The American Thyroid Association (ATA) recommendations for selecting benign nodules for repeat fine needle aspiration cytology (FNAC) during follow-up are accurate and useful, according to study results published in Thyroid.
The 2015 ATA guidelines recommend an ultrasound-based risk stratification system for identifying thyroid nodules appropriate for repeat FNAC and for planning the required follow-up of patients with prior benign cytology. The objective of the current study was to determine the accuracy of the ATA ultrasound risk-adapted approach for repeating FNAC in patients with benign nodules.
The retrospective study included 1010 (mean diameter 22±9.9 mm; mean volume 4.7±8.1 cm3) benign thyroid nodules that underwent routine repeat FNAC after a mean follow-up of 4 plus or minus 2.6 years. Of these, 976 (96.6%) nodules were confirmed benign, 31 (3.1%) were reclassified as indeterminate, and 3 (0.3%) were considered suspicious/malignant.
After exclusion, the final study sample included 990 thyroid nodules, of which 980 (99%) were benign and 10 (1%) were classified as malignant. Ultrasound assessment was available in 874 (88.3%) cases, and 609 (69.7%) nodules were classified as very low/low suspicion, 170 nodules (19.4%) were classified as intermediate suspicion, and 95 (10.9%) as high-risk nodules according to the ultrasound characteristics.
The rate of missed cancer diagnosed at the time of the repeated FNAC increased with elevation in ultrasound risk class: 0.8% in the very low/low suspicion, 1.2% in the intermediate suspicion, and 3.1% in the highly suspicious nodules. Moreover, in the subgroup of nodules classified as low-risk, the rate of missed cancer was 0.7% in nodules with no changes in the ultrasound findings and was 3.2% in nodules that developed more worrisome radiologic features during follow-up.
A greater than 50% change of nodule volume on ultrasound at the time of the repeated FNAC was reported in 408 (45.7%) nodules, and an increase greater than 20% of greater than or less than 2 nodule diameters greater than 2 mm was recorded in 463 (53%) nodules. The rate of missed cancer showed no difference between nodules with evidence of growth and nodules that remained stable (1% vs 1.2%, respectively; P >.99).
Although there was no correlation between that rate of missed cancer and the sonographic risk class in the whole group of nodules and in the subgroup of nodules with stable volume, the rate of missed cancer was significantly higher in high-risk nodules with evidence of nodule growth (6.4%) during follow-up when compared with very low-/low-risk (0.4%) and intermediate-risk (1.3%) nodules.
The 2015 ATA ultrasound risk stratification system was found to be highly accurate in identifying nodules that did not require a second FNAC, with a negative predictive value of 99.1%.
The study had several limitations, according to the researchers, including the retrospective design, potential selection bias, and lack of histologic diagnosis in many cases.
“Our results confirm the accuracy of the ATA recommendations in selecting benign nodules for FNAC repetition during the follow-up. An additional cytological evaluation may be avoided in benign thyroid nodules with low-risk US features, regardless of the evidence of growth during the follow-up,” concluded the researchers.
Maino F, Bufano A, Dalmazio G, et al. Validation of American Thyroid Association ultrasound risk-adapted approach for repeating cytology in benign thyroid nodules. Published online Aug 19, 2020. Thyroid. doi: 10.1089/thy.2020.0351