Fine-needle aspiration diagnosis of the follicular variant of papillary carcinoma

BACKGROUND, The follicular variant of papillary carcinoma (FVPC) presents significant diagnostic difficulty using fine-needle aspiration (FNA). Diagnoses by FNA vary considerably and usually are categorized as follicular proliferations. METHODS. Conventional Papanicolaou, Diff-Quik, and hematoxylin and eosin stained FNAs from 16 cases of histologically confirmed FVPC were examined retrospectively. Each case was evaluated with respect to easily recognizable architectural and cytologic features. These were defined, ranked, and recorded for side-by-side comparison and identification of statistical significance. Similar fea tures in six follicular carcinomas, seven follicular adenomas, and six adenomatous multinodular goiters were evaluated and compared as well. RESULTS. Eight of 16 FVPC cases (including 5 macrofollicular variants) previously were diagnosed on FNA as a follicular neoplasm or follicular lesion, 6 were diagnosed as a papillary carcinoma or FVPC, and the remaining 2 were diagnosed as atypical. The cellularity and amount of colloid varied considerably between cases. Monolayered, twisted epithelial sheets and microfollicles or macrofollicles were the predominant microarchitecture. Powdery chromatin and easily identifiable nuclear grooves were present in 15 cases (94%), and intranuclear cytoplasmic (INC) inclusions were present in 11 cases (69%). These three features proved to be statistically significant in distinguishing FVPC from the other follicular lesions. No case exhibited true papillary clusters or psammoma bodies. Cases of follicular adenoma, follicular carcinoma, and adenomatous goiter shared many of these features, but notably lacked INC inclusions and abundant nuclear grooves. CONCLUSIONS, Nuclear features such as abundant grooves, powdery chromatin, and INC inclusions were statistically significant and present in combination in the majority of cases of FVPC compared with the other follicular proliferations examined. Cancer (Cancer Cytopathol) 1998;84:349-54. (C) 1998 American Cancer Society.