A 47-year-old man, with a history of aortic valve replacement 28 years earlier, was admitted to the emergency department with a right cervical mass and a superior vena cava syndrome. Thoracic angio-CT revealed a giant ascending aorta aneurysm, with an intramural thrombus and dissection flap, compressing the superior vena cava. Emergency surgery was performed, confirming those findings. The dissection had ruptured but was contained by surrounding structures, creating a false-aneurysm that compressed the superior vena cava. The aneurysm was excluded and the aorta was replaced by a Dacron conduit, thereby decompressing the upper mediastinum. The patient made an uneventful recovery.