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

Two-Stage Fiberoptic Intubation in an Infant With a Rare Congenital Laryngopharyngo-Cutaneous Fistula: A Case Report

Branchial arches represent embryological precursors of the face, neck, and pharynx, and developmental abnormalities of these branchial arch derivatives can lead to airway anomalies. We report definitive repair of the fistula in an infant with a rare congenital laryngopharyngo-cutaneous fistula. This is the first report that describes a 2-stage fiberoptic intubation, a challenging technique performed for airway management of the aforementioned fistula in a patient with a difficult airway.

Transient connection or origin of the inferior pharyngeal constrictor during fetal development: A study using human fetal sagittal sections

The inferior pharyngeal constrictor (IPC) originates from the thyroid and cricoid cartilages and inserts to the pharyngeal raphe. In serial sagittal sections of 37 embryos and fetuses at 6-15 weeks (crown rump length 15-115mm), we found (1) the IPC connecting to the sternothyroideus and thyrohyoideus muscles (16 fetuses at 6-11 weeks) or (2) the cricothyroideus muscle (6 fetuses at 12-15 weeks) in addition to the usual cricoid origin. These aberrant connections were most likely to be transient origins of the IPC not from a hard tissue but nearby striated muscles. In four of the latter six specimens, a tendinous band from the IPC inferior end connected to the cricothyroideus muscle to provide a digastric muscle-like appearance. These aberrant connections with nearby muscles seemed to become separated by a growing protrusion of the thyroid cartilage. Therefore, these aberrant origins were, even if developed, most likely to be "corrected" to the adult morphology during midterm or late prenatal period. The aberrant or transient origin of the IPC seemed to result from a discrepancy in growth of the cartilage and muscles. Such a discrepancy in growth seems to resemble the IPC wrapping around the superior cornu of thyroid cartilage. In addition, a final or adult-like morphology was found in two of the present 37 fetal specimens. It seemed to suggest a significant redundancy in growth rate of the laryngeal structures.

Is the ultimobranchial body a reality or myth: a study using serial sections of human embryos

Reported morphologies of the ultimobranchial body had varied between researchers: a cluster of mitotic cells, a duct-like structure and a rosette-like cell mass. To clarify the true morphology, we studied tilted horizontal sections of 20 human embryos (crown-rump length 5-18 mm; 4-6 weeks). The sections displayed a ladder-like arrangement of the second to fourth endodermal pouches and, in 5 early embryos we found the fifth pouch attached to the fifth ectodermal groove near the fourth pharyngeal arch artery. The bilateral fifth pharyngeal pouches protruded anterolaterally to form a U-shaped lumen surrounding the arytenoid swelling. The third to fifth pouches were each characterized by a pedal-shaped inferior end. We identified several types of cell clusters as candidates for the ultimobranchial body, but morphologically most of them were, to various degrees, likely to correspond to the blind end of the lower pouch when cut tangentially. Because of the topographical relation to the common carotid artery, a cyst-like structure with a cell cluster seemed to be the most likely candidate of the ultimobranchial body (a common anlage of the thymus and parathyroid). However, we were not able to deny a possibility that a certain plane cutting the pouch end incidentally provided such a cyst-like structure in sections. At any stage, the ultimobranchial body might not appear as a definite structure that is discriminated from others with routine staining. A concept of the ultimobranchial body might be biased by comparative anatomy that shows the ultimobranchial gland in adult birds and reptiles.

Temporal and spatial requirements for Hoxa3 in mouse embryonic development

Hoxa3(null) mice have severe defects in the development of pharyngeal organs including athymia, aparathyroidism, thyroid hypoplasia, and ultimobranchial body persistence, in addition to defects of the throat cartilages and cranial nerves. Some of the structures altered in the Hoxa3(null) mutant embryos are anterior to the described Hoxa3 gene expression boundary: the thyroid, soft palate, and lesser hyoid horn. All of these structures develop over time and through the interactions of multiple cell types. To investigate the specific cellular targets for HOXA3 function in these structures across developmental time, we performed a comprehensive analysis of the temporal and tissue-specific requirements for Hoxa3, including a lineage analysis using Hoxa3(Cre). The combination of these approaches showed that HOXA3 functions in both a cell autonomous and non-cell autonomous manner during development of the 3rd and 4th arch derivatives, and functions in a neural crest cell (NCC)-specific, non-cell autonomous manner for structures that were Hoxa3-negative by lineage tracing. Our data indicate that HOXA3 is required for tissue organization and organ differentiation in endodermal cells (in the tracheal epithelium, thymus, and parathyroid), and contributes to organ migration and morphogenesis in NCCs. These data provide a detailed picture of where and when HOXA3 acts to promote the development of the diverse structures that are altered in the Hoxa3(null) mutant. Data presented here, combined with our previous studies, indicate that the regionally restricted defects in Hoxa3 mutants do not reflect a role in positional identity (establishment of cell or tissue fate), but instead indicate a wider variety of functions including controlling distinct genetic programs for differentiation and morphogenesis in different cell types during development.

Expression of carbonic anhydrase IX in human fetal joints, ligaments and tendons: a potential marker of mechanical stress in fetal development?

Carbonic anhydrase type IX (CA9) is known to express in the fetal joint cartilage to maintain pH against hypoxia. Using paraffin-embedded histology of 10 human fetuses at 10-16 weeks of gestation with an aid of immunohistochemistry of the intermediate filaments, matrix components (collagen types I and II, aggrecan, versican, fibronectin, tenascin, and hyaluronan) and CA9, we observed all joints and most of the entheses in the body. At any stages examined, CA9-poisitive cells were seen in the intervertebral disk and all joint cartilages including those of the facet joint of the vertebral column, but the accumulation area was reduced in the larger specimens. Glial fibrillary acidic protein (GFAP), one of the intermediate filaments, expressed in a part of the CA9-positive cartilages. Developing elastic cartilages were positive both of CA9 and GFAP. Notably, parts of the tendon or ligament facing to the joint, such as the joint surface of the annular ligament of the radius, were also positive for CA9. A distribution of each matrix components examined was not same as CA9. The bone-tendon and bone-ligament interface expressed CA9, but the duration at a site was limited to 3-4 weeks because the positive site was changed between stages. Thus, in the fetal entheses, CA9 expression displayed highly stage-dependent and site-dependent manners. CA9 in the fetal entheses seemed to play an additional role, but it was most likely to be useful as an excellent marker of mechanical stress at the start of enthesis development.

Expression of carbonic anhydrase in the fetal eye and extra-ocular tissues

Carbonic anhydrases (CAs) plays a critical functional role in the ciliary body and retina for maintenance of microenvironment. With immunohistochemistry using orbital contents from 8 human fetuses (12-16 weeks of gestation), we examined expressions of CAs isozymes-1, 2, 3, 6, 7 9 and 12 and found strong reactivity of CA9 in extra-ocular fibrous tissues in the anterior and posterior eyes. CA9 is known to express in the fetal joint cartilage to maintain pH against hypoxia: actually, in the present specimens, the SO pulley and its tendon was strongly positive for CA9. The CA9-positive anterior fibrous tissues were positive for smooth muscle actin and connected the orbital aspect of the 4 rectus muscle with the palpebral conjunctiva, whereas the posterior tissue was negative for smooth muscle actin and corresponded to the lateral insertion tendon of the orbitalis muscle. The anterior CA9-positve tissues seemed to correspond to the primitive form of the sleeve and pulley system. Any of matrix substances (collagen types I and II, aggrecan, versican, fibronectin, tenascin and hyaluronan) displayed a distribution pattern specific for the CA9-positive fibrous tissues. Therefore, whether or not CA9 was positive in the fibrous tissue seemed not to depend on the tissue components such as the extracellular matrix and intermediate filaments but to suggest a stressful condition such as hypoxia, unsuitable base balance and/or under mechanical stress.

Initial stage of fetal development of the pharyngotympanic tube cartilage with special reference to muscle attachments to the tube

Fetal development of the cartilage of the pharyngotympanic tube (PTT) is characterized by its late start. We examined semiserial histological sections of 20 human fetuses at 14-18 weeks of gestation. As controls, we also observed sections of 5 large fetuses at around 30 weeks. At and around 14 weeks, the tubal cartilage first appeared in the posterior side of the pharyngeal opening of the PTT. The levator veli palatini muscle used a mucosal fold containing the initial cartilage for its downward path to the palate. Moreover, the cartilage is a limited hard attachment for the muscle. Therefore, the PTT and its cartilage seemed to play a critical role in early development of levator veli muscle. In contrast, the cartilage developed so that it extended laterally, along a fascia-like structure that connected with the tensor tympani muscle. This muscle appeared to exert mechanical stress on the initial cartilage. The internal carotid artery was exposed to a loose tissue facing the tubal cartilage. In large fetuses, this loose tissue was occupied by an inferior extension of the temporal bone to cover the artery. This later-developing anterior wall of the carotid canal provided the final bony origin of the levator veli palatini muscle. The tubal cartilage seemed to determine the anterior and inferior margins of the canal. Consequently, the tubal cartilage development seemed to be accelerated by a surrounding muscle, and conversely, the cartilage was likely to determine the other muscular and bony structures.

Fetal development and variations in the cartilages surrounding the human external acoustic meatus

In contrast to the osseus part that develops from the tympanic ring of the squamous part of the temporal bone after birth, there is little information on fetal development of the cartilages surrounding the human external acoustic meatus. Using routine histology and immunohistochemistry, we examine sections of 22 fetuses (CRL 100-270mm) to study the development of these cartilages. Early external ear cartilages are composed of three groups: (1) a ring-like cartilage at the putative tragus on the anterior side of the meatus, (2) two or three bar-like cartilages along the inferior wall of the meatus, and (3) a plate-like cartilage in a skin fold for the putative helix on the posterior side. In contrast to the first and second pharyngeal arch cartilages, all the external ear cartilages express glial fibrillary acidic protein. Notably, the bar-like cartilages along the meatus are connected with a fascia-like structure to the second pharyngeal arch cartilage. Later, with considerable individual variation, new cartilage bars extend from the inferior cartilages to the superior side of the meatus. Thus, via an intermediate stage showing a chain of triangular elastic cartilages, a chain of bar-like cartilages on the inferior side appears to change into a complex of H-shaped cartilages. Numerous ceruminous glands are seen in the thick subcutaneous tissue overlying the cartilaginous part of the meatus. However, they do not insert into the cartilage. The external ear cartilages develop much earlier than, and independently of, the osseus part.