One, or occasionally two, thyroid nodules may exhibit autonomy (Fig. 17.56). Such nodules are very rarely malignant. They occur more frequently in areas of iodine deficiency, such as southern Europe. The development of hyperthyroidism from a hot nodule in the thyroid depends on the available iodine and the size of the nodule: the larger the nodule, the more likely is it to be toxic. Administration of iodine can induce the onset of hyperthyroidism. The size of a nodule can be assessed by ultrasound, and its functional capacity by a radioiodine or technetium scan. Some malignant tumours that pre- sent as solitary nodules can trap technetium but fail to organify iodine, so their true nature is best revealed by a radioiodine scan. It is not usually necessary to biopsy hot nodules since they are rarely
