Risk of Malignancy in Thyroid Nodules Using the American College of Radiology Thyroid Imaging Reporting and Data System in the NIFTP Era

Recently, the American College of Radiology (ACR) proposed a Thyroid Imaging Reporting and Data System (TI-RADS) for thyroid nodules based on ultrasonographic features. It is important to validate this classification in different centres. The present study evaluated the risk of malignancy in solid nodules>1 cm using ACR TI-RADS. The risk of malignancy was defined including noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) and after its exclusion from malignant tumours. For the present study, the original images were revised, and each nodule was assigned to one of the TI-RADS levels proposed for solid nodules: TR3, TR4, or TR5. This risk of malignancy was significantly different for the three levels: 1.7%, 11.2%, and 60.6% for TR3, TR4, and TR5, respectively, when NIFTP was included, and 0.6%, 7.9%, and 60.2% for TR3, TR4, and TR5, respectively, when NIFTP was excluded from malignant tumours. The nodules corresponding to NIFTP were classified according to ACR as TR3 in 28.5% of cases, TR4 in 67.8%, and TR5 in only 3.5%. The nodules corresponding to cancer were classified according to ACR as TR3 in only 2.3% of cases, TR4 in 27%, and TR5 in 70.5%. In conclusion, this study shows the validity of the ACR TI-RADS for solid thyroid nodules, even after the exclusion of NIFTP from malignant tumours.