This is a medical question of type : exams and tests 
 How to diagnose Primary CNS Lymphoma ? 
 Tests that examine the eyes, brain, and spinal cord are used to detect (find) and diagnose primary CNS 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.    -   Neurological exam : A series of questions and tests to check the brain, spinal cord, and nerve function. The exam checks a persons mental status, coordination, ability to walk normally, and how well the muscles, senses, and reflexes work. This may also be called a neuro exam or a neurologic exam.    -   Slit-lamp eye exam : An exam that uses a special microscope with a bright, narrow slit of light to check the outside and inside of the eye.    -   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 brain and spinal cord. A substance called gadolinium is injected into the patient through a vein. The gadolinium collects around the cancer cells so they show up brighter in the picture. This procedure is also called nuclear magnetic resonance imaging (NMRI).     -   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.     -   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 of tumor cells. The sample may also be checked for the amounts of protein and glucose. A higher than normal amount of protein or lower than normal amount of glucose may be a sign of a tumor. This procedure is also called an LP or spinal tap.     -   Stereotactic biopsy : A biopsy procedure that uses a computer and a 3-dimensional (3-D) scanning device to find a tumor site and guide the removal of tissue so it can be viewed under a microscope to check for signs of cancer. The following tests may be done on the samples of tissue that are removed:                -  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.      -  Immunohistochemistry : A 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.      -  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. Other tests, such as fluorescence in situ hybridization (FISH), may also be done to look for certain changes in the chromosomes.             -   Complete blood count (CBC) with differential : A procedure in which a sample of blood is drawn and checked for the following:                - The number of red blood cells and platelets.      -  The number and type of white blood cells.      -  The amount of hemoglobin (the protein that carries oxygen) in the red blood cells.      -  The portion of the blood sample made up of red blood cells.               -   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. An unusual (higher or lower than normal) amount of a substance can be a sign of disease.