Improving Outcome of Superior Mediastinal Lymph Node Dissection During Esophagectomy: A Novel Approach Combining Continuous and Intermittent Recurrent Laryngeal Nerve Monitoring.

OBJECTIVE: This study aimed at demonstrating the effects and learning curve of utilizing combined intermittent and continuous recurrent laryngeal nerve (RLN) monitoring for lymphadenectomy during esophagectomy. BACKGROUND: RLN lymphadenectomy is oncologically important but is technically demanding. Vocal cord (VC) palsy as a result from RLN injury, carries significant morbidities. METHODS: This is a retrospective study of consecutive esophageal squamous cell carcinoma (ESCC) patients who underwent transthoracic esophagectomy from 2010 to 2020. Combined nerve monitoring (CNM) included: CNM which involved a periodic stimulating left vagal electrode and intermittent nerve monitoring which utilized a stimulating probe to identify the RLNs. The integrity of the RLNs was assessed both intermittently and continuously. This technique was introduced in 2014. Patients were divided into "before CNM" and "CNM" groups. The primary outcome was the difference in number of RLN lymph nodes harvested and VC palsy rate. Learning curves were demonstrated by cumulative sum (CUSUM) analysis. RESULTS: Two hundred and fifty-five patients were included with 157 patients in "CNM" group. The mean number of RLN lymph nodes harvested was significantly higher (4.31 vs 0.45, P < 0.0001) for the "CNM" group. VC palsy rates were significantly lower (17.8% vs 32.7%, P = 0.007). There was an initial increase in VC palsy rate, peaked at around 46 cases. The increase in lymph nodes harvested above the mean plateaued at around 96 cases. CONCLUSIONS: CNM helped improve bilateral RLN lymphadenectomy. Lymph node harvesting was increased with reduction of VC palsy after a learning curve.

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.

Functional recurrent laryngeal nerve regeneration using a silicon tube containing a collagen gel in a rat model.

In this study, we examined the effect of differing gap lengths on regeneration of transected recurrent laryngeal nerves using silicon tubes containing type I collagen gel and the ability of this regeneration to result in restoration of vocal fold movements in rats. We simulated nerve gaps in Sprague-Dawley rats by transecting the left recurrent laryngeal nerves and bridged the nerve stumps using silicon tubes containing type 1 collagen gel. Three experimental groups, in which the gap lengths between the stumps were 1, 3, or 5 mm, were compared with a control group in which the nerve was transected but was not bridged. After surgery, we observed vocal fold movements over time with a laryngoscope. At week 15, we assessed the extent of nerve regeneration in the tube, histologically and electrophysiologically. We also assessed the degree of atrophy of the thyroarytenoid muscle (T/U ratio). Restoration of vocal fold movements was observed in 9 rats in the 1-mm group, in 6 rats in the 3-mm group, and in 3 rats in the 5-mm group. However, in most rats, restoration was temporary, with only one rat demonstrating continued vocal fold movements at week 15. In electromyograph, evoked potentials were observed in rats in the 1-mm and 3-mm groups. Regenerated tissue in the tube was thickest in the 1-mm group, followed by the 3-mm and 5-mm groups. The regenerated tissue showed the presence of myelinated and unmyelinated nerve fibers. In assessment of thyroarytenoid muscle atrophy, the T/U ratio was highest in the 1-mm group, followed by the 3-mm and 5-mm groups. We successfully regenerated the nerves and produced a rat model of recurrent laryngeal nerve regeneration that demonstrated temporary recovery of vocal fold movements. This rat model could be useful for assessing novel treatments developing in the future.

Effect of intraoperative nerve monitoring on postoperative vocal cord palsy rates after thyroidectomy: European multicentre registry-based study.

BACKGROUND: Intraoperative nerve monitoring (IONM) of the recurrent laryngeal nerve (RLN) predicts the risk of vocal cord palsy (VCP). IONM can be used to adapt the surgical strategy in order to prevent bilateral VCP and associated morbidity. Controversial results have been reported in the literature for the effect of IONM on rates of VCP, and large multicentre studies are required for elucidation. METHODS: Patients undergoing first-time thyroidectomy for benign thyroid disease between May 2015 and January 2019, documented prospectively in the European registry EUROCRINE®, were included in a cohort study. The influence of IONM and other factors on the development of postoperative VCP was analysed using multivariable regression analysis. RESULTS: Of 4598 operations from 82 hospitals, 3542 (77·0 per cent) were performed in female patients. IONM was used in 4182 (91·0 per cent) of 4598 operations, independent of hospital volume. Postoperative VCP was diagnosed in 50 (1·1 per cent) of the 4598 patients. The use of IONM was associated with a lower risk of postoperative VCP in multivariable analysis (odds ratio (OR) 0·34, 95 per cent c.i. 0·16 to 0·73). Damage to the RLN noted during surgery (OR 24·77, 12·91 to 48·07) and thyroiditis (OR 2·03, 1·10 to 3·76) were associated with an increased risk of VCP. Higher hospital volume correlated with a lower rate of VCP (OR 0·05, 0·01 to 0·13). CONCLUSION: Use of IONM was associated with a low rate of postoperative VCP.

ANTECEDENTES: La monitorización nerviosa intraoperatoria (intraoperative nerve monitoring, IONM) del nervio laríngeo recurrente (recurrent laryngeal nerve, RLN) predice el riesgo de parálisis de la cuerda vocal (vocal cord palsy, VCP). La IONM se puede utilizar para adaptar la estrategia quirúrgica con el objetivo de prevenir la VCP bilateral y la morbilidad asociada. La literatura describe resultados controvertidos de la influencia de la IONM sobre las tasas de VCP, por lo que se requieren grandes estudios multicéntricos para aclararlo. MÉTODOS: De mayo de 2015 a enero de 2019, las tiroidectomías efectuadas como primera intervención quirúrgica por patología tiroidea benigna - documentadas prospectivamente en el registro europeo EUROCRINE© - se incluyeron en un estudio de cohortes. La influencia de la IONM y otros factores sobre el desarrollo de VCP postoperatoria fueron analizados utilizando un análisis de regresión multivariable. RESULTADOS: De 4.598 operaciones efectuadas en 82 hospitales e incluidas en el estudio, 3.542 (77,0%) fueron realizadas en mujeres. La IONM se utilizó en 4.182 de 4.598 (91,0%) operaciones independientemente del volumen del hospital. La VCP postoperatoria se diagnosticó en 50 de 4.598 (1,1%) pacientes. La utilización de IONM se asoció con un menor riesgo de VCP postoperatoria en el análisis multivariable (razón de oportunidades, odds ratio, OR 0,34 (i.c. del 95% 0,16-0,73)). La detección de lesión del RLN durante la cirugía (OR 24,77 (12,91 a 48,07)) y la tiroiditis (OR 2,03 (1,10 a 3,76)) se asociaron con un riesgo aumentado de VCP. Un elevado volumen de casos se correlacionó con menor frecuencia de VCP (OR 0,05 (0,01 a 0,13)). CONCLUSIÓN: La utilización de la IONM se asoció con una baja tasa de VCP postoperatoria.

Correlation Between Electrophysiological Changes and Outcomes of Vocal Cord Function in 1764 Recurrent Laryngeal Nerves with Visual Integrity During Thyroidectomy.

Background: The correlation between the injured recurrent laryngeal nerve (RLN) with incomplete loss of signal (LOS) and the outcomes of vocal cord function is still not well understood. This large cohort validation study was aimed to evaluate the effectiveness of the warning criterion, the reduction of the R2p/R2d ratio, in neuromonitoring during thyroidectomy. Methods: A total of 1108 consecutive patients (1764 nerves) with normal vocal cord function undergoing monitored thyroidectomy were included. Standardized intraoperative neuromonitoring procedures were strictly followed, after complete dissection of RLN, the exposed RLN was routinely stimulated at the lowest proximal end (R2p signal) and the most distal end near the laryngeal entry point (R2d signal). If the reduction of the R2p/R2d ratio (([R2d - R2p]/R2d) × 100%) reached >20%, the whole exposed RLN would be checked to pinpoint the injured area of the nerve. Results: Visual anatomical integrity of the RLN was ensured in all 1764 nerves. Eighteen nerves had complete LOS, and the other 97 nerves had incomplete LOS where the reduction of the R2p/R2d ratio ranged from 21% to 84%. Postoperative temporary vocal cord paralysis (VCP) was noted in 11 (61.1%) RLNs with complete LOS and 16 (16.5%) RLNs with incomplete LOS, where the reduction of the R2p/R2d ratio ranged from 63% to 84%. The positive predictive value of a R2p/R2d ratio >63% for postoperative VCP was 79.4%. Conclusions: Testing and comparing the R2p and R2d signals were useful to detect RLN neurophysiologic injury, elucidating the mechanism of nerve injury and predicting vocal cord function. Determining R2p-R2d was found to be essential and can be applied in routine neuromonitoring thyroidectomy.

Selective stimulation of human intrinsic laryngeal muscles: Analysis in a mathematical three-dimensional space.

OBJECTIVES/HYPOTHESIS: Standard stimulating methods using square waves do not appropriately restore physiological control of individual intrinsic laryngeal muscles (ILMs). To further explore our earlier study of evoked orderly recruitment by quasitrapezoidal (QT) currents, we integrated the contribution of the cricothyroideus (CT) with attention to mutual activation in an additional patient, based on recent studies of appropriate responses via strict recurrent laryngeal nerve (RLN) stimulation. STUDY DESIGN: Basic science study. METHODS: The patient received functional electrical stimulation (FES) with QT pulses at 5 Hz, 60 to 2,000 µAmp, 100 to 500 µs pulse width, 0 to 500 µs decay. Ipsilateral electromyography (EMG) responses were calculated using the average maximum amplitude, area under the curve, and the root mean square of the rectified amplitude waveforms. The thyroarytenoideus (TA), posterior cricoarytenoideus (PCA), lateral cricothyroideus (LCA), and the CT were each interrogated via two monopolar electrodes, values were recorded in MATLAB, exported to Excel, and analyzed. Individual and mutual recruitment configurations and activation delays with stimulation were explored using multiple regression and exploration factor analyses. RESULTS: A total of 868 EMG data points based on 18 trials and up to 11 subtrials were captured from each of the four ILMs. Various combinations of pulse amplitude, pulse width, and exponential decay were found to produce significant (P ≤ .001) individual ILM responses. CT mirrored the LCA, whereas the TA and PCA exhibited separate interactions along shared trajectories in a three-dimensional space. CONCLUSIONS: FES calibrated to individual and coupled ILMs offers promise for restoring normal and pathological contraction patterns via strict RLN stimulation. LEVEL OF EVIDENCE: 5 Laryngoscope, 130:967-973, 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.

Vocal Fold Reconstruction Using an Autologous Pedicled Fat Flap in a Rabbit Model.

OBJECTIVES/HYPOTHESIS: We evaluated the efficacy of a vocal fold reconstruction technique using a vascularized autologous pedicled fat (PEFA) flap in a rabbit model of vocal fold paralysis. STUDY DESIGN: Animal model. METHODS: The study included 30 male New Zealand White rabbits; 20 received vocal fold reconstructions (PEFA group) and 10 served as normal controls (control group). The right recurrent laryngeal nerve was resected, and simultaneous PEFA flap reconstruction was performed. The PEFA flap, including a pre-epiglottic fat and thyroid perichondrium, was elevated and implanted through a window at the inferior border of the thyroid cartilage. Histological and high-speed video analyses of vocal fold vibration were performed 1 month after PEFA reconstruction. The maximum amplitude of vocal fold vibration and the dynamic glottal gap were used to assess vocal fold vibration. RESULTS: The histological findings showed that the lamina propria ratio (lamina propria pixels/total vocal fold pixels) and the total number of vocal fold pixels were similar between the PEFA and control groups. Vocal fold vibration analyses indicated that the maximum amplitude differences in the vibration were slightly lower in the PEFA group. However, the dynamic glottal gap of the vocal fold was not significantly different between the PEFA group and the control group. CONCLUSIONS: The PEFA flap vocal fold reconstruction technique maintained the vocal fold area without a significant reduction in vocal fold vibration in a rabbit model. LEVEL OF EVIDENCE: NA Laryngoscope, 130:1770-1774, 2020.

Postoperative Hypoparathyroidism in Thyroid Surgery: Anatomic-Surgical Mapping of the Parathyroids and Implications for Thyroid Surgery.

Hypoparathyroidism remains one of the most common complications in thyroid surgery. This study aims for an improved understanding of the complexity of the blood supply and the localisation of the parathyroids compared to the two most important intraoperative landmarks: the inferior laryngeal nerve (ILN) and Zuckerkandl's tubercle (ZT). We examined 103 laryngeal compounds to classify the blood supply and the localisation of the parathyroids. For intraoperative localisation we defined a Cartesian coordinate system with the ZT plane as x-axis and the course of the inferior laryngeal nerve as y-axis. The inferior thyroid artery (ITA) mainly supplies the parathyroids, whereas the superior thyroid artery provides a backup supply. It must be pointed out that 8.2% of parathyroids receive their blood directly from the thyroid gland. 73.5% of all parathyroids lie within 1 cm of the ILN and 1 cm cranial and 2.5 cm caudal to the ZT plane. Our described perimeters mark the most crucial areas during surgery and provide the surgeon with an anatomic mapping showing areas of special carefulness needed. One should keep bearing in mind all possible blood supply types of the parathyroids and therefore all branches should be handled with care.

Assessing pathological changes within the nucleus ambiguus of horses with recurrent laryngeal neuropathy: An extreme, length-dependent axonopathy.

INTRODUCTION: Equine recurrent laryngeal neuropathy (RLN) is a naturally occurring model of length-dependent axonopathy characterized by asymmetrical degeneration of recurrent laryngeal nerve axons (RLn). Distal RLn degeneration is marked, but it is unclear whether degeneration extends to include cell bodies (consistent with a neuronopathy). METHODS: With examiners blinded to RLN severity, brainstem location, and side, we examined correlations between RLN severity (assessed using left distal RLn myelinated axon count) and histopathological features (including chromatolysis and glial responses) in the nucleus ambiguus cell bodies, and myelinated axon count of the right distal RLn of 16 horses. RESULTS: RLN severity was not associated with RLn cell body number (P > .05), or degeneration. A positive correlation between the left and right distal RLn myelinated axon counts was identified (R2 = 0.57, P < .05). DISCUSSION: We confirm that RLN, a length-dependent distal axonopathy, occurs in the absence of detectable neuronopathy.

Recurrent Laryngeal Nerve Morbidity: Lessons from Endoscopic via Bilateral Areola and Open Thyroidectomy Technique.

BACKGROUND AND AIM: Elucidating the mechanism of recurrent laryngeal nerve (RLN) injuries through intraoperative electromyographic (EMG) and laryngeal examination approaches may deepen our knowledge regarding its prevention strategies. To date, no studies have been reported on the mechanism of RLN injury caused by endoscopic thyroidectomy via bilateral areola approach (ETBAA). METHODS: Both intraoperative EMG profiles and postoperative laryngeal examination were used to investigate the mechanisms of RLN injury and compare the safety aspects between ETBAA and open thyroidectomy approach (OTA). RESULTS: This study examined 1420 nerves at risk. The mean follow-up period was 17 ± 4 (range 6-48) months. The incidence of vocal cord paralysis was 4.1% (59/1420). The number of cases with decreased EMG signals and vocal cord palsy was higher in ETBAA group than in OTA group (P < 0.05). The left RLNs in ETBAA group were at higher risk compared to the right nerves. CONCLUSIONS: The results of the current study indicate that ETBAA exhibits higher risk of RLN injury. The topic includes a video.

Animal Study to Evaluate the Effect of Carbon Dioxide Insufflation on Recurrent Laryngeal Nerve Function in Transoral Endoscopic Thyroidectomy.

Data with regard to potential recurrent laryngeal nerve (RLN) compromise caused by intra-neck CO2 insufflation during transoral endoscopic thyroidectomy vestibular approach (TOETVA) are missing. RLN electromyographic (EMG) profiles, metabolic and hemodynamic parameters (oxygen saturation, heart rate, blood pressure, experimental time, CO2 partial pressure, pH, O2 partial pressure), central venous pressure (CVP), airpocket temperature and pressure were recorded in a TOETVA animal model. Twelve pigs were randomly divided into different groups according to increasing CO2 insufflation pressures. Nerves segments were then collected for histopathology. Significant variation of metabolic and hemodynamic parameters were registered when CO2 insufflation pressures increased x3 and x5 the baseline parameters. Combined EMG amplitude drop and latency increase also were documented. There was no significant change in the intraluminal temperature. RLNs structure were preserved with normal axons, no fibrosis, and no vacuolization and without loss of myelinated fibers during the experiment. RLN EMG profiles (but not histology) were altered when CO2 insufflation pressures increased.

Continuous Vagal Neuromonitoring Using the Laryngeal Adductor Reflex: Can Preincision Dyssynchrony Predict Intraoperative Nerve Behavior?

OBJECTIVE: The laryngeal adductor reflex (LAR) is an airway-protective response triggered by sensory laryngeal receptors and resulting in bilateral vocal fold adduction. The normal morphology of the early R1 response resembles that of the compound muscle action potential (CMAP). However, in a small subset of patients, the morphology is dyssynchronous with multiple peaks. This study investigates whether preoperative LAR dyssynchrony predicts intraoperative nerve behavior during thyroid surgeries. STUDY DESIGN: Retrospective case-control study. SETTING: US academic health center. SUBJECTS AND METHODS: Opening and closing LAR waveforms from 200 patients with normal preoperative laryngeal examinations monitored continuously during thyroid surgeries using the LAR were analyzed. Area under the curve (AUC) and number of "events" during surgery (defined as any transient decline in AUC >50% baseline) were determined for patients who demonstrated opening dyssynchronous LAR traces compared to demographically matched controls. RESULTS: Six patients had opening dyssynchronous LAR traces. These patients had significantly greater declines in R1 AUC than demographically matched patients with opening synchronized R1 traces (P = .007). Upon thyroid removal, 1 patient converted from a dyssynchronous to synchronous trace. CONCLUSIONS: Preincision dyssynchronous LAR waveforms may indicate subclinical, potentially reversible, neuropathy of the recurrent laryngeal nerve (RLN) and predict intraoperative RLN behavior. Preincision knowledge of R1 dyssynchrony can facilitate surgical planning as such patients may glean particular benefit from continuous intraoperative nerve monitoring, frequent tissue relaxation, and saline irrigation as means to minimize nerve stress intraoperatively.

Asymmetric recurrent laryngeal nerve conduction velocities and dorsal cricoarytenoid muscle electromyographic characteristics in clinically normal horses.

The dorsal cricoarytenoid (DCA) muscles, are a fundamental component of the athletic horse's respiratory system: as the sole abductors of the airways, they maintain the size of the rima glottis which is essential for enabling maximal air intake during intense exercise. Dysfunction of the DCA muscle leads to arytenoid collapse during exercise, resulting in poor performance. An electrodiagnostic study including electromyography of the dorsal cricoarytenoid muscles and conduction velocity testing of the innervating recurrent laryngeal nerves (RLn) was conducted in horses with normal laryngeal function. We detected reduced nerve conduction velocity of the left RLn, compared to the right, and pathologic spontaneous activity (PSA) of myoelectrical activity within the left DCA muscle in half of this horse population and the horses with the slowest nerve conduction velocities. The findings in this group of horses are consistent with left sided demyelination and axonal loss, consistent with Recurrent Laryngeal Neuropathy (RLN), a highly prevalent degenerative disorder of the RLn in horses that predominantly affects the left side. The detection of electromyographic changes compatible with RLN in clinically unaffected horses is consistent with previous studies that identified "subclinical" subjects, presenting normal laryngeal function despite neuropathologic changes within nerve and muscle confirmed histologically.

Successful Thoracic Endovascular Aortic Repair in Ortner's Syndrome.

We present the case of an 89-year-old man with 3-month history of hoarseness and no other significant clinical manifestations. Flexible laryngoscopy revealed a paralyzed left vocal cord, and contrast-enhanced computed tomography showed a thoracic dissecting aortic aneurysm of the distal aortic arch and proximal descending aorta. The aortic aneurysm was repaired through implantation of an endovascular stent graft, and the patient was discharged uneventfully after a week. The false lumen was completely thrombosed, and the patient had a partial resolution of hoarseness at the 1-year follow-up.

Hoarseness after radical surgery with systematic lymph node dissection for primary lung cancer.

OBJECTIVES: Radical surgery with systematic upper mediastinal node dissection for primary lung cancer can cause recurrent laryngeal nerve (RLN) paralysis, but this is poorly reported. METHODS: We retrospectively reviewed the clinical data for consecutive patients who underwent radical surgery for primary lung cancer with an observation period of at least 12 months. During follow-up, hoarseness and vocal fold movement were assessed clinically and laryngoscopically, respectively. RESULTS: Of the 365 patients included in this study, 22 (6.0%) experienced hoarseness as a complication. All 22 patients who experienced hoarseness had undergone upper mediastinal node dissection. Although 1 of the 22 patients refused to undergo laryngoscopy, we assessed the vocal fold movement in the remaining patients (95.5%). Among these, 5 patients (23.8%) had right RLN paralysis, and 15 (71.4%) had left RLN paralysis and showed no sign of RLN paralysis. Over 1-24 months, vocal cord movement improved in 61.1% (11/18); and over 1-28 months, hoarseness improved in 72.7% (16/22). All patients with right RLN paralysis improved without further treatment. CONCLUSIONS: We conclude that extensive follow-up is necessary to discern whether hoarseness is a temporary or permanent complication of radical surgery in patients with primary lung cancer who have undergone systematic lymph node dissection.

Automated Quantification of Vocal Fold Motion in a Recurrent Laryngeal Nerve Injury Mouse Model.

OBJECTIVES/HYPOTHESIS: The goal of this study was to objectively examine vocal fold (VF) motion dynamics after iatrogenic recurrent laryngeal nerve (RLN) injury in a mouse surgical model. Furthermore, we sought to identify a method of inducing injury with a consistent recovery pattern from which we can begin to evaluate spontaneous recovery and test therapeutic interventions. STUDY DESIGN: Animal model. METHODS: The right RLN in C57BL/6J mice was crushed for 30 seconds using an aneurysm clip with 1.3-N closing force. Transoral laryngoscopy enabled visualization of VF movement prior to surgery, immediately post-crush, and at two endpoints: 3 days (n = 5) and 2 weeks (n = 5). VF motion was quantified with our custom motion-analysis software. At each endpoint, RLN samples were collected for transmission electron microscopy for correlation with VF motion dynamics. RESULTS: Our VF tracking software permitted automated quantification of several measures of VF dynamics, such as range and frequency of motion. By 2 weeks post-injury, the frequency of VF movement on the right (injured) side equaled the left, yet range of motion only partially recovered. These objective outcome measures enabled detection of VF dysfunction that persisted at 2 weeks post-crush. Transmission electron microscopy images revealed RLN degeneration 3 days post-crush and partial regeneration at 2 weeks, consistent with functional results obtained with automated VF tracking. CONCLUSIONS: Our motion-analysis software provides novel objective, quantitative, and repeatable metrics to detect and describe subtle VF dysfunction in mice that corresponds with underlying RLN degeneration and recovery. Adaptation of our tracking software for use with human patients is underway. LEVEL OF EVIDENCE: NA Laryngoscope, 129:E247-E254, 2019.