Lamina propria of the human vocal fold: histomorphometric study of collagen fibers.
BACKGROUND
Since the seminal work of M. Hirano, which defined the three-layered lamina propria of the human vocal fold, there has been confusion in the labeling of each layer. Recent studies described the composition of fibers and interstitial molecules within the lamina propria leading to various biomechanical properties. However, collagen fibers appear as the most important structure component.


METHODS
We used an optical analysis and the picrosirius-polarization method to describe collagen fibers from six adult and two fetal human larynges fixed in formalin and frontally sectioned in the middle part of the vocal fold.


RESULTS
The deep layer of the lamina propria is the most densely organized band of collagen fibers penetrating the superficial muscle bundles of the vocal muscle. The mean thickness of this layer is about 36% of the lamina propria and shows a network of strongly birefringent fibers (collagen type I and III). The superficial layer of the lamina propria is a narrow band of collagen fibers immediately below the basement membrane of the epithelium. The mean thickness of this layer is about 13% of the lamina propria and shows strong birefringent fibers. The intermediate layer is the less densely organized band between the deep and superficial layers. The mean thickness of this layer is about 51% of the lamina propria and shows clear, green weakly birefringent fibers characterized as collagen type III. The fetal lamina propria contains only a monolayer distribution of loose collagen fibers between the epithelium and the vocal muscle.


CONCLUSIONS
These results help describe the distribution of collagen fibers within the lamina propria of the human vocal fold and have implications to understand the cover-body theory of voice production both in the adult and newborn.
Prades
Jean-Michel
JM
Department of Anatomy, Faculty of Medicine, CHU Nord, Saint-Etienne, France. Jean.Michel.Prades@univ-st-etienne.fr
Dumollard
Jean Marc
JM
Duband
Sébastien
S
Timoshenko
Andrei
A
Richard
Céline
C
Dubois
Marie Dominique
MD
Martin
Christian
C
Peoc'h
Michel
M
D000368:Aged; D001391:Azo Compounds; D002102:Cadaver; D003094:Collagen / Q000032:analysis*; D005333:Fetus / Q000033:anatomy & histology; D006801:Humans; D008859:Microscopy, Polarization; D008875:Middle Aged; D013194:Staining and Labeling; D014827:Vocal Cords / Q000033:anatomy & histology* / Q000737:chemistry / Q000196:embryology
D001391:Azo Compounds; C009798:C.I. direct red 80; D003094:Collagen