Renal Artery Stenosis (cont.)
How common is renal artery stenosis?
Narrowing of the kidney arteries is more common in individuals 50 years of
age and older. It is estimated that some degree of narrowing (greater than 50%)
is found in about 18% of adults between 65-75 years of age and 42% of those
older than 75 years of age. This may be due to the fact that atherosclerosis is
more common in this age group.
In younger patients, the narrowing of the renal artery usually is due to the
thickening of the artery (fibromuscular dysplasia) and it is more common in
women than men.
It is estimated that renal artery stenosis accounts for approximately 1% of
mild to moderate cases of high blood pressure. It may be responsible for more
than 10% of cases of severely elevated or difficult to treat high blood pressure
(hypertension).
What are the symptoms of renal artery stenosis?
In general, renal artery stenosis is not associated with any obvious or
specific symptoms. Suspicious signs for renal artery stenosis include:
- high blood pressure that responds poorly to treatment;
- severe high blood pressure that develops prior to age 30 or greater than
age 50;
- an incidental finding (discovered through routine tests or tests performed
for another condition) of one small kidney compared to a normal sized one on the
other side.
Typically, unilateral (one-sided) renal artery stenosis may be related to
high blood pressure whereas bilateral (two-sided) renal artery stenosis is more
often related to diminished kidney function.
What problems does renal artery stenosis cause?
When the circulating blood volume becomes depleted as a
result of, for example, dehydration or bleeding, the blood flow to the kidneys
is likewise reduced. The normal physiologic reaction to a decrease in blood flow to the
kidneys is a complex hormonal response by the kidneys, called the
renin-angiotensin-aldosterone system.
This hormonal system is activated as a defense against
low blood pressure and low circulating blood volume. The kidney senses a
possible decrease in the circulating blood when blood flow through these vessels
is reduced. As a result, there are increased blood levels of the hormone
angiotensin 2, which causes
narrowing of the small blood vessels in the kidneys.
This, together with increased blood aldosterone levels
(another hormone), promotes salt retention by the kidneys, and works to maintain
blood pressure and restore blood volume. Accordingly, this hormonal system is
protective in response to reduced circulation of blood to the kidneys that is caused either by
volume depletion, as described, or by reduced blood pressure.
This otherwise normal hormonal response can become
abnormal (pathologic) when
the decreased blood flow to the kidneys results from a narrowing of diseased
renal arteries. In this situation, the kidneys receive less blood flow, which
then signals a sense of depletion of the circulating blood volume, despite the
fact that the blood volume is actually normal. So, the diminished renal blood
flow, by stimulating the production of angiotensin 2 and aldosterone, can lead
to an abnormal increase of blood pressure (renovascular hypertension).
Next: Who should be screened for renal artery stenosis? »
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