Approximately 29000 primary benign and malignant central nervous system tumours are diagnosed in the United States each year (CBTRUS, 1998). Histological diagnosis, location, biological tendency to infiltrate into surrounding brain, surgical resectability, and patient age at diagnosis are strong determinants of their associated morbidity and mortality. Although primary brain tumours are generally resistant to cytotoxic therapies, recent advances in chemotherapy, radiation therapy, and drug delivery in conjunction with more novel therapeutics based upon molecular and cellular biological mechanisms have created new opportunities for prolonging life and preserving the quality of life for brain tumour patients. Even though primary tumours occur infrequently (less than 2%) relative to more common systemic neoplasms such as breast, lung and prostate, they contribute substantially to cancer morbidity because they present at early- to midadult life and can rapidly cause neurological disability.

The World Health Organization (WHO) has established a histopathological classification system that divides primary brain tumours into nine separate categories on the basis of routine histochemical and immunohistochemical criteria intended to identify the cell of tumour origin (Table 87.1) (Kleihues et al., 1993). This classification scheme is a standard for pathological diagnosis and clinical decision making. It is generally recognized that all classification schemes available to date have many limitations and need to incorporate molecular and genetic criteria that reflect cellular origins and distinct pathways of transformation. The WHO category of Tumours derived from neuroepithelial tissue consists of nine subcategories that include the most common glial tumours: astrocytoma, oligodendroglioma, ependymoma, and mixed glioma. In adults, gliomas represent the largest proportion of primary brain tumours, accounting for approximately 50% of the total. Meningiomas are the next most common comprising approximately 20–25%, followed by pituitary adenomas, nerve sheath tumours and primary CNS lymphoma that each represent less than 10% of all primary brain tumours (CBTRUS, 1998). A brief summary of the most common gliomas and meningiomas follows. A more comprehensive and detailed description of primary brain tumours can be found in Tumors of the Central Nervous System(Burger & Scheithauer, 1994).

Astrocytomas

Astrocytomas are the most common of the gliomas. These tumours have a predilection for the cerebral hemispheres and occur in a range of aggressiveness or tumour ‘grade’ that, along with patient age at diagnosis, strongly predicts the tumour's biological behaviour and patient survival (Figs. 87.1 and 87.2).