US Features of Thyroid Malignancy: Pearls and Pitfalls

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US Features of Thyroid Malignancy: Pearls and Pitfalls
Introduction

Thyroid nodules are very common and may be observed at ultrasonography (US) in 50% of the adult population. Thyroid malignancy is relatively rare and is diagnosed in approximately 25,000 patients per year in the United States (1). The most common cause of benign thyroid nodules is nodular hyperplasia (2). Although less than 7% of thyroid nodules are malignant (2), it is critical that they be accurately identified. The imaging modality of choice for the investigation of thyroid nodules is high-resolution US. US is commonly misperceived as unhelpful in distinguishing between benign and malignant thyroid nodules. Although individual US features may be of limited value, when multiple signs of thyroid malignancy appear in combination it is possible to make an accurate prediction. The nodule then may be further assessed with fine-needle aspiration (FNA).

Scintigraphy is not used routinely to assess thyroid nodules. It is primarily of use in patients with a suppressed thyroid-stimulating hormone level, in whom it allows assessment of the functional activity of a thyroid nodule and of the whole gland. A functioning, or “hot,” thyroid nodule is rarely malignant, with only a few reported cases of such malignancy (3-10). Although a nonfunctioning, or “cold,” nodule at scintigraphy is commonly thought to indicate an increased risk of thyroid malignancy, as many as 77% of cold thyroid nodules may be benign (4,11). Thyroid scintigraphy therefore is unhelpful for differentiating a benign nodule from a malignant one, and its utility for the routine evaluation of thyroid nodules is limited.