Two imaging tests are used to diagnose brain cancer: computed tomography and magnetic resonance imaging (MRI). Both are performed after giving a patient an injection of a radioactive material called a contrast agent, which will cause abnormal tissue to show up more clearly on the scan.

In computed tomography, also called CT or CAT scanning, a scanner moves around the body taking X-rays, which a computer then combines to make a three-dimensional image of the inside of the body. MRI is a more expensive test that provides a similar but more accurate image of the interior of the body using strong magnets, radio waves and a computer.

The next step, if these imaging tests reveal the presence of a tumor, is to take a sample of the tissue, or biopsy. A neuropathologist will examine the tissue to determine the type and grade of the tumor. Depending on the location of the tumor, the biopsy may be taken stereotactically or during a craniotomy. The tumor will be removed during this procedure if possible.

In stereotactic surgery or biopsy, the tumor location within the brain is determined using a three-dimensional coordinate system and a series of imaging tests. The surgeon will then insert his or her instruments into the brain through a small opening in the skull, using the coordinates to reach the tumor. He or she may also be guided by a computer system. In a craniotomy, a section of the skull is removed to allow the surgeon access to a larger part of the brain.