False negative rate of fine-needle aspiration in thyroid nodules: impact of nodule size and ultrasound pattern

Background To retrospectively evaluate the false negative rate of ultrasound-guided fine needle aspiration (FNA) according to the nodule size and ultrasound pattern. Methods We included 432 consecutive thyroid nodules from 384 patients who underwent ultrasound-guided FNA with benign results (>= 1 cm). The false negative rate in the nodules was assessed according to the nodule size and ultrasound pattern based on the Korean-Thyroid Imaging Reporting and Data System (K-TIRADS). Results The overall false negative rate was 3.2%. There was a trend toward an increasing false negative rate as the K-TIRADS score increased (P < .001). In low or high suspicion nodules (K-TIRADS 3 and 5), there was no significant difference in false negative rate according to the nodule size; however, among the intermediate suspicion nodules (K-TIRADS 4), the false negative rate was higher in large nodules (>= 3 cm, P = .039). Conclusion The impact of nodule size on the false negative rate differed according to the ultrasound pattern.