Comparison of EMG amplitudes recorded by ipsilateral and contralateral electrodes placement during using trans-thyroid cartilage recording method in thyroid surgery.

Objectives: The feasibility and reliability of trans-thyroid cartilage EMG recording method (TCERM) during intraoperative monitoring (IONM) of the recurrent laryngeal nerve (RLN) in thyroid surgery have been established. This study compared two different recording electrode placements on the ipsi-lateral and contra-lateral lamina of the thyroid cartilage (TC). Methods: Fifty consecutive patients undergoing total thyroidectomy with 100 RLNs at risk were enrolled. Two paired subdermal needle electrodes were inserted into the subperichondrium of the bilateral TC lamina to record electromyography (EMG) signals. The channel leads from the TC electrodes were connected to the patient interface with two different modes. In A-mode, the electrode leads were placed ipsi-laterally, and channel 1 monitored the left RLN and channel 2 monitored the right RLN respectively. In B-mode, the electrode leads were placed contra-laterally, and channels 1 and 2 simultaneously monitored the same side of the RLN. The amplitudes of four EMG signals (V1-R1-R2-V2) recorded by A-mode and B-mode were compared. Results: All EMG amplitudes of V1-R1-R2-V2 signals recorded with B-mode were all above 500µV and significantly higher than those with A-mode (p<0.001). No false loss of signal, electrode dislodgement, or needle-related complications were noted during IONM. Postoperatively, all patients had symmetrical vocal cord movement. Lower EMG amplitudes were observed in older and male patients. Histopathology and laterality showed no significant differences in EMG amplitude. Conclusion: During using TCERM in thyroid surgery, the recording electrodes should be placed contra-laterally on the TC lamina. This approach ensures high and stable EMG signals, which are important for high-quality IONM of the RLN.

Intraoperative Neuromonitoring Using a Single Transcartilage Needle Electrode During Thyroidectomy.

OBJECTIVES: Application of transcartilage needle electrode for intraoperative neuromonitoring (IONM) during thyroidectomy has been considered an alternative method of electromyography (EMG) tube recording. However, needle electrodes must be inserted into both sides of the thyroid cartilage with exposure of the cartilage lamina. We sought to evaluate the feasibility of applying a single ipsilateral transcartilage needle electrode for IONM during unilateral hemithyroidectomy. METHODS: Thirty-four patients underwent IONM during unilateral thyroidectomy. A dual disposable needle electrode was inserted obliquely into the inferior lower third of the ipsilateral lamina of the thyroid cartilage. Patients were classified as deep (≥ 5 mm) or superficial (< 5 mm) by the depth of the needle electrode inserted into the thyroid cartilage. Without using an EMG tube, IONM was done according to the standardized procedure using a single needle electrode only. RESULTS: IONM was successful in all nerves at risk. Amplitude of the EMG signal was stable during the surgery, with no cases presenting loss of signal. Amplitude of the signal from vagal and recurrent laryngeal nerve stimulation was significantly lower when needle insertion was superficial (< 5 mm). None of the patients showed postoperative vocal cord paralysis, and complications related to needle electrode were not identified. CONCLUSION: IONM using a single ipsilateral transcartilage needle electrode during unilateral hemithyroidectomy was feasible with no significant complications. It may serve as an alternative method of IONM with the advantage of minimal exposure of the thyroid cartilage lamina. LEVEL OF EVIDENCE: 4 Laryngoscope, 131:448-452, 2021.

Tic Movement of Thyroid Cartilage as a Cause for Localized Cerebral Embolism: Mimics of Embolic Stroke of Undetermined Source with Non-Stenotic Carotid Plaque.

Several studies have suggested that non-stenotic carotid plaque was a risk factor for embolic stroke of undetermined source in some patients. However, individual backgrounds of these patients is unclear. We encountered a 64-years-old female with cerebral emboli, from an apparently stable non-stenotic carotid plaque (only 1.42mm thick) at the distal left common carotid artery, caused by violent tic movement of thyroid cartilage under well controlled dyslipidemia. Even though the plaque appeared thin and stable, mechanical stimulation could cause multiple, unnaturally localized emboli by stimulation-induced atherogenesis and plaque rupture, resulting in a misdiagnose of embolic stroke of undetermined source with non-stenotic carotid plaque.

New placement of recording electrodes on the thyroid cartilage in intra-operative neuromonitoring during thyroid surgery.

OBJECTIVE: During thyroid surgery, extreme caution is needed not to harm the recurrent laryngeal nerve and to avoid vocal cord palsy. Intra-operative neuromonitoring became increasingly popular as an adjunct to the gold standard of visual identification of the recurrent laryngeal nerve (RLN). Electromyographic (EMG) responses are normally recorded by electrodes attached to the endotracheal tube. Alteration in position can lead to false loss of signal. We developed thyroid cartilage electrodes that can be fixed directly onto the thyroid cartilage. STUDY DESIGN: Prospective clinical cohort METHODS: Thyroid surgery with intra-operative neuromonitoring using both endotracheal tube-based electrodes and thyroid cartilage electrodes was performed in 25 patients undergoing thyroid surgery. EMG data were collected and reported as median and interquartile ranges (IQR), and the results were compared with the x Wilcoxon signed-rank test for paired measurements. RESULTS: After stimulating vagal nerve (VN), recurrent laryngeal nerve (RLN) and external branch of the superior laryngeal nerve (EBSLN), significantly higher EMG amplitudes were measured before and after thyroid resection for the thyroid cartilage (TC) electrodes, in all comparisons except for the right VN. At the level of the left EBSLN, median amplitude of 560 mV (IQR 190-1050) before and 785 mV (IQR 405-3670) after resection was noted. At the level of the right EBSLN, median amplitude of 425 µV (IQR 257-698) before and 668 mV (IQR 310-1425) after resection was noted. Median amplitudes of 760 mV (IQR 440-1180) and 830 mV (IQR 480-1490) were noted at the left RLN, median amplitudes of 695 mV (IQR 405-1592) and 1078 mV (IQR 434-1895) were noted at the right RLN. CONCLUSION: Thyroid cartilage electrodes appear to be a feasible and reliable alternative for endotracheal electrodes.

Comparison of EMG signals recorded by surface electrodes on endotracheal tube and thyroid cartilage during monitored thyroidectomy.

A variety of electromyography (EMG) recording methods were reported during intraoperative neural monitoring (IONM) of recurrent laryngeal nerve (RLN) in thyroid surgery. This study compared two surface recording methods that were obtained by electrodes on endotracheal tube (ET) and thyroid cartilage (TC). This study analyzed 205 RLNs at risk in 110 patients undergoing monitored thyroidectomy. Each patient was intubated with an EMG ET during general anesthesia. A pair of single needle electrode was inserted obliquely into the TC lamina on each side. Standard IONM procedure was routinely followed, and EMG signals recorded by the ET and TC electrodes at each step were compared. In all nerves, evoked laryngeal EMG signals were reliably recorded by the ET and TC electrodes, and showed the same typical waveform and latency. The EMG signals recorded by the TC electrodes showed significantly higher amplitudes and stability compared to those by the ET electrodes. Both recording methods accurately detected 7 partial loss of signal (LOS) and 2 complete LOS events caused by traction stress, but only the ET electrodes falsely detected 3 LOS events caused by ET displacement during surgical manipulation. Two patients with true complete LOS experienced temporary RLN palsy postoperatively. Neither permanent RLN palsy, nor complications from ET or TC electrodes were encountered in this study. Both electrodes are effective and reliable for recording laryngeal EMG signals during monitored thyroidectomy. Compared to ET electrodes, TC electrodes obtain higher and more stable EMG signals as well as fewer false EMG results during IONM.

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

PURPOSE: To describe the anatomical course of the intralaryngeal portion of the inferior laryngeal nerve (ILN) and to standardize the surgical access to its thyroarytenoid branch (TAb) through the thyroid cartilage. METHODS: Under surgical microscopy, 33 adult human excised larynges were dissected, to expose the intralaryngeal portion of ILN. The point of entry of TAb, ILN's terminal branch, in the thyroarytenoid (TA) muscle was determined and correlated with thyroid cartilage dimensions. RESULTS: After entering the larynx, the ILN consistently traveled between the thyroid cartilage and the lateral cricoarytenoid muscle in an anterior and slightly cranial course. The distance from the point of entry of the TAb in the TA muscle to the midline (TAb-H) and to the inferior border (TAb-V) of the thyroid cartilage differed according to gender. In females, mean distances of TAb-H and TAb-V were 20.5mm and 5.2mm and in males, 22.3mm and 5.9mm, respectively. CONCLUSION: The intralaryngeal course of the inferior laryngeal nerve presents low variability and measures from landmarks in the thyroid cartilage help to estimate the point of entry of thyroarytenoid branch in thyroarytenoid muscle.

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

ABSTRACT PURPOSE: To describe the anatomical course of the intralaryngeal portion of the inferior laryngeal nerve (ILN) and to standardize the surgical access to its thyroarytenoid branch (TAb) through the thyroid cartilage. METHODS: Under surgical microscopy, 33 adult human excised larynges were dissected, to expose the intralaryngeal portion of ILN. The point of entry of TAb, ILN's terminal branch, in the thyroarytenoid (TA) muscle was determined and correlated with thyroid cartilage dimensions. RESULTS: After entering the larynx, the ILN consistently traveled between the thyroid cartilage and the lateral cricoarytenoid muscle in an anterior and slightly cranial course. The distance from the point of entry of the TAb in the TA muscle to the midline (TAb-H) and to the inferior border (TAb-V) of the thyroid cartilage differed according to gender. In females, mean distances of TAb-H and TAb-V were 20.5mm and 5.2mm and in males, 22.3mm and 5.9mm, respectively. CONCLUSION: The intralaryngeal course of the inferior laryngeal nerve presents low variability and measures from landmarks in the thyroid cartilage help to estimate the point of entry of thyroarytenoid branch in thyroarytenoid muscle.

Anatomical localization of the motor entry point in the thyroarytenoid muscle.

INTRODUCTION: The aim of this study was to localize the motor entry point (MEP) of the thyroarytenoid muscle. METHODS: Eight cadaver larynges were dissected. A virtual plane was used to represent the MEP in a coordinate (X/Y/Z) system. The inferior border of the thyroid cartilage was linked to the center of the anterior arc of the cricoid cartilage (the Y-axis). The X-axis was set perpendicular to the Y-axis; the Z-axis passed through the posterior border of the thyroid lamina from the height of the insertion point. RESULTS: The mean X, Y, and Z coordinates were 6.2 mm, 9.1 mm, and 11.0 mm, respectively. The calculated angles of the lateral and superior deflections were 29.4° and 35.8°, respectively. The calculated insertion depth, that is, the distance from the insertion point to the MEP, was 15.6 mm. CONCLUSIONS: These results may help to improve the accuracy of needle insertion during diagnostic laryngeal electromyography or laryngeal electromyography-guided injections.

The thyroid foramen: a systematic review and surgical considerations.

This study presents an analytic review about the trait of the thyroid foramen. A detailed description about the demographics, frequency, embryology, morphometry, possible content, topography, clinical and surgical considerations is provided. The overall frequency was 28.3% in adults, 15% in children and neonates, 40.6% in embryos and fetuses. The content of the thyroid foramina was a neurovascular bundle in 41.2% of studies. An equal number of studies define a nerve as the common content, while only in 17.6% the usual content was a vessel. Interestingly, in 11.8% the content was just connective tissue or a pit. An updated classification is presented taking into account all the possible content that can cross through a thyroid foramen. The variant is of high interest for surgeons intervening in the larynx due to potential complications such as local bleeding and unwanted neural impairment. The oblique line of the thyroid lamina acts as the best topographical landmark to identify any aberrant anatomy related to a thyroid foramen.

Relative direction and position of recurrent laryngeal nerve for anatomical configuration.

The present study aims to describe the course of the recurrent laryngeal nerve (RLN) using the tracheoesophageal groove (TEG) at the cricothyroid joint as a base line, and the configuration of RLN and inferior thyroid artery (ITA) for careful dissection in thyroid surgery. The RLN of left side is likely to be found posterior to ITA and course mainly from 0 degrees up to 30 degrees based on TEG near cricothyroid joint while the nerve of right side is likely to be found anterior to ITA in right side and course mainly from 15 degrees up to 45 degrees based on TEG. The contacting point of RLN with ITA locate from the tip of cricoid cartilage at about three tenth of the distance from the tip of cricoid cartilage to sternal notch without reference to individual body size. 70 cadavers were investigated. The angle of RLN from TEG was measured at the cricothyroid joint. The relative position of RLN to ITA was classified. The location of the contacting point of RLN with ITA was measured and converted as an index. These findings suggest the area for careful dissection near cricothyroid joint, the configuration of RLN for identifying the nerve.

Useful landmarks in arytenoid adduction and laryngeal reinnervation surgery.

OBJECTIVE: Knowledge of the location of the muscular process of the arytenoid cartilage and the recurrent laryngeal nerve is essential to performing a successful arytenoid adduction and laryngeal reinnervation surgery. We describe external landmarks useful in locating these structures. STUDY DESIGN: Cadaveric laryngeal dissection. METHODS: Posterior laryngeal dissection was performed in 16 human larynges. The position of the muscular process of the arytenoid was measured bilaterally relative to the inferior and superior borders of the thyroid lamina. The recurrent laryngeal nerve was followed distally from slightly below the level of the cricothyroid joint to its genu where its vertical course changes to an oblique intralaryngeal course. RESULTS: The muscular process of the arytenoid was usually found halfway between the roots of the superior and inferior cornu of the thyroid lamina. The recurrent laryngeal nerve was found just deep to the cricothyroid joint and lateral to the posterior cricoarytenoid muscle. There were no other nerves in this area. CONCLUSIONS: This study finds that the superior and inferior borders of the thyroid lamina are useful intraoperative landmarks to locate the muscular process of the arytenoid. The cricothyroid joint provides a good starting point to locate the recurrent laryngeal nerve, which can be identified slightly deeper between it and the posterior cricoarytenoid muscle.

The incidence of the foramen thyroideum in Turkish population.

This study was undertaken to investigate the incidence and characteristics of the foramen thyroideum (FT) in Turkish population. A total of 50 cadaver specimens were dissected which were a randomly selected sample of population from the criminal laboratory of the Republic of Turkey's Ministry of Justice (Istanbul). Larynges were dissected with a surgical SMZ 10 Nikon stereomicroscope. Six of the 50 specimens dissected had distinctly identifiable foramina with neurovascular component. One specimen had bilateral foramina, five specimens had unilateral foramina, and two had it in the left side, three in the right. One specimen had a double foramen in the left side. All of them were male and contained neurovascular components. Our data showed 12% incidence of FT in Turkish population.

The external laryngeal nerve: surgical and anatomic considerations. Report of 50 total thyroidectomies.

This surgical anatomy study aimed to evaluate the possibility of identifying the external laryngeal nerve during thyroid surgery and the possible variations of nerves at risk. Fifty patients underwent total thyroidectomies during a period of 12 months. Using a neurostimulator, the distal motor branch of the external laryngeal nerve was searched. Electrical stimulation of a nervous branch aimed to provoke a global contraction of the cricothyroid in order to identify with certitude the external laryngeal nerve. The external laryngeal nerve was identified in 20% of cases. Its course was, with almost equal frequency, either (1) between the vessels of the superior thyroid pedicle or (2) superficial and anterior to the fascia of the cricothyroid muscle. The external laryngeal nerve is hard to find during thyroid surgery, even with a neurostimulator. It can be vulnerable during thyroid surgery but only in cases of anatomic variations. Searching for the nerve systematically during thyroid surgery does not seem to be useful. Several precautions when dissecting the superior pole of the thyroid gland seem to be necessary and sufficient to respect the external laryngeal nerve.

A Lei de Wagner-Grossman é aplicável nas paralisias da laringe? / Is the Wagner-Grossman's law aplicable to laryns paralysis?

Objetivos: O presente trabalho teve como objetivo determinar os fatores que podem influenciar a posiçäo assumida pela prega vocal (PV), em casos de paralisia dos nervos laríngeos recorrente (NLR) e superior (NLS). Material e método: Para tanto, foram utilizados ratos, nos quais se provocou a paralisia da PV de acordo com os seguintes procedimentos: Grupo A: realizados cortes no NLR em alturas diferentes, em 20 ratos; Grupo B: realizados cortes no NLR e de fibras do músculo cricotireóideo, em 15 ratos; Grupo C: realizado corte do NLR, obedecendo o movimento da PV no ciclo respiratório, em 7 ratos. Discussäo: Observou-se que a prega vocal permanecia em posiçäo pára-mediana (PPM) na grande maioria dos casos, mesmo quando as fibras do músculo cricotireóideo foram seccionadas ou o músculo foi denervado. Nesta última situaçäo, observou-se que em 20 por cento dos ratos, a PV se mantinha em posiçäo lateral (PL). Nos casos em que o corte do NLR se fazia segundo o ciclo respiratório, a posiçäo da prega era PPM, mesmo quando o corte ocorria em inspiraçäo. Neste caso, a PV, entäo abduzida, se desloca rapidamente para a linha mediana, como se estivesse sendo puxada. Conclusäo: Conclui-se que, nos ratos, a posiçäo da PV independe da reinervaçäo, da sincinesia e da inervaçäo residual, principalmente do músculo cricotireóideo. O movimento da PV quando da secçäo do NLR durante a inspiraçäo sugere a açäo de forças elásticas

[Variants in the position of the ansa cervicalis in man]. / Varianty polozheniia sheinoi petli u cheloveka.

29 cadaveric specimens of head and neck obtained from adults of both sexes following fixation in 5% formaldehyde were the material for the study. 43 samples of cervical ansa were examined. The investigation demonstrated that in the majority of cases (60.5%) cervical ansa was located exterior to internal jugular vein. The variants with the high position of cervical ansa in respect to the upper margin of thyroid cartilage were found in the samples with cervical ansa lying interiorly to the internal jugular vein.

Three-dimensional distribution of neuromuscular junctions in human cricothyroid.

Microinjections of myoneural blocking agents are effective in the treatment of strabismus and have been proposed as a possible technique to treat spastic dysphonia. The success of such a technique would rely on a precise knowledge of the neuromuscular junction distribution in the laryngeal muscle to be injected. In view of the possibility of an involvement of the cricothyroid muscle in spastic dysphonia or other neuromuscular disorders, we determined the three-dimensional distribution of neuromuscular junctions in the human cricothyroid muscle. Cricothyroid muscles obtained from autopsy cases were fixed, sectioned, and processed for the histochemical localization of neuromuscular junction acetylcholinesterase. Using serial sections and a computer interfaced X-Y digitizer, the neuromuscular junctions were referenced to various anatomic landmarks and the neuromuscular junction distribution and reconstructed in three dimension using computer graphics.