This is a medical question of type : exams and tests 
 How to diagnose Childhood Non-Hodgkin Lymphoma ? 
 Tests that examine the body and lymph system are used to detect (find) and diagnose childhood non-Hodgkin lymphoma. The following tests and procedures may be used:         -   Physical exam and history : An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patients health habits and past illnesses and treatments will also be taken.    -   Blood chemistry studies : A procedure in which a blood sample is checked to measure the amounts of certain substances released into the blood by organs and tissues in the body, including electrolytes, uric acid, blood urea nitrogen (BUN), creatinine, and liver function values. An unusual (higher or lower than normal) amount of a substance can be a sign of disease.    -   Liver function tests : A procedure in which a blood sample is checked to measure the amounts of certain substances released into the blood by the liver. A higher than normal amount of a substance can be a sign of cancer.    -   CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.    -   PET scan (positron emission tomography scan): A procedure to find malignant tumor cells in the body. A small amount of radioactive glucose (sugar) is injected into a vein. The PET scanner rotates around the body and makes a picture of where glucose is being used in the body. Malignant tumor cells show up brighter in the picture because they are more active and take up more glucose than normal cells do. Sometimes a PET scan and a CT scan are done at the same time. If there is any cancer, this increases the chance that it will be found.    -   MRI (magnetic resonance imaging): A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body. This procedure is also called nuclear magnetic resonance imaging (NMRI).    -   Lumbar puncture : A procedure used to collect cerebrospinal fluid (CSF) from the spinal column. This is done by placing a needle between two bones in the spine and into the CSF around the spinal cord and removing a sample of the fluid. The sample of CSF is checked under a microscope for signs that the cancer has spread to the brain and spinal cord. This procedure is also called an LP or spinal tap.    -   Chest x-ray : An x-ray of the organs and bones inside the chest. An x-ray is a type of energy beam that can go through the body and onto film, making a picture of areas inside the body.    -   Ultrasound exam: A procedure in which high-energy sound waves (ultrasound) are bounced off internal tissues or organs and make echoes. The echoes form a picture of body tissues called a sonogram. The picture can be printed to be looked at later.
                         - A biopsy is done to diagnose childhood non-Hodgkin lymphoma: Cells and tissues are removed during a biopsy so they can be viewed under a microscope by a pathologist to check for signs of cancer. Because treatment depends on the type of non-Hodgkin lymphoma, biopsy samples should be checked by a pathologist who has experience in diagnosing childhood non-Hodgkin lymphoma.    One of the following types of biopsies may be done:         -   Excisional biopsy : The removal of an entire lymph node or lump of tissue.     -   Incisional biopsy : The removal of part of a lump, lymph node, or sample of tissue.    -   Core biopsy : The removal of tissue or part of a lymph node using a wide needle.    -   Fine-needle aspiration (FNA) biopsy : The removal of tissue or part of a lymph node using a thin needle.        The procedure used to remove the sample of tissue depends on where the tumor is in the body:         -   Bone marrow aspiration and biopsy : The removal of bone marrow and a small piece of bone by inserting a hollow needle into the hipbone or breastbone.    -   Mediastinoscopy : A surgical procedure to look at the organs, tissues, and lymph nodes between the lungs for abnormal areas. An incision (cut) is made at the top of the breastbone and a mediastinoscope is inserted into the chest. A mediastinoscope is a thin, tube-like instrument with a light and a lens for viewing. It also has a tool to remove tissue or lymph node samples, which are checked under a microscope for signs of cancer.    -   Anterior mediastinotomy : A surgical procedure to look at the organs and tissues between the lungs and between the breastbone and heart for abnormal areas. An incision (cut) is made next to the breastbone and a mediastinoscope is inserted into the chest. A mediastinoscope is a thin, tube-like instrument with a light and a lens for viewing. It also has a tool to remove tissue or lymph node samples, which are checked under a microscope for signs of cancer. This is also called the Chamberlain procedure.    -   Thoracentesis : The removal of fluid from the space between the lining of the chest and the lung, using a needle. A pathologist views the fluid under a microscope to look for cancer cells.        If cancer is found, the following tests may be done to study the cancer cells:          -   Immunohistochemistry : A laboratory test that uses antibodies to check for certain antigens in a sample of tissue. The antibody is usually linked to a radioactive substance or a dye that causes the tissue to light up under a microscope. This type of test may be used to tell the difference between different types of cancer.    -   Flow cytometry : A laboratory test that measures the number of cells in a sample, the percentage of live cells in a sample, and certain characteristics of cells, such as size, shape, and the presence of tumor markers on the cell surface. The cells are stained with a light-sensitive dye, placed in a fluid, and passed in a stream before a laser or other type of light. The measurements are based on how the light-sensitive dye reacts to the light.     -   Cytogenetic analysis : A laboratory test in which cells in a sample of tissue are viewed under a microscope to look for certain changes in the chromosomes.    -   FISH (fluorescence in situ hybridization): A laboratory test used to look at genes or chromosomes in cells and tissues. Pieces of DNA that contain a fluorescent dye are made in the laboratory and added to cells or tissues on a glass slide. When these pieces of DNA attach to certain genes or areas of chromosomes on the slide, they light up when viewed under a microscope with a special light. This type of test is used to find certain gene changes.    -   Immunophenotyping : A laboratory test used to identify cells, based on the types of antigens or markers on the surface of the cell. This test is used to diagnose specific types of lymphoma by comparing the cancer cells to normal cells of the immune system.