RENAL ARTERY STENOSIS

Essentials of Diagnosis

Produced by atherosclerotic occlusive disease (80–90% of patients) or fibromuscular dysplasia (10–15%).

Hypertension.

Acute renal failure in patients starting therapy with an ACE inhibitor.

General Considerations
The two most common forms of renal artery stenosis are atherosclerotic ischemic renal disease and fibromuscular dysplasia. The prevalence of this condition has been estimated only by autopsy and angiographic studies. Approximately 5% of Americans with hypertension suffer from renal artery stenosis.
Atherosclerotic ischemic renal disease accounts for nearly all cases of renal artery stenosis. It occurs most commonly in those over 45 years of age with a history of atherosclerotic disease. Other risk factors include renal insufficiency, diabetes mellitus, tobacco use, and hypertension.
Clinical Findings
SYMPTOMS AND SIGNS
Patients with atherosclerotic ischemic renal disease may have refractory hypertension, new-onset hypertension in an older patient, pulmonary edema with poorly controlled blood pressure, and acute renal failure upon starting an ACE inhibitor. In addition to hypertension, physical examination may reveal an audible abdominal bruit on the affected side. Fibromuscular dysplasia primarily affects young women. Unexplained hypertension in a young woman is reason to screen for this disorder.
LABORATORY FINDINGS
Laboratory values can show elevated BUN and serum creatinine levels in the setting of significant renal ischemia.
IMAGING
Abdominal ultrasound discloses asymmetric kidney size when one renal artery is affected out of proportion to the other. Three prevailing methods used for screening are Doppler ultrasonography, captopril renography, and magnetic resonance angiography (MRA). Doppler ultrasonography is highly sensitive and specific (> 90% with an experienced ultrasonographer) and relatively inexpensive. However, this method is extremely operator and patient dependent. Measurements of blood flow must be made at the aorta and along each third of the renal artery in order to assess the disease. This test is a poor choice for patients who are obese, unable to lie supine, or have interfering bowel gas patterns.
Captopril renography capitalizes on the difference in renal perfusion with and without ACE inhibitors. A kidney distal to a significant stenosis requires high angiotensin II levels to maintain adequate perfusion. With an ACE inhibitor, perfusion is markedly diminished. The affected kidney enhances less, whereas the unaffected one enhances more in the setting of a captopril challenge. Sensitivity ranges from 75% to 100% and specificity from 60% to 90%. This procedure is not as accurate in moderate to severe kidney disease.
MRA is an excellent but expensive way to screen for renal artery stenosis. Sensitivity is 99–100%. Specificity ranges from 71% to 96%. Turbulent blood flow can cause false-positive results.
Renal angiography is the gold standard for diagnosis. CO2 subtraction angiography can be used in place of dye when the risk of dye nephropathy exists—eg, in diabetic patients with renal insufficiency. Lesions are most commonly found in the proximal third or ostial region of the renal artery. The risk of atheroembolic phenomena after angiography is not trivial in this population, ranging from 5% to 10%. Fibromuscular dysplasia has a characteristic “beads-on-a-string” appearance on angiography.
Treatment
Treatment of atherosclerotic ischemic renal disease is controversial. Options include medical management, angioplasty with or without stenting, and surgical bypass. Angioplasty might reduce the number of antihypertensive medications but does not significantly change outcome in comparison to patients medically managed. Stenting produces significantly better angioplastic results. However, blood pressure is equally improved, and serum creatinines are similar at of observation. Angioplasty is equally as effective as, and safer than, surgical revision. Treatment of fibromuscular dysplasia with percutaneous transluminal angioplasty is often curative.

Balk E et al. Effectiveness of management strategies for renal artery stenosis: a systematic review. Ann Intern Med. 2006 Dec 19;145(12):901-12. Epub 2006 Oct 24. [PMID: 17062633]

Bloch MJ et al. Clinical insights into the diagnosis and management of renovascular disease. An evidence-based review. Minerva Med. 2004 Oct;95(5):357–73. [PMID: 15467512]

Kalra PA et al. Atherosclerotic renovascular disease in United States patients aged 67 years or older: risk factors, revascularization, and prognosis. Kidney Int. 2005 Jul;68(1):293–301. [PMID: 15954920]

Korsakas S et al. Delay of dialysis in end-stage renal failure: prospective study on percutaneous renal artery interventions. Kidney Int. 2004 Jan;65(1):251–8. [PMID: 14675057]

Nordmann AJ et al. Balloon angioplasty versus medical therapy for hypertensive patients with renal artery obstruction. Cochrane Database Syst Rev 2003;(3):CD002944. [PMID: 12917937]

Safian RD et al. Renal artery stenosis. N Engl J Med. 2001 Feb 8;344(6):431–42. [PMID: 11172181]