Nonrecurrent Laryngeal Nerve and Associated Anatomical Variations: The Art of Prediction

MC, Lynrah ZA, Chakraborty S, Deka A, Lynser D. Non-recurrent Laryngeal Nerve - A Rare Anatomical Anomaly that Increases the Risk of Nerve Injury during Thyroidectomy

Introduction

Nonrecurrent laryngeal nerve (NRLN), a rare anatomical variation of recurrent laryngeal nerve, is a branch of the vagus nerve (Morais M, Capela-Costa J, Matos-Lima L, Costa-Maia J (2015) Nonrecurrent Laryngeal Nerve and Associated Anatomical Variations: The Art of Prediction. Eur Thyroid J 4(4):234-238). On the right side, the prevalence of NRLN is 0.3-0.8%, while on the left side, it is extremely rare with a prevalence of 0.004%.

Case-Report

A female in her twenties presented with thyroid swelling for 3 years with an ultrasound neck showing a TIRADS IV lesion in the left thyroid lobe. Contrast-enhanced tomography of the neck reported a lesion in the left thyroid lobe causing mass effect in the form of contralateral deviation of trachea and splaying of bilateral common carotid arteries from its common origin - probability of thyroid neoplasm along with aberrant right subclavian artery with a retroesophageal course was noted. Intraoperatively, the right laryngeal nerve was identified near its entry point in right cricothyroid joint and was traced laterally and was found to be nonrecurrent lying superior to inferior thyroid artery. Total thyroidectomy was done preserving the left recurrent laryngeal nerve and right non recurrent laryngeal nerve.

Conclusion

NRLN should be suspected in cases with vascular anomalies based on preoperative imaging. Meticulous dissection during thyroid surgery for identification of the recurrent laryngeal nerve or NRLN is still considered to be the precise approach to avoid nerve injury.

Non-recurrent Laryngeal Nerve During Intraoperative Neuromonitoring Thyroidectomy: A Case Report and Literature Review

Complete and precise knowledge of the neck anatomy and its eventual anomalies is crucial while performing a safe thyroid and parathyroid surgery. Embryo-genetic malformations of the IV branchial arch can lead to an uncommon anatomical alteration known as non-recurrent inferior laryngeal nerve. Its prevalence varies between 0.7% for the dextral branch and 0.04% for the sinistral. In these cases, the inferior laryngeal nerve branches originate directly from the cervical vagus nerve, entering the larynx without hooking, on the right side around the subclavian artery or on the left around the aortic arch. The presence of a non-recurrent laryngeal nerve is challenging, due to the increased risks of iatrogenic damage to the nerve, which results in hoarseness, dysphagia, glottal obstruction, vocal cords palsy, and serious airway impairment. We present the case of a 58-year-old woman. The patient was admitted to our department for a nodule classified as Bethesda IV in the right thyroid lobe. Through the use of intraoperative neuromonitoring (IONM), surgeons detected intraoperatively a non-recurrent laryngeal nerve. A subsequent computed tomography scan confirmed an anomalous right subclavian artery branching from the left aortic arch, the Lusoria Artery. Anatomical variants represent pitfalls in this case and an accurate knowledge of the neck region is imperative while performing thyroid surgery. Devices such as IONM are useful for detecting abnormalities that may lead to iatrogenic damages.

A case report of the rare non recurrent laryngeal nerve in a resource limited setting: The first Ethiopian documentation

INTRODUCTION AND IMPORTANCE

A non-recurrent laryngeal nerve (NRLN) is an unusual variant of the recurrent laryngeal nerve. It is seen in 0.3-0.8 % of individuals. During neck surgery, the NRLN is predisposed to be injured due to its abnormal anatomic position which results in vocal cord paralysis.

CASE PRESENTATION

We report two patients who underwent thyroid surgery. The indication for surgery was controlled toxic diffuse goiter and multinodular goiter with pressure symptoms in the first and second patients respectively. Intraoperatively we employed the lateral approach using the inferior thyroid artery as a landmark to dissect for the RLN. Once we couldn't find the nerve in its normal position the possibility of NRLN came into picture. Through gentle dissection between the larynx and the carotid sheath the nerve was found entering the larynx directly at right angle in both cases and the diagnosis of NRLN was made and intraoperative pictures were taken.

CLINICAL DISCUSSION

The NRLN is a rare congenital anomaly of the recurrent laryngeal nerve. It is almost always diagnosed on the right side. Three types have been described. In most cases, the NRLN is diagnosed intraoperative. Both of our patients had type 2A right sided NRLN which was diagnosed intraoperative.

CONCLUSION

Through intraoperative careful dissection and search the RLN can be identified and also its rare anomaly, the NRLN, can be diagnosed and injury to the nerve can be avoided.

The triad of non-recurrent laryngeal nerve; three associated predicting variants in the era of nerve monitoring: A case report

INTRODUCTION AND IMPORTANCE

The prediction and early identification of non-recurrent laryngeal nerve (RLN) may minimize risk of injury. It could be associated with other coincident variants that predict non-RLN, leading to its proper identification.

CASE PRESENTATION

A patient with multinodular goiter underwent total thyroidectomy under intraoperative neuromonitoring (IONM) guidance. Preoperative thoracic computerized tomography (CT) scan/angiography revealed aberrant right subclavian artery (ARSA). During thyroid surgery, the vagus nerve (VN) was identified in the neurovascular bundle. An anatomic variation of the VN was observed, as it was medially placed in relation to the common carotid artery (CCA). Pre-dissection electrophysiological stimulus of the VN (V1) was negative. Thus, a right non-RLN was identified with careful surgical dissection. The branching point of the non-RLN on the VN was identified, and non-RLN was fully exposed until the laryngeal entry. IONM revealed that V1 signal was negative if derived distal to the non-RLN separation, and positive if derived proximal to the non-RLN separation.

CLINICAL DISCUSSION

ARSA detected by preoperative CT scan is associated with non-RLN. The medial course of the VN in relation to the CCA was found as a coincident anatomic variant with the non-RLN. Absence of pre-dissection V1 signal by IONM was an electrophysiological variant associated with the non-RLN.

CONCLUSION

ARSA is a reliable variant for predicting the non-RLN. VN medial to the CCA and absence of electrophysiological V1 signal could precisely predict the non-RLN. Therefore, the coincidence of three anatomical and electrophysiological variants with non-RLN could lead to the prediction of non-RLN.

Abu Dhabi Neural Mapping (ADNM) during Minimally Invasive Thyroidectomy Enables the Early Identification of Non-Recurrent Laryngeal Nerve and Prevents Voice Dysfunction

The aim of this study was to evaluate the diagnostic accuracy of a neuromonitoring protocol—the Abu Dhabi Neural Mapping protocol (ADNM)—using a new device, Nim-Vital™, during minimally invasive thyroidectomy in the early identification of non-recurrent laryngeal nerve (n-RLN) problems and the preservation of its function. Method: Patients with thyroid disorders that required thyroid resection, who were admitted to the Department of Surgery at Burjeel Hospital, Abu Dhabi, between January and July 2022, were included in the study. The data were extracted from a prospective database and were analyzed retrospectively. All nerves at risk were identified and exposed at seven precisely defined anatomical points, with strict adherence to the intraoperative technical steps of neuromonitoring. These were sequentially applied to the vagal nerve (VN), the superior laryngeal nerve (SLN), and the recurrent laryngeal nerve (RLN). In the next step after the creation of the skin-platysma flap, the strap muscle’s lateral border was moved from the medial limb of the sternocleidomastoid without using any electrical device and without any manipulation of the thyroid gland. The VN was exposed in the carotid sheath and then stimulated using a monopolar probe at a precisely defined point above the clavicle, using anatomical landmarks. Results: In total, 136 women with a mean age of 40 years (range 18–74) and 36 men with a mean age of 42 (range 21–66), demonstrating 270 nerves at risk, were included in the analysis. Indications for surgery were malignancy in 70 cases, toxic goiter/Graves in 23 cases, retrosternal goiter in 21, and symptomatic multinodular goiter in 64 cases. Of these, 100 patients received a total thyroidectomy, 46 received a right lobectomy, and 24 received a left lobectomy only. For a total thyroidectomy, the median skin-to-skin surgery duration was 52 min (range 24–104 min) and the median hospital stay was 2 days (range 1–4 days). In 4 cases (4/146; 2.74%) the pre-dissection stimulation of the vagal nerve (VN1) at the ADNM’s precisely defined point did not create any signal or proper EMG-curve that indicated the existence of the non-RLN. Proximal dissection of the right VN at a precisely defined point by the ADNM’s level of incisura of the larynx created a positive signal. The separation point of the right non-RLN from the VN was discovered in all four patients. The postoperative video-laryngoscopy confirmed bilateral mobile vocal cords in all cases. Conclusions: Following the ADNM protocol during thyroid surgery minimizes the risk of a non-laryngeal nerve injury and prevents voice dysfunction.

A case report-nonrecurrent laryngeal nerve and associated vascular anomalies: the role of imaging

The anomalous position of nonrecurrent laryngeal nerve (NRLN) predisposes it to injury during thyroid surgery. The presence of right aberrant subclavian artery is a strong indicator of having an NRLN. Here, we are presenting a case report of an NRLN and role of imaging in its prediction.

Utility of intraoperative neuromonitoring in detecting recurrent nerve's anatomical anomalies during thyroidectomy

Anatomical variations such as a non-recurrent laryngeal nerve (NRLN) are very rare (reported rates within 0.6-1% to the right side and only four cases to the left side) but they can lead to serious risk of nerve lesion during thyroidectomy. It is known that to prevent inferior laryngeal nerve lesions, it is mandatory to obtain a correct and wide exposure of the nerve during all kind of thyroid surgeries but in case of laryngeal nerve position anomalies, it is hard to achieve a safe nerve identification. Continuous intraoperative neuromonitoring (C-IONM) technology can detect the presence of NRLN. In this study we present seven cases of NRLN incidentally found during our last 10-year experience, in a total of 1074 procedures, including total thyroidectomy and lobectomy. Three out of seven cases were identified with the help of C-IONM. On the other hand, the other four cases of non-recurrent laryngeal nerve were identified during an extensive dissection of the thyroid lodge. We registered no nerve palsy in the group of patients who underwent surgery with the help of C-IONM, while we had two nerve palsies (out of four cases) in the group of patients without the help of C-IONM. In our experience we also registered a reduction of surgery time when we used the C-IONM. In our opinion C-IONM is a safe method to discover anatomical anomalies such as a non-recurrent laryngeal nerve and may help to reduce nerve palsy rate.

Duplicated Vagus Nerve in Adolescence: Case Report and Review of Literature

BACKGROUND

Vagus nerve stimulation (VNS) has become an increasingly popular procedure for the treatment of epilepsy and depression. Significant complications or side effects associated with VNS surgery may result from either the inadvertent direct injury to the vagus nerve as part of the surgical approach, placement of the electrode, or the concomitant stimulation of vagal efferent fibers. To mitigate these effects, the recognition of anatomic variants that may place the nerve at increased risk is necessary.

CASE DESCRIPTION

During microsurgical dissection of the carotid sheath for the implantation of a vagus nerve stimulator in a 17-year-old male patient with refractory epilepsy, additional nonidentified nerve tissue was found running parallel to the vagus nerve. These fibers were two thirds of the thickness of the vagus nerve and ran medial to it, from the most superior to the most inferior aspect of the carotid sheath dissection, found at a distance of at least 4 cm in a craniocaudal direction. This duplicated nerve did not appear to branch from the vagal trunk nor exit the sheath but rather paralleled the course of the vagus nerve. The parallel course and the proximity of the unidentified nerve make this structure likely to be a duplicated vagus nerve.

CONCLUSIONS

This is the first reported case of cervical vagus nerve duplication presented in the literature. Surgeons performing VNS implantations should be cognizant of this potential anomaly in order to avoid inadvertent injury to the nerve.

Nonrecurrent Laryngeal Nerve in the Era of Intraoperative Nerve Monitoring

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.