To find out whether cancer cells have passed into the cerebrospinal fluid (CSF) which surrounds the brain and the spinal cord.

This test involves putting a needle into the spine and letting some of the fluid drain out.

Your child will be asked to lie on his/her side and to curl up slightly so that his/her back rounds towards the doctor.

A fine needle is inserted into his/her back between two vertebral bones in the lower spine and a few drops of the fluid are removed. Sometimes drugs are injected into the fluid at the same time as part of the treatment. This test is done under sedation or under local anaethetic (EMLA).