Guidelines for managing thyroid nodules are highly dependent on risk stratification based on sonographic findings. The purpose of this study is to evaluate the risk stratification system used by the American College of Radiology Thyroid Imaging Reporting and Data System (TIRADS).

Patients with thyroid nodules who underwent sonography and fine-needle aspiration were enrolled in a multiinstitutional study. The sonographic nodule features evaluated in the study were composition, echogenicity, margins, and echogenic foci. Images were reviewed by two radiologists who were blinded to the results of cytologic analysis. Nodules were assigned points for each feature, and the points were totaled to determine the final TIRADS level (TR1-TR5). The risk of cancer associated with each point total and final TIRADS level was determined.

A total of 3422 nodules, 352 of which were malignant, were studied. The risk of malignancy was closely associated with the composition, echogenicity, margins, and echogenic foci of the nodules (p < 0.0001, in all cases). An increased aggregate risk of nodule malignancy was noted as the TIRADS point level increased from 0 to 10 (p < 0.0001) and as the final TIRADS level increased from TR1 to TR5 (p < 0.0001). Of the 3422 nodules, 2948 (86.1%) had risk levels that were within 1% of the TIRADS risk thresholds. Of the 474 nodules that were more than 1% outside these thresholds, 88.0% (417/474) had a risk level that was below the TIRADS threshold.

The aggregate risk of malignancy for nodules associated with each individual TIRADS point level (0-10) and each final TIRADS level (TR1-TR5) falls within the TIRADS risk stratification thresholds. A total of 85% of all nodules were within 1% of the specified TIRADS risk thresholds.