Is ultrasound combined with computed tomography useful for distinguishing between primary thyroid lymphoma and Hashimot's thyroiditis?

Introduction: The aim of the study is to investigate the usefulness of ultrasound combined with computed tomography (CT) for distinguishing between primary thyroid lymphoma (PTL) and Hashimoto’s thyroiditis (HT). Material and Methods: The investigation was conducted retrospectively in 80 patients from January 2000 to July 2018. All patients underwent pathological test to be classified into two groups: PTL group and HT group. The cut-off value of CT density was determined using receiver-operating characteristic (ROC) curve analysis. The accuracy, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of diagnosis for thyroid by CT alone, ultrasound alone, and the combination of CT plus ultrasound were calculated respectively. Results: Of the 80 study patients, 27 patients were PTL, 53 patients were HT. Mean CT density had a sensitivity of 90.6 % and a specificity of 88.9 % at a cut off values of 53.5 HU, with area under the curve (AUC) 0.88. Ultrasound combined with CT had the highest specificity, accuracy, PPV compared with CT alone and ultrasound alone (P value <0.05). Conclusions: Features such as extremely hypoechogenicty, enhanced posterior echo, cervical lymphadenopathy in ultrasound image and linear high density strand signs, very low density in CT image have high sensitivity and specificity in thyroid lymphoma. Therefore, ultrasound combined with CT may be useful for distinguishing between PTL and HT.