Malignancy Risk Stratification in Thyroid Nodules with Benign Results on Cytology: Combination of Thyroid Imaging Reporting and Data System and Bethesda System

The indications of repeat fine-needle aspiration (FNA) for thyroid nodules with benign results of the Bethesda system were investigated. A total of 1,398 nodules were classified according to the Thyroid Imaging Reporting and Data System (TIRADS). TIRADS category 3 included nodules without solidity, hypoechogenicity or marked hypoechogenicity, microlobulated or irregular margins, microcalcifications, and taller-than-wide shape on ultrasonography (US). Categories 4a, 4b, 4c, and 5 included nodules with one, two, three or four, or five suspicious US features, respectively. The malignancy risks, and odds ratio (OR) with 95 % confidence interval (CI) were calculated. Analyses were performed for all nodules, nodules > 10 mm, and nodules a parts per thousand currency sign10 mm. Of 1.398 nodules, 43 (3.1 %) were malignanct. The malignancy risks of benign nodules with categories 3, 4a, and 4b were 0.7, 1.2, and 0.7 %, respectively, whereas those for nodules with categories 4c and 5 were 9.8 and 22.2 %, respectively. The ORs of nodules with categories 4c and 5 were 19.4 (95 % CI 5.0-76.2) and 50.6 (95 % CI 10.4-245.0), respectively. In nodules > 10 mm, the malignancy risks of categories 4c and 5 were 2.7 and 20 %, respectively, and the ORs were 10.7 (95 % CI 1.2-93.7) and 236.1 (95 % CI 12.6-4426.4), respectively. In nodules a parts per thousand currency sign 10 mm, the malignancy risks of categories 4c and 5 were 12.6 and 22.6 %, respectively, and the ORs were 10.1 (95 % CI 1.3-78.0) and 18.9 (95 % CI 2.1-168.9), respectively. Repeat US-guided FNA should be considered in benign thyroid nodules with three or more suspicious US features regardless of size.