Structural tympanic membrane changes in secretory otitis media and cholesteatoma.
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BACKGROUND
Otitis media may predispose for retraction pathologic abnormality later in life. A weakening of the collagen fiber bundles in the lamina propria of the tympanic membrane (TM) is a prerequisite for the formation of a retraction pocket. Various collagen types have different tensile strength. The collagen-type distribution in the TM during otitis media and cholesteatoma has not been reported before.
METHODS
The collagen contents of TM biopsies from child patients with longstanding secretory otitis media without retraction pockets were compared with pars tensa cholesteatomas using immunohistochemical staining for collagen Types I to IV. The histology was also investigated using transmission electron microscopy.
RESULTS
The outer epithelium was in some biopsies thickened with evidence of edema. The biopsies showed an intact lamina propria with positive immunohistochemical staining for collagen Types I to III and showed normal collagen fiber bundles on electron microscopy. The outer epithelium of the cholesteatomas showed marked thickness variations and signs of edema. There was a presence of normal collagen fiber bundles in smaller parts of all cholesteatomas, positive for collagen Types I to II. In other parts, only scattered collagen fibers were found.
CONCLUSIONS
Tympanic membrane biopsies from patients with longstanding secretory otitis media may show a thickening of the outer epithelium. Collagen Types I to III are present in the lamina propria, and no ultrastructural changes of the collagen fiber bundles are observed. Collagen is found in cholesteatomas in the remnants of the lamina propria, with positive staining for collagen Types I and II, whereas Type III seems to be lacking.
