The two most common causes of unilateral renal artery stenosis are atheromatous plaques and fibromuscular hyperplasia. Atheromatous stenoses are most frequently found in the proximal third of the renal artery and present in the middle-aged and elderly. In contrast, fibromuscular hyperplasia involves the middle and distal thirds of the renal artery and is the most common cause of renal artery stenosis in young patients.
Plasma renin activity may be normal in patients with unilateral renal artery stenosis, but in some series, elevated peripheral venous levels of plasma renin activity have been found in up to sixty per cent of patients. Such patients may also have an exaggerated response of renin to dynamic function tests such as diuretic administration or sodium depletion.
