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.