The Effects of External Beam Irradiation on Ear Cartilage: An Animal Model

Abstract

Adjuvant therapy of the head and neck has become the mainstay for treatment of head and neck malignancies. Although important for local control, complications do arise with the use of this adjuvant therapy. We have recently noted changes in the ear architecture in patients that have undergone postoperative irradiation therapy. In an attempt to identify changes in the cartilage thickness, we conducted an animal model to determine the etiology of our clinical observation. Eighteen New Zealand white rabbits were utilized. Three experimental irradiated groups were designed for single dose external cobalt60 beam therapy at 20, 25 and 30 Gy. The right ear served as matched nonirradiated control. After two months the cartilage underwent quantitative histomorphometric analysis using an inverted microscope, digitized camera and computer software. Irradiation did not significantly affect the thickness of cartilage upon comparing control and irradiated groups. There was no change seen in vascularity or tissue composition that could be identified. In conclusion, it appears that alterations in thickness of the cartilage did not result in the clinical examples demonstrated. The etiology to the changes noted clinically are unknown, but may be related to fibrosis and scarring of the dermis/epidermis. Further evaluation is warranted.