MON-382 Reappraisal of the Role of Ultrasonography-Guided Fine Needle Aspiration Biopsy in the Management of Autonomously Hyperfunctioning Thyroid Nodules

Abstract Disclosure: H. Kim: None. J. Park: None. A. Hong: None. J. Yoon: None. H. Kang: None. Background: Autonomously hyperfunctioning thyroid nodules are generally believed to have very low chances of malignancy. Clinical guidelines recommend not performing fine needle aspiration biopsy (FNAB) on these lesions irrespective of their size. However, a reappraisal of the need to perform FNAB is warranted because recent studies suggest the malignancy rate of toxic nodules may have been underestimated.Methods: We reviewed patients with toxic nodules who visited Chonnam National University Hwasun Hospital from 2003 to 2023. A control group was selected from the population with nontoxic nodules who underwent FNAB in 2023. Laboratory tests and ultrasonographic findings of the nodules were analyzed.Results: Toxic nodules were more likely to be single (77.8% vs. 38.4%, p<0.001) and larger (3.94 cm vs. 1.78 cm, p<0.001) compared to nontoxic nodules. Nontoxic nodules tended to exhibit ultrasonographic features associated with a higher malignancy risk (K-TIRADS 3: 28.0%, K-TIRADS 4: 28.4%, K-TIRADS 5: 42.0%) compared to toxic nodules (K-TIRADS 3: 55.6%, K-TIRADS 4: 42.6%, K-TIRADS 5: 1.9%). The malignancy rate was higher in nontoxic nodules (25.6% vs. 3.7%, p<0.001), but the malignancy rate in other nodules or the contralateral thyroid gland was similar (16.7% vs. 9.2%, p=0.139). This resulted in a malignancy rate of 16.7% for toxic nodules and 25.6% for nontoxic nodules (p=0.014).Conclusion: We believe that when deciding whether to perform FNAB for thyroid nodules, ultrasonographic findings should take priority over serum TSH levels. Presentation: Monday, July 14, 2025