Incidental detection of an invasive thymoma during thallium-201 imaging for coronary artery disease

Thallium-201 (Tl-201) is widely used for myocardial perfusion imaging, but is also reported to have potential tumor-seeking properties. Tl-201 uptake has been described in various malignant diseases, including thymic tumors. Thymomas are the most frequent tumors of the anterior mediastinum, and chest pain is one of the major presentation symptoms. Sometimes, a thymoma may be overlooked on chest plain film. We report on a case of a 63-year-old man who had a history of hypertension and suffered from intermittent chest pain for several weeks. He underwent a Tl-201 stress test to evaluate the presence of coronary artery disease, and during the test, abnormal uptake over focal extracardiac activity in the left upper mediastinum was incidentally revealed. Furthermore, chest computed tomography identified a 6-cm left anterior mediastinal mass. Mediastinal tumor resection was carried out, and the pathological examination demonstrated an invasive epithelial-type thymoma, which had invaded the left innominate vein. Subsequently, the patient received postoperative radiotherapy and thenceforth responded well to treatment. A Tl-201 scan has the potential to play a part in tumor detection and clinical assessment of therapeutic effects.