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Wilms tumors are most often found when they start to cause symptoms like swelling in the belly, but by this point they have often grown quite large. They can be found earlier with tests such as an ultrasound (a test that uses sound waves and a computer to make pictures of your insides). But because Wilms tumors are so rare, it doesn't make sense to do ultrasound exams if a child has no Wilms tumor risk factors. There are no blood tests or other tests that are useful in looking for Wilms tumors in healthy children.

On the other hand, looking for Wilms tumor is very important for children who have syndromes or birth defects known to be linked to this disease. Most doctors recommend exams and ultrasound on a regular basis (maybe every 3 or 4 months until the age of 7) to find any kidney tumors early – when they are small and have not spread to other organs.

Wilms tumor can also run in families, although this is rare. Talk to your doctor if you have family members who have had Wilms tumor. If you do, the children in your family may need to have regular exams.

Signs and symptoms of Wilms tumor

Wilms tumors can be hard to find early. They often grow quite large without causing any symptoms. Children may look healthy and seem normal. The first sign is usually a swelling or hard lump in the belly. Chances are parents will notice the swelling. Some children may also have other symptoms such as:

  • Stomach pain
  • Fever
  • Sick stomach (nausea)
  • Not wanting to eat
  • Constipation
  • Blood in the urine
  • Shortness of breath

Wilms tumors can also sometimes cause high blood pressure. This does not usually result in symptoms on its own, but in rare cases it can get high enough to cause problems such as bleeding inside the eye or even a change in consciousness.

Other things often cause these symptoms, so alone they do not mean your child has a kidney tumor. Still, if your child has any of these symptoms, check with your child's doctor so that the cause can be found and treated, if needed.

Medical history and physical exam

If your child has signs or symptoms that suggest he or she may have a kidney tumor, the doctor will ask questions to check for risk factors and to learn more about the child’s symptoms. The doctor will then do an exam to look for possible signs of Wilms tumor or other health problems. Lab tests on samples of blood and urine may also be done at this time (see “Lab tests” below).

Imaging tests

If the doctor thinks your child might have a kidney tumor, he or she will likely order one or more imaging tests listed below. These tests make different types of pictures of organs inside the body. Imaging tests may be done:

  • To find out whether there is a tumor in the kidney and if it is likely to be a Wilms tumor
  • To learn how far the tumor may have spread
  • To help guide surgery or radiation therapy
  • To see if treatment is working

These are some of the imaging tests that may be done:

Ultrasound: For this test, your child lies on a table while a small wand is moved across the skin over the kidney so that it can be looked at from different angles. This test uses sound waves to make pictures of the inside of the body. The echoes made by most kidney tumors look different from those of normal kidney tissue.

This is often the first test done if the doctor thinks your child may have a Wilms tumor. It does not use radiation and allows the doctor to see the whole belly (abdomen). Ultrasound is also very useful when looking for tumor growing into the main veins around the kidney. This helps doctors know how much surgery may be needed.

CT (computed tomography) scan: This test uses x-rays to take many pictures of the body. The pictures are then combined by a computer to give a detailed cross-sectional image. A CT scan is one of the most useful methods of finding a mass inside the kidney. It is also used to see whether the cancer has spread beyond the kidney.

Your child will need to lie still on a table while the scan is being done. During the test, the table slides in and out of the scanner, a ring-shaped machine that surrounds the table. Some people feel a bit confined by the ring they have to lie in while the pictures are being taken. Some doctors may give younger children medicine to help keep them calm or even asleep during the test. Spiral CT is now used in many places. This type of CT scan uses a faster machine.

Your child may be asked to drink a contrast dye or have a contrast dye put into a vein. This helps better outline organs in the body. The dye may cause some flushing (a feeling of warmth, especially in the face). Some people are allergic and get hives. Rarely, more serious reactions like trouble breathing or low blood pressure can happen. Be sure to tell the doctor if your child has any allergies or has ever had a reaction to any dye used for x-rays.

MRI (magnetic resonance imaging): MRI uses radio waves and strong magnets instead of x-rays to take pictures. Like CT scans, MRIs show a cross-section of the body, but in more detail. This can help doctors see if the cancer is in a major blood vessel near the kidney. They may also be used to look for possible spread of cancer to the brain or spinal cord if doctors are concerned the cancer may have spread there.

MRI scans take longer than CT scans – often up to an hour. Your child has to lie inside a narrow tube and the machine also makes buzzing and clicking noises that may be disturbing. Your child may be given drugs to help him or her relax or sleep during this test. Newer, more open MRI machines may be another option for some children.

Chest x-ray: Chest x-rays are used to see whether the Wilms tumor has spread to the lungs. If a CT scan of the chest is done, this test is not needed.

Bone scan: Bone scans can help find cancer that has spread to bones. Doctors don't usually order this test unless they think your child has a type of Wilms tumor that is likely to spread. For this test, a small amount of radioactive material is put into a vein. It collects in areas of diseased bone and can be seen with a special camera.

Lab tests

Certain blood tests are done to count the number of white blood cells and red blood cells and to measure other substances in the blood. Urine may be tested, too. These tests are not used to find Wilms tumor, but they give an idea of the child's overall health. They also provide clues about how well the liver and kidneys are working.

Kidney biopsy/surgery

In most cases, imaging tests tell doctors enough to decide whether your child has a Wilms tumor. But the only way to know for sure is when a piece of the tumor is removed and checked under a microscope. This is called a biopsy. It will also tell whether the tumor has favorable or unfavorable histology. (See the section "What is Wilms tumor?" for more on histology.)

In most cases, the biopsy is done during surgery to treat the tumor (see the "Surgery" section). Less often, a biopsy is done with a long, hollow needle as a separate test before surgery.


Last Medical Review: 08/01/2012
Last Revised: 08/01/2012