A single institution experience with the new bethesda system for reporting thyroid cytopathology: correlation with existing cytologic, clinical, and histological data

Abstract

Our goal was to evaluate the Bethesda system (TBS) in comparison to the previously used system at our institution. One hundred consecutive thyroid fine needle aspirations (FNAs) and 45 consecutive indeterminate FNAs were reviewed by two cytopathology-boarded pathologists, diagnosed based on TBS and correlated with management and follow-up. Re-evaluation led to a diagnosis change in 48% of cases. Thirty-nine percent of benign cases were unsatisfactory under TBS. For malignant diagnoses the positive predictive value (PPV) was unchanged, while the negative predictive value (NPV) was slightly improved using TBS. Both the PPV and NPV were improved for actionable diagnoses. Inter-observer variability across all categories was in moderate agreement. Clinical management of both follicular lesion (FL) and indeterminate cases ranged from none to immediate surgery. Repeat FNA resolved the diagnosis in 50% of indeterminate cases. Indeterminate cases had an overall malignancy rate of 27%; higher in pre- (46%) than post-TBS cases (8%). Inter-observer variability between the reviewing pathologists and the original pathologists for indeterminate cases was fair, and between the two reviewing pathologists was moderate. Using TBS criteria increased the unsatisfactory rate and led to improved prediction of malignancy and actionable diagnoses. The pre-Bethesda diagnosis of FL at our institution led to inconsistent clinical management. Clinical management of patients with indeterminate diagnoses was essentially unchanged following adoption of TBS. The moderate inter-observer agreement between the reviewing pathologists may be related to level of cytology experience, strict adherence to TBS, and the exclusive use of cytomorphology for diagnosis.

Keywords: Bethesda; atypia; cytopathology; thyroid.