The usefulness of preoperative computed tomography and intraoperative neuromonitoring identification of the nonrecurrent inferior laryngeal nerve

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.

Variant anatomy of non-recurrent laryngeal nerve: when and how should it be taught in surgical residency?

INTRODUCTION

While the performance of a thyroidectomy is generally associated with a low risk of injury to the recurrent laryngeal nerve (RLN), the presence of a non-recurrent nerve (NRLN) increases the risk of this complication. Generally, the intraoperative detection via visual appreciation of variant anatomy of the RLN has been regarded as poor, possibly due to a lack of knowledge of both the normal and aberrant anatomy of the RLN.

MATERIALS AND METHODS

Articles for the review were searched through PubMed using the search terms and their combinations: "non-recurrent laryngeal nerve," "thyroidectomy," "injury," "palsy," "variant anatomy," and "residency," from January 1, 2000, to December 2022. Papers considered for the review were the articles published in English, with additional classic and articles of surgical importance retrieved from the reference list of papers. Only papers relevant to the scope of the review were considered for this review.

FINDINGS

The NRLN has been found to be associated with concurrent vascular abnormalities, such as the presence of an aberrant right subclavian artery (ARSA) or an arteria lusoria originating from the aortic arch. However, it seems that both the normal as well as aberrant anatomy of the RLN is currently not emphasized enough during postgraduate surgical training. With the increased use of intraoperative neuromonitoring (IONM), detection of NRLN has become possible through appropriate neural mapping during thyroid surgery, besides other pointers such as visualization during surgery, computerised tomography, and duplex ultrasound scans to visualize the variant vascular anatomy. There is also a possible role for cadaveric courses, either during medical school or in a post-graduate setting-adapted to the student's level to teach the variant anatomy. With the development of newer techniques such as artificial intelligence, there are potential new options for teaching and training anatomy in the near future.

CONCLUSIONS AND RELEVANCE

Adequate knowledge of the normal and aberrant anatomy of the RLN remains essential for the best outcomes in thyroid surgery, even in the era of the IONM. Moving forward, the knowledge of (aberrant) anatomy should be made an integral part of the core competencies of both medical students and surgical trainees. It is imperative that leaders of the different field work closely together to combine their knowledge towards providing their trainees with the best possible training options.

Preservation of the nonrecurrent laryngeal nerve using intraoperative nerve monitoring during endoscopic thyroidectomy

A 40-year-old woman underwent right lobe thyroidectomy for thyroid nodules that increased in size from 17 mm to 33.5 mm within 1 year. Identification of arteria lusoria using computed tomography suggested the presence of a right nonrecurrent laryngeal nerve (RNRLN). Endoscopic thyroidectomy was performed under general anesthesia. The right vagal nerve was first identified between the common carotid artery and jugular vein. A positive response was confirmed via intraoperative neuromonitoring (IONM), implying that the RNRLN did not branch from the central side of the stimulated point of the vagal nerve. The RNRLN was confirmed using IONM around the middle to lower pole of the right thyroid gland. The right thyroid lobe was successfully removed, with meticulous preservation of the RNRLN. The motion of the vocal cord, examined by an ear-nose-throat doctor postoperatively, was intact. We demonstrated the efficacy of IONM in patients with RNRLN who underwent endoscopic thyroidectomy.

Surgical Skills and Technological Advancements to Avoid Complications in Lateral Neck Dissection for Differentiated Thyroid Cancer

Neck dissection is a surgical procedure reserved for thyroid cancer cases with clinically evident lymphatic invasion. Although neck dissection is a reliable and safe procedure, it can determine a significant morbidity involving a variety of structures of nervous, vascular and endocrine typology. A careful pre-operative study is therefore essential to better plan surgery. Surgical experience, combined with accurate surgical preparation and merged with adequate and specific techniques, can certainly help reduce the percentage of complications. In recent years, however, technology has also proved to be useful. Its crucial role was already recognized in the safeguard of the integrity of the laryngeal nerve through neuro-monitoring, but new technologies are emerging to help the preservation also of the parathyroid glands and other structures, such as the thoracic duct. These surgical skills combined with the latest technological advancements, that allow us to reduce the incidence of complications after neck dissection for thyroid cancer, will be reported in the present article. This topic is of significant interest for the endocrine and metabolic surgeons' community.

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: 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.

Intrathyroidal carotid artery and nonrecurring right recurrent laryngeal nerve: A case report

BACKGROUND

When performing thyroidectomy, knowledge of normal anatomy and variants is vital to avoid injuring nearby structures. Typically, the bilateral carotids course posterolateral to the thyroid gland. We describe a rare variant of an intrathyroidal carotid artery, not previously described in the literature.

METHODS

A 23-year-old woman with a strong family history of thyroid cancer presented with a left thyroid nodule, and a fine-needle aspiration biopsy revealing papillary thyroid carcinoma. She underwent total thyroidectomy.

RESULTS

Intraoperatively, the carotid was found coursing centrally through the right lobe parenchyma, associated with an ipsilateral nonrecurrent recurrent laryngeal nerve (NRLN) entering the cricothyroid joint superolaterally.

CONCLUSION

This is, to our knowledge, the first report of such an anatomic variant in the medical literature. Aberrant carotid artery anatomy may potentially cause life-threatening surgical complications and should be considered preoperatively. Furthermore, recognition of concurrent recurrent laryngeal nerve (RLN) anomalies with vascular variations allows identification of nonrecurrent nerves.

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.

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.

Efficient, effective, safe procedure to identify nonrecurrent inferior laryngeal nerve during thyroid surgery

BACKGROUND

The nonrecurrent inferior laryngeal nerve (NRILN) is always associated with the aberrant subclavian artery. CT images can detect this vascular anomaly, which predicts an NRILN. The purpose of this study was to report our procedure to identify the NRILN in patients with the aberrant subclavian artery.

METHODS

Four of 730 patients undergoing thyroid operation in our hospital were preoperatively diagnosed with aberrant subclavian artery by CT of the neck. To avoid vocal cord paralysis, we approached the vagal nerve first before dissecting the paratracheal region to discover the separation point of the NRILN from the vagal nerve.

RESULTS

The NRILN was identified without difficulty in all 4 patients. No patients showed vocal cord paralysis.

CONCLUSION

Approaching the vagal nerve first before dissecting the paratracheal region is an efficient, effective, and safe procedure to identify an NRILN in patients who are preoperatively diagnosed as having the aberrant subclavian artery.