Sonographic features of follicular variant of papillary thyroid carcinoma (FV-PTC) and diagnostic performance of the 2017 ACR TI-RADS in FV-PTC

To find the sonographic features of follicular variant of papillary thyroid carcinoma (FV-PTC) and evaluate the diagnostic performance of 2017 ACR TI-RADS in FV-PTC.

From June 2017 to June 2019, 104 FV-PTC patients (106 nodules) and 337 classic papillary thyroid carcinoma (C-PTC) patients (343 nodules) with both sonograms and pathologic results were included. Sonographic features of FV-PTC and C-PTC were evaluated and compared, and 2017 ACR TI-RADS scores and levels were calculated.

Pathologically, the incidence of Hashimoto’s thyroiditis and extrathyroidal extension was higher in the FV-PTC group. Most of both the FV-PTC and C-PTC groups were diagnosed as PTC or suspicious PTC by fine-needle aspiration biopsy (FNAB). FV-PTC tended to be isoechoic, while most nodules of C-PTC were hypoechoic or very hypoechoic. Compared with C-PTC, FV-PTC had lower percentages of a taller-than-wide shape (11.3% vs. 46.6%) and lobulated or irregular margin (33.0% vs. 61.8%), and a higher percentage of extrathyroidal extension (20.8% vs. 8.2%). FV-PTC featured macrocalcifications, whereas punctate echogenic foci were more frequently seen in the C-PTC group. Other characteristic US appearances of FV-PTC included uneven hypoechoic halo and peripheral vascularity. The mean TI-RADS score of FV-PTC cases was lower in the FV-PTC group, 11.3%, 44.3%, and 42.5% of which were categorized as TI-RADS 3, 4, and 5, respectively.

FV-PTC features isoechoic appearance, macrocalcifications, uneven hypoechoic halo, and peripheral vascularity on US, with lower incidences of microcalcifications and taller-than-wide shape, and tends to have lower TI-RADS scores and levels. For the nodules categorized as TI-RADS 3 or 4, the FNAB criteria should be broaden when these nodules have FV-PTC US features.