Follow up or FNAB?: Malignancy Rates of ACR TI‐RADS 4 and 5 Thyroid Nodules <10 mm in Diameter

Objective The aim of this study is to ascertain the rate of malignancy in nodules that are less than 10 mm in diameter in the TR‐4 and TR‐5 categories, as defined by the American College of Radiology Thyroid Imaging and Reporting Data System 2017 whitepaper and to open a discussion on the strategy of approach to PTMCs. Study Design Prospective cohort study. Setting Single academic medical center. Methods All thyroid ultrasound examinations were performed by 2 senior radiologists with consensus. The fine‐needle aspiration biopsy procedure was performed under the guidance of ultrasound. All patients underwent surgery, except for those with benign cytology. Results Among 60 nodules, 15 nodules (25%) were classified as TR‐4 and 45 nodules (75%) as TR‐5. Based on cytological analysis, 12 of the 15 nodules classified in the TR‐4 category (80%) were benign, while 3 nodules (20%) were classified as nonbenign. In the assessment of 45 TR‐5 nodules, 30 (66.7%) were identified as nonbenign, while the remaining 15 (33.3%) were classified as benign. Surgery was performed on all 33 patients with nonbenign FNAB results, and the histopathological results confirmed malignancy in 3 TR‐4 nodules (20%) and in 29 TR‐5 nodules (64.4%). Conclusion Our study highlights that TR‐4 and TR‐5 thyroid nodules smaller than 10 mm exhibit high malignancy rates. Despite limitations such as small sample size and single‐center design, our findings support the consideration of FNAB in selected <10 mm nodules, particularly when active surveillance is unsuitable.