Application of the Bethesda Classification for Thyroid Fine-Needle Aspiration: Institutional Experience and Meta-analysis

Abstract

Context.—Fine-needle aspiration (FNA) biopsies have been an important component in the preoperative evaluation of thyroid nodules. Until the introduction of the Bethesda System for Reporting Thyroid Cytopathology (BSRTC) in 2008, individual institutions had developed their own diagnostic categories. The BSRTC proposed 6 categories in an attempt to standardize reporting of thyroid FNA. Objective.—To present a 15-year experience of thyroid FNA at one institution, including data before and after introduction of the BSRTC. The risk of malignancy is compared with the meta-analysis of high-quality published data. Data Sources.—Data sources were PubMed, a manual search of references, and institutional data. Conclusions.—The diagnostic categories developed at our institution were similar to those proposed by the BSRTC, with best fit into the 6 categories easily accomplished and reported in the final 2 years of the study. Significant differences were noted in the frequencies of cases in diagnostic categories Benign (II; P = .003), Suspicious for follicular neoplasm/Follicular neoplasm (IV; P < .001), and Malignant (VI; P = .003) after the introduction of the BSRTC. Eighteen published articles met the criteria for inclusion in the meta-analysis. The risk of malignancy in each category in our institution was similar to that determined in the meta-analysis, except for Insufficient for diagnosis (I; 20% versus 9%–14%). Meta-analysis showed an overlapping 95% CI of risk of malignancy between Atypia of undetermined significance/Follicular lesion of undetermined significance (III; 11%–23%) and Suspicious for follicular neoplasm/Follicular neoplasm (IV; 20%–29%), suggesting similar risks of malignancy. The use of newer molecular tests for these indeterminate cases may further refine risk assessment.