Distribution of Collagen in the Lamina Propria of the Human Vocal Fold

OBJECTIVES: To describe the arrangement of collagen fibers in the lamina propria of the human vocal fold. STUDY DESIGN: Analysis of the lamina propria of the vocal fold obtained from human cadavers. METHODS: The Picrosirius-polarization method was used to visualize collagen fibers. RESULTS: Analysis of 20 human vocal folds by the Picrosirius-polarization method permitted the visualization of two fiber populations arranged in three layers in the lamina propria: two layers of thick, strongly birefringent collagen fibers (collagen type I), one immediately below the epithelium and another more dense layer in the deep region superficially to the vocal muscle, penetrating between muscle fibers. The third layer consisted of fine, weakly birefringent fibers (collagen type III) located between the two layers of thick fibers. In addition, the collagen fibers in the lamina propria showed an intertwined network arrangement in the form of a "wicker basket." CONCLUSIONS: This basket-like configuration better explains how the vocal fold is able to stretch even though it contains nonstretchable fibers and to modulate the frequency of the voice under the action of the intrinsic musculature of the larynx. Segmental areas of disarray of the basket-like structure of the collagen layers were systematically observed in older patients. Thus, it is possible that vocal alterations occurring in the elderly might be the result of a loss of histoarchitectural arrangement of the collagen system and its relationship with the lamina propria and underlying musculature.