A simplified Bethesda System for reporting thyroid cytopathology using only four categories improves intra- and inter-observer diagnostic agreement and provides non-overlapping estimates of malignancy risks.

Our previous study utilizing the 2008 NCI six-category system (also known as The Bethesda System) for reporting thyroid fine-needle aspirations (FNA) identified considerable overlap in diagnosis and in assigned malignancy risk estimates for the "follicular lesion of undetermined significance (FLUS)" and "follicular neoplasm (FN)" categories and for the "suspicious for malignancy (Susp)" and "malignant" categories. We proposed a simplified Bethesda System for reporting thyroid FNAs that provided four non-overlapping, statistically significant, and more clinically relevant diagnostic categories: unsatisfactory, benign, FLUS/FN, and Susp/malignant. In the current study, six cytopathologists participated in a blinded retrospective review of 60 thyroid FNAs and kappa statistics were utilized to compare the intra- and inter-observer diagnostic agreements obtained using the six-category and the simplified four-category schemes. Surgical follow-up was used to determine which scheme provided more discrete malignancy risk estimates. Use of the simplified four-category scheme significantly improved intra- and inter-observer diagnostic agreement levels, significantly increased the sensitivity of FNA for a diagnosis of carcinoma in the subsequently resected thyroid glands, and provided non-overlapping malignancy risk estimates for each diagnostic category.