A lymphangiogram is a special x-ray of the lymph nodes and lymph vessels. Lymph nodes produce white blood cells (lymphocytes) that help fight infections. The lymph nodes also filter and trap cancer cells.

The lymph nodes and vessels are not usually seen on a normal x-ray, so a dye or radioisotope (radioactive compound) is injected into the body to highlight the area being studied.

The test is done in a hospital radiology department or a health care provider's office.

If you are having the test done because of leg or arm swelling, you may be offered a sedative before the test to help you relax. You sit in a special chair or on an x-ray table. The health care provider cleans your feet, and then injects a small amount of blue dye into the webbing between your toes.

Thin, bluish lines appear on the top of the foot within 15 minutes. These lines identify the lymph channels. The health care provider numbs the area, makes a small surgical cut into one of the larger blue lines, and inserts a thin flexible tube into a lymph channel. This is done for each foot. Dye (contrast medium) flows through the tube very slowly, over a period of 60 to 90 minutes.

A special x-ray machine, called a fluoroscope, projects the images on a TV monitor. The health care provider uses the images to follow the dye as it spreads through the lymphatic system up your legs, groin, and along the back of the abdominal cavity.

Once the dye is completely injected, the catheter is removed and stitches are used to close the surgical cut. The area is bandaged. X-rays are taken of the legs, pelvis, abdomen, and chest areas. More x-rays may be taken the next day.

If the test is being done to see if breast cancer or melanoma has spread, the blue dye is mixed with a radioactive compound. Special cameras watch how the tracer spreads along lymph channels to outlying nodes. This can help surgeons better understand where the cancer has spread when a biopsy is being performed.

You must sign a consent form. You may be asked to not eat or drink for several hours before the test. You may wish to empty your bladder just before the test.

Tell the health care provider if you are pregnant or you have bleeding problems. Also mention if you've had allergic reactions to x-ray contrast material or any iodine-containing substance.

If you having this test done with sentinel lymph node biopsy (for breast cancer and melanoma), you will need to prepare for the operating room. A surgeon and anesthesiologist will tell you how to prepare for the procedure.

Some patients feel a brief sting when the blue dye and numbing medicines are injected. You may feel pressure as the dye starts to flow into your body, particularly behind the knees and in the groin area.

The surgical cuts will be sore for a few days. The blue dye causes urine and stool discoloration for about 2 days. Your skin and possibly vision will temporarily appear blue.

A lymphangiogram is used with lymph node biopsy to determine the possible spread of cancer and the effectiveness of cancer therapy.

Contrast dye and x-rays are used to help determine the cause of swelling in an arm or leg and check for diseases that may be caused by parasites.

Additional conditions under which the test may be performed:

• Hodgkin's lymphoma
• Non-Hodgkin's lymphoma

Enlarged nodes (swollen glands) that have a foamy appearance may be a sign of lymphatic cancer.

Nodes or parts of the nodes that do not fill with the dye suggest a blockage and may be a sign of cancer spreading through the lymph system. Blockage of the lymph vessels may be caused by tumor, infection, injury, or previous lymphatic surgery.

Talk to your doctor about the meaning of your specific test results.

Risks related to the injection of the dye (contrast medium) may include:

• Allergic reaction
• Fever
• Infection
• Inflammation of the lymph vessels

There is low radiation exposure. However, most experts feel that the risk of most x-rays is smaller than other risks we take every day. Pregnant women and children are more sensitive to the risks of the x-ray.

The dye (contrast medium) can stay in the lymph nodes for up to 2 years.