Coloured 3D computed tomography (CT) scan of a patientIllustrations heart (centre-left) and aorta (bodyIllustrations main artery, large red tube), with a lower thoracic aortic aneurysm (bulge at centre-right). An aneurysm is the bulging of a section of a blood vessel which occurs when the blood vessel wall becomes weakened and thin. The exact cause is not fully known but risk factors include smoking, age, genetics and high blood pressure. Symptoms vary depending on where the aneurysm occurs, but generally include pain in the affected area. In some cases, aneurysms can rupture, which can lead to severe internal bleeding and death. Surgical intervention is possible where there is a risk of this occurring.