Diagnostic Performance and Radiocytological Correlation of ACR TI-RADS in Thyroid Nodules Using Bethesda-Reported FNAC as the Reference Standard

Objectives

This study aimed to evaluate the diagnostic performance and radiocytological concordance of American College of Radiology Thyroid Imaging Reporting and Data System (ACR TI-RADS) categories for thyroid nodules, using fine-needle aspiration cytology (FNAC) reported according to the Bethesda System as the reference standard. METHODOLOGY This cross-sectional study included 134 adults aged 18–80 years presenting with clinically suspected thyroid nodules to the Department of Radiology, FC Teaching Hospital, Peshawar. High-resolution ultrasound was performed with a high-frequency linear transducer, and nodules were scored for composition, echogenicity, shape, margins, and echogenic foci. Two radiologists independently reviewed ultrasound findings while blinded to cytology. Ultrasound-guided FNAC was subsequently performed and categorised by the Bethesda System. For the submitted analysis, Bethesda IV–VI constituted the cytologically high-risk reference category and ACR TI-RADS TR4–TR5 constituted a positive ultrasound test. Sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy were calculated. RESULTSMean participant age was 44.8 ± 12.6 years, and 102 (76.1%) were female. Thirty-eight nodules (28.4%) were classified as Bethesda IV–VI. ACR TI-RADS demonstrated 89.5% sensitivity, 85.4% specificity, 70.8% positive predictive value, 95.3% negative predictive value, and 86.6% overall accuracy. Higher TI-RADS categories were significantly associated with higher-risk Bethesda cytology (p<0.001).

Conclusion

ACR TI-RADS showed strong diagnostic discrimination and a particularly high negative predictive value against Bethesda-reported FNAC. Structured ultrasound risk stratification may support biopsy selection and reduce avoidable procedures, although indeterminate Bethesda categories should not be interpreted as histologically proven malignancy in this clinical cohort.