Utility of Six Ultrasound-Based Risk Stratification Systems in the Diagnosis of AUS/FLUS Thyroid Nodules

Rationale and Objectives: To estimate the diagnostic performance of the currently used ultrasound (US)-based risk stratification systems (RSSs) (American Thyroid Association, American Association of Clinical Endocrinologists, American College of Endocrinology, and Association Medici Endocrinology Medical Guidelines for Clinical Practice for the Diagnosis and Management of Thyroid Nodules, European Thyroid Association Guidelines for Ultrasound Malignancy Risk Stratification of Thyroid Nodules in Adults [EU-TIRADS], American College of Radiology Thyroid Imaging Reporting and Data System [ACR-TIRADS], Chinese Guidelines for Ultrasound Malignancy Risk Stratification of Thyroid Nodules [C-TIRADS], and Thyroid Imaging Reporting and Data System Developed by Kwak et al [Kwak-TIRADS]) for atypia of undetermined significance or follicular lesion of undetermined significance (AUS/FLUS) thyroid nodules. Materials and Methods: This retrospective study included 514 consecutive AUS/FLUS nodules in 481 patients with final diagnosis. The US characteristics were reviewed and classified using the categories defined by each RSS. The diagnostic performance was evaluated and compared using a generalized estimating equation method. Results: Of the 514 AUS/FLUS nodules, 148 (28.8%) were malignant and 366 (71.2%) were benign. The calculated malignancy rate increased from the low-risk to high-risk categories for all RSSs (all P < .001). Interobserver correlation for both US features and RSSs showed substantial to almost perfect agreement. The diagnostic efficacy of Kwak-TIRADS (AUC = 0.808) and C-TIRADS (AUC = 0.804) were similar (P = .721) and higher than those of other RSSs (all P < .05). The EU-TIRADS and Kwak-TIRADS exhibited similar sensitivity (86.5% vs 85.1%, P = .739) and were only higher than that of the C-TIRADS (all P < .05). The specificity of C-TIRADS and ACR-TIRADS were similar (78.1% vs 72.1%, P = .06) and were higher than those of other RSSs (all P < .05). Conclusion: Currently used RSSs can provide risk stratification for AUS/FLUS nodules. Kwak-TIRADS and C-TIRADS have the highest diagnostic efficacy in identifying malignant AUS/FLUS nodules. A detailed knowledge of the benefits and shortcomings of the various RSSs is essential.