An aneurysm is a blood-filled bulge in the wall of a blood vessel.
Aneurysms can occur in arteries at the base of the brain. An aortic aneurysm occurs in the main artery carrying blood from the left ventricle of the heart.
When the size of an aneurysm increases, there is a risk of rupture resulting in severe haemorrhage (bleeding) bringing on additional complications or (in the worst case) death.
Aneurysms can be hereditary or caused by disease, both of which cause the wall of the blood vessel to weaken.