Follicular variant of papillary carcinoma: Cytologic findings on FNAB samples - Experience with 16 cases

Between January 1, 1992 and December 31, 1997, a cytopathological diagnosis of follicular variant of papillary thyroid carcinoma (FVPC) was made on a series of 16 out of 18 patients with palpable nodules who underwent fine-ne edle aspiration biopsy (FNAB) in our Department. The results of aspiration biopsy were followed by histopathological examination of the surgically exc ised tissues. There were three false-negative aspirations (16.6%), of which two were probably bound to fine-needle sampling and one due to a mixture o f benign and malignant cells which had originally gone unrecognized. The ac curacy of the cytopathologic diagnosis in this variant was 88.8%. An analysis of the diagnostic cytopathological criteria was performed, whic h demonstrated the importance of both architectural features (monolayered a nd branching sheets, microacinar structures, and their combinations) and nu clear features (presence of nuclear grooves). Background-bound,features wer e mainly represented by dense, nonfilamentous colloid. The cytopathologic findings in FVPC were compared to those found in a serie s of 10 usual papillary carcinomas (UPC) and 10 follicular neoplasms (FN). These latter had originally been diagnosed by FNAB and were subsequently cl assified histologically as follicular adenoma (n = 6), follicular carcinoma (n = 3), or adenomatoid colloid nodule (n = 1). Statistical evaluation was performed on the cytopathological findings in th e three classes of lesions (FVPC. UPC, and FN) as to their presence and rel ative frequency or absence by using a nonparametric one-way ANOVA (Kruskall -Wallis) and, where necessary, a Mann-Whitney U test. Papillary cellular fragments and multinucleated giant cells (P < 0.005), no nfilamentous dense colloid, squamoid cells, and syncytia were significantly more represented in UPC than in FVPC (P < 0.05), while histiocytes were si gnificantly more frequent in FVPC (P < 0.005). Other nuclear and/or backgro und features were significant only in the distinction between papillary car cinomas as a group and FN. The cytological differential diagnosis of the FVPC is briefly discussed wit h relevance to the possible pitfalls caused by its peculiar cyto- and histo morphology. <(c)> 2001 Wiley-Liss, Inc.