Non‐marked hypoechogenic nodules: multicenter study on the thyroid malignancy risk stratification and accuracy based on TIRADS systems comparison

Background and Objectives: The aim of the study was to evaluate the predictive value of the ultrasound criterion “non‐marked hypoechogenicity” for malignancy and to determine whether classification of these nodules as TIRADS 3 could improve the overall accuracy of consequently adjusted M‐TIRADS score. Materials and Methods: A total of 767 patients with 795 thyroid nodules were subject to ultrasonography examination and ultrasound‐guided fine needle aspiration biopsy. Nodules were classified by Kwak TIRADS and modified (M‐TIRADS) categories 4A, 4B, and 5 according to number of suspicious US features (marked hypoechogenicity, microlobulated or irregular margins, microcalcifications, taller‐than‐wide shape, metastatic lymph nodes). Non‐marked hypoechoic nodules were classified as TIRADS 3. Results: Thyroid nodules were classified as TIRADS 2, 3, 4A, 4B, and 5 in 14.5, 57.5, 14.2, 8.1, and 5.7%, respectively. Only histopathologic results (125 nodules underwent surgery) and highly specific cytology results (Bethesda II, VI) were accepted as a standard of reference, forming a sub‐cohort of 562/795 nodules (70.7%). Malignancy was found in 7.7%. Overall, M‐TIRADS showed sensitivity/specificity of 93.02/81.31%, and for PPV/NPV, these were 29.2/99.29%, respectively (OR—18.62). Irregular margins showed the highest sensitivity and specificity (75.68/93.74%, respectively). In TIRADS 3 category, 37.2% nodules were isoechoic, 6.6% hyperechoic, and 52.2% hypoechoic (there was no difference of malignancy risk in hypoechoic nodules between M‐TIRADS and Kwak systems—0.9 vs. 0.8, respectively). Accuracy of M‐TIRADS classification in this cohort was 78.26% vs. 48.11% for Kwak. Conclusions: The non‐marked hypoechoic nodule pattern correlated with low risk of malignancy; classification of these nodules as TIRADS 3 significantly improved the predictive value and overall accuracy of the proposed M‐TIRADS scoring with malignancy risk increase in TIRADS 4 categories by 20%; and no significant alteration of malignancy risk in TIRADS 3 could contribute to reducing overdiagnosis, obviating the need for FNA.