Wilms Tumor - Childhood: Diagnosis

Approved by the Cancer.Net Editorial Board, 01/2022

ON THIS PAGE: You will find a list of common tests, procedures, and scans that doctors use to find the cause of a medical problem. Use the menu to see other pages.

Doctors use many tests to find, or diagnose, a Wilms tumor. They also do tests to learn if the cancer has spread to another part of the body from where it started. If the cancer has spread, it is called metastasis. Doctors may also do tests to learn which treatments could work best.

For most types of tumors, a biopsy is the only sure way for the doctor to know if cancer is present. In a biopsy, the doctor takes a small sample of tissue for testing in a laboratory. If a biopsy is not possible, the doctor may suggest other tests that will help make a diagnosis.

How a Wilms tumor is diagnosed

There are many tests used for diagnosing a Wilms tumor. Not all tests described here will be used for every child. Your child’s doctor may consider these factors when choosing a diagnostic test:

  • The type of cancer suspected

  • Your child's signs and symptoms

  • Your child's age and general health

  • The results of earlier medical tests

In addition to a physical examination, the following tests may be used to diagnose a Wilms tumor:

  • Blood/urine tests. Doctors will take samples of your child’s blood and urine. The results of these tests will help the doctor learn more about the tumor and your child’s general health.

  • X-ray. An x-ray is a way to create a picture of the structures inside of the body, using a small amount of radiation.

  • Ultrasound. An ultrasound uses sound waves to create a picture of the internal organs. A transmitter that emits sound waves is moved over the body. A tumor creates different echoes of the sound waves than healthy tissue, so when the waves are bounced back to a computer and changed into images, the doctor can find a tumor inside the body. The procedure is painless.

  • Computed tomography (CT or CAT) scan. A CT scan takes pictures of the inside of the body using x-rays taken from different angles. A computer combines these pictures into a detailed, 3-dimensional image that shows any abnormalities or tumors. A CT scan can be used to measure the tumor’s size. Sometimes, a special dye called a contrast medium is given before the scan to provide better detail on the image. This dye can be injected into a person's vein or given as a pill or liquid to swallow.

    The first CT scan of the abdomen and pelvis will help show if the Wilms tumor has spread from the kidney into the blood vessels, particularly the inferior vena cava. The inferior vena cava is the major vein that carries blood from the legs, pelvis, and abdomen to the heart. If this is the case, the doctor will often recommend chemotherapy before surgery (see Types of Treatment). A chest CT scan may be used to find out if the tumor has spread to the lungs.

  • Magnetic resonance imaging (MRI). An MRI uses magnetic fields, not x-rays, to produce detailed images of the body. MRI can be used to measure the tumor’s size. A special dye called a contrast medium is given before the scan to create a clearer picture. This dye can be injected into a person's vein or given as a pill or liquid to swallow.

  • Bone x-ray and bone scan. Bone x-rays and bone scans look for cancer in the bones of children who have a rare kidney tumor called clear cell sarcoma. A bone scan uses a radioactive tracer to look at the inside of the bones. The amount of radiation in the tracer is too low to be harmful. The tracer is injected into a person's vein. It collects in areas of the bone and is detected by a special camera. Healthy bone appears lighter to the camera, and areas of injury, such as those caused by cancer, appear dark and stand out on the image.

  • Surgery or biopsy. For children with a mass in the kidney that appears to be a stage I or stage II Wilms tumor, a surgeon usually performs an abdominal operation called a laparotomy. This surgery removes the affected kidney and tumor. If the tumor is too large to be removed, or if it has an abnormal appearance on CT or MRI scans, the surgeon will only perform a biopsy. A biopsy is the removal of a small amount of tissue for examination under a microscope.

    A pathologist then analyzes the sample(s) to determine whether tumor cells are present. If they are, the pathologist will also identify the cell type, which will help the doctor recommend an initial treatment. A pathologist is a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease.

    People who have what looks like bilateral Wilms tumors (see Introduction) based on scans will usually not have a biopsy at the time of diagnosis. Instead, they usually start chemotherapy and then have surgery within 12 weeks after diagnosis. 

  • Chromosome tests. The pathologist may test the tumor tissue removed during the biopsy for changes in chromosomes 1 and 16. A tumor with changes in chromosome 1 is linked to worse outcomes after treatment. And, a tumor with changes in both of these chromosomes does not respond as well to standard treatment. Current research studies use more chemotherapy to treat children with a Wilms tumor that has these changes (see Types of Treatment).

After diagnostic tests are done, your child’s doctor will review the results with you. If the diagnosis is a Wilms tumor, these results also help the doctor describe the tumor. This is called staging.

The next section in this guide is Stages. It explains the system doctors use to describe the extent of the disease. Use the menu to choose a different section to read in this guide.