Early structural changes in the rat tympanic membrane during pneumococcal otitis media.

The early inflammatory reaction in the rat tympanic membrane was studied during the first 36h following inoculation of Streptococcus pneumoniae type 3 in the middle ear cavity. Otomicroscopic examination showed only minor signs of inflammation in the early stages although changes at the light microscopic level were pronounced. This reaction differed significantly between the pars flaccida and pars tensa of the tympanic membrane. Three hours after inoculation, edema and infiltration with polymorphonuclear leukocytes and macrophages were found in the pars flaccida whereas in the pars tensa no polymorphonuclear leukocytes were noted until after 12h. This reaction was most prominent after 36h. In the pars flaccida, mitoses occurred frequently among the cells of the simple squamous epithelium, which changed into a double-layered cuboidal epithelium. These findings demonstrate that an inflammatory reaction starts earlier in the pars flaccida than in the pars tensa of the tympanic membrane.