Histomorphometric Estimation of Air Cell Development in Experimental Otitis Media

Abstract

The objectives of this study were to examine the effect of acute otitis media on the bony development of the growing middle ear air cell system with a reliable and concise stereologic histomorphometric method and to generate a standard baseline growth plot for the middle ear of the rat. The authors conducted a histomorphometric analysis of bullar volume during the entire growth period after early induction of unilateral otitis media. The authors conducted undecalcified processing of 27 rat skulls sectioned horizontally at various ages from 20 to 83 days after unilateral transtympanic injection of Streptococcus pneumoniae at 19 days postpartum. Stereologic estimation of bullar volume was performed in the experimental and the control ear with Cavalieri's principle. Body mass and air cell volume were plotted as functions of subject age using standard developmental equations on the experimental results. Volumes of the middle ear air cell system were consistently smaller in the otitis ears. Bullar growth was completed at 60 days regardless of otitis history, but body mass was increasing throughout the experimental period. A single incident of otitis media introduced early in life is sufficient to significantly reduce the final volume of the bulla in rats. This finding may mimic the effect of otitis media contracted in early childhood on the development of the mastoid air cells. The standard growth plot provides a timeframe for studies of signaling molecules responsible for bone modeling in pneumatization.