Atherosclerosis. Coloured three-dimensional computed tomography (CT) scan of an atheroma plaque (orange, centre) in the internal carotid artery in the neck. This fatty deposit narrows the vessel and restricts the blood flow (atherosclerosis). It often results from high levels of cholesterol in the blood. Large plaques may be removed surgically, and diseased vessels can be replaced with grafts. The common carotid arteries lie on either side of the neck, each dividing into an internal and an external branch at the carotid sinus. They supply the head and neck with oxygenated blood.