Morphological and functional asymmetry of the human recurrent laryngeal nerve

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

INTRODUCTION

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

METHODS

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

RESULTS

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

DISCUSSION

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

Why Sports Should Embrace Bilateral Asymmetry: A Narrative Review

(1) Background: Asymmetry is ubiquitous in nature and humans have well-established bilateral asymmetries in their structures and functions. However, there are (mostly unsubstantiated) claims that bilateral asymmetries may impair sports performance or increase injury risk. (2) Objective: To critically review the evidence of the occurrence and effects of asymmetry and sports performance. (3) Development: Asymmetry is prevalent across several sports regardless of age, gender, or competitive level, and can be verified even in apparently symmetric actions (e.g., running and rowing). Assessments of bilateral asymmetries are highly task-, metric-, individual-, and sport-specific; fluctuate significantly in time (in magnitude and, more importantly, in direction); and tend to be poorly correlated among themselves, as well as with general performance measures. Assessments of sports-specific performance is mostly lacking. Most studies assessing bilateral asymmetries do not actually assess the occurrence of injuries. While injuries tend to accentuate bilateral asymmetries, there is no evidence that pre-existing asymmetries increase injury risk. While training programs reduce certain bilateral asymmetries, there is no evidence that such reductions result in increased sport-specific performance or reduced injury risk. (4) Conclusions: Bilateral asymmetries are prevalent in sports, do not seem to impair performance, and there is no evidence that suggests that they increase injury risk.

Unilateral Vocal Fold Immobility After Prolonged Endotracheal Intubation

Importance

Endotracheal intubation and mechanical ventilation are life-saving treatments for acute respiratory failure but are complicated by significant rates of dyspnea and dysphonia after extubation. Unilateral vocal fold immobility (UVFI) after extubation can alter respiration and phonation, but its incidence, risk factors, and pathophysiology remain unclear.

Objectives

To determine the incidence of UVFI after prolonged (>12 hours) mechanical ventilation in a medical intensive care unit and investigate associated clinical risk factors for UVFI after prolonged mechanical ventilation.

Design, Setting, and Participants

This subgroup analysis of a prospective cohort study was conducted in a single-center medical intensive care unit from August 17, 2017, through May 31, 2018, among 100 consecutive adult patients who were intubated for more than 12 hours. Patients were identified within 36 hours of extubation and recruited for study enrollment. Those with an established tracheostomy prior to mechanical ventilation, known laryngeal or tracheal pathologic characteristics, or a history of head and neck radiotherapy were excluded.

Exposure

Invasive mechanical ventilation via an endotracheal tube.

Main Outcomes and Measures

The incidence of UVFI as determined by flexible nasolaryngoscopy.

Results

One hundred patients (62 men [62%]; median age, 58.5 years [range, 19.0-87.0 years]) underwent endoscopic evaluation after extubation. Seven patients had UVFI, of which 6 cases (86%) were left sided. Patients with hypotension while intubated (odds ratio [OR], 10.8; 95% CI, 1.6 to ∞), patients requiring vasopressors while intubated (OR, 16.7; 95% CI, 2.4 to ∞), and patients with a preadmission diagnosis of peripheral vascular disease (OR, 6.2; 95% CI, 1.2-31.9) or coronary artery disease (OR, 5.1; 95% CI, 1.0-25.5) were more likely to develop UVFI.

Conclusions and Relevance

Unilateral vocal fold immobility occurred in 7 of 100 patients in the medical intensive care unit who were intubated for more than 12 hours. Unilateral vocal fold immobility was associated with inpatient hypotension and preadmission vascular disease, suggesting that ischemia of the recurrent laryngeal nerve may play a role in disease pathogenesis.

Pre-low raising in Cantonese and Thai: Effects of speech rate and vowel quantity

Although pre-low raising (PLR) has been extensively studied as a type of contextual tonal variation, its underlying mechanism is barely understood. This paper explored the effects of phonetic vs phonological duration on PLR in Cantonese and Thai and examined how speech rate and vowel quantity interact with its realization in these languages, respectively. The results for Cantonese revealed that PLR always occurred before a large falling excursion (i.e., high-low); in other tonal contexts, it was observed more often in faster speech. In the Thai corpus, PLR also occurred before large falling excursions, and there was more PLR in short vowels. These results are discussed in terms of possible accounts of the underlying mechanism of PLR.

Vagus Nerve Stimulation-Induced Laryngeal Motor Evoked Potentials: A Possible Biomarker of Effective Nerve Activation

Vagus nerve stimulation (VNS) therapy is associated with laryngeal muscle activation and induces voice modifications, well-known side effects of the therapy resulting from co-activation of the recurrent laryngeal nerve. In this study, we describe the non-invasive transcutaneous recording of laryngeal motor evoked potentials (LMEPs), which could serve as a biomarker of effective nerve activation and individual titration in patients with drug-resistant epilepsy. We recruited drug-resistant epileptic patients treated for at least 6 months with a VNS. Trains of 600-1200 VNS pulses were delivered with increasing current outputs. We placed six skin electrodes on the ventral surface of the neck, in order to record LMEPs whenever the laryngeal muscular threshold was reached. We studied the internal consistency and the variability of LMEP recordings, and compared different methods for amplitude calculation. Recruitment curves were built based on the stimulus-response relationship. We also determined the electrical axis of the LMEPs dipole in order to define the optimal electrode placement for LMEPs recording in a clinical setting. LMEPs were successfully recorded in 11/11 patients. The LMEPs threshold ranged from 0.25 to 1 mA (median 0.50 mA), and onset latency was between 5.37 and 8.77 ms. The signal-to-noise ratio was outstanding in 10/11 patients. In these cases, excellent reliability (Intraclass correlation coefficient, ICC > 0.90 across three different amplitude measurements) was achieved with 10 sample averages. Moreover, our recordings showed very good internal consistency (Cronbach's alpha > 0.95 for 10 epochs). Area-under-the-curve and peak-to-peak measurement proved to be complementary methods for amplitude calculation. Finally, we determined that an optimal derivation requires only two recording electrodes, aligned on a horizontal axis around the laryngeal prominence. In conclusion, we describe here an optimal methodology for the recording of VNS-induced motor evoked responses from the larynx. Although further clinical validation is still necessary, LMEPs might be useful as a non-invasive marker of effective nerve activation, and as an aid for the clinician to perform a more rational titration of VNS parameters.

Intraoperative monitoring of the recurrent laryngeal nerve by vagal nerve stimulation in thyroid surgery

The aim of the present study was to evaluate the thyroarytenoid muscle response during bilateral thyroid surgery using vagal nerve stimulation. 195 patients (390 nerves at risk) underwent a total thyroidectomy. The recurrent laryngeal nerve's function was checked by analyzing the amplitude and the latency of the thyroarytenoid muscle's responses after a vagal nerve's stimulation (0.5 and 1 mA) using the NIM3 Medtronic system. All patients were submitted to preoperative and postoperative laryngoscopy. 20 patients get no thyroarytenoid muscle response to the vagal nerve stimulation, and 14 postoperative recurrent laryngeal nerve palsies were confirmed (3.8 %). Two palsies were present after 6 months (0.51 %). All the patients with muscle's response have normal mobility vocal fold. The test sensitivity was 100 % and the test specificity was 98 %. Physiologically, the mean latencies of the muscular potentials for the right RLN were, respectively, 3.89 and 3.83 ms (p > 0.05) for the stimulation at 0.5 and 1 mA. The mean latencies for the left RLN were, respectively, 6.25 and 6.22 ms for the stimulation at 0.5 and 1 mA (p > 0.05). The difference of the latencies between the right and the left nerve was 2.30 ms (1.75-3.25 ms) with a stimulation of 0.5 or 1 mA (p < 0.05). Thyroarytenoid muscle's response via a vagal nerve stimulation showed a functional asymmetry of the laryngeal adduction with a faster right response. Surgically, this method can predict accurately an immediate postoperative vocal folds function in patients undergoing a bilateral thyroid surgery.

Variaciones anatómicas del nervio laríngeo recurrente en una muestra de población colombiana

<p>Introducción. El nervio laríngeo recurrente (NLR), originado en el nervio vago, se encuentra relacionado con diferentes estructuras a nivel del tórax y del cuello, además de estar inmerso en diversos procesos nosológicos y quirúrgicos que pueden resultar en alteraciones funcionales; alteraciones que van desde la disfonía y la afonía hasta la muerte por obstrucción de la vía aérea. Estas complicaciones, específicamente las quirúrgicas, pueden cursar con secuelas permanentes del 0.3% al 3% de los casos y transitorias del 3% al 8%. Objetivo. Analizar el origen, el trayecto, los ramos y las relaciones anatómicas del nervio laríngeo recurrente en una muestra de 58 plastrones cervicocardiopulmonares y digestivos de población colombiana. Materiales y métodos. Estudio descriptivo analítico transversal con disección de 58 plastrones cervicocardiotorácicos seleccionados por muestreo a conveniencia. Resultados. Se determinó que el 100% de los plastrones disecados cuentan con un sitio de llegada usual; de igual modo, la descripción de la relación entre el NLR y la arteria tiroidea inferior (ATI) arrojó que la disposición más frecuente, tanto del NLR derecho como izquierdo, fue posterior a la ATI. Asimismo, se reportó el primer caso en Colombia y el décimo en el mundo del triángulo del nervio laríngeo recurrente (TNLR). Conclusiones. La disposición del NLR derecho e izquierdo es frecuentemente posterior a la ATI; de igual forma, es importante tener en cuenta la existencia del TNLR durante los abordajes quirúrgicos, especialmente en tiroidectomías.</p>

Similarities in the surface area/volume ratio in the fibers of the recurrent laryngeal nerve can explain the symmetry in the vocal fold mobility?

We demonstrate in this paper that although there are statistical differences for all morphometric data [axon length, axon diameter, myelinated fiber diameter and degree of the myelination (g-Ratio)] between the fibers of recurrent laryngeal nerve right and left, the surface area/volume ratio in the fibers of both nerves is exactly the same (1/1.7). Thereby, this paper presents the hypothesis that this similarity between the nerves can actually trigger a considerable synchrony in mobility of the intrinsic muscles of the larynx that control of the vocal folds.

Stuttering as a trait or state - an ALE meta-analysis of neuroimaging studies

Stuttering is a speech disorder characterised by repetitions, prolongations and blocks that disrupt the forward movement of speech. An earlier meta-analysis of brain imaging studies of stuttering (Brown et al., 2005) revealed a general trend towards rightward lateralization of brain activations and hyperactivity in the larynx motor cortex bilaterally. The present study sought not only to update that meta-analysis with recent work but to introduce an important distinction not present in the first study, namely the difference between 'trait' and 'state' stuttering. The analysis of trait stuttering compares people who stutter (PWS) with people who do not stutter when behaviour is controlled for, i.e., when speech is fluent in both groups. In contrast, the analysis of state stuttering examines PWS during episodes of stuttered speech compared with episodes of fluent speech. Seventeen studies were analysed using activation likelihood estimation. Trait stuttering was characterised by the well-known rightward shift in lateralization for language and speech areas. State stuttering revealed a more diverse pattern. Abnormal activation of larynx and lip motor cortex was common to the two analyses. State stuttering was associated with overactivation in the right hemisphere larynx and lip motor cortex. Trait stuttering was associated with overactivation of lip motor cortex in the right hemisphere but underactivation of larynx motor cortex in the left hemisphere. These results support a large literature highlighting laryngeal and lip involvement in the symptomatology of stuttering, and disambiguate two possible sources of activation in neuroimaging studies of persistent developmental stuttering.

Framework Surgery for Treatment of Unilateral Vocal Fold Paralysis

Laryngeal framework surgery is the current gold standard treatment for unilateral vocal fold paralysis. It provides a permanent solution to glottic insufficiency caused by injury to the recurrent laryngeal nerve. Various modifications to the original Isshiki type I laryngoplasty procedure have been described to improve voice and swallowing outcomes. The success of this procedure is highly dependent on the experience of the surgeon as it epitomizes the intersection of art and science in the field. The following article reviews the evidence, controversies, and complications related to laryngoplasty for unilateral vocal fold paralysis. It also provides a detailed analysis of how and when arytenoid-positioning procedures should be considered, and summarizes the literature on postoperative outcomes.

Vocal fold motion impairment in multiple system atrophy

OBJECTIVES/HYPOTHESIS

Multiple system atrophy (MSA) is a degenerative neurologic disorder that can affect vocal fold mobility. Our aim was to further elucidate the impact of vocal fold motion impairment (VFMI) in MSA.

STUDY DESIGN

Retrospective case series.

METHODS

We undertook a retrospective review of all MSA patients reporting voice or respiratory symptoms from 1975 to 2010 at Mayo Clinic Rochester who also received otolaryngologic examination.

RESULTS

Thirty-eight MSA patients demonstrated VFMI. Median duration of vocal or respiratory symptoms prior to diagnosis of MSA was 12.0 months (range, 1-60 months). Stridor was present in 25 (68%) of patients. There was bilateral VFMI in 32 (82.4%) of the patients and isolated VFMI of the left true vocal fold (TVF) in six (17.6%) of the patients. No patients had isolated right VFMI. There was isolated unilateral or bilateral paresis in 21 (55.3%) of the patients and unilateral or bilateral complete paralysis in 15 (39.5%) of the patients. One patient presented with left TVF paralysis and right TVF paresis, whereas one other patient had findings of right TVF paralysis and left TVF paresis comprising the remaining 5.2% of patients with VFMI. The median survival after diagnosis of VFMI was 51.6 months. Unilateral or bilateral TVF paralysis was statistically associated with a decreased overall survival (P = .0384). The presence of stridor was not associated with adverse prognosis.

CONCLUSIONS

The increasing severity of VFMI negatively impacts overall survival in patients with MSA. Therefore, otolaryngologic examination is warranted at the time of MSA diagnosis.

Left-right asymmetry in neck lymph nodes distribution in patients with bilateral laryngeal cancer

OBJECTIVE

We aimed to examine left-right asymmetry in involved and total neck lymph nodes distribution in patients with bilateral laryngeal cancer in the present study.

METHODS

Forty-six patients with bilateral laryngeal cancer was included the study. The oncologic database of our otorhinolaryngology department was used. The right and left lymph node with and without involvement by cancer cells counts were retrieved from pathological reports.

RESULTS

The numbers of both involved and total neck lymph nodes were significantly higher on right side than on left side for all neck levels in laryngeal malignancies.

CONCLUSIONS

The results of the present study suggest the existence of a left-right asymmetry in neck lymph node distribution and in the neck lymph node distribution involved by laryngeal cancer cells. The stronger cell-mediated immune activity in the left side of humans may be associated with the blocking of the metastatic invasion of cancer cells from laryngeal malignancies in the left body side.