What is Renal Artery Stenosis?

Renal artery stenosis is a narrowing of the arteries that supply blood from the heart to the kidneys. When the renal arteries decrease in diameter, blood flow to the kidneys is restricted. If both renal arteries are affected, the function of the kidneys may be impaired, eventually leading to renal failure. High blood pressure is a common result of renal artery stenosis that affects only one of the arteries.

Most cases of renal artery stenosis are caused by atherosclerosis, meaning the blood vessel wall hardens and narrows from the inside. This is similar to what can happen to arteries in the heart. Advanced age, cigarette smoking, and diabetes are all risk factors that increase the chance of atherosclerosis. Patients with high cholesterol levels and high blood pressure are also at higher risk for blood vessel problems.

There are generally no specific symptoms associated with renal artery stenosis. Severe high blood pressure that begins prior to age 30 or after age 50 and does not respond well to typical blood pressure medications may be suspicious. Often, renal artery stenosis is found incidentally through other tests when a physician discovers that one of a patient's kidneys is smaller than the other.

If a physician suspects renal artery stenosis, he or she will conduct imaging tests, functional tests, or a combination of the two to confirm the diagnosis. Imaging tests show the artery itself so that a physician can determine if it has narrowed and, if so, to what extent. Functional tests help determine whether the narrowing of the arteries is enough to cause kidney impairment or high blood pressure.

The most accurate imaging test is an angiogram, but it is not commonly used due to the risk of complications from the invasive procedure. An angiogram involves a catheter inserted through the groin into the heart and down into the renal arteries. A dye is then injected and x-rays are taken to analyze the degree of narrowing of the arteries. Magnetic resonance angiography (MRA) or computed tomographic angiography tests are less invasive. They are performed by injecting a dye into the body and then analyzing pictures of the renal arteries to determine if any narrowing is present.

Functional tests include the captopril renogram and the plasma renin activity test. The captopril renogram measures kidney activity following an injection of a radioactive substance. If activity is more pronounced in one kidney, it may indicate that the functionality of the other is impaired due to renal artery stenosis. A plasma renin activity test analyzes whether one kidney shows higher activity of the hormone renin than the other kidney, as higher renin activity generally indicates that renal artery stenosis is present.

In mild cases, no treatment may be necessary, and a physician may opt to simply monitor the patient's blood pressure and kidney function on a regular basis. High blood pressure caused by renal artery stenosis is usually treated with the same blood pressure medications as any other patient. In cases where the renal artery or arteries have narrowed more than 75%, surgery may be necessary to widen the blood vessel.