Clinical relevance and surgical anatomy of non-recurrent laryngeal nerve: 7 year experience

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.

Systematic Review and Meta-Analysis: Recurrent Laryngeal Nerve Variants and Their Implication in Surgery and Neck Pathologies, Using the Anatomical Quality Assurance (AQUA) Checklist

INTRODUCTION

The recurrent laryngeal nerve (RLN) is the structure responsible for sensory and motor innervation of the larynx, and it has been shown that its lesion due to a lack of surgical rigor led to alterations such as respiratory obstruction due to vocal cords paralysis and permanent phonation impairment. The objectives of this review were to know the variants of the RLN and its clinical relevance in the neck region.

METHODS

This review considered specific scientific articles that were written in Spanish or English and published between 1960 and 2022. A systematic search was carried out in the electronic databases MEDLINE, WOS, CINAHL, SCOPUS, SCIELO, and Latin American and Caribbean Center for Information on Health Sciences to compile the available literature on the subject to be treated and was enrolled in PROSPERO. The included articles were studies that had a sample of RLN dissections or imaging, intervention group to look for RLN variants, or the comparison of the non-recurrent laryngeal nerve (NRLN) variants, and finally, its clinical correlations. Review articles and letters to the editor were excluded. All included articles were evaluated through quality assessment and risk of bias analysis using the methodological quality assurance tool for anatomical studies (AQUA). The extracted data in the meta-analysis were interpreted to calculate the prevalence of the RLN variants and their comparison and the relationship between the RLN and NRLN. The heterogeneity degree between included studies was assessed.

RESULTS

The included studies that showed variants of the RLN included in this review were 41, a total of 29,218. For the statistical analysis of the prevalence of the RLN variant, a forest plot was performed with 15 studies that met the condition of having a prevalence of less than 100%. As a result, the prevalence was shown to be 12% (95% CI, SD 0.11 to 0.14). Limitations that were present in this review were the publication bias of the included studies, the probability of not having carried out the most sensitive and specific search, and finally, the authors' personal inclinations in selecting the articles.

DISCUSSION

This meta-analysis can be considered based on an update of the prevalence of RLN variants, in addition to considering that the results show some clinical correlations such as intra-surgical complications and with some pathologies and aspects function of the vocal cords, which could be a guideline in management prior to surgery or of interest for the diagnostic.

Intra-Operative Detection of a Left-Sided Non-Recurrent Laryngeal Nerve during Vagus Nerve Stimulator Implantation

Left sided non-recurrent laryngeal nerves (NRLN) are very rarely observed during surgery in the head and neck region. Arising directly from the cervical aspect of the vagus nerve, the NRLN lies in a vulnerable position distant from its normal location. NRLNs are normally associated with embryological branchial arch aberrations and subsequent vascular anomalies. The anomalous course of the NRLN makes it more susceptible to injury during surgery in the neck region. Knowledge of this anatomical variant will reduce the potential for injury and resultant vocal cord paralysis. During microsurgical dissection of the carotid sheath for the implantation of a vagus nerve stimulator in a 19-year-old female patient with refractory epilepsy, a moderate-sized branch of the main vagus nerve trunk was identified postero-medially within the carotid sheath. Intra-operative stimulation of this nerve resulted in a compound muscle evoked potential from the left vocal cord. Thus, this branch was confirmed to be a left-sided NRLN. The patient had no associated vascular anomalies. This is first reported case of a left-sided NRLN found during VNS insertion. Awareness of the possibility of an NRLN is imperative to prevent iatrogenic injury. A medial location of the vagus nerve within the carotid sheath should alert the surgeon to the possible presence of an NRLN. The absence of fourth branchial arch remnant anomalies is not a guarantee as to the absence of a left-sided NRLN. The addition of intra-operative nerve monitoring for vagus nerve stimulator (VNS) implantation procedures should be strongly considered to help avoid iatrogenic injury.

Anatomical variation in the right non-recurrent laryngeal nerve reported from studies using pre-operative arterial imaging

The right non-recurrent (inferior) laryngeal nerve (NRLN) is a rare anatomical variant associated with an arterial anomaly, the aberrant right subclavian artery (ARSA), that is detectable by pre-operative imaging (POI) using computed tomography and/or ultrasound. Most surgical studies have utilized two major types, NRLNs arising near the upper pole of the thyroid gland (type 1), vs. at a lower level (type 2) but with two subtypes defined by relationships to the inferior thyroid artery (ITA). This review found 8 English language surgical studies using POI that reported at least 1 NRLN and had anatomical information; of the 88 right NRLNs, 69.3% were classified as type 2 and 30.7% as type 1. Meta-analysis yielded a weighted proportion of 74.0% for type 2, but with substantial heterogeneity. For a subgroup of 5 POI studies with information on subtypes, 22 (59.5%) of 37 type 2 nerves were type 2a (i.e., running at or above the ITA). Similarly, a separate review of large surgical series without POI found that 60.4% of all 91 type 2 NRLNs were type 2a. The study findings should be relevant to the increasing numbers of anterior neck surgeries including bilateral thyroidectomies. A need was identified for studies on inter-observer reliability (agreement) among surgeons on NRLN types, and on injury rates (and related symptoms) by the type of NRLN.

Nonrecurrent laryngeal nerve in thyroid surgery: Frequency, anatomical variations according to a new classification and surgery consideration

BACKGROUND

The nonrecurrent laryngeal nerve (NRLN) is a rare embryologically derived variant of the RLN. We aimed to identify the proportion of NRLN (during thyroidectomy), classify clinical NRLN types, and recommend some surgical considerations.

METHOD

In this prospective study, from May 2017 to September 2018, our hospital carried out 2158 thyroid operations. We reported the NRLN rate and distinguished NRLN into four types.

RESULTS

Overall, NRLN had an incidence rate of 0.74% (16 out of 2158 total thyroid surgeries). We did not detect any patient with left-sided NRLN. The traveling patterns of the nerves could be classified as descending (12.5%), vertical (25%), ascending (37.5%), or V-shaped (25%).

CONCLUSION

The NRLN is a rare variation of the RLN. From our experience, we recommend the guidelines will help surgeons to avoid NRLN injury.

Ipsilateral nonrecurrent laryngeal nerve palsy and delayed palsy of the contralateral recurrent laryngeal nerve in a case of third-time reoperative thyroid surgery

The occurrence of nonrecurrent laryngeal nerve and delayed nerve palsy of the contralateral nerve occurring simultaneously has never been described. A 67-year-old woman underwent reoperative completion thyroidectomy for enlarging thyroid nodules with recurrent hyperthyroidism and obstructive symptoms. Preoperative computed tomography of the neck showed a large compressive goitre with an aberrant right subclavian artery. At surgery, a type 1 nonrecurrent laryngeal nerve was found and inadvertently transected due to dense adhesions. It was repaired with ansa cervicalis graft. A fully preserved and functional recurrent laryngeal nerve was seen on the contralateral side at the end of surgery. However, the patient developed a delayed palsy on day 4 of the recurrent laryngeal nerve requiring a tracheostomy. Following successful speech and swallowing therapy, the patient was decannulated with good phonation and recovery of the left cord. Patients are at risk of bilateral nerve injury and late onset palsy in reoperative thyroid surgery. Management can be challenging and should be recognised to ensure appropriate therapy.

Anatomic Characteristics, Identification, and Protection of the Nonrecurrent Laryngeal Nerve during Thyroidectomy

Objective

We aimed to investigate the anatomical features and variation pattern of the nonrecurrent laryngeal nerve (NRLN), summarize the methods for identifying the NRLN before and during thyroidectomy, and share experiences regarding preventing and treating its injury.

Study Design

Retrospective case data analysis.

Setting

First Affiliated Hospital of Harbin Medical University.

Subjects and Methods

Between January 2002 and May 2016, 7392 patients underwent thyroidectomy in our hospital. Of them, 28 patients with NRLN were identified, and their clinical data were retrospectively analyzed.

Results

This study included 7392 patients in which the recurrent laryngeal nerves (RLNs) were routinely identified during surgery. The presence of NRLN was intraoperatively confirmed in 28 patients. All the NRLNs were located on the right side and its overall incidence was 0.37%. Five of the NRLNs were classified as type I, 19 as type IIa, and 4 as type IIb. Of the 28 cases, 4 NRLNs were injured during surgery, in which primary end-to-end anastomosis or local seal with corticosteroid injection was performed as a remedy. In the 4 patients with NRLN injury, 2 presented with postoperative hoarseness that indicated vocal cord paralysis confirmed by laryngoscope; the other 2 patients’ voices had no significant changes.

Conclusion

The NRLN, which is rare in clinical practice and predominantly right-sided, is anatomically more complex and variant at a higher risk of surgical injury. The key factors to accurately identify NRLN and to effectively prevent its injury include careful interpretation of auxiliary examination results before surgery, raising awareness of its presence, meticulous dissection, and routine exposure of the RLN during surgery.

The Non-Recurrent Laryngeal Nerve: a meta-analysis and clinical considerations

Background

The Non-Recurrent Laryngeal Nerve (NRLN) is a rare embryologically-derived variant of the Recurrent Laryngeal Nerve (RLN). The presence of an NRLN significantly increases the risk of iatrogenic injury and operative complications. Our aim was to provide a comprehensive meta-analysis of the overall prevalence of the NRLN, its origin, and its association with an aberrant subclavian artery.

Methods

Through March 2016, a database search was performed of PubMed, CNKI, ScienceDirect, EMBASE, BIOSIS, SciELO, and Web of Science. The references in the included articles were also extensively searched. At least two reviewers judged eligibility and assessed and extracted articles. MetaXL was used for analysis, with all pooled prevalence rates calculated using a random effects model. Heterogeneity among the included studies was assessed using the Chi² test and the I² statistic.

Results

Fifty-three studies (33,571 right RLNs) reported data on the prevalence of a right NRLN. The pooled prevalence estimate was 0.7% (95% CI [0.6–0.9]). The NRLN was found to originate from the vagus nerve at or above the laryngotracheal junction in 58.3% and below it in 41.7%. A right NRLN was associated with an aberrant subclavian artery in 86.7% of cases.

Conclusion

The NRLN is a rare yet very clinically relevant structure for surgeons and is associated with increased risk of iatrogenic injury, most often leading to temporary or permanent vocal cord paralysis. A thorough understanding of the prevalence, origin, and associated pathologies is vital for preventing injuries and complications.

Intermittent neural monitoring of the recurrent laryngeal nerve in surgery for recurrent goiter

Reoperative thyroid surgery is still challenging even for skilled surgeons, and is associated with a higher incidence of complications, such as hypoparathyroidism and recurrent laryngeal nerve (RLN) palsy. Displacement of the RLN, scar tissue from previous neck surgery and difficulty in maintaining good hemostasis are risk factors in reoperations. The prevalence of RLN injury in reoperative thyroid surgery ranges as high as 12.5% for transient injury and up to 3.8% for permanent injury. Bilateral paresis can also occur during reoperations, and is a dangerous complication influencing the quality of life, sometimes requiring tracheostomy. RLN identification is the gold standard during thyroidectomy, and the use of intraoperative neuromonitoring (IONM) can be a valuable adjunct to visual identification. This technique can be used to identify the RLN and the external branch of the superior laryngeal nerve (EBSLN), both of which are standardized procedures. The aim of this review was to evaluate the use of intermittent neural monitoring of the RLN in surgery for recurrent goiter, and to assess the prevalence of RLN injury while using IONM reported in the current literature.

Electrophysiological identification of nonrecurrent laryngeal nerves

OBJECTIVES/HYPOTHESIS

The nonrecurrent laryngeal nerve (NRLN) is a common anatomic variation of the right recurrent laryngeal nerve (RLN), which has been associated with an increased risk of injury during thyroid and parathyroid surgery. We suggest that early successful identification using intraoperative nerve monitoring (IONM) and preservation of this variant will help the surgeon to avoid injury to this nerve. Our objective was to examine the electrophysiological parameters of the NRLN and the efficacy of IONM for successful identification of the NRLN.

STUDY DESIGN

Retrospective database analysis.

METHODS

This is a retrospective study of a prospectively collected database of all patients who underwent thyroid and parathyroid surgeries by a single surgeon at a tertiary care center over 3 years (n = 481). Patients' demographic data and operative reports, including the IONM reports, were reviewed. Average stimulation thresholds with resulting amplitudes and latencies were compared. Preoperative and postoperative laryngoscopy were performed in all cases.

RESULTS

We identified 15 NRLNs (2.2%) in a total 682 laryngeal nerves. No left-sided NRLNs were observed. The average right vagus latency in the NRLN group was shorter than that of the RLN group (2.40 ms ± 0.49 ms vs. 3.43 ms ± 1.03 ms; P < .001). No statistically significant difference was observed between the initial amplitudes of the right vagus nerves in the two groups (713.67 μV ± 208.71 μV vs. 816.22 μV ± 470.45 μV; P = .14). All NRLN cases exhibited normal functioning of vocal cords on postoperative laryngoscopy.

CONCLUSIONS

IONM is highly effective in the identification of the NRLN. Right vagus nerve latency in the NRLN group was found to be significantly shorter than in the RLN group. Early identification of the NRLN allowed cautious preservation of the NRLN, resulting in excellent postoperative outcomes. The rate of NRLN identification may be improved by routine use of IONM.

LEVEL OF EVIDENCE

4 Laryngoscope, 127:2189-2193, 2017.