How Are Wilms Tumors Diagnosed?

Wilms tumors are usually found when a child is brought to a doctor because of symptoms he or she is having. The doctor might suspect a child has a Wilms tumor because of the physical exam or other test results, but the diagnosis can only be made for certain by taking out a small piece of the tumor and looking at it under a microscope.

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 want to get a complete medical history to learn more about the symptoms and how long they have been there. The doctor may also ask if there’s a family history of cancer or birth defects, especially in the genitals or urinary system.

The doctor will examine your child for possible signs of a kidney tumor or other health problems. The focus will probably be on the abdomen (belly) and on any increase in blood pressure, which is another possible sign of a kidney tumor. Blood and urine samples might also be collected and tested (see “Lab tests” below).

Imaging tests

If the doctor thinks your child might have a kidney tumor, he or she will probably get one or more of the imaging tests below. These tests use sound waves, x-rays, magnetic fields, or radioactive substances to create pictures of the inside of the body. Imaging tests are done for a number of reasons, including:

  • To help find out if there is a tumor in the kidney(s), and if so, if it's likely to be a Wilms tumor
  • To learn if and how far the tumor has spread, both in the kidney and to other parts of the body
  • To help guide surgery or radiation therapy
  • To look at the area after treatment to help determine if it has worked

Ultrasound (sonogram)

Ultrasound is often the first imaging test done if the doctor suspects your child has a Wilms tumor (or another type of tumor in the abdomen). This test is easy to have, does not use radiation, and it gives the doctor a good view of the kidneys and the other organs in the abdomen. It's also very useful when looking for tumor growing into the main veins coming out of the kidney. This can help in planning for surgery, if it's needed.

Computed tomography (CT, CAT) scan

The CT scan uses x-rays to make detailed cross-sectional images of parts of your child’s body, including the kidneys. This is one of the most useful tests to look for a tumor inside the kidney. It’s also helpful for checking whether a cancer has grown into nearby veins or has spread to organs beyond the kidney, such as the lungs. Your child will need to lie very still on a table while the scans are being done. Younger children may be given medicine to help keep them calm or even asleep during the test to help make sure the pictures are clear.

Magnetic resonance imaging (MRI) scan

An MRI scan might be done if the doctor needs to see very detailed images of the kidney or nearby areas. For example, it might be done if there’s a chance that a kidney tumor might have reached a major vein (the inferior vena cava) in the abdomen. An MRI scan might 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.

Your child may have to lie inside a narrow tube, which is confining and can be distressing. The test also requires a person to stay still for several minutes at a time. Younger children may be given medicine to help keep them calm or even asleep during the test.

Chest x-ray

Chest x-rays may be done to look for any spread of Wilms tumor to the lungs, as well as to have a baseline view of the lungs to compare with other x-rays that might be done in the future. This test might not be needed if a CT scan of the chest is done.

Bone scan

Bone scans can help show if cancer has spread to bones. Doctors don’t usually order this test unless they think your child has a type of Wilms tumor that's likely to spread.

Lab tests

Lab tests might be done to check urine and blood samples if your child’s doctor suspects a kidney problem. They may also be done after a Wilms tumor has been found.

A urine sample may be tested (urinalysis) to see if there are problems with the kidneys. Urine may also be tested for substances called catecholamines. This is done to make sure your child doesn’t have another kind of tumor called neuroblastoma. (Neuroblastomas often start in the adrenal glands, which are just on top of each kidney.)

Kidney biopsy/surgery

Most of the time, imaging tests can give doctors enough information to decide if a child probably has a Wilms tumor, and therefore if surgery should be done. But the actual diagnosis of Wilms tumor is made when a small piece of the tumor is removed and checked under a microscope. The cells in Wilms tumors have a distinct appearance when looked at this way. Doctors also look at the sample to determine the histology of the Wilms tumor (favorable or unfavorable), as described in What is Wilms tumor?

In most cases, a sample is removed during surgery to treat the tumor (see the Surgery section). Sometimes if the doctors are less certain about the diagnosis or if they aren’t sure the tumor can be removed completely, a sample of the tumor may be taken during a biopsy as a separate procedure before surgery. 

See Testing Biopsy and Cytology Specimens for Cancer to learn more about different types of biopsies, how the biopsy samples are tested in the lab, and what the results might tell you.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: March 6, 2015 Last Revised: February 16, 2016

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