There is no sex predominance. Thymomas arise from thymic epithelium. Most thymomas are slow-growing tumors. This is determined at surgery and is not a histologic diagnosis. Local invasion of the pleura occurs frequently.
Distant metastases are infrequent.
The chest radiograph shows an anterior mediastinal mass that is round or oval with either smooth or lobulated margins. CT is superior to radiography at demonstrating anatomic relationships with surrounding structures. MRI has similar success at defining the tumor and the surrounding mediastianal structures. . The signal characteristics are not adequate, however, to differentiate benign from malignant thymomas. Calcification is demonstrated in a minority of patients with thymoma.