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. But even if the doctor is fairly sure a child has a Wilms tumor because of the results of a physical exam or other tests, the diagnosis is only made for certain once a sample of the tumor is removed and looked at under a microscope.

Signs and symptoms of Wilms tumor

Wilms tumors can be hard to find early because they can often grow quite large without causing any symptoms. Children may look healthy and play normally. The first sign is usually swelling or a hard mass in the abdomen (belly), which parents may notice while bathing or dressing the child. It feels firm and is often large enough to be felt on both sides of the belly. It is usually not painful, but it may cause belly pain in some cases. Some children with Wilms tumor may also have fever, nausea, loss of appetite, shortness of breath, constipation, or blood in the urine.

Wilms tumors can also sometimes cause high blood pressure. This does not usually cause 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.

Many of the signs and symptoms above are more likely to be caused by something other than 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 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 Wilms 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 this cancer. 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 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 been effective

Ultrasound (sonogram)

Ultrasound uses sound waves to create images of internal organs. For this test, your child lies on a table while a small, microphone-like instrument called a transducer is placed on the skin (which is first lubricated with a gel). It is moved across the skin over the kidney so that it can be viewed from different angles.

The transducer gives off sound waves and picks up the echoes as they bounce off the tissues in 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 distinguish some types of cancerous and non-cancerous kidney tumors from one another. In addition, ultrasound is 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.

This is often the first imaging test done if the doctor suspects your child has a Wilms tumor because it is 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. 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. 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. Your child will need to lie still on a table while they are being done. During the test, the table slides in and out of the scanner, a ring-shaped machine that completely surrounds the table. Some people feel a bit confined by the ring they have to lie in while the pictures are being taken. 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. Many medical centers now use spiral CT (also known as helical CT), which completes the scan more quickly. It also gives more detailed pictures and lowers the dose of radiation received during the test.

A CT scan is one of the most useful tests to look for a mass inside the kidney. It is also helpful in checking whether a cancer has spread to organs and tissues beyond the kidney, such as the lungs.

Magnetic resonance imaging (MRI) scan

Like CT scans, MRI scans provide detailed images of soft tissues in the body. But MRI scans use radio waves and strong magnets instead of x-rays (and therefore don't expose your child to radiation). The energy from the radio waves is absorbed and then released in a pattern formed by the type of body tissue and by certain diseases. A computer translates the pattern into a very detailed image of parts of the body.

A contrast material called gadolinium may be injected into a vein before the scan to better see details. The contrast material 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.

MRI scans show more detailed images than CT and ultrasound. They may be done if there's a chance that the cancer is in a major vein (the inferior vena cava) in the abdomen. 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.

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. 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 low-level radioactive material is injected into a vein (intravenously, or IV). The substance settles in areas of damaged bone throughout the entire 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 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 distinguish between these conditions, other imaging tests such as plain x-rays or MRI scans, or even a bone biopsy might be needed.

Lab tests

Lab tests may 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 may 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 liver and kidneys are working.

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 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 characteristic appearance when looked at this way. This is also when doctors 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 obtained 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 obtained first during a biopsy as a separate procedure. The biopsy may be done either surgically or using a long, hollow needle that is inserted through the skin and into the tumor.