Ultrasonographic Characteristics of the Follicular Variant Papillary Thyroid Cancer According to the Tumor Size

Follicular variant papillary thyroid cancer (FVPTC) is the second most common subtype after conventional PTC. We compared ultrasonographic (US) features of FVPTC to those of conventional PTC according to tumor size. We reviewed US findings, pathologic reports, and medical charts of 249 PTC patients with surgically proven disease (83 FVPTCs, 166 conventional PTCs) at our institution from January 2007 to December 2012. FVPTCs were divided into PTC-like and follicular neoplasm (FN)-like based on sonographic characteristics. PTC-like features were defined as having at least one malignant feature (taller-than-wide shape, infiltrative margin, marked hypoechogenicity, and micro-calcifications), whereas FN-like cancers showed oval solid features without malignant features. FVPTCs showed a higher rate of FN-like features than conventional PTCs. Of 166 conventional PTCs, 13 (7.8%) had FN-like features and 153 (92.2%) had PTC-like features, whereas of the 83 FVPTCs, 31 (37.3%) had FN-like features and 52 (62.7%) had PTC-like features. Macro-FVPTCs showed a higher rate of FN-like features than micro-FVPTCs (P < 0.001). Of 21 macro-FVPTCs, 18 (85.7%) had FN-like features and 3 (14.3%) had PTC-like features, whereas of the 62 micro-FVPTCs, 13 (21%) had FN-like features and 49 (79%) had PTC-like features. There were no differences in multifocality, extrathyroidal invasion, and lymph node metastasis between PTC-like FVPTCs and FN-like FVPTCs. FVPTCs showed fewer sonographic malignant features than conventional PTCs. In particular, FVPTCs larger than 1 cm had a more frequent benign sonographic appearance. Therefore, if fine-needle aspiration result is suspicious for PTC in a nodule larger than 1 cm with no suspicious US features, the possibility of FVPTC might be considered.

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.