Malignant brain tumours differ from cancers at most other sites in that their malignant potential is almost exclusively due to their local infiltrative growth within the brain around the region in which they arose. Staging systems comparable to those for other cancers is therefore inppropriate.
There is only rarely metastatic disease to distant sites, although some tumours such as the medulloblastoma (germ cell tumour, primary brain lymphoma and ependymoma), may seed/spread throughout the CSF space due to the 'shedding-off' of tumour cells into the CSF.
The extent of the growth is assessed by MRI scanning of the brain/spine at the time of diagnosis.
