Value of Ultrasound and Cytological Classification System to Predict the Malignancy of Thyroid Nodules with Indeterminate Cytology

Although fine-needle aspiration cytology is considered the gold standard for evaluating thyroid nodules, in about 10–30% of the cases, cytology is indeterminate. This study aimed to determine the value of cytological classification system and ultrasound (US) to predict malignancy in indeterminate thyroid nodule. This retrospective analysis enrolled 80 patients surgically treated at a single center, 75% (60) with benign vs. 25% (20) with malignant lesions at final histology. The clinical, scintigraphic, sonographic, and cytological classification (Bethesda) variables were analyzed in these selected cases of indeterminate cytology, and a prediction model was designed after the multivariate analysis. There was a 25% prevalence of malignancy (20/80). There were no differences in gender, serum thyroid-stimulating hormone and FT4 levels, thyroid auto-antibodies, thyroid dysfunction, and scintigraphic results between benign and malignant nodule groups. The border irregularity in sonographic study was at increased risk for malignancy. The cytological analysis based on Bethesda System (category IV) was an independent predictor for malignancy in indeterminate thyroid nodules. After the multivariate analysis, the model obtained showed border irregularity and Bethesda System category IV as predictive factors of malignancy in indeterminate thyroid nodules, featuring 76.9% of accuracy. This study confirmed a significant increase of risk for malignancy in thyroid nodules with indeterminate cytology showing Bethesda System category IV and suspicious features at US. These findings enhance our current limited predictive armamentarium and can be used to guide surgical decision making.