Development and maturation of the pediatric human vocal fold lamina propria.

OBJECTIVE: To identify characteristic patterns of maturation of the human vocal fold lamina propria as it develops into a mature structure.
METHODS: Histologic evaluation of sectioned true vocal folds from 34 archived larynges ages 0 to 18 years using hematoxylin-eosin, trichrome, Alcian blue pH 2.5, Weigert reticular, and Miller's elastin stain. LOCATION: Pathology department at a tertiary care children's hospital.
RESULTS: At birth and shortly thereafter, there exists a relative hypercellular monolayer of cells throughout the lamina propria. By 2 months of age, there are the first signs of differentiation into a bilaminar structure of distinct cellular population densities. Between 11 months and 5 years, two distinct patterns are seen: 1) this bilaminar structure and 2) a lamina propria where there exists a third more hypocellular region immediately adjacent to the vocalis muscle (this region is similar to the superficial hypocellular region found just deep to the surface epithelium). By 7 years of age, all of the specimens exhibit this transition between the middle and the deeper layers according to differential density of cell populations. A lamina propria structure defined by differential fiber composition (elastin and collagen fibers) is not present until 13 years of age and then is present throughout adolescence.
CONCLUSIONS: Using the classic adult model of fiber composition and density to differentiate the layered structure of the lamina propria of the human vocal fold may not adequately allow for a thorough description of the process of maturation and development. Rather, distinct regions of cell density are seen as early as 2 months postpartum, and the model of cellular distribution may serve better to describe the lamina propria as it develops. Cell-signaling processes that shape the formation of the lamina propria appear to produce layered populations of differential cell density that in turn will later produce differential fiber compositions. Early development therefore can be followed by evaluating the maturation of these differing cell populations. Future studies are needed to quantify these cell distribution patterns, to study the cell signaling processes that trigger this maturation, and to correlate these findings with mechanical modeling.