Cytomorphologic Diversity of Papillary Thyroid Carcinoma

Cytologic features of papillary thyroid carcinoma (PTC) have been extensively documented in literature. However, PTC variants can prove to be diagnostically challenging on fine needle aspiration cytology (FNAC).

To study the FNAC features of PTC and its variants and explore the causes for misdiagnosis.

This is a retrospective study. All cases of histopathologically (HP) confirmed cases of PTC during a 2-year period (January 2012 to December 2013) with presurgical FNAC were included. The cytologic findings and FNAC diagnosis of each case were documented and compared with the HP report. The misdiagnosed cases were reviewed to look for any cytological clues and reasons for misdiagnosis.

A total of 58 cases were included. The overall diagnostic accuracy was 55.6% which improved to 64.8% on including suspicious for PTC cases. Follicular variant was the most misdiagnosed variant; 41.2% of the cases were called follicular neoplasm. Oncocytic variant showed cells with abundant eosinophilic cytoplasm along with bizarre giant cells. Warthin tumor-like variant showed cells with moderate eosinophilic cytoplasm with close apposition of lymphocytes in a background of reactive lymphocytes and lymphoid tangles. Cystic variant was paucicellular. Columnar cell variant showed tall columnar cells with nuclear stratification. Cribriform-morular variant showed syncytial sheets of cells and hyaline globules.

PTC variants have distinct cytomorphological features. In some variants (follicular, columnar cell), nuclear grooves and inclusions may not be apparent, contributing to the diagnostic confusion. Benign nodule adjacent to the tumor can dominate the FNAC smear and lead to misdiagnosis.