PubMed2000
BACKGROUND: The morphological development of the human larynx during the first years of life has previously not been studied in detail and has mainly been described on a qualitative basis. This study seeks to provide detailed morphometric data on the regular anatomy of the vocal cords, the subglottic airway and the tracheal airway dimensions gained from plastinated whole organ serial sections of 43 infant larynges and to determine morphological changes with age. Such information may be useful for the understanding of pediatric airway disease or for laryngeal surgery in children. MATERIAL AND METHODS: The larynges of 43 children aged 1 to 60 months were plastinated. Whole organ serial sections were obtained by cutting the resulting specimen with a diamond band saw. Morphometry of whole-organ sections was accomplished using a high resolution, computer-based image analyzer. The total length of the glottis, length of the cartilaginous and ligamentous glottis, subglottic cartilaginous cross-section, subglottic airway and tracheal airway were determined for each specimen. RESULTS: The subglottic airway increases considerably in size during the first 2 years of life (from 13 to 28 mm2 in the means). Further growth seems to follow a linear mode. The relative proportion of the mucosal lining of the subglottic airway decreases likewise. While it occupies approximately 50% of the subglottic cartilaginous cross-section during the first two years of age, its relative proportion decreases to some 30 to 40% between age three to five. Other than in adults, and comparable to most mammals, the cartilaginous glottis accounts for 60 to 75% of the vocal folds' length in children under two years of age. The anterior ligamentous part of the glottis outsizes its posterior cartilaginous portion during the third year of life. CONCLUSION: This study supplies detailed morphometric data on the growth and structure of the human larynx during the first years of life that have not been available to date. Previous studies on the anatomical configuration of the infant larynx have focused on the the perinatal larynx, the prepuberal and puberal larynx, and the development of collagen fibres in the developing larynx. The human larynx has undergone significant evolutionary adaptations. Among them are the descent of the larynx, the capability of vocal fold adjustment in length, tension and shape, and the prominent configuration of the membranous part of the vocal folds as opposed to the cartilaginous part. The infant larynx is not just a miniature of the adult organ. It shows differences in its position relative to the vertebrate column, in the composition of cartilages and soft tissues, and in environmental adaptation. The present study is the first to supply detailed morphometric data on the growth and structure of the human larynx during the first five years of life and on the morphological changes of the larynx during this period. From these data it seems that some of the adaption of the human larynx as opposed to other vertebrates are not fully developed at birth, but undergo postnatal maturation. The relative proportions of the cartilaginous and membranous parts of the vocal folds clearly demonstrate this maturation process: While the posterior "respiratory" glottis accounts for some sixty to 75% of the total glottic length in newborns, its relative proportion decreases throughout the first years of life and finally equals the proportions of the adult larynx. Other than in adults, and in accordance with the literature, no sexual dimorphism of the larynx could be detected in this series of infant larynges. Morphometric data on the growth and structure of the human vocal folds and the subglottic airway during childhood are presented. Plastinated whole organ serial sections were used in the study to show the infant laryngeal morphology. The study provides quantitative anatomical data of clinical interest that light up the anatomy of the pediatric airways.