Fetal development of the human epiglottis revisited: appearance of GFAP-positive mesenchymal cells and fibrous connections with other laryngeal and lingual structures.

The fetal anatomy of the human epiglottis has not yet been fully described. We investigated the histology (paraffin-embedding) of 18 mid-term fetuses at 7-25 weeks of gestation (three fetuses each at 7, 9, 12, 15, 20 and 25 weeks). A mesenchymal condensation of the epiglottic cartilage appears posterior and somewhat superior to the hyoid body at 9 weeks, but at 12 and 15 weeks, the root or inferior part descends to the level of the thyroid cartilage. The covering epithelium stains much darker with hematoxylin than other pharyngeal epithelia. After 20 weeks, the epiglottis again protrudes superiorly beyond the hyoid body. In contrast to other laryngeal cartilage anlagen, the mesenchymal condensation of the epiglottis begins to express glial fibrillary acidic protein (GFAP) at 15 weeks. At the same stage, mucosal glands begin invading into the epiglottic mesenchyme. The developing cartilage becomes penetrated and fragmented by abundant mucosal glands up until 25 weeks. The thyro-epiglottic ligament seems to develop from the GFAP-positive mesenchymal condensation, whereas the hyo-epiglottic ligament is likely to originate from the fasciae of lingual muscles. Epithelial-mesenchymal interaction is strongly suggested in the development of the epiglottic cartilage and concomitant glands.

Anatomical dimensions of larynx, epiglottis and cricoid cartilage in foetuses and their relationship with crown rump length.

BACKGROUND: Advances in perinatal care and increased use of diagnostic and interventional procedures on foetal airway demand a clear understanding of their normal anatomy and development. This study is aimed at determining the normal dimensions of larynx, cricoid cartilage and epiglottis and their correlation to age and crown rump length (CRL). METHOD: After approval from institutional ethics committee and written parental informed consent, laryngeal measurements were taken from 79 foetuses of varying CRL from 30 to 299 mm. The entire larynx from the tip of epiglottis to lowest extension of thyroid gland was isolated and preserved. In small foetuses (30-165 mm) the measurements were taken under a dissecting microscope. In foetuses above the CRL of 165 mm, the measurements were taken with help of Vernier Calliper. RESULTS: Foetuses were analysed for dimensions based on CRL. The length of the larynx significantly increased in comparison to CRL (P < 0.001). Similar measurements were observed for transverse diameter, anteroposterior diameter and inter-cartilaginous distance of larynx, the anterior height of arch and posterior height of lamina of cricoid cartilage and the length and breadth of epiglottis. The internal anteroposterior and transverse diameter of cricoid cartilage showed no correlation with CRL. CONCLUSION: All the measured parameters of larynx, epiglottis and cricoid cartilage showed positive correlation with the CRL except the internal diameters of cricoid.

Development of epithelia in the ectopic transplant of the fetal rat epiglottis.

Embryonic in situ development is strictly regulated within the specific microenvironment of developing tissues. However, for regenerative medicine purposes (supplementation of damaged tissues/organs), transplantation to ectopic sites has been considered. To investigate developmental potential of fetal epiglottic epithelia at an ectopic site, fetal epiglottis was transplanted under the kidney capsule and its development compared to fetal and adult epiglottis. Seventeen-day-old Fischer rat epiglottides were microsurgically isolated under a dissecting microscope and transplanted under the kidney capsule of adult males. After 14 days, classic histology and immunohistochemical detection of the Proliferating Cell Nuclear Antigen (PCNA) were done in isolated and accordingly fixed transplants. The 17-day-old fetal epiglottis and adult epiglottis were processed in the same way. The 17-day-old fetal epiglottides were covered with immature epithelium expressing PCNA in almost all cells. Adult epiglottis was covered with two types of epithelia (stratified squamous epithelium and ciliated pseudostratified epithelium). In the stratified squamous epithelium PCNA was abundantly expressed in the basal cell layer and absent from more superficial and more differentiated cells. Transplants survived well during the experimental period. On their surface ciliated pseudostratified epithelium could be easily recognized, but squamous epithelium was almost absent. PCNA was expressed in basal cells of the ciliated pseudostratified epithelium and was absent from the more differentiated superficial cells. It seems that at this ectopic site further differentiation of the epiglottic epithelia can proceed but differentiation of squamous epithelium seems not to be favored. It seems that this ectopic site is optimal for further differentiation of the epiglottic epithelium towards ciliated pseudostratified epithelium.

Differentiation of epiglottal epithelia during prenatal and postnatal human development.

Differentiation of epiglottal epithelia during human development was for the first time investigated by the light microscopy and documented in celoidine collection of human embryos from the Archive of the Department of Histology and Embryology, School of Medicine University of Zagreb, Croatia. At 6 weeks epiglottal swelling was found to be covered by a simple squamous epithelium consisting of a single layer of cells. At 8 weeks epithelium changed to a two-layered cuboidal epithelium which at the end of the 8th week transformed to multilayered columnar epithelium without cilia and goblet cells. In the one-day-old newborn, the majority of epiglottis was found to be covered by the mature ciliated columnar pseudostratified epithelium with goblet cells while only a minor part of the oral surface next to the tongue by the stratified squamous epithelium. This unexpected finding is in contrast to the domination of the stratified squamous epithelium found at the age of 13 years and in 35-years-old adult. Reversal of proportion covered by different types of epithelia between birth and puberty /adulthood is probably connected to the establishment of the air-flow which could be stimulating for differentiation of stratified squamous epithelium.

Bronchus-associated lymphoid tissue (BALT) and larynx-associated lymphoid tissue (LALT) are found at different frequencies in children, adolescents and adults.

The lung in 98 and the larynx in 51 consecutive autopsies (age: 17th gestational week to 99 years) were studied for the presence of organized lymphoid tissue in the epiglottis and in the wall of larger bronchi. Bronchus-associated lymphoid tissue (BALT) was seen in about 40% of patients younger than 20 years of age but in older patients only in exceptional cases. In the wall of the epiglottis, however, larynx-associated lymphoid tissue (LALT) was found at a frequency of approximately 80% in patients younger than 20 years and in 56% of the patients older than 20 years. The clinical relevance of LALT as a physiological entry site for antigens or for vaccination protocols using aerosols needs to be studied in further experiments.

Bifid epiglottis.

The true bifid epiglottis is a rare congenital anomaly typically discovered during the evaluation of stridor in an infant or newborn. While it is not classified as a specific syndrome, there are frequent associations of other congenital anomalies with the bifid epiglottis. These include midline defects (such as microphallus, hypospadius, imperforate anus, and midline laryngeal cleft), endocrine disorders (including congenital hypopituitarism), and central nervous system neoplasms, including hypothalamic hamartoblastoma. The embryogenesis and options for surgical management of this anomaly are reviewed, and one case is presented in detail.

Squamous carcinoma of the epiglottis with sebaceous differentiation. Report of a case.

A case of squamous cell carcinoma with sebaceous metaplasia arising in the epiglottis is reported. Extracutaneous neoplasms that show sebaceous differentiation have been mainly described in the major salivary glands. To date only one case of prominent sebaceous differentiation in a carcinoma arising in the vallecula has been reported. In the present paper we describe a similar case arising in the larynx.

Morphology, histochemistry, and differentiation of the cat's epiglottic cartilage: a supporting organ composed of elastic cartilage, fibrous cartilage, myxoid tissue, and fat tissue.

BACKGROUND: In carnivores, the supporting organ of the epiglottis is usually called "epiglottic cartilage" (EC) although it is composed of elastic cartilage and unilocular fat storing cells. We studied the cat's EC in order to decide whether these fat storing cells are true adipocytes or fat storing (dedifferentiated) chondrocytes. METHODS: ECs were studied in cat embryos at gestation days 40 and 60, in newborn, postnatal, and adult cats. We used classical staining methods, immunohistochemistry, and transmission electron microscopy to identify the different kinds of tissues contributing to the EC and to follow their differentiation. RESULTS: The cat's EC was defined by a layer of coarse collagen fibers representing a tunica albuginea. This tunica covered irregularly formed and irregularly sized areas of elastic cartilage, fibrous cartilage, myxoid tissue, and lobules of unilocular fat cells. All these tissue showed regular morphology. Adipocytes were provided with continuous basal laminae and fat lobules were well supplied with capillaries. Alcianophilia of ground substance was observed in all tissue components but was strongest in elastic cartilage. Most islets of elastic cartilage adhered to the tunica albuginea of the EC at one surface and were connected to the opposite surface by coarse strands of connective tissue traversing the organ. Intercalated areas of fibrous cartilage contained fuchsinophilic collagen bundles. Myxoid tissue was characterized by stellate cells in alcianophilic ground substance with intermingled fuchsinophilic bundles. All kinds of supporting tissues combined with each other without clear demarcation. Immunohistochemistry revealed strong reactivity for S-100 of chondrocytes, myxoid cells, and fat cells. Chondrocytes and myxoid cells also stained for glial fibrillary acidic protein, neurofilament protein 200, and neuron specific enolase. During development, condensation of mesenchymal cells indicated the blastema of the EC at gestation day 40. At day 60, delicate collagen fibrils indicated the future tunica albuginea, faint alcianophilia was noted in the ground substance, and multilocular fat cells were scattered throughout the blastema. At birth, alcianophilia was moderate and multilocular fat cells were numerous. Three weeks after birth, single and grouped unilocular fat cells were seen, alcianophilia of ground substance was prominent, and former blastema cells presented as ramified myxoid cells. Eight weeks after birth, the EC primarily consisted of myxoid tissue, but the first islets of cartilage were seen in the center of myxoid areas. Unilocular fat cells already formed lobules. CONCLUSIONS: These results show that in the cat EC a) differentiation of adipocytes precedes differentiation of all the other tissue components, and b) differentiation of myxoid tissue precedes differentiation of cartilage. It is concluded that myxoid tissue may serve as a precursor of fibrous and elastic cartilage.

Electron microscopic study on the epiglottic mucosa in human fetuses.

The differentiation of the epiglottic mucosa in human fetuses has so far been studied only by light microscopy. So, we studied the epiglottic mucosa in human fetuses (at gestational ages from the 7th to 21st week) by scanning (SEM) and transmission electron microscopies (TEM), and could disclose more detailed features of cellular differentiation of this mucosa. These results and the review of the literatures lead to the following conclusions: 1. Primary cilia appeared in the epiglottic mucosa around the 7th week of gestation. 2. Ciliated cells and the stratified squamous epithelium of the lingual surface appeared at the similar period as reported by others, but our study revealed that the squamous cells are immature even at the 21st week. 3. Glycogen granules in non-ciliated cells decreased paralleling the differentiation of the cells, suggesting that they provide a source of energy necessary for the cell differentiation.

A quantitative study of cat epiglottal taste buds during development.

To quantify the development of upper airway chemoreceptors, epiglottal taste buds were counted in cat fetuses, kittens and adults. Taste buds with structural characteristics similar to those in the adult were observed in all fetuses close to term and in kittens from birth. During the first postnatal week a mean of 76 taste buds was present on the kitten epiglottis and by adulthood 800 were observed. The number of taste buds increased as a logarithmic function of both age and weight, but the correlation with weight is better than that with age. The presence of epiglottal taste buds from very early developmental stages suggests that these receptors may mediate the reflex apnoea and swallowing that occur in response to chemical stimulation of the larynx in newborns.

Quantitative analysis of developing epiglottal taste buds in sheep.

Epiglottal taste buds of the sheep increase in number during development, and continue to increase until the epiglottis has reached its adult size. However, since the increase in taste bud numbers is paralleled by increase in the surface area of the epiglottis, the density of taste buds decreases progressively in the fetus and newborn. After birth the density remains relatively constant. From examination of the morphological stages of epiglottal taste bud development, we conclude that taste buds are originally produced by de novo formation, but that further increase in numbers is effected by division of existing, developing taste buds. Because of the large number of taste buds, and the maintenance of their density on the epiglottis, it is concluded that they have an important functional role in upper airway protective reflexes.