Unusual false aneurysm of the ascending aorta associated with ruptured acute type A aortic dissection

False aneurysm of the thoracic aorta unrelated to trauma, or to previous aortic or cardiac surgery, is extremely rare. We encountered a case of ascending aortic false aneurysm formation associated with ruptured acute type A aortic dissection. The false aneurysm, which was contained by thin connective tissue surrounding the aortic wall, was located beside the false lumen of the dissected ascending aorta, expanding toward the transverse sinus. We immediately decided to perform an emergency operation. We noted the large entry site at the anterior wall of the dissected ascending aorta after resection of the flap. We identified the false aneurysm arising from a small tear of the false lumen. Graft replacement of the ascending aorta using a tube graft was performed. The postoperative course was satisfactory. This pathology was believed to be not only a consequence of hemostasis, but also a process of re-rupture of the dissected aorta.