Middle ear effusion caused by mechanical stimulation of the external auditory canal. An experimental study in the rat

Mechanical stimulation of the external auditory canal (EAC) in rat, either by scratching or exposure to a stream of air, caused effusion behind an intact ear-drum both in the experimental ear and in the contralateral one. Histologically the pars flaccida appeared oedematous, especially its lamina propria; and was infiltrated by inflammatory cells indicating a vascular leakage. Determination of the histamine level of the content of the middle ear cavity showed elevated levels, not only in the experimental ear but also in the contralateral. This increased level of histamine was recorded as long as 24 hours after stimulation. Though the mechanisms involved are not known, new ideas about the initiation of otitis media with effusion are inferred.