Differentiation of the Follicular Variant of Papillary Thyroid Carcinoma From Classic Papillary Thyroid Carcinoma: An Ultrasound Analysis and Complement to Fine-Needle Aspiration Cytology.

Objectives: It is difficult to establish a diagnosis of the follicular variant of papillary thyroid carcinoma (PTC) using fine-needle aspiration cytology (FNAC). Preoperative features on ultrasound (US) imaging are different between follicular PTC and classic PTC. This study developed a risk score system to differentiate follicular PTC from classic PTC and to correlate the risk score of follicular PTC with its FNAC categories and pathologic features.

Methods: The US features, FNAC results, and pathologic reports of 156 follicular PTC nodules and 152 classic PTC nodules from 296 patients with PTC along with their clinical characteristics were reviewed retrospectively. A risk score system based on US features was developed by multivariate logistic regression to differentiate classic PTC from follicular PTC nodules. The risk scores were then correlated with the FNAC category and pathologic features of the nodules.

Results: The US risk score (5 × echogenicity + 3 × calcifications + 3 × marginal regularity) had an area under the receiver operating characteristic curve of 0.85 and a cutoff value of 8.0, with specificity of 87% and sensitivity of 69% for predicting a classic PTC nodule. The follicular PTC nodules with low Bethesda categorization (I-III) had a median US risk score of 6 (range, 0-11), which was higher than that of nodules with high categorization (IV-VI; median, 3; range, 0-11).

Conclusions: The US risk score may be useful in differentiating classic PTC from follicular PTC and complementary to FNAC in identifying follicular PTC.