Radiological–Cytological Correlation of Thyroid Nodules: Role of Ultrasound Elastography and Bethesda Classification

Background: Thyroid nodules are common and the majority of these are harmless, but some are malignant. The use of conventional ultrasonography and fine-needle aspiration cytology (FNA) are fundamental for the evaluation of thyroid nodules, but these categories could be difficult to distinguish. The use of ultrasound elastography can also add some information about tissue stiffness, and when used in conjunction with Bethesda cytological classification, may enhance risk stratification. The aim is to test the correlation between ultrasound elastography results and Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) classification in the risk stratification of thyroid nodule, and to examine the diagnostic efficacy of the combined radiological-pathological approach for malignant diagnosis of thyroid nodule. Material and Methods: Prospective observational diagnostic correlation study done in 150 patients who had thyroid nodules. All 167 thyroid nodules were assessed by both conventional B-mode ultrasound and ultrasound elastography. Elastographic characteristics were classified into soft, intermediate or stiff patterns and quantitative Young's modulus was measured, if applicable. Fine-needle aspiration cytology (FNA) guided by the USG was performed and the diagnosis given was based on the Bethesda classification. Patients who underwent thyroid surgery were also assessed by histopathological examination as the reference method for assessing malignancy. The correlation between elastographic interpretation and Bethesda category was analyzed and its diagnostic value compared with the value of Bethesda cytology, and with the combined interpretation, by sensitivity, specificity, predictive values, diagnostic accuracy and receiver operating characteristic analysis. Results: Among the 167 thyroid nodules, Bethesda Category II was the most frequent cytological category, accounting for 75 (44.9%) nodules, followed by Category III with 37 (22.2%) and Category IV with 25 (15.0%) nodules. Type 1 soft elastography was predominant among Bethesda II nodules, whereas the proportion of Type 3 stiff elastography increased progressively with increasing Bethesda risk. Type 3 elastography was observed in 78.6% of Bethesda V nodules and 85.7% of Bethesda VI nodules. The mean Young's modulus was higher among high-risk Bethesda V–VI nodules than Bethesda II nodules. The combined elastography and Bethesda approach demonstrated a sensitivity of 89.5%, specificity of 91.2%, positive predictive value of 73.9%, negative predictive value of 97.0% and overall diagnostic accuracy of 90.1%. The area under the ROC curve was 0.93. Conclusion: USG elastography demonstrated a clear association with Bethesda cytological risk, with increasing tissue stiffness observed among nodules with higher-risk cytological categories. The combined radiological-pathological approach demonstrated excellent discriminatory ability and high diagnostic accuracy for thyroid malignancy. Integration of elastography with Bethesda cytology may therefore provide valuable complementary information for thyroid nodule risk stratification, particularly in cytologically indeterminate lesions.

Keywords: Thyroid nodules; Ultrasound elastography; Shear wave elastography; Bethesda System; Fine-needle aspiration cytology; Thyroid malignancy; Diagnostic accuracy; Radiological-pathological correlation.