Thyroid FNA cytology cases Incidence and Malignancy Rates of Diagnoses in the Bethesda System for Reporting Thyroid Aspiration Cytology: An Institutional Experience

Abstract

The Bethesda System for Reporting Thyroid Cytopathology (BSRTC) was developed in 2008 to facilitate more accurate communication of thyroid fine-needle aspiration (FNA) interpretations between clinicians and cytopathologists. 1 This system, which we adopted in 2010, classifies FNA results into six general diagnostic categories, namely, I) nondiagnostic or unsatisfactory, II) benign, III) atypia of undetermined significance or follicular lesion of undetermined significance, IV) follicular neoplasm or suspicious for a follicular neoplasm, V) suspicious for malignancy, and VI) malignant. 1 Each of these categories is associated with a risk of malignancy as follows: I) 1-4%, II) 0-3%, III) 5-15%, IV) 15-30%, V) 60-75%, and VI) 97-99%. 1 Although this system is useful, some studies that have investigated these risks have had controversial results, especially for category III. Furthermore, other studies have reported differences in malignancy rates among different institutions and have offered various explanations. In this study, we determined the distribution of FNA results and malignancy rates in each diagnostic category of the BSRTC in our hospital to determine whether our cytopathologists are using this system properly. Specifically, by analyzing data from individual cytopathologists, we hoped to ascertain whether our hospital has consistent FNA results in each diagnostic category. Finally, we suggest ways to improve the accuracy of classifying FNA diagnoses. MATERIALS AND METHODS Thyroid FNA cytology cases We retrospectively analyzed 1,538 patients who had thyroid nodules that were diagnosed by FNA between October 1, 2011, and December 31, 2011, in Gangnam Severance Hospital in Korea. This study met criteria for exemption from review from the institutional review board. Each FNA diagnosis was made independently by one of four cytopathologists. Each thyroid aspiration sample was analyzed by using liquid-based preparation or conventional smear. Some FNAs were originally performed by other hospitals; however, in these cases, the slides were re- Background: The Bethesda System for Reporting Thyroid Cytopathology (BSRTC) uses six diagnostic categories to standardize communication of thyroid fine-needle aspiration (FNA) interpretations between clinicians and cytopathologists. Since several studies have questioned the diagnostic accuracy of this system, we examined its accuracy in our hospital. Methods: We calculated the incidences and malignancy rates of each diagnostic category in the BSRTC for 1,730 FNAs that were interpreted by four cytopathologists in Gangnam Severance Hospital between October 1, 2011, and December 31, 2011. Results: The diagnostic incidences of categories I-VI were as follows: 13.3%, 40.6%, 9.1%, 0.4%, 19.3%, and 17.3%, respectively. Similarly, the malignancy rates of these categories were as follows: 35.3%, 5.6%, 69.0%, 50.0%, 98.7%, and 98.9%, respectively. In categories II, V, and VI, there were no statistically significant differences in the ranges of the malignancy rates among the four cytopathologists. However, there were significant differences in the ranges for categories I and III. Conclusions: Our findings suggest that institutions that use the BSRTC should regularly update their diagnostic criteria. We also propose that institutions issue an annual report of incidences and malignancy rates to help other clinicians improve the case management of patients with thyroid nodules. Incidence and Malignancy Rates of Diagnoses in the Bethesd