Etiologic factors in non-suppurative otitis media.

Two observations in non-suppurative otitis media, namely the serous fluid and the tympanic membrane retraction, may have separate explanations as to the etiologic factors. The first is the obstruction of the collecting lymphatic tubules of the middle ear and eustachian tube as they drain to the retropharyngeal lymphatics. This leads to a transudation of fluid in the middle ear or serous fluid. The second observation, retraction of the tympanic membrane, may be due to an absence or significant reduction of the surface tension lowering substance (Surface Active Membrane) of the eustachian tube, preventing the transmission of air to the middle ear from the nasopharynx.