pathology

Last reviewed 01/2018

• 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.

Reference:

• (1) Acute otitis media:virtual classroom of the american academy of paediatrics