Effects of irradiation on the rat middle ear mucosa. A scanning electron microscopic study.

Adult Sprague-Dawley rats (n = 64) were used in this study to replicate in an animal model tissue change formed clinically during radiotherapy for the treatment of head and neck malignancy. Gamma irradiation was administered to both ears of each rat, using a cobalt-60 machine. A total dose of 30 Gy was administered, with 500 cGy/fraction given on 6 consecutive days to a time-dose fractionation value of 81. Animals were then sacrificed at sequential intervals. The tympanic bullae were removed and the mucosa was processed for scanning electron microscopy. Tissue findings indicated that irradiation might initially have no influence on the clearance activity of the middle ear. However, ultrastructural changes showed stagnation of secretion between cilia, falling off and different directions of the cilia, fused or collapsed cilia, and eustachian tube dysfunction (with mucosal edema). These findings possibly account for the occurrence of middle ear effusions in patients during and after radiotherapy for head and neck malignancy. It is our concept that insertion of a ventilation tube is necessary if abnormal mucociliary function appears, in order to clear and prevent the accumulation of any middle ear effusions and prevent further mucociliary dysfunction.