A Mixed Model of Clinical Characteristics, Strain Elastography and ACR-TIRADS Predicts Malignancy in Small Thyroid Nodules: A Prospective Single-Center Study

Background and Objectives: To identify clinical, ultrasound (US) and real-time elastography (RTE) characteristics indicative of malignancy in small thyroid lesions. Materials and Methods: 141 consecutive patients with incidentally discovered solid thyroid nodules (diameter ≤ 10 mm) by neck US were assessed, and RTE was performed. The nodules were classified per American (ACR-TIRADS) and European (EU-TIRADS) criteria; US-guided FNA was conducted on EU-TIRADS 5 nodules. The US and RTE features of nodules classified as benign (Bethesda II) or malignant (Bethesda V and VI) were compared. Results: 41 nodules were classified as EU-TIRADS 5. Their Fine Needle Aspiration (FNA) cytology was Bethesda II (n = 11), III-IV (n = 3), V (n = 10) or VI (n = 17). Bethesda V–VI patients had a higher rate of autoimmune thyroiditis (p = 0.015) and higher ACR-scoring points (p < 0.001) compared with Bethesda II. The elastography ratio was equal between the groups (p = 0.584). In logistic regression analysis, ACR-scoring points predicted FNA results, with an area under the curve (AUC) of 0.993 (sensitivity 92.6% and specificity of 100%). The clinical model (age, body mass index, sex, autoimmunity, L-thyroxine treatment, nodule diameter, elastography ratio) achieved an AUC of 0.744. A “mixed” model, combining clinical characteristics with the ACR scoring points, achieved perfect performance (AUC = 1.000), predicting FNA results with 100% sensitivity and specificity. Conclusions: The proposed “mixed model” can predict Bethesda V–VI in thyroid nodules <10 mm, allowing for the selection of those needing further evaluation.