Renal Artery Stenosis (cont.)
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. This 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. 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.
Next: What functional tests are used for the diagnosis of renal artery stenosis? »
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