Renal artery stenosis



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Overview
Renal artery stenosis is the narrowing of the renal artery, most often caused by atherosclerosis or fibromuscular dysplasia. This narrowing of the renal artery can impede blood flow to the target kidney. Hypertension and atrophy of the affected kidney may result from renal artery stenosis, ultimately leading to renal failure if not treated.

Etiology
Atherosclerosis is the predominant cause of renal artery stenosis in the majority of patients, usually those with a sudden onset of hypertension at age 50 or older. Fibromuscular dysplasia is the predominant cause in young patients, usually females under 40 years of age. A variety of other causes exist. These include arteritis, renal artery aneurysm, extrinsic compression (eg. neoplasms), neurofibromatosis, and fibrous bands.

Pathophysiology
The macula densa of the kidney senses a decreased systemic blood pressure due to the pressure drop over the stenosis. The response of the kidney to this decreased blood pressure is activation of the renin-angiotension aldosterone system, which normally counteracts low blood pressure, but in this case lead to hypertension (high blood pressure). The decreased perfusion pressure (caused by the stenosis) leads to decreased blood flow (hypoperfusion) to the kidney and a decrease in the GFR. If the stenosis is long standing and severe the GFR in the affected kidneys never increases again and (pre-renal) renal failure is the result.

Signs and symptoms
Most cases of renal artery stenosis are asymptomatic, and the main problem is high blood pressure that cannot be controlled with medication. Deterioration in renal function may develop if both kidneys are poorly supplied, or when treatment with an ACE inhibitor is initiated. Some patients present with episodes of flash pulmonary edema (sudden left ventricular heart failure).

Differential Diagnosis

 * Acute renal failure
 * Atherosclerosis
 * Chronic glomerulonephritis
 * Hypersensitivity nephropathy
 * Hypertension
 * Malignant hypertension
 * Nephrosclerosis
 * Renovascular hypertension
 * Uremia

Diagnosis
A clinical prediction rule is available to guide diagnosis.


 * refractory hypertension - high blood pressure that can not be controlled adequately with antihypertensives
 * auscultation (with stethoscope) - bruit ("rushing" sound) on affected side, inferior of the costal margin
 * captopril challenge test
 * captopril test dose effect on the differential renal function as measured by MAG3 scan.
 * renal artery arteriogram

Ultrasonography
Image courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology

Doppler USG
Images courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology

Magnetic Resonance Angiography
Images courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology

Treatment
When high-grade renal artery stenosis is documented and blood pressure cannot be controlled with medication, or if renal function deteriorates, renal artery stenosis is often treated invasively. Renal artery stenosis is most commonly treated by endovascular techniques (i.e. angioplasty with or without stenting). A 2003 meta-analysis found that angioplasty was safe and effective in this context. There are ongoing clinical trials to compare medical management and angioplasty with stenting to medical management alone. These include CORAL and ASTRAL, both scheduled to report results in 2010. In addition to endovascular treatment, surgical resection and anastomosis is a rarely-used option.

Life Style Modification
The first step in treating RAS is making lifestyle changes that promote healthy blood vessels in general. Exercising, controlling weight, and choosing healthy foods may help to keep arteries disease free and flexible. Smoking cessation is one of the best things to save kidneys and other organs.

Blood Pressure Control
RAS causes high blood pressure, which can damage the kidneys. Damaged kidneys, in turn, can make your blood pressure even higher. If left uncontrolled, this vicious cycle can lead to kidney failure and damage the heart and blood vessels throughout the body.

Controlling renovascular hypertension is often difficult but usually achievable. It may require two or more different kinds of blood pressure medicine. Blood pressure medicines work in different ways.

Sometimes, by combining two or more blood pressure medicines that work in different ways, you may be able to control your blood pressure and stop the progression of kidney failure. Each type of blood pressure medicine has its own potential side effects; therefore, the choice of medicine is best determined by you and your doctor.

In addition to antihypertensives, prescription of a cholesterol lowering drug to prevent the plaques from forming in the arteries, and a blood-thinner, such as aspirin, to help the blood flow more easily through the arteries.

Angioplasty and stenting
Angioplasty is a procedure in which a catheter is put into the renal artery, usually through the groin, just as in a conventional angiogram. In addition, for angioplasty, a tiny balloon at the end of the catheter can be inflated to flatten the plaque against the wall of the artery. Then your doctor may position a small mesh tube, called a stent, to keep plaque flattened and the artery open.

Surgery
If RAS advances until the artery is nearly or completely blocked, the patient may need surgery to open up the flow of blood to the kidney. Different types of surgery for RAS include the following:

Endarterectomy
In an endarterectomy, a vascular surgeon removes the plaque

Bypass surgery
To create a bypass, a vascular surgeon uses a vein or synthetic tube to connect the kidney to the aorta. This new path serves as an alternate route for blood to flow around the blocked artery into the kidney.

Examples of Renal Artery Stenosis



 * Right Renal Artery Stenosis




 * Aortogram of Bilateral Renal Artery Stenosis



Reference
Nierenarterienstenose Nierarteriestenose