DIAGNOSTIC ACCURACY OF FNAC IN THYROID SWELLINGS BY KEEPING HISTOPATHOLOGY AS GOLD STANDARD

Abstract

Background: Fine needle aspiration cytology (FNAC) is considered the primary diagnostic investigation for the evaluation of thyroid nodules due to its safety, cost-effectiveness, and minimally invasive nature. It plays a crucial role in distinguishing benign lesions from malignant thyroid nodules and guiding further clinical management. The diagnostic performance of FNAC varies among different populations due to differences in patient characteristics, sampling techniques, and cytopathological interpretation. Therefore, validation of FNAC accuracy against histopathology remains essential for establishing its reliability in specific clinical settings.

Objective: To determine the diagnostic accuracy of fine needle aspiration cytology (FNAC) in diagnosing malignant thyroid nodules, using histopathological examination as the gold standard reference method.

Methods: A cross-sectional validation study was conducted in the Department of Surgery, Ghulam Muhammad Mahar Medical College Hospital, Sukkur, Sindh, Pakistan. A total of 150 patients presenting with clinically solitary thyroid nodules and fulfilling the predefined inclusion criteria were enrolled through non-probability consecutive sampling. All participants underwent fine needle aspiration cytology followed by surgical excision and histopathological examination. FNAC findings were compared with final histopathological results using a 2×2 contingency table. Diagnostic performance was assessed by calculating sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall diagnostic accuracy with 95% confidence intervals.

Results: Among the 150 enrolled patients, 28 (18.7%) thyroid nodules were confirmed as malignant on histopathological examination. FNAC correctly identified 20 malignant cases, resulting in a sensitivity of 71.4%. The test demonstrated a specificity of 94.3%, correctly classifying 115 out of 122 benign nodules. The positive predictive value was 74.1%, negative predictive value was 93.5%, and the overall diagnostic accuracy of FNAC was 90.0%. Eight malignant nodules were missed on FNAC, indicating a false-negative rate of 28.6%.

Conclusion: FNAC demonstrated high specificity, negative predictive value, and overall diagnostic accuracy for detecting malignant thyroid nodules in this study population, supporting its role as an effective first-line diagnostic tool. However, the relatively lower sensitivity and observed false-negative rate highlight the importance of correlating FNAC findings with clinical assessment, imaging characteristics, and follow-up evaluation. A benign FNAC result should therefore be interpreted cautiously in patients with suspicious clinical or radiological features.