Diagnostic Traps in Papillary Thyroid Carcinoma: Correlation of The Bethesda System for Reporting Thyroid Cytopathology with Histopathology: A Case Series

Abstract

Fine-needle aspiration cytology is a widely used first-line tool for evaluating thyroid lesions, with histopathology serving as the diagnostic gold standard. Despite its advantages, interpretation challenges arise due to overlapping cytomorphologic features, suboptimal sample adequacy, and inter-observer variability, occasionally leading to discordance and affecting patient management. This case series describes four diagnostically challenging cases of classical papillary thyroid carcinoma in which initial cytological interpretations differed from final histopathological findings. Each case was re-evaluated systematically with emphasis on adequacy of the aspirate, radiologic correlation, characteristic cytological features, and potential diagnostic pitfalls. Contributing factors such as papillary hyperplasia mimics, misleading ultrasound impressions, and low cellularity were analyzed to understand the basis of discordance. Final diagnoses were established through multidisciplinary collaboration among the surgeon, radiologist, and cytopathologist. Case 1 was initially reported as a benign colloid nodule (TBSRTC II) but was later confirmed as classical papillary carcinoma with nodal metastasis. Case 2 was categorized as AUS (TBSRTC III); histopathology revealed classical papillary carcinoma, infiltrating follicular subtype. Case 3 was diagnosed as follicular neoplasm (TBSRTC IV) on cytology, while final evaluation confirmed NIFTP. Case 4, also categorized as follicular neoplasm (TBSRTC IV), was ultimately diagnosed as encapsulated angioinvasive follicular variant of papillary thyroid carcinoma. TBSRTC remains a robust and standardized framework for thyroid cytology, providing consistent terminology and risk stratification. However, diagnostic limitations persist, emphasizing the need for meticulous cytologic assessment, close radiologic correlation, and interdisciplinary collaboration to minimize discordance and improve patient outcomes.