Renal Artery Stenosis (cont.)

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How is renal artery stenosis diagnosed?

Several tests exist to detect any evidence of renal artery stenosis. They can be divided into imaging tests and functional tests. The imaging tests provide a picture of the blood vessel and its anatomy and reveal the degree of narrowing. The functional tests provide information about whether the narrowing is significant enough to cause the high blood pressure or kidney dysfunction. Each of these tests has advantages and shortcomings.

What are the common imaging tests to evaluate renal artery stenosis?

An angiogram of the renal arteries is the best test available to detect the degree of narrowing. However, angiography is not the primary test and is performed only for those patients who have evidence of stenosis on less invasive testing, such as ultrasound, CT Angio, or MR Angio. Angiography is a preliminary portion of a procedure, which will generally culminate in angioplasty and possibly stenting to treat a stenosis identified on less invasive testing.

The angiogram of the renal arteries is similar to an angiogram of the heart and involves insertion of a catheter through the groin into the main artery (the aorta), that is advanced to the level of the renal arteries. These tests are most commonly performed through the groin, but arteries in other parts of the body, such as the arms, can be used equally well. A dye is injected, and x-ray images are taken to see the caliber of the blood vessel and extent of the narrowing.

An angiogram is considered an invasive test (insertion of the catheter inside the body) and therefore is not widely used because of the risk of complications. This test also may not determine if narrowing is truly significant to cause the problem or not, and so it may be necessary to combine this with a functional test. Generally, a narrowing of greater than 75% by angiogram is considered significant enough to cause high blood pressure or kidney dysfunction. An additional advantage of an angiogram is that if a treatable narrowing is seen, it may be fixed at the same time via angioplasty or by placing a stent (described in more detail below).

Other less invasive imaging tests are available to detect renal artery stenosis, but they are not generally as accurate as the angiogram and could potentially miss some cases of correctable disease. The most commonly used additional imaging tests are:

  • Magnetic resonance angiography
  • Computed tomographic angiography
  • Duplex Doppler ultrasonography

Magnetic resonance angiography (MRA) is similar to a magnetic resonance imaging (MRI). Contrast dye is injected into the blood via a vein in the arm, and pictures of the specific area of the body (in this case the renal arteries) are taken and analyzed. The accuracy (specificity and sensitivity) of this test is reasonable. This test cannot be done in patients with metal implants, pacemakers, or claustrophobia (fear of closed spaces). It may be used in people with mild to moderate, but not severe, kidney problems.

Computed tomographic angiography is similar to a computed tomography (CT scan) and has reasonable accuracy. This is also done by injecting a contrast dye into the blood and taking pictures of the renal arteries. This is not recommended in people with moderate to severe kidney problems as it may make the problem worse.

Doppler ultrasound is the least invasive imaging test for renal artery stenosis. It is performed similarly to a regular ultrasound by placing a probe on the abdomen to visualize the flow across the renal arteries and also to measure any narrowing. Its accuracy is similar to the other tests above, but its advantage is that it can measure the size of the narrowing as well as the flow across it. The disadvantage of this test is that it is time-consuming and may take up to a couple of hours to complete. It is also very operator-dependent, meaning that the accuracy of the result is dependent upon the expertise and experience of the ultrasound technician.

Medically Reviewed by a Doctor on 2/7/2014

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