Fibromuscular dysplasia is a congenital disorder involving thickening of the arterial wall and is a cause of renal artery stenosis in younger adults, particularly women 20 to 40 years old.Fibrous tissue grows in the wall of the renal artery and narrows it.It often has the appearance of 'beads on a string'. This is due to abnormalities in the fibromuscular lining of the artery that often results in 'webs' that restrict blood flow through the artery. These webs often respond to simple balloon dilatation.Fibromuscular dysplasia can affect other vascular territories as well and is sometimes seen as a cause for carotid artery stenosis which may affect the risk of stroke.