In humans, thyroid nodules are common, occurring in over half of individuals over 50 years of age (1). Over 95% of these thyroid nodules are benign, small to moderate in size, and are not associated with clinical or biochemical signs of hyperthyroidism. Some of these patients that present with a single thyroid nodule are later found to have many benign enlarged nodules within the thyroid (ie, multinodular goiter), some of which will develop signs of hyperthyroidism (toxic nodular goiter; Plumber's disease). Although the underlying cause of most human thyroid nodules is not known, a low-iodine diet, Hashimoto's thyroiditis, or prior radiation treatment can contribute to nodule development.
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