Microsurgical anatomy of the superior and recurrent laryngeal nerves

Screening for Vocal Fold Movement Impairment in Children Undergoing Esophageal and Airway Surgery

INTRODUCTION

Children undergoing cervical and/or thoracic operations are at risk for recurrent laryngeal nerve injury, resulting in vocal fold movement impairment (VFMI). Screening for VFMI is often reserved for symptomatic patients.

OBJECTIVE

Identify the prevalence of VFMI in screened preoperative patients prior to an at-risk operation to evaluate the value of screening all patients at-risk for VFMI, regardless of symptoms.

METHODS

A single center, retrospective review of all patients undergoing a preoperative flexible nasolaryngoscopy between 2017 and 2021, examining the presence of VFMI and associated symptoms.

RESULTS

We evaluated 297 patients with a median (IQR) age of 18 (7.8, 56.3) months and a weight of 11.3 (7.8, 17.7) kilograms. Most had a history of esophageal atresia (EA, 60%), and a prior at-risk cervical or thoracic operation (73%). Overall, 72 (24%) patients presented with VFMI (51% left, 26% right, and 22% bilateral). Of patients with VFMI, 47% did not exhibit the classic symptoms (stridor, dysphonia, and aspiration) of VFMI. Dysphonia was the most prevalent classic VFMI symptom, yet only present in 18 (25%) patients. Patients presenting with a history of at-risk surgery (OR 2.3, 95%CI 1.1, 4.8, p = 0.03), presence of a tracheostomy (OR 3.1, 95%CI 1.0, 10.0, p = 0.04), or presence of a surgical feeding tube (OR 3.1, 95%CI 1.6, 6.2, p = 0.001) were more likely to present with VFMI.

CONCLUSION

Routine screening for VFMI should be considered in all at-risk patients, regardless of symptoms or prior operations, particularly in those with a history of an at-risk surgery, presence of tracheostomy, or a surgical feeding tube.

LEVEL OF EVIDENCE

3 Laryngoscope, 133:3564-3570, 2023.

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.

Mediastinal anatomical landmarks, their variants and tips for video-assisted thoracoscopic navigation during oesophageal extirpation

Purpose

There is no systematic description of primary anatomical landmarks that allow a surgeon to reliably and safely navigate the superior and posterior mediastinum’s fat tissue spaces near large vessels and nerves during video-assisted endothoracoscopic interventions in the prone position of a patient. Our aim was to develop an algorithm of sequential visual navigation during thoracoscopic extirpation of the esophagus and determine the most permanent topographic and anatomical landmarks allowing safe thoracoscopic dissection of the esophagus in the prone position.

Methods

The anatomical study of the mediastinal structural features was carried out on 30 human cadavers before and after opening the right pleural cavity.

Results

For thoracoscopic extirpation of the esophagus in the prone position, anatomical landmarks are defined, their variants are assessed, and an algorithm for their selection is developed, allowing their direct visualization before and after opening the mediastinal pleura.

Conclusion

The proposed algorithm for topographic and anatomical navigation based on the key anatomical landmarks in the posterior mediastinum provides safe performance of the video-assisted thoracoscopic extirpation of the esophagus in the prone position.

Pediatric Unilateral Vocal Fold Immobility

Vocal fold immobility in children can affect breathing, swallowing, and speech function. Although sometimes idiopathic, it is often caused by injury to the recurrent laryngeal nerve during cardiac surgery. A detailed history and physical examination can identify risk factors, which affect the rate of resolution and overall prognosis. Fiberoptic laryngoscopy can be used to confirm the diagnosis and evaluate laryngeal anatomy. Many treatment options exist to improve function and quality of life, including vocal fold injection and laryngeal innervation. [Pediatr Ann. 2021;50(7):e286-e291.].

Unmapped landmarks around branches of the Superior Laryngeal Nerve: An exploratory cadaveric study

Objectives

Preserving the External Branch of Superior Laryngeal Nerve (EBSLN) and Internal Branch of Superior Laryngeal Nerve (IBSLN) is essential during thyroidectomy. However, due to potential distortions caused by large goitres, the present anatomical landmarks used to identify these nerves are flawed. Although under such circumstances, bony landmarks may offer more stable reference points, not much has been explored in this regard. This study measures the distance between the most vulnerable points of the EBSLN and IBSLN and their relatively unexplored bony landmarks, such as the hyoid bone and thyroid notch as well as soft-tissue landmarks like the origin of the Superior Thyroid Artery (STA) and carotid bifurcation.

Methods

An exploratory cadaveric study was conducted in a medical school affiliated with a tertiary care hospital. The detailed analysis included 13 sides from 8 cadavers.

Results

The average distance from the EBSLN piercing site to the greater cornua of the hyoid bone, thyroid cartilage prominence, origin of the STA, and carotid bifurcation was 35.1(±7.2) mm, 33.3(±3.8) mm, 25.7(±6.3) mm, and 31.5(±5.0) mm, respectively and from the IBSLN piercing site was 15.9(±5.9) mm, 32.9(±4.7) mm, 16.3(±4.2) mm, and 20.7(±5.9) mm, respectively. For most cadavers, the distal EBSLN had Cernea type 2a-like relationship with the STA. Certain variations were also observed in the way these nerves branched with respect to the origin of the STA.

Conclusions

This study provides metric information (linear measurements) regarding the distance between the branches of SLN and certain unique landmarks. This could potentially aid in minimising intraoperative trauma to these branches.

Topographic anatomy of the ınternal branch of the superior laryngeal nerve

PURPOSE

The aim of this study was to investigate the surgical and topographical anatomy of the internal branch of the superior laryngeal nerve (ibSLN) in laryngectomy patients.

METHODS

Patients aged 36-90 years old who underwent a total laryngectomy operation with a diagnosis of laryngeal carcinoma participated in the study. Fifteen patients who underwent a total laryngectomy operation between June 2015 and November 2016 were included in the study. A total of 29 superior laryngeal nerves (SLN) of 15 patients were studied. The position of the nerve was photographed before the thyrohyoid membrane (THM) was passed during dissection. The relationship and course of the ibSLN with respect to the superior laryngeal artery (SLA) were observed. The distance to adjacent formations and branching variants were examined along the course of the nerve.

RESULTS

Of the total 29 ibSLN, 17 were divided into three branches and 12 into two branches. In all cases except for one, the ibSLN course after piercing the THM was determined. The ibSLN penetrated the THM at a mean of 12.0 ± 2.61 mm (6-16 mm) from the superior border of the thyroid cartilage. The ibSLN penetrated the THM with a mean distance of 9.34 ± 1.65 (6-12) mm from the inferior border of the hyoid bone.

CONCLUSION

Our study demonstrated the surgical and topographical features of the ibSLN with respect to the THM, and provided a more precise knowledge of its anatomy in laryngectomy patients. It thus may help head and neck surgeons identify this nerve.

Functional vagotopy in the cervical vagus nerve of the domestic pig: implications for the study of vagus nerve stimulation

OBJECTIVE

Given current clinical interest in vagus nerve stimulation (VNS), there are surprisingly few studies characterizing the anatomy of the vagus nerve in large animal models as it pertains to on-and off-target engagement of local fibers. We sought to address this gap by evaluating vagal anatomy in the pig, whose vagus nerve organization and size approximates the human vagus nerve.

APPROACH

Here we combined microdissection, histology, and immunohistochemistry to provide data on key features across the cervical vagus nerve in a swine model, and compare our results to other animal models (mouse, rat, dog, non-human primate) and humans.

MAIN RESULTS

In a swine model we quantified the nerve diameter, number and diameter of fascicles, and distance of fascicles from the epineural surface where stimulating electrodes are placed. We also characterized the relative locations of the superior and recurrent laryngeal branches of the vagus nerve that have been implicated in therapy limiting side effects with common electrode placement. We identified key variants across the cohort that may be important for VNS with respect to changing sympathetic/parasympathetic tone, such as cross-connections to the sympathetic trunk. We discovered that cell bodies of pseudo-unipolar cells aggregate together to form a very distinct grouping within the nodose ganglion. This distinct grouping gives rise to a larger number of smaller fascicles as one moves caudally down the vagus nerve. This often leads to a distinct bimodal organization, or 'vagotopy'. This vagotopy was supported by immunohistochemistry where approximately half of the fascicles were immunoreactive for choline acetyltransferase, and reactive fascicles were generally grouped in one half of the nerve.

SIGNIFICANCE

The vagotopy observed via histology may be advantageous to exploit in design of electrodes/stimulation paradigms. We also placed our data in context of historic and recent histology spanning multiple models, thus providing a comprehensive resource to understand similarities and differences across species.

Analysis of Vocal Fold Motion Impairment in Neonates Undergoing Congenital Heart Surgery

Importance

Vocal fold motion impairment (VFMI) is a known risk factor following congenital heart surgery (CHS). The impact of this diagnosis on utilization and outcomes is unknown.

Objective

To evaluate the cost, postprocedure length of stay (PPLOS), and outcomes for neonates with VFMI after CHS.

Design, Setting, and Participants

A cross-sectional analysis of the 2012 Kids' Inpatient Database (KID) of neonates who underwent CHS was carried out. The KID is an administrative data set of patients, aged 20 years or younger, and contains data on more than 10 million hospitalizations from 44 states. The KID is limited to inpatient hospitalization and contains discharge summary level of data. Patients were limited to those who were born during the hospitalization and those who were aged 28 days or younger at the time of admission for CHS. A weighted total of 4139 neonates who underwent CHS were identified, of which 3725 survived. The proportion of neonates diagnosed with VFMI was 264 (6.92%) of 3725.

Exposures

Congenital heart surgery.

Main Outcomes and Measures

Cost of inpatient hospital stay, postprocedure length of stay, odds of pneumonia, gastrostomy tube placement, and tracheostomy tube placement. Risk-adjusted generalized linear models examined differences in cost and PPLOS between neonates who underwent CHS and were diagnosed with VFMI and those who were not. Risk-adjusted logistic regression compared the odds of selected outcomes (gastrostomy, tracheostomy, pneumonia). Models were weighted to provide national estimates.

Results

Of 3725 neonates (aged 0-28 days), 2203 (59.1%) were male and 1517 (40.7%) were female. Neonates diagnosed with VFMI had significantly higher total cost by $34 000 (95% CI, 2200-65 000) and PPLOS by 9.1 days (95% CI, 4.6-13.7) compared with those who did not. When PPLOS was included as a covariate in the model for cost, presence of VFMI was no longer significant. There were no differences in odds of pneumonia, gastrostomy, or tracheostomy.

Conclusions and Relevance

Vocal fold motion impairment after CHS was associated with significant increases in cost owing to increased PPLOS. These findings provide a foundation to further investigate standardized screening for VFMI following CHS; early identification and treatment may decrease cost and PPLOS.

Preclinical Comparison of Thermal Tissue Effects from Traditional Electrosurgery and a Low-Temperature Electrosurgical Device during Anterior Cervical Discectomy and Fusion

Background

Exposure of the anterior cervical spine requires dissection in proximity to critical neurovascular structures. Monopolar electrosurgical (ES) devices generate heat in contacted tissues, resulting in thermal damage and temperature change. This study examined depth of thermal injury and temperature change associated with use of a low-temperature electrosurgical device (LTD) compared to traditional electrosurgery during a cadaveric anterior cervical discectomy and fusion (ACDF) dissection.

Methods

ACDF was performed, using ES or LTD, on cervical spines (C3-4 and C4-5) from 2 fresh human cadavers with intact neck soft tissues and no history of surgery. Cadavers were maintained at 22-23°C, and fiber-optic temperature sensors (Neoptix, Québec City, Québec, Canada) were placed near relevant structures to measure changes during dissection. Depth of thermal injury was assessed by hematoxylin and eosin and Masson's trichrome histology of fixed tissue specimens.

Results

Use of the LTD resulted in a statistically significant reduction in temperature change at platysma (3.0 ± 1.04 vs. 11.41 ± 3.10°C, P = .003), carotid sheath (7.32 ± 1.13 vs. 15.57 ± 2.56°C, P = .007), and longus colli (6.11 ± 1.32 vs. 12.9 ± 3.62°C, P = .016) compared to ES. Temperature change at the trachea was similar between groups (6.06 ± 1.99 vs. 4.96 ± 1.89°C, P = .528). Histology showed that LTD produced less mean and maximal depth of thermal injury compared to ES (mean: 0.5 vs. 1.2 mm; max: 0.9 vs. 1.8 mm; P < .05).

Conclusions

The results of this pilot study demonstrate that anterior cervical spine exposure using an LTD reduces tissue temperature change and depth of thermal injury compared to ES.

Clinical Relevance

Although exploratory, these results suggest that use of an LTD during ACDF may reduce the extent of thermal tissue injury during dissection. Future studies in live animal models are warranted to determine if thermal injury is a potential cause of common exposure-related complications, such as dysphagia and dysphonia.

Anatomical study of the left superior mediastinal lymphatics for tracheal branches of left recurrent laryngeal nerve-preserving mediastinoscope-assisted surgery in esophageal cancer

PURPOSE

Curative treatment of esophageal cancer requires meticulous superior mediastinal lymphadenectomy, in addition to esophagectomy, because superior mediastinal lymph node metastases are common in esophageal cancer. When preserving the tracheal branches of the left recurrent laryngeal nerve (RLN), good anatomical understanding is required for confirmation of the positional relationships between the courses of lymphatic vessels, lymph node distribution, and the left RLN and its tracheal branches. We performed a detailed anatomical examination of these relationships.

METHODS

Macroscopic anatomical observation and histological examination was performed on cadavers. In addition to hematoxylin and eosin staining, immunostaining using antipodoplanin antibody D2-40 (podoplanin) was performed to identify the lymphatic vessels.

RESULTS

The tracheal branches of the left RLN were clearly observed, but no lymphatic vessels crossing the ventral or dorsal side of the branches were identified either macro-anatomically or histologically.

CONCLUSION

No complex lymphatic network structure straddling the plane composed of tracheal branches of the left RLN was found in the left superior mediastinum. This suggests that dissection of the lymph nodes around the left RLN via the pneumomediastinum method using the left cervical approach may allow preservation of the tracheal branches of the left RLN by maintaining dissection accuracy.

A Multicenter Review of Superior Laryngeal Nerve Injury Following Anterior Cervical Spine Surgery

STUDY DESIGN

A retrospective multicenter case-series study; case report and review of the literature.

OBJECTIVE

The anatomy and function of the superior laryngeal nerve (SLN) are well described; however, the consequences of SLN injury remain variable and poorly defined. The prevalence of SLN injury as a consequence of cervical spine surgery is difficult to discern as its clinical manifestations are often inconstant and frequently of a subclinical degree. A multicenter study was performed to better delineate the risk factors, prevalence, and outcomes of SLN injury.

METHODS

A retrospective multicenter case-series study involving 21 high-volume surgical centers from the AO Spine North America Clinical Research Network. Medical records for 17 625 patients who received subaxial cervical spine surgery from 2005 to 2011 were reviewed to identify occurrence of 21 predefined treatment complications. Descriptive statistics were provided for baseline patient characteristics. A retrospective review of the neurosurgical literature on SLN injury was also performed.

RESULTS

A total of 8887 patients who underwent anterior cervical spine surgery at the participating institutions were screened, and 1 case of SLN palsy was identified. The prevalence ranged from 0% to 1.25% across all centers. The patient identified underwent a C4 corpectomy. The SLN injury was identified after the patient demonstrated difficulty swallowing postoperatively. He underwent placement of a percutaneous gastrostomy tube and his SLN palsy resolved by 6 weeks.

CONCLUSIONS

This multicenter study demonstrates that identification of SLN injury occurs very infrequently. Symptomatic SLN injury is an exceedingly rare complication of anterior cervical spine surgery. The SLN is particularly vulnerable when exposing the more rostral levels of the cervical spine. Careful dissection and retraction of the longus coli may decrease the risk of SLN injury during anterior cervical surgery.

Recovery of laryngeal function after intraoperative injury to the recurrent laryngeal nerve

Loss of function in the recurrent laryngeal nerve (RLN) during thyroid/parathyroid surgery, despite a macroscopically intact nerve, is a challenge which highlights the sensitivity and complexity of laryngeal innervation. Furthermore, the uncertain prognosis stresses a lack of capability to diagnose the reason behind the impaired function. There is a great deal of literature considering risk factors, surgical technique and mechanisms outside the nerve affecting the incidence of RLN paresis during surgery. To be able to prognosticate recovery in cases of laryngeal dysfunction and voice changes after thyroid surgery, the surgeon would first need to define the presence, location, and type of laryngeal nerve injury. There is little data describing the events within the nerve and the neurobiological reasons for the impaired function related to potential recovery and prognosis. In addition, very little data has been presented in order to clarify any differences between the transient and permanent injury of the RLN. This review aims, from an anatomical and neurobiological perspective, to provide an update on the current understandings of surgically-induced injury to the laryngeal nerves.

Bilateral internal superior laryngeal nerve palsy of traumatic cervical injury patient who presented as loss of cough reflex after anterior cervical discectomy with fusion

Injury to the bilateral internal branch of superior laryngeal nerve (ibSLN) brings on an impairment of the laryngeal cough reflex that could potentially result in aspiration pneumonia and other respiratory illnesses. We describe a patient with traumatic cervical injury who underwent bilateral ibSLN palsy after anterior cervical discectomy with fusion (ACDF). An 75-year-old man visited with cervical spine fracture and he underwent ACDF through a right side approach. During the post-operative days, he complained of high pitched tone defect, and occasional coughing during meals. With a suspicion of SLN injury and for the work up for the cause of aspiration, we performed several studies. According to the study results, he was diagnosed as right SLN and left ibSLN palsy. We managed him for protecting from silent aspiration. Swallowing study was repeated and no evidence of aspiration was found. The patient was discharged with incomplete recovery of a high pitched tone and improved state of neurologic status. The SLN is an important structure; therefore, spine surgeons need to be concerned and be cautious about SLN injury during high cervical neck dissection, especially around the level of C3-C4 and a suspicious condition of a contralateral nerve injury.

Variations in the Locations of the Recurrent Laryngeal Nerve in Relation to the Ligament of Berry

Injury to the recurrent laryngeal nerve (RLN) is one of the most common iatrogenic complications of thyroid surgery. The anatomical course of the nerve also increases its susceptibility to injury and many variations have been documented in the literature. The topographical relationship of the RLN to the ligament of Berry has been extensively studied over the past decades. The consensus in the literature is divided with several authors reporting the nerve to be embedded within the ligament and others reporting a constant finding of the nerve being posterolateral to the ligament. A new operative concept has been recently introduced as a possible resolution for the conflicting reports among authors. Further investigations are needed, however, to assess its reliability and overall effects on clinical outcomes.

Endoscopic excision of C2 Osteoid Osteoma: a technical case report

PURPOSE

The Authors illustrate the feasibility of an open biopsy and complete excision of Osteoid Osteoma involving the C2 vertebral body performed via endoscopic anterior cervical approach.

METHODS

A 23-year-old male patient with history of delayed diagnosis of cervical Osteoid Osteoma underwent evaluation and surgical treatment: the minimally invasive procedure and techniques were described. The clinical features, the radiological findings and the outcome were assessed. Complications and local recurrences were also recorded.

RESULTS

There were no intra- or post-operative complications. Immediately after surgery the typical Osteoid Osteoma related pain disappeared. At three years follow-up the patient was asymptomatic and considered disease-free: CT-scan and x-Ray showed no local recurrence and C2-C3 interbody fusion with cervical plate in site.

CONCLUSIONS

The endoscopic transcervical surgery represents an interesting option for the treatment of these diseases in difficult areas of the upper cervical spine, also minimizing soft tissue trauma and collateral damage allows patients a faster and complete return to normal function. To our knowledge this is the first report of cervical spine tumor removal using this minimally invasive approach.

Ultrasound-Guided Bilateral Superior Laryngeal Nerve Block to Aid Awake Endotracheal Intubation in a Patient with Cervical Spine Disease for Emergency Surgery

Ultrasound has been widely used to locate nerves for various nerve blocks. The potential advantages of using ultrasound imaging for nerve blocks include reduction in the amount of local anaesthetic required, improved success rate, reduced time to perform the block and reduced complication rate. We describe the successful performance of ultrasound-guided bilateral superior laryngeal nerve block to facilitate awake fibreoptic intubation in a patient presenting for emergency surgery on the cervical spine.

Cricothyroid muscle function and vocal fold stability in exercising horses

OBJECTIVES

To determine (1) if the cricothyroid muscle had respiratory-related electromyographic (EMG) activity that increased with respiratory effort and (2) if bilateral cricothyroid myotomy resulted in vocal fold instability and collapse in exercising horses.

STUDY DESIGN

Experimental.

ANIMALS

Seven (3 EMG; 4 cricothyroid myotomy) Standardbred horses.

METHODS

Three horses exercised on a treadmill at speeds corresponding to the speed that produced maximum heart rate (HR(max)), 75% of maximum heart rate (HR(75%max)), and 50% of maximum heart rate (HR(50%max)) for 60 seconds at each speed while EMG activity of the cricothyroid muscle and nasopharyngeal pressures were measured. Another 4 normal horses were exercised on the treadmill at HR(max) and HR(75%max) for 60 seconds at each speed before and after bilateral cricothyroid myotomy. Upper airway pressures were measured and videoendoscopic examinations were performed and videotaped at each speed.

RESULTS

Peak phasic EMBG activity of the cricothyroid muscle was coincident with inspiration and increased with treadmill speed. Bilateral cricothyroid myotomy resulted in vocal fold collapse in all horses. Mean peak inspiratory pressures were significantly more negative compared with control values at both HR(max) and HR(75%max).

CONCLUSIONS

Cricothyroid muscle dysfunction may be implicated in vocal fold collapse and likely causes inspiratory airway obstruction in exercising horses.

CLINICAL RELEVANCE

Conditions compromising cricothyroid muscle function or motor innervation could result in vocal fold collapse.

Surgical anatomy of the internal branch of the superior laryngeal nerve

The internal branch of the superior laryngeal nerve (ibSLN) may be injured during anterior approaches to the cervical spine, resulting in loss of laryngeal cough reflex, and, in turn, the risk of aspiration pneumonia. Such a risk dictates the knowledge regarding anatomical details of this nerve. In this study, 24 ibSLN of 12 formaldehyde fixed adult male cadavers were used. Linear and angular parameters were measured using a Vernier caliper, with a sensitivity of 0.1 mm, and a 1 degrees goniometer. The diameter and the length of the ibSLN were measured as 2.1+/-0.2 mm and 57.2+/-7.7 mm, respectively. The ibSLN originates from the vagus nerve at the C1 level in 5 cases (20.83%), at the C2 level in 14 cases (58.34%), and at the C2-3 intervertebral disc level in 5 cases (20.83%) of the specimens. The distance between the origin of ibSLN and the bifurcation of carotid artery was 35.2+/-12.9 mm. The distance between the ibSLN and midline was 24.2+/-3.3 mm, 20.2+/-3.6 mm, and 15.9+/-4.3 mm at the level of C2-3, C3-4, and at the C4-5 intervertebral disc level, respectively. The angles of ibSLN were mean 19.6+/-2.6 degrees medially with sagittal plane, and 23.6+/-2.6 degrees anteriorly with coronal plane. At the area between the thyroid cartilage and the hyoid bone the ibSLN is the only nerve which traverses lateral to medial. It is accompanied by the superior laryngeal artery, a branch of the superior thyroid artery. The ibSLN is under the risk of injury as a result of cutting or compression of the blades of the retractor at this level. The morphometric data regarding the ibSLN, information regarding the distances between the nerve, and the other consistent structures may help us identify this nerve, and to avoid the nerve injury.