Diagnostic Performance of ACR TI-RADS, EU-TI-RADS, and Individual Ultrasound Features for Predicting Thyroid Malignancy: A Histopathology-Validated Analysis of Surgically Excised Nodules.

objectiveThe primary objective was to compare the histopathology-validated diagnostic performance of the American College of Radiology Thyroid Imaging Reporting and Data System (ACR TI-RADS) and the European Thyroid Imaging Reporting and Data System (EU-TI-RADS) for predicting malignancy in surgically excised thyroid nodules. Secondary objectives were to evaluate the discriminatory contribution of individual ultrasound features, characterize threshold-specific classification errors, examine performance by malignant histological subtype, and assess the potential influence of within-patient clustering.

methodsIn this retrospective secondary analysis of an institutional review board-approved cohort, 284 surgically excised thyroid nodules from 233 patients (170 female, 73.0%; mean age: 43.5 ± 10.9 years) were analysed using postoperative histopathology as the reference standard. Nodules were categorized using ACR TI-RADS and EU-TI-RADS. Diagnostic performance was assessed using receiver operating characteristic (ROC) analysis and threshold-based 2×2 contingency tables. Sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) were reported as n/N (%), with 95% confidence intervals. Confusion matrix analysis was performed to evaluate true-positive, false-positive, true-negative, and false-negative classifications. Because some patients contributed more than one nodule, the potential influence of within-patient clustering was evaluated using cluster-size characterization and a single-index-nodule sensitivity analysis. Multivariable regression modelling and formal interobserver agreement analysis were not performed and are addressed in the Limitations section.

resultsHistopathology identified 150/284 malignant nodules (52.8%) and 134/284 benign nodules (47.2%). ACR TI-RADS showed the highest discriminatory performance (AUC of 0.950 for point score and 0.948 for categories), followed by EU-TI-RADS (AUC of 0.933). At clinically relevant thresholds, ACR TI-RADS TR4 or higher identified 131/150 malignant nodules and correctly classified 127/134 benign nodules, yielding sensitivity 87.3%, specificity 94.8%, and accuracy 90.8%. EU-TI-RADS category 4 or higher identified 130/150 malignant nodules and correctly classified 130/134 benign nodules, yielding a sensitivity of 86.7%, a specificity of 97.0%, and an accuracy of 91.5%. ACR TI-RADS produced slightly fewer false-negative classifications, whereas EU-TI-RADS produced fewer false-positive classifications.

conclusionsACR TI-RADS and EU-TI-RADS both demonstrated excellent histopathology-validated diagnostic performance in this surgically enriched cohort. Differences between the systems mainly reflected distinct classification error profiles rather than clear superiority of one system. Feature-level and confusion matrix analyses provided additional clinically relevant information, but the findings should be interpreted in the context of surgical-selection bias and may not be directly generalizable to unselected thyroid nodule populations. Because this was a surgically enriched cohort with a malignancy prevalence of 52.8%, predictive values should not be extrapolated to unselected screening or surveillance populations. Sensitivity, specificity, and AUC may also differ in unselected populations because of spectrum and verification bias. Prospective multicenter validation is required.