Type II collagen induced tympanosclerosis model in guinea pigs

Immunohistochemical quantitation of collagen types I, II, IV and V in the ventilated and non-ventilated rabbit middle ear with otitis media with effusion

Morphometric quantitation of the area fractions of collagen types I, II, IV and V was determined in the normal rabbit middle ear mucosa and in relation to otitis media with effusion (OME) using a three-layered peroxidase-antiperoxidase technique. The effects of substituting normal low-oxygen middle ear gas (non-ventilated) with atmospheric air (ventilated) were studied in both healthy ears and ears with OME. Based upon previous histological examinations in rabbits, only ears with OME for more than 8 weeks were included to ensure the presence of chronic inflammation (COME). Atmospheric air was introduced into the middle ears by insertion of ventilation tubes or by an enlarged myringotomy. Collagen type I was predominant in all groups studied. The area fractions of collagen types I, II and IV were increased significantly in COME, with collagen type II elevated in particular. Ventilation of the normal ears resulted in a significantly increased area fraction of cells, while the area fractions and distributions of the collagen types were unaffected. None of the ventilated ears in COME improved or healed spontaneously. The total fraction of collagen in COME was not changed significantly by the introduction of atmospheric air. However, the individual distribution of the collagen types was altered, with significantly larger area fractions of types II and V found in ventilated ears with COME. Possible explanations for the differences found are discussed, including the role of oxygen-derived free radicals.

Pathogenesis of tympanosclerosis

In spite of the wealth of information on the clinical, histologic, and pathologic aspects of tympanosclerosis, the pathogenesis of tympanosclerosis is still unclear. In an attempt to understand the pathogenesis, 319 human temporal bones from 196 individuals with otitis media were studied. The extent and nature of tympanosclerosis and the characteristics of the otitis media associated with it were studied. Forty-five temporal bones from 35 individuals with otitis media were found to have tympanosclerosis, giving an incidence of 14.1%. It was seen most commonly in individuals over 40 years of age (86.7%). The male-to-female ratio was 1.6:1. The most common site of occurrence was the tympanic membrane (88.9%). Tympanosclerosis was seen more often in the anterior and posterior inferior quadrants of the tympanic membrane and that, too, in a central position. Tympanosclerosis was seen more commonly in temporal bones with irreversible inflammatory changes, and in this group, late plaques were more commonly seen than early or intermediate plaques. Audiometric charts failed to show any direct relationship between extent of tympanosclerosis and the severity of hearing loss. The only audiometric finding of any consequence was a mixed hearing loss in the presence of middle ear tympanosclerosis.