Validation of the modified 4-tiered categorization system through comparison with the 5-tiered categorization system of the 2015 American Thyroid Association guidelines for classifying small thyroid nodules on ultrasound

Background: The purpose of this study was to validate the modified 4-tiered categorization system and to compare stratification of malignancy risk in small thyroid nodules with the 2015 American Thyroid Association (ATA) management guidelines. Methods: From January 2015 to December 2015, 737 thyroid nodules measured ≥ 1 cm and <2 cm were included in this study. Each nodule was assigned a category with the ultrasonographic patterns described by the 2015 ATA guidelines. Results: On univariate analysis, there was no difference of malignancy risk between low suspicion and very low suspicion nodules (P =.584). Therefore, we suggested a modified 4-tiered categorization, which combines very low suspicion and low suspicion nodules into the “revised low suspicion” category. Specificity, positive predictive value (PPV) and accuracy were higher with the modified 4-tiered categorization system (P <.001 for all). Conclusion: The modified 4-tiered categorization system allows more efficient management with better diagnostic performance than the 2015 ATA categorization system in small thyroid nodules.