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

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.

Usefulness of intraoperative nerve monitoring for giant type AB thymoma combined with an aberrant right subclavian artery: a case report

BACKGROUND

Abnormal tumor vascularization and escalating tumor size represent two major impediments that make cancer surgery impossible or complicated.

CASE PRESENTATION

Herein, we report the case of a giant thymoma (type AB) in a 58-year-old woman who presented with cough and yellow sputum. The thymoma grew extensively from the neck to the upper mediastinum. The patient exhibited an aberrant right subclavian artery and a non-recurrent inferior laryngeal nerve. Intraoperative nerve monitoring facilitated the identification and preservation of vital nerves spanning the neck and chest, including the non-recurrent inferior laryngeal nerve. Furthermore, the tumor was divided naturally along the constriction, and a good field of view was acquired to identify abnormal right subclavian arteries and nerves that ran deep in the tumor and surgical field. The tumor was safely removed without complications using intraoperative nerve monitoring, and the thymoma that grew extensively from the neck to the upper mediastinum and was associated with an aberrant right subclavian artery was resected.

CONCLUSION

Intraoperative nerve monitoring was helpful in identifying the non-recurrent inferior laryngeal nerve and left recurrent laryngeal nerve.

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.

Artificial intelligence-augmented, label-free molecular imaging method for tissue identification, cancer diagnosis, and cancer margin detection

Label-free high-resolution molecular and cellular imaging strategies for intraoperative use are much needed, but not yet available. To fill this void, we developed an artificial intelligence-augmented molecular vibrational imaging method that integrates label-free and subcellular-resolution coherent anti-stokes Raman scattering (CARS) imaging with real-time quantitative image analysis via deep learning (artificial intelligence-augmented CARS or iCARS). The aim of this study was to evaluate the capability of the iCARS system to identify and differentiate the parathyroid gland and recurrent laryngeal nerve (RLN) from surrounding tissues and detect cancer margins. This goal was successfully met.

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.

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.

Morphology and Functional Anatomy of the Recurrent Laryngeal Nerve with Extralaryngeal Terminal Bifurcation

Anatomical variations of the recurrent laryngeal nerve (RLN), such as an extralaryngeal terminal bifurcation (ETB), threaten the safety of thyroid surgery. Besides the morphology of the nerve branches, intraoperative evaluation of their functional anatomy may be useful to preserve motor activity. We exposed 67 RLNs in 36 patients. The main trunk, bifurcation point, and terminal branches of bifid nerves were macroscopically determined and exposed during thyroid surgery. The functional anatomy of the nerve branches was evaluated by intraoperative nerve monitoring (IONM). Forty-six RLNs with an ETB were intraoperatively exposed. The bifurcation point was located along the prearterial, arterial, and postarterial segments in 11%, 39%, and 50% of bifid RLNs, respectively. Motor activity was determined in all anterior branches. The functional anatomy of terminal branches detected motor activity in 4 (8.7%) posterior branches of 46 bifid RLNs. The motor activity in posterior branches created a wave amplitude at 25–69% of that in the corresponding anterior branches. The functional anatomy of bifid RLNs demonstrated that anterior branches always contained motor fibres while posterior branches seldom contained motor fibres. The motor activity of the posterior branch was weaker than that of the anterior branch. IONM may help to differentiate between motor and sensory functions of nerve branches. The morphology and functional anatomy of all nerve branches must be preserved to ensure a safer surgery.

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.