Unveiling Variations: A Comprehensive Comparison of Five Globally Used Thyroid Cytology Reporting Systems With Histopathological Correlation.

Introduction Accurate cytological assessment is pivotal for managing thyroid lesions and various global reporting systems are in use, such as the globally acclaimed The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC), alongside other reporting systems namely, the Japanese Reporting System for Thyroid Aspiration Cytology (JRSTAC), Italian Consensus for the Classification and Reporting of Thyroid Cytology (ICCRTC), the UK Royal College of Pathologists System for Reporting Thyroid Cytopathology (UK RCPath), the Royal College of Pathologists of Australasia and Australian Society of Cytology Classification System (RCPA/ASC). Notably, variations exist among these systems which are influenced by country-specific statistics. Given the lack of large-scale data in India and the difference in prevalence of diagnostic entities compared to the western population, this study aimed to identify reporting systems suitable for the Indian population focusing on distinguishing neoplastic from non-neoplastic lesions. Materials and methods A cross-sectional analysis of 40 thyroid cytology cases with histopathological correlation was conducted. Pathologists independently assessed cytology slides using JRSTAC, ICCRTC, RCPA/ASC, UK RCPath and TBSRTC. Five performance indicators, sensitivity, specificity, positive predictive value (PPV) of neoplastic conditions, negative predictive value (NPV) of non-neoplastic conditions, diagnostic accuracy and two quality indicators, percentage of Atypia of undetermined significance (AUS) and AUS/Malignant ratio were analyzed and compared. Results Among 40 cases, 22 cases were neoplastic (16 papillary thyroid carcinoma, six follicular adenoma) and 18 non-neoplastic (14 multinodular goiter, four lymphocytic thyroiditis). Specific patterns emerged in cases labeled "Non-diagnostic", prompted questions about categorizing inadequately cellular cases as "benign" in light of the presence of specific findings. All reporting systems showed 100% specificity in detecting non-neoplastic and neoplastic conditions in Category 1 and Category 6 respectively. Performance and quality indicators varied among reporting systems with TBSRTC (PPV of neoplastic cases 85.71%, NPV of non-neoplastic cases 70.58%, specificity 85.7%, sensitivity 70.58%, diagnostic accuracy 60%, AUS percentage 22.5% and AUS/Malignant ratio 3%) and RCPA/ASC (PPV of neoplastic cases 76.47%, NPV of non-neoplastic cases 70.58%, specificity 75%, sensitivity 72.2%, diagnostic accuracy 62.5%, AUS percentage 15% and AUS/Malignant ratio 3%) showing better results. Conclusion Among the five thyroid cytology reporting systems studied, TBSRTC and RCPA/ASC showed better overall performance results and quality indicators were close to benchmark. Better performance by TBSRTC 2023 could be due to the detailed criterion mentioned per category with subcategorization of AUS and suspicious for malignancy by features of cytological and architectural atypia. Similarly, RCPA/ASC has subcategorized AUS with defined criteria and certain background features were included as an isolated criterion for the suspicious for malignancy category. These defined criteria outlined in TBSRTC and RCPA/ASC played a crucial role in minimizing and reclassifying cases from the indeterminate categories (AUS and suspicious for malignancy) into well-defined categories with established management protocols.