Multimodal Diagnostic Cross-Check: A Correlative Study of Fine-Needle Aspiration Cytology, Ultrasonography, Thyroid Profile, and Histopathology in Thyroid Swellings

Background: Thyroid swellings are common in surgical and endocrine practice, and accurate preoperative discrimination of benign from malignant nodules guides surgical decision-making and avoids unnecessary intervention. Preoperative work-up typically combines fine-needle aspiration cytology (FNAC), ultrasonography (USG) with Thyroid Imaging Reporting and Data System (TI-RADS) scoring, and serum thyroid-stimulating hormone (TSH) measurement, with histopathological examination (HPE) as the reference standard. Objectives: To evaluate the diagnostic performance and correlation of FNAC (Bethesda System), the American College of Radiology (ACR) TI-RADS USG, and serum TSH status against histopathological examination as the reference standard. Methods: In this single-center, prospective, cross-sectional study conducted from June 2024 to May 2025, 178 consecutive patients underwent clinical evaluation, serum TSH measurement, USG using ACR TI-RADS, and FNAC, with results reported according to the Bethesda System. Sixty-eight patients (38.20%) underwent surgery, with HPE as the reference standard. Diagnostic performance estimates were calculated only in this surgically verified subgroup, with 95% Wilson score confidence intervals (CIs). Results: The mean age was 44.88 ± 15.34 years. Of the 178 patients, 108 (60.67%) were female (female-to-male ratio, 1.54:1). Hypothyroidism was the most common thyroid functional state, occurring in 103 (57.87%) patients. Among the 68 operated patients, malignant or borderline histopathology, including non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), was confirmed in 36 (52.94%) patients. FNAC showed sensitivity of 58.33%, specificity of 100.00%, positive predictive value (PPV) of 100.00%, negative predictive value (NPV) of 68.09%, and accuracy of 77.94% (κ = 0.57). USG showed sensitivity of 75.00%, specificity of 78.12%, PPV of 79.41%, NPV of 73.53%, and accuracy of 76.47% (κ = 0.53). The Bethesda category correlated strongly with HPE (χ² = 50.43, P < 0.0001); thyroid functional status did not (P = 0.309). Conclusions: Within the surgically verified subgroup, FNAC and USG TI-RADS provided complementary diagnostic information. FNAC showed high specificity and PPV but limited sensitivity, whereas USG TI-RADS showed higher sensitivity with lower specificity. Interpretation is limited by partial histopathological verification.