Renal Artery Stenosis

Renal artery stenosis (RAS) is a narrowing of the artery that leads to the kidney. When this happens, the blood supply to the kidney is blocked. This can lead to an elevation in blood pressure (hypertension) or even kidney (renal) failure if both kidneys are affected.

The two kidneys are bean-shaped organs, each about the size of a fist. They are located just below the rib cage, one on each side of the spine. The arteries that carry blood to the kidneys—called the renal arteries—branch off directly from the abdominal aorta, the main vessel from the heart that supplies blood to most of the body's organs.

Healthy kidneys filter out wastes and extra fluid from the blood that passes through them. Those wastes and extra fluid become urine, which flows from the kidneys to the bladder through tubes called ureters. Urine is stored in the bladder until released through urination.

Rear view of the kidneys showing the renal arteries. Source: Wikimedia Commons

Other Names

• Renal artery occlusion
• Stenosis of the renal artery
• Fibromuscular dysplasia (FMD)

Signs and Symptoms

RAS can be silent, meaning there may not be any symptoms, until it becomes severe. The first sign of RAS may be high blood pressure that stays high despite appropriate medications. High blood pressure caused by RAS is called renovascular hypertension. The diagnosis of RAS is not based on blood pressure alone because many conditions can cause the blood pressure to rise. If high blood pressure develops suddenly in the absence of a family history of hypertension, RAS may be suspected.^[1]

Causes

In the overwhelming majority of cases, RAS is caused by atherosclerosis which is a hardening of the kidney arteries. Thus, RAS develops when a material called plaque builds up on the inner wall of one or both of the renal arteries. The plaque makes the artery wall hard and narrow. This narrowing reduces or cuts off the blood supply, possibly damaging the kidney. The damaged kidney is less efficient at removing wastes and extra fluid from the blood. This plaque is similar to plaques blocking the arteries supplying the heart, which cause heart attacks, and those blocking arteries supplying the brain, which cause strokes.

Anatomic drawing of the kidneys. An inset shows a magnified cross-section of the renal artery. Plaque is building up on the inner wall of the artery and blocking blood flow to the kidney. Source:NIH

When the kidneys fail, wastes and extra fluid build up in the blood. This condition, called uremia, causes nausea, headaches, fatigue, and swelling in the legs and abdomen. With total kidney failure, patients will need dialysis or a kidney transplant to stay alive.

Diagnosis

In some cases, the turbulent blood flow through a narrowed renal artery can be heard through a stethoscope; the sound is known as a bruit and is helpful during the initial examination phase. The absence of a bruit, however, by no means excludes the possibility of RAS.

For a more accurate diagnosis, the doctor may order an ultrasound or an angiogram to get a picture of the artery. An ultrasound uses harmless sound waves to create images of internal organs; it does not require intravenous injection or oral administration of any substances. Ultrasound can help determine the size and structure of the kidney; Doppler ultrasound can also measure the speed of the blood flow within the renal arteries.^[2] An angiogram is a special kind of x ray in which a thin, flexible tube called a catheter is threaded through the large arteries, often from the groin, to the artery of interest—in this case, the renal artery. A special dye is injected through the catheter so the renal artery will show up clearer on the x ray. The advantage of angiograms is that they give a better picture and therefore more accurate diagnosis of RAS; the disadvantage is that this procedure is more invasive.

More recently, doctors will use a computerized tomography (CT) scans or a magnetic resonance angiogram (MRA) to evaluate RAS. CT scans use multiple x-ray images combined by a computer to create a three-dimensional image of your internal organs. MRAs use moving magnets to create similar three-dimensional images. CT scans and MRAs are less invasive than conventional angiograms, but the results may not be as clear or accurate. Researchers are exploring ways to improve these imaging techniques and make them more reliable for evaluating RAS.

Treatment

Approaches to RAS are threefold:

• preventing RAS from getting worse
• treating high blood pressure that results from RAS
• relieving the blockage of the renal arteries

The first step in treating RAS is making lifestyle changes that promote healthy blood vessels in general. Exercising, controlling weight, and choosing healthy foods will help keep the arteries clean and flexible. Quitting is one of the best things that a person can do to save the kidneys and other organs.^[3]

Medications

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, it may be possible to control 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 the patient and their doctor.

In addition to blood pressure medicines, a doctor may prescribe 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.

Therapies

If RAS advances until the artery is nearly or completely blocked, surgery may be necessary to open up the flow of blood to the kidney.^[4] Different types of surgery for RAS include the following:

• 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 the doctor may position a small mesh tube, called a stent, to keep plaque flattened and the artery open.
• Endarterectomy. In an endarterectomy, a vascular surgeon cleans out the plaque, leaving the inside lining of the artery smooth and clear.
• 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.^[5]

Chances of Developing

Risk factors

People are at greater risk of developing RAS if they smoke or are overweight. RAS is most common in men between the ages of 50 and 70, but women and younger adults can also have it. High cholesterol, diabetes, and a family history of cardiovascular disease are also risk factors for RAS. High blood pressure is both a cause and result of RAS.

Research

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) conducts and supports research into many kinds of kidney disease, including RAS. Researchers supported by the NIDDK are exploring ways to improve the diagnosis of this disease using new MRA techniques that provide more information about blood flow to the kidney and how well the kidney is functioning. These studies will point the way to more effective treatments for RAS and healthy kidneys.

Other Resources

• American Urological Association Foundation]
• [Society for Vascular Surgery]
• [National Kidney and Urologic Diseases Information Clearinghouse]

References

1. ↑ HOLLEY KE, HUNT JC, BROWN AL Jr, KINCAID OW, SHEPS SG. RENAL ARTERY STENOSIS. A CLINICAL-PATHOLOGIC STUDY IN NORMOTENSIVE AND HYPERTENSIVE PATIENTS. Am J Med. 1964 Jul;37:14-22. Citation
2. ↑ Hildreth CJ, Lynm C, Glass RM. JAMA patient page. Renal artery stenosis. JAMA. 2008 Nov 5;300(17):2084. Citation | Full Text
3. ↑ Bloch MJ, Basile J. Diagnosis and management of renovascular disease and renovascular hypertension. J Clin Hypertens (Greenwich). 2007 May;9(5):381-9. Abstract
4. ↑ Khosla S. Renal artery stenosis: a review of therapeutic options. Minerva Cardioangiol. 2005 Feb;53(1):79-91. Abstract | PDF
5. ↑ Dejani H, Eisen TD, Finkelstein FO. Revascularization of renal artery stenosis in patients with renal insufficiency. Am J Kidney Dis. 2000 Oct;36(4):752-8. Abstract