A study of utility of MR image for the diagnosis of thymic tumors

MR imaging was performed in 25 patients with thymic tumors (five with non-invasive thymomas, 15 with invasive thymomas, and five with thymic carcinomas), and the MR imaging appearance was compared with the pathological findings. Non-invasive thymomas showed generally oval or round masses with well-defined margins and homogeneous intensity on T1- and T2-weighted images. Invasive thymomas showed a multinodular appearance in 79% (11/15) of cases, and an internodular difference in signal intensity (IDSI) in 64% (7/11) on T2-weighted images. It was considered that the IDSI on T2-weighted images correlated pathologically with the hemorrhagic and/or necrotic areas and hyalinization. The IDSI seemed to be a characteristic finding of invasive thymomas. The histological findings and MRI imaging appearance of thymomas were compared. The predominantly epithelial type showed a low incidence of nodular appearance but showed marked IDSI on T2-weighted images. Therefore, it is more likely that the predominantly epithelial type induced more varied intratumoral changes than other types. Extension of thymic carcinomas was similar to that of invasive thymomas on MR imaging, but thymic carcinomas showed no definite nodular appearance. In conclusion, MR images in thymic tumors were useful for not only determining the morphology of the tumor but also characterizing the tissue. Therefore, MR imaging can be a useful modality to correlate with the histological findings and biological behavior of thymic tumors. (author)