Comparison of Diagnostic Yield Between Fine Needle Aspiration Cytology and Core Needle Biopsy in the Diagnosis of Thyroid Nodule

<b>Background/Objectives</b>: This study aimed to evaluate the effectiveness of core needle biopsy (CNB) by comparing its diagnostic yield to fine needle aspiration cytology (FNAC) across primary and secondary examinations. <b>Methods</b>: This retrospective review analyzed medical records of patients who visited Soonchunhyang University Cheonan Hospital between January 2021 and August 2023 for thyroid nodule evaluation. Demographic data and the malignancy risk of thyroid nodules were collected based on the 2021 Korean Thyroid Imaging Reporting and Data System. FNAC and CNB results, classified using the Bethesda system for reporting thyroid cytopathology and diagnostic categories for thyroid CNB, were categorized as either "conclusive" or "inconclusive." The rates of conclusive results in the primary examination and nodules transitioning from inconclusive to conclusive results during the secondary examination were analyzed. Finally, the diagnostic yields of FNAC and CNB were assessed using histopathological findings from surgically excised nodules. <b>Results</b>: The rate of nodules classified as "conclusive" was significantly higher in the CNB group than that in the FNAC group. Among nodules subjected to secondary examination, only the group with FNAC followed by CNB demonstrated a significant improvement in the rate of transition from inconclusive to conclusive results. Although FNAC and CNB showed comparable sensitivity and accuracy, the specificity of CNB was greater than that of FNAC. <b>Conclusions</b>: This study confirms the clinical utility of CNB by demonstrating its higher rate of conclusive results than FNAC. Future prospective studies, including cost-benefit analyses, are warranted to further define the indications for CNB.