Central nervous system (CNS) tumours are both numerically and clinically important. They share a similar incidence with acute leukaemia, making them the commonest group of solid tumours. However, such a statement masks the histological and clinical diversity of this group of tumours. Included within the category are both classically described ‘benign’ and ‘malignant’ tumour types. Outside the brain, these terms confer a meaningful prediction of the risk of tumour spread, tumour recurrence, sensitivity to treatment, and subsequent prognosis. The application of these terms within the brain is less clear cut, as additional factors such as the age of the patient and the anatomical site of the tumour are also critical factors which dictate life expectancy. Furthermore, the histological grading of tumours can underestimate malignant potential either because of sampling error in heterogenous tumours or because tumours evolve into a more malignant phenotype.

The commonest tumour type is the astrocytic tumour that can be classified as either high grade (malignant) or low grade (benign). High grade astrocytic tumours are rare but are associated with a very poor prognosis because of their propensity to recur locally, and spread within the CNS. Low grade astrocytic tumours include a wide variety of discrete histological entities that tend to grow slowly and recur many years after primary diagnosis. The commonest malignant tumours are in the embryonic tumour group, which includes medulloblastoma and primitive neuroectodermal tumours (MB/PNET). Many of the tumours carry an abysmal prognosis for survival: diffuse intrinsic brainstem gliomas 0–15%,1 2 glioblastoma multiforme 0%, and anaplastic astrocytomas 30%.3 4 Even an embryonal tumour such as MB/PNET carries a five year survival of only 60% and a lower 10 year survival.5 One unifying theme in all these tumours is their occurrence in a developing CNS that is vulnerable to local effects of …