surgeon in identifying the nerve, it may also be detected intraoperatively by intraoperative nerve monitoring. 6,10,11 Failure in identification of the nerve or overlooking the possibility of the nonrecurrent laryngeal nerve may result in serious sequelae of nerve damage, ipsilateral injury may lead to permanent hoarseness and bilateral injury may result in severe dyspnea or aphonia. 4…”

Nonrecurrent Laryngeal Nerve: Precise Detection by Electrophysiological Nerve Monitoring

“…Our results of the present case demonstrate the importance of IONM, and especially right V1 stimulation and signal detection, in predicting the presence of the non-RLN at an early stage of thyroidectomy. Previous reports based on IONM application in non-RLN cases also verify the role of a negative V1 signal in enhancing both the detection and safe identification of the non-RLN [ 4 , 6 , 8 - 10 ].…”

“…The absence of both a signal and an electrophysiological wave amplitude at this level reveals a disorder of signal transmission by motor fibers of the inferior neural system to the intrinsic laryngeal musculature. Taking into account the proximal branching of the laryngeal nerve from the VN as an anatomical variation, the absence of motor function after distal V1 stimulation reveals the presence of the nonrecurrent course of the nerve [ 6 ]. In our patient, the absence of electrical conductivity in the motor nerve after the right distal VN stimulation (d-V1) urged us to dissect along the VN proximally, with serial electrophysiological stimulation, until the separation point of the non-RLN.…”

“…The VN signal was negative if the stimulator probe contact point was located distal to the non-RLN separation and positive if it was located proximal to the separation. Therefore, a negative right V1 signal at the distal point appeared as an early intraoperative indicator of the non-RLN [ 6 ].…”

Coexistence of Right Nonrecurrent Nerve and Bifurcated Recurrent Laryngeal Nerve Pointed by Zuckerkandl's Tubercle

“…One of these variations is the nonrecurrent course of the nerve. The incidence of non-RLN has been reported to be between 0.3% and 1.3% in previous series [4-7]. Therefore, the nonrecurrent course is a rare anatomical variation of the inferior laryngeal nerve.…”