Coloured 3D computed tomography (CT) angiogram scan of a blood clot (thrombus, centre) in the left common carotid artery of a 62 year old male patient. The interior surface is irregular suggesting the presence of atheroma plaques. These fatty deposits narrow the artery and restrict the blood flow (atherosclerosis). The damage to the walls can also cause the formation of a thrombus, which can disrupt blood flow. A thrombus can be fatal if it blocks blood flow to a vital organ, such as the brain. The common carotid arteries lie on either side of the neck and carry blood to the head.