A systematic approach to assess the strengths and limitations of cytomorphology in the diagnosis of the follicular variant of papillary thyroid carcinoma.

OBJECTIVE: To identify the most useful cytomorphological features of follicular variant of papillary thyroid carcinoma (FVPTC). METHODS: Fine needle aspiration cytological features of seven histologically proven FVPTCs were systematically evaluated in a blinded manner for various architectural, nuclear, cytoplasmic and background features with special reference to nuclear morphology. RESULTS: Most smears were moderate to highly cellular with clustered and/or repetitive microfollicles, rare macrofollicles and minimal thick gummy colloid. Six of seven cases showed significant nuclear crowding/overlapping. Fairly uniform nucleomegaly (mostly three to five times the size of a mature lymphocyte) of intact neoplastic cells and enlarged naked nuclei were prominent features in all seven cases, whereas enlarged ovoid nuclei were seen in two cases. Chromatin was fine to coarsely granular and evenly distributed. Occasional nuclear grooves (NGs) and intranuclear cytoplasmic inclusions (INCIs) were seen in five and three cases, respectively. This refined approach led to a precise diagnosis of FVPTC in six cases, which were earlier interpreted as various follicular lesions. Follicular hyperplasia was excluded by the absence of significant amounts of colloid and atretic naked nuclei, whilst the possibility of follicular adenoma or follicular carcinoma was excluded by the presence of one or more features suggestive of papillary thyroid carcinoma. CONCLUSIONS: Our study showed a high cell yield, microfollicular pattern, nuclear overcrowding/overlapping, scanty gummy colloid and enlarged naked nuclei as the most consistent features of FVPTC. Although inconsistent, features such as enlarged ovoid nuclei and syncytial clusters were complementary to the diagnosis in the absence of NGs and INCIs.