Abstract
Ultrasound is a useful tool for examination of thyroid nodules, especially when making the diagnosis of papillary thyroid cancer, which accounts for about 90% of thyroid malignancies. Ultrasound features suggestive of malignancy are irregular shape, hypoechogenicity, ill-defined margin, absence of hypoechoic rim, fine echogenic dots, taller than wide shape, and solid structure. Application of fine-needle aspiration cytology is considered based on these ultrasound features and the maximum diameters of the nodules. Japanese criteria recommend fine-needle aspiration cytology for nodules with many malignant features on ultrasound when the diameter is over 5 mm. When nodules have some single malignant feature, fine-needle aspiration cytology is recommended for nodules over 10 mm. The criteria for recommendation of fine-needle aspiration cytology in the United States or South Korea indicate that fine-needle aspiration cytology is recommended for suspicious nodules 1 cm or over in diameter. Inconsistency exists in the diameter of nodules for which fine-needle aspiration cytology is recommended among Japan, South Korea, and the United States.
