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

Abstract

EARLY experimental and clinical studies suggested that the thyroid gland was relatively resistant to irradiation (1, 2). More recently, either external or internal irradiation of the thyroid gland has been employed with success in the treatment of patients with Graves' disease, with certain thyroid carcinomas and with intractable cardiac disease. Destructive lesions of the thyroid glands of various animals have been produced by the administration of I131 (radioactive iodine) (3). These more recent observations have indicated that functional and structural injury of thyroid tissue may be caused by various forms of radiations. In the few histologic reports of irradiated human thyroid glands, many different lesions have been attributed to irradiation. Our studies have suggested that not all the changes observed in irradiated human thyroid glands are actually due to irradiation but may have been caused by disease, aging or the effects of drugs (4, 5). The main purpose of the present investigation was to study further and to compare the histologic effects of various forms of ionizing radiation on 58 normal and hyperplastic human thyroid glands. In this report, we are describing and illustrating the lesions observed in human thyroid glands internally irradiated from I131, externally irradiated with x-rays or neutrons, or irradiated from radon seeds implanted in the thyroid gland. We are emphasizing 1) the differentiation of lesions due to irradiation from those occurring from other causes; 2) the histogenesis and the significance of radiation injury in the thyroid gland; 3) the relation of radiation injury to the altered course of Graves' disease; and 4) the relationship of the epithelial proliferative reactions in the irradiated thyroid gland to the possible development of thyroid neoplasms.