Diagnostic accuracy of fine needle aspiration cytology in comparison with thyroid ultrasound for solitary thyroid nodule taking histopathology as gold standard

Abstract

Background: Solitary thyroid nodules are a common clinical finding requiring accurate diagnostic differentiation between benign and malignant nodules. Ultrasound plays an important role in initial assessment, while fine needle aspiration cytology (FNAC) provides cytological confirmation. This study compared the diagnostic efficacy of the ultrasound-based Thyroid Imaging Reporting and Data System (TIRADS) and FNAC, using histopathology as the gold standard.

Methods: This prospective, cross-sectional study was conducted over 12 months from September 2023 to August 2024 on 70 patients with solitary thyroid nodules at the Department of Pathology, Lahore General Hospital, Lahore. Each participant underwent ultrasound and FNAC, with results compared with final histopathological findings. Diagnostic metrics, ROC curves, cross-tabulations, logistic regression, and concordance analysis were used for evaluation.

Results: Out of 70 patients, 19 cases were malignant and 51 were benign. ROC curve analysis revealed superior diagnostic performance of FNAC (AUC=0.856) compared to TIRADS (AUC=0.605). FNAC demonstrated higher sensitivity (78.95%), specificity (92.16%), and overall accuracy (88.57%). TIRADS showed high specificity (100%) but low sensitivity (21.05%). Chi-square tests confirmed significant associations of both methods with histopathology (TIRADS p=0.0052 and Bethesda p<0.001), with FNAC showing a stronger correlation. Logistic regression confirmed FNAC as the only independent predictor of malignancy. There is significant concordance between TIRADS and the Bethesda classification system, with a kappa value of 0.298 and p-value <0.001.

Conclusion: FNAC via the Bethesda system is a significantly more reliable diagnostic tool than ultrasound-based TIRADS for solitary thyroid nodules.