Thyroid Ultrasound > Introduction > Clinical Significance

Clinical Significance

Thyroid carcinoma is the most frequent type of endocrine cancer (95% of all endocrine cancers) in the United States, with 33,500 new cases diagnosed each year (40 per million per year) but only 1,500 deaths annually (6 deaths per million per year), mainly due to uncommon, aggressive forms of the disease. Autopsy studies show that 50% of patients with a clinically normal thyroid have nodules. In the Framingham population study, nodules were found by palpation in 6.4% of women and 1.5% of men. By ultrasound, many more nodules are detected. Location and size of nodule, size of neck and skill of examiner affect detection on physical exam, which are usually greater than 1 cm. With current ultrasound technology, even nodules as small as 1 mm may be evident.

The only well-established risk factor for differentiated thyroid cancer is external head and neck radiation, especially during infancy. Papillary thyroid carcinoma may occur in several rare inherited syndromes, including familial adenomatous polyposis, Gardner's syndrome, and Cowden's disease. Malignancy is more common in adults >60, men’s nodules are more likely to be cancer and malignancy is more common in children age >10 more common than <10.

The use of external-beam irradiation in children and young adults in the 1950s and 1960s for acne and tonsillitis has been shown to result in an increased incidence of papillary cancer, usually 15 years after exposure. Irradiation for soft tissue malignancy, such as Hodgkin’s lymphoma, have an increased incidence of thyroid nodules and cancer.

With the odds of malignancy in biopsied nodes being only approximately 1 in 20, and thyroid cancer accounting for only 0.5% of all cancer deaths, a sensible strategy for determining which nodules should undergo FNA is essential. The most common appearance for papillary thyroid carcinoma is a solitary, solid hypoechoic nodule with ill-defined borders, microcalcifications, and internal vascularity. Although no single feature can distinguish benign from malignant nodules, taking all sonographic features (see below table from Ultrasound Clinics Apr 2009) into account can shed some light on which nodules should undergo further testing.

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