Diagnostic Role of The Bethesda System of Reporting Thyroid Cytopathology and Immunohistochemistry as an Adjunct to Fine Needle Aspiration Cytology in Differentiating Benign and Malignant Thyroid Lesions: A Cross-sectional Study

Abstract

Introduction: Fine Needle Aspiration Cytology (FNAC) plays a crucial role in the preoperative assessment of thyroid nodules. The Bethesda System of Reporting Thyroid Cytopathology (TBSRTC; 2023) is a standardised system for reporting thyroid FNAC. However, diagnostic challenges can occur in each category of TBSRTC. Aim: To categorise thyroid FNAC according to TBSRTC and revisit the challenges of cytological diagnosis in each category. Materials and Methods: A cross-sectional, observational study was conducted from November 2018 to April 2020 (18 months) in the Department of Pathology at ABVIMS and Dr. RML Hospital in New Delhi, India. The study included all 470 thyroid FNA cases received in the department from patients presenting with palpable thyroid nodules or ultrasonographically detected solid thyroid lesions, regardless of their age or sex. The cases were classified according to TBSRTC. Diagnostic tests were used to calculate sensitivity, specificity, Negative Predictive Value (NPV), Positive Predictive Value (PPV), and diagnostic accuracy of TBSRTC. Immunoexpression for Human Bone Marrow Endothelium marker-1 (HBME-1) and p63 was studied in Bethesda III to VI category cases, i.e., atypia of undetermined significance (AUS), Suspicious for Malignancy (SFM) and malignant cases only, and not in categories I and II. Results: The study included 470 thyroid FNA cases with a mean age of 39.72 years. Cytohistological follow-up was available for 50 cases, of which six cases were discordant and the remaining 44 cases were concordant. The sensitivity, specificity, PPV, NPV, and diagnostic accuracy of TBSRTC were calculated as 50%, 97.06%, 32%, 80.49%, and 82%, respectively. Three cases with diagnostic challenges were revisited and discussed. Immunohistochemistry was performed on a total of 33 FNAC cases. However, histological follow-up was available for only 18 cases, of which seven cases were diagnosed as Papillary Thyroid Carcinoma (PTC) on histological follow-up. HBME-1 and p63 were positive in 57.14% and 42.86% of these cases, respectively. Conclusion: The TBSRTC, 2023, is an excellent reporting system for thyroid FNA and serves as an initial investigative tool for thyroid lesions. Present study findings reveal that it has high specificity and diagnostic accuracy. The Risk of Malignancy (ROM) was comparable to other studies, except for the Bethesda II category. Immunoexpression of HBME-1 and p63 was useful in isolated cases; however, it is not sufficient for cytological diagnosis.