Biopsy 
• The diagnosis can be suggested by the above tests, but tumor tissue must be obtained by biopsy or surgery to
  confirm the tumor type and grade.
• Sometimes the tumor is small or in an area of the brain where it cannot be easily approached or safely
  removed. In such cases a special procedure called a stereotactic biopsy can be performed. A computer is used
  to plot a pathway to the tumor based upon a CT or MRI image. A small-caliber needle is then passed through
  the brain to the site of the tumor and a biopsy is obtained. This approach has proved to be very safe and
  effective in establishing a tissue diagnosis. In many cases it can be performed under local anesthesia. Patients
  can usually be discharged from the hospital the following day.
• When the tumor is accessible, a neurosurgeon may recommend an open operation (craniotomy) to attempt to
  remove some or nearly all of the tissue. Tumor samples will be sent for diagnosis at the time of the
  craniotomy.