[CT diagnosis of malignant thymoma]

Computed tomography (CT) findings of six cases of malignant thymoma were analyzed with eight cases of benign thymoma as a control and the usefulness of CT in their differential diagnosis was evaluated. 1) Three of the malignant thymomas showed a flat shape, while none of the benign ones showed such a configuration. All of the latter were round or oval. 2) The margin of the tumor was irregular and lobulated with evidence of invasion in 4 of the malignant thymomas. All of the benign tumors showed a smooth margin. 3) Intrathoracic metastasis was noted in 2 of the malignant thymomas. 4) CT numbers of the tumors overlapped in both benign and malignant thymomas. 5) Thus the CT observation of the shape, margin, and invasiveness of a tumor as well as evidence of intrathoracic metastasis makes the differential diagnosis between benign and malignant thymomas possible in most cases.