Fine needle aspiration cytology of thyroid follicular neoplasm: cytohistologic correlation and accuracy

Abstract

Background: This study evaluated the accuracy of fine needle aspiration cytology (FNAC) in cases of follicular neoplasm (FN) on the basis of histologic diagnosis, and reviewed the cytologic findings of FN according to the FNAC.

Methods: Among the 66 cases diagnosed with thyroid FN by FNAC during the 7-year period from 2003 to 2009, 36 cases that had undergone thyroid surgery were available for review. Cytologic diagnosis was compared with the histologic diagnosis of each case.

Results: Among the 36 cases with a cytologic diagnosis of thyroid FN, histologic diagnosis was as follows: 20 follicular adenomas (55.6%), 3 Hurthle cell adenomas (8.3%), 2 follicular carcinomas (5.6%), 8 nodular goiters (22.2%), 2 papillary carcinomas (5.6%), and 1 Hashimoto's thyroiditis (2.8%), resulting in a diagnostic accuracy of FNAC for thyroid FN of 69.5%.

Conclusions: This study shows that FNAC for thyroid FN is a useful primary screening method because when FN is diagnosed by FNAC, the rate of FN histologic diagnosis is relatively high, however, adequate sampling and experience is a prerequisite for this procedure.

Keywords: Fine needle aspiration cytology; Follicular neoplasm; Thyroid gland.

Fig. 1

Cytologic features of follicular adenoma (FA). (A) Low power view of fine needle aspiration cytology (FNAC) shows high cellularity composed of abundant microfollicles. (B) The crowded follicular cells have homogenous nuclear morphology composed of round nuclei, evenly dispersed, granular chromatin and faint nucleoli. (C) Microfollicles contain small amounts of colloid. (D) Hurthle cell type. The aspirate is very cellular and consists almost exclusively of Hurthle cells in small crowded arrangements. (E) Hurthle cell type. High-power view shows an abundant, finely granular cytoplasms and enlarged, variable sized, eccentrically located nucleus. (F) FNAC of follicular carcinoma (FC) confirmed by histologic diagnosis shows abundant syncytial clusters and small follicles similar to FA. (G) High-power view of FC shows more predominantly abundant, dispersed, isolated cells than FA in both cases. (H) FNAC (cytological misdiagnosis of Hurthle cell neoplasm [HCN]) of HCN with Hurthle cell change confirmed by histologic diagnosis shows abundant syncytial clusters composed exclusively of Hurthle cells. (I) Papillary carcinoma, oncocytic variant misdiagnosed as FA, with Hurthle cell type as determined by FNAC, showing definitive nuclear inclusion and mitosis. (J) Hashimoto's thyroiditis confirmed by histologic diagnosis misdiagnosed as FA, with Hurthle cell type as determined by FNAC, showing abundant Hurthle cells and a few lymphocytes.