It has been recognized that the endotoxins of gram-negative bacteria are responsible in the pathogenesis of otitis media with effusion, sustaining the inflammatory response after an acute primary infection has been cleared. Using a scanning electron microscope, the authors studied the change of middle ear mucosa of guinea pigs after applying endotoxin through the tympanic membrane into the middle ear cavity. Serous effusions were observed from the 2nd through the12th day after the local application. Edema and congestion of the middle ear mucosa were also found. The density and the activity of secretory cells were increased. An increase in number of microvilli on the non-ciliated cells was also noted. Some ciliated cells showed the abnormal figures such as short cilia, decreased number of cilia, knobformation, compound cilia and elongated cilia. The changes were similar to those observed in the human middle ear mucosa of otitis media with effusion. From these findings, it is conjectured that endotoxin is one of the causative factors in the pathogenesis of otitis media with effusion.
