Follicular variant of papillary carcinoma of the thyroid: to what extent is fine-needle aspiration reliable?

We have reappraised the fine-needle aspirates (FNAs) of 5 cases of the follicular variant of papillary carcinoma of the thyroid (FVPCT). Three of these had been performed on cold thyroid nodules and had been diagnosed as follicular proliferations. The remaining 2 had been performed on cervical lymphadenopathies and had been diagnosed as metastatic papillary carcinoma, probably of thyroid origin. Careful reassessment of the slides did not allow any change of the original diagnoses. We found two constant cytologic features present in all cases studied: syncytial clusters without acinar formation, and monolayered sheets. Nonconstant findings included: follicular pattern, ropy colloid, multinucleated giant cells (MGCs), and nucleoli in FNAs performed on thyroid nodules, and papillae, pseudonuclear inclusions, nuclear grooves, MGCs, and nucleoli in FNAs performed on cervical lymphadenopathies. Our findings suggest that the cytologic diagnosis of FVPCT is very difficult if based solely on the cytologic features seen in FNAs, and that it is necessary to resort to the study of surgical specimens if a definitive diagnosis is to be achieved. We are also of the opinion that more weight should be given to the aforementioned nonconstant findings when faced by a thyroid aspirate with cell richness, syncytial clusters without acinar formation, and monolayered sheets.