Risk of Malignancy and Risk of Neoplasia in the Bethesda Indeterminate Categories: Study on 4,532 Thyroid Fine-Needle Aspirations from a Single Institution in India

Abstract

Objectives: To determine the frequency of category 3 (atypia of undetermined significance [AUS]/follicular lesion of undetermined significance [FLUS]), category 4 (follicular neoplasm), and category 5 (suspicious for malignancy) of The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC), the risk of malignancy (ROM) and the risk of neoplasia (RON) in these categories. Study Design: A retrospective 6-year audit of 4,532 thyroid fine-needle aspirations (FNA) reported as per the TBSRTC from a single institution with cytohistological correlation in 335 cases. Results: The frequency of categories 3, 4, and 5 was 2.5, 3.9, and 0.5%, respectively; the upper and lower bound estimates of ROM being 58.3, 23.6, 75% and 5.1, 5, and 12.5%, respectively. AUS/FLUS (n = 116) cases were subcategorized as AUS, AUS-HC (Hürthle cell), AUS-PTC (AUS-papillary thyroid carcinoma not excluded), FLUS, FLUS-FH (favor hyperplasia), FLUS-HC, and FLUS-PTC. The AUS/FLUS malignancy ratio was 1:3.8. The sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of FNA thyroid was 80.5, 85.9, 80.7, 85.7, and 82.4%, respectively. Conclusion: Implementation of TBSRTC aided in achieving internal quality control in reporting thyroid FNA cytology. The AUS/FLUS frequency was 2.5%, which is at the lower range of the recommended rate and was associated with a higher than recommended upper bound estimate, but a comparable lower bound estimate of ROM.