MR Imaging of Thymic Epithelial Neoplasms

Thymic epithelial neoplasms are malignant lesions that originate from the thymus and include thymoma, thymic carcinoma, and thymic neuroendocrine tumors. Although computed tomography (CT) is typically considered the imaging modality of choice for identifying thymic tumors, characterizing the primary neoplasm, and staging of disease, the role of magnetic resonance (MR) imaging continues to expand. MR imaging is effective in distinguishing thymic epithelial neoplasms and other malignant tumors from benign lesions in the prevascular mediastinum, can be used to characterize and stage thymic tumors in those patients with contraindications to contrast-enhanced CT, and can reveal morphologic features of thymic tumors. At least 15 different stage classifications have been proposed for thymic epithelial neoplasms and used to varying degrees in clinical practice. Recently, an official, consistent tumor node metastasis (TNM) staging system has been recognized by the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC), based on an analysis of a retrospective database performed by the International Association for the Study of Lung Cancer (IASLC) and the International Thymic Malignancy Interest Group (ITMIG). In this article, we discuss the appropriate utilization of MR imaging in the evaluation of patients with thymic epithelial neoplasms, key imaging features of the tumors, and the impact of imaging findings on overall staging.