Narrowed renal artery. Coloured frontal angiogram of the abdomen of a 48-year-old patient with stenosis (narrowing) of the left renal artery. The large blood vessel running from top to bottom is the aorta, the main artery of the body. The two renal arteries, which serve the kidneys, branch from the aorta (upper centre). The left renal artery has become narrowed (indicated by arrow). The most common cause of stenosis is atheroma, fatty deposits that thicken the inner coat of the arteries. Treatment is with either balloon angioplasty or a stent to re-open the artery. Angiograms are produced by taking an X-ray after injecting a patient with a radio-opaque contrast medium.