Structural changes in the middle ear tissues of the rat after fractionated irradiation.

Chronic suppurative otitis media often ensues in patients treated with irradiation against a head and neck tumor. In an experimental study, rats were exposed to irradiation to evaluate the sensitivity of the middle ear to an accumulated irradiation dose of 20-45 Gy. Observed otomicroscopically, all animals appeared to have normal tympanic membranes and no fluid developed in the middle ear space. Ten days after the irradiation, minor structural changes had occurred in the pars flaccida. The keratinizing epithelium had thickened and mitoses were seen histologically. The lamina propria was edematous and contained polymorphonuclear cells and macrophages. The middle ear mucosa from all other tissue sites appeared normal. Six months after irradiation only minor changes in the pars flaccida were evident: the lamina propria was thin and inelastic and macrophages were present in the stroma. It is inferred from this study that the middle ear of the rat is relatively resistant to irradiation.