Sonographic Features of the Follicular Variant of Papillary Thyroid Carcinoma

Abstract

The follicular variant of papillary thyroid carcinoma tends to have relatively benign sonographic features, such as hypoechogenicity, well-defined margins, an oval shape, and no microcalcifications, but most lesions were correctly classified as malignant by both sonography and FNAB. The possibility of FVPTC should be considered when thyroid nodules with a relatively benign sonographic appearance have suspicious or malignant FNAB results.

RASMutations in Thyroid FNA Specimens Are Highly Predictive of Predominantly Low-Risk Follicular-Pattern Cancers

“…Radiographic features suggestive of malignancy in histologically follicular lesions, the type predominating in this study, are far less well characterized. The use of Doppler flow ultrasonography for the assessment of intranodular vascularity was reported to improve the detection of otherwise bland-appearing lesions with follicular histology (23,25,36). Although we found a relatively high specificity and PPV for the preoperative ultrasonographic identification of nodules with suspicious features, even when including Doppler flow assessment, most of the histologically follicular cancers evaluated in this series were missed by ultrasound.…”

“…Negative predictive value (NPV) and sensitivity were therefore only 13% and 38%, respectively, demonstrating the significant limitations of ultrasound evaluation of nodules with RAS mutations. Even inclusion of Doppler flow assessment for increased intranodular vascularity, which has been reported to improve the diagnostic yield in histologically follicular lesions such as FVPTC and FTC, was of only limited benefit (23)(24)(25). In a subset of 10 of 51 nodules with this finding, malignancy was present in 9 of 10 hypervascular nodules.…”

Malignancy risk and characteristics of thyroid nodules with two consecutive results of atypia of undetermined significance or follicular lesion of undetermined significance on cytology

“…Malignancies with one AUS/FLUS diagnosis had a significantly higher proportion of conventional PTC, whereas two consecutive AUS/FLUS diagnoses had a significantly higher proportion of a follicular variant of PTC than those with one AUS/FLUS diagnosis (P=0.011 and 0.009). The follicular variant of PTC is associated with relatively benign US features [18,19] and, thus, after an initial AUS/FLUS diagnosis, these nodules would be more likely to undergo repeat FNA rather than immediate surgery. The US features established as suspicious for malignancy are those suggestive of conventional PTC [10,13,17], and nodules with such features are more likely to undergo surgery after an initial diagnosis of AUS/FLUS.…”

European Thyroid Association Guidelines for Ultrasound Malignancy Risk Stratification of Thyroid Nodules in Adults: The EU-TIRADS

“…6) should be included in this category, and FNA should be considered if 1 or more of the nodules is >20 mm. It should be pointed out, however, that an entirely solid isoechoic nodule corresponds in <4% of cases to a follicular cancer or a follicular variant of PTC [28-31]. In contrast, even minimal cystic changes are in favor of benignity [32].…”