Thyroid Nodule Ultrasonography: Margins and Shape

Abstract

The sonographic appearance of a thyroid nodule can help distinguish a benign from suspicious nodule. Smooth margins are often found in benign thyroid lesions. Infiltrative, irregular, and lobulated margins have been associated with malignancy and further evaluation with ultrasound-directed needle biopsy should be considered. Extrathyroidal extension of a nodule on ultrasound is also highly suggestive of malignancy as well as invasion of the nodule beyond the thyroid capsule. The shape of a thyroid nodule is determined by the ratio of the nodule’s antero-posterior diameter and transverse diameter, as measured in the transverse plane. A “taller than wide” nodule, in which the antero-posterior to transverse ratio is greater than 1, has also been found to be associated with malignancy. In this chapter, we review the sonographic features for the various types of thyroid nodule margins and shape and provide clinical examples of each.