Nonrecurrent Laryngeal Nerve in the Era of Intraoperative Nerve Monitoring

Anatomical variations of recurrent laryngeal nerve: a systematic review and meta-analyses

PURPOSE

The aim of this systematic review and meta-analysis was to systematically review and perform a meta-analysis on the anatomical variations of the RLN.

METHODS

We performed online research for studies that addressed anatomical variations of the RLN and laterality, published between 2015 and 2021. We found 230 articles, and nine were included.

RESULTS

Eight variations were found, with Type I prevailing (41.17%; 95% CI 19.44-64.88), extra laryngeal divergence of the RLN. The other types were: II-fan shape; III-distance greater than 5 mm to the cricothyroid joint; IV-thickening and adipopexy in the elderly; V-non-recurrent laryngeal nerve; VI-intracranial branch; VII-tortuous ascending RLN; and VIII-combination between the inferior branch of the NV and the ascending trunk of the RLN. Types I (p = 0) and III (p < 0.01) prevailed on the left and types II (p < 0.01) and V (p < 0.01) on the right.

CONCLUSIONS

It was observed that variations occurred due to the path of the RLN to the entrance to the larynx, its shape, and the age of the evaluated individual. The most frequent variation and side were, respectively, Type I, extra laryngeal divergence and left.

Non-Recurrent Laryngeal Nerve: A Rare Anatomical Entity in a Patient Undergoing Hemithyroidectomy

A non-recurrent laryngeal nerve (NRLN) is a common anatomical modification with an occurrence rate ranging from 0.5% to 0.7% in surgical procedures related to thyroid pathology [1]. In this condition cervical vagus nerve reaches the larynx directly, increasing the likelihood of vocal cord palsy. Non-RLN injury can be reduced by anticipating it and identifying it early. This case report describes how a non-recurrent inferior laryngeal nerve was discovered intraoperatively during systemic dissection, averting intra-operative nerve injury. A 40-year-old female reported to the department of Otorhinolaryngology and Head and Neck Surgery Outpatient Clinic for a nodular tumor in her neck that has been increasing for the previous five years. The colloid multi-nodular thyroid of the right lobe was confirmed by a fine needle aspiration cytology (FNAC). The patient was lined up for a surgical procedure requiring resection of the right lobe of the thyroid. A non-recurrent right inferior laryngeal nerve was discovered during surgery. The operation and recovery went smoothly, and there was no change in his voice in subsequent follow-ups. For those who are related to this professional line, this presentation provides a summary of what a non-recurrent laryngeal nerve looks like during surgery. This is critical for anyone undergoing diagnostic and surgical procedures which demand to be invasive in the region involving the neck and upper thorax, as it lowers the risk of iatrogenic nerve injury. A solitary trauma of this nerve can induce irreversible hoarseness, whereas a multilateral lesion might result in aphonia and potentially deadly dysphonia.

The Role of Anatomical Imaging and Intraoperative Neuromonitoring (IONM) for Successful Prediction of a Nonrecurrent Laryngeal Nerve

A nonrecurrent laryngeal nerve (NRLN) is a rare anatomical variant of laryngeal nerves that branches directly from the vagus nerve. The anatomical abnormality makes it difficult to identify the NRLN and results in high incidence of accidental nerve injury during surgery. A 76-year-old woman complained of swelling in the right side of her neck and visited our university hospital for further examination. Ultrasonography showed a right thyroid lobe mass with calcification and fine needle aspiration biopsy was classified as class III. Computed tomography revealed that the right subclavian artery branched directly from the descending aorta without branching from the brachiocephalic artery and ran behind the esophagus. Since it was afraid that the accidental injury of NRLN was likely to occur, a right thyroid lobe dissection using intraoperative neuromonitoring (IONM) was performed. After separating the connective tissue on the thyroid capsule from the right side of the trachea to the inferior pole laterally, the NRLN running across the level of the inferior margin of the cricoid cartilage was identified by using IONM 0.5 mA stimulation. After complete dissection of right thyroid lobe, we again stimulated the NRLN by 0.5 mA and the electromyographic response was confirmed. The pathological analysis confirmed nodular hyperplasia without malignancy; the condition was diagnosed as an adenomatous goiter. There was no vocal cord dysfunction and hoarseness after the surgery. IONM contributed to the prevention of NRLN injury during the surgery. We believe that it is important to confirm the presence or absence of an aberrant subclavian artery on preoperative imaging, and that IONM should be considered to identify the NRLN to prevent vocal cord paralysis if its presence is suspected.

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

INTRODUCTION

The recurrent laryngeal nerve gains its name because after branching from the vagus nerve, it turns superiorly (recur) around the subclavian artery on the right and around the ligamentum arteriosum on the left, the nonrecurrent nerve has a straight direct course to the larynx and doesn't follow this course. It presents mostly on the right side. The presence of this variation places the nerve at higher risk of injury during neck surgery especially thyroid operations.

CASE PRESENTATION

A 45-year-old lady presented with painless thyroid enlargement for 1 year. Thyroid examination showed a 3-cm firm nodule at the right thyroid lobe with normal thyroid function tests. Right thyroid lobectomy was done and the histopathology showed a benign follicular lesion. During surgery, we discovered 2 nonrecurrent laryngeal nerves at the right side which were arising from the vagus nerve and both were entering the larynx.

CONCLUSION

Failure in identification of the nerve or overlooking the possibility of the non-recurrent laryngeal nerve may result in a serious sequelae of nerve damage, ipsilateral injury may lead to permanent hoarseness and bilateral injury may result in severe dyspnea or aphonia. Currently, there are 3 types of nonrecurrent laryngeal nerve courses. Type 1 passes near to the superior thyroid vessels. Type 2 (2A) passes parallel to the inferior thyroid artery and has a transverse course above it. Type 3 (2B) passes parallel to the inferior thyroid artery and transversely between branches of or under the inferior thyroid artery, we can add to this classification type 4, which are 2 nonrecurrent laryngeal nerves (double nerves) passing above and parallel to the inferior thyroid artery.

Nonrecurrent Laryngeal Nerve: Precise Detection by Electrophysiological Nerve Monitoring

Complication-free thyroid surgery is mainly based on the motor integrity of the recurrent laryngeal nerve (RLN). The nonrecurrent laryngeal nerve (non-RLN) is a rare anatomical variation that may increase the risk of vocal cord palsy. Early identification and exposure of the non-RLN may minimize injury risk. This case report presents functional detection of the non-RLN by intraoperative neuromonitoring (IONM).

Total thyroidectomy was performed under the guidance of IONM on a patient with bulky multinodular goiter. The first step of IONM is pre-dissection stimulation (V1) of the right vagus nerve (VN). V1 at a standard distal point was negative as indicated by the absence of both a sound signal and wave amplitude. The right VN was then followed proximally and dissected under the guidance of IONM. This dissection established a proximal point creating a positive signal that led us to determine the separation point of the non-RLN. The right non-RLN arising from the proximal VN was identified and fully exposed until laryngeal entry. Its motor integrity was confirmed with post-dissection signals. The left RLN was identified at the usual anatomical position that was fully exposed and preserved during thyroid surgery. Total thyroidectomy was then accomplished without complication. The postoperative period was uneventful. Postoperative laryngoscopy confirmed normal vocal cord function.

The non-RLN is accurately identified by IONM during the early part of the thyroid surgery. The absence of a distal VN signal is predictive of the non-RLN. IONM-guided proximal dissection of the right VN leads to the identification of the non-RLN. The prediction of the non-RLN by the absence of a VN signal during an early stage of surgery may prevent or minimize the risk of nerve injury.

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

The recurrent laryngeal nerve (RLN) has many anatomical variations and various relations with adjacent structures. Identification and total exposure of the cervical part of the RLN was performed during operations on the thyroid gland. An extremely rare anatomical variation of the nerve was encountered during the surgical procedure. Coexistence of both right RLN and non-RLN was observed in one patient surgically treated with total thyroidectomy. We first exposed the right RLN with an extralaryngeal terminal bifurcation at its usual position. Thereafter, we also identified an ipsilateral non-RLN joining the anterior branch of the RLN just before laryngeal entry. A Zuckerkandl's tubercle has pointed out the junction of the two nerves. In this period, the incidence of coexistence of non-RLN and RLN was 0.2% in our series. A non-recurrent course is a rare anatomical variation of the inferior laryngeal nerve. The coexistence of both non-RLN and RLN is an extremely rare anatomical finding which should be taken into account during thyroid surgery.