Ultrasound elastography in the evaluation of solid thyroid nodules.

Abstract

Introduction: Ultrasound elastography has recently emerged as a dynamic technique that uses high resolution ultrasonography to provide an estimation of tissue stiffness by measuring the degree of distortion under the application of an external force. Objective: The aim of this study was to evaluate the diagnostic accuracy of ultrasound elastography in the differentiation of malignant and benign thyroid nodules, using fine needle aspiration cytology as a standard reference. Study Design: A prospective cross-sectional study. Setting: Kenyatta National Hospital and University of Nairobi, Department of Diagnostic Imaging and Radiation Medicine (DDIRM), Sample Size: A total of 84 patients were evaluated over a period of 6 months, from July 2014 to December 2014. Materials and Methods: Study subjects:Patients from KNH thyroid clinic who had a provisional diagnosis of nodular thyroid disease and fulfilled the inclusion criteria for the study. Ethical considerations: Ethical approval and clearance was obtained from the KNH-UON Ethics Review Board. Methodology: Conventional B-mode ultrasonography and ultrasound elastography was done on solid thyroid nodules. Ultrasound elastography included an elastography colour scale score system (1 to 5) and offline acquisition of stain ratios (cutoff of greater than or equal to 4 as malignant). Correlation with fine needle aspiration cytology/ histopathology was subsequently done. A data collection form was used to record all the relevant data. Statistical analysis: Data analysis was performed using the STATA version 12. Statistical significance was set at p < 0.05. Results: A total of 173 solid thyroid nodules in 84 patients were examined. Majority, 72/84 (85.7%) were females, while 12/84 (14.3%) were males. The median age range was 40 to 50 years. Most patients presented with multiple thyroid nodules, 53/84 (63%). x Elastography scores of 1 to 3 produced 124 true negative (benign) cases, while elastography scores 4 and 5 revealed 39 true positive (malignant) cases on FNA/Histopathology. Sensitivity of 0.91 and specificity of 0.97 was obtained using the elastography score system for thyroid cancer diagnosis. Positive predictive value of 90.9% and Negative predictive value of 96.9%. Diagnostic accuracy of the technique was 93.17%. Strain ratio acquisitions for the same thyroid nodules revealed a sensitivity of 0.89 and specificity of 0.96, positive predictive value of 88.6% and Negative predictive value of 96.1% in the differential diagnosis of benign and malignant thyroid nodules. However, there were 5 false positive and 5 false negative findings which markedly reduced the reliability of elastography. Conclusion: This study has shown that ultrasound elastography has no added benefit in determining whether a thyroid nodule is likely malignant and the final diagnosis should solely depend on FNA cytology and histopathology findings.