Frequencies and malignancy rates of 6-tiered Bethesda categories of thyroid nodules according to ultrasound assessment and nodule size

Background: The malignancy risk of thyroid nodules differs according to Bethesda category, ultrasound features, and nodule size. Methods: In 2725 thyroid nodules that underwent ultrasound-guided fine-needle aspiration, frequencies and malignancy rates of Bethesda categories were compared according to size and ultrasound assessment. Results: When comparing the ultrasound suspicious nodules ≤10 mm and >10 mm, the frequency of the benign cytology was statistically higher in the >10 mm group, whereas the nondiagnostic and suspicious for malignancy cytology were higher in the ≤10 mm group. In ultrasound suspicious nodules ≤10 mm, the malignancy rate of the benign cytology group was higher but that of the suspicious for malignancy cytology group was lower than the >10 mm group. Conclusion: Benign and suspicious for malignant cytological results are more reliable in thyroid nodules >10 mm compared to ≤10 mm displaying suspicious ultrasound features.