Cricothyroid Muscle Research Articles

Coactivation of the Laryngeal Muscles in Pigs Without External Neural Control Indicates Existence of an Intrinsic Neuronal Network

Electrophysiological studies of the larynx expose the mechanisms by which voice production is controlled. Previous studies have revealed certain phenomena during laryngeal oscillations that suggest a complex control mechanism.Starting from the principle of agonist-antagonist muscular pairing, the aim of this study was to gain a deeper insight into the function of the cricothyroid and thyroarytenoid muscles, both central to voice production.Electromyographic recordings were used to determine the response of the two muscles to different stimulation situations in an ex-vivo animal model of the denervated larynx of pigs (n=26).Using a set of different experiments, it was shown that when one muscle (cricothyroid or thyroarytenoid muscle) was electrically stimulated, a response was observed in the other muscle, which in the otherwise denervated larynx was caused only by the applied stimulation and exhibited the characteristics of compound action potentials. This response was reproducible in all larynxes examined and was present bidirectionally. No response was registered in the absence of stimulation.Results show the existence of coactivation of the cricothyroid and thyroarytenoid muscles in the absence of external innervation hinting at the presence of a localized neuronal network of the larynx that has not been described previously. Further morphological investigation is needed to determine the presence of this internal laryngeal neuronal network.

Prognostic significance of T3b in papillary thyroid carcinoma: Appropriateness of classifying T3bN0M0 in patients aged 55years or older into stage II.

Papillary thyroid carcinoma (PTC) often extends to adjacent organs. According to the 8th Tumor-Node-Metastasis Classification, extension to the strap muscles was graded as T3b. We investigated the prognostic impact of T3b and the appropriateness of T3b in patients aged ≥55years who were classified as stage II. We enrolled 7811 patients with M0 PTC who underwent initial surgery at the Kuma Hospital (Kobe, Japan) between January 2007 and December 2016. Tumor extension was divided into T3b, T4a1 (extension to the tracheal adventitia, tracheal cartilage, esophageal muscle layer, recurrent laryngeal nerve, cricothyroid, and inferior constrictor muscles), and sT4a2 (extension to the subcutaneous soft tissues, tracheal mucosa, esophageal mucosa, internal jugular vein, brachiocephalic vein, larynx, pharynx, and sternocleidomastoid muscle). In patients ≥55years, the local recurrence-free survival (LR-FS), distant recurrence-free survival (DR-FS), and cause-specific survival (CSS) rates of T3bN0M0 were significantly poorer than those of T1/T2N0M0 but did not significantly differ from those of T3aN0M0. The LR-FS, DR-FS, and CSS rates of T3b stage II patients did not differ from those of T4a1 stage III patients but were significantly better than those of T4a2 stage III patients. T3b was an independent predictor of local recurrence and distant recurrence but not of death due to carcinoma in the multivariate analysis. In patients aged <55years with M0 PTC, T3b had no prognostic value in both analyses. T3bM0 patients are appropriate to be classified as stage II in patients ≥55years but be kept in stage I in patients <55years.

A computational study of the influence of thyroarytenoid and cricothyroid muscle interaction on vocal fold dynamics in an MRI-based human laryngeal model.

A human laryngeal model, incorporating all the cartilages and the intrinsic muscles, was reconstructed based on MRI data. The vocal fold was represented as a multilayer structure with detailed inner components. The activation levels of the thyroarytenoid (TA) and cricothyroid (CT) muscles were systematically varied from zero to full activation allowing for the analysis of their interaction and influence on vocal fold dynamics and glottal flow. The finite element method was employed to calculate the vocal fold dynamics, while theone-dimensional Bernoulli equation was utilized to calculate the glottal flow. The analysis was focused on the muscle influence on the fundamental frequency (fo). We found that while CT and TA activationincreased the fo in most of the conditions, TA activationresulted in a frequency drop when it was moderately activated. We show that this frequency drop was associated with the sudden increase of the vertical motion when the vibration transited from involving the whole tissue to mainly in the cover layer. The transition of the vibration pattern was caused by the increased body-cover stiffness ratio thatresulted from TA activation.

Biomechanics of sound production in high-pitched classical singing

Voice production of humans and most mammals is governed by the MyoElastic-AeroDynamic (MEAD) principle, where an air stream is modulated by self-sustained vocal fold oscillation to generate audible air pressure fluctuations. An alternative mechanism is found in ultrasonic vocalizations of rodents, which are established by an aeroacoustic (AA) phenomenon without vibration of laryngeal tissue. Previously, some authors argued that high-pitched human vocalization is also produced by the AA principle. Here, we investigate the so-called “whistle register” voice production in nine professional female operatic sopranos singing a scale from C6 (≈ 1047 Hz) to G6 (≈ 1568 Hz). Super-high-speed videolaryngoscopy revealed vocal fold collision in all participants, with closed quotients from 30 to 73%. Computational modeling showed that the biomechanical requirements to produce such high-pitched voice would be an increased contraction of the cricothyroid muscle, vocal fold strain of about 50%, and high subglottal pressure. Our data suggest that high-pitched operatic soprano singing uses the MEAD mechanism. Consequently, the commonly used term “whistle register” does not reflect the physical principle of a whistle with regard to voice generation in high pitched classical singing.

Current opinion on laryngeal electromyography

PurposeThis study evaluates expert opinion on laryngeal electromyography (LEMG). MethodsA cross-sectional design was used to conduct an online survey of LEMG experts in 2021. They were questioned about the number LEMG performed annually, type of electrodes used, sector worked in, pain during the test, placement of the needle electrodes, interpretation of electrical muscle parameters, diagnosis of neuromuscular injury, prognostic sensitivity in vocal fold paralysis (VFP), laryngeal dystonia, tremor and synkinesis and quantifying LEMG. ResultsThirty-seven professionals answered (23 Spanish and 14 from other countries), with a response rate of 21.56%. All physicians used LEMG. 91.9% had one- or two-years’ experience and 56.8% performed 10–40 LEMG per year. 70.3% were otolaryngologists and 27%, neurologists. In 89.1% of cases, a team of electrodiagnostic physician and otolaryngologist performed LEMG. 91.3% of Spanish respondents worked in Public Health, 7.14% of other nationalities; 37.8% in a university department. Bipolar concentric needles electrodes were used by 45.9% and monopolar concentric by 40.5%. 57% professionals considered good patients’ tolerance to the test. LEMG sensitivity was regarded as strong, median and interquartile range were 80.0 [60.0;90.0] to diagnose peripheral nerve injuries, less for other levels of lesions, and strong to evaluate prognosis, 70.0 [50.0;80.0]. Respondents believe locate the thyroarytenoid and the cricothyroid muscles with the needle, 80.0 [70.0;90.0], as opposed to 20.0 [0.00;60.0] the posterior cricoarytenoid. The interpretation of the electrical parts of the LEMG was strong, 80.0 [60.0;90.0]. LEMG identify movements disorders, 60.0 [20.0;80.0], and synkinesis, 70.0 [30.0;80.0]. The professionals prefer quantitative LEMG, 90.0 [60.0;90.0]. ConclusionsThe experts surveyed consider LEMG that is well tolerated by patients. The insertional and spontaneous activity, recruitment and waveform morphology can be assessed easily. LEMG is mainly useful in the study of peripheral nerve injuries, and its value in VFP prognosis is considered strong.

Analysis of vocal fold movement characteristics in patients with laryngeal neurogenic injury

Objective:To analyze the characteristics of vocal fold movement and glottic closure in patients with laryngeal neurogenic injury. Methods:A total of 185 patients with vocal fold paralysis diagnosed by laryngeal electromyography as neurogenic damage to cricothyroid muscle, thyreoarytenoid muscle and posterior cricoarytenoid muscle were enrolled, they were divided into unilateral vocal fold paralysis group and bilateral vocal fold paralysis group, respectively, and superior laryngeal paralysis group, recurrent laryngeal nerve paralysis group and vagal nerve paralysis group according to nerve injury. The characteristics of vocal fold movement and glottic closure were analyzed under strobe laryngoscope. The qualitative evaluation of vocal fold movement was fixed vocal fold, reduced vocal fold movement and normal vocal fold movement, and the qualitative evaluation of glottic closure was glottic closure and glottic imperfection. The results were analyzed statistically. Results:The proportion of normal, reduced and fixed vocal fold motion in bilateral vocal fold paralysis group was significantly different from that in unilateral vocal fold paralysis group（P<0.05）, the composition of normal and reduced vocal fold motion in bilateral vocal fold paralysis group（47.70%） was significantly greater than that in unilateral vocal fold paralysis group（12.27%）. There was no significant difference between the proportion of glottic closure and glottic imperfecta in bilateral vocal fold paralysis group and unilateral vocal fold paralysis group（P<0.05）. The proportion of decreased vocal fold motion in superior laryngeal nerve paralysis group（50.00%） was higher than that in recurrent laryngeal nerve paralysis group（9.32%） and vagal nerve paralysis group（9.00%）. The proportion of decreased and fixed vocal fold motion in superior laryngeal nerve paralysis group, recurrent laryngeal nerve paralysis group and vagal nerve paralysis group was statistically significant（P<0.05）.There was no significant difference in glottic closure among the three groups（P<0.05）. Conclusion:Vocal fold movement characteristics of patients with laryngeal neurogenic injury were mainly vocal fold fixation, or normal or weakened vocal fold movement. There may be missed diagnosis of unilateral vocal fold paralysis in clinical practice. In half of the patients with superior laryngeal nerve palsy, vocal fold movement is characterized by vocal fold fixation.

The Relationship between Posture and Muscle Tensive Dysphonia in Teachers: A Systematic Scoping Review.

Teachers usually present work-related pain such as neck pain. Their posture could be the cause of these problems; indeed, it is often a sway-back posture. Furthermore, teachers can also experience problems with their voice such as dysphonia, specifically muscle tension dysphonia (MTD). This scoping review aims to find the correlation between teachers' posture and MTD. It also studies how a posture-based treatment can influence this disorder. Randomized controlled trials, controlled clinical trials, prospective cohort studies, and cross-sectional studies that considered the relationship between posture and MTD and that included teachers in their sample. The search led to an initial number of 396 articles; after the screening process, a final number of eight articles were included. A total of 303 patients were analyzed and all showed altered alignment of the head around the cervical spine with hypertonus of the cricothyroid, suprahyoid, and sternocleidomastoid muscles. Although MTD is a disorder with a multifactorial etiology, the articles revealed a correlation between posture and MTD related to a forward protraction of the cervical spine with a hypertonus of the laryngeal and hyoid musculature. This study also detected that an intervention in posture could reduce vocal disorders.

Register transitions in an in vivo canine model as a function of intrinsic laryngeal muscle stimulation, fundamental frequency, and sound pressure level.

Phonatory instabilities and involuntary register transitions can occur during singing. However, little is known regarding the mechanisms which govern such transitions. To investigate this phenomenon, we systematically varied laryngeal muscle activation and airflow in an in vivo canine larynx model during phonation. We calculated voice range profiles showing average nerve activations for all combinations of fundamental frequency (F0) and sound pressure level (SPL). Further, we determined closed-quotient (CQ) and minimum-posterior-area (MPA) based on high-speed video recordings. While different combinations of muscle activation favored different combinations of F0 and SPL, in the investigated larynx there was a consistent region of instability at about 400 Hz which essentially precluded phonation. An explanation for this region may be a larynx specific coupling between sound source and subglottal tract or an effect based purely on larynx morphology. Register transitions crossed this region, with different combinations of cricothyroid and thyroarytenoid muscle (TA) activation stabilizing higher or lower neighboring frequencies. Observed patterns in CQ and MPA dependent on TA activation reproduced patterns found in singers in previous work. Lack of control of TA stimulation may result in phonation instabilities, and enhanced control of TA stimulation may help to avoid involuntary register transitions, especially in the singing voice.

Analysis of the relationship between emotion intensity and electrophysiology parameters during a voice examination of opera singers.

Emotions and stress affect voice production. There are only a few reports in the literature on how changes in the autonomic nervous system affect voice production. The aim of this study was to examine emotions and measure stress reactions during a voice examination procedure, particularly changes in the muscles surrounding the larynx. The study material included 50 healthy volunteers (26 voice workers - opera singers, 24 control subjects), all without vocal complaints. All subjects had good voice quality in a perceptual assessment. The research procedure consisted of 4 parts: an ear, nose, and throat (ENT)‑phoniatric examination, surface electromyography, recording physiological indicators (heart rate and skin resistance) using a wearable wristband, and a psychological profile based on questionnaires. The results of the study demonstrated that there was a relationship between positive and negative emotions and stress reactions related to the voice examination procedure, as well as to the tone of the vocal tract muscles. There were significant correlations between measures describing the intensity of experienced emotions and vocal tract muscle maximum amplitude of the cricothyroid (CT) and sternocleidomastoid (SCM) muscles during phonation and non-phonation tasks. Subjects experiencing eustress (favorable stress response) had increased amplitude of submandibular and CT at rest and phonation. Subjects with high levels of negative emotions, revealed positive correlations with SCMmax during the glissando. The perception of positive and negative emotions caused different responses not only in the vocal tract but also in the vegetative system. Correlations were found between emotions and physiological parameters, most markedly in heart rate variability. A higher incidence of extreme emotions was observed in the professional group. The activity of the vocal tract muscles depends on the type and intensity of the emotions and stress reactions. The perception of positive and negative emotions causes different responses in the vegetative system and the vocal tract. Int J Occup Med Environ Health. 2024;37(1):84-97.

Development of the hyolaryngeal architecture in horseshoe bats: insights into the evolution of the pulse generation for laryngeal echolocation

BackgroundThe hyolaryngeal apparatus generates biosonar pulses in the laryngeally echolocating bats. The cartilage and muscles comprising the hyolarynx of laryngeally echolocating bats are morphologically modified compared to those of non-bat mammals, as represented by the hypertrophied intrinsic laryngeal muscle. Despite its crucial contribution to laryngeal echolocation, how the development of the hyolarynx in bats differs from that of other mammals is poorly documented. The genus Rhinolophus is one of the most sophisticated laryngeal echolocators, with the highest pulse frequency in bats. The present study provides the first detailed description of the three-dimensional anatomy and development of the skeleton, cartilage, muscle, and innervation patterns of the hyolaryngeal apparatus in two species of rhinolophid bats using micro-computed tomography images and serial tissue sections and compares them with those of laboratory mice. Furthermore, we measured the peak frequency of the echolocation pulse in active juvenile and adult individuals to correspond to echolocation pulses with hyolaryngeal morphology at each postnatal stage.ResultsWe found that the sagittal crests of the cricoid cartilage separated the dorsal cricoarytenoid muscle in horseshoe bats, indicating that this unique morphology may be required to reinforce the repeated closure movement of the glottis during biosonar pulse emission. We also found that the cricothyroid muscle is ventrally hypertrophied throughout ontogeny, and that the cranial laryngeal nerve has a novel branch supplying the hypertrophied region of this muscle. Our bioacoustic analyses revealed that the peak frequency shows negative allometry against skull growth, and that the volumetric growth of all laryngeal cartilages is correlated with the pulse peak frequency.ConclusionsThe unique patterns of muscle and innervation revealed in this study appear to have been obtained concomitantly with the acquisition of tracheal chambers in rhinolophids and hipposiderids, improving sound intensity during laryngeal echolocation. In addition, significant protrusion of the sagittal crest of the cricoid cartilage and the separated dorsal cricoarytenoid muscle may contribute to the sophisticated biosonar in this laryngeally echolocating lineage. Furthermore, our bioacoustic data suggested that the mineralization of these cartilages underpins the ontogeny of echolocation pulse generation. The results of the present study provide crucial insights into how the anatomy and development of the hyolaryngeal apparatus shape the acoustic diversity in bats.

Comparative anatomy of the vocal apparatus in bats and implications for the diversity of laryngeal echolocation

Abstract Most of over 1400 extant bat species produce high-frequency pulses with their larynx for echolocation. However, the debate about the evolutionary origin of laryngeal echolocation in bats remains unresolved. The morphology of the larynx is known to reflect vocal adaptation and thus can potentially help in resolving this controversy. However, the morphological variations of the larynx are poorly known in bats, and a complete anatomical study remains to be conducted. Here, we compare the 3D laryngeal morphology of 23 extant bat species of 11 different families reconstructed by using iodine contrast-enhanced X-ray microtomography techniques. We find that, contrary to previously thought, laryngeal muscle hypertrophy is not a characteristic of all bats and presents differential development. The larynges of Pteropodidae are morphologically similar to those of non-bat mammals. Two morphotypes are described among laryngeal echolocating bats, illustrating morphological differences between Rhinolophoidea and Yangochiroptera, with the main variations being the cricothyroid muscle volume and the shape of the cricoid and thyroid cartilages. For the first time we detail functional specialization for constant frequency echolocation among Rhinolophoidea. Lastly, the nasal-emitting taxa representing a polyphyletic group do not share the same laryngeal form, which raises questions about the potential modular nature of the bat larynx.

Cricothyroid Muscle Dysfunction Affects Aerodynamic Performance in Patients with Unilateral Vocal Fold Paralysis.

Emerging evidence has revealed that cricothyroid (CT) muscle dysfunction in unilateral vocal fold paralysis (UVFP) further impairs patients' voices. Given that CT muscle dysfunction does not influence vocal fold position, the mechanism of voice dysfunction induced by dysfunction of CT muscle in UVFP patients remains controversial. This study compares aerodynamics between UVFP patients with and without CT muscle involvement. This cross-sectional study recruited patients with UVFP manifesting dysphonia, and UVFP was confirmed with videolaryngoscopy and laryngeal electromyography (LEMG). Voice analysis and aerodynamic tests were further performed. Patients with (CT+ group) and without (CT- group) CT muscle involvement were compared. A total of 175 patients (40 in the CT+ group and 135 in the CT- group) with UVFP were analyzed. The CT+ group showed lower maximal sound pressure level (SPL) (P=0.039), mean SPL (P=0.042), peak air pressure (P<0.001), mean peak air pressure (P<0.001) and aerodynamic power (P=0.004) than the CT- group. The decrease in SPL, peak air pressure, and aerodynamic power in UVFP patients with CT muscle dysfunction suggests that the effect of CT muscle dysfunction is mediated by a change in aerodynamics.

Vocal Fold Paresis and Voice Outcomes following Vocal Fold Mass Excision.

To correlate the surgical results of vocal fold mass excision with pre-operative existence of vocal fold paresis. Data were collected on 66 patients who underwent excision of benign vocal fold masses from 2015 to 2020. The pre- and post-operative strobovideolaryngoscopy (SVL) examinations for all patients included were evaluated blindly by three otolaryngologists using THE Voice-Vibratory Assessment with Laryngeal Imaging (VALI) Form for scar severity, mucosal wave, free edge contour, glottal closure, and phase closure. The success of mass excision surgery was determined based on the presence of the following criteria post-operatively: 1) improved mucosal wave motion 2) improved phase closure or glottic closure 3) improved free edge contour and 4) lack of worsening of vocal fold scar severity. Surgery was considered successful if 3 or 4 criteria were met, partially successful if 1 or 2 criteria were met, and unsuccessful if no criteria were met. The percent recruitment of the thyroarytenoid, posterior cricoarytenoid (PCA), and cricothyroid muscles were used evaluated the severity of paresis as mild (70-99% recruitment), moderate (40-60% recruitment), or severe (0-39% recruitment). VHI-10 scores were used as subjective measures of pre- and post-operative voice. Sixty-six patients (26 male, 40 female) were included in this study, with a mean age of 37.25 ± 16.6 (range 18-78). Twelve patients had no evidence of VF paresis noted during the initial clinical evaluation; and 52 patients had paresis and had undergone laryngeal EMG. 81% of these patients had mild paresis, 12.8% had moderate paresis, and 5.8% had severe paresis. Based on pre- and post-operative strobovideolaryngoscopy, there was improvement in mucosal wave in 44.9% of cases, improvement of phase or glottic closure in 85.4% of cases, improved free edge contour in 95.5% of cases, and worsening of scar in 38.5% of cases. 39.6% of surgeries were fully successful, 33.3% of surgeries were partially successful, and 27.1% were not successful. There was a significant correlation between female gender and vocal fold paresis (P=0.048). Paresis severity did not correlate with complete or partial surgical success (P=0.956), pre-operative VHI-10 scores (P=0.519), post-operative VHI-10 scores (P=0.563), or strobovideolaryngoscopy parameters. Unilateral and bilateral paresis did not correlate with any other parameter of surgical success (P >0.05). This study suggests that there is no correlation between pre-operative vocal fold paresis and voice outcomes after mass excision surgery, that the majority of mass excision surgeries (72.9%) are successful based on improvement in stroboscopic parameters, and that the proportion of patients with moderate and severe paresis is consistent across all laryngeal nerves.

Laryngeal photobiomodulation: application sites, interferences from body mass index and skin phototype.

Establish points on the neck, correspondent to the laryngeal topography, where to apply Low Level Light therapy (LLLT), to evaluate the incidence of light through variables such as skin phototype and body mass index (BMI). This is a cross-sectional, analytical, observational study, carried out with 15 vocally healthy women, between 18 and 50 years of age, who were divided into three groups, according to BMI and skin phototype. Six anatomical reference points were established to locate the larynx and its musculature, with visual monitoring by videonasolaryngoscopy, to assess light reach (present/absent) and degree of illumination (from very weak to very strong) in the larynx during the LASER application at doses of 3J, 6J and 9J. A flexible endoscope was used for visual monitoring during the LASER application, and subsequent image analysis. The light reached the larynx at doses of 3J, 6J and 9J, in the anterior commissure of the vocal folds, membranous (thyroarytenoid muscle) and cartilaginous portions of the vocal fold and the cricothyroid muscle. The degree of LASER light illumination decreased in overweight and obese participants and increased in moderate brown and dark brown skin phototypes. Data suggest that the LLLT penetrates differently according to skin phototype and BMI, being more evident in individuals with Fitzpatrick IV and V phototypes and less evident with higher BMI levels. The evidence that the LASER light reaches the larynx in specific anatomical points provides direction for the standardization of its use in voice practice.

Intraoperative cricothyroid muscle electromyography may contribute to the monitorization of the external branch of the superior laryngeal nerve during thyroidectomy.

In thyroid surgery, both the recurrent laryngeal nerve (RLN) and external branch of the superior laryngeal nerve (EBSLN) should be preserved for maintaining the vocal cord functions. We aimed to evaluate whether EMG of the CTM applied after the superior pole dissection provided additional informative data to the IONM via ETT or not, regarding the EBSLN function. The prospectively collected data of the patients, who have undergone thyroidectomy with the use of IONM for the exploration of both the RLN and EBSLN between October 2016 and March 2017, were evaluated retrospectively. Patients over 18 years of age with primary thyroid surgery for malignant or benign thyroid disease, and whom were applied CTM EMG with a needle electrode after the completion of thyroidectomy were included in the study. In the study, each neck side was evaluated as a separate entity considering the EBSLN at risk. The data of 41 patients (32 female, 9 male) (mean age, 46.7+9.1; range, 22-71) were evaluated. Sixty seven EBSLNs out of 26 bilateral and 15 unilateral interventions were evaluated. With EBSLN stimulation after the superior pole dissection, positive glottic EMG waveforms via ETT were obtained in 45 (67.2%) out of 67, and the mean glottic amplitude value was 261+191 μV (min-max: 116-1086 μV). Positive EMG responses via the CTM EMG were achieved from all of the 67 EBSLNs (100%) with stimulation using a monopolar probe at the most cranial portion above the area of divided superior pole vessels. The mean value of CTM amplitudes via CTM EMG obtained with EBSLN stimulation was 5268+3916 μV (min-max:1215 -19726 μV). With EBSLN stimulation, the mean CTM EMG amplitude was detected significantly higher than the mean vocal cord amplitude (p<0.0001). The CTM EMG provided more objective quantifiable data regarding the EBSLN function (100% vs 67,2%, p<0.001). In addition to the IONM via ETT, intraoperative post-dissection CTM EMG via needle electrode is a safe, simple and applicable method that may provide significant additional informative data to IONM with ETT by obtaining and recording objective quantitative data related to the EBSLN function.

Pathophysiological Mechanisms Underlying Unilateral Vocal Fold Paralysis in Female Patients: An Ultrasonographic Study.

Laryngeal ultrasonography (LUS) has been suggested as an alternative diagnostic tool for unilateral vocal fold paralysis (UVFP). The present study applied LUS and quantitative laryngeal electromyography (LEMG) in female UVFP patients to investigate the pathophysiologic mechanisms of UVFP. In this cross-sectional study, vocal fold (VF) length parameters included resting and phonating VF length measured using B-mode LUS, and color Doppler vibrating length (CDVL) measured using the color Doppler mode. Forty female patients with UVFP were enrolled, among whom 11 and 29 were assigned to the thyroarytenoid (TA) muscle+cricothyroid (CT) muscle group (with CT involvement) and the TA (without CT involvement) group, respectively. In the TA group, the turn frequency in thyroarytenoid-lateral cricoarytenoid (TA-LCA) on the paralyzed side, as observed through LEMG, correlated with the VF length during the resting phase (R=0.368, P=0.050) and CDVL values (R=0.627, P=0.000) on the paralyzed side. In the TA+CT group, the turn ratio in the CT muscle correlated with the normalized phonatory vocal length change (nPLC; R=0.621, P=0.041) on the paralyzed side. CDVL and nPLC are two parameters that can be utilized to predict the turn frequencies of TA-LCA in UVFP cases without CT involvement, and the turn ratio of CT in cases of UVFP with CT involvement, respectively. The findings suggest that LUS, as a noninvasive tool, can serve as an alternative method for assessing the severity of laryngeal nerve injury and offer valuable insights into the pathophysiology of UVFP.

Neurophysiology of the Superior Laryngeal Nerve in an In Vivo Rat Model.

The superior laryngeal nerve (SLN) is fundamental in laryngeal sensation, cough reflex, and pitch control. SLN injury has substantial consequences including altered sensation, aspiration, and dysphonia. To date, in vivo measurement of the SLN remains elusive. The purpose of this study was to assess the feasibility of recording motor and sensory evoked potentials in a rat SLN model. Twenty-two rat hemi-laryngeal preparations (n = 11) were obtained from 4-month-old Sprague-Dawley rats and included in this study. Compound motor action potentials (CMAPs) and motor unit number estimation (MUNE) were calculated by stimulating the SLN at the point of medial extension near the carotid artery and by placing a recording electrode on the cricothyroid muscle. Sensory response was determined through stimulation of the SLN and laryngoscopic visualization of a laryngeal adductor reflex (LAR). SLN and cricothyroid muscle cross-sections were stained and histologic morphometrics were quantified. Laryngeal evoked potentials were successfully obtained in all trials. Mean CMAP latency and negative durations were 0.99 ± 0.57 ms and 1.49 ± 0.57 ms, respectively. The median MUNE was 2.06 (IQR 1.88, 3.51). LAR was induced with a mean intensity of 0.69 ± 0.20 mV. Mean axon count, myelin thickness, and g-ratio were 681 ± 192.2, 1.72 ± 0.26, and 0.45 ± 0.04, respectively. This study demonstrates the feasibility of recording evoked response potentials following SLN stimulation. We hypothesize that this work will provide a tractable animal model to study changes in laryngeal sensation and cricothyroid motor function with aging, neurodegenerative disease, aspiration, or nerve injury. NA Laryngoscope, 134:1778-1784, 2024.

Current opinion on laryngeal electromyography

PurposeThis study evaluates expert opinion on laryngeal electromyography (LEMG). MethodsA cross-sectional design was used to conduct an online survey of LEMG experts in 2021. They were questioned about the number LEMG performed annually, type of electrodes used, sector worked in, pain during the test, placement of the needle electrodes, interpretation of electrical muscle parameters, diagnosis of neuromuscular injury, prognostic sensitivity in vocal fold paralysis (VFP), laryngeal dystonia, tremor and synkinesis and quantifying LEMG. ResultsThirty-seven professionals answered (23 Spanish and 14 from other countries), with a response rate of 21.56%. All physicians used LEMG. 91.9% had one- or two-years’ experience and 56.8% performed 10–40 LEMG per year. 70.3% were otolaryngologists and 27%, neurologists. In 89.1% of cases, a team of electrodiagnostic physician and otolaryngologist performed LEMG. 91.3% of Spanish respondents worked in Public Health, 7.14% of other nationalities; 37.8% in a university department. Bipolar concentric needles electrodes were used by 45.9% and monopolar concentric by 40.5%. 57% professionals considered good patients’ tolerance to the test. LEMG sensitivity was regarded as strong, median and interquartile range were 80.0 [60.0;90.0] to diagnose peripheral nerve injuries, less for other levels of lesions, and strong to evaluate prognosis, 70.0 [50.0;80.0]. Respondents believe locate the thyroarytenoid and the cricothyroid muscles with the needle, 80.0 [70.0;90.0], as opposed to 20.0 [0.00;60.0] the posterior cricoarytenoid. The interpretation of the electrical parts of the LEMG was strong, 80.0 [60.0;90.0]. LEMG identify movements disorders, 60.0 [20.0;80.0], and synkinesis, 70.0 [30.0;80.0]. The professionals prefer quantitative LEMG, 90.0 [60.0;90.0]. ConclusionsThe experts surveyed consider LEMG that is well tolerated by patients. The insertional and spontaneous activity, recruitment and waveform morphology can be assessed easily. LEMG is mainly useful in the study of peripheral nerve injuries, and its value in VFP prognosis is considered strong.

Intraoperative monitoring of the recurrent laryngeal nerve in thyroid gland surgery

In Thyroid surgery, the two novel approaches are the trans-axillary Robotic thyroidectomy and the trans-oral and sub-chin techniques.During these surgical approaches is mandatory to recognise the Anatomy. The lower laryngeal nerves originate from the X cranial nerve (vagus nerve) and innervate all the intrinsic muscles of the larynx except for the cricothyroid muscles (which are innervated by the superior laryngeal nerve instead). The "recurring" name is due to the course in the opposite direction to the nerve of origin.Neuro-monitoring of recurrent laryngeal nerves is the most important of the recent technological innovations. However it is of fundamental importance for the operator to remember that this method does not prevent recurrent nerve injury. On the other hand a two stage thyroidrctomy can avoid a tracheostomy thanks to neuro-monitoring.

Recurrent laryngeal nerve’s course running anteriorly to a thyroid tumor

The thyroid gland's neurovascular relationship is commonly portrayed as the recurrent laryngeal nerve (RLN) coursing posteriorly to the thyroid gland. We report a rare case with the RLN running anteriorly to a thyroid tumor. A 56-year-old Japanese woman underwent a thyroidectomy for a benign thyroid tumor. Preoperatively, computed tomography confirmed that part of the tumor had extended into the mediastinum and was descending posteriorly up to the brachiocephalic artery. Intraoperatively, when the sternothyroid muscle was incised to expose the thyroid gland, a cord (nerve)-like structure was observed directly anterior to the thyroid tumor. Although the course of this cord-like structure was clearly different from the "traditional" course of the right RLN, the possibility that the structure was the RLN could not be excluded. The structure was traced back in order to preserve it; we saw that it entered the larynx at the lower margin of the cricothyroid muscle and approximately at the level of the cricothyroid junction through the back of the normal thyroid tissue. With intraoperative neuromonitoring, the structure was identified as the RLN. As a result, the course of the RLN run anterior to the tumor but then posterior to the 'normal thyroid' i.e. into it normal anatomical position. Had we assumed that the RLN was behind the thyroid tumor, we would have damaged the RLN. It would not be possible to diagnose this abnormal running course of the RLN reliably before surgery, but extra care should be taken in similar cases, that is, when a large thyroid tumor is descending posteriorly up to the brachiocephalic artery on the right side.