UTILITY OF ULTRASOUND ELASTOGRAPHY IN DIFFERENTIATING BENIGN FROM MALIGNANT THYROID NODULES

Abstract

Background: Ultrasound elastography is an imaging technique used for the evaluation of tissue stiffness by measuring the degree of tissue deformation in response to the application of external force. Methodology: In this prospective comparative study, a total of 52 thyroid nodules from 44 euthyroid patients undergoing fine needle aspiration cytology (FNAC) were assessed. Elastography was performed by a single experienced sonologist, wherein the nodules were graded as per elastography scoring (ES), and the strain ratio (SR) for each nodule was computed. Final histopathology findings of the patients undergoing surgery were compared to elastography findings, and measures of diagnostic accuracy to differentiate between benign and malignant nodules were determined. Results: Thirty (68.2%) females and 14 (31.8%) males, with a mean age of 45.18±11.23 years, were assessed. Fourteen (31.8%) patients underwent thyroidectomy, and histopathology was reported for 18 (34.6%) nodules. In all, nine (17.3%) nodules were malignant, and 43 (82.7%) nodules were considered benign. ES demonstrated a sensitivity of 88.9%, specificity of 88.3%, PPV of 61.5% and NPV of 97.4% to identify benign thyroid nodules. The mean SR for benign nodules was significantly lower as compared to malignant nodules (2.72±0.62 vs. 4.52±0.75, P<0.0001). The optimal cut-point value for SR to differentiate benign and malignant thyroid nodules was determined to be 3.8, with the sensitivity, specificity, PPV, and NPV being 88.9%, 95.4%, 80%, and 94.6%, respectively. Of the six nodules classified as Bethesda category-III or IV on FNAC, histopathological diagnosis was follicular carcinoma in one nodule (Bethesda category-IV), four were diagnosed with follicular adenoma, and one with colloid goitre. The ES of the nodule with follicular carcinoma was malignant, while amongst the rest, two nodules were classified as benign, and three nodules as malignant. The SR of the follicular carcinoma was 4.3, while the mean strain ratio in remaining nodules was 3.48 (P=0.001). Conclusion: Ultrasound elastography has good diagnostic efficacy for the differentiation of benign from malignant thyroid nodules. It can potentially reduce the rates of unnecessary fine needle-aspiration biopsy. However, whether elastography score or strain ratio will be useful in diagnosis of nodules which are indeterminate on FNAC is open to further studies.