Nonrecurrent inferior laryngeal nerve without vascular anomaly as a genuine entity

The Nonrecurrent Laryngeal Nerve Without Abnormal Subclavian Artery: Report of Two Cases and Review of the Literature

As a variant of recurrent inferior laryngeal nerve (RILN), the nonrecurrent inferior laryngeal nerve (NRILN) is closely related to the occurrence of abnormal subclavian artery (ASA). The nonrecurrent inferior laryngeal nerve has been found in patients without arterial abnormalities, which is seen in the coexistence of NRILN and RILN, but it is easily confused with sympathetic-inferior laryngeal anastomosis branch (SILAB). We encountered 2 right NRILN patients without ASA during thyroid surgery. This article summarizes the characteristics of these cases and proposes methods to distinguish the coexistence of NRILN and RILN from SILAB. So far, 11 articles have reported 16 cases of NRILN without arterial abnormalities. In patients without artery abnormality, the vagus nerve could send out a descending branch NRILN at the bifurcation of the carotid artery and enter the larynx after anastomosis with RILN. Adequate dissection of the carotid sheath may avoid confusion with SILAB, and neural monitoring is also expected to provide a reference for the identification.

Carotid Endarterectomy for a Patient with a Right-sided Aortic Arch and Aberrant Left Subclavian Artery Predicting a Left Non-recurrent Inferior Laryngeal Nerve: A Case Report and Literature Review

Cardiovascular malformations during embryogenesis can lead the inferior laryngeal nerve to branching directly from the cervical vagus nerve and entering the larynx. This rare anatomical variation is known as a non-recurrent inferior laryngeal nerve (NRILN), and increases the risk of accidental injury resulting in postoperative vocal cord paralysis during neck surgery. We report a case of an 83-year-old man who presented with left symptomatic internal carotid artery stenosis with a right-sided aortic arch and aberrant left subclavian artery (ALSCA). We performed carotid endarterectomy (CEA) using intraoperative neuromonitoring to avoid NRILN injury. To the best of our knowledge, this is the first report of searching for a left NRILN by electrophysiology during CEA. Neurovascular surgeons need to understand the variations of the NRILN associated with congenital cardiovascular anomalies and effective use of intraoperative nerve monitoring (IONM). We discuss the embryological origin, IONM, and surgical pitfalls of this case.

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.

Relation of Nonrecurrent Laryngeal Nerve with Zuckerkandl's Tubercle

The nonrecurrent laryngeal nerve (NRLN) is a rare anatomical variation of the recurrent laryngeal nerve (RLN) that may hinder the identification and preservation of this nerve during surgery and is associated with increased iatrogenic risks. Zuckerkandl's tubercle (ZT) is considered a useful reference for locating the RLN during thyroid surgery. We report the case of an asymptomatic patient with a 23 mm uninodular goitre suspicious for cancer. Ultrasound examination showed a hypoechoic nodule with regular contours and microcalcifications. The patient had normal thyroid-stimulating hormone and thyroxine levels, and aspiration biopsy was suspicious for follicular cancer. She was treated with total thyroidectomy after the intraoperative examination confirmed the presence of a papillary thyroid carcinoma. The standard approach to the RLN below the inferior thyroid artery was used on both sides. The nerve displayed anatomical variation in the nonrecurrent form (NRLN) on the right side and was associated with another variation that was not found in the consulted literature. It was completely surrounded by thyroid tissue in the region of ZT, and the surgeon was forced to remove it from within the thyroid tissue. This combination of anatomical variations seems to be quite rare. Knowledge of the anatomy of the RLN and its variations, as well as its identification and careful dissection, is essential to avoid injury to the nerve during surgical procedures.

Recurrent Laryngeal Nerve Paralysis after Esophagectomy: Respiratory Complications and Role of Nerve Reconstruction

Recurrent laryngeal nerve paralysis (RLNP) after esophagectomy is a common complication and associated with aspiration pneumonia. In this study, we assessed the risk of RLNP and the usefulness of immediate reconstruction of recurrent laryngeal nerve (RLN) to prevent respiratory complications after esophagectomy. Seven hundred and eighty-two consecutive patients underwent an esophagectomy with three-field lymph node dissection, simultaneous gastric conduit reconstruction, and cervical anastomosis. Vocal cord function was observed using a flexible laryngoscope. Reconstruction between RLN and ipsilateral vagus nerve was performed during esophagectomy. RLNP was observed in 229 (29.3%) of the patients after esophagectomy: 198 unilateral and 31 bilateral cases. Of the 198 unilateral RLNP, vocal cord paralysis was observed predominantly on the left side (82.7%). RLNP was significantly associated with postoperative respiratory complications (P < 0.001) requiring a tracheotomy (P < 0.001) and mechanical ventilation (P < 0.001) and was also associated with esophagogastric anastomotic leakage (P = 0.015); consequently, the postoperative hospital stay was longer for patients with RLNP (P < 0.001). A longer operation time (P < 0.001) and advanced age (P = 0.038) were identified as significant independent predictors of RLNP. Resection of the RLN together with metastatic nodes was performed in 29 cases. The patients underwent RLN reconstruction (n = 11) had a significantly shorter postoperative hospital stay than those without RLN reconstruction (n = 18) (P = 0.019). In conclusion, RLNP was related to a poorer postoperative course among patients undergoing an esophagectomy. New surgical technologies are recommended for prevention of RLNP.

Relationship of vocal cord paralysis to the coil diameter of vagus nerve stimulator leads

OBJECT

This investigation was done to examine, following implantation of vagus nerve stimulators, the relationship of vocal cord paralysis to the inner diameter of the coils used to attach the stimulator lead to the nerve.

METHODS

All data in this investigation were collected, as mandated by the FDA, by the manufacturer of vagus nerve stimulators and were made available without restrictions for analysis by the authors. The data reflect all initial device implantations in the United States for the period from 1997 through 2012.

RESULTS

Vocal cord paralysis was reported in 193 of 51,882 implantations. In patients aged 18 years and older, the incidence of paralysis was 0.26% when the stimulator leads had coil diameters of 3 mm and 0.51% when the leads had 2-mm-diameter coils (p < 0.05). Across all age groups, the incidence of vocal cord paralysis increased with age at implantation for leads having 2-mm-diameter coils.

CONCLUSIONS

In patients aged 18 years and older, vocal cord paralysis occurred at almost twice the rate with the implantation of vagus nerve stimulator leads having 2-mm-diameter coils than with leads having 3-mm-diameter coils. The incidence of vocal cord paralysis increases with patient age at implantation.

Increased prediction of right nonrecurrent laryngeal nerve in thyroid surgery using preoperative computed tomography with intraoperative neuromonitoring identification

Background

A nonrecurrent laryngeal nerve (NRLN) is a rare but potentially serious anatomical variant. Although the incidence is reported to be 0.3% to 1.3%, it carries a much higher risk of palsy during thyroid surgery. The objective of this study is to investigate the usefulness of computed tomography (CT) for preoperative identification and intraoperative neuromonitoring identification (IONM) of NRLN in thyroid cancer patients.

Methods

The preoperative neck CT scans from 1,574 patients who needed thyroid surgery were examined. Absence of the brachiocephalic artery (BCA) and the presence of arteria lusoria were defined as positive with NRLN. Systematic intraoperative neuromonitoring (IONM) was also carried out for these 1,574 patients to localize and identify NRLN. A negative electromyography (EMG) response from lower vagal stimulation but a positive EMG response from the upper position indicated the occurrence of an NRLN.

Results

Nine NRLN (0.57%) were intraoperatively identified out of the 1,574 patients, and no patient with a NRLN showed preoperative clinical symptoms related to NRLN. Prior to the operation, surgeons identified only seven suspected NRLN cases based on identification of arteria lusoria. But a review of CT scans revealed that all cases could be identified by vascular anomalies. All patients were successfully detected at an early stage of operation using intraoperative neuromonitoring (IONM). Postoperative vocal cord function was normal in all patients.

Conclusions

CT of the neck is a reliable method for predicting NRLN before thyroid cancer surgery. However, some image features can be easily missed. Neurophysiology helps the surgeon to identify the NRLNs more precisely. Combining the two evaluation methods may decrease the incidence of nerve palsy, especially in cases of NRLN. Considering that CT is expensive, requires an X-ray, and achieves less information than ultrasound (US) concerning thyroid nodules, we suggest that applying US and IONM is more reasonable.

Coexisting right nonrecurrent and right recurrent inferior laryngeal nerves: a rare and controversial entity: report of a case and review of the literature

Variations in the course of the recurrent laryngeal nerve (RLN) can occur, including the development of a nonrecurrent inferior laryngeal nerve (NRILN). Rarely, both a right RLN and a right NRILN have been reported in the same patient, merging before they enter the larynx. A case is presented, including images, and the literature concerning this rare anatomical finding is reviewed, including studies suggesting alternative explanations for these cases. Fourteen previously reported cases of coexisting RLN and NRILN were identified, all involving the right side. Some cases were associated with an anomalous origin of the right subclavian artery and some were not. The alternative explanations that a communicating branch of the sympathetic nerve, which joins the RLN, is mistaken for an NRILN or that a collateral branch from an NRILN is mistaken for an RLN in these cases are also considered. Surgeons must be aware of these unusual variations to minimize nerve injury during neck surgery.

Detecting and identifying nonrecurrent laryngeal nerve with the application of intraoperative neuromonitoring during thyroid and parathyroid operation

PURPOSE

The nonrecurrent laryngeal nerve (NRLN) is a rare anatomical variant but associated with high risk of nerve injury during thyroid and parathyroid operations. Therefore, intraoperative detection and verification of NRLN are necessary.

METHOD

A total of 390 consecutive patients who underwent thyroid and parathyroid operations (310 RLNs dissected on the right side and 293 nerves on the left side) were enrolled. Electrically evoked electromyography was recorded from the vocalis muscles via an endotracheal tube with glottis surface recording electrodes. At an early stage of operation, vagal nerve was routinely stimulated at the level of inferior thyroid pole to ensure normal path of RLN. If there is a negative response from lower position but positive response from upper vagal stimulation, it indicates the occurrence of a NRLN, and we localize its separation point and path.

RESULTS

Four right NRLNs (1.3%) without preoperative recognition were successfully detected at an early stage of operation. Three patients were operated on for thyroid disease, one for parathyroid adenoma and all were associated with right aberrant subclavian artery. All NRLNs were localized and identified precisely with intraoperative neuromonitoring. Functional integrity of all nerves was confirmed by the intraoperative neuromonitoring and postoperative laryngeal examination.

CONCLUSIONS

Vagal stimulation at the early stage of operation is a simple, useful, and reliable procedure to detect and identify the NRLN.