Thyroid Bethesda Atypia of Undetermined Significance or Follicular Lesion of Undetermined Significance (AUS/FLUS): A Heterogenous Group

BACKGROUND: The Bethesda system of reporting thyroid cytopathology (BSRTC) was introduced in 2007. The third category of atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) poses difficulties for the pathologist, and different papers have been published varying the risks of malignancy. AIMS: (1) Evaluation of the cytological features of thyroid lesions according to BSRTC. (2) After resection, correlation with histopathological report to evaluate the risk of malignancy (ROM) and the risk of neoplasm (RON). (3) Division of category III into six subgroups based on cytological findings and assessment of ROM and RON. MATERIALS AND METHODS: A total of 282 patients with diagnosed thyroid lesions underwent fine-needle sampling under ultrasound guidance. Smears were prepared and stained with May–Grunwald–Giemsa stain and Papanicolaou stain. RESULTS: Of 282 cases, there were 9 cases (3.1%) of category I, 157 cases (55.8%) of category II, 24 cases (8.5%) of category III, 20 cases (7.1%) of category IV, 14 cases (4.8%) of category V, and 58 cases (20.7%) of category VI. The RON was 60, 17.1, 63.1, 77.7, 91.7, and 98.2% and the ROM was 60, 14.3, 26.3, 38.9, 91.7, and 96.3% in categories I, II, III, IV, V, and VI, respectively. The RON was 0, 75, 50, 100, 66.6, and 100% and the ROM was 0, 25, 50, 100, 16.6, and 0% in subgroups 1, 2, 3, 4, 5, and 6, respectively. We have proposed a system of subgrouping AUS/FLUS that may help to dispel the confusion generated by an AUS/FLUS report, and provide with a more exact and reproducible diagnostic and prognostic tool.