Malignancy risk stratification in thyroid nodules with nondiagnostic results at cytologic examination: Combination of thyroid imaging reporting and data system and the bethesda system

Purpose: To evaluate the malignancy risks of thyroid nodules with nondiagnostic results at ultrasonography (US)-guided fine-needle aspiration biopsy (FNAB) and the criteria for selecting those for repeat US-guided FNAB according to the thyroid imaging reporting and data system (TIRADS).

Materials and This retrospective study was approved by the institutional Methods: review board, and the requirement to obtain informed consent was waived. Five hundred forty-eight nondiag-nostic nodules were included. US features of internal composition, echogenicity, margin, calcifications, shape, and vascularity were evaluated, and thyroid nodules were classified according to TIRADS. TIRADS category 3 included nodules without any suspicious features of solidity, hypoechogenicity or marked hypoechogenicity, microlobu-lated or irregular margins, microcalcifications, and taller-than-wide shape. Categories 4a, 4b, 4c, and 5 included nodules with one, two, three or four, or five suspicious US features. The malignancy risk was calculated.

Results: Of the 548 nodules, 40 (7.3%) were malignant and 508 (92.7%) were benign. The malignancy risks of categories 3 and 4a nodules were 0.8% and 1.8%, respectively, whereas the malignancy risks of categories 4b, 4c, and 5 nodules were 6.1%, 14.4%, and 31%. In the 294 nodules larger than 10 mm, the malignancy risks of categories 3, 4a, 4b, 4c, and 5 nodules were 0.9%, 1.3%, 0%, 15%, and 33%, respectively. In the 254 nodules measuring 10 mm or smaller, the malignancy risks of categories 3, 4a 4b, 4c, and 5 nodules were 0%, 2.7%, 14%, 14.3%, and 31%.

Conclusion: Nondiagnostic thyroid nodules without suspicious US features and those with one suspicious feature can be followed up with US, but nondiagnostic nodules with two or more suspicious features should undergo repeat US-guided FNAB.