Magnetic resonance imaging (MRI) angiogram showing a large aneurysm of the descending thoracic aorta (centre). The patient is a 32-year-old male patient with Marfan syndrome. Marfan syndrome is a genetic disorder of the body's connective tissues. It can cause the walls of the blood vessels to become weak and dilated. This change in blood vessels often affects the aorta, causing an increased risk of aneurysm forming. The MRI scan also shows aneurysmal dilatations of the subclavian arteries (top).