HISTOLOGIC EFFECTS OF VARIOUS TYPES OF IONIZING RADIATION ON NORMAL AND HYPERPLASTIC HUMAN THYROID GLANDS*†

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Abstract
This study is concerned with histologic changes in human thyroid glands following admn. of various forms of internal and external radiation. The lesions observed in thyroid glands irradiated with I131, X-rays, radon or neutrons were qualitatively similar. Acute epithelial injury, associated with necrotizing vasculitis and thrombosis, was the initial lesion resulting from high dosage irradiation. Follicular atrophy accompanied by perifollicular fibrosis was characteristic of the late irradiation reaction. Bizarre thyroid epithelial cells with hyperchromatic nuclei were observed in many irradiated glands, particularly the hyperplastic ones, and were believed due to overstimulation and exhaustion, rather than to the direct effect of irradiation. Cellular changes due to irradiation were found only in glands subjected to high dosage of irradiation and examined relatively soon after the exposure. A significantly high incidence of Hashimoto thyroiditis was found in hyperplastic thyroid glands irradiated with I131 or X-rays. This lesion was regarded as one effect of irradiation of the hyperplastic gland. The epithelial proliferative reaction in 2 of these glands led to the late development of multiple adenomas. These findings suggest the possibility of eventual development of malignant lesions in the irradiated hyperplastic human thyroid gland.