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 based on a physical exam or other tests, but the diagnosis can only be made for certain once a sample of the tumor is removed and looked at 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 to look for possible signs of a kidney tumor or other health problems. The main focus will likely be on the abdomen and on any increase in blood pressure, which is another possible sign of a kidney tumor. Blood and urine samples might also be collected at this time for testing (see “Lab tests” below).
If the doctor thinks your child might have a kidney tumor, he or she will probably order 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 is likely to be a Wilms tumor
- To learn how far the tumor may have spread, both within 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
- more details on the imaging tests discussed here, see our document Imaging (Radiology) Tests.
This is often the first imaging test done if the doctor suspects your child has a Wilms tumor because it’s easy to have, it does not use radiation, and it gives the doctor a good view of the kidneys and the other organs in the abdomen.
Ultrasound uses sound waves to create images of internal organs. For this test, your child lies on a table while a small wand called a transducer is placed on the skin (which is first lubricated with a gel) over the belly. It gives off sound waves and picks up the echoes as they bounce off the kidney. The echoes are converted by a computer into a black and white image on a screen.
The echo patterns made by most kidney tumors look different from those of normal kidney tissue. Different echo patterns also can help doctors tell some types of cancerous and non-cancerous kidney tumors apart from one another.
Ultrasound is also very useful when looking for tumor thrombus (tumor growing into the main veins coming out of the kidney). This helps in planning for surgery, if it is needed.
The test is not usually painful, but it might cause some discomfort if the transducer is pressed down hard on the abdomen.
Computed tomography (CT, CAT) scan
The CT scan is an x-ray test that produces detailed cross-sectional images of parts of your child’s body, including organs such as the kidneys. This is one of the most useful tests to look for a mass inside the kidney. It’s also helpful in checking whether a cancer has grown into nearby veins or has spread to organs and tissues beyond the kidney, such as the lungs.
Instead of taking one picture, like a regular x-ray, a CT scanner takes many pictures as it rotates around your child while he or she lies on a table. A computer then combines these pictures into images showing slices of the part of the body being studied.
Before the scan, your child may be asked to drink a contrast solution and/or get an intravenous (IV) injection of a contrast dye that better outlines abnormal areas in the body. Your child may need an IV line for the dye. The contrast 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 occur. Be sure to tell the doctor if your child has any allergies or has ever had a reaction to any contrast material used for x-rays.
CT scans take longer than regular x-rays. A CT scanner has been described as a large donut, with a narrow table in the middle opening. Your child will need to lie still on the table while the scans are being done. During the test, the table slides in and out of the scanner. Younger children may be given medicine to help keep them calm or even asleep during the test to help make sure the pictures come out well.
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.
Like CT scans, MRI scans provide detailed images of soft tissues in the body. But MRI scans use radio waves and strong magnets to create the images instead of x-rays and don’t expose your child to radiation.
A contrast material called gadolinium may be injected into a vein before the scan to better see details. It usually does not cause allergic reactions, but it can cause other problems in children with kidney disease, so doctors are careful when they use it.
MRI scans take longer than CT scans – often up to an hour. Your child may have to lie inside a narrow tube, which is confining and can be distressing. Newer, more open MRI machines may help with this, but the test still requires staying still for long periods of time. The MRI machine also makes loud buzzing and clicking noises that your child may find disturbing. Younger children may be given medicine to help keep them calm or even asleep during the test.
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. If a CT scan of the chest is done, this test is not needed.
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 is likely to spread.
For this test, a small amount of low-level radioactive material is injected into a vein (intravenously, or IV). (The amount of radioactivity used is very low and will pass out of the body within a day or so.) The substance settles in areas of damaged bone throughout the skeleton over the course of a couple of hours. Your child then lies on a table for about 30 minutes while a special camera detects the radioactivity and creates a picture of the skeleton. Younger children may be given medicine to help keep them calm or even asleep during the test.
Areas of active bone changes will appear as hot spots on the skeleton – that is, they attract the radioactivity. These areas may suggest the presence of cancer, but other bone diseases can also cause the same pattern. To help tell these apart, other tests such as plain x-rays or MRI scans of the bone might be needed.
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 diagnosis of Wilms tumor has been made.
A urine sample may be tested (urinalysis) to look for blood and other substances in the urine to see if there are problems with the kidneys. The 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 gland, which lies just above the kidney.)
Blood tests are not used to find Wilms tumors, but they can sometimes show if a child has kidney problems. They can also be done to check a child’s general health (especially before surgery) and to look for side effects during treatment such as chemotherapy. These may include tests to count the number of white blood cells, red blood cells, and blood platelets, and tests to measure certain chemicals and salts in the blood that give clues about how well the kidneys and liver are working.
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 sample of the tumor is removed and looked at 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 was described in the section “What is Wilms tumor?”
In most cases, the 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 are not sure the tumor can be removed completely, a sample of the tumor may be taken during a biopsy as a separate procedure done before surgery. The biopsy may be done either as a type of surgery or using a long, hollow needle that’s inserted through the skin and into the tumor.
See Testing Biopsy and Cytology Specimens for Cancer to learn more about different types of biopsies, how the tissue is used in the lab for disease diagnosis, and what the results will tell you.
Last Medical Review: 09/17/2013
Last Revised: 02/14/2014