Cytological features of solid variants of papillary thyroid carcinoma: a fine needle aspiration cytology study of 18 cases.

Objective Solid variants of papillary thyroid carcinoma ( SV- PTC) are rare, and there have been few reports describing the cytological findings of such variants. Methods The cytological features of cellular specimens aspirated from 18 histologically confirmed SV- PTC cases were evaluated, retrospectively. Results Solid and small papillary clusters were observed in 14 (77.8%) and 13 (72.2%) cases, respectively. The incidences of large papillary clusters (11.1%) and sheet-like arrangements (11.1%) were low. Nuclear features were consistent with conventional PTC. The background was clean, and there were no colloid materials, foamy histiocytes, multinucleated giant cells, psammoma bodies, or necrotic materials. Conclusions Solid clusters and small papillary clusters in conjunction with a clean background are diagnostic clues that indicate SV- PTC cytologically. It is thought that small papillary clusters reflect the micropapillary growth pattern seen within the lumen of middle-sized follicular structures. The presence of nuclear findings typical of conventional PTC and the absence of mitotic figures and necrotic materials are important for distinguishing SV-PTC from poorly differentiated carcinoma. [ABSTRACT FROM AUTHOR]