Malignancy risk and false-negative rate of fine needle aspiration cytology in thyroid nodules ≥4.0 cm

We aimed to evaluate malignancy rate and to determine false negativity of fine needle aspiration biopsy (FNAB) in thyroid nodules ≥4.0 cm.

The medical records of patients who underwent thyroidectomy between January 2007 and December 2014 were reviewed. Demographic and clinical data as well as preoperative ultrasonography findings were analyzed. The nodules in these patients were grouped as ≥4.0 cm and <4.0 cm according to ultrasonography measurements. Nodules <4.0 cm were further divided into 1.0-3.9 cm and <1.0 cm. Histopathologically malignant nodules with preoperative benign cytology were defined as having false-negative FNAB.

There were 1,008 nodules that measured ≥4.0 cm, 4,013 nodules that measured 1.0-3.9 cm, and 540 that measured nodules <1.0 cm. Based on histopathologic findings, 8.5%, 10.2%, and 25.6% of nodules ≥4.0 cm, 1.0-3.9 cm, and <1.0 cm were malignant, respectively (P < .001). There was no significant difference between 1.0-3.9-cm and ≥4.0-cm nodules with respect to malignancy (P = .108). False-negativity rates were 4.7% in nodules ≥4.0 cm, 2.2% in nodules measuring 1.0-3.9 cm, and 4.8% in <1.0-cm nodules. Nodules measuring <1.0 cm and ≥4.0 cm had similar false-negativity rates (P = .93), while 1.0-3.9-cm nodules had statistically lower false-negativity rates than those found in the other two groups (P = .03 and P < .001, respectively).

Of the nodules that were operatively excised, nodules ≥4.0 cm had a similar risk of malignancy as nodules 1.0-3.9 cm. The rate of false-negative FNAB in nodules ≥4.0 cm was twice as high as in nodules 1.0-3.9 cm; however, we do not think it is high enough to recommend a routine operation when cytology results are benign.