Diagnostic accuracy of follicular variant of papillary thyroid carcinoma in fine-needle aspirates processed by ultrafast Papanicolaou stain

Abstract

Detection of follicular variant (FV) of papillary carcinoma (PC) of the thyroid is considered difficult in cytology. Various ancillary studies have been used to increase the sensitivity in the detection of FVPC in fine-needle aspiration (FNA). We previously reported that the clear nuclei of PC became conspicuous in Ultrafast Papanicolaou (UFP)-stained smears. This study reports our experience on using this UFP-induced artifact in the detection of FVPC. Over an 11-year period, 5637 ultrasound-guided thyroid FNAs were performed. All samples were smeared and air-dried. Diff-Quik stain was used to assess the colloid and UFP stain was used to study the nuclei. Histologic follow-up was available from 125 cases. Of the 107 aspirates with diffuse "grape-like" watery clear nuclei, histologic follow-up showed 94 PCs, 8 follicular adenomas containing atypical nuclei, and 5 nonneoplastic lesions. Of the 18 aspirates with focal clear nuclei, histologic follow-up showed 6 PCs, 8 follicular adenomas, and 4 nonneoplastic nodules. As reported previously, histologic follow-up of 147 FNAs contained follicles with normal nuclei showed 107 true follicular neoplasms, 32 hyperplastic nodules, and 8 FVPC. The sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy in the detection of PC were 93.6%, 94.9%, 93.6%, 94.9%, and 94.3%, respectively, when follicular adenomas containing atypical nuclei were counted as encapsulated FVPC; and 92.6%, 85.6%, 80%, 94.9%, and 88.3%, respectively, when follicular adenomas containing atypical nuclei were counted as benign. UFP stain is one of the options to increase the sensitivity of detection of FVPC in preoperative FNA, and to triage microfollicular nodules into those that require surgery no matter how small, and those which can be followed when small.