Ultrasound of thyroid nodules.

Thyroid nodules can be detected in 4% to 8% of the adult population by palpation, but in 40% to 50% of the population by ultrasound. The overwhelming majority of these represent benign hyperplastic nodules or adenomas. Approximately 5% of nodules are malignant, with papillary carcinoma representing approximately 75% to 80% of primary thyroid malignancies. Although many sonographic features have been studied as a means of distinguishing benign from malignant nodules, ultrasound-guided fine-needle aspiration with cytologic evaluation remains a mainstay in the management of palpable and incidentally detected nodules. This article reviews the current techniques for sonographic evaluation of the thyroid and the imaging features of the various types of thyroid nodules.