The diagnosis of a brain tumor requires a number of tests. Other conditions can cause similar symptoms, making the diagnosis of a brain tumor complicated. Initially, a physician will obtain the patient’s complete medical history and perform a physical examination. The examination will include a detailed neurological examination to assess the patient’s brain and spinal cord functions. If a brain tumor is suspected, a number of diagnostic procedures may be indicated, including:

• CAT scan (computed axial tomography). This x-ray procedure produces detailed cross-sectional images of the body. It may be done with contrast material (dye) that can help outline structures in the body. For brain tumors, a CAT scan can show the exact location of the tumor.
  
  
• MRI (magnetic resonance imaging). An MRI uses radio waves, magnets and a computer to create a detailed image of the body. It can produce cross-sectional images from a number of different angles. MRIs are useful in detecting brain tumors because they outline soft tissues as well as bones. Sn MRI can also help detect some conditions associated with brain tumors, such as  swelling or hemorrhaging (bleeding). According to the American Cancer Society (ACS), an MRI or CAT scan will detect a brain tumor, if present, 95 percent of the time.
  
  
• Magnetic resonance spectroscopy. This test uses radio waves similar to an MRI, but the waves interact with atoms within the brain tumor tissues. The result is an image that highlights some features of the tumor that may not be clearly seen in an MRI. Use of this technique for diagnosis of brain tumors is still experimental.
  
  
• PET scan (positron emission tomography).  In this test, a radioactive glucose (sugar) substance is injected into the patient and images are taken of the brain. The cancer cells react with the glucose substance and provide information about the chemistry of the tumor. A PET scan is usually not used for the initial diagnosis of a brain tumor but provides physicians with supplemental information about its metabolism and can help detect the spread of cancer.
  
  
• Angiography.  This imaging test uses a special dye injected into the patient’s bloodstream. The dye flows through the blood vessels in the brain and can be seen on an x-ray. It provides physicians with information as to how the tumor is supplied with blood. It is often used to help physicians plan their surgery.
  
  
• Spinal tap (also called lumbar puncture).  A needle is placed in the lower back under local anesthesia and a small sample of cerebrospinal fluid is extracted. The fluid is examined under a microscope for the presence of cancer cells. Lumbar punctures are particularly important with people suspected of having brain lymphomas. In this type of brain cancer, the lymphoma cells often spread into the spinal fluid.
  
  
• Biopsy.  A biopsy is the removal of tissue from a tumor for examination by a pathologist for cancer cells. To obtain a sample for diagnosis, a neurosurgeon may surgically open the skull and remove a piece of the tumor. In some situations, the neurosurgeon may be able to remove the tissue sample through a stereotactic biopsy. In this procedure, a small hole is drilled into the skull and a thin needle is carefully guided into the tumor. With the help of a CAT or MRI scan and a computer to localize the tumor, a tissue sample is removed through the needle. 
  
  Through a biopsy sample, a pathologist can determine if the tumor is benign (non-cancerous) or malignant (cancerous) as well as the exact cell type and grade (severity). A biopsy is the definitive way to diagnose cancer.