Introduction: We aimed to investigate malignancy rates in atypia of undetermined significance (AUS) subcategories and their association with cytomorphologic and ultrasonographic features.
Methods: A total of 201 thyroid nodules with AUS cytology that underwent surgical resection were analyzed, including 169 AUS-nuclear (AUS-N) and 32 AUS-other (AUS-O) nodules. Cytomorphological and ultrasonographic features, along with the American College of Radiology Thyroid Imaging Reporting and Data System (ACR-TIRADS) and the European Thyroid Imaging Reporting and Data System (EU-TIRADS) classifications, were analyzed to assess the association between malignancy and AUS subcategories.
Results: The overall risk of malignancy (ROM) for AUS nodules was 19.4%, with a significantly higher rate observed in the AUS-N subgroup compared to AUS-O (21.9% vs. 6.3%, p = 0.04). A significantly higher ROM was observed in nodules with irregular margin, taller-than-wide shape, microcalcification, hypoechogenicity, and solid composition (OR = 9.63, 5.81, 3.33, 2.14, and 2.07, respectively). A statistically significant difference in ROM was observed across ACR-TIRADS and EU-TIRADS categories within the AUS nodules (p < 0.001 for both) and the AUS-N group (p = 0.001 and <0.001). A marked increase in ROM was observed with nuclear overlapping, pseudoinclusions, and enlargement (OR: 9.16, 4.47 and 2.80, respectively), while oncocytic atypia was associated with a reduced risk (OR: 0.44). In multivariate analysis, nuclear overlapping, pseudoinclusions, and sonographic irregular margins remained as independent predictors of malignancy (OR = 6.97, 6.09, and 5.79, respectively).
Conclusion: To our knowledge, this is the first study to demonstrate a significant association between ACR-TIRADS classification and malignancy risk in the AUS-N subcategory.
Keywords: ACR-TIRADS; Architectural atypia; EU-TIRADS; Nuclear atypia; Risk of malignancy.
© 2025 S. Karger AG, Basel.