Intranuclear cytoplasmic inclusions in fine-needle aspiration smears of papillary thyroid carcinoma: a study of its morphological forms, association with nuclear grooves, and mode of formation.

Intranuclear cytoplasmic inclusion (INCI) and nuclear grooves in fine-needle aspiration (FNA) smears of papillary thyroid carcinoma (PTC) represent cytoplasmic invaginations into the nucleus. Although formation of INCIs is linked to nuclear grooves, they seldom exist together. This study was undertaken to find out the various morphological forms of INCIs, their relation to nuclear grooves, and mode of formation. FNA smears of 54 PTC cases were studied for various forms of INCI, nuclear chromatin pattern, nuclear grooves, and nuclear notches. A differential count of INCIs was made in 19 cases having > or =10 INCIs per 200 neoplastic cells. INCIs were present in 48 (88.9%) of 54 PTC cases. Round INCIs were present in 46 (85.2%) cases, followed by oval (48.1%), tear drop/flask-shaped (18.5%), irregular (14.8%), planoconvex/semicircular (13%), rectangular (9.3%), spindle-shaped (3.7%), and bilobed (3.7%). A differential count of INCIs also showed that the round form was the commonest (76.3%). The oval and other forms constituted 19.5 and 4.2%, respectively. INCIs and nuclear grooves were present together in a cell in 15 (27.8%) cases. The formation of INCIs as a cytoplasmic invagination into the nucleus was shown cytomorphologically in rare cells. For the first time in this study, the various morphological forms of INCIs, and the extent of their coexistence with nuclear grooves, (have been highlighted) and showed their mode of formation shown at a light microscopic level. Copyright 2005 Wiley-Liss, Inc.