The early development of the larynx in staged human embryos. I. Embryos of the first five weeks (to stage 15)

Development of the foregut and the formation of the trachea and esophagus in rat embryos. A symphony of confusion

Introduction: During embryonic development, the trachea emerges from an area of the foregut, which is often referred to as "anterior" or "common" foregut tube or simply foregut. To explain this process of differentiation, four competing models exist to date. The outgrowth and watershed models propose a foregut that remains constant in length. In the outgrowth model, the trachea buds off and elongates from the foregut, while in the watershed model, a mesenchymal wedge splits the growing foregut into the trachea and esophagus. In contrast, the septation model proposes a cranial splitting and thus a shortening of the "common" foregut tube into the trachea and esophagus by an emerging septum. Finally, the splitting and extension model describes an interaction of cranial splitting of the foregut and simultaneous caudal tracheal and esophageal growth. Methods: Here we examine the development of the undifferentiated foregut by micro computed tomography, which allows precise measurements. Results: Our results show that this area of the foregut transforms into the larynx, a process, which is independent from tracheal and esophageal development. Discussion: These observations are only consistent with the outgrowth model.

Survey of the Development of Laryngeal Epithelium

An overview of the developing laryngeal epithelium has been presented to establish the norm. The sequential relationships of the formation of the protective laryngeal covering, cellular and glandular, have been reviewed. The topographical distribution of the epithelial elements in the human larynx are illustrated in the adult and contrasted in the child. Unique and previously undescribed cellular ultrastructure and transition areas have been identified. Biological integration of form and function is again well illustrated in the epithelium of the human larynx.

A Case Report of Absent Epiglottis in Children With Nager Syndrome: Its Impact on Swallowing

OBJECTIVE

This clinical report is the first literature report exploring the issues of an absent epiglottis in children diagnosed with Nager syndrome. Absent epiglottis has previously been described in children with Pierre Robin sequence and other syndromes.

CONCLUSION

The function of the epiglottis and its contribution to swallowing has always been debated. In this article and from our literature review, we felt that absent epiglottis possibly contributed to the aspiration risk and may partly explain the long-term feeding issues in these children despite corrective surgeries.

Development and morphogenesis of human wrist joint during embryonic and early fetal period

The development of the human wrist joint has been studied widely, with the main focus on carpal chondrogenesis, ligaments and triangular fibrocartilage. However, there are some discrepancies concerning the origin and morphogenetic time-table of these structures, including nerves, muscles and vascular elements. For this study we used serial sections of 57 human embryonic (n = 30) and fetal (n = 27) specimens from O'Rahilly stages 17-23 and 9-14 weeks, respectively. The following phases in carpal morphogenesis have been established: undifferentiated mesenchyme (stage 17), condensated mesenchyme (stages 18 and 19), pre-chondrogenic (stages 19 and 20) and chondrogenic (stages 21 and over). Carpal chondrification and osteogenic processes are similar, starting with capitate and hamate (stage 19) and ending with pisiform (stage 22). In week 14, a vascular bud penetrates into the lunate cartilaginous mold, early sign of the osteogenic process that will be completed after birth. In stage 18, median, ulnar and radial nerves and thenar eminence appear in the hand plate. In stage 21, there are indications of the interosseous muscles, and in stage 22 flexor digitorum superficialis, flexor digitorum profundus and lumbrical muscles, transverse carpal ligament and collateral ligaments emerge. In stage 23, the articular disc, radiocarpal and ulnocarpal ligaments and deep palmar arterial arch become visible. Radiate carpal and interosseous ligaments appear in week 9, and in week 10, dorsal radiocarpal ligament and articular capsule are evident. Finally, synovial membrane is observed in week 13. We have performed a complete analysis of the morphogenesis of the structures of the human wrist joint. Our results present new data on nervous and arterial elements and provide the basis for further investigations on anatomical pathology, comparative morphology and evolutionary anthropology.

Septation of the respiratory and digestive tracts in human embryos: crucial role of the tracheoesophageal sulcus

Esophageal atresia and tracheoesophageal fistula, common malformations of the respiratory and digestive tracts, are of unsettled pathogenesis. Part of the difficulty in understanding these abnormalities arises from the uncertainties about the normal developmental processes in the region. This study examined the development and fate of the tracheoesophageal septum. Normal human embryos from the Carnegie Embryological Collection and fetuses from the Hopkins Pathology Collection were examined, and reconstructions of selected specimens were made from photomicrographs of serial histologic sections. The results show that the lung bud appears in Carnegie stage 12, rapidly enlarges, and bends caudally, thereby producing a sulcus between the foregut and the respiratory system on its caudal aspect. The cranial aspect of this tracheoesophageal sulcus remains fixed at the levels of the first cervical vertebra throughout subsequent embryonic and fetal development. At the same time the trachea and esophagus elongate to bring those part of the respiratory and digestive systems into their definitive anatomic positions. Examination of the tracheoesophageal sulcus shows that its growth-limiting properties may be explained by its catenoidal configuration. Catenoidal, or saddle-shape, sulci have been shown to have similar regional growth-limiting properties in the embryonic heart. These regions contrast with outwardly convex regions in both the developing heart and lung where growth of the tissues occurs. The observations made here suggest that the origin of the tracheoesophageal malformations must be sought in a configurational abnormality in the area of the developing lung bud in Carnegie stage 12.

The human larynx at the end of the embryonic period proper. 2. The laryngeal cavity and the innervation of its lining

The laryngeal cavity was studied in eight serially sectioned embryos of stage 23 and in three early fetuses, and graphic reconstructions were prepared. After the isolation of the tracheal from the pharyngeal cavity during stages 16 through 22, a communication (not necessarily the pharyngotracheal duct) appears again during stage 23. At this time (8 postovulatory weeks) the laryngeal cavity comprises 1) the coronal and parts of the sagittal clefts of the vestibule (uniting later at the laryngeal inlet); 2) the ventricles, which are not yet completely formed; and 3) the subglottic cavity, which appeared already in earlier stages. The characteristic events of stage 23 are the dissolution of the epithelial lamina and the development of the ventricles. The disruption of the epithelial lamina is an active process that comprises rearrangement and growth, but not loss of cells. The ventricles, which begin as solid outgrowths in stage 20, do not represent fifth pharyngeal pouches. They now point toward the middle of the still paired thyroid laminae and are not at the level of the future glottis, which lies more caudally. In the absence of the median part of the soft palate, the nasopharynx communicates widely with the oral cavity. The epithelium of the respiratory tube, including the larynx, resembles that of the pharynx and esophagus in being pseudostratified columnar and showing a clear basement membrane. It is ciliated over that part of the epiglottis that surmounts the arytenoid swellings, and also over the tip and back of the latter. The transitional area between the laryngopharynx and the esophagus is already innervated by the recurrent laryngeal nerve. Nerve fibers have not yet reached the epithelium of the coronal cleft and the ventricles, but fibers are present near the sagittal cleft of the vestibule. The sensory innervation of the pharynx and larynx has been followed and plotted for the first time in an embryo, and previously unrecorded silver-impregnated receptors have been observed.

Laryngeal dysgenesis

A case of a previously undescribed anomaly of the larynx is presented and offers insight and support of current concepts of fetal laryngeal development. The patient possessed unilateral absence of true and false vocal cords, laryngeal ventricle, and saccule. Current concepts of embryological development would place the development of this anomaly and most of the patient's other multiple anomalies in the period of the 6th to 9th weeks of fetal life. This report lends substantiation to the stages of laryngeal development by demonstrating an aberration in the normal sequential development. Additionally, the time period of this maldevelopment is suggested by the concurrence of multiple other anomalies. Aspects of laryngeal embryology relevant to laryngeal maldevelopment are reviewed.

Chevalier Jackson lecture. Respiratory and alimentary relations in staged human embryos. New embryological data and congenital anomalies

The early development of the digestive and respiratory systems is summarized in relation to embryonic staging. It has frequently been emphasized that the digestive and respiratory tubes do not arise from a common chamber, that they pursue separate courses as soon as the lung bud appears, that a mesenchymal septum comes to intervene between them, and that the two tubes rapidly acquire independent outer coats. Some commonly held views such as the supposed caudorostral separation of the trachea from the esophagus, have been shown to be incorrect. These ideas often arose from the use of unstable landmarks during development. It is pointed out that, for 3 weeks after its appearance, the tracheoesophageal separation point remains at a constant level, whereas the tracheal bifurcation descends. The application of valid embryological data to the interpretation of several congenital anomalies has been shown to be of value. Although the modes of origin in some instances are still obscure, considerable advance has been made in understanding the timing of the relevant events.

Congenital laryngeal atresia. Histopathologic study of two cases

Two specimens of laryngeal atresia were studied. In the first case stenosis was hard due to noncanalization of the anterior cricoid cartilage. In the second case there was a soft stenosis from limited canalization of the endoluminal soft tissue. Additionally, the first case had a posterior cleft with a persistent pharyngotracheal duct. The stenotic soft-tissue elements in both cases contained striated muscle fibers that interdigitated across the midline. The mucosa on the inferior surface of the hard stenosis was grossly thickened and contained large mucous glands. The embryologic significance of these anomalies is discussed. Presumably these cases represent anomalies caused by different embryologic events.

The human larynx at the end of the embryonic period proper. I. The laryngeal and infrahyoid muscles and their innervation

The larynx at stage 23 (about 27-32 mm C-R, 8 postovulatory weeks) is being studied in detail, and findings on the musculature and its innervation are presented here. Serial sections of six embryos all belonging to the one developmental stage were investigated and compared, and graphic reconstructions were made from five of the specimens. All the infrahyoid and most of the major laryngeal muscles are present, and their innervation follows closely the adult pattern. The ary-epiglottic and thyro-epiglottic apparently may or may not be identifiable. The vocalis is beginning to differentiate and is noted here in the embryonic period proper for the first time. The histological degree of development of the intrinsic laryngeal muscles is not as advanced as that of adjacent muscles in the neck, including the infrahyoid group. Variation within this one stage of development are small but definite. They include differences in the position, level, and shape of the skeletal components, and the precise position and extent of development of some of the muscles.

Laryngeal development and congenital lesions

In considering laryngeal development, functional development and the comparative anatomical approach of Sir Victor Negus must be included in addition to classical morphological development; postnatal questions are considered in addition to embryological and fetal development.

Clinical correlation of anomalies of the supraglottic larynx with the staged sequence of normal human laryngeal development

The clinical correlation of the authors' observations on human laryngeal development with existing literature supports the suggestion that earlier concepts, specifically by Frazer, may not be valid. It is further proposed that development of the human larynx may similarly correspond in man to that of the rat. Congenital laryngeal malformations are fundamentally associated with a disturbance of epithelial mesenchymal interactions, particularly related to a premature arrest of the normally vigorous epithelial activity.

The timing and sequence of events in the development of the human digestive system and associated structures during the embryonic period proper

A documented scheme of the early development of the human digestive system is presented. It is based on (1) reports of workers who personally studied staged embryos, and (2) personal observations and confirmations. The necessity of studying staged embryos in order to determine the precise sequence of developmental events is stressed.

Laryngotracheoesophageal cleft: the anterior approach

Laryngotracheoesophageal cleft was reported by Richter in 1792 after he examined an infant at autopsy and found a common lumen of esophagus and laryngotrachea. The next case was not noted until 1949 by Finlay. A recent review shows 40 cases in the world literature to date. Successful surgical approaches to some of these problems have basically employed a lateral pharyngotomy technique. In the case presented herein, the exact pathology was obscured by a severe tetralogy of Fallot and recurrent pneumonitis from a suspected high H-type tracheoesophageal fistula. The length of this cleft prompted an anterior approach with laryngo-fissure, cricoidotomy, and division of four tracheal rings for a complete and successful repair. Thorough endoscopy of all infants suspected of any laryngeal anomaly would yield an earlier diagnosis and opportunity for reconstruction of the cleft.

The timing and sequence of events in the development of the limbs in the human embryo

A documented scheme of the early development of the human limbs is presented. It is based on (1) published and unpublished personal observations, and (2) reports of other workers who personally studied staged human embryos. The necessity of studying staged embryos in determining the precise sequence of developmental events is stressed.

Some aspects of fetal laryngeal development

Some aspects of morphological and physiological development of the fetal larynx are presented. Histochemical confirmation and determinations of fetal glandular activity are needed. Anomalous development of the larynx is still conjecture, but congenital cystic formation with glandular development appears possible after the fifth month of human fetal life.