Clinical Outcome for Atypia of Undetermined Significance in Thyroid Fine-Needle Aspirations

In the Bethesda System for reporting thyroid fine-needle aspirations (FNAs), atypia of undetermined significance (AUS) is a category with limited reported follow-up and outcome data. We report a retrospective analysis of our institution's experience during nearly 4.5 years with a tiered classification scheme conforming to the Bethesda System in which repeated FNA was recommended for most patients with an initial AUS diagnosis. Of 4,691 thyroid FNAs, 512 (10.9%) had a diagnosis of AUS. Cytologic or histologic outcome data were available for 331 cases (64.6%), of which 240 (72.5%) were benign and 91 (27.5%) were malignant. Of patients with a surgical diagnosis, there was no statistically significant difference in malignancy rate among patients who went directly to surgery after a single AUS diagnosis (37/90 41%), patients having 2 successive AUS FNA diagnoses (22/51 43%), and patients with a benign aspirate after AUS (2/7 29%). Although AUS confers an intermediate risk of malignancy, guidelines recommending repeated FNA for most cases should be reevaluated.