Cerebral aneurysm treatment. Lateral coloured 3D computed tomography (CT) angiogram scan of the treatment of an aneurysm (blood vessel swelling, centre left) in the brain of a 57-year-old man. An aneurysm is a blood-filled dilation in a blood vessel wall. It is caused by a weakening of the vessel wall, which may be caused by hardening of the vessel (atherosclerosis), high blood pressure or injury. If left untreated an aneurysm can rupture, which is often fatal. Here, a rupture of the aneurysm was treated with a type of brain surgery (trepanation) to relieve pressure on the brain from the bleeding, along with the insertion of a neurosurgical clip at the level of the middle cerebral artery.