After childhood medulloblastoma has been diagnosed, tests are done to find out if there is tumor remaining or if cancer cells have spread.

The extent or spread of cancer is usually described as stages. For childhood medulloblastoma, risk groups are used instead of stages. Risk groups are described by the amount of remaining tumor or spread of cancer cells within the central nervous system (brain and spinal cord) or to other parts of the body. It is important to know the risk group in order to plan treatment. The following tests and procedures may be used to determine the risk group:

• 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 areas inside 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).
• Lumbar puncture: A procedure used to collect cerebrospinal fluid from the spinal column. This is done by placing a needle into the spinal column. This procedure is also called an LP or spinal tap.
• Bone marrow aspiration and biopsy: The removal of bone marrow, blood, and a small piece of bone by inserting a hollow needle into the hipbone or breastbone. A pathologist views the bone marrow, blood, and bone under a microscope to look for signs of cancer.
• Bone scan: A procedure to check if there are rapidly dividing cells, such as cancer cells, in the bone. A very small amount of radioactive material is injected into a vein and travels through the bloodstream. The radioactive material collects in the bones and is detected by a scanner.

The following risk categories are used for childhood medulloblastoma:

Average risk

Childhood medulloblastoma is called an average risk if all of the following are true:

• The child is older than 3 years of age.
• The tumor is at the very back of the brain.
• All of the tumor was removed by surgery or there was a very small amount remaining.
• The cancer has not spread to other parts of the body.

Poor risk

Childhood medulloblastoma is called a poor risk if any of the following are true:

• The child is younger than 3 years of age.
• The tumor is not at the very back of the brain.
• Some of the tumor was not removed by surgery.
• The cancer has spread to other parts of the body.

In general, cancer is more likely to recur (come back) in patients in the poor risk group.