The possible aetiological factors associated with thyroid carcinoma are listed in Fig. 16.24. In the past, the two major aetiological factors were thought to be iodine deficiency with its accompanying maintained stimulation of thyroid-stimulating hormone (TSH), and malignant change in a long-standing adenoma. Epidemiological surveys have not confirmed any excess incidence of thyroid malignancy in iodine-deficient areas. Current opinion is that malignant change in an adenoma must be a rare event since adenomas are common and follicular carcinomas are rare.
