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.

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.

Changes of laryngeal parameters during intrauterine life.

OBJECTIVE: Increased care of fetal and neonatal airways has led to advances in neonatal medicine. The early diagnosis and treatment of respiratory diseases require a detailed knowledge of fetal airway anatomy and development. The aim of this study was to determine the anatomical development of the thyroid and cricoid cartilages and their structural variability during fetal life. MATERIAL AND METHODS: The study was performed on the thyroid and cricoid cartilages of 55 human fetal larynges of both sexes, between the ages of 13 and 27 weeks of intrauterine life. Numerous measurements of the thyroid and cricoid cartilages were performed. RESULTS: Correlations between the obtained results were calculated in relation to the crown-rump (C-R) length of human fetuses and to sex. The structural variability of the thyroid and cricoid cartilages of human male and female fetuses in subsequent weeks of intrauterine life was observed. In both genders a correlation between laryngeal size and fetal crown-rump length, regardless of sex, was found. The thyroid cartilage presents a sexual dimorphism. CONCLUSIONS: The results of this study can be useful in the analysis of prenatal examinations, and in planning the treatment of airway emergencies.

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.

Ceratocricoid muscle: an embryological and anatomical study.

This study aimed to document the prevalence and morphology of the ceratocricoid muscle in a large sample of fetuses and adults and to explain its possible origin in a sample of embryos. Forty-five embryos, thirty-four fetuses, and ninety human larynges from adults with no known laryngeal pathology were studied. The muscle was observed in 23% of the fetal sample and in 14% of the adult sample. No significant differences were observed in the laterality in any of the groups. The ceratocricoid muscle is attached between the cricoid lamina and the inferior horn of the thyroid cartilage and also into the capsule of the cricothyroid joint. The muscle is innervated by several branches (between one and three) from the anterior division of the recurrent laryngeal nerve as it courses behind the cricothyroid joint. The ceratocricoid muscle develops from tissue within the mesenchymal bridge which connects the external and internal laryngeal sphincters or rings from embryonic stages 15-20. The close relationship of the ceratocricoid muscle to the recurrent laryngeal nerve could mean that it can exert pressure on this nerve. This may be a possible explanation for the causation of certain idiopathic recurrent laryngeal nerve palsies.

Fetal cricotracheal manipulation: effects on airway healing, cricoid growth and lung development.

The last decade has seen significant advance in the surgical management of pediatric subglottic stenosis, which remains one of the most fascinating problems of the laryngotracheal complex (LTC). Refined techniques for operating on these fragile structures should reduce cricotracheal scarring to a minimum, thus avoiding a lot of severe postoperative complications in a tricky moment of laryngeal's growing up. Experimental works indicates that the LTC growth is variously affected by longitudinal anterior, posterior or lateral incisions and actually the indications for laringotracheoplasty or cricotracheal resection in children with subglottic stenosis are still unclear. Reports on fetal manipulation of cricotracheal tissues are lacking as well as early effects on airway healing, LTC growth and lung development. The aim of this study was to evaluate if the airway mucosal healing is regenerative and scarless after cricotracheal manipulation in fetuses of New Zealand White Rabbits (NZWRFs). The consequences of fetal incisions on the cricoid growth and lung development are also examined, in a group of 12 NZWRFs, manipulated at 25+/-1 days of gestational age. The does underwent halothane anesthesia and all received a bilateral longitudinal cricoidotracheotomy. Twenty sham-operated fetuses were submitted to a limited cervicotomy (control's group). At the time of retrieval (31+/-0.5 days), en bloc laryngotracheobronchial tree and lungs were collected and processed for histological and morphometric analysis. Parameters recorded included: 1) histological full-thickness examinations focusing on inflammation, foreign body reaction, fibrosis, neochondrogenesis; 2) morphometric analysis, including the fetal Subglottic Diameter (FSD), the fetal Subglottic Area (FSA), the Radial Alveolar Count (rAC) and Computer Assisted Morphometric Colorimetry (CAmc); 3)analysis of lung hypoplasia (LH) by means of lung weight/body weight (LW/BW) ratio, protein and DNA indexes; 4) finally, different fractions of lung tissue phospholipids for lung maturity assessment were studied. Student's t test, when indicated, was performed for statistical analysis (p <0.05 = significant). There was no maternal mortality in this study. Ten fetuses were available for a final evaluation (16.6% mortality). In one case only, an incomplete closure of the fetal cricoidotomy was seen and could be probably due to a technical mistake. Mean fetal subglottic diameter and area were respectively 0.13+/-0.05 mm and 3.15+/-0.45 mm2 in both groups. As well as in fetal dermal repair, regeneration of the airway cartilage and mucosa were complete and scarless. LW/BW ratio, DNA content and analysis of different fractions of phospholipids were similar in experimental vs. the control group. These findings suggest that the healing processes were fibrosis-free and without evidence of scars. A complete closure of the incisions was achieved without stenosis of the fetal subglottic region. In addition, it seems that the fetal cricoidotracheotomy doesn't interfere with the laryngeal function which coordinate the amount of liquid leaving the lungs via the trachea. In addition, only a small leakage of amniotic fluid is shown and this could be responsible for normal and mature lungs.

Apoptosis in the developing human cricoid cartilage: a pilot study.

Apoptosis is widely recognized as a major phenomenon in normal development. Deficiencies in this process may lead to developmental abnormalities such as congenital subglottic stenosis. We studied apoptosis using in situ end labeling of the 3'-OH ends of fragmented DNA in 5 progressively older, normal, human cricoid cartilage specimens. Results show that apoptosis is a very active process in fetal and neonatal tissue. The process gradually slows with advancing age. In the 4- and 13-year-old specimens, minimal to no apoptosis was seen. We conclude that apoptosis plays a critical role in the intraluminal and extraluminal expansion of the cricoid cartilage.

Growth and development of the human cricoid cartilage: an immunohistochemical analysis of the maturation sequence of the chondrocytes and surrounding cartilage matrix.

OBJECTIVES: The goal was to determine maturational changes in the human cricoid cartilage. STUDY DESIGN: The study involved immunohistochemical staining of collagen II (a marker of proliferating chondrocytes), matrilin-1 (a marker of post-proliferative chondrocytes), and collagen X (a marker of hypertrophic chondrocytes). Specimens included uninjured human cricoid cartilages at 18 and 41 weeks' gestation and 1, 4, and 13 years postpartum. RESULTS: This study demonstrated that type II collagen peaks in concentration at approximately 41 weeks' gestation. Matrilin-1 is present in progressively lower concentration in the central core of the cricoid ring, but the peripheries of the ring contain the protein in relatively high concentration. Type X collagen is not expressed in the age groups tested. CONCLUSIONS: These biochemical markers lend further support to a chondrocyte proliferative phase that slows between 1 and 4 years of age. Chondrocytes then enter a phase histologically similar to the hypertrophic phase but are biochemically different than hypertrophic chondrocytes destined for endochondral ossification.

Novel cell proliferation marker for identification of a growth center in the developing human cricoid.

BACKGROUND: Developmental histomorphology of the human cricoid cartilage has never been well described. Regional growth centers in the cricoid have been hypothesized, but have never been demonstrated in histological sections. OBJECTIVES: To apply Mib-1 immunostaining, a monoclonal antibody directed at a nuclear proliferation marker, in human cricoids to identify a growth center and to study the changing histomorphology of the developing cricoid. DESIGN: Immunohistochemical Mib-1 studies were performed on postmortem cricoid sections of 2 fetuses (gestational age, 18.5 and 33 weeks), 1 newborn (full term, 41 weeks), and 3 children (aged 1, 4, and 13 years, respectively). Cell counts, surface areas, and organizational patterns of the chondrocytes were studied and described in hemotoxylin-eosin-stained sections. RESULTS: Differential Mib-1 staining was found. The 18.5-week fetus showed diffuse cell proliferation throughout the cricoid. The cricoid sections of the 33-week fetus and 1-year-old child revealed a distinct ring of proliferation in the outer third of the cricoid ring. The 4- and 13-year-old exhibited no cell proliferation. Histomorphologically, with increasing age came chondrocyte hypertrophy, decreasing cell count per standard square, and increasing organization from a scattered to radial columnar pattern. CONCLUSIONS: Growth of the cricoid involves a diffuse pattern of cell proliferation throughout the cricoid in fetal tissue. At term and until age 1 year, the region of proliferation is more restricted to the outer subperichondrial surface. By age 4 years, cell proliferation has stopped. Histomorphologic changes in the developing cricoid include decreasing cell counts per standard unit area, but increasing surface area with age. The aging chondrocytes develop an increasingly organized layout to form a radially arranged columnar pattern similar to that in the growth plate of the developing limb bud.

Laryngeal clefts: a histopathologic study and review.

The histopathologic findings in a case of laryngeal cleft studied by serial sectioning, and a literature review of this clinical entity are presented. The primary micropathologic findings include a cleft deformity of the posterior cricoid lamina, and alterations in muscle differentiation involving the interarytenoid and posterior cricoarytenoid muscles. Possible embryogenic mechanisms are discussed. The clinical picture is characterized by signs and symtpoms of aspiration with airway obstruction, and definitive diagnosis is achieved by endoscopic examination. Treatment consists of surgical repair, although some patients with type 1 laryngeal clefts may be managed on a conservative trial. The need for uniform classification of laryngeal clefts in future reporting is emphasized.