Morphologic spectrum of papillary carcinoma of the thyroid: role of cytology in identifying the variants

OBJECTIVE: To evaluate the efficacy of fine needle aspiration cytology (FNAC) in the diagnosis of morphologic variants of papillary carcinoma of the thyroid (PCT) and to determine the reasons for misdiagnosis in discrepant cases on cytology. STUDY DESIGN: Fine needle aspiration smears from 158 histologically proven cases of PCT were blindly reviewed and an attempt made to subclassify them into different variants on the basis of various architectural and morphologic features. Cytohistologic correlation was performed to assess the efficacy of cytology in correctly identifying these variants. RESULTS: In cases with satisfactory aspirates, the diagnosis of papillary carcinoma was correctly made in 112 of 139 (80.5%) histologically proven cases of PCT. Subclassification was correct in 87 of 96 (90.6%) cases of classic papillary carcinoma and in 25 of 43 (58.1%) of the other variants of PCT with adequate aspirates. Cytohistologic agreement was 100% in columnar cell variant (CCV) and high grade variant (HGV). Although there was overlap in the morphologic features of tall cell variant (TCV) and Hürthle cell variant, cytology correctly identified 60% and 76.4% of these cases, respectively. The accuracy of cytology was limited in diagnosing follicular variant as only 50% of these cases could be correctly typed on cytology. Nodular fascitis-like stroma and diffuse sclerosis variants could not be diagnosed on cytology. CONCLUSION: Though FNAC is of limited value in typing the variants of PCT due to overlapping morphologic features, it can provide clues to the diagnosis in certain aggressive variants such as TCV, CCV and HGV. Early diagnosis in these cases can assist clinicians with management.