The impact of using the Bethesda System for reporting thyroid cytology diagnostic criteria on the follicular lesion of undetermined significance category

Abstract

The Bethesda System for Reporting Thyroid Cytology (TBSRTC) refines the definition of and provides specific diagnostic criteria for the category of atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS). This study was conducted to review our institutional experience with thyroid nodules interpreted as FLUS using TBSRTC diagnostic criteria. A SNOMED (Systemized Nomenclature of Medicine) search of the electronic pathology database in our institution for the period of January 2011 to June 2012 was conducted to identify thyroid aspirates previously interpreted as FLUS using TBSRTC diagnostic criteria. Allcases were followed for at least 6 months. Follow-up information including clinical/imaging monitoring, repeat fine-needle aspiration, and/or subsequent surgical intervention, along with the corresponding cytologic diagnosis and/or histologic diagnosis were collected for each case. Cytology-histology concordance was evaluated for aspirates with surgical follow-up. We identified a total of 122 FLUS cases and follow-up information was available in 100 cases. Among the 100 cases, 31 appeared clinically stable and showed no size change on ultrasonographic imaging; 9 were reclassified as benign non-neoplastic by a repeat fine-needle aspiration; and 60 received surgical treatments. The follow-up histology revealed 26.7% (16 of 60) papillary thyroid carcinoma, 25% (15 of 60) follicular adenoma, and 48.3% (29 of 60) non-neoplastic nodules (nodular hyperplasia or lymphocytic thyroiditis). Compared with historical control subjects from our institution, the current study demonstrates that adhering to TBSRTC diagnostic criteria yields a higher prediction of histology-proven neoplasia (25% versus 14.9%) and malignancy (26.7% versus 9.2%) for the FLUS category.