Persistent structural changes in the middle ear mucosa of the rat, after an experimentally induced episode of pneumococcal otitis media.

To examine the effect of a transient episode of purulent AOM on the middle ear mucosa, an animal model was used. Histological examination was performed after inoculation of pneumococci into the rat middle ear. At 4, 8 and 12 days, and at 2 months after the inoculation, rats were sacrificed on each occasion and samples taken from specific areas of the middle ear mucosa. Structural alterations were noted at all mucosal sites. The normally flat epithelium had become more cuboidal or cylindrical, and numerous ciliated cells occurred in areas originally devoid of these cells. Epithelial cells penetrated the subepithelium forming gland-like structures. In the early phase, day 4 and day 8, inflammatory cells invaded the subepithelial layer except in the tympanic membrane. At 2 months, with the tympanic membrane otimicroscopically and histologically normalized, the structural changes of the mucosa still persisted indicating that a transient episode of pneumococcal otitis media can cause persisting mucosal changes.