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

Lowered hyoid bone overlapping the thyroid cartilage in CT angiograms

BACKGROUND

The ventral enclosure of the thyroid cartilage by a collapsed hyoid bone (CHB) is poorly encountered in previous research. It was aimed to observe whether or not these malformations could be found and detailed anatomically in a consistent lot of computed tomography (CT) files.

METHODS

Two hundred archived CT angiograms were explicitly observed for the CHB anatomical variant.

RESULTS

Different possibilities of CHB were found in 6/200 cases, five males and one female. The symmetrical overlap of the thyroid cartilage by the hyoid body was found in one male case. In three cases, two males and one female, there was asymmetrical overlapping due to tilted hyoid bones. In one male case with such asymmetrical CHD, an ossified anterior longitudinal ligament was noted: the tips of the superior horns of the thyroid cartilage reached lateral to it, thus being retropharyngeal. A different male case had a lowered hyoid with a greater horn fused to the superior horn of the thyroid cartilage, with an interposed ossified triticeal cartilage. In the last male case, the right greater horn collapsed laterally to an ossified triticeal cartilage fused with the thyroid cartilage's superior horn.

CONCLUSIONS

The CHB is an undeniable anatomical possibility of an atavism that alters conventional anatomical and surgical landmarks. Different anatomical components of the hyoid bone can descend uni- or bilaterally.

β-Catenin signaling is essential for mammalian larynx recanalization and the establishment of vocal fold progenitor cells

Congenital laryngeal webs result from failure of vocal fold separation during development in utero Infants present with life-threatening respiratory problems at birth, and extensive lifelong difficulties in breathing and voicing. The molecular mechanisms that instruct vocal fold formation are rarely studied. Here, we show, for the first time, that conditional inactivation of the gene encoding β-catenin in the primitive laryngopharyngeal epithelium leads to failure in separation of the vocal folds, which approximates the gross phenotype of laryngeal webbing. These defects can be traced to a series of morphogenesis defects, including delayed fusion of the epithelial lamina and formation of the laryngeal cecum, failed separation of the larynx and esophagus with reduced and disorganized cartilages and muscles. Parallel to these morphogenesis defects, inactivation of β-catenin disrupts stratification of epithelial cells and establishment of p63⁺ basal progenitors. These findings provide the first line of evidence that links β-catenin function to the cell proliferation and progenitor establishment during larynx and vocal fold development.

Switching of the Laryngeal Cavity From the Respiratory Diverticulum to the Vestibular Recess: A Study Using Serial Sagittal Sections of Human Embryos and Fetuses

A cecum-like protrusion of the pharynx (the laryngeal cecum or vestibular recess [VR]) develops immediately anterior to the laryngeal part of the respiratory diverticulum. An expansion of the VR has been well described, whereas the fate of the diverticulum is still obscure, although its pharyngeal opening corresponds to the glottis. We observed sagittal sections of 10 embryos (five specimens at 5-6 weeks and another five at 7-8 weeks) and eight fetuses at 25-30 weeks. At 5-6 weeks, a lumen of the laryngeal part of the respiratory diverticulum appeared, and subsequently, the VR opened into the epithelial lamina. Because of this discrete separation, it seemed unlikely that the pharyngeal pouches contributed to the laryngeal epithelium. At 6-7 weeks, the VR exhibited a high boot-shaped lumen with canalization to the diverticular lumen at the level of the cricoid cartilage. Thus, in a midline area between the bilateral arytenoid cartilages, double laryngeal lumina were evident, separated by the thick midline epithelial lamina. At 25-30 weeks, the inferior part of the VR lumen had become enlarged because of the destruction of the epithelial lamina along the arytenoid and corniculate cartilages. In contrast, candidates for the initial diverticular lumen remained as epithelial slits in the anterosuperior side of the transverse arytenoid muscle. Therefore, the final anterior and lateral laryngeal walls seemed to originate from the VR with canalization, in contrast to the part of the posterior wall derived from the initial diverticular wall.

Ontogeny of the mouse vocal fold epithelium

This investigation provides the first systematic determination of the cellular and molecular progression of vocal fold (VF) epithelium development in a murine model. We define five principal developmental events that constitute the progression from VF initiation in the embryonic anterior foregut tube to fully differentiated and functional adult tissue. These developmental events include (1) the initiation of the larynx and vocal folds with apposition of the lateral walls of the primitive laryngopharynx (embryonic (E) day 10.5); (2) the establishment of the epithelial lamina with fusion of the lateral walls of the primitive laryngopharynx (E11.5); (3) the epithelial lamina recanalization and separation of VFs (E13.5-18.5); (4) the stratification of the vocal folds (E13.5-18.5); and (5) the maturation of vocal fold epithelium (postnatal stages). The illustration of these morphogenetic events is substantiated by dynamic changes in cell proliferation and apoptosis, as well as the expression pattern of key transcription factors, FOXA2, SOX2 and NKX2-1 that specify and pattern the foregut endoderm. Furthermore, we documented the gradual conversion of VF epithelial cells from simple precursors expressing cytokeratins 8 and 18 in the embryo into mature stratified epithelial cells also expressing cytokeratins 5 and 14 in the adult. Interestingly, in the adult, cytokeratins 5 and 14 appear to be expressed in all cell layers in the VF, in contrast to their preferential localization to the basal cell layer in surrounding epithelium. To begin investigating the role of signaling molecules in vocal fold development, we characterized the expression pattern of SHH pathway genes, and how loss of Shh affects vocal fold development in the mutant. This study defines the cellular and molecular context and serves as the necessary foundation for future functional investigations of VF formation.

TRAF4 deficiency leads to tracheal malformation with resulting alterations in air flow to the lungs

TRAF4 is one of six identified members of the family of TNFR-associated factors. While the other family members have been found to play important roles in the development and maintenance of a normal immune system, the importance of TRAF4 has remained unclear. To address this issue, we have generated TRAF4-deficient mice. Despite widespread expression of TRAF4 in the developing embryo, as well as in the adult, lack of TRAF4 expression results in a localized, developmental defect of the upper respiratory tract. TRAF4-deficient mice are born with a constricted upper trachea at the site of the tracheal junction with the larynx. This narrowing of the proximal end of the trachea results in respiratory air flow abnormalities and increases rates of pulmonary inflammation. These data demonstrate that TRAF4 is required to regulate the anastomosis of the upper and lower respiratory systems during development.

Comparison of perinatal and adult multi-innervation in human laryngeal muscle fibers

The innervation of human laryngeal myofibers appears distinct from that of skeletal myofibers, because some of them exhibit multiple neuromuscular junctions. We attempted to understand the significance of the multi-innervation phenomenon by comparing intrinsic laryngeal muscles obtained from autopsies of a fetus, a stillbirth, and a 7-month-old infant to muscles from adults. In longitudinal sections (40 to 60 microm thick) the cholinesterase sites and the nerve terminals were stained simultaneously for light microscopy. Multi-innervation reached no more than 23% at 7 months, and this percentage decreased notably with age. Until 7 months, end plates were innervated either by single or by multiple axons (unineuronal and polyneuronal innervation), whereas in adults, the pattern was exclusively unineuronal. Moreover, the structure of neuromuscular junctions in the young was limited to 1 spot of acetylcholinesterase, while in adults the end plate zones increased in size and complex axon terminals were observed. These observations are consistent with a delayed maturation of human laryngeal innervation compared to that of skeletal muscles.

Morphology of the human larynx during the first five years of life studied on whole organ serial sections

The morphologic development of the human larynx during the first years of life is poorly understood to date. This study used plastinated whole organ serial sections to determine the growth and structure of the infant larynx. The larynges of 43 children 1 to 60 months old were plastinated. Whole organ serial sections were obtained by cutting the resulting specimen with a diamond band saw. The slices were then submitted to computer-assisted morphometric investigation. We found that the subglottic airway rapidly increases in size during the first 2 years of life. Further growth follows a linear mode. The relative proportion of the mucosal lining decreases likewise. In contrast to that in adults, and comparable to that in most mammals, the cartilaginous glottis accounts for 60% to 75% of the vocal folds' length at <2 years. No sexual dimorphism of the larynx exists during childhood. This study supplies detailed morphometric data on the growth and structure of the human larynx during the first years of life. It is the first to use plastinated whole organ serial sections for morphology of the pediatric larynx. Therefore, this study provides quantitative anatomic data of clinical interest that have not been available to date.

Studies of the cranial base in 23 patients with cri-du-chat syndrome suggest a cranial developmental field involved in the condition

The purpose of the present study was to investigate the cranial base on profile radiographs of patients with cri-du-chat syndrome and to relate the findings to current knowledge of brain malformation in an attempt to localize the developmental field affected in cri-du-chat syndrome. The material of profile radiographs of 23 patients was collected in Denmark in the 1970s. Twenty-two patients had terminal deletions of chromosome 5 (5p13.3, 5p14.1, 5p14.2, and 5p14.3), and one patient had an interstitial deletion. The cranial base angle (n-s-ba) was in most cases reduced and in no cases increased compared to age-related standards for normal individuals. Malformations in the bony contours of the sella turcica and the clivus occurred in cri-du-chat patients with terminal deletions. This specific cranial base region develops around the notochord at the location from where the rhombencephalic-derived brainstem, pons, and cerebellum have developed dorsally, and from where the neurons to the larynx have migrated ventrally. As the cranial base, the cerebellum and the larynx are involved in cri-du-chat syndrome, and attention is drawn to a new developmental field which comprises the dorsum sellae, clivus, cerebellum, and larynx. This field seemingly originates from the same notochordal location. The study has demonstrated a cranial base malformation in cri-du-chat patients, which ought to be elucidated in future research and combined with neurological and chromosomal investigations.

Subglottic branch of the superior laryngeal nerve in the dog penetrates the cricoid cartilage

The topographic anatomical study on the distribution pattern of the superior laryngeal nerve (SLN) in the larynx was studied in thirteen adult dogs. The ramus posterior of the SLN divides into two branches; the interarytenoid branch (IA) and the pharyngoesophageal branch (PE). The IA on both sides connect to the cricoid ganglion (CG) in the midline at the cranial border of the cricoid cartilage. Posterior glottic branches arise from the IA, run over the cricoid cartilage, and distribute fibers to the posterior wall of the glottis. Every specimen observed in the present study possessed the CG and the posterior glottic branches. The subglottic branch derives from the IA near the cricoid ganglion, and passes through the cricoid foramen (CF) (Yoshida, 1986). The subglottic branch distributes fibers to the subglottic mucous membrane covering the cricothyreoid ligament. The CF and the subglottic branch were observed on both sides of seven specimens out of thirteen dogs. They were also observed on only one side in three specimens, and were not detectable on either side in the three remaining specimens. The silver impregnation applied in the semimicroscopic dissection facilitated identification of the precise localization and the topographic arrangement of ganglia and nerve bundles.

Three-dimensional analysis of murine laryngeal development

This study defines the critical stages in the prenatal development of the mouse larynx. Three-dimensional computer-generated solid model reconstructions display the changing anatomic relationships during laryngeal development from the earliest respiratory primordium to the mature laryngeal vestibule. These reconstructions demonstrate that the laryngeal vestibule forms as a result of a cephalocaudal separation of the epithelial lamina, thereby establishing communication between the laryngeal cecum and the pharyngoglottic duct. These results support the hypothesis that the cause of congenital supraglottic and glottic malformations is an incomplete separation of this epithelial lamina. The infraglottic lumen remains patent during laryngeal development. Continued lengthening of the foregut between the infraglottis and the carina forms the trachea. This is contrary to the 19th-century concept of an ascending tracheoesophageal septum. Formation of the laryngeal cartilages, muscles, and innervation is portrayed by the reconstructions; with minor variations, they correlate closely with earlier wax reconstructions of human laryngeal development. Future research with this animal model can provide additional insights into the complex mechanisms involved in congenital malformations of the larynx.

Prenatal diagnosis of Fraser syndrome at 18.5 weeks gestation, with autopsy findings at 19 weeks

Sonography permitted the diagnosis of Fraser syndrome (cryptophthalmos-syndactyly syndrome) at 18.5 weeks of gestation in a fetus whose parents had had a previous affected child. The karyotype of that child was 46,XX,inv(9)(p11q21); the karyotype of the phenotypically normal father and of the fetus was 46,XY,inv(9)(p11q21). Findings on sonography included oligohydramnios with nonvisualization of kidneys, hypertelorism and microphthalmia, and markedly enlarged lungs. On autopsy at 19 weeks, findings included renal agenesis, cryptophthalmos with multiple abnormalities of the eyes and ocular adnexa, laryngeal atresia, pulmonary hyperplasia with accelerated maturation, absence of the Eustachian tube with connective tissue occupying the tympanic cavity and bone occluding the external acoustic meatus, and soft-tissue webbing between the digits. This is the second reported instance of prenatal diagnosis of Fraser syndrome in the second trimester. The histopathologic findings in Fraser syndrome at this gestational age, in particular the eye and ear, have not been described previously.

The human rhombencephalon at the end of the embryonic period proper

The human rhombencephalon at 8 postovulatory weeks (stage 23) is described and illustrated for the first time with the aid of silver-impregnated sections and graphic reconstructions. The motor and sensory trigeminal nuclei were among those studied, and the latter was found to be almost contiguous to the dentate nucleus. Fibers to the principal sensory nucleus join the mesencephalic trigeminal tract, which also seems to be connected with the motor fibers. Fine fibers from the sensory root join the tractus solitarius, which appears to receive connections from the facial, glossopharyngeal, and vagal nerves. Main and accessory abducent nuclei are evident. A part (the Kappenkern des Facialisknies) of the nucleus funiculi teretis is particularly prominent. The presence of the pyramidal decussation during the embryonic period is noted for the first time. The arrangement of nuclei and tracts at 8 weeks is shown to be closely similar to that present in the newborn, and it is likely that the rapid growth of the rhombencephalon during the embryonic period proper is associated with correspondingly early functional activity.