CLASSIFICATION

Most recent classifications of brain tumours build on the 1926 work of Bailey and Cushing.² This classification named tumours after the cell type in the developing embryo/fetus or adult which the tumour cells most resembled histologically. The cell of origin of the majority of brain tumours is unknown as no pre-malignant states are recognised, as is the case in some epithelial tumour forms. In some tumours, cells may be so atypical that it is difficult to compare them with any normal cell type—hence the use of terms such as glioblastoma. Many unsound or illogical terms have remained in the classifications, as once established in a complex medical setting they are difficult to change. In this paper the terminology and definitions of the World Health Organization classification of 2000 will be exclusively used.¹ There are more than 120 entities in this classification and here we will concentrate on those that most frequently occur in adults and children. These are the pilocytic astrocytomas, ependymomas, and medulloblastomas in children, and the diffuse astrocytic tumours (including astrocytoma, anaplastic astrocytomas, and glioblastomas), oligodendrogliomas, and meningiomas in adults.

Tumours of the central nervous system often have a wide morphological spectrum and classification is dependent on the recognition of areas with the characteristic histology for a particular tumour type. Immunocytochemical methods may be required to demonstrate the expression by the tumour cells of an antigen typically expressed by a particular cell type and thus to assist in classification. Unfortunately there are …