MRI of the Thyroid for Differential Diagnosis of Benign Thyroid Nodules and Papillary Carcinomas

OBJECTIVE. The purpose of this study was to evaluate the diagnostic performance of MRI in differentiating thyroid papillary carcinomas from benign thyroid nodules. MATERIALS AND METHODS. The study included 36 patients who had solid thyroid nodules detected by thyroid sonography and underwent MRI. A total of 42 solid thyroid nodules, including 28 benign nodules (maximal diameter range, 6-95 mm; mean diameter [+/- SD], 23.3 +/- 18.1 mm) and 14 papillary carcinomas (maximal diameter range, 11-35 mm; mean, 21.7 +/- 8.1 mm) were histopathologically diagnosed. The T1 and T2 signal intensity ratio (SIR) of each thyroid nodule was calculated by measuring the mean signal intensity divided by that of paraspinal muscle. Apparent diffusion coefficient (ADC) values of nodules were also computed. The SIRs and ADCs were then compared between benign nodules and papillary carcinomas. RESULTS. The mean T2 SIR (p < 0.0001) and ADC (p < 0.0001) were significantly lower for papillary carcinomas than for benign nodules, but no significant difference was found in T1 SIR (p = 0.54). The sensitivity, specificity, and AUC for the differentiation of papillary carcinomas were 86%, 100%, and 0.929, respectively, on T2 SIR; 93%, 93%, and 0.929, respectively, on ADC; and 93%, 93%, and 0.929, respectively, on combined T2 SIR and ADC. CONCLUSION. Papillary thyroid carcinomas could be accurately differentiated from benign nodules on the basis of MRI T2 SIR or ADC values.