Narrowed neck artery. Coloured angiogram of the left carotid artery (black, centre) in the neck of a 56 year old patient. This profile view shows the jaw at left and the back of the head at right. This artery has severe stenosis (narrowing, lower centre), which reduces the blood flow to the head and to the brain and can cause a stroke (cerebrovascular accident). Stenoses can be caused by fatty deposits on the internal wall of the artery (atherosclerosis), or by a blood clot in a healthy artery. It can also arise from an embolism, when a particle or gas bubble in the blood becomes trapped. Surgery is required to open and repair the artery. Angiograms are produced by injecting an X-ray opaque dye into blood vessels.