Brainstem control of vocalization and its coordination with respiration.

Phonation critically depends on precise controls of laryngeal muscles in coordination with ongoing respiration. However, the neural mechanisms governing these processes remain unclear. We identified excitatory vocalization-specific laryngeal premotor neurons located in the retroambiguus nucleus (RAmVOC) in adult mice as being both necessary and sufficient for driving vocal cord closure and eliciting mouse ultrasonic vocalizations (USVs). The duration of RAmVOC activation can determine the lengths of both USV syllables and concurrent expiration periods, with the impact of RAmVOC activation depending on respiration phases. RAmVOC neurons receive inhibition from the preBötzinger complex, and inspiration needs override RAmVOC-mediated vocal cord closure. Ablating inhibitory synapses in RAmVOC neurons compromised this inspiration gating of laryngeal adduction, resulting in discoordination of vocalization with respiration. Our study reveals the circuits for vocal production and vocal-respiratory coordination.

Laryngeal reinnervation for paediatric vocal cord palsy: a systematic review.

OBJECTIVE: This systematic review aims to provide an overview of the current evidence-base for paediatric surgical reinnervation in unilateral and bilateral vocal fold palsies in clinical practice. We aim to assess patient demographics, surgical technique and pre- and post-operative outcome measures. METHODS: A systematic literature review was performed and reported according to international PRISMA recommendations. A comprehensive search of PubMed, Embase, and Cochrane CENTRAL databases for relevant publications for all available dates with appropriate MESH search criteria was performed. Articles were categorised by four authors independently. A pooled summative analysis was carried out to allow review of demographic and outcome data. RESULTS: Our systematic PRISMA approach resulted in 19 papers being selected for inclusion and analysis with 179 patients undergoing reinnervation (153 unilateral, 26 bilateral). The youngest patient was 1.9 years. Iatrogenic injury to recurrent laryngeal nerve most common aetiology (65.4% and 19.2% of unilateral and bilateral vocal fold palsies, respectively). Patent ductus arteriosus ligation was the single most common procedure resulting in unilateral vocal fold palsies (43.1% of cases). Statistically significant improvements in subjective and objective outcomes for both voice and swallowing were seen. Meta-analysis was able to be performed on the particularly evident improvements in GRBAS score and Maximum Phonation Time (MPT). GRBAS scores improved by 3.64 (p < 0.01, 95% CI 2.65 to 4.63). MPT showed a statistically significant improvement of 5.26 s (p < 0.05, 95% CI 4.28 to 6.24). No major complications were reported. CONCLUSION: The current published evidence on one-hundred and seventy-nine paediatric surgical reinnervation procedures demonstrates its role as a safe and effective treatment for both unilateral and bilateral vocal fold palsies. Anatomically it has been shown to improve vocal fold tone, bulk and position. Both post-operative voice and swallowing outcomes show improvement as well as associated quality of life measures.

Intraoperative trans-laryngeal ultrasound (LUSG) of the vocal cord is a novel method of confirming the recurrent laryngeal nerve (RLN) integrity during thyroid and neck surgery.

BACKGROUND: Eliciting a normal electromyography signal has been the usual method to confirm the functional integrity of the recurrent laryngeal nerve during intraoperative nerve monitoring. Given that oscillations of the vocal cord can be detected with trans-laryngeal ultrasound when the ipsilateral recurrent laryngeal nerve is stimulated with the endotracheal tube in situ, we aimed to compare the accuracy and cost of this novel method with the conventional electromyography method. METHODS: Consecutive patients who underwent elective thyroid, parathyroid or neck dissection procedures were included. The NIM-Neuro 3.0 system was used. Endotracheal tube-based surface electrodes were utilized for electromyography signal recording. Standard anesthetic technique was adopted. Recurrent laryngeal nerve integrity was verified by both detection methods (laryngeal ultrasound and electromyography) independently. Vocal cord function was validated by flexible direct laryngoscopy postoperatively. For each method, concurrence with flexible direct laryngoscopy was defined as "true-positive" or "true-negative," based on the presence or absence of vocal cord paresis. Accuracy was calculated as the sum of all true positives and negatives divided by the total of nerves-at-risk. The cost of each method was calculated. RESULTS: One hundred and four patients were eligible. Total number of nerves-at-risk was 155. Based on flexible direct laryngoscopy findings, the test sensitivity, specificity, positive predictive value, and negative predictive value of intraoperative laryngeal ultrasound were 75.0%, 99.3%, 85.7%, and 98.6%, respectively, while those of electromyography were 87.5%, 98.0%, 70.0%, and 99.3%, respectively. The prognostic accuracy in laryngeal ultrasound versus electromyography was comparable (98.1% vs 97.4%). The cost of the laryngeal ultrasound per operation was less than electromyography ($82 vs $454). CONCLUSION: Laryngeal ultrasound has a similar detection accuracy to electromyography during intraoperative nerve monitoring. Apart from being a cheaper alternative, laryngeal ultrasound may be useful when there is unexplained loss of electromyography signals during surgery and may play a role in the intraoperative nerve monitoring troubleshooting algorithm.

Unilateral vocal nerve resection alters neurogenesis in the avian song system in a region-specific manner.

New neurons born in the adult brain undergo a critical period soon after migration to their site of incorporation. During this time, the behavior of the animal may influence the survival or culling of these cells. In the songbird song system, earlier work suggested that adult-born neurons may be retained in the song motor pathway nucleus HVC with respect to motor progression toward a target song during juvenile song learning, seasonal song restructuring, and experimentally manipulated song variability. However, it is not known whether the quality of song per se, without progressive improvement, may also influence new neuron survival. To test this idea, we experimentally altered song acoustic structure by unilateral denervation of the syrinx, causing a poor quality song. We found no effect of aberrant song on numbers of new neurons in HVC, suggesting that song quality does not influence new neuron culling in this region. However, aberrant song resulted in the loss of left-side dominance in new neurons in the auditory region caudomedial nidopallium (NCM), and a bilateral decrease in new neurons in the basal ganglia nucleus Area X. Thus new neuron culling may be influenced by behavioral feedback in accordance with the function of new neurons within that region. We propose that studying the effects of singing behaviors on new neurons across multiple brain regions that differentially subserve singing may give rise to general rules underlying the regulation of new neuron survival across taxa and brain regions more broadly.

Perceptual Evaluation of Vocal Fold Vibratory Asymmetry.

OBJECTIVES: Laryngeal vibratory asymmetry occurring with paresis may result in a perceptually normal or abnormal voice. The present study aims to determine the relationships between the degree of vibratory asymmetry, acoustic measures, and perception of sound stimuli. STUDY DESIGN: Animal Model of Voice Production, Perceptual Analysis of Voice. METHODS: In an in vivo canine model of phonation, symmetric and asymmetric laryngeal vibration were obtained via graded unilateral recurrent laryngeal nerve (RLN) stimulation simulating near paralysis to full activation. Phonation was performed at various contralateral RLN and bilateral superior laryngeal nerve stimulation levels. Naïve listeners rated the perceptual quality of 182 unique phonatory samples using a visual sort-and-rate task. Cepstral peak prominence (CPP) was calculated for each phonatory condition. The relationships among vibratory symmetry, CPP, and perceptual ratings were evaluated. RESULTS: A significant relationship emerged between RLN stimulation and perceptual rating, such that sound samples from low RLN levels were preferred to those from high RLN levels. When symmetric vibration was achieved at mid-RLN stimulation, listeners preferred samples from symmetric vibration over those from asymmetric vibration. However, when symmetry was achieved at high RLN levels, a strained voice quality resulted that listeners dispreferred over asymmetric conditions at lower RLN levels. CPP did not have a linear relationship with perceptual ratings. CONCLUSIONS: Laryngeal vibratory asymmetry produces variable perceptual differences in phonatory sound quality. Though CPP has been correlated with dysphonia in previous research, its complex relationship with quality limits its usefulness as clinical marker of voice quality perception. LEVEL OF EVIDENCE: NA, basic science Laryngoscope, 131:2740-2746, 2021.

Nerve Injury During Ultrasound-Guided Thyroid Biopsy-A First Reported Complication of Permanent Vocal Fold Paralysis.

Needle biopsy is a well-established component in the evaluation of thyroid nodules. The biopsy is usually performed with an ultrasound guidance and consists of either fine-needle aspiration or core needle biopsy. Although these terms are often used interchangeably, their difference is important. To our knowledge, we discuss the first reported case of biopsy-proven laryngeal nerve injury and permanent vocal fold paralysis following ultrasound-guided core biopsy of the thyroid. We advocate this complication be discussed as part of the consent process.

A prospective study evaluating the feasibility and accuracy of very early postoperative translaryngeal ultrasonography in the assessment of vocal cord function after neck surgery.

BACKGROUND: Early recognition of postoperative vocal cord palsy enhances postoperative care. Translaryngeal ultrasonography can assess vocal cord function accurately and noninvasively, but it is unclear whether it is feasible or accurate when done immediately after extubation in the recovery room owing to possible interference from laryngeal swelling. This study assessed the feasibility and accuracy of translaryngeal ultrasonography in this setting. METHODS: Consecutive patients undergoing neck operations were subjected to translaryngeal ultrasonography and flexible direct laryngoscopy 1 day before and day 7 after thyroidectomy and parathyroidectomy. Translaryngeal ultrasonography was performed early in the recovery room immediately after extubation in the operating room. A standardized assessment protocol was used. Patient parameters were compared between those with assessable and unassessable vocal cords. RESULTS: Sixty-five patients (91 recurrent laryngeal nerves-at-risk) were analyzed after excluding 2 male patients who failed preoperative translaryngeal ultrasonography. Fifty-six patients underwent thyroidectomy and 9 parathyroidectomy. The median age (range) was 57 (46-69); 44 (68%) were women. Sixty-one patients (94%) had assessable bilateral vocal cords on translaryngeal ultrasonography in the recovery room. Translaryngeal ultrasonography in the recovery room findings corresponded completely with day-7 findings on direct laryngoscopy. Long operative time was associated with nonassessable vocal cords on translaryngeal ultrasonography in the recovery room (P = .026). CONCLUSION: Very early postoperative translaryngeal ultrasonography in the recovery room after neck surgery is highly feasible and accurate. Long operative time may hinder the use of translaryngeal ultrasonography in the recovery room.

Fibrin Gel Suspended Autologous Chondrocytes as Cell-based Material for long-term Injection Laryngoplasty.

OBJECTIVES/HYPOTHESIS: Injection laryngoplasty of materials for unilateral vocal-fold paralysis has shown various results regarding the long-term stability of the injected material. We evaluated a fibrin-gel based cell suspension with autologous chondrocytes in-vitro and in-vivo as long-term-stable vocal-fold augmentation material in an animal model. STUDY DESIGN: This study compises an in vitro cell-culture part as well as an in vivo animal study with New Zealand White Rabbits. METHODS: In in-vitro experiments, auricular chondrocytes harvested from 24 New Zealand White Rabbits cadavers were cultivated in pellet cultures to evaluate cartilage formation for 4 weeks using long-term-stable fibrin gel as carrier. Injectability and injection volume for the laryngoplasty was determined in-vitro using harvested cadaveric larynxes. In-vivo 24 Rabbits were biopsied for elastic cartilage of the ear and autologous P1 cells were injected lateral of one vocal cord into the paraglottic space suspended in a long-term-stable fibrin gel. Histologic evaluation was performed after 2, 4, 12, and 24 weeks. RESULTS: During 12-week pellet culture, we found extracellular matrix formation and weight-stable cartilage of mature appearance. In-vivo, mature cartilage was found in two larynxes (n = 6) at 4 weeks, in four (n = 6) at 12 weeks, and in five (n = 6) at 24 weeks mostly located in the paraglottic space and sometimes with spurs into the vocalis muscle. Surrounding tissue was often infiltrated with inflammatory cells. Material tended to dislocate through the cricothyroid space into the extraglottic surrounding tissue. CONCLUSIONS: A cell-based approach with chondrocytes for permanent vocal-fold augmentation has not previously been reported. We have achieved the formation of structurally mature cartilage in the paraglottic space, but this is accompanied by difficulties with dislocated material, deformation of the augmentation, and inflammation. LEVEL OF EVIDENCE: N/A Laryngoscope, 131:E1624-E1632, 2021.

Crumley's Classification of Laryngeal Synkinesis: A Comparison of Laryngoscopy and Electromyography.

OBJECTIVES/HYPOTHESIS: Applying the principles of misdirected nerve regeneration to the larynx, Roger Crumley in 1989 coined the term laryngeal synkinesis (LS) which he later (2000) classified into 4 types (type I - good voice, type II - involuntary twitches and poor voice, type III - adduction during inspiration, type IV - abduction during phonation). Neurophysiological data were not available for all LS patients at that time. The current study was undertaken to utilize and test the Crumley classification for a clinical interrater comparison and, secondly, compare predicted with actual laryngeal electromyography (LEMG) results. STUDY DESIGN: Descriptive study. METHODS: Laryngoscopic and LEMG data of patients with unilateral vocal fold paralysis (VFP) of 6 months duration or longer were combined for retrospective evaluation. Forty-five data sets were available for laryngoscopic classification by two local laryngologists and by Roger Crumley. Twenty-three data sets with complete thyroarytenoid (TA) and posterior cricoarytenoid (PCA) - EMG data were used to compare predicted with actual LEMG results. RESULTS: Local laryngologists were able to classify 24 of 45, Crumley 30 of 45 cases into one of the 4 synkinesis types. There was substantial agreement between examiners (Cohens Kappa 0.66 [P < .001]). Comparison of predicted and actual LEMG data showed only moderate agreement. EMG sykinesis rates were lower in TA than in PCA and highest in Crumley type I cases. CONCLUSION: The Crumley classification is helpful in describing and understanding synkinesis. It does not always correlate predictably with actual LEMG data. A complete LEMG mapping of all intrinsic muscles may improve understanding of chronic VFP. LEVEL OF EVIDENCE: 4. Laryngoscope, 131:E1605-E1610, 2021.

Medialization Thyroplasty and Arytenoid Adduction for Management of Neurological Vocal Fold Immobility.

Vocal fold immobility can be either unilateral or bilateral and partial or complete. The aim of this chapter is to discuss the management of unilateral paresis using medialization thyroplasty with or without arytenoid adduction as a means of treating neurogenic causes as opposed to mechanical fixation. Medialization thyroplasty is an open surgical procedure that is performed under local or general anesthesia. Essentially, it aims to close the glottic gap, approximating both vocal folds together and thereby allowing for restoration of the efficiency of the larynx. The glottic gap results from atrophy of the affected vocal fold and in so doing results in glottic insufficiency which causes voice breathiness, strain, fatigue, aspiration, and swallowing difficulties that make up the bulk of symptoms associated with this condition. Unlike injection laryngoplasty, medialization thyroplasty does not increase the "bulk" of the atrophic vocal fold but merely brings the fold closer to its unaffected partner. Besides the obvious lateralization, there is occasionally a third dimensional component to the affected fold. The slipping and prolapse forward of the arytenoid cartilage due to atrophy of the muscles supporting it and the natural declination of the facet joint it rests on cause a vertical drop of the level of the affected vocal fold that may not be remedied with the medialization procedure, hence requiring arytenoid adduction. Although attempts to medialize the vocal fold have been described in the past with limited access, the basic premise of creating a window in the thyroid cartilage remains central. The differences between materials used, their respective strengths and weaknesses, the pitfalls and pearls in achieving a good closure and improvement in voice, swallow, and safety of the airway are all discussed accordingly.

Injection Laryngoplasty for Management of Neurological Vocal Fold Immobility.

Injection laryngoplasty as used in this chapter is synonymous with the term "injection augmentation." Injection augmentation is a technique designed to enhance glottic closure in patients with glottic insufficiency, or failure of glottic closure, by injecting material into the lateral aspect of the vocal fold to move the vibrating surface to the midline. This type of injection augments the vocal fold and improves glottic closure. Injection augmentation originated over 100 years ago. However, the current indications, techniques, and materials have changed significantly. Paralysis, defined as loss of function due to neu-rological injury, remains a common cause of glottic insufficiency. In cases of paralysis, nerve function to adduct the vocal folds for voice production and coughing is interrupted, bilaterally or unilaterally, and the glottis becomes insufficient. While unilateral vocal fold paralysis remains the most common indication for vocal fold injection augmentation, due to the development of newer injectable materials and less invasive injectable techniques, surgeons routinely perform injection augmentation for glottic insufficiency due to other causes such as vocal fold paresis, vocal fold atrophy, presbylarynx, vocal fold scar, and soft tissue loss. Additionally, there is an increasing performance of vocal fold injection in the awake patient. This allows for immediate feedback and reduced anesthetic risk. Outcomes assessment for injection augmentation remains varied by lack of consensus and large-scale studies to identify the factors most instrumental in documenting optimal results. We review the history of injection laryngoplasty, the indications for injection, choice of injectate, outcomes, complications, and future directions of injection laryngoplasty for augmentation.

Methods of surgical treatment of bilateral vocal fold paralysis.

Bilateral vocal fold paralysis presents as their complete or partial immobilisation. The median or paramedian position of vocal folds contributes to the narrowing of the airway at the level of the glottis and manifests as inspiratory dyspnoea. For many years iatrogenic injury of recurrent laryngeal nerves during thyroidectomy has been viewed as the most common underlying reason. It is very often a lifethreatening condition requiring not only corticosteroid administration and intubation, which only constitute a short-term symptomatic therapy, but also surgical intervention, including tracheostomy. The most common surgical methods implemented in bilateral vocal fold paralysis include posterior cordectomy, arytenoidectomy, and, more and more commonly, re-innervation. Other techniques used in restoring airway patency include laterofixation, botulinum toxin injection, and laryngeal stimulation, which is still under research. Stem cell and gene therapy are also being researched. Notably, the main purpose of surgical treatment is the provision of airway patency with the preservation of the phonatory and protective functions of the larynx.

Bilateral Selective Laryngeal Reinnervation for Bilateral Vocal Fold Paralysis in Children.

Importance: Bilateral vocal fold paralysis (BVFP) in pediatric patients is a challenging entity with multiple causes. Traditional approaches to managing BVFP include tracheostomy, arytenoidectomy, suture lateralization, cordotomy, and posterior cricoid enlargement. These interventions are used to create a stable airway but risk compromising voice quality. Objectives: To assess the use of bilateral selective laryngeal reinnervation (SLR) surgery to manage BVFP and restore dynamic function to the larynx in pediatric patients. Design, Setting, and Participants: In this case series performed at 2 tertiary care academic institutions, 8 pediatric patients underwent bilateral SLR to treat BVFP (5 patients with iatrogenic BVFP and 3 with congenital BVFP) from November 2004 to August 2018 with follow-up for at least 1.5 years. Interventions: Bilateral selective laryngeal reinnervation surgery. Main Outcomes and Measures: Flexible laryngoscopy findings, subjective and objective measures of voice quality, subjective swallowing function, and decannulation in patients who were previously dependent on a tracheostomy tube. Results: Participants included 6 boys and 2 girls with a median age of 9.3 (range, 2.2 to 18.0) years at the time of surgery. All 8 patients were decannulated; 6 patients had preoperative tracheostomies and 2 had perioperative tracheostomies. Voice quality, as measured using the GRBAS (grade, roughness, breathiness, asthenia, strain) scale, improved in 6 of 8 patients after reinnervation, and swallowing was not impaired in any patients. In 2 patients, GRBAS scale scores remained the same before and after surgery. Inspiratory vocal fold abduction was observed on both sides in 5 patients and on 1 side in 2 patients, with no active abduction observed in 1 patient. The follow-up period was more than 5 years in 7 of 8 patients and at least 1.5 years in all patients. Conclusions and Relevance: Bilateral SLR appears to be a promising treatment option for children with BVFP; it is currently the only option, to our knowledge, with the potential to restore abductor and adductor vocal fold movement. In patients with complete paralysis, this procedure may provide a strategy for airway management and restoration of the dynamic function of the larynx. It could be considered as a first-line technique before endolaryngeal or airway framework procedures, which carry a risk of compromising voice quality.

Cortical-Basal Ganglia-Cerebellar Networks in Unilateral Vocal Fold Paralysis: A Pilot Study.

OBJECTIVES/HYPOTHESIS: To evaluate differences in cortical-basal ganglia-cerebellar functional connectivity between treated unilateral vocal fold paralysis (UVFP) and healthy control cohorts using resting-state functional magnetic resonance imaging (RS-fMRI). STUDY DESIGN: Cross-sectional. METHODS: Ten UVFP study patients treated by type I thyroplasty and 12 control subjects underwent RS-fMRI on a 3-Tesla scanner to evaluate differences in functional connectivity of whole-brain networks. Spontaneous RS-fMRI data were collected using a gradient echo planar pulse sequence, preprocessed, and analyzed to compare seed-to-voxel maps between the two cohorts. Seeds were placed in the caudate, putamen, and globus pallidus divisions of the basal ganglia in both hemispheres. Group contrasts were tested for statistical significance using two-tailed unpaired t tests corrected for multiple comparisons with a cluster false discovery rate threshold of P < .05. RESULTS: UVFP patients demonstrated increased connectivity between both caudate nuclei and the precuneus, a node of the default mode network, compared to healthy controls. Both caudate nuclei also showed decreased connectivity with the left cerebellar hemisphere. The putamen and globus pallidus divisions of the basal ganglia were not abnormally connected to other brain structures. CONCLUSIONS: UVFP patients treated by type I thyroplasty exhibited long-term alterations of cortical-basal ganglia-cerebellar networks thought to be important for self-referential voice quality awareness and learning processes that compensate for changes to the paralyzed hemilarynx. This pilot study on relatively small cohorts adds to growing evidence for persistent central nervous system changes in treated UVFP. Replication studies with larger numbers of subjects will be essential to validate and extend findings. LEVEL OF EVIDENCE: 3b Laryngoscope, 130:460-464, 2020.

Nonselective Reinnervation as a Primary or Salvage Treatment of Unilateral Vocal Fold Palsy.

OBJECTIVES/HYPOTHESIS: Demonstration of voice improvement and long-term stability following nonselective unilateral laryngeal reinnervation (ULR) in patients with unilateral vocal fold paralysis (UVFP) and severe denervation. A subgroup of patients on whom ULR was performed as a salvage technique following unsuccessful medialization was analyzed separately. STUDY DESIGN: Prospective cohort study. METHODS: The ansa cervicalis-recurrent laryngeal nerve anastomosis technique was performed in all patients. Pre- and postoperative voice analysis included voice questionnaires, voice assessment by senior laryngologists using the Hirano Voice Scale, and computer-assisted voice analysis at defined time points over the course of 36 months. Laryngeal electromyography (LEMG) and spirometry were performed before and 1 year after ULR. RESULTS: Significant linear improvement of mean voice quality over time was observed in the majority of parameters measured in 48 ULR patients and in eight ULR salvage patients. LEMG 1 year after ULR showed new recruitment. Mean voice quality remained stable during follow-up in all ULR patients and in the ULR salvage group. CONCLUSIONS: Nonselective ULR in UVFP is a reliable and stable therapeutic option for patients with high expectations concerning voice quality. The effect is stable in long-term results. It is also a viable option for patients in whom conventional voice surgery failed to improve voice quality. We therefore propose ULR as salvage option in UVFP. LEVEL OF EVIDENCE: 2b Laryngoscope, 130:1756-1763, 2020.

Inter-rater reliability of seven neurolaryngologists in laryngeal EMG signal interpretation.

PURPOSE: Laryngeal electromyography (LEMG) has been considered as gold standard in diagnostics of vocal fold movement impairment, but is still not commonly implemented in clinical routine. Since the signal interpretation of LEMG signals (LEMGs) is often a subjective and semi-quantitative matter, the goal of this study was to evaluate the inter-rater reliability of neurolaryngologists on LEMGs of volitional muscle activity. METHODS: For this study, 52 representative LEMGs of 371 LEMG datasets were selected from a multicenter registry for a blinded evaluation by 7 experienced members of the neurolaryngology working group of the European Laryngological Society (ELS). For the measurement of the observer agreement between two raters, Cohen's Kappa statistic was calculated. For the interpretation of agreements of diagnoses among the seven examiners, we used the Fleiss' Kappa statistic. RESULT: When focusing on the categories "no activity", "single fiber pattern", and "strongly decreased recruitment pattern", the inter-rater agreement varied from Cohen's Kappa values between 0.48 and 0.84, indicating moderate to near-perfect agreement between the rater pairs. Calculating with Fleiss' Kappa, a value of 0.61 showed good agreement among the seven raters. For the rating categories, the Fleiss' Kappa value ranged from 0.52 to 0.74, which also showed a good agreement. CONCLUSION: A good inter-rater agreement between the participating neurolaryngologists was achieved in the interpretation of LEMGs. More instructional courses should be offered to broadly implement LEMG as a reliable diagnostic tool in evaluating vocal fold movement disorders in clinical routine and to develop future algorithms for therapy and computer-assisted examination.

Vagal schwannomas of the head and neck: A comprehensive review and a novel approach to preserving vocal cord innervation and function.

BACKGROUND: Schwannomas, benign tumors arising from neurolemmocytes, are the most common type of peripheral nerve tumors. Extracranial schwannomas are most often found in the parapharyngeal space, commonly involving the vagus nerve to cervical sympathetic trunk. Vagal schwannomas present several unique clinical and therapeutic challenges. METHODS: A comprehensive literature review was conducted on 197 articles reporting 235 cases of cervical vagal schwannomas. Presenting symptoms, treatment approach, and postoperative outcomes were recorded and analyzed. RESULTS: Vagal schwannomas commonly present as asymptomatic neck masses. When they become symptomatic, surgical resection is the standard of care. Gross total resection is associated with higher postoperative morbidity compared to subtotal resection. Initial reports using intraoperative nerve monitoring have shown improved nerve preservation. Recurrence rates are low. CONCLUSION: The combination of intermittent nerve mapping with novel continuous vagal nerve monitoring techniques may reduce postoperative morbidity and could represent the future standard of care for vagal schwannoma treatment.

Sensory feedback independent pre-song vocalizations correlate with time to song initiation.

The song of the adult male zebra finch is a well-studied example of a learned motor sequence. Song bouts begin with a variable number of introductory notes (INs) before actual song production. Previous studies have shown that INs progress from a variable initial state to a stereotyped final state before each song. This progression is thought to represent motor preparation, but the underlying mechanisms remain poorly understood. Here, we assessed the role of sensory feedback in the progression of INs to song. We found that the mean number of INs before song and the progression of INs to song were not affected by removal of two sensory feedback pathways (auditory or proprioceptive). In both feedback-intact and feedback-deprived birds, the presence of calls (other non-song vocalizations), just before the first IN, was correlated with fewer INs before song and an initial state closer to song. Finally, the initial IN state correlated with the time to song initiation. Overall, these results show that INs do not require real-time sensory feedback for progression to song. Rather, our results suggest that changes in IN features and their transition to song are controlled by internal neural processes, possibly involved in getting the brain ready to initiate a learned movement sequence.