Structural changes in the rat middle ear mucosa due to endotoxin and eustachian tube obstruction

The middle ears of 48 rats were used to examine the effects of endotoxin in jection, eustachian tube obstruction or a combination of eustachian tube ob struction and endotoxin injection. Animals were frilled after 1, 2, 4, or 1 2 weeks and the middle ears processed for light and scanning electron micro scopy. Compared to the normal middle ear mucosa, the epithelial layer was m ore pseudostratified, cuboidal or cylindrical after endotoxin injection or obstruction of the eustachian tube. In the early phase, numerous ciliated c ells occurred in areas originally almost devoid of these cells. At 3 months , degeneration of ciliated cells was observed. The combination of eustachia n tube obstruction and endotoxin injection also induced a more pseudostrati fied, cuboidal or cylindrical epithelium with an increased number of goblet cells, However, an early decrease occurred in the number of ciliated cells in the tympanic orifice of the eustachian tube. Furthermore, inflammatory cells, mainly PMNs, macrophages and lymphocytes, invaded the subepithelial layer after eustachian tube obstruction and endotoxin injection. These stru ctural changes resulted in an impairment of the mucociliary transport syste m for clearance of the middle ear cavity. For this reason we believe that b oth endotoxin and eustachian tube obstruction or dysfunction play an import ant role in inducing persistent mucosal changes in the middle ear cavity, t hereby prolonging otitis media with effusion.