Follicular variant of papillary carcinoma - Cytologic and histologic correlation

The cytologic diagnosis of follicular variant of papillary thyroid carcinom a (FVPTC) can be difficult owing to the paucity of nuclear changes of papil lary carcinoma and overlapping features with other follicular-derived lesio ns. We report our fine-needle aspiration (FNA) experience with 17 histologi cally proved cases of FVPTC with a preceding FNA. AIL cases showed increase d cellularity and a background of moderate to abundant thin watery colloid with variable amounts of thick eosinophilic colloid. The cells were arrange d mainly in monolayer sheets and syncytial fragments; occasional microfolli cle formation with abundant fine eosinophilic cytoplasm was seen. Nuclear e nlargement was a consistent finding in all cases. Only 5 cases showed promi nent nuclear features of papillary carcinoma. Histologic examination showed encapsulated follicular-patterned nodules with multifocal random distribut ion of nuclear features of papillary carcinoma that were more pronounced in the subcapsular locations of the lesions. This morphologic heterogeneity e xplains the variability seen in FNA specimens of FVPTC and may result in fa lse-negative diagnoses. We believe that these findings should be considered when interpreting follicular lesions, suspicion of an FVPTC should be conv eyed in the cytopathology report, which may prompt intraoperative assessmen t to avoid a second surgical intervention for completion thyroidectomy.