Ultrasonographic Characteristics of Thyroid Nodules with Nondiagnostic and Atypia of Undetermined Significance in Fine-Needle Aspiration Cytology.

Objectives:This study aimed to investigate ultrasound (US) features of thyroid nodules categorized as nondiagnostic (ND) and atypia of undetermined significance (AUS) according to the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) and their potential implications for clinical management. Materials and Methods:A retrospective study was conducted on patients who underwent thyroid nodules FNAC between 2019 and 2023. Nodules falling into the ND and AUS categories were analyzed for US features, nodule size, composition, echogenicity, shape, margin, echogenic foci, the distribution of the American College of Radiology's Thyroid Imaging Reporting and Data System (ACR TI-RADS) categories, and other parameters. The study included a total of 1,199 patients and 1,252 nodules (ND: 1110; AUS: 142). Results:No significant differences in age, gender, nodule features, echogenicity, shape, margin, echogenic foci, TI-RADS scores, localization, number of nodules, or thyroid parenchymal disease presence were found between the ND and AUS categories (p > 0.05). Also, no statistically significant difference in nodule size (<10 mm vs. ≥10 mm) existed between the ND and AUS categories (p = 0.475). Both showed predominantly solid composition and hyperechoic/isoechoic echogenicity. High proportions of TI-RADS 4 nodules were observed in both groups, with 727 (65.5%) in ND and 95 (66.9%) in AUS. Conclusion:This study found no statistically significant differences in US characteristics between the ND and AUS categories, indicating potential similarities in their radiological appearances. Also, no significant difference in nodule size (<10 mm and ≥10 mm) was observed between these categories. Clinical management should consider further investigations, including repeat FNAC, due to the diagnostic challenges and malignancy risk in both categories.