Benign cytology does not rule out malignancy in thyroid nodules larger than 4 cm

Background For thyroid nodules >= 4 cm, the accuracy of fine-needle aspiration biopsy (FNAB) is controversial and the approach is unclear. We aimed to compare FNAB and operation of thyroid nodules and to determine the accuracy of FNAB. Material and Methods All total thyroidectomies performed between January 2015 and December 2021 were evaluated. In the study, 301 patients were included. Euthyroid patients with preoperative thyroid ultrasound, FNAB results and operation results were recorded retrospectively. Results The nodule size was <4 cm in 79.1% of the patients, and >= 4 cm in 20.9%. In patients with nodule size >= 4 cm, 50.8% of FNAB results were reported as benign, and 43.7% of these patients were found to be malignant at the end of the operation. In nodules <4 cm, 36.8% of the patients whose FNAB results were found to be benign were malignant. False-negativity rate was found to be quite high in >= 4 cm nodules. Conclusions For thyroid nodules, diagnostic lobectomy may be necessary because the false-negative rate of FNAB was high, especially in nodules >= 4 cm. In addition, intermediate results, such as AUS/FN, have a higher risk of malignancy in nodules of >= 4 cm compared to nodules of <4 cm.