Renal Artery Stenosis

Renal artery stenosis is narrowing of one or both arteries supplying the kidneys. The kidney beyond the narrowing receives less perfusion and interprets this as low circulating volume, even when the patient is actually hypertensive. Juxtaglomerular cells respond by releasing renin. Renin activates the renin-angiotensin-aldosterone system (RAAS), producing angiotensin II and aldosterone. Angiotensin II constricts blood vessels, while aldosterone promotes sodium and water retention. Blood pressure rises because the kidney is trying to restore what it perceives as inadequate renal blood flow. Atherosclerosis causes more than 90% of renal artery stenosis in adults. It commonly occurs in people with established vascular disease or cardiovascular risk factors. Fibromuscular dysplasia is a nonatherosclerotic cause more often seen in younger women. These causes matter because they create different clinical patterns, but both can produce renovascular hypertension. The stenotic kidney also depends on angiotensin II to constrict its efferent arteriole and maintain glomerular filtration pressure. In a person with bilateral stenosis, or stenosis affecting a solitary functioning kidney, suddenly reducing angiotensin II can lower intraglomerular pressure enough to reduce GFR. This explains why renal...