Subglottic region: normal topography and possible clinical implications

High-Resolution Profiling of Human Vocal Fold Cellular Landscapes With Single-Nuclei RNA Sequencing

INTRODUCTION

The function of the vocal folds (VFs) is determined by the phenotype, abundance, and distribution of differentiated cells within specific microenvironments. Identifying this histologic framework is crucial in understanding laryngeal disease. A paucity of studies investigating VF cellular heterogeneity has been undertaken. Here, we examined the cellular landscape of human VFs by utilizing single-nuclei RNA-sequencing.

METHODS

Normal true VF tissue was excised from five patients undergoing pitch elevation surgery. Tissue was snap frozen in liquid nitrogen and subjected to cellular digestion and nuclear extraction. Nuclei were processed for single-nucleus sequencing using the 10X Genomics Chromium platform. Sequencing reads were assembled using cellranger and analyzed with the scanpy package in python.

RESULTS

RNA sequencing revealed 18 global cell clusters. While many were of epithelial origin, expected cell types, such as fibroblasts, immune cells, muscle cells, and endothelial cells were present. Subcluster analysis defined unique epithelial, immune, and fibroblast subpopulations.

CONCLUSION

This study evaluated the cellular heterogeneity of normal human VFs by utilizing single-nuclei RNA-sequencing. With further confirmation through additional spatial sequencing and microscopic imaging, a novel cellular map of the VFs may provide insight into new cellular targets for VF disease.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:3193-3200, 2024.

Measurement of the lengths of different sections of the upper airway and their predictive factors

BACKGROUND

No studies have been conducted to define the lengths of the upper airway's different segments in normal healthy adults.

AIMS/OBJECTIVES

This study aimed to determine the length of the subglottis and extrathoracic trachea and the factors affecting it.

MATERIAL AND METHODS

This was an observational retrospective review study. Included 102 adult patients who underwent CT scan during the quiet inspiration phase of the upper airway.

RESULTS

The results revealed significant positive linear relationships between height and both anterior and posterior subglottic measurements (p < 0.001). Additionally, a statistically significant, moderately strong negative correlation between age and extrathoracic tracheal measurements (p > 0.001) was observed. Men exhibited longer anterior (p < 0.001) and posterior (p > 0.001) subglottic measurements. In both sexes, the average length of the anterior subglottis was 14.16 (standard deviation [SD]: 2.72) mm, posterior subglottis was 14.51 (SD: 2.85) mm and extrathoracic trachea was 66.37 (SD: 13.71) mm.

CONCLUSION AND SIGNIFICANCE

We concluded that a normal healthy adult's anterior subglottis length is 6.3-19.3 mm (mean: 14.16 [SD: 2.72] mm), posterior subglottis length is 6.1-20.0 mm (mean: 14.51 [SD: 2.85] mm) and extrathoracic trachea length is 25.2-98.5 mm (mean: 66.37 [SD: 13.71] mm). Age, height and sex affected the upper airway length.

CT and MR anatomy of the larynx and hypopharynx

Imaging of the larynx and hypopharynx is frequently requested to assess the extent of neoplasms beyond the field of view of endoscopic evaluation. The combination of optical and cross-sectional imaging allows tumors to be classified according to AJCC/UICC guidelines. A thorough understanding of laryngeal and hypopharyngeal anatomy is crucial to guide the radiological eye along the possible pathways of the spread of diseases and to guide differential diagnoses. Computed tomography (CT) has been the first cross-sectional imaging technique used to evaluate the larynx and hypopharynx; its spatial resolution combined with volumetric capability and the use of injectable contrast medium made CT the working horse in the assessment of neoplastic and inflammatory diseases. In the last two decades, magnetic resonance (MR) supported CT in the most challenging cases, when the optimal contrast resolution due to the multisequence portfolio is needed to assess the neoplastic involvement of laryngeal cartilages, paraglottic space(s), and extra laryngeal spread. The aim of this paper is to give a comprehensive radiological overview of larynx and hypopharynx complex anatomy, combining in vivo images, anatomical sections, and images of ex vivo specimens.

Establishment of an immortalized human subglottic epithelial cell line

Objective

Translational research into subglottic disease is restricted by the availability of primary human tissue originating from this subsite. Primary epithelial cells are also limited by their inability to survive beyond several divisions in culture outside of the body. Specific subglottic cell lines, useful for in vitro studies, have not yet been described. We therefore demonstrate what we believe to be the first immortalized subglottic epithelial cell line.

Methods

Subglottic tissue was derived from a single adult patient's neoplasia‐free human subglottic brushing specimen. Cells were immortalized using a lentiviral vector expressing simian virus 40 T antigen. Karyotyping was performed on the transformed cells using single nucleotide polymorphism array comparative genomic hybridization. Transformed cells were phenotypically characterized by light microscopy, immunohistochemistry, and electrophysiology studies.

Results

The immortalized subglottic cell line (SG01) was able to divide successfully beyond 20 passages. Karyotyping demonstrated no significant genomic imbalance after immortalization. The cells demonstrated normal epithelial morphology and cytokeratin expression throughout. SG01 cells were also successfully cultured at air–liquid interface (ALI). At ALI cells demonstrated cilia, mucus production, and relevant ion channel expression.

Conclusion

The novel SG01 subglottic epithelial cell line has been established. This cell line provides a unique resource for researchers to investigate subglottic diseases, such as subglottic stenosis.

Level of Evidence

NA. Laryngoscope, 129:2640–2645, 2019

Depth-kymography: high-speed calibrated 3D imaging of human vocal fold vibration dynamics

We designed and developed a laser line-triangulation endoscope compatible with any standard high-speed camera for a complete three-dimensional profiling of human vocal fold vibration dynamics. With this novel device we are able to measure absolute values of vertical and horizontal vibration amplitudes, length and width of vocal folds as well as the opening and closing velocities from a single in vivo measurement. We have studied, for the first time, the generation and propagation of mucosal waves by locating the position of its maximum vertical position and the propagation velocity. Precise knowledge about the absolute dimensions of human vocal folds and their vibration parameters has significant importance in clinical diagnosis and treatment as well as in fundamental research in voice. The new device can be used to investigate different kinds of pathological conditions including periodic or aperiodic vibrations. Consequently, the new device has significant importance in investigating vocal fold paralysis and in phonosurgical applications.

The glottis and subglottis: an otolaryngologist's perspective

The complexity of the glottic and subglottic region in terms of anatomy and function make this region challenging in evaluation and treatment. A thorough understanding of the complex anatomy is necessary for the management of patients who have dysphonia, vocal fold paralysis, glottic or subglottic stenosis, or complications, which may present after prolonged intubation or surgical interventions in the upper airway and the thorax.

Anatomical definition of the subglottic region

BACKGROUND

Due to laryngeal neoplasia, as well as infectious and autoimmune diseases, the subglottic region is of great clinical relevance. However, descriptions of the subglottic structures are inconsistent. The aim of our study was to present a precise analysis of the subglottic region and derive functional and clinical conclusions.

METHODS

Histological, histochemical and immunohistochemical investigations as well as scanning electron microscopy were performed and combined with injection techniques applied to the subglottic region of the larynges of 33 body donors.

RESULTS

The three-dimensional extensions of the subglottic region were newly defined: the inferior arcuate line of the vocal cord was defined as the cranial border. The lower margin of the cricoid is the caudal border. Craniolaterally, the elastic cone and, further caudally, the cricoid form the border. Therefore, the definition presented comprises heretofore unnamed ventral and dorsal parts of the lower larynx. The subglottic region can be described as cylindrical, becoming smaller in the cranial direction, following the elastic cone. The ventral boundary is formed by the median part of the cricothyroid ligament (ligamentum conicum), the dorsal part by the cricoid cartilage. The walls of the subglottis are divided into three or four layers composed of collagenous and elastic fibres in which seromucous glands are embedded. Subglottic blood vessels including a tight subepithelial capillary plexus were delineated.

CONCLUSION

The new definition of the subglottic extensions presented is helpful and essential for precise laryngeal tumour classification. The results indicate that the boundaries are unlikely to counteract tumour progression in the subglottis. Furthermore, the findings suggest that these structures contribute to temperature regulation of breath, protection against inflammation as well as breath frequency and depth-dependent mucus secretion.

Cricothyroidotomy: A clinical anatomy review

The safe and successful performance of a cricothyroidotomy demands a working and yet specific knowledge of anatomy. An ignorance or misunderstanding of anatomy may result in failure or complications. The Educational Affairs Committee of the American Association of Clinical Anatomists has highlighted the importance of clinical anatomy for several invasive procedures. This review is building on their work and contribute further to the understanding of the anatomical framework, particularly the pitfalls and complications related to performing a cricothyroidotomy.

Transoral laser microresection for cancer of the larynx involving the anterior commissure

OBJECTIVE

To share the authors' experience of transoral laser microresection in the treatment of squamous cell carcinoma of the anterior commissure of the larynx.

STUDY DESIGN

Retrospective review of 39 patients with squamous carcinoma involving the anterior commissure of the larynx, all managed with transoral laser microresection between September 1996 and December 2001. Twenty-three patients had pT1 or pT2 cancers. Sixteen patients had pT3 or pT4 disease, two with N2b neck metastases. Twenty patients had cancers exhibiting spread to the subglottis. Twenty-five patients had received prior treatment(s).

METHODS

Specific data points entered into a portable database were retrospectively verified against the patient's electronic medical record. Sorting and analysis were completed in a desktop spreadsheet. We evaluated tumor recurrence, cause of death, tracheostomy, hospital length of stay, and voice quality.

RESULTS

None of the 17 patients with early cancers (pT1 or pT2a) had local recurrence, and none received postoperative radiotherapy. Five of the 22 patients with intermediate or advanced disease (pT2b/pT3 or pT4 cancer) required second treatments for persistent or recurrent disease. Of these, two had small residual foci amenable to second-stage resection by laser. One patient developed a prelaryngeal soft tissue recurrence and retained his larynx after wide local excision and radiotherapy. Two patients (both previously irradiated) developed delayed recurrences requiring total laryngectomy. Four retreated patients remained alive without disease. One patient died of other causes. Voice remained no worse after transoral laser microresection in 19 patients. It was one level worse (on a scale of 0 to 5) for 16 patients. Eleven patients received temporary tracheotomies, some for airway, some for exposure. Twelve patients left the hospital on a same-day basis. The average hospital stay was 3.3 days.

CONCLUSION

Transoral laser microsurgery is one of the options to be considered for the treatment of squamous cell cancer involving the anterior commissure of the larynx.

Results of radiotherapy for primary subglottic squamous cell carcinoma

PURPOSE

To retrospectively evaluate the outcome after radical radiotherapy (RT) and surgical salvage and assess the risk of late toxicity for patients with primary subglottic squamous cell carcinoma treated at our center.

METHODS AND MATERIALS

Between 1971 and 1996, 43 patients with primary squamous cell carcinoma of the subglottis (35 men, 8 women) were treated with radical RT. All received megavoltage irradiation, most commonly to a dose of 50-52 Gy in 20 fractions during 4 weeks (39 patients). The median follow-up was 4.2 years.

RESULTS

Local control was achieved with RT alone in 24 (56%) of the 43 patients: 7 of 11 with T1, 8 of 12 with T2, 4 of 8 with T3, and 5 of 12 with T4. The 5-year actuarial local relapse-free rate was 52%. Subsequent local control was achieved in 11 of the 13 patients with failed RT and attempted surgical salvage, for an ultimate local control rate of 81.4% (35 of 43). The 5-year overall and cause-specific actuarial survival rate was 50.3% and 66.9%, respectively. No patients developed Grade 3 or 4 late radiation morbidity.

CONCLUSION

These data support the use of primary RT in the treatment of patients with primary squamous cell carcinoma of the subglottis as an appropriate treatment approach providing an option for laryngeal conservation.

Regulation of vocal fold transepithelial water fluxes

Vocal fold hydration is critical to phonation. We hypothesized that the vocal fold generates bidirectional water fluxes, which are regulated by activity of the Na(+)-K(+)- ATPase. Western blots and immunohistochemistry demonstrated the presence of the alpha-subunit Na(+)-K(+)-ATPase in the canine vocal fold (n = 11). Luminal cells, basal and adjacent one to two layers of suprabasal cells within stratified squamous epithelium, were immunopositive, as well as basolateral membranes of submucosal seromucous glands underlying transitional epithelia. Canine (n = 6) and ovine (n = 14) vocal fold mucosae exhibited transepithelial potential differences of 8.1 +/- 2.8 and 9.3 +/- 1.3 mV (lumen negative), respectively. The potential difference and short-circuit current (ovine = 31 +/- 4 microA/cm(2); canine = 41 +/- 10 microA/cm(2)) were substantially reduced by luminal administration of 75 microM acetylstrophanthidin (P < 0.05). Ovine (n = 7) transepithelial water fluxes decreased from 5.1 +/- 0.3 to 4.3 +/- 0.3 microl x min(-1) x cm(-2) from the basal to luminal chamber and from 5.2 +/- 0.2 to 3.9 +/- 0.3 microl x min(-1) x cm(-2) from the luminal to basal chamber by luminal acetylstrophanthidin (P < 0.05). The presence of the Na(+)-K(+)-ATPase in the vocal fold epithelium and the electrolyte transport derived from its activity provide the intrinsic mechanisms to regulate cell volume as well as vocal fold hydration.