Development of the human true vocal fold: Depth of cell layers and quantifying cell types within the lamina propria

Objectives: We sought to further describe the development of the 3-layered human vocal fold in children and to quantify macrophage and myofibroblast concentrations in each layer. Methods: We used an optical analysis software package to examine 8 longitudinally sectioned human vocal folds that had been fixed in formalin (ages 2 days to 14 years). Results: The 2-day-old vocal fold contained only a monolayer of cells. This became a bilayer by 5 months, and a trilayer began to become evident by 7 years. The percent of total depth represented by the superficial layer of the lamina propria (SLP) gradually decreased with age. The SLP made up 22% of the total lamina propria by age 7 years; this percentage approximates that in the adult vocal fold. Macrophages and myofibroblasts were predominately found in the SLP, and began to be apparent by 11 months of age. Conclusions: These results help describe the development of human voice and may have implications as to when phonosurgical therapy can be considered for children.