Section 11. Kidney and Urinary Tract Disorders

Chapter 145. Blood Vessel Disorders of the Kidneys

Topics: Introduction | Blockage of the Renal Arteries | Atheroembolic Kidney Disease | Cortical Necrosis | Malignant Nephrosclerosis | Renal Vein Thrombosis

Blockage of the Renal Arteries

There are two renal arteries--one supplies blood to the right kidney, the other to the left kidney. These arteries branch into many smaller arteries. Blockage of the renal artery or one of its large or medium-sized branches is rare. Most often a blockage occurs when a clot moves from elsewhere in the body and lodges in the renal artery (embolus). Typically, such clots originate as fragments from a larger clot in the heart or from the breakup of a fatty deposit (atheroma) in the aorta.

Alternatively, a blockage may result when a blood clot forms in the renal artery itself, usually where the artery has been injured. A sudden injury may be caused by a medical procedure, such as surgery, angiography, or angioplasty. A clot may also develop where the renal artery has been gradually injured or damaged by atherosclerosis, arteritis (inflammation of arteries), or an aneurysm (a slow-forming bulge in the wall of the artery).

A tear in the lining of the aorta or the renal artery can cause a sudden obstruction of blood flow; a tear may also cause the artery to rupture. Diseases that cause the walls of arteries to become thicker and less elastic because of deposits of fatty material (atherosclerosis) or the development of fibrous material (fibrodysplasia) may predispose vessels to tears. These disorders can lead to significant narrowing and partial blockage of the renal arteries even when there is no blood clot; when this occurs, the condition is called renal artery stenosis.

See the sidebar Fibrodysplasia: A Cause of Renal Artery Blockage.

Symptoms

A partial blockage of the renal arteries usually does not cause any symptoms. However, as the blockage worsens, a person may have a steady aching pain in the lower back or occasionally in the lower abdomen. A partial blockage may gradually lead to high blood pressure, or a sudden worsening of previous high blood pressure may occur when a person has gradual and progressive narrowing of one or both renal arteries. If the person is given an angiotensin-converting enzyme (ACE) inhibitor or an angiotensin II blocker to treat high blood pressure, kidney function may decline rapidly. The effect is reversible if the drug is discontinued promptly.

If a blockage is the result of a clot that has moved to and lodged in one of the renal artery segments, the person may have clots elsewhere in the body, such as in the intestines, brain, and the skin of the fingers and toes. These clots may cause pain in these areas as well as small ulcers or gangrene, or a small stroke.

A complete blockage of one of the renal arteries may cause fever, nausea, vomiting, and back pain. Rarely, a blockage causes bleeding that turns the urine red or dark brown. Complete blockage of both renal arteries--or of one renal artery in people who have only one kidney--completely stops urine production and shuts down the kidneys (acute kidney failure).

Diagnosis

A doctor may suspect a blockage based on the person's symptoms. Laboratory tests, such as a complete blood count and urinalysis (microscopic examination of the urine), may add further clues. The amount of lactate dehydrogenase in the blood is often increased; lactate dehydrogenase is an enzyme that is often released when organ damage has occurred.

Because none of the symptoms or laboratory tests can specifically identify a blockage, a doctor needs to perform imaging tests of the kidneys to demonstrate that they are not functioning properly. Intravenous urography or radionuclide scanning can show absent or diminished blood flow to the affected kidney. However, neither of these procedures can distinguish between kidney infarction and other conditions that result in poor kidney function. Retrograde urography or ultrasound may be needed to make this distinction.

Angiography is one of the best procedures a doctor can use to confirm the diagnosis. However, angiography is performed only if the doctor is considering surgery to relieve the blockage. An alternative is a special type of computed tomography (spiral CT), which can accurately show a blockage. Doctors may monitor how well kidney function recovers by repeating ultrasound or radionuclide scanning at frequent intervals.

Treatment

Treatment is aimed at preventing further deterioration of blood flow and restoring blood flow that has been blocked. In the case of blood clots, the usual treatment is with anticoagulant drugs (see Section 14, Chapter 173); these drugs are given first intravenously and then by mouth for longer periods of time. Anticoagulants prevent the initial clot from enlarging and additional clots from forming. Drugs that dissolve clots (thrombolytics (see Section 14, Chapter 173)) may be more effective than anticoagulants. However, thrombolytic drugs improve kidney function only when the artery is not completely blocked or when clots can be dissolved quickly. After 3 hours, permanent damage and infarction are likely.

Surgery is sometimes performed to open an artery blocked by a clot, but this treatment has a greater risk of complications and death and does not improve kidney function more than anticoagulant or thrombolytic drugs alone. Drug treatment is almost always preferred to surgery. However, when the cause is injury, the artery must be repaired.

To relieve a blockage caused by atherosclerosis or fibrodysplasia of a renal artery, a doctor may thread a balloon catheter from the femoral artery in the groin to the renal artery. The balloon is then inflated to force open the obstructed area. This procedure is called percutaneous transluminal angioplasty. When doctors perform this procedure, they may place a short hollow tube (stent) in the artery to prevent the blockage from occurring again. Anticoagulant drugs are also often used after this procedure. When angioplasty is unsuccessful, surgery is needed to remove or bypass a blockage caused by atherosclerosis or fibrodysplasia.

Although kidney function may improve with treatment, it usually is not restored completely. The person's outlook is poor when clot fragments from other parts of the body are involved because similar clots often cause problems in the brain, liver, intestines, and feet at the same time.