Objective: To evaluate prospectively the diagnostic accuracy of the thyroid imaging reporting and data system (TI-RADS) and its interobserver agreement and to estimate the reduction of indications of fine-needle aspiration biopsies (FNABs).
Design: A prospective comparative study was designed.
Methods: In 2 years, 4550 nodules in 3543 patients were prospectively scored using a flowchart and a six-point scale and then submitted to US-FNAB. Results were read according to the Bethesda system. Histopathological results were available for 263 cases after surgery. Sensitivity, specificity, negative predictive value (NPV) and positive predictive value, and accuracy were calculated for the gray-scale score, elastography, and a combination of both methods. Interobserver agreement was calculated using the kappa statistic. The reduction in the number of FNABs was estimated.
Results: When compared with cytopathological results, sensitivity, specificity, NPV, and accuracy were 95.7, 61, 99.7, and 62% for the TI-RADS gray-scale score; 74.2, 91.1, 98, and 90% for elastography; and 98.5, 44.7, 99.8, and 48.3% for a combination of both methods respectively. When compared with histopathological results, the sensitivity of the gray-scale score, elastography, and a combination of both methods were 93.2, 41.9, and 96.7% respectively. Interobserver agreement for the six-point scale and the recommendation for biopsy were substantial (κ value=0.72 and 0.76 respectively). The reduction in the number of FNABs was estimated to be 33.8%.
Conclusion: The TI-RADS score has high sensitivity and NPV for the diagnosis of thyroid carcinoma. A hard nodule should always be considered as suspicious for malignancy but elastography cannot be used alone. Combination of elastography with gray-scale can be used to improve sensitivity or specificity. Interobserver agreement and decrease in unnecessary biopsies are significant.