Objectives: We undertook (1) to measure the cell density within the lamina propria of the neonatal vocal folds and (2) to examine changes in cell density in the lamina propria with increasing gestational age of the neonatal vocal folds.
Methods: Intact neonatal larynges were obtained from fresh cadaveric specimens. Hematoxylin and eosin-stained slides were used to visualize the laryngeal structures, and photomicrographs of the vocal folds were taken at 100x magnification. The cell density of the lamina propria was calculated by counting the cells within each of five 100-microm2 regions within the study area, and the totals were then averaged for each area.
Results: A total of 62 sections from 14 larynges with gestational ages of 19 to 36 weeks were examined. Histologic analysis revealed a uniform appearance of the vocal fold without apparent layers. The cell density of the lamina propria was 30 or more cells per 100 microm2 for 51.2% of larynges with less than 27 weeks of gestation. However, only 14.3% of the larynges with 27 or more weeks of gestation had an average cell density of 30 or more cells per region (p < 0.005).
Conclusions: As described by previous studies, the lamina propria of the neonatal vocal folds is a hypercellular monolayer. The process of vocal fold maturation appears to occur earlier than previously thought, with decreasing cell density in the lamina propria by 27 weeks' gestation.