Pathology

Primary brain tumour pathology is extremely varied reflecting diverse histogenesis. The most widely used classification system is the WHO 1993 scheme. Gliomas are the most common tumours. Their behaviour and prognosis are strongly linked to histological subtype. Benign tumours (e.g. meningiomas) are not uncommon and some malignant non-glial tumours carry a good prognosis (medulloblastoma, pineal

Table 25.1 Syndromes associated with primary brain tumours

Predisposing syndrome

Tumour

Neurofibromatosis type 1

Glioma

Neurofibromatosis type 2

Glioma, meningioma, Schwannoma

Li-Fraumeni syndrome

Glioma

von Hippel-Lindau syndrome

Cerebellar haemangioblastoma

Gardener's syndrome

Glioma

Familial glioma

Glioma

Tuberose sclerosis

Subependymal giant cell astrocytoma

germinoma). Precise histological identification is therefore essential to appropriate management.

Primary brain tumours rarely metastasize outside the CNS but are highly infiltrative, with a tendency to spread along white matter tracts to more distant regions of the brain, a feature which contributes to their resistance to treatment. Spread through cerebrospinal fluid (CSF) to remote areas of the neuraxis is a feature of germ cell tumours, medulloblastoma, and other primitive neuroectodermal tumours. This has important implications for their treatment.

The dominant prognostic features for the majority of brain tumours are usually a combination of histological type and clinical features such as age and performance status. Therefore, staging systems that are commonly used for other tumour types are rarely used for brain tumours. Molecular changes associated with glioblastoma are:

♦ Type 1—loss of tumour suppression (p53 mutation in 65%)

—oncogene upregulation —chromosome changes —younger patients

—may arise in pre-existing low-grade tumour —better prognosis

♦ Type 2—mainly chromosome changes

—oncogene overexpression —older patients —poor prognosis

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