Stenosis – [Renal Artery Case]
Renal artery stenosis (narrowing) is a decrease in the diameter (width) of the artery supplying blood to the kidney. The resulting restriction of blood flow to the kidneys may lead to impaired kidney function (renal failure) and high blood pressure (hypertension). This type of hypertension is referred to as renovascular hypertension (“reno” for kidney and “vascular” for blood vessel), and accounts for about 5% of patients with hypertension. Renovascular hypertension occurs when the artery to one of the kidneys is narrowed (unilateral stenosis), while renal failure occurs when the arteries to both kidneys are narrowed (bilateral stenosis). The decreased blood flow to both kidneys increasingly impairs renal function.
What problems does renal artery stenosis cause?
When the circulating blood volume becomes depleted as a result of dehydration or bleeding, for example, the blood flow to the kidneys likewise is reduced. The normal physiologic reaction to a decrease in renal blood flow is a hormonal response by the kidneys, the renin-angiotensin-aldosterone system. This hormonal system is activated as a defense against low blood pressure and low circulating blood volume. As a result, there are increased blood levels of the hormone angiotensin 2, which causes narrowing of the small arterioles (a small branch of an artery that leads to the capillaries). This, together with increased blood aldosterone, which promotes salt retention by the kidneys, 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 just described, or by reduced blood pressure. This can lead to an abnormal increase of blood pressure (renovascular hypertension).
How is renal artery stenosis diagnosed?
In younger patients, the narrowing of the renal artery usually is due to the thickening of the artery (fibromuscular hyperplasia), while in older individuals, the narrowing is usually caused by atherosclerosis (cholesterol deposits in the artery). Screening for a narrowed renal artery can be accomplished non-invasively (without entering the body) by a procedure called “renal isotope imaging.” Using pre-medication for this procedure with an ACE inhibitor drug accentuates the findings and thereby improves the test’s ability to detect renal artery stenosis. Other non-invasive techniques for renal imaging are Doppler ultrasonography and magnetic resonance imaging with the MRI computer specifically set to image the blood vessels (MR angiography). If the screening tests are abnormal, an x-ray angiography is performed where dye is injected into the femoral artery of the lega and displays the channel (lumen) of the renal arteries.
What surgical procedures are available for renal artery stenosis?
Typically at the time of the angiography, an angioplasty is done. In this procedure, a tiny balloon is inflated in the lumen (the space in the interior of the artery) of the artery to dilate the narrowed artery. A stent (tubular device to prevent recurrence of the narrowing) may be placed in the artery.
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