Thoracic Aortic Aneurysms By Mark A Farber, MD, FACS, University of North Carolina; Federico E Parodi, MD, University of North Carolina School of Medicine Reviewed / Revised Jun 2022 | Modified Sep 2022 View Patient Education Etiology Symptoms and Signs Diagnosis Prognosis Treatment Key Points Topic Resources Widened Mediastinum Thoracic Aortic Aneurysm A thoracic aortic diameter ≥ 50% larger than normal is considered an aneurysm (normal diameter varies by location).