Myringotomized tympanic membranes cultured in vitro do not develop myringosclerosis

The aim of this study was to evaluate the development of myringosclerosis in in vitro-cultured tympanic membranes. Sprague-Dawley rats were myringotomized bilaterally and the tympanic membranes were excised after sacrifice. The explants were placed in inserts in wells filled with a nutrient medium. Every second day the tympanic membranes were photodocumented and after 9 days the explants were prepared for histology. On the 4th day the explants had attached to the bottom of the inserts and the specimens had thickened. From the perforation borders and the dissection edges a thin outgrowth was extending across the surface. By Day 9 the perforation had clearly diminished in size when examined in a stereomicroscope. In a light microscope the keratin layer was seen to protrude towards the centre of the perforation and, at the borders, epithelial cells were bridging the gap. Neither the pars tensa nor the pars flaccida showed any sclerotic lesions. The pars flaccida had thickened and the basal cells of the outer keratinized epithelium had invaded the connective tissue. Inflammatory cells were sparse in both the pars tensa and pars flaccida. The in vitro-cultured myringotomized tympanic membrane therefore shows a similar healing pattern to that in vivo. However, inflammatory reactions are sparse and there is no development of myringosclerosis.