Histological structure of vocal fold lamina propria in foetal larynx

Investigation of the Clinical Potential of Polarization-Sensitive Optical Coherence Tomography in a Laryngeal Tumor Model

BACKGROUND

The vocal cord tissue consists of three anatomical layers from the surface to deep inside: the epithelium that contains almost no collagen, the lamina propria that is composed of abundant collagen, and the vocalis muscle layer. It is clinically important to visualize the tissue microstructure using a non-invasive method, especially in the case of vocal cord nodules or cancer, since histological changes in each layer of the vocal cord cause changes in the voice. Polarization-sensitive optical coherence tomography (PS-OCT) enables phase retardation measurement to evaluate birefringence of tissue with varied organization of collagen fibers in different tissue layers. Therefore, PS-OCT can visualize structural changes between normal and abnormal vocal cord tissue.

METHOD

A rabbit laryngeal tumor model with different stages of tumor progression was investigated ex-vivo by PS-OCT. A phase retardation slope-based analysis, which quantifies the birefringence in different layers, was conducted to distinguish the epithelium, lamina propria, and muscle layers.

RESULTS

The PS-OCT images showed a gradual decrease in birefringence from normal tissue to advanced tumor tissue. The quantitative analysis provided a more detailed comparison among different stages of the rabbit laryngeal tumor model, which was validated by the corresponding histological findings.

CONCLUSION

Differences in tissue birefringence was evaluated by PS-OCT phase retardation measurement. It is also possible to indirectly infer the dysplastic changes based on the mucosal and submucosal alterations.

The influence of premature birth on laryngeal development for phonation

INTRODUCTION

Dysphonia is a known consequence of premature birth, and is usually associated with endotracheal intubation in the neonatal period or surgical ligation of persistent patent ductus arteriosus. Recently, cases of dysphonia, in the absence of these causative factors, have been reported.

OBJECTIVES

This review seeks to identify literature pertaining to those aspects of laryngeal development that may potentially be disrupted by premature birth. The purpose of the review is to determine whether there is any possible anatomical or physiological explanation for dysphonia to arose solely from premature birth.

METHODS

This scoping review was conducted in accordance with the guidelines prescribed by Arskey and O'Malley (2005). Fifteen relevant papers were identified. Results were categorized into age-related categories, to identify changes in the developmental trajectory. Based on the results of the literature search, a further category of unphonated larynges was added.

RESULTS

Potential differences in the laryngeal framework (e.g., the development of the cricoid cartilage and the shape of the glottis) and vocal fold histology, depending on gestational age and post-natal phonation were identified. Much literature focused on the macula flavae, however, the layers of the lamina propria were also discussed.

DISCUSSION

It is unclear whether the process of differentiation of the layers of the lamina propria, which commences in the second to third months of life in term-born infants, is disrupted by prematurity. Further, development of the macula flavae continues until at least 28 weeks' gestation. Preterm children may not phonate immediately after birth, which may also affect laryngeal development.

The Macula Flava of the Human Vocal Fold as a Stem Cell Microenvironment

1. There is growing evidence to suggest that the cells in the maculae flavae are tissue stem cells of the human vocal fold and maculae flavae are a candidate for a stem cell niche. 2. The latest research shows that the cells in the human maculae flavae are involved in the metabolism of extracellular matrices that are essential for the viscoelasticity in the human vocal fold mucosa as a vibrating tissue, and considered to be important cells in the growth, development, and aging of the human vocal fold mucosa. 3. The cells in the human maculae flavae possess proteins of all three germ layers, indicating they are undifferentiated and have the ability of multipotency. 4. The cell division in the human adult maculae flavae is reflective of asymmetric self-renewal and cultured cells form a colony-forming unit. Therefore, the phenomenon gives rise to the strong possibility that the cells in the human maculae flavae are tissue stem cells. 5. Recent research suggests that the cells in the human maculae flavae arise from the differentiation of bone marrow cells via peripheral circulation. 6. The hyaluronan concentration in the maculae flavae is high and contains cells which possess hyaluronan receptors, indicating that the maculae flavae are hyaluronan-rich matrix, which is required for a stem cell niche. 7. A proper microenvironment in the maculae flavae of the human vocal fold mucosa is necessary to be effective as a stem cell niche maintaining the stemness of the contained tissue stem cells.

Collagen fiber and versican distribution within the lamina propria of fetal vocal folds

OBJECTIVES

To analyze the presence and distribution of collagen fibers and versican in human vocal fold lamina propria of fetal larynges.

STUDY DESIGN

Cross sectional analysis of cadaveric vocal folds of human fetuses.

METHODS

Seven fetal larynges obtained from 28- to 36-week-old fetuses were analyzed with the Picrosirius-polarization method, immunohistochemistry, and image analysis.

RESULTS

Collagen fibers within the lamina propria exhibited a monolaminar distribution pattern and spatial arrangement in "wicker basket." Versican distribution was larger in the superficial and intermediate layers when compared to the deep layer.

CONCLUSION

Our findings suggest that collagen and versican distribution and arrangement within the lamina propria in the developing fetus are important for vocalization at birth.

Histologic structure and development of the laryngeal macula flava

The laryngeal maculae flavae (MF) have been previously described as cellular condensations at the extremities of the vocal cords, but the exact nature and role of the MF are unknown. The purpose of this study is a histomorphological analysis of the nature and development of the MF in human vocal cords, from the beginning of fetal life to adulthood. Eighty-six larynges, from the fetus at 12 weeks of amenorrhea (WA) to adulthood, were collected from autopsies and studied by light microscopy with hematoxylin and eosin, orcein, and Alcian blue staining and pS 100 immunostaining. Our observations allowed us to separate the fetal development of the MF into 4 periods. The first corresponds to the appearance of the posterior MF between 13 and 15 WA. In the second period, the anterior MF appeared between 16 and 18 WA, allowing definition of the intermacular space. Fibrous structures, composed of collagen and elastic fibers, of the MF and intermacular space developed between 20 and 33 WA. The last period, from 33 WA to birth, corresponded to a maturation of these structures. In adults, the histologic structure of the MF presented a concentric peripheral fibrous layer associated with a central cellular component. Structural analysis of the MF concludes in favor of the chondroid nature of the macular cell. These observations bring into question the current knowledge on the MF. From these observations, the role of the MF in the developing vocal cord is discussed.

Extracellular matrix of Reinke's space in some pathological conditions

OBJECTIVE

Reinke's space (RS) is a highly specific structure in which the majority of vocal fold pathology occurs. The vibratory equivalents of structurally normal RS are regular vocal fold vibrations and normal glottic mucosal waves. Recently, RS has been considered to be composed not only of fibres but also of extracellular matrix (ECM), which is an extremely important component of a normal mucosal wave. As Reinke's oedema (RO) is characterized by excessive ECM in RS, we investigated the cell activity in RO tissue which is possibly responsible for excessive ECM production.

MATERIAL AND METHODS

Tissue samples were obtained from 20 RO patients during microlaryngeal surgery. Tissue was analysed histochemically using the AgNOR method and the proliferation activity was assessed immunohistochemically using Ki67 monoclonal antibodies.

RESULTS

AgNOR activity was detected in prominent stromal cells in 16 patients. Also, more pronounced activity, compared to the surrounding control tissue, was demonstrated in the epithelial cells of 17 patients using a Ki67 proliferation marker. Electron microscopy showed thickening and decomposition of the basement membrane in all RO tissue samples.

CONCLUSIONS

Vocal fold mucosa that has been damaged by smoking and phonotrauma may react by producing excessive ECM, resulting in RO. Both epithelial and stromal cells are in a state of higher metabolic activity, indicating their role in this production.

Histological structure of the vocal fold in the human larynx

Histological analysis of the human vocal folds, focused particularly on the lamina propria of the vocal muscle of fetuses, infants, and adults in horizontal laryngeal sections, allowed us to show the differences in morphology and composition according to the laryngeal development. Our results indicate that the origin of the vocal fold is independent of the origin of the other portions of the larynx, and the influence of the zone known as macula flava in the maturation of the vocal fold is an age-related process.

Macula flava in the vocal fold of human fetus

The histological analysis of fetal vocal folds (in humans) in serial horizontal sections revealed a dense cell accumulation at the anterior and posterior ends of the vocal fold. Macula flava posterior was identified in all analysed specimens and macula flava anterior in those older than 18 weeks. Maculae flavae are composed of mesenchymal immature cells which gradually originate from cartilaginous cells of the arytenoid or mesenchymal immature cells of the anterior commissure tendon. Macula flava posterior presents the continuation of the arytenoid and there is no delineation between macula flava anterior and anterior commissure tendon. Since macula flava posterior extends its protrusion to the place of the most intensive connective tissue organization (which begins already in fetal life), it has been concluded that both maculae have an important influence to the specific organization and differentiation of connective tissue in the lamina propria of the fetal vocal fold.