Although diffusion weighted MR imaging (DWI) has been accepted as a valuable tool for malignancies, its role in the evaluation of anterior mediastinal masses has not been elucidated. The aim of this study was to evaluate the accuracy of DWI in distinguishing benign from malignant diseases and its performance in assessing thymic epithelial neoplasms (TEN).
METHOD AND MATERIALSAfter approval by our institutional review board, we retrospectively reviewed 38 patients with an anterior mediastinal mass who were referred for a chest MRI. DWI images were performed with low- and high-b-values (b =0, 800 s/mm2) as well ADC maps. MRI analysis was performed qualitatively by one chest radiologist using apparent diffusion coefficient (ADC) measurements. Summary of ADC were provided in mean, SD, median, and range by different groups for each test (Table 1). Anterior mediastinal mass diagnosis was classified according to pathology diagnosis, and TEN were classified according to WHO classification and Masaoka-Koga staging system.
RESULTSOf the 38 study patients, 26 had malignant lesions and 12 had benign lesions. Malignant lesions included: thymoma (n=21), thymic carcinoma (n=2), and one of each: teratoma, lymphoma, and schwannoma. Benign lesions included: lymphangiona (n=1), thymic and pericardial cyst (n=7) and thymic hyperplasia (n=4). Of the patients with thymomas, 11 patients had early disease (stage I/II) and 10 had advanced disease (stage III/IV). We found that mean ADC value was statistically significant in differentiating benign from malignant masses (3.63 SD0.80 vs 2.30, SD=0.0.75, p<0.001), benign thymic masses from TEN (3.63, SD=0.80 vs 2.19, SD=0.66, p<0.0001) as well as in differentiating TEN from non-thymic mediastinal neoplasms (2.19, SD=0.66 vs 3.19, SD=0.93, p=0.0261). However, ADC values could not be used to differentiate low-grade thymomas, high-grade thymomas and thymic carcinomas according to WHO classification and early from late stage thymomas per Masaoka-Koga Staging System.
CONCLUSIONOur study shows that DWI is a valuable tool in differentiating benign from malignant lesions in the anterior mediastinum and is helpful in the evaluation of newly diagnosed mediastinal masses.
CLINICAL RELEVANCE/APPLICATIONDWI MRI is a noninvasive, reliable, and reproducible imaging tool that helps in the assessment and differentiation of benign from malignant mediastinal masses.
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Brett W. Carter, MD - 2015 Honored Educator
Mylene T. Truong, MD - 2015 Honored Educator
Edith M. Marom, MD - 2015 Honored Educator