This is a medical question of type : exams and tests 
 How to diagnose Childhood Astrocytomas ? 
 Tests that examine the brain and spinal cord are used to detect (find) childhood astrocytomas. The following tests and procedures may be used:         -   Physical exam and history : An exam of the body to check general signs of health. This includes 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, and 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.     -  Visual field exam: An exam to check a persons field of vision (the total area in which objects can be seen). This test measures both central vision (how much a person can see when looking straight ahead) and peripheral vision (how much a person can see in all other directions while staring straight ahead). The eyes are tested one at a time. The eye not being tested is covered.    -   MRI (magnetic resonance imaging) with gadolinium : A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of the brain and spinal cord. A substance called gadolinium is injected into 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). Sometimes magnetic resonance spectroscopy (MRS) is done during the same MRI scan to look at the chemical makeup of the brain tissue.
                    Childhood astrocytomas are usually diagnosed and removed in surgery. If doctors think there may be an astrocytoma, a biopsy may be done to remove a sample of tissue. For tumors in the brain, a part of the skull is removed and a needle is used to remove tissue. Sometimes, the needle is guided by a computer. A pathologist views the tissue under a microscope to look for cancer cells. If cancer cells are found, the doctor may remove as much tumor as safely possible during the same surgery. Because it can be hard to tell the difference between types of brain tumors, you may want to have your child's tissue sample checked by a pathologist who has experience in diagnosing brain tumors.     The following test may be done on the tissue that was removed:         -   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. An MIB-1 test is a type of immunohistochemistry that checks tumor tissue for an antigen called MIB-1. This may show how fast a tumor is growing.        Sometimes tumors form in a place that makes them hard to remove. If removing the tumor may cause severe physical, emotional, or learning problems, a biopsy is done and more treatment is given after the biopsy.   Children who have NF1 may form a low-grade astrocytoma in the area of the brain that controls vision and may not need a biopsy. If the tumor does not continue to grow or symptoms do not occur, surgery to remove the tumor may not be needed.