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 replicat e in an animal model tissue change formed clinically during radiothera py for the treatment of head and neck malignancy. Gamma irradiation wa s 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 we re then sacrificed at sequential intervals. The tympanic bullae were r emoved and the mucosa was processed for scanning electron microscopy. Tissue findings indicated that irradiation might initially have no inf luence on the clearance activity of the middle ear. However, ultrastru ctural changes showed stagnation of secretion between cilia, falling o ff and different directions of the cilia, fused or collapsed cilia, an d eustachian tube dysfunction (with mucosal edema). These findings pos sibly account for the occurrence of middle ear effusions in patients d uring and after radiotherapy for head and neck malignancy. It is our c oncept that insertion of a ventilation tube is necessary if abnormal m ucociliary function appears, in order to clear and prevent the accumul ation of any middle ear effusions and prevent further mucociliary dysf unction.