The anatomy of the inferior laryngeal nerve

Selective Electrical Surface Stimulation to Support Functional Recovery in the Early Phase After Unilateral Acute Facial Nerve or Vocal Fold Paralysis

This article addresses the potential clinical value of surface electrical stimulation in the acute phase of denervation after the onset of facial nerve or recurrent laryngeal nerve paralysis. These two nerve lesions are the most frequent head and neck nerve lesions. In this review, we will work out several similarities concerning the pathophysiology features and the clinical scenario between both nerve lesions, which allow to develop some general rules for surface electrical stimulation applicable for both nerve lesions. The focus is on electrical stimulation in the phase between denervation and reinnervation of the target muscles. The aim of electrostimulation in this phase of denervation is to bridge the time until reinnervation is complete and to maintain facial or laryngeal function. In this phase, electrostimulation has to stimulate directly the denervated muscles, i.e. muscle stimulation and not nerve stimulation. There is preliminary data that early electrostimulation might also improve the functional outcome. Because there are still caveats against the use of electrostimulation, the neurophysiology of denervated facial and laryngeal muscles in comparison to innervated muscles is explained in detail. This is necessary to understand why the negative results published in several studies that used stimulation parameters are not suitable for denervated muscle fibers. Juxtaposed are studies using parameters adapted for the stimulation of denervated facial or laryngeal muscles. These studies used standardized outcome measure and show that an effective and tolerable electrostimulation of facial and laryngeal muscles without side effects in the early phase after onset of the lesions is feasible, does not hinder nerve regeneration and might even be able to improve the functional outcome. This has now to be proven in larger controlled trials. In our view, surface electrical stimulation has an unexploited potential to enrich the early therapy concepts for patients with unilateral facial or vocal fold paralysis.

An anatomical study of the anterior wall of the hypopharyngeal and the cervical esophageal junction

OBJECTIVE

The upper esophageal sphincter plays a significant role by forming a physical barrier at the junction of the hypopharynx and the cervical esophagus. As few studies have focused on the ventral aspect of this junction, the contribution of the anterior wall of the cervical esophagus to upper esophageal sphincter function remains unknown. The purpose of this study was to examine the muscle fibers' arrangement at the junction, especially of those forming its anterior wall.

METHODS

Thirteen specimens from 13 Japanese cadavers were analyzed. Six specimens were dissected macroscopically, while the remaining seven were examined histologically.

RESULTS

The outer longitudinal layer of the proximal esophagus was well-developed anterolaterally. The uppermost fibers of the inner circular layer of the esophagus ascended longitudinally. The anterolateral part of the outer longitudinal layer and the uppermost region of the inner circular layer were continuous with the median tendinous band, in turn reaching superior to the cricoid cartilage. Histological analysis showed that the tendinous band was also continuous with the superior part of the perichondrium of the cricoid cartilage and with the aponeurosis of the transverse and oblique arytenoids.

CONCLUSION

The well-developed anterolateral region of the outer longitudinal layer and the uppermost fibers of the inner circular layer were continuous with the median tendinous band, which reached superior to the cricoid cartilage. The contraction of the proximal esophagus may result in protrusion of the anteromedian esophageal wall into the lumen, thereby supporting the closure of the upper esophageal sphincter.

Cervical vagus nerve morphometry and vascularity in the context of nerve stimulation - A cadaveric study

Vagus nerve stimulation (VNS) has become a well-established therapy for epilepsy and depression, and is emerging to treat inflammatory disease, with the cervical vagus nerve (CVN) as major stimulation site. CVN morphometries are missing for VNS, considering its variability. Morphometric data were obtained from CVNs in 27 cadavers, including branching patterns and histology. Cross-sectional area, greater and lesser diameters averaged 7.2 ± 3.1 mm², 5.1 ± 1.5 and 4.1 ± 1.3 mm, and were ≤11.0 mm², ≤7.0 and ≤5.8 mm in 90% of the specimens, respectively. Midline distance (position lateral to the laryngeal eminence) and skin distance (anterior-posterior from skin) averaged 34.5 ± 6.2 and 36.2 ± 9.4 mm, ≤49.0 and ≤41.0 mm in 90%, respectively. Nerve dimensions and surface topography correlated closely, but without gender-, side- or branching-dependent differences. The nerve fascicle number averaged 5.2 ± 3.5. Vagal arteries were observed in 49% of the cases. Negative correlations were found for age and cross-sectional area, as well as subperineural vessel count. Detailed anatomical data on the CVN and its vascularity are given, forming the morphometric basis for VNS refinement, filling an evident gap in light of the CVN being a structure with variable positions and branching. A 35 × 35-mm rule may apply for the CVN position, irrespective of branching or positional variation.

Bilateral patterns and motor function of the extralaryngeal branching of the recurrent laryngeal nerve

PURPOSE

To evaluate the bilateral patterns and motor function of the extralaryngeal branches (ELB) of the recurrent laryngeal nerve(RLN).

METHODS

This study included 500 consecutive patients who underwent total thyroidectomy. Intraoperative nerve monitoring (IONM) was used in 230 patients. Demographic data, indications for surgery, the bilateral patterns of ELB of the RLN, electromyographic activity of the ELB, distance between the branching point to the entrance into the larynx, and the rate of postoperative morbidity were analyzed.

RESULTS

The overall rate of ELB was 27.6% (276/1000). A single trunk of the RLN on both sides was found in 269 (54%) patients, whereas ELB on both sides was observed in 45 (9%) patients. The rates of ELB on the left and right sides were 26.6 and 28.6%, respectively. Of the 89 branched nerves which were dissected using IONM, an evoked motor response was present in 100% of the anterior branches and 5.6% of the posterior branches. The mean branching distance of the RLN was significantly greater in female patients than in male patients on the left side (p = 0.031). The patterns of ELB showed no significant difference in male and female patients. The rates of postoperative transient and permanent hypoparathyroidism and unilateral RLN palsy were 21.6 and 2.8%, and 3.2 and 0.8%, respectively. The rate of RLN palsy was higher in branched nerves compared to those with a single trunk (0.75 vs 0.3%; p = 0.2).

CONCLUSION

Unilateral ELB of the RLN might be observed in approximately 1/4 of the patients, while bilateral branching is rare. A few number of posterior branches of the RLN can have motor function. The RLN's with ELB might have a higher risk of injury compared to those with a single trunk.

Abnormal distance of the extralaryngeal bifurcation point of the recurrent laryngeal nerve from the cricothyroid joint

The extralaryngeal bifurcation point of the recurrent laryngeal nerve (RLN) is typically located in a mean distance of 0–2 cm from the cricothyroid joint (CTJ). In the presented case though, the left RLN was unexpectedly identified bifurcating in a mean distance of 7 cm from the left CTJ in a young woman with multinodular goiter during total thyroidectomy. The RLN was carefully exposed throughout its course for the avoidance of iatrogenic injury of the nerval structure. The operation was uneventful. The present manuscript aims to highlight a scarce anatomic variation and its implications for thyroidectomy. Rare anatomic variations of the RLN such as the presented one encumber thyroid surgery and represent a severe risk factor of RLN injury. Meticulous operative technique combined with surgeons’ perpetual awareness concerning this peculiar anatomical aberration leads to an injury-free thyroid surgery.

Reinnervation of the diaphragm by the inferior laryngeal nerve to the phrenic nerve in ventilator-dependent tetraplegic patients with C3-5 damage

The aim of this study was to evaluate the feasibility of unilateral diaphragmatic reinnervation in humans by the inferior laryngeal nerve. This pilot study included chronically ventilated tetraplegic patients with destruction of phrenic nerve motoneurons. Five patients were included. They all had a high level of tetraplegia, with phrenic nerve motor neuron destruction. They were highly dependent on ventilation, without any possibility of weaning. They did not have other chronic pathologies, especially laryngeal disease. They all had diaphragmatic explorations to diagnose the destruction of the motoneurons of the phrenic nerves and nasoendoscopy to be sure that they did not have laryngeal or pharyngeal disease. Then, surgical anastomosis of the right phrenic nerve was performed with the inferior laryngeal nerve, by a cervical approach. A laryngeal reinnervation was performed at the same time, using the ansa hypoglossi. One patient was excluded because of a functional phrenic nerve and one patient died 6 months after the surgery of a cardiac arrest. The remaining three patients were evaluated after the anastomosis every 6 months. They did not present any swallowing or vocal alterations. In these three patients, the diaphragmatic explorations showed that there was a recovery of the diaphragmatic electromyogram of the right and left hemidiaphragms after 1 year. Two patients had surgical diaphragmatic explorations for diaphragmatic pacing 18-24 months after the reinnervation with excellent results. At 36 months, none of the patients could restore their automatic ventilation. In conclusion, this study demonstrated that diaphragmatic reinnervation by the inferior laryngeal nerve is effective, without any vocal or swallowing complications.

Non-recurrent laryngeal nerve with a coexisting contralateral nerve demonstrating extralaryngeal branching

Non-recurrence and extralaryngeal branching are 2 of the more frequently encountered anomalies of the recurrent laryngeal nerve. If not anticipated intraoperatively, these abnormalities can put the nerve at risk, with subsequent vocal cord palsy. It is therefore important to report on and understand these abnormalities. We present a unique case of a non-recurrent laryngeal nerve with a coexisting contralateral nerve demonstrating extralaryngeal branching. This case allows us to demonstrate the importance of arteria lusoria in head and neck surgery, and to conclude that non-recurrence and extralaryngeal branching can occur separately within individual nerves in the same patient. The case also highlights the importance of a systematic intraoperative approach to the identification of every recurrent laryngeal nerve, especially in bilateral procedures having already exposed an anomalous nerve on one side.

Positional Relations of the Cervical Vagus Nerve Revisited

OBJECTIVES

The cervical part of the vagus nerve (CVN) has become an important target for stimulation therapy to treat epilepsy and psychiatric conditions. For this purpose, the CVN is visualized in the carotid sheath, assuming it to be localized dorsomedially between the carotid artery (CA) and the internal jugular vein (JV). The aim of our morphological study was therefore to revisit the CVN relationships to the CA and JV, hypothesizing it to have common variations to this classical textbook anatomy.

MATERIALS AND METHODS

Positional relations of the CVN, CA and JV were investigated in the carotid sheath of 35 cadavers at the C3 to C6 level. Positional relations of the CVN, CA and JV were documented on the basis of a 3 × 3 chart.

RESULTS

Eighteen different arrangements of the CVN, CA and JV were observed. The typical topographic relationship of the CVN dorsomedially between the CA and JV was only found in 42% of all cases. The CVN was located dorsally or (dorso-)laterally to the CA in 80% and dorsally or (dorso-)medially of the JV in 96% of all cases.

CONCLUSIONS

Classical textbook anatomy of the CVN is only present in a minority of cases. Positional variations in contrast to textbook anatomy are considerably more frequent than previously described, which might be a hypothetical morphological explanation for the lack of efficacy or side effects of CVN stimulation. Furthermore, the position of the CVN relative to the internal jugular vein is more consistent than to the CA.

The Anastomoses of the Recurrent Laryngeal Nerve in the Larynx: A Meta-Analysis and Systematic Review

OBJECTIVES

The recurrent laryngeal nerve and its branches form a great variety of anastomoses. These nerve communications can alter the innervation patterns of the laryngeal muscles and can affect both the diagnosis and treatment of paralyzed vocal cords. The aim of this study was to assess the prevalence and anatomical characteristics of the laryngeal nerve connections, and to review their function and clinical significance.

STUDY DESIGN

Meta-analysis and systematic review.

METHODS

The major electronic databases were thoroughly searched to identify all studies reporting data on the anastomoses of the laryngeal nerves. Data on the prevalence of each type of anastomosis were extracted and pooled into a meta-analysis using MetaXL version 3.0 (EpiGear International Pty. Ltd., Wilston, Queensland, Australia).

RESULTS

Twenty-two cadaveric studies (n = 1404 hemilarynges) were included in the meta-analysis. The two most common communications were Galen's anastamosis and the arytenoid plexus. The pooled prevalence estimate for Galen's anastamosis was 76.7% (95% confidence interval [CI]: 59.0-90.0), of which the single trunk type was most common (92.3%). The arytenoid plexus had a pooled prevalence estimate of 79.7% (95% CI: 41.1-100).

CONCLUSIONS

Owing to the high prevalences and variability of nerve connections in the larynx, detailed anatomical knowledge of these anastomoses can be crucial for the accurate interpretation of laryngoscopy results, reducing iatrogenic injury during surgical procedures, and facilitating the development of novel strategies for treating laryngeal paralyses.

Surgical approach to the thyroarytenoid branch of the inferior laryngeal nerve through the thyroid cartilage

PURPOSE

To describe the anatomical course of the intralaryngeal portion of the inferior laryngeal nerve (ILN) and to standardize the surgical access to its thyroarytenoid branch (TAb) through the thyroid cartilage.

METHODS

Under surgical microscopy, 33 adult human excised larynges were dissected, to expose the intralaryngeal portion of ILN. The point of entry of TAb, ILN's terminal branch, in the thyroarytenoid (TA) muscle was determined and correlated with thyroid cartilage dimensions.

RESULTS

After entering the larynx, the ILN consistently traveled between the thyroid cartilage and the lateral cricoarytenoid muscle in an anterior and slightly cranial course. The distance from the point of entry of the TAb in the TA muscle to the midline (TAb-H) and to the inferior border (TAb-V) of the thyroid cartilage differed according to gender. In females, mean distances of TAb-H and TAb-V were 20.5mm and 5.2mm and in males, 22.3mm and 5.9mm, respectively.

CONCLUSION

The intralaryngeal course of the inferior laryngeal nerve presents low variability and measures from landmarks in the thyroid cartilage help to estimate the point of entry of thyroarytenoid branch in thyroarytenoid muscle.

Extralaryngeal branching of the recurrent laryngeal nerve: a meta-analysis of 28,387 nerves

Introduction

The recurrent laryngeal nerves (RLN) are branches of the vagus nerve that go on to innervate most of the intrinsic muscles of the larynx. Historically, the RLN has been considered to branch after it enters the larynx, but numerous studies have demonstrated that it often branches before. The wide variability of this extralaryngeal branching (ELB) has significant implications for the risk of iatrogenic injury. We aimed to assess the anatomical characteristics of ELB comprehensively.

Methods

Articles on the ELB of the RLN were identified by a comprehensive database search. Relevant data were extracted and pooled into a meta-analysis of the prevalence of branching, branching pattern, distance of ELB point from the larynx, and presence of positive motor signals in anterior and posterior ELB branches.

Results

A total of 69 articles (n = 28,387 nerves) from both intraoperative and cadaveric modalities were included in the meta-analysis. The overall pooled prevalence of ELB was 60.0 % (95 % CI 52.0–67.7). Cadaveric and intraoperative subgroups differed with prevalence rates of 73.3 % (95 % CI 61.0–84.0) and 39.2 % (95 % CI 29.0–49.9), respectively. Cadavers most often presented with a ELB pattern of bifurcation, with a prevalence of 61.1 %, followed by no branching at 23.4 %. Branching of the RLN occurred most often at a distance of 1–2 cm (74.8 % of cases) prior to entering the larynx. A positive motor signal was most often noted in anterior RLN branches (99.9 %) but only in 1.5 % of posterior branches.

Conclusions

The anatomy of the RLN is highly variable, and ELB is likely to have been underreported in intraoperative studies. Because of its high likelihood, the possibility of ELB needs to be assessed in patients to prevent iatrogenic injury and long-term postoperative complications.

Electronic supplementary material

The online version of this article (doi:10.1007/s00423-016-1455-7) contains supplementary material, which is available to authorized users.

Motor function of the recurrent laryngeal nerve: Sometimes motor fibers are also located in the posterior branch

BACKGROUND

The function of the extralaryngeal branches of the recurrent laryngeal nerve (RLN) has yet to be described precisely. The goal of this study was to evaluate the incidence and motor function of the extralaryngeal branches of the RLN.

METHODS

Our study group consisted of 335 consecutive patients undergoing thyroid and parathyroid operations in whom the branches of the RLNs (n = 200) were evaluated with intraoperative nerve monitoring and by measuring the distance from the point of branching of the RLN into anterior and posterior branches and the entry of the individual branches into the larynx-defined as the branching distance. Anterior and posterior branches of the RLN were assessed separately by electromyography (using a standard electromyography endotracheal tube) for adduction and by finger palpation for abduction. The RLNs were classified as having motor function only in the anterior branches (Group 1) or function both in the anterior and posterior branches (Group 2).

RESULTS

There were 185 RLNs in Group 1 and 15 RLNs in Group 2, assessed by intraoperative nerve monitoring. Motor function was detected in all anterior branches of the RLN (100%) and in 8% of the posterior branches. The mean branching distance was greater in Group 2 compared with Group 1 (24.1 ± 13.6 mm, 17.3 ± 8.5 mm, respectively, P = .045).

CONCLUSION

Although the anterior branch of RLN always has motor function, the posterior branch also has motor function in about 8% of patients. The probability of detecting motor function in the posterior branch was greater among early branching RLNs, which have a greater branching distance. The surgeon should remember that posterior branches may contain motor fibers and protect these branches to avoid postoperative vocal cord dysfunction.

Human vagus nerve branching in the cervical region

BACKGROUND

Vagus nerve stimulation is increasingly applied to treat epilepsy, psychiatric conditions and potentially chronic heart failure. After implanting vagus nerve electrodes to the cervical vagus nerve, side effects such as voice alterations and dyspnea or missing therapeutic effects are observed at different frequencies. Cervical vagus nerve branching might partly be responsible for these effects. However, vagus nerve branching has not yet been described in the context of vagus nerve stimulation.

MATERIALS AND METHODS

Branching of the cervical vagus nerve was investigated macroscopically in 35 body donors (66 cervical sides) in the carotid sheath. After X-ray imaging for determining the vertebral levels of cervical vagus nerve branching, samples were removed to confirm histologically the nerve and to calculate cervical vagus nerve diameters and cross-sections.

RESULTS

Cervical vagus nerve branching was observed in 29% of all cases (26% unilaterally, 3% bilaterally) and proven histologically in all cases. Right-sided branching (22%) was more common than left-sided branching (12%) and occurred on the level of the fourth and fifth vertebra on the left and on the level of the second to fifth vertebra on the right side. Vagus nerves without branching were significantly larger than vagus nerves with branches, concerning their diameters (4.79 mm vs. 3.78 mm) and cross-sections (7.24 mm2 vs. 5.28 mm2).

DISCUSSION

Cervical vagus nerve branching is considerably more frequent than described previously. The side-dependent differences of vagus nerve branching may be linked to the asymmetric effects of the vagus nerve. Cervical vagus nerve branching should be taken into account when identifying main trunk of the vagus nerve for implanting electrodes to minimize potential side effects or lacking therapeutic benefits of vagus nerve stimulation.

Relationship between the Branches of the Recurrent Laryngeal Nerve and the Inferior Thyroid Artery

Objectives:

The relationship between the recurrent laryngeal nerve (RLN) and the inferior thyroid artery (ITA) is an important and helpful landmark for isolating the RLN and its branches during surgery. In the present study, we aimed to define and classify in detail all of the possible relationships between the two anatomic structures and their branches.

Methods:

We examined 100 specimens (200 sides) from cadavers of 76 men and 24 women who were between 16 and 90 years of age at the time of death. After anatomic dissection was performed, the relationship between the RLN and the ITA was noted for each side and documented in the form of high-resolution photographs.

Results:

The relationships of both structures and their branches were classified into 6 types. Details were verified regarding the relationships between the main trunks, between the trunks and branches, and between the branches, as follows: Type A (ITA trunk to RLN trunk); type B (ITA branches to RLN trunk); type C (ITA trunk to RLN branches); type D (ITA branches to RLN trunk and RLN branches); type E (ITA branches to RLN branches); and type F (others).

Conclusions:

Despite the various anatomic and surgical studies already performed, in the present study we tried to demonstrate all types of relationships between the RLN and the ITA and their branches and devise a new, detailed classification of the possible relationships between the two structures.

Motor and sensory branching of the recurrent laryngeal nerve in thyroid surgery

INTRODUCTION

Recognition of extralaryngeal bifurcation of the recurrent laryngeal nerve (RLN) is crucial, because inadvertent intraoperative division may lead to significant morbidity. The purpose of this study was to examine the incidence of extralaryngeal bifurcation of the RLN and the distance that the initial bifurcation occurs from the cricothyroid insertion site of the RLN. We also sought to demonstrate the location of the RLN branches containing a predominance of motor fibers.

METHODS

This prospective study of 220 patients with data on 310 RLNs collected the type of operation, incidence of bifurcation, distance from the cricothyroid insertion point to the point of initial bifurcation, and location of the motor fibers by assessing a stimulus response on the Medtronic NIMS as they relate to the laryngeal muscles.

RESULTS

A total of 310 RLNs in 220 patients were studied. There were 133 RLNs (42.9%) that bifurcated before entering the larynx. These bifurcations occurred 51.1% on the right, 48.9% on the left, and 33.3% bilaterally. The median branching distance from the cricothyroid membrane on the right was 6.33 mm, and on the left was 6.37 mm. In all bifurcated RLNs, the motor fibers were located exclusively in the anterior branches.

CONCLUSION

Extralaryngeal bifurcation was found in 42.9% of the RLNs in this case series. The motor fibers are located in the anterior branches. Great caution is therefore required after the presumed identification of the RLN to ensure there is no unidentified anterior branch.

Recurrent laryngeal nerve landmarks revisited

BACKGROUND

The aim of this work was to evaluate, to prove their reliability, the different surgical landmarks previously proposed as a mean to locate the recurrent laryngeal nerve (RLN).

METHODS

The necks of 143 (68 male and 76 female) human adult embalmed cadavers were examined. RLN origin and length and its relationship to different landmarks were recorded and results compared with those previously reported. Statistical comparisons were performed using the chi-square test (significance, p ≤ .05).

RESULTS

Mostly, RLN is located anterior to the tracheoesophageal sulcus (41.6%), posterior to the inferior thyroid artery (35.8%), lateral to Berry's ligament (88.1%), below the inferior rim of the inferior constrictor muscle (90.4%), and entering the larynx before its terminal division (54.6%).

CONCLUSIONS

The position of the RLN in relation to those structures classically considered as landmarks is highly variable. The most reliable relationships are those with Berry's ligament or the inferior constrictor muscle.

Recurrent laryngeal nerve: significance of the anterior extralaryngeal branch

INTRODUCTION

Recognition of extralaryngeal branching of the recurrent laryngeal nerve (RLN) is crucial, because inadvertent operative division may lead to significant postoperative morbidity. The purpose of this study was to examine the incidence of extralaryngeal bifurcation of the RLN and to demonstrate the location of the motor fibers within the branches of the RLN.

METHODS

Prospective study on 99 patients over 1 year with operative data collected on the branching of a total of 137 RLNs. Operative data obtained included the type of operation, incidence of nerve bifurcation, the distance from the inferior border of the cricothyroid to the point of bifurcation, and the location of the motor fibers to the intrinsic muscles of the larynx within the branches of the RLN.

RESULTS

The RLN was seen intra-operatively in all patients. A total of 137 (right 69, left 68) RLNs in 99 patients undergoing thyroidectomy (total 29; hemi 51), parathyroidectomy (16) and central lymph node dissection (3) were studied. Overall, 46 RLNs (34%) bifurcated prior to entry into the larynx. These bifurcations occurred on the right in 27 (59%) and left 19 (41%). Bilateral bifurcation occurred in 12 (27%) of the 44 patients who underwent bilateral dissections. The median branching distance from the cricothyroid membrane on the right was 8.3 ± 2.5 mm, and on the left was 7.5 ± 1.8 mm. In all bifurcated RLNs, the motor fibers to the vocal cords were located exclusively in the anterior branches.

CONCLUSION

Extralaryngeal bifurcation was found in 34% of the RLNs in this case series. The motor fibers of RLN are located in the anterior branch while the posterior branch is only sensory in function. Great caution is, therefore, required after the presumed identification of the RLN to ensure there is no unidentified anterior branch. Identification of the anterior branch may lead to decreased risk of postoperative nerve injury.

Intraoperative Monitoring of the Recurrent Laryngeal Nerve during Thyroidectomy: A Standardized Approach (Part 1)

One of the most feared complications in thyroid surgery is injury to the superior laryngeal nerve or recurrent laryngeal nerve. Neural identification during surgery is insufficient to assess nerve injury. Intraoperative nerve monitoring of the vagal nerve and recurrent laryngeal nerve during thyroid surgery is a new adjunct designed to allow better identification of nerves at risk and therefore reduce complications related to their injury. This new working tool does not substitute adequate surgical technique but merely provides the surgeon with an adjunct to routine visual identification and functional assessment. The use of nerve monitoring requires standardization of the monitoring procedure. Pursuant to this, we will discuss in two related articles the current state of the art standardized technique of nerve monitoring in thyroid surgery. The aim of part 1 is to provide a concise overview of nerve monitoring in thyroid surgery and its effectiveness. This will include a brief review of the surgical anatomy of the recurrent laryngeal nerve and the key landmarks used to identify the nerve during surgery. Part 2 will describe how to perform the standardized nerve monitoring in a step by step fashion during thyroid surgery which will diminish variable results and misleading information associated with a nonstandardized nerve monitoring procedure.

The motor fibers of the recurrent laryngeal nerve are located in the anterior extralaryngeal branch

OBJECTIVE

This study aimed to establish the prevalence of extralaryngeal bifurcation of the recurrent laryngeal nerve (RLN) and investigate the location of the motor fibers to the intrinsic muscles of the larynx within the branches of the RLN.

SUMMARY OF BACKGROUND DATA

Recognition of extralaryngeal branching of the RLN is important, because inadvertent division of a branch may lead to significant vocal cord palsy despite the operator believing the nerve was preserved.

METHODS

Prospective operative data on branching of the RLN were collected in 579 patients undergoing thyroidectomy or open parathyroidectomy over a 3 year period and nerve integrity monitoring was utilized to document the position of the motor fibers of the last 176 RLNs. Adduction of the vocal cords was detected by the electromyography-endotracheal tube and abduction by finger palpation of muscle contraction in the posterior cricoarytenoid.

RESULTS

A total of 838 RLN were studied (right--432, left--406). Bifurcations occurred on the right in 111 (25.7%) and left 93 (22.9%). Bilateral bifurcation occurred in 23 (8.9%) of bilaterally dissected nerves. Overall 176 RLNs in 118 patients were assessed by the nerve integrity monitoring. Of these 41 (23.3%) were bifid RLN. In all 41 (100%) cases of bifid RLN, motor fibers for both adduction and abduction of the vocal cords were located exclusively in the anterior branches of RLN, and none in the posterior branches.

CONCLUSION

Extralaryngeal bifurcation of RLN is a common anatomical variant. The motor fibers of RLN are located in the anterior branch, for both adduction and abduction. Great care is therefore required following the presumed identification of the RLN to ensure there is no unidentified anterior branch.

Risk factors for transient vocal cord palsy after thyroidectomy

Background

Transient recurrent laryngeal nerve palsy affects to 5–10 per cent of patients after extracapsular thyroidectomy. This prospective study assessed the impact of surgical injury and extralaryngeal branching of the inferior laryngeal nerve (ILN) on vocal cord dysfunction (VCD).

Methods

Total thyroidectomy or lobectomy was performed in 188 patients, with 302 ILNs at risk. The anatomy of the ILN and degree of injury to the nerve, based on the Laryngeal Nerve Injury Score (LNIS), were recorded. Fibreoptic laryngoscopy was performed a mean(s.d.) of 10·6(4·1) days after thyroidectomy.

Results

Some 37·4 per cent of ILNs showed extralaryngeal branching. In all, 10·9 per cent of patients developed VCD; 4·3 per cent had paresis and 6·6 per cent paralysis. All paretic and all but one paralytic cords recovered fully after 61(17) days. VCD was more frequently associated with branched than non-branched ILNs (15·8 versus 8·1 per cent; P = 0·022). Injuries were more common in branched nerves (mean(s.e.m.) total LNIS 0·94(0·08) versus 0·51(0·05); P < 0·001). Branched nerves were more likely to be associated with VCD (odds ratio 2·2 (95 per cent confidence interval 1·1 to 4·5)).

Conclusion

Branched ILNs suffer more surgical injuries and are twice as likely to be associated with VCD.

Extralaryngeal division of the recurrent laryngeal nerve: a new description for the inferior laryngeal nerve

Extralaryngeal division of the recurrent laryngeal nerve was contradictory in the literature. We aimed to investigate extralaryngeal division of the nerve, and also propose a new description for the inferior laryngeal nerve. Sixty specimens (120 sides) were examined for this project, including 41 men and 19 women cadavers between the ages of 40 and 89 years at death. In one right side, terminal segment of the nerve gave off many small branches surrounding the inferior thyroid artery then reaching the larynx, trachea, thyroid gland and esophagus. In eight sides, terminal segment of the nerve had no extralaryngeal division and entered the larynx as a single trunk. In 110 sides, the nerve had extralaryngeal division. One hundred and three nerves had two laryngeal and one to three extralaryngeal branches. Two types were described in this group. In type I (66 nerves), both branches arose from the same level of nerve. Type I had two subtypes: type Ia, the origin of the branches was just below the inferior constrictor muscle; type Ib, the origin of the branches was 15-35 mm below the muscle. In type II (37 nerves), the laryngeal branches arose just 3-5 mm above the extralaryngeal branches. We observed that the laryngeal and extralaryngeal branches arose generally from the same point of the recurrent laryngeal nerve. The inferior laryngeal nerve is thus very short, or even nonexistent. Therefore, we suggest that if the term "superior laryngeal nerve" is a given, standard, and accepted term, then the term "inferior laryngeal nerve" should also be accepted instead of the term "recurrent laryngeal nerve."

The innervation of the posterior cricoarytenoid muscle: exploring clinical possibilities

Manipulation of the nerve supply to the posterior cricoarytenoid (PCA) muscle has potential for ameliorating the symptoms of some neurologic conditions such as abductor spasmodic dysphonia. The anatomy of the nerve supply to the PCA is better understood than in previous eras, but the anatomical understanding has not translated to clinical application yet. Microscopic dissection allowed the identification and measurement of the branches from the recurrent laryngeal nerves (RLNs) to the PCA in 43 human cadaver larynges. The cricothyroid (CT) joint was the primary landmark for measurement. Other structural measurements were also made on the larynges. All of the PCA muscles received innervation from the anterior division of the RLN. The number of direct branches from the RLN ranged from 1 to 5 (average 2.3) More than 70% of PCA muscles also received 1-3 branches off of the branch to the interarytenoid (IA) muscle. Less than half of PCA muscles received any kind of nerve branches from the posterior division of the RLN. Branches to the PCA most commonly departed the main RLN in its vertical segment and all entered the muscle from its deep surface. All branches departed the RLN within an average of 9.5mm from the CT joint; the branch to the IA occurs distal to this point. The innervation to the PCA is complex and redundant, and the segment of the RLN supplying those branches is difficult to expose safely. For these reasons, selective denervation or reinnervation procedures limited to the nerve branches may be technically difficult. When needing only to denervate the PCA, this can be accomplished by removing a portion of the PCA and the underlying nerve supply. Surgical technique should be based upon the understanding of the anatomy of the PCA muscle and its nerve supply.

Extralaryngeal bifurcation of the recurrent laryngeal nerve: a common variation

Extralaryngeal bifurcation and trifurcation of the recurrent laryngeal nerve (RLN) is not well described in anatomical texts. This significant anatomical variation is important because prevention of vocal cord paralysis requires preservation of all branches of the RLN. The aim of this study was to examine the prevalence of extralaryngeal bifurcation of the RLN seen during thyroid/parathyroid surgeries. All patients undergoing total thyroidectomy, hemithyroidectomy and parathyroidectomy (excluding all minimally invasive procedures) carried out by a single endocrine surgeon from November 2003 to December 2004 were included. Operative data obtained prospectively included the location of the nerve, number of branches and the distance in millimetres from the inferior border of the cricothyroid to the point of bifurcation. A total of 213 (right = 114, left = 99) RLN in 137 patients were studied. Seventy-seven (36%) nerves bifurcated or trifurcated before entry into the larynx. Bifurcations were more common on the right (43%) than on the left (28%) (P = 0.05). Trifurcations were seen in eight nerves, seven on the right and one on the left (P = 0.05). Bilaterally branched RLN were observed in 14 (18%) of 77 patients undergoing a bilateral procedure. One non-RLN was identified on the right. The median distance from the cricothyroid to the point of division was 18 mm on the right and 13 mm on the left. Extralaryngeal division of the RLN is a common anatomical variant occurring more frequently on the right. Unseen branches of the RLN are at risk of injury during surgery. Therefore, great care is required following presumed identification of the RLN to ensure that there are no other unidentified branches.

Sensitivity and Specificity of Intraoperative Recurrent Laryngeal Nerve Stimulation Test for Predicting Vocal Cord Palsy after Thyroid Surgery

INTRODUCTION

Recurrent laryngeal nerve (RLN) palsy after thyroidectomy, although infrequently encountered, can decrease quality of life. In addition to the hoarseness that occurs with unilateral RLN palsy, bilateral RLN palsy leads to dyspnea and often to life-threatening glottal obstruction. Therefore, intraoperative awareness of the nerve's status is of great importance. This study examined the sensitivity and specificity of a palpation technique to detect contraction of the posterior cricoarytenoid muscle (PCA) through the posterior hypopharyngeal wall while the RLN was being stimulated with a disposable nerve stimulator during thyroid surgery (the laryngeal palpation test) to predict postoperative RLN deficits.

METHODS

A total of 2197 RLNs in 1376 patients were identified to be at risk of injury during thyroidectomy performed between July 2003 and August 2004. Postoperative RLN integrity was assessed using direct laryngoscopy or laryngofiberoscopy to visualize vocal fold mobility.

RESULTS

Altogether, 76 RLNs failed to elicit a PCA contraction in response to nerve stimulation, and 80 cases of temporary vocal cord palsy and 21 cases of permanent vocal cord palsy were recognized on postoperative evaluation. For postoperative vocal cord palsy, the sensitivity and specificity of the laryngeal palpation test were 69.3% and 99.7%, respectively, with a positive predictive value of 92.1% and negative predictive value of 98.5%. For permanent vocal cord palsy, the sensitivity and specificity were 85.7% and 97.3%, respectively, with a positive predictive value of 23.7% and negative predictive value of 99.8%.

CONCLUSIONS

The laryngeal palpation test is not a particularly useful method for predicting the level of RLN function after thyroidectomy. All patients must be examined postoperatively by direct laryngoscopy or laryngofiberoscopy to check vocal cord mobility. Even if there is no contraction of the PCA and we detect vocal cord palsy immediately after surgery, vocal cord palsy often recovers within 1 year when visual preservation of RLN is successful.

Laryngeal branching pattern of the inferior laryngeal nerve, before entering the larynx

The objective of the present work was to investigate the laryngeal branching pattern of the inferior laryngeal nerve (ILN) in detail before the branches entered the larynx. In 49 specimens 96 sides were examined for this project, including 27 males and 22 female cadavers. In 7 sides (7.3%, 5 on the left and 2 on the right) the ILN passed as a single trunk into the larynx below the inferior constrictor muscle. In 82 sides (85.4%, 40 on the left and 42 on the right) two laryngeal branches originated from the nerve. The nerve divided either just before entering the larynx (58.3%, 24 on the left and 32 on the right) or 15-32 mm below the inferior constrictor muscle (27.1%, 16 on the left and 10 on the right). In 69 sides (71.8%), the anterior and/or posterior laryngeal branches subdivided into one or two sub-branches. The anterior (observed in 49 sides, 51%) and posterior laryngeal branches supplied all intrinsic laryngeal muscles except the cricothyroid muscle and the mucosa below the vocal cords, respectively, while their sub-branches reached the cricopharyngeal part of the inferior constrictor muscle, esophagus and/or the thyroid gland. In 7 sides (7.3%, 4 on the left and 3 on the right) the nerve divided into three laryngeal branches. In conclusion, the branching pattern of the nerve may be important pitfalls of the thyroidal and laryngeal surgery. Owing to this the surgeon should keep in mind the risk of extra laryngeal division of the nerve and not confuse laryngeal and extra laryngeal branches.

A study of routine exposure of recurrent laryngeal nerve during thyroid surgery

One of the main complications of thyroid surgery is injury to recurrent laryngeal nerve (RLN), which causes severe morbidity to the patient in postoperative period. To find out the incidence of RLN injury and its consequences, a prospective study was done in a group of 142 cases during the years 1999-2000. Different types of thyroidectomies for various diseases lbw of the thyroid gland, wherein a routine identification and exposure of the P-R was done through out its full course till its entry into the larynx at cricothyroid membrane. Three cases of temporary RLN injury were found and not a single case of permanent nerve injury was seen during our study. Three cases of nonre current LN were found on the right side of the gland. The temporary injury of the nerve completely recovered during 2-5 months of follow-up. We present some reviews of the literature to provide various authors, views and experiences regarding injury of RLN associated with thyroid urgery.

Variability in nerve patterns of the adductor muscle group supplied by the recurrent laryngeal nerve

INTRODUCTION

Accurate knowledge of the nerve supply of each individual muscle is needed to achieve a successful selective reinnervation of the larynx. The aim of the present work was to study the nerve supply of the adductor laryngeal muscles supplied by the recurrent laryngeal nerve.

STUDY DESIGN

Morphologic study of human larynges.

METHODS

The muscular nerve supply was studied in a total sample of 75 human larynges obtained from necropsies (47 males and 28 females, age range from 41-95 years) and examined by careful dissection using a surgical microscope.

RESULTS

The arytenoid muscle received one branch from each recurrent nerve. In 88% of cases, this branch arose in a common trunk with the upper branch of the posterior cricoarytenoid muscle. In 8% of cases, the nerve for the arytenoid muscle also had a branch going to the lateral cricoarytenoid muscle. The arytenoid muscle also received from one to three pairs of branches from the posterior division of the internal laryngeal nerve; these were interconnected ipsi- and contralaterally and were also connected to the two branches coming from the recurrent laryngeal nerve. The lateral cricoarytenoid muscle received from one to six branches from the recurrent nerve, but in 5.8% of cases, it also received a twig from a connecting branch between the recurrent nerve and the external (5.6%) or the internal laryngeal nerves (0.2%). The thyroarytenoid muscle received from one to four branches from the recurrent nerve, but in 5.6% of cases, it also received a twig from a connecting branch between the recurrent nerve with the external (4.6%) or the internal (1%) laryngeal nerves.

CONCLUSION

No abductor or adductor division of the recurrent laryngeal nerve was found in the present study. In 88% of cases, the nerve supply to the arytenoid muscle (adductor) and the posterior cricoarytenoid muscle (abductor) arose from a common trunk, which in 8% of cases, also had a branch to the lateral cricoarytenoid muscle. Furthermore, the high incidence of branches innervating the adductor muscles from connections between the recurrent laryngeal nerve and the internal and external laryngeal nerves led us to reconsider the contribution of these nerves in the supply to this muscle group.

The inferior laryngeal nerve: surgical and anatomic considerations. Report of 251 thyroidectomies

This surgical anatomic study aimed to determine (1) the anatomic relation of the laryngeal inferior nerve with the inferior thyroid artery, (2) the existence of extralaryngeal branches of division of the nerve and (3) the size of the nerve seen macroscopically. Two hundred and fifty-one patients underwent thyroid surgery during a period of 30 months. There were 50 males and 201 females. The male population underwent 28 total thyroidectomies, 13 left lobectomies and 9 right lobectomies. The female population underwent 124 total thyroidectomies, 33 left lobectomies and 44 right lobectomies. On the right side: the nerve was found superficial to the artery in 70.24% of females and 51.35% of males, the nerve was divided in 23.81% of females and 21.62% of males and seemed unusually thin in 14.29% of females and 5.41% of males. On the left side: the nerve was found superficial to the artery in 87.26% of females and 95.12% of males, the nerve was divided in 15.29% of females and 14.63% of males and seemed unusually thin in 10.83% of females and 2.44% of males. In conclusion, the inferior laryngeal nerve is characterized by its important anatomic variations, especially on the right side. These variations might be different even between males and females. Knowledge of these variations is very important in order to best identify and preserve the inferior laryngeal nerve during thyroid surgery.

Variability of the nerve supply patterns of the human posterior cricoarytenoid muscle

OBJECTIVES/HYPOTHESIS

To achieve a successful selective reinnervation of the larynx, an accurate knowledge of the nerve supply of each individual muscle is required. The posterior cricoarytenoid muscle, the only abductor or respiratory muscle of the larynx, plays a vital role in cases of recurrent palsy and orthotopic transplantation. Descriptions of the posterior cricoarytenoid muscle nerve supply pattern vary considerably. The goal of the present study was to establish an accurate morphological description of the posterior cricoarytenoid muscle nerve supply in a large sample of human larynges.

STUDY DESIGN

Morphologic study of human larynges.

METHODS

The posterior cricoarytenoid muscle nerve supply was studied in a total sample of 75 human larynges obtained from necropsies (47 male and 28 female samples; age range, 41-95 y) and examined by careful dissection using a surgical microscope.

RESULTS

The posterior cricoarytenoid muscle nerve supply in all cases (100%) came from the anterior division of the recurrent nerve. However, in six cases (4%) a small branch also arose from the ramus anastomoticus. The number of branches coming from the anterior division varied, ranging from one to six. The two-branch pattern was the most frequent (42.7%), followed by the three-branch pattern (34%) and the one-branch pattern (7.3%). The remaining 16% of cases showed patterns of four, five, or six branches. When two or more branches were present, a connection between them was observed in 64% of cases. Five different types of origin of the various branches were observed along the course of the recurrent nerve in relation to the cricothyroid joint: type a, vertical segment below the cricothyroid joint (7.5%); type b) vertical segment behind the cricothyroid joint (40.5%); type c) vertical segment just above the cricothyroid joint (16%); type ) from the genu, in common with the arytenoid branch, above the cricothyroid joint and just below the cricoarytenoid joint (34%); and type e) oblique segment (2%).

CONCLUSION

Despite the variability of the innervation of the posterior cricoarytenoid muscle and its strong connection with the interarytenoid nerve, this should not preclude successful reinnervation.

Histology of nerves and muscles in adductor spasmodic dysphonia

To elucidate the etiology and pathophysiology of spasmodic dysphonia, we examined the adductor branch of the recurrent laryngeal nerve and the lateral cricoarytenoid muscle from 9 consecutive patients with this disorder who were previously treated with botulinum toxin. Histologic examination revealed average muscle fiber diameters ranging from 21 to 57 microm. Botulinum toxin treatment-related muscle atrophy was observed up to 5 months after injection. Endomysial fibrosis was present in all samples. Histochemical analysis in 8 patients revealed type 2 fiber predominance in 7 patients and fiber type grouping in 2. Type-specific muscle fiber size changes were not present. Nerve samples were examined in plastic sections. In 8 patients the nerves contained homogeneous, large-diameter myelinated nerve fibers and sparse small fibers. One patient had a relatively increased proportion of small myelinated nerve fibers. Overall, the nerve fiber diameter was slightly larger in patients than in controls. These findings may implicate the central nervous system in the pathophysiology of adductor spasmodic dysphonia.

Prevalence of long-term upper aerodigestive symptoms after uncomplicated bilateral thyroidectomy

BACKGROUND

Subjective nonspecific upper aerodigestive symptoms (UADS) are not uncommon after thyroidectomy. Their type, duration, and prevalence, however, have not been investigated in a controlled design. The objective of this study was to investigate the prevalence of UADS after thyroidectomy.

METHODS

A consecutive cohort of 60 patients who had undergone uncomplicated total (n = 38) or near total (n = 22) thyroidectomy were investigated retrospectively at a mean of 4 years after surgery. An independent unblinded researcher interviewed each patient and asked for the presence or frequency of voice changes, cough, dysphagia, neck strangling, and annual incidence of common colds, before and after thyroidectomy. Sixty patients, matched for age, sex, and smoking habits, who had undergone laparoscopic cholecystectomy during the same years served as control subjects.

RESULTS

The prevalence of UADS was similar before thyroidectomy (13%) and cholecystectomy (15%). After operation, UADS had a higher prevalence among thyroidectomized patients: nonspecific voice changes (28% vs 3%), neck strangling (22% vs 0%), and impaired swallowing (15% vs 3%) (P < or = .02 in each). Neck strangling was associated with voice changes and dysphagia (P < or = .03 each).

CONCLUSIONS

Subjective UADS are common long after thyroidectomy. These symptoms may be related to injury to the extrinsic perithyroidal neural plexus innervating the pharyngeal and laryngeal structures.

Benign Anatomical Mistakes: The Correct Anatomical Term for the Recurrent Laryngeal Nerve

The term recurrent laryngeal nerve has been adopted by Nomina Anatomica (1989) and Terminologia Anatomica (1998) to describe this vagus branch from its origin, its turn dorsally around the subclavian artery and the aortic arch, and its cranial pathway until it reaches its terminal organs in the neck. However, there is still much confusion, and either the terms inferior and recurrent laryngeal nerve are used interchangeably or inferior laryngeal nerve is considered the terminal branch of the recurrent laryngeal nerve. We hereby feel that it is necessary to reassess the term and we propose the term inferior laryngeal nerve for the entire nerve under consideration, from its orgin from the vagus nerve to its destinations, including traheal, esophageal, and pharyngeal branches. If the term superior laryngeal nerve is a given, standard and accepted term in the anatomical terminology, then logically the term inferior laryngeal nerve should also be accepted, as opposed to it. Of course the upward travel of the inferior laryngeal nerve is “recurrent”. When nonrecurrence is encountered together with an arteria lusoria, a retroesophageal right subclavian artery or a right aortic arch, we consider that the term nonrecurrent inferior laryngeal nerve should be used to describe the deviation from the normal.

A Loop-Forming Duplicate Recurrent Laryngeal Nerve: Report of a Case and Clinical Relevance in Thyroid Surgery

This is a report of a unilateral loop-forming duplicate recurrent laryngeal nerve and its clinical relevance. A 72-year-old woman with a giant goiter underwent a total thyroidectomy. At operation we identified two recurrent laryngeal nerves on the right side and one on the left side. The nerve on the right was smaller and displaced laterally by the. goiter, whereas the other was adjacent to the trachea and behind the goiter, and it was accidentally divided. Both nerves were united before innervating the larynx. The divided nerve was microsurgically reanastomosed but a postoperative assessment revealed hoarseness. This case report of an anomalous loop-forming duplicate recurrent laryngeal nerve indicates that it may not be sufficient to identify a single recurrent laryngeal nerve on one side during thyroid surgery especially when the observed recurrent nerve is relatively smaller than usual.

The recurrent laryngeal nerve: related vascular anatomy

This study was based on 34 recurrent laryngeal nerve dissections after arterial casting with red-colored latex. The aim was to provide specific information about the perineural microvasculature. This study established the following points: 1. a great anatomic variability does exist; 2. the laryngeal nerve is usually in relation to the posterior branch of the inferior thyroid artery; and 3. this vascular branch is sometimes replaced with a vascular network. In all cases, this microvascularization must be preserved during thyroid surgery.