in otitis media there is an infection of the whole of the middle ear cleft, i.e. the Eustachian tube, tympanic cavity, attic, mastoid antrum and air cells.
colonization of nasopharynx with S. pneumoniae, H. influenzae, or M. catarrhalis predispose to otitis media (1)
this results in aspiration of infected inoculum through the eustachian tube into the middle ear space
aspiration is promoted by following mechanisms (1)
nasal obstruction that increases the positive pressure in the nasopharyngeal space
eustachian tube dysfunction that produces a negative pressure in the middle ear space
the mucous membrane is thus invaded by organisms which cause inflammation, oedema and exudate - pus is a later consequence of bacterial infection.
the Eustachian tube is closed by oedema and so prevents aeration and drainage
the drum bulges due to increased pressure from the pus
perforation of the tympanic membrane results, caused by necrosis. There is continual drainage of the ear until the infection resolves.
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