Malignancy risk with atypia of undetermined significance finding on thyroid nodule FNA: clinical experience from a tertiary institution

The Bethesda System for Reporting Thyroid Cytopathology from 2009 introduced a new category in thyroid nodule fine-needle aspiration (FNA) findings named atypia of undetermined significance (AUS), which usually appears in around 5% of FNA findings. Our study aimed to assess the utility of AUS finding in determining the risk of malignancy in thyroid nodules. In our study, 160 patients with AUS finding on initial FNA were regularly followed-up. Total and specific malignancy rates were calculated after receiving histopathologic confirmation or histopathologic/cytologic exclusion of malignancy. Eventually 80 (50%) patients were referred to surgery, with malignancy rate of 37.5% on histopathology. Another 52 (32.5%) patients were confirmed to have benign nodules on repeat FNA. After combining results obtained from histopathologic reports with those obtained from cytologic follow-up, total malignancy rate was 22.72%. However, malignancy was confirmed in only one (5.26%) of 19 patients with AUS finding on repeat FNA with surgical and histopathologic follow-up. In conclusion, FNA is an extremely useful tool for clinicians to discriminate patients to be referred to surgery and those that can be followed-up safely without the need for further invasive procedures.