Consistency in the distribution of Bethesda System for Reporting Thyroid Cytology (BSRTC) Categories over 9 years: A single institute, retrospective study

Abstract

The Bethesda System for Reporting Thyroid Cytopathology (BSRTC) has evolved since it was first introduced in 2009 to become a worldwide accepted cytologic analysis reference, due to its simplicity and reproducibility. To date, the consistency of BSRTC throughout time has yet to be investigated. Retrospective single institution case series with chart review of all patients who underwent FNAs for a thyroid nodule in our institution between the years 2010 to 2018 with a documented BSRTC classification. Data collection included demographics, risk factors, sonographic evaluation, nodule size, and final pathology when feasible. The main outcome is the difference in the rates of BSRTC categories benign, AUS, FN, SFM, and malignant (BSRTC II-VI, respectively) between the study years. A total of 2830 thyroid nodules were included. BSRTC II-VI distribution was 83.9% (2,373), 8.2%, (232), 2.7% (75), 3.3% (93), and 2.0% (57) respectively. There was no significant change in the overall trend of each BSRTC category distribution throughout the study. There was a significant increase in the benign cytology rate (BSRTC II) in 2011 compared to 2015 and 2018 (76.4% compared to 88.7% and 87.6%, respectively. p < 0.005) alongside a significant decline in the AUS category rate (BSRTC III) between the same years (13.0% compared to 4.8% and 5.5%, respectively. p < 0.005). BSRTC showed consistency throughout the study across all observed categories. An overlap between AUS and benign may exist, possibly due to the heterogenic definition of AUS as reflected in the 2023 BSRTC subclassification for AUS.