Utility of cell block as an adjunct to liquid-based cytology for diagnosing papillary thyroid carcinoma

Although liquid-based cytology (LBC) has gained popularity among clinical laboratories, it is unclear whether it is equivalent to conventional smears for making a definite diagnosis of papillary thyroid carcinoma (PTC). The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) suggests a definite diagnosis of PTC is preferred when there are at least one of three features (papillary architecture, psammomatous calcifications, and frequent pseudonuclear inclusions) plus other typical cytomorphological findings. This study evaluated whether an additional cell block (CB), prepared from the residual LBC material, could help improve the diagnosis of PTC.

A total of 62 cases with both ThinPrep LBC and CB preparations and histopathological follow-up of PTC were retrieved between November 2016 and March 2019. The ThinPrep LBC and CB slides were reviewed separately to identify any papillary architecture, psammomatous calcifications, or pseudonuclear inclusions for diagnosing PTC.

Among the 51 cases with cytological diagnosis of PTC in the LBC+CB slides, the CB provided additional diagnostic information in 15 cases, which were initially diagnosed as suspicious for PTC based on the LBC slides alone. This information included papillary architecture (n=11), psammomatous calcification (n=1) and pseudonuclear inclusions (n=5). The number of specimens in the 51 cases containing at least one of the three features increased from 42 (LBC) to 51 (LBC+CB). The accuracy for diagnosing PTC increased from 58.1% for LBC alone to 82.3% for the LBC+CB examination.

An adjunctive CB preparation may improve the LBC technique for diagnosing PTC.