Understanding oncocytic lesions of thyroid: a cytomorphological insight in the light of “The Bethesda System for Reporting Thyroid Cytopathology III”

Abstract Background: Fine-needle aspiration cytology (FNAC) is a vital tool for evaluating thyroid lesions. Altered follicular cells, referred to as oncocytic or Hürthle cells, can be seen in various thyroid conditions. The World Health Organization now recognizes Hürthle cell neoplasms as a separate pathological entity. Materials and Methods: This prospective study was conducted in the Department of Pathology over 18 months. Patients presenting with thyroid swelling and referred for FNAC by clinicians were included. The aspirated samples were stained with Giemsa and Papanicolaou stains and examined under a microscope. Results: A total of 200 cases were analyzed, with oncocytic cells identified in 120 cases. The majority were thyroiditis (64.16%), followed by colloid goiter with oncocytic changes (25.83%). According to the Bethesda System for Reporting Thyroid Cytopathology, 182 cases (91%) were classified as Category II, making it the most common diagnostic group. The indeterminate categories—Category III (1%), Category IV (2.5%), Category V (1%), and Category VI (2%)—together accounted for 6.5% of cases. Oncocytic neoplastic lesions showed cells arranged in sheets, lacking intracellular lymphocytes and containing little to no colloid ( P < 0.001, statistically significant). Conclusion: Autoimmune thyroiditis (Bethesda Category II) emerged as the most common thyroid lesion associated with oncocytic cells in this study. The presence of oncocytic cells within follicles and scattered singly favors a diagnosis of neoplastic lesions. Differentiating these lesions is of prognostic significance.