Renal Vein Thrombosis

Renal vein thrombosis

Definition

Renal vein thrombosis develops when a blood clot forms in the renal vein, which is the blood vessel that carries blood from the kidneys back to the heart. The disorder is not common.

Description

Normally, kidneys rid the body of wastes by filtering the wastes into the bladder where they exit the body through the urine. When one or more blood vessels in the kidneys become narrowed (renal artery stenosis) because of debris and plaque build-up, or blocked because of a blood clot (renal vein thrombosis), the kidneys are unable to function properly. There is usually a rise in blood pressure, and kidney failure can occur without prompt treatment.

The onset of renal vein thrombosis can be rapid (acute) or gradual.

Blood clots in the renal arteries are uncommon, but when they do occur, there is a risk of pulmonary embolism, a dangerous condition that occurs when the clot or a portion of the clot dislodges and travels to the lungs. There is also an increased risk of congestive heart failure, a condition in which the heart's pumping power is weaker than normal.

Demographics

Renal vein thrombosis occurs in both infants and adults. The number of people who suffer from renal vein thrombosis is difficult to determine, as many do not show symptoms, and the disorder is diagnosed only by specific tests. Ninety percent of pediatric cases of renal vein thrombi occur in infants less than one year old; 75 percent occur in infants under one month of age.

Causes and symptoms

Causes

In children, most cases of renal vein thrombosis are thought to be caused by an episode of severe dehydration . Severe dehydration decreases blood volume and causes the blood to clot more readily. Symptoms occur rapidly.

In adults, renal vein thrombosis can be caused by injury to the abdomen or back, malignant kidney tumors growing into the renal vein, scar formation (stricture) and other blockages in the vein, or kidney diseases that cause degenerative changes in the cells of the renal tubules (nephrotic syndrome).

Renal vein thrombosis is more common in patients with nephrotic syndrome, although studies have shown high variability among these patients, with rates of 5 to 62 percent reported. Nephrotic syndrome is marked by abnormally low levels of albumin (hypoalbuminemia), abnormally high levels of cholesterol in the blood (hypercholesterolemia), and fluid retention (edema). Minimal change disease is a form of nephrotic syndrome seen in children, characterized by swelling and weight (from fluid retention), foamy urine, and loss of appetite.

Symptoms

Acute onset of renal vein thrombosis at any age causes pain in the lower back and sides of the abdomen, fever , bloody urine, decreased urine output, and sometimes kidney failure.

Other symptoms include high blood pressure or a "whooshing" sound heard by the physician when he or she places a stethoscope on the abdomen. This sound is the result of blood attempting to pass through the blocked vessel. The doctor may also feel an enlarged kidney during a physical exam. Some patients have no symptoms.

When to call the doctor

If the child has any of these symptoms, the parent should seek emergency medical care:

• a high fever of 102° F, or 38.9°C, or above
• sudden onset of lower back pain
• sudden, severe leg swelling
• difficulty breathing
• blood in the urine
• decreased urination

If the child has any of these symptoms of dehydration, the parent should give the child clear fluids and an oral rehydrating solution, such as Pedialyte, and contact the child's pediatrician:

• dry mouth
• increased or excessive thirst
• few or no tears when crying
• dark yellow urine
• irritability
• low energy or severe weakness
• lightheadedness or fainting
• sunken abdomen, eyes, and cheeks

Diagnosis

A physician makes the diagnosis of renal vein thrombosis based on the presence of symptoms and the results of a medical examination and diagnostic tests. When examining the child, the doctor will palpate (feel) the child's abdomen to detect kidney enlargement. The doctor will listen to the child's heartbeat with a stethoscope. He or she will also place the stethoscope over the child's abdomen; when renal vein thrombosis is present, the doctor may hear an abnormal "whooshing" as blood tries to flow through the blocked vessel.

Urine tests and blood tests are usually performed. If nephrotic syndrome is present, the urine test may indicate an abnormally large quantity of protein, and the blood test may show abnormally high levels of cholesterol.

Vascular ultrasound is a non-invasive ultrasound method used to examine blood circulation and detect the presence of blood clots. During a vascular ultrasound, an ultrasound transducer (small hand-held device) is placed over the area being examined. The transducer generates high-frequency sound waves through the tissues. These sound waves reflect off blood cells moving within the blood vessels, allowing the radiologist to calculate their speed. The sound waves are measured, recorded, and displayed on a computer screen.

Other tests that may be used to detect a blood clot include computed tomography scans (CT scans) and magnetic resonance imaging (MRI).

A less common test used to diagnose renal vein thrombosis is renal venography, also called renal angiography, an x-ray examination of the renal veins after a contrast material (dye) has been injected. This test may be performed to locate the narrowing or blockage in the renal vein. During this test, a catheter (long, thin tube) is inserted into the vein in the groin area (femoral vein) and threaded first into the right kidney and then into the vein of the other kidney. Blood samples may be taken from each kidney for further testing. The contrast material is injected through the catheter into each vein and x rays are taken. This test is not common, since other less invasive imaging tests, including MRI and CT scans, are available to aid the physician in making an accurate diagnosis.

Treatment

One of the major goals of treatment is to prevent the blood clot in the renal vein from detaching and moving into the lungs (pulmonary embolism), where it can cause serious complications.

Clot-busting medications, such as tissue plasminogen activator (t-PA, also called streptokinase enzymes or thrombolytic drugs), may be given to help dissolve the renal clot. Clot busters must be administered quickly and properly through several specifically timed intravenous infusions according to a rigid protocol established for each drug and the body weight of each patient. Research has shown that these medications are most effective when given within two hours of the onset of symptoms.

Anticoagulant medications, including heparin or warfarin and low-dose aspirin, may be prescribed to prevent existing blood clots from enlarging and to prevent the formation of new clots. The use of these medications in children remains controversial because of the risk of Reye's syndrome . Sometimes the potential benefits of these medications outweigh the risk of side effects. Researchers agree that more studies are needed to determine the proper dosage and effectiveness of aspirin and other anticoagulant medications in children.

Bedrest or limited activity may be recommended for a brief period.

Severe dehydration requires medical treatment with intravenous (IV) fluids and may require hospitalization . IV therapy can be followed with oral rehydration as the child's condition improves.

If the renal artery is partially or completely blocked, an interventional catheter-based procedure may be performed. During the catheterization, a long, slender tube called a catheter is inserted into a vein or artery and slowly directed to the blocked blood vessel, using x-ray guidance (angiography). A specialized balloon tip or other device at the end of the catheter can be used to open the blocked or narrowed vessel. The balloon is rapidly inflated and deflated to open or widen the area. In some patients, a stent (metal mesh tube) can be placed to act as a scaffold and hold the area open.

Intra-arterial thrombolysis involves threading a catheter with clot-busting medication through a large blood vessel in the groin to the site of the clot. Using renal angiography, doctors pinpoint the precise location of the blockage and deliver the medication to that spot.

Endarterectomy and surgical bypass are two surgical treatment options, but they are not common in children. In a renal endarterectomy, a vascular surgeon removes the blockage from the inner lining of the renal artery. Bypass surgery reroutes the blood flow around the narrowed or blocked sections of the renal artery. Rarely, when there is a complete blockage of the renal vein in infants, the kidney must be surgically removed.

KEY TERMS

Albumin —A blood protein that is made in the liver and helps to regulate water movement in the body.

Anticoagulant drug —A drug used to prevent clot formation or to prevent a clot that has formed from enlarging. Anticoagulant drugs inhibit clot formation by blocking the action of clotting factors or platelets. They fall into three groups: inhibitors of clotting factor synthesis, inhibitors of thrombin, and antiplatelet drugs.

Antiplatelet drug —Drugs that inhibit platelets from aggregating to form a plug. They are used to prevent clotting and alter the natural course of atherosclerosis.

Arteriosclerosis —A chronic condition characterized by thickening, loss of leasticity, and hardening of the arteries and the build-up of plaque on the arterial walls. Arteriosclerosis can slow or impair blood circulation. It includes atherosclerosis, but the two terms are often used synonymously.

Artery —A blood vessel that carries blood away from the heart to the cells, tissues, and organs of the body.

Blood clotting —Also called coagulation. A natural process in which blood cells and fibrin strands clump together to stop bleeding after a blood vessel has been injured.

Clot —A soft, semi-solid mass that forms when blood coagulates.

Clot busters —Also called thrombolytics. Medications used to break up a blood clot.

Clotting factors —Substances in the blood, also known as coagulation factors, that act in sequence to stop bleeding by triggering the formation of a clot. Each clotting factor is designated with a Roman numeral I through XIII.

Coagulate —To clot or cause hemostasis; in electro-surgery, to cause tissue dehydration without cutting.

Computed tomography (CT) —An imaging technique in which cross-sectional x rays of the body are compiled to create a three-dimensional image of the body's internal structures; also called computed axial tomography.

Dehydration —An excessive loss of water from the body. It may follow vomiting, prolonged diarrhea, or excessive sweating.

Embolism —A blood clot, air bubble, or mass of foreign material that travels and blocks the flow of blood in an artery. When blood supply to a tissue or organ is blocked by an embolism, infarction, or death of the tissue the artery feeds, occurs. Without immediate and appropriate treatment, an embolism can be fatal.

Embolus —Plural, emboli. An embolus is something that blocks the blood flow in a blood vessel. It may be a gas bubble, a blood clot, a fat globule, a mass of bacteria, or other foreign body that forms somewhere else and travels through the circulatory system until it gets stuck.

Hypercoagulable state —(Also called thromboembolic state or thrombophilia.) A condition characterized by excess blood clotting.

Hypertension —Abnormally high arterial blood pressure, which if left untreated can lead to heart disease and stroke.

Intravenous (IV) therapy —Administration of fluids or medications through a vein, usually in the hand or arm.

Magnetic resonance imaging (MRI) —An imaging technique that uses a large circular magnet and radio waves to generate signals from atoms in the body. These signals are used to construct detailed images of internal body structures and organs, including the brain.

Nephrologist —A physician who specializes in treating diseases of the kidney.

Platelet —A cell-like particle in the blood that plays an important role in blood clotting. Platelets are activated when an injury causes a blood vessel to break. They change shape from round to spiny, "sticking" to the broken vessel wall and to each other to begin the clotting process. In addition to physically plugging breaks in blood vessel walls, platelets also release chemicals that promote clotting.

Stenosis —A condition in which an opening or passageway in the body is narrowed or constricted.

Thrombolysis —The process of dissolving a blood clot.

Thrombolytics —Drugs that dissolve blood clots. Thrombolytics are used to treat embolisms.

Thrombus —A blood clot that forms within a blood vessel or the heart.

Ultrasonography —A medical test in which sound waves are directed against internal structures in the body. As sound waves bounce off the internal structure, they create an image on a video screen. Ultrasonography is often used to diagnose fetal abnormalities, gallstones, heart defects, and tumors. Also called ultrasound imaging.

Urologist —A physician who specializes in the anatomy, physiology, diseases, and care of the urinary tract (in men and women) and male reproductive tract.

Blood pressure medications may be prescribed to treat high blood pressure, and other medications may include diuretics, beta blockers, ACE inhibitors, and calcium channel blockers. Some of these drugs have not been extensively studied in children, and a specific pediatric dose has not been established.

Nutritional concerns

Impaired kidneys cause an increased level of phosphorus in the blood, which interferes with calcium absorption. In addition, damaged kidneys cannot activate vitamin D, which is needed to absorb calcium. Dietary changes may include limiting foods high in phosphorus, such as dairy products, meat, and poultry. A phosphate binder may be recommended to keep phosphorus in the bowel (so it does not interfere with calcium absorption) where it is excreted during a bowel movement. Calcium or vitamin D supplements also may be recommended. To maintain adequate nutrition , a registered dietitian can help parents and children implement specific dietary changes.

Prognosis

Most cases of renal vein thrombosis resolve over time, without permanent injury to the kidneys. Acute renal failure can occur with severe dehydration. Death from renal vein thrombosis is rare, and is often caused by the blood clot detaching and lodging in the heart or lungs.

Prevention

Renal vein thrombosis cannot be prevented. Preventing dehydration by maintaining fluids in the body may help reduce the risk of renal vein thrombosis.

Parental concerns

Most cases of renal vein thrombosis resolve without complication. When a child has been diagnosed with renal vein thrombosis, it is important to follow the doctor's recommendations for follow-up checkups to closely monitor his or her condition. If an anticoagulant medication has been prescribed, it is important to keep all scheduled laboratory appointments so the effectiveness of the medication can be evaluated.

If the child has developed any new symptoms, the parents should call the child's doctor.

Resources

BOOKS

"Vascular Diseases of Acute Onset: Renal Vein Thrombosis." In The Merck Manual of Diagnosis and Therapy. 17th ed. Eds. Mark H. Beers and Robert Berkow. Indianapolis, IN: John Wiley and Sons, Inc., 1999.

ORGANIZATIONS

American Kidney Fund. 6110 Executive Blvd., Suite 1010, Rockville, MD 20852. (800) 638-8299. <www.akfinc.org>

National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). 2 Information Way, Bethesda, MD 20892-3570. (800) 891-5389. nddic@info.niddk.nih.gov. <www.niddk.nih.gov>

National Kidney and Urologic Diseases Information Clearinghouse. 3 Information Way, Bethesda, MD 20892-3580. (800) 891-5390. nkudic@info.niddk.nih.gov. <http://kidney.niddk.nih.gov>

National Kidney Foundation. 30 East 33rd St., New York, NY 10016. (800) 622-9010 or (212) 889-2210. info@kidney.org. <www.kidney.org>

WEB SITES

VascularWeb. Provided by the Society for Vascular Surgery. <www.vascularweb.org>

Angela M. Costello