Follicular variant of papillary thyroid carcinoma: distinct biologic behavior based on ultrasonographic features.

Background: Follicular variants of papillary thyroid carcinoma (FVPTCs) have dichotomous ultrasonographic (US) features. We investigated the differences in the biologic behavior of FVPTC according to US features.

Methods: We reviewed the US findings, pathologic reports, and medical charts of 75 consecutive patients with FVPTC who underwent surgery at our institution from January 2006 to December 2008. FVPTCs were divided into PTC-like and follicular neoplasm (FN)-like based on US findings. PTC-like nodules were defined as having at least one accepted malignant feature (a taller-than-wide shape, an infiltrative margin, marked hypoechogenicity, and micro- or macrocalcifications), whereas FN-like nodules showed oval solid features without malignant features. The prognostic factors were compared.

Results: Of the 75 FVPTCs, 42 (56%) were PTC-like and 33 (44%) were FN-like. The mean tumor size of PTC-like FVPTC was significantly smaller than that of FN-like FVPTC (p=0.0483). PTC-like FVPTC showed a significantly higher rate of multifocality than FN-like FVPTC (48% and 15% respectively; p=0.0031). Extrathyroidal extension occurred in 55% of PTC-like FVPTCs compared to 12% of FN-like FVPTCs (p=0.0001). Lymph node metastasis was more frequent in PTC-like FVPTC than in FN-like FVPTC (36% vs. 12%; p=0.0197). PTC-like FVPTC had a higher stage than FN-like FVPTC (p=0.0001). These significant factors persisted in multivariate analysis. Only one recurrence and one distant metastasis were identified, and both occurred in PTC-like FVPTC.

Conclusions: FVPTC with malignant US features seems to behave in a more aggressive fashion than FVPTC without malignant US features. US can help predict the behavior of FVPTC.