How Is Rhabdomyosarcoma Diagnosed?
Certain signs and symptoms might suggest that a person has rhabdomyosarcoma (RMS), but tests are needed to find out for sure.
Medical history and physical exam
If your child has symptoms that could be from RMS (or another type of tumor), the doctor will want to get a complete medical history to find out more about the symptoms and how long your child has had them. The doctor will also examine your child to look for possible signs of RMS or other health problems. For example, the doctor might be able to see or feel an abnormal lump or swelling.
If the doctor suspects your child might have RMS (or another type of tumor), tests will be needed to find out. These might include imaging tests, biopsies, and/or lab tests.
Imaging tests use x-rays, magnetic fields, radioactive substances, or sound waves to create pictures of the inside of the body. Imaging tests can be done for a number of reasons, including:
- To help find out if a suspicious area might be cancer
- To determine the extent of a tumor or learn how far a cancer has spread
- To help determine if treatment is working
People who have or may have RMS will get one or more of these tests.
X-rays are sometimes used to look for tumors, but their use is limited mainly to looking at bones because they don’t show much detail in internal organs. A chest x-ray is sometimes done to look for cancer that might have spread to the lungs, although it isn’t needed if a chest CT scan is being done.
Computed tomography (CT) scan
The CT scan uses x-rays to make detailed cross-sectional images of parts of the body, including soft tissues such as muscles. 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 of slices of the part of the body being studied.
This test can often show a tumor in detail, including how large it is and if it has grown into nearby structures. It can also be used to look at nearby lymph nodes, as well as the lungs or other areas of the body where the cancer might have spread.
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 will help better outline abnormal areas. Your child may need an IV line for the contrast dye. The dye can 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 (especially to iodine or shellfish) 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 that slides in and out of the middle opening. Your child will need to lie still on the table while the scan is being done. Younger children may be given medicine to help keep them calm or even asleep during the test.
Magnetic resonance imaging (MRI) scan
Like CT scans, MRI scans give 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. A contrast material called gadolinium may be injected into a vein before the scan to help show details better. This contrast material usually does not cause allergic reactions.
This test might be used instead of a CT scan to look at the tumor and the tissues around it. MRI is especially useful if the tumor is in certain parts of the body, such as the head and neck, an arm or leg, or the pelvis. MRI scans can help determine the exact extent of a tumor, because they can show the muscle, fat, and connective tissue around the tumor in great detail. This is important when planning surgery or radiation therapy. MRI is also very useful if your child’s doctor is concerned about possible spread to the spinal cord or brain.
MRI scans take longer than CT scans – often up to an hour. Your child may have to lie on a table that slides 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. Newer, more open MRI machines, which are less confining, might be an option, but the test still requires staying still for long periods of time. The MRI machine also makes loud buzzing and clicking noises that can be disturbing. Sometimes, younger children are given medicine to help keep them calm or even asleep during the test.
A bone scan can help show if a cancer has spread to the bones, and is often part of the workup for anyone with RMS. This test is useful because it provides a picture of the entire skeleton at once.
For this test, a small amount of low-level radioactive material is injected into a vein (IV). The amount of radioactivity used is very low and will pass out of the body within a day or so. Over a couple of hours, the substance settles in abnormal areas of bone throughout the body. 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 can be given medicine to help keep them calm or even asleep during the test.
Areas of active bone changes attract the radioactivity and show up as “hot spots” on the scan. These areas may suggest cancer in an area, but other bone diseases can also cause the same pattern, so other tests such as plain x-rays or MRI scans, or even a bone biopsy might be needed.
Positron emission tomography (PET) scan
For a PET scan, a radioactive substance (usually a type of sugar related to glucose, known as FDG) is injected into the blood. The amount of radioactivity used is very low and will pass out of the body in a day or so. Because cancer cells in the body are growing quickly, they will absorb large amounts of the sugar.
After about an hour, your child will lie on a table in the PET scanner for about 30 minutes while a special camera creates a picture of areas of radioactivity in the body. The picture is not detailed like a CT or MRI scan, but it provides helpful information about the whole body.
PET scans are not used routinely to help diagnose RMS, but they can sometimes be helpful in finding out if suspicious areas seen on other imaging tests (such as bone scans or CT scans) are tumors. PET scans can also be repeated during treatment to monitor the cancer over time.
Some machines can do a PET and CT scan at the same time (PET/CT scan). This lets the doctor compare areas of higher radioactivity on the PET scan with the more detailed appearance of that area on the CT scan.
Ultrasound uses sound waves and their echoes to make a picture of internal organs or tumors. For this test, a small, microphone-like instrument called a transducer is moved around on the skin (which is first lubricated with gel). It gives off sound waves and picks up the echoes as they bounce off the organs. The echoes are converted by a computer into an image on a screen.
Ultrasound can be used to see if tumors in the pelvis (such as prostate or bladder tumors) are growing or shrinking over time. (This test can’t be used to look at tumors in the chest because the ribs block the sound waves.)
This is an easy test to have, and it uses no radiation. Your child simply lies on a table, and a doctor or technician moves the transducer over the part of the body being looked at.
To learn more about these and other imaging tests, see our document Imaging (Radiology) Tests.
The results of imaging tests might strongly suggest that someone has RMS, but a biopsy (removing some of the tumor for viewing under a microscope and other lab testing) is the only way to be certain. Usually several different kinds of lab tests are done on the biopsy sample to sort out what kind of tumor it is.
Biopsies can be done in several ways. The approach used depends on where the tumor is, the age of the patient, and the expertise and experience of the doctor doing the biopsy.
The most common biopsy approach is to remove a small piece of tumor during surgery while the patient is under general anesthesia (asleep). In some cases, nearby lymph nodes are also removed to see if the tumor has spread to them. The samples are then sent to a lab and tested.
If for some reason a surgical biopsy can’t be done, a less invasive biopsy using a thin, hollow needle may be done. There are 2 kinds of needle biopsies, each of which has pros and cons.
Core needle biopsy: For a core needle biopsy, the doctor inserts a hollow needle into the tumor to withdraw a piece of it (known as a core sample). If the tumor is just under the skin, the doctor can guide the needle into the tumor by touch. But if the tumor is deep inside the body, imaging tests such as ultrasound or CT scans might be needed to help guide the needle into place. The removed core sample is then sent to the lab for testing.
The main advantage of a core needle biopsy is that it does not require surgery, so there is no large incision. Depending on where the tumor is, adults and older children might not need general anesthesia (where they are asleep for the biopsy), but some younger children might. On the other hand, the specimen is smaller than with a surgical biopsy, and if the needle isn’t aimed correctly, it might miss the cancer. If the specimen is not a good sample of the tumor, another biopsy will be needed.
Fine needle aspiration (FNA) biopsy: For this technique, the doctor uses a very thin, hollow needle attached to a syringe to withdraw (aspirate) a small tumor sample. An FNA biopsy is best suited for tumors that can be reached easily (such as those just under the skin), although it can also be used for tumors deeper in the body.
The downside of FNA is that the sample is very, very small. The pathologist must be experienced with this technique and be able to decide which lab tests will be most helpful on a very small sample. In cancer centers that have the experience to extract the most information from very small amounts of tissue, FNA can be a valuable – though certainly not foolproof – way to diagnose RMS, but it is not usually the preferred biopsy technique.
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 can tell you.
Bone marrow aspiration and biopsy
These tests aren’t used to diagnose RMS, but they are often done after the diagnosis to find out if the tumor has spread to the bone marrow (the soft inner parts of certain bones).
The 2 tests are usually done at the same time. The samples are usually taken from the back of both of the pelvic (hip) bones, but in some patients they may be taken from other bones.
These tests might be done during the surgery to treat the main tumor (while the child is still under anesthesia), or they might be done as a separate procedure.
If the bone marrow aspiration is being done as a separate procedure, the child lies on a table (on his or her side or belly). After cleaning the skin over the hip, the doctor numbs the area and the surface of the bone with local anesthetic, which can briefly sting or burn. In most cases, the child is also given other medicines to help them relax or even be asleep during the procedure. A thin, hollow needle is then inserted into the bone, and a syringe is used to suck out a small amount of liquid bone marrow.
A bone marrow biopsy is usually done just after the aspiration. Small pieces of bone and marrow are removed with a slightly larger needle that is pushed down into the bone. Once the biopsy is done, pressure will be applied to the site to help stop any bleeding.
The samples of bone and marrow are sent to the lab, where they are looked at and tested for cancer cells.
Lumbar puncture (spinal tap)
Lumbar puncture is not a common test for RMS, but it might be done for tumors in the head near the covering of the brain (the meninges). This test is used to look for cancer cells in the cerebrospinal fluid (CSF), which is the liquid that bathes the brain and spinal cord.
For this test, the doctor first numbs an area in the lower part of the back near the spine. The doctor may also recommend that the child be given something to make him or her sleep so the spinal tap can be done without difficulty or causing harm. A small, hollow needle is then inserted between the bones of the spine to withdraw some of the fluid, which is then sent to the lab for testing.
Lab tests on the biopsy samples
A doctor called a pathologist looks at the biopsy samples under a microscope to see if they contain cancer cells. If cancer is found, the next step is to figure out if it is RMS. In rare cases, the pathologist can see that the cancer cells have small muscle striations, which confirms that the cancer is RMS. But most often, other lab tests are needed to be sure.
The pathologist might use special stains on the samples to identify the type of tumor. The stains contain special proteins (antibodies) that attach to substances in RMS cells but not to other cancers. The stains produce a distinct color that can be seen under a microscope. This lets the pathologist know that the tumor is a rhabdomyosarcoma.
Sometimes the tumor will also be tested for gene or chromosome changes, such as those discussed in the section “ Do we know what causes rhabdomyosarcoma?”
If a diagnosis of RMS is made, the pathologist will also use these tests to help determine which kind of RMS it is. This is important because it affects how the cancer is treated. For example, alveolar rhabdomyosarcoma (ARMS), which tends to be more aggressive, typically requires more intense treatment than embryonal rhabdomyosarcoma (ERMS).
No blood test can be used to diagnose RMS. But certain blood tests may be helpful once a diagnosis has been made.
A complete blood count (CBC) measures the levels of white blood cells, red blood cells, and platelets in the blood. If the CBC result is abnormal at the time of diagnosis it could mean the cancer has spread to the bone marrow, where these blood cells are made.
Standard blood tests are done often to check a child’s general health both before treatment (especially before surgery) and during treatment (such as chemotherapy) to look for possible problems or side effects. These tests often include a CBC to monitor bone marrow function and blood chemistry tests to measure how well the liver and kidneys are working.
Last Medical Review: November 20, 2014 Last Revised: November 21, 2014