Diagnostic Accuracy of Gray-Scale Ultrasonography and Colour Doppler in Differentiating Benign and Malignant Thyroid Nodules: An FNAC-Correlated Study

Abstract

 Background: Thyroid nodules are common, but only a small proportion are malignant. Gray-scale ultrasonography is the principal imaging modality for thyroid evaluation, while colour Doppler provides complementary information regarding nodule vascularity. Accurate ultrasound-based risk assessment can improve the selection of nodules requiring FNAC. Aim: To determine the diagnostic accuracy of gray-scale ultrasonography and colour Doppler in differentiating benign and malignant thyroid nodules, using FNAC as the reference standard. Materials and Methods: This hospital-based analytical cross-sectional diagnostic-accuracy study included 65 patients with thyroid lesions evaluated in the Departments of Radio-diagnosis and Pathology, Navodaya Medical College and Hospital, Raichur, from December 2017 to August 2019. Gray-scale ultrasonography assessed composition, echogenicity, shape, margins, calcification, halo and cervical lymphadenopathy. Colour Doppler assessed the presence and distribution of vascularity. Ultrasonographic diagnoses were correlated with FNAC findings. Sensitivity, specificity, PPV, NPV, accuracy, odds ratios and Cohen’s kappa were calculated with 95% CIs. Fisher’s exact test or the Fisher-Freeman-Halton exact test was applied, with considered statistically significant. Results: FNAC classified 63 (96.9%) lesions as benign and 2 (3.1%) as malignant papillary carcinomas. Ultrasonography correctly differentiated all benign and malignant lesions, yielding sensitivity, specificity, PPV, NPV and binary accuracy of 100%. However, the sensitivity and PPV had wide 95% CIs of 15.8-100.0%. Both malignant nodules had mixed composition, irregular shape, irregular margins and microcalcifications. Irregular shape and irregular margins were significantly associated with malignancy (OR 86.43; 95% CI 3.45-2,167.36; each). Microcalcification demonstrated the strongest association (corrected OR 635.00; 95% CI 10.33-39,038.61; ). Colour Doppler patterns differed significantly between benign and malignant lesions (); combined intranodular and perinodular vascularity occurred in both malignant nodules (). Overall exact lesion-specific accuracy was 92.3% (95% CI 83.0-97.5%), with almost perfect agreement between ultrasonography and FNAC (, ). Conclusion: Combined gray-scale ultrasonography and colour Doppler demonstrated excellent agreement with FNAC. Irregular shape, irregular margins, microcalcifications and combined intranodular-perinodular vascularity were important indicators of malignancy. However, because only two malignant nodules were included, the apparently perfect binary diagnostic performance should be interpreted cautiously and validated in larger histopathology-correlated studies.