Cases of undifferentiated pleomorphic sarcoma of the thoracic aorta are rare, and usually present with embolic events, renovascular hypertension, or back pain. Mural-based undifferentiated pleomorphic sarcomas that present as ruptured saccular aneurysms are extremely rare and are difficult to differentiate from mycotic aneurysms or penetrating atherosclerotic ulcers. Herein, we report a case of histopathologically proven undifferentiated pleomorphic sarcoma arising from the wall of the descending thoracic aorta that manifested as a mass after thoracic endovascular aortic repair for the treatment of a ruptured saccular aneurysm. We present findings obtained by CT and PET to provide helpful information for the accurate diagnosis and appropriate treatment of future cases.
