Is identification and dissection of the external laryngeal nerve necessary during thyroidectomy? A prospective study.

BACKGROUND: Compared to the recurrent laryngeal nerve, the EBSLN (or external laryngeal nerve) is less studied in terms of its course and relationship with the thyroid gland. This is a prospective intraoperative study designed to identify the anatomical variations of the EBSLN in relation to the IPC, the superior thyroid pedicle, and the point where the nerve crosses the STA. Additionally, the study aims to propose a technical procedure for its preservation. METHODS: We conducted a prospective study of 50 patients (total of 100 nerves) undergoing total thyroidectomy at the Department of Surgery 'B' in Ibn Sina Hospital, Rabat. Intraoperatively, the EBSLN was visually identified and preserved before ligating the superior thyroid vessels. Each nerve was categorized using established classification systems. RESULTS: The overall pooled EBSLN identification rate was 82%. Cernea type IIa (nerves crossing the STA less than 1 cm above the upper edge of the superior thyroid pole) and Friedman type II (nerves piercing the lower fibers of the IPC) were the most prevalent (64% and 44%, respectively). Kierner type IV (nerves crossing the branches of the STA immediately above the upper pole of the thyroid gland) was represented in 27% of cases. CONCLUSION: A better understanding of surgical anatomy of the neck allows for better results of thyroidectomy by preserving the external and recurrent laryngeal nerves.

Study on Microsurgical Anatomy of External Branch of Superior Laryngeal Nerve Related to Carotid Endarterectomy.

OBJECTIVE: To explore the methods of protecting the external branch of the superior laryngeal nerve during carotid endarterectomy through microsurgical anatomic study of the external branch of the superior laryngeal nerve in cadaveric specimens. METHODS: A total of 30 cadaveric specimens (60 sides) were dissected to measure the thickness of the external branch of the superior laryngeal nerve. A triangular area was exposed, bounded by the lower border of the digastric muscle superiorly, the medial edge of the sternocleidomastoid muscle laterally, and the upper border of the superior thyroid artery inferiorly. The probability of the occurrence of the external branch of the superior laryngeal nerve in this area was observed and recorded. The distance among the midpoint of the external branch of the superior laryngeal nerve in this area with the tip of the mastoid process and the angle of the mandible as well as the bifurcation of the common carotid artery was measured and recorded. RESULTS: Among 30 specimens of cadaveric heads (60 sides) examined 53 external branches of the superior laryngeal nerve were observed while 7 were absent. Of the 53 branches observed, 5 were located outside the anatomic triangle region mentioned above, while the remaining 48 branches were located within the anatomic triangle region with a probability of ~80%. The thickness of the midpoint of the external branches of the superior laryngeal nerve within the anatomic triangle region was 0.93 mm (0.72-1.15 mm [±0.83 SD]), located 0.34 cm [-1.62-2.43 cm (±0.96 SD)] posterior to the angle of the mandible, 1.28 cm (-1.33 to 3.42 cm (±0.93 SD)] inferiorly; 2.84 cm (0.51-5.14 cm±1.09 SD) anterior to the tip of the mastoid process, 4.51 cm (2.82-6.39 cm±0.76 SD) inferiorly; 1.64 cm [0.57-3.78 cm (±0.89 SD)] superior to the bifurcation of the carotid artery. CONCLUSIONS: During carotid endarterectomy procedure, using the cervical anatomic triangle region, as well as the angle of the mandible, the tip of the mastoid process, and the bifurcation of the carotid artery as anatomic landmarks, is of significant clinical importance for protecting the external branches of the superior laryngeal nerve.

Variations in the course of the externalbranch of the superior laryngeal nerveand their importance in surgicalprocedures: an experimental cadaveric study.

<br><b>Introduction:</b> Injury of the external branch of the superior laryngeal nerve can cause a hoarse or weak voice due to the functional loss (dysergia) of the cricothyroid muscle. Defining the anatomical variations of the external branch of the superior laryngeal nerve and estimating their frequency are crucial for surgical interventions.</br> <br><b>Aim:</b> To reveal the topography of the external branch in the Anatolian population, to prevent injury of it during the surgical intervention in the anterior neck region.</br> <br><b>Material and methods:</b> 26 bilateral hemilarynges (4 females, 22 males) were dissected. The morphometric and morphological features of the external branch were examined. The obtained results were compared statistically, left and right.</br> <br><b>Results:</b> Landmarks such as the thyroid gland and laryngeal prominence were determined for the detection of the external branch. The variations of the course of the external branch and the points of piercing the cricothyroid muscle or inferior pharyngeal constrictor muscle were evaluated.</br> <br><b>Discussion:</b> Although safe approaches have been described for nerve protection during neck surgeries, injuries may occur during preliminary surgery as the mentioned nerve is thinner and more superficial than other branches of the vagus nerve. However, it can be detected more easily and safely by knowing the defined anatomical landmarks and morphological variations of the external branch.</br> <br><b>Conclusion:</b> The anatomical variations described can be a safe and important guide in surgeries of the anterior neck region.</br>.

Variations of the external branch of the superior laryngeal nerve during its course and its importance in surgical approaches: an experimental cadaveric study.

INTRODUCTION: Injury of the external branch of the superior laryngeal nerve can cause a hoarse or weak voice due to the functional loss (dysergia) of the cricothyroid muscle. Defining the anatomical variations of the external branch of the superior laryngeal nerve and estimating the frequency of it, it makes crucial for surgical interventions. AIM: To reveal the topography of the external branch in the Anatolian population, to prevent injury of it during the surgical intervention in the anterior neck region. MATERIALS AND METHODS: Twenty-six bilateral hemilarynges (4 females, 22 males) were dissected. The morphometric and morphological features of the external branch were examined. The obtained results were compared statistically left and right. RESULTS: Landmarks such as the thyroid gland and laryngeal prominence were determined for the detection of the external branch. The variations of the course of the external branch and the points of piercing the cricothyroid muscle or inferior constrictor pharyngeal muscle were evaluated. DISCUSSION: Although safe approaches have been described for nerve protection during neck surgeries, it can expose injuries during preliminary surgery approaches as the nerve is thinner and more superficial than other branches of the vagus nerve. However, it can be detected more easily and safely during the surgical approach by knowing the defined anatomical landmarks and morphological variations of the external branch. CONCLUSION: The anatomical variations described can be a safe and important guide in surgical approaches to be applied in the anterior neck region.

Surgical landmarks for identification and preservation of the internal branch of the superior laryngeal nerve.

OBJECTIVE: To determine the topographical anatomic features of the internal branch of the superior laryngeal nerve (ibSLN) at the thyrohyoid membrane entrance area in relation to certain consistent anatomical structures. MATERIALS: METHODS: Twenty-two fresh adult head cadavers (9 male, 13 female; age range 52-95 years) with no signs of abnormality in the neck were dissected to determine the anatomic relationship of ibSLN and superior border of thyroid cartilage, thyroid notch, carotid bifurcation, hyoid corpus, and hyoid greater cornu. RESULTS: The topographical relationship between ibSLN and superior border of thyroid cartilage, thyroid notch, carotid bifurcation, hyoid corpus, and hyoid greater cornu was identified bilaterally in all cadavers. According to the measures, danger zone and safe zone areas for surgical could be predicted and for surgical manipulations as well. CONCLUSION: We provided the surgical anatomy and important landmarks for determining the internal branch of superior laryngeal nerve in the thyrohyoid membrane entrance region to avoid surgical damage during surgeries of this region.

Superior Laryngeal Nerve Palsy After Anterior Cervical Diskectomy and Fusion: A Case Report and Cadaveric Description.

BACKGROUND AND IMPORTANCE: Superior laryngeal nerve (SLN) injury after high cervical dissection can result in changes in vocal pitch due to cricothyroid denervation and dysphagia with aspiration risk because of decreased sensation of the supraglottic larynx. CLINICAL PRESENTATION: We describe a 69-year-old singer with cervical spondylotic myelopathy who underwent elective C3/4 and C4/5 anterior cervical diskectomy and fusion. Postoperatively, the patient reported changes in his voice, most noticeable with higher registers. A number of studies confirmed severe right superior laryngeal neuropathy. A cadaveric description included to highlight anatomic relationships critical in minimizing risk of SLN injury during an anterior cervical diskectomy and fusion approach. CONCLUSION: The SLN is a critical structure vulnerable to iatrogenic injury during high cervical dissections for anterior approaches to the spine. Therefore, it is critical for spine surgeons to have a firm understanding of SLN anatomy for these approaches.

Effects of Laryngeal Vibratory Asymmetry and Neuromuscular Compensation on Voice Quality.

INTRODUCTION: Vibratory asymmetry and neuromuscular compensation are often seen in laryngeal neuromuscular pathology. However, the ramifications of these findings on voice quality are unclear. This study investigated the effects of varying levels of vibratory asymmetry and neuromuscular compensation on cepstral peak prominence (CPP), an analog of voice quality. STUDY DESIGN: In vivo canine phonation model. METHODS: Varying degrees of vocal fold vibratory asymmetry were achieved by stimulating one recurrent laryngeal nerve (RLN) over 11 levels from threshold to maximal muscle activation. For each of these levels, phonation was induced at systematically varied combinations of neuromuscular compensation: three levels each of contralateral RLN stimulation (80%, 90%, and 100% of maximal), superior laryngeal nerve (SLN) activation (0%, 50%, and 100% of maximal), and airflow levels (500, 700, and 900 mL/s). Vocal fold symmetry was determined by assessing the opening phase of the vibratory cycle in high-speed video recordings. Voice quality was estimated acoustically by calculating CPP for each voice sample. RESULTS: Eight hundred twenty-two phonatory conditions with varying degrees of vibratory asymmetry were evaluated. CPP was highest at vibratory symmetry. Increasing levels of asymmetry resulted in significant decreases in CPP. CPP increased significantly with increasing contralateral RLN activation. CPP was significantly higher at 50% SLN activation than 0% or 100% SLN activation. CONCLUSION: Voice quality, as approximated by CPP, is best at vibratory symmetry and deteriorates with increasing degrees of asymmetry. Voice quality may be improved with neuromuscular compensation by increased adduction of the contralateral vocal fold or increased vocal fold tension at mid-levels of SLN activation. LEVEL OF EVIDENCE: NA, Basic Science Laryngoscope, 132:130-134, 2022.

The Anatomical and Clinical Significance of the Superior Laryngeal Nerve.

OBJECTIVE: This study summarizes the anatomical features of the superior laryngeal nerve in Chinese to enable the rapid location of the superior laryngeal nerve during an operation. STUDY DESIGN: Retrospective analysis of anatomical data. SETTING: Hangzhou First People's Hospital Affiliated to Nanjing Medical University. METHODS: A total of 71 embalmed human cadavers (132 heminecks) were examined over 3 months. The length and diameter of the internal and external branches of the superior laryngeal nerve and their relationships with different landmarks were recorded. RESULTS: The total length of the internal branch of the superior laryngeal nerve was 23.4 ± 6.9 mm. The length of the external branch of the superior laryngeal nerve was 47.7 ± 11.0 mm. Considering the midpoint of the lower edge of the thyroid cartilage as the starting point and using that edge as a horizontal line, when the entry point is above that line, the external branch of the superior laryngeal nerve can be found within 41.1 mm and at an angle of 57.2°. When the entry point is below the lower edge of the thyroid cartilage, the external branch of the superior laryngeal nerve can be found within 34.0 mm and at an angle of 36.5°. CONCLUSION: The superior laryngeal nerve in Chinese people has distinct anatomical characteristics. This article provides a new method of quickly locating the external branch of the superior laryngeal nerve during the operation, which can reduce the probability of damaging the external branch of the superior laryngeal nerve.

Anatomical Variations in Recurrent Laryngeal Nerves in Thyroid Surgery.

OBJECTIVE: To study terminal bifurcation of recurrent laryngeal nerves (RLNs) with original direction to larynx entry and to decrease the risk of vocal cord paralysis in thyroid patients. METHODS: The RLNs of 294 patients (482 sides) were dissected according to the branches into the larynx, and the original direction of each RLN trunk in thyroid surgery was recorded. RESULTS: (1) About 30.9% of the RLNs gave off multiple branches into the larynx. (2) Two and 3 branches of RLNs into the larynx were found in 25.5% and 5.4% of the cases, respectively. (3) In 0.4% or 2 cases, the RLN trunk combined with the inferior branch of the vagus nerve. (4) Nonrecurrent laryngeal nerve appeared in 2 cases. (5) On the left side, 68.0%, 25.6%, and 6.4% of cases were found with 1, 2, and 3 bifurcations of RLN to larynx entry, respectively. On the right side, 69.8%, 25.8%, and 4.4% cases were identified with 1, 2, and 3 bifurcations of RLN to larynx entry, respectively. (6) The combining dissection approach was proved as successful and safe for protecting the RLN with no permanent RLN paresis. CONCLUSIONS: Because of the anatomical variation in RLNs with extralaryngeal bifurcation, it is necessary to increase the awareness of surgeons about these variations so as to protect bifurcated nerves in thyroid surgery.

Two Concomitant Right Nonrecurrent Laryngeal Nerves Encountered During Thyroidectomy (Type 4 Course): Reported for the First Time.

INTRODUCTION: The recurrent laryngeal nerve gains its name because after branching from the vagus nerve, it turns superiorly (recur) around the subclavian artery on the right and around the ligamentum arteriosum on the left, the nonrecurrent nerve has a straight direct course to the larynx and doesn't follow this course. It presents mostly on the right side. The presence of this variation places the nerve at higher risk of injury during neck surgery especially thyroid operations. CASE PRESENTATION: A 45-year-old lady presented with painless thyroid enlargement for 1 year. Thyroid examination showed a 3-cm firm nodule at the right thyroid lobe with normal thyroid function tests. Right thyroid lobectomy was done and the histopathology showed a benign follicular lesion. During surgery, we discovered 2 nonrecurrent laryngeal nerves at the right side which were arising from the vagus nerve and both were entering the larynx. CONCLUSION: Failure in identification of the nerve or overlooking the possibility of the non-recurrent laryngeal nerve may result in a serious sequelae of nerve damage, ipsilateral injury may lead to permanent hoarseness and bilateral injury may result in severe dyspnea or aphonia. Currently, there are 3 types of nonrecurrent laryngeal nerve courses. Type 1 passes near to the superior thyroid vessels. Type 2 (2A) passes parallel to the inferior thyroid artery and has a transverse course above it. Type 3 (2B) passes parallel to the inferior thyroid artery and transversely between branches of or under the inferior thyroid artery, we can add to this classification type 4, which are 2 nonrecurrent laryngeal nerves (double nerves) passing above and parallel to the inferior thyroid artery.

The Internal Superior Laryngeal Nerve in Humans: Evidence for Pure Sensory Function.

OBJECTIVES: To determine if the internal branch of the superior laryngeal nerve (iSLN) provides direct motor innervation to the interarytenoid muscle, a laryngeal adductor critical for airway protection. We studied the iSLN-evoked motor response in the interarytenoid and other laryngeal muscles. If the iSLN is purely sensory, there will be no detectable short latency motor response upon supramaximal stimulation, indicating the absence of a direct efferent conduction path. STUDY DESIGN: Intraoperative case series. METHODS: In seven anesthetized patients undergoing laryngectomy for unilateral laryngeal carcinoma, the iSLN of the unaffected side was electrically stimulated intraoperatively with 0.1-ms pulses of progressive intensities until supramaximal stimulation was reached. Electromyographic responses were measured in the ipsilateral interarytenoid, thyroarytenoid, and cricothyroid muscles. RESULTS: None of the subjects exhibited short-latency interarytenoid motor responses to iSLN stimulation. Supramaximal electrical stimulation of the intact iSLN evoked ipsilateral motor responses with long latencies: 18.7-38.5 ms in the interarytenoid (n = 6) and 17.8-24.9 ms in the thyroarytenoid (n = 5). Supramaximal stimulation of the recurrent laryngeal nerve evoked ipsilateral motor responses with short latencies: 1.6-3.9 ms in the interarytenoid (n = 6) and 1.6-2.7 ms in the thyroarytenoid (n = 6). CONCLUSION: The iSLN provides no functional efferent motor innervation to the interarytenoid muscles. The iSLN exclusively evokes an interarytenoid motor response via afferent activation of central neural circuits that mediate the laryngeal reflex arc. These findings suggest that the role of the iSLN in vital laryngopharyngeal functions, such as normal swallowing and protection of the airway from aspiration, is purely sensory. LEVEL OF EVIDENCE: 4 Laryngoscope, 131:E207-E211, 2021.

Anatomía topográfica del nervio laríngeo superior: importancia quirúrgica en las tiroidectomías / Topographic anatomy of the upper laryngeal nerve: surgical importance in thyroidectomies

En las cirugías sobre la glándula tiroides se ha prestado mucha atención al manejo del nervio laríngeo inferior y de las glándulas paratiroides, no así del ramo lateral del nervio laríngeo superior, el cual es satélite del pedículo vascular superior de la glándula tiroides. El manejo del polo superior de la glándula tiroides requiere de un conocimiento acabado de su anatomía topográfica del área y está determinada por sus relaciones más importantes, dadas por el citado nervio y la arteria tiroidea superior principalmente. En este trabajo se pretende estudiar estas relaciones en base a la disección meticulosa del triángulo laringo-esternotiroideo ("Triángulo de Joll") de 25 cadáveres adultos formolizados. Como hallazgo relevante se informa que los "nervios en riesgo", según la clasificación de Cernea, que se basa en una distancia menor a un centímetro en el entrecruzamiento del nervio con la arteria tiroidea superior con respecto al polo superior de la glándula tiroides, es del 52 % para el lado derecho y 44 % para el lado izquierdo del cuello. El origen bajo de la arteria a nivel de la bifurcación carotídea se presenta asociada a un mayor número de "nervios en riesgo" en el lado izquierdo. Según el punto de penetración del ramo lateral del nervio laríngeo superior en el músculo constrictor inferior de la faringe se establece la clasificación de Friedman, muy útil sobre todo en cirugías ayudadas por la neuroestimulación. En esta clasifiacción los "nervios en riesgo" son aquellos que transcurrren superficial al músculo, mientras que los "nervios protegidos" serían aquellos que perforan el músculo en su porción superior. En este trabajo los "nervios en riesgo" se presentaron del lado izquierdo en el 56 % de los casos y del derecho en el 60 %, mientras que los "nervios protegidos" en el 24 % y 16 %, respectivamente.

In surgeries on the thyroid gland, much attention has been given to the management of the inferior laryngeal nerve and parathyroid glands, but not the external branch of the given by the aforementioned nerve and the superior thyroid artery. This paper intends to study these relationships based on the meticulous dissection of the larynx-sternothyroid triangle ("Joll triangle") of 25 formolized adult corpses. As a relevant finding, it is reported that the " nerves at risk" according to the Cernea classification, which is based on the distance less than one centimeter at the intersection of the nerve with the superior thyroid artery with respect to the upper pole of the gland, is 52 % for the right side and 44 % for the left side of the neck. The low origin of the artery at the level of the carotid bifurcation is associated with a greater number of "nerves at risk" on the left side. According to the penetration point of the external branch of the superior laryngeal nerve in the inferior pharyngeal constrictor muscle, the Friedman classification is established, very useful especially in surgeries aided by neurostimulation. In this classification the "nerves at risk" are those that run superficially to the muscle, while the protected nerves would be those that pierce the muscle in its upper part. In tis work, the "nerves at risk" presented on the left side in 56 % of the cases and the right side in 60 %, while those "protected" in 24 % and 16 % respectively.

Anatomía quirúrgica de las glándulas tiroides y paratiroides / Surgycal anatomy of the thyroid and parathyroid glands

Nuestro objetivo es lograr un relato de los detalles anatómicos que ayude al cirujano a conseguir intervenciones seguras, se elude el estilo de las anatomías descriptivas o topográficas tratando de producir una anatomía verdaderamente quirúrgica. Para ello se mencionan las fascias, estructuras capsulares y ligamentos que envuelven a la tiroides. Se hace hincapié en la vascularización, principalmente en lo referente a la arteria tiroidea inferior, fundamental para la localización del nervio recurrente. También en lo relacionado con el conjunto del drenaje venoso, que con su complicada distribución dificulta notablemente la disección. Relatamos minuciosamente las variantes anatómicas y las anomalías que afectan a la estructura de la región, su conocimiento es fundamental ante la posibilidad de que el cirujano encuentre en sus operaciones alguna de ellas. Describimos el aspecto, las relaciones y lo referente a la localización de las glándulas paratiroides, detalles necesarios para evitar su resección inopinada en las tiroidectomías y para el reconocimiento de la glándula patológica en el hiperparatiroidismo

The aim of this article is describe the anatomical details that helps the surgeon to achieve safe surgeries, the style of descriptive or topographic anatomies is avoided trying to produce a truly surgical anatomy. For this, fascias, capsular structures and ligaments that surround the thyroid gland are mentioned. Emphasis is placed on vascularization, mainly in relation to the inferior thyroid artery, essential for the location of the recurrent nerve. Also in relation to the whole of the venous drainage, which with its complicated distribution makes dissection remarkably difficult. We carefully describe the anatomical variants and the anomalies that affect the structures of the region, their knowledge is fundamental to the possibility that the surgeons finds in their surgeries. We describe the appearance, the relationships and the reference to the location of the parathyroid glans. Neccesary details to avoid their inopinate resection in thyroidectomies and for the recognition of the pathological gland in the hyperparathyroidism

The Human Laryngeal Innervation Revisited-The Role of the Neural Connections.

In spite that vascular inconvenients or immunological rejections have been solved in relation with larynx transplant, a successful functional reinnervation has not been achieved. Some studies have suggested that laryngeal nerve connection may contain motor fibers, which could explain unexpected evoked responses in electromyographic studies or the different positions adopted of the vocal folds after similar nerve lesions. Ten patients with unexpected evoked responses after laryngeal nerve stimulation were selected. All the patients underwent a total laryngectomy due to oncological causes. In every case, laryngeal nerve connections were observed. All of them were morphologic and histologic processed for choline-acetyltransferase immunohistochemistry. The presence of motor axons in the nerve connections has been demonstrated, which would explain that the motor innervation to the laryngeal muscles could be dual through these variable connections. This also would justify the difficulty of carrying out laryngeal nerve reinnervation procedures. Anat Rec, 302:646-651, 2019. © 2018 Wiley Periodicals, Inc.

Selective laryngeal reinnervation: can rerouting of the thyrohyoid nerve simplify the procedure by avoiding the use of a nerve graft?

PURPOSE: The objective of this study was to record the descriptive and metric anatomical characteristics of the thyrohyoid nerve with the aim of rerouting it in a selective laryngeal reinnervation procedure. METHODS: An anatomical study was performed on ten formalin-embalmed cadavers. The origin of the thyrohyoid nerve and the superior root of the ansa cervicalis, the location of the thyrohyoid nerve ending in the thyrohyoid muscle, and the recurrent laryngeal nerve were established. Then, a rerouting of the thyrohyoid nerve was performed. We measured the length of thyrohyoid nerve, the distance between the thyrohyoid nerve ending and the recurrent laryngeal nerve at the horizontal level of the cricothyroid joint before and after the rerouting, and the distance between the origin of the thyrohyoid nerve and the superior root of the ansa cervicalis. RESULTS: The thyrohyoid nerve was identified on both sides in all the cases. The average length of the thyrohyoid nerve was 27 mm. The end of the thyrohyoid nerve was found in 100% of the cases at the upper outer quarter of the thyrohyoid muscle. After the rerouting, an average reduction of 30% of the distance between the end of the thyroid nerve and the recurrent laryngeal nerve at the horizontal level of the cricothyroid joint was measured. CONCLUSION: The rerouting of the thyrohyoid nerve provided a reduction in the length of the nerve graft in laryngeal reinnervation. Moreover, the constancy of the thyrohyoid nerve and its characteristics make it a valuable anatomical base for laryngeal reinnervation and laryngeal innervated allotransplantation.

Diagnosis, anatomy, and electromyography profiles of 73 nonrecurrent laryngeal nerves.

BACKGROUND: The purpose of this work was to compare methods of detecting nonrecurrent laryngeal nerves (NRLNs). METHODS: Specificity and sensitivity were compared in three NRLN detection methods: CT, electromyography (EMG), and A-B point comparison. RESULTS: A total of 73 intraoperative pictures and 36 CT details of NRLNs are presented. Incidence of NRLN was 0.39%. Type I NRLN accounted for 50.7%, type IIA 45.2%, type IIB 4.1%. The NRLN median latency was 2.13 ms vs 3.00 ms median in an RLN control group (P < .001). When the threshold was set to 2.5 ms, EMG latency detection had 96.7% sensitivity and 91.6% specificity for detecting NRLN, and the A-B point comparison algrithm had 97.3% sensitivity and 92.5% specificity. Combining EMG latency detection with A-B point comparison achieved 100% sensitivity and specificity for detecting NRLN. CONCLUSION: This is the largest series of NRLN presented in the literature. Latency shorter than 2.50 ms combined with the A-B point comparison method is the ideal algorithm procedure for early NRLN identification.

Surgical anatomy of the external branch of the superior laryngeal nerve: a systematic review and meta-analysis.

PURPOSE: To provide a comprehensive evidence-based assessment of the anatomical characteristics of the external branch of the superior laryngeal nerve (EBSLN). MATERIALS AND METHODS: A thorough systematic search was performed on the major electronic databases PubMed, EMBASE, Cochrane library, and ScienceDirect to identify eligible studies. Data were extracted and pooled into a meta-analysis. The primary outcomes were the EBSLN identification rate (total number of EBSLN identified divided by the total number of dissected hemilarynges) and the prevalence of various EBSLN types. RESULTS: A total of 56 studies (n = 13,444 hemilarynges) were included. The overall pooled EBSLN identification rate was 89.24% (95% CI 85.49-92.49). This rate was higher for cadaveric (95.00%; 95% CI 89.73-99.35) compared to that reported in intraoperative studies (86.99%; 95% CI 82.37-91.01). Significantly higher identification rates were reported for studies in which intraoperative nerve monitoring was used (95.90%; 95% CI 94.30-97.25) compared to those which only relied on direct visual identification of the EBSLN (76.56%; 95% CI 69.34-83.08). Overall, Cernea type IIa (nerves crossing the superior thyroid artery less than 1 cm above the upper edge of the superior thyroid pole) and Friedman type 1 (nerves running their entire course superficial to the inferior pharyngeal constrictor) were the most prevalent (41.84%; 95% CI 33.28-48.08 and 50%; 95% CI 29.90-65.62, respectively). The combined prevalence of Cernea IIa and IIb (nerves crossing the superior thyroid artery below the upper edge of the superior thyroid pole) was higher in intraoperative studies compared to that in cadaveric studies (64.3% vs 49.4%). The EBSLN coursed medial to the superior thyroid artery in 70.98% (95% CI 55.14-84.68) of all cases. CONCLUSION: The use of intraoperative nerve monitoring improves EBSLN identification rates. In light of the highly variable anatomical patterns displayed by the EBSLN, thorough pre-operative knowledge of its anatomy can be crucial in minimizing incidences of its iatrogenic injury.

Origin of superior thyroid artery: under the surgeon's knife / Origem da artéria tireoidea superior: sob o bisturi do cirurgião

The major arterial supply to the thyroid gland is from the superior and inferior thyroid arteries, arising from the external carotid artery and the thyrocervical trunk respectively. The external laryngeal nerve runs in close proximity to the origin of the superior thyroid artery in relation to the thyroid gland. The superior thyroid artery is clinically important in head and neck surgeries. Objectives: To locate the origin of the superior thyroid artery, because wide variability is reported. To provide knowledge of possible variations in its origin, because it is important for surgical procedures in the neck. Methods: The origin of the superior thyroid artery was studied by dissecting sixty adult human hemineck specimens from donated cadavers in a Department of Anatomy. Results: The highest incidence observed was origin of the superior thyroid artery from the external carotid artery (88.33%), whereas origin from the common carotid bifurcation only occurred in 8.33%. However, in 3.33% of cases, the superior thyroid artery originated from the common carotid artery and in a single case, the external laryngeal nerve did not cross the stem of the superior thyroid artery at all, but ran ventral and parallel to the artery. Conclusions: It is important to rule out anomalous origin of superior thyroid artery and verify its relationship to the external laryngeal nerve prior to ligation of the artery in thyroid surgeries, in order to prevent iatrogenic injuries. Moreover, because anomalous origins of the superior thyroid artery are only anatomic variants, thorough knowledge of these is decisive for head and neck surgeries

O suprimento arterial principal para a glândula tireoide provém das artérias tireoideas superior e inferior, que têm origem na artéria carótida externa e no tronco tireocervical, respectivamente. O nervo laríngeo externo faz um percurso bem próximo à origem da artéria tireoidea superior em relação à glândula tireoide. A artéria tireoidea superior é clinicamente importante em cirurgias da cabeça e do pescoço. Objetivos: Localizar a origem da artéria tireoidea superior, considerando a ampla variabilidade descrita na literatura; e oferecer informações sobre possíveis variações em sua origem, devido à importância disso para procedimentos cirúrgicos realizados no pescoço. Métodos: A origem da artéria tireoidea superior foi estudada dissecando-se 60 espécimes de hemipescoço adulto de cadáveres humanos doados ao Departamento de Anatomia. Resultados: A maior incidência observada foi da artéria tireoidea superior com origem na artéria carótida externa (88,33%), enquanto a origem na bifurcação da artéria carótida comum ocorreu em apenas 8,33%. No entanto, em 3,33% dos casos, a artéria tireoidea superior teve origem na artéria carótida comum, e em um único caso, o nervo laríngeo externo não cruzou o tronco da artéria tireoidea superior em nenhum momento, embora tenha cursado ventral e paralelamente a essa artéria. Conclusões: É importante descartar origem anômala da artéria tireoidea superior e confirmar sua relação com o nervo laríngeo externo antes da ligadura da artéria em cirurgias da tireoide, para evitar efeitos iatrogênicos. Além disso, como origens anômalas da artéria tireoidea superior são apenas variantes anatômicas, o conhecimento detalhado dessas variações é decisivo para cirurgias da cabeça e do pescoço

Variations of the origin of superior thyroid artery and its relationship with the external branch of superior laryngeal nerve.

INTRODUCTION: The superior thyroid artery, the main atrial supply of neck region, is branched from the external carotid artery as a first branch, but it may also arise from the common carotid artery and its bifurcation. The external branch of superior laryngeal nerve runs parallel to it and later crossing the artery either above or below the upper pole of the thyroid gland. OBJECTIVE: This study aimed at evaluating the variations of the origin of superior thyroid artery and its relationship with the external branch of the superior laryngeal nerve. METHODS: A descriptive study was conducted on 43 embalmed cadavers. The anterior triangle of the neck region was dissected bilaterally. The presence or absence of STA and its origin, branching pattern, relationship with the external branch of the superior laryngeal nerve, level of origin in relation to the lamina of the thyroid cartilage and level of carotid bifurcation were observed and recorded. RESULT: The superior thyroid artery arises from the external carotid artery in 44.2%, common carotid bifurcation in 27.9% and common carotid artery in 26.7% of cadavers. In one of the cadaver, the superior thyroid artery arises from lingual artery. The origin of superior thyroid artery was significantly associated with its branching pattern and level of common carotid artery bifurcation. The mean distance from the upper pole of the thyroid gland to the level where an external branch of superior laryngeal nerve turns medially from superior thyroid artery was found to be 1.04cm. CONCLUSION: The wide range of variations of the superior thyroid artery on its origin and relationship with adjacent structures is a common phenomenon. The clinicians should be aware of those variations.

External laryngeal nerve landmarks revisited.

BACKGROUND: Because external laryngeal nerve (ELN) iatrogenic damage is frequent during neck surgery, its precise localization has been highly recommended. This study analyzes the different surgical landmarks previously proposed and the anatomy of the collateral and terminal branches of the ELN. METHODS: The necks of 157 (77 men and 80 women) human adult embalmed cadavers were examined. The ELN origin, length, and relationship to different landmarks were recorded and results statistically compared with those previously reported. RESULTS: The ELN is located deep to the ascending pharyngeal vein in 100% of patients. In most patients, it crosses the carotid axis at the thyroid artery origin level (47% of patients), passes medial to it (89% of patients), and shows an intramuscular trajectory through the inferior constrictor of the pharynx (80% of patients). CONCLUSION: The ELN position, in relation to classical landmarks, is highly variable. The most reliable relationships are those with the ascending pharyngeal vein or with the superior thyroid artery.