SUPERStudy: Renal artery stenosis

Introduction: Renal artery stenosis is the narrowing of one or both renal arteries or their branches, which may ultimately lead to kidney failure and hypertension. 

Etiology: The most common cause of renal artery stenosis is atherosclerosis followed by fibromuscular dysplasia.  

Atherosclerotic: mostly men; Older patients; 80 – 90% of patients 

Fibromuscular: mostly women; Young Caucasian females; 10 – 15% of patients  

Other risk factors: Diabetes mellitus, hyperlipidemia, tobacco use, angiotensin-receptor antagonists can cause kidney failure in bilateral artery stenosis

Pathogenesis: Atherosclerotic lesions are most commonly found in the proximal third or ostial region of the renal artery; progressive narrowing leads to decreased blood supply to the kidneys, resulting in kidney dysfunction, ischemia and systemic complications.

Clinical Manifestation: 

Renovascular hypertension: Renovascular hypertension is the most common sequela of renal artery occlusive disease. It is the most common cause of secondary hypertension and is potentially correctable;  systolic and diastolic upper abdominal bruits; diastolic hypertension of greater than 115 mmHg; rapid onset of hypertension after the age of 50 years; a sudden worsening of mild to moderate essential hypertension; hypertension that is difficult to control with three or more antihypertensives; development of renal insufficiency after angiotensin-converting enzyme inhibitors or angiotensin receptor blockers; development of hypertension during childhood (age < 30 years); 

-Multiple episodes of flash pulmonary edema; can lead to CKD and ESRD.

Diagnosis 

Labs: Hypokalemia, elevated renin and aldosterone levels; elevated serum creatinine. 

Doppler ultrasonography: asymmetric kidney size if one renal artery is primarily affected, or small hyperechoic kidneys  (high sensitivity/specificity, inexpensive, widely available but operator-dependent)

Computed tomographic angiography/Magnetic resonance angiography: high accuracy, noninvasive, but requires contrast;  Fibromuscular dysplasia has a characteristic “beads-on-a-string” appearance.  

Intra-Renal angiography: the gold standard for diagnosis of renal artery stenosis; but invasive, expensive, and requires contrast. 

Captopril renal scanning is a functional study that assesses renal perfusion before and after administration of the angiotensin-converting enzyme inhibitor captopril. 

Treatment 

Atherosclerotic renovascular disease 

Medical management: Medical therapy should include blockade of the renin-angiotensin system, blood pressure control, cessation of tobacco, statins, and aspirin. Revascularization should be considered.

Factors favoring medical therapy only: Controlled blood pressure with stable renal function (e.g., stable renal insufficiency); Stable renal artery stenosis without progression on surveillance studies (e.g., serial duplex ultrasound); Advanced age and/or limited life expectancy; Extensive comorbidity that make revascularization too risky; High risk for or previous experience with atheroembolic disease; Other concomitant renal parenchymal diseases that cause progressive renal dysfunction (e.g., interstitial nephritis, diabetic nephropathy), particularly with proteinuria. 

Factors favoring medical therapy with revascularization for renal artery stenosis: Progressive decline in GFR during treatment of systemic hypertension; Failure to achieve adequate blood pressure control with optimal medical therapy (medical failure); Rapid or recurrent decline in the GFR in association with a reduction in systemic pressure; Decline in the GFR during therapy with ACE inhibitors or ARBs; Recurrent congestive heart failure in a patient in whom left ventricular dysfunction does not fully explain the cause; in patients with significant stenosis (usually more than 70% luminal occlusion) of both renal arteries or of one renal artery in a patient with a solitary functioning kidney. 

Vascular repair: 

Percutaneous transluminal renal angioplasty (PTRA) with or without stenting. 

Surgical vascular repair: if PTRA fails, a lesion is not amenable to stenting/PTRA, or a patient is undergoing aortic surgery for aneurysm repair. 

Surgical procedures: Endarterectomy, either transrenal or transaortic

Fibromuscular dysplasia: Treatment of fibromuscular dysplasia with percutaneous transluminal angioplasty is often curative, which is in stark contrast to treatments for atherosclerotic disease.

SUPERPoint: Unexplained hypertension in a woman younger than 40 years should raise suspicion for fibromuscular dysplasia

SUPERFormula: Patient with flash pulmonary edema + severe or refractory or new-onset hypertension + abdominal bruit + congestive heart failure + Hypokalemia, elevated renin and aldosterone levels = Renal artery stenosis