The impact of atypia/follicular lesion of undetermined significance on the rate of malignancy in thyroid fine-needle aspiration: Evaluation of the Bethesda System for Reporting Thyroid Cytopathology

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The Bethesda System for Reporting Thyroid Cytopathology (BSRTC) was developed to refine definitions and improve clinical communication and management. This study evaluates the impact of the BSRTC in a large cohort of patients undergoing thyroidectomy before and after its adoption at a single institution.


The records from 469 patients in the pre-BSRTC (n = 187) and post-BSRTC (n = 282) periods were reviewed. Cytologic categories in group 1 included nondiagnostic, benign, follicular/Hürthle neoplasm, suspicious for malignancy, and malignant. Atypia/follicular lesion of undetermined significance (AUS/FLUS) was included in group 2. The percentage of each fine-needle aspiration (FNA) category, malignancy rate per category, and rate of AUS/FLUS utilization were calculated.


Group 1 FNA results included 3% (n = 6) nondiagnostic, 48% (n = 89) benign, 17% (n = 32) follicular/Hürthle, 13% (n = 25) suspicious for malignancy, and 19% (n = 35) malignant. Group 2 results included 4% (n = 11) nondiagnostic, 34% (n = 96) benign, 29% (n = 82) AUS/FLUS, 12% (n = 33) follicular/Hürthle, 10% (n = 29) suspicious for malignancy, and 11% (n = 31) malignant. The rate of cancer changed from 25% to 36% for follicular/Hürthle lesions. AUS/FLUS was utilized in 154 of 1095(14%) FNAs reviewed with a malignancy rate of 20%.


The new AUS/FLUS category was used more often than recommended (14%) with a higher than expected rate of malignancy (20%). Rigorous cytopathology to histopathology correlation is needed to accurately reflect the malignancy rates of the different BSRTC categories at each individual institution. Clinical management should be tailored based on such institutional findings.

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