THE INTERMEDIATE LAYER - A MORPHOLOGIC STUDY OF THE ELASTIN AND HYALURONIC-ACID CONSTITUENTS OF NORMAL HUMAN VOCAL FOLDS

The lamina propria of vocal folds are important in voice production. W e evaluated the morphologic features of elastin and hyaluronic acid, t wo important constituents of the lamina propria. Thirty normal human v ocal folds were obtained from patients dying of traumatic causes witho ut vocal fold injury. These tissues were immediately prepared for hist ologic and ultrastructural examination by standard methods. For specif ic study of the ultrastructure of the layers of the lamina propria, si x vocal folds were divided horizontally through the midplane of the la mina propria. We found that the elastin composition of the vocal folds is variable, the largest amount being seen in the midportion on elast in-van Gieson (EVG) staining and ultrastructural evaluation. The super ficial layer of the lamina propria contains fewer large elastin fibers . In this region, we found that elastin was predominantly composed of elaunin and oxytalan, which stain poorly with EVG. Using computer-assi sted image analysis, we quantified the differences in elastin composit ion between the layers. The amount of elastin varied between men and w omen, and these differences could not be accurately measured by the me thods employed. Hyaluronic acid was abundant especially in the midport ion of the lamina propria and was significantly more abundant in men t han women on quantification. The significance of these observations in normal vocal folds is discussed.