Central nervous system tumours cause considerable morbidity and have a high mortality rate. The overall incidence is 5/100 000 population year, and malignant gliomas alone account for 2.5 per cent of all deaths due to cancer.

The WHO classification of central nervous system tumours is shown in Table 1 596. Over 50 per cent of cerebral tumours are neuroepithelial in origin; metastatic tumours (15 per cent), meningiomas (15 per cent) and pituitary tumours (8 per cent) account for the other common tumours of the central nervous system. Little is known of their aetiology. Although there is an increased incidence of central nervous system tumours in neurofibromatosis (glioma, meningioma, and acoustic neuroma), tuberous sclerosis (astrocytoma) and Von Hippel-Lindau syndrome (haemangioblastoma), no other genetic or environmental risk factors are known.

All tumours of the central nervous system present with one or a combination of raised intracranial pressure, focal signs (see Table 2 597), and epilepsy. The remainder of this chapter will focus on gliomas and metastatic tumours, the most common central nervous system tumours seen in adults, and on posterior fossa tumours, most commonly seen in children.

Gliomas account for approximately 50 per cent of adult central nervous system tumours in adults, and are usually supratentorial. The tumour represents a proliferation of one of the glial cell types (astrocytes, oligodendrocytes, ependymal cells, and neuroglial precursors), but within any tumour a mixture of cells may be found. Gliomas are divided into four histological grades, according to the presence or absence of mitoses, necrosis, endothelial proliferation, and nuclear atypia. Grade 1/2 tumours, usually present with a long history (years), suggesting very slow growth; median survival of patients is long. Grade 4 gliomas (glioblastoma multiforme) invariably present with a history of just a few weeks or months and show a good initial response to steroids, but carry a poor prognosis.

A careful history and detailed examination, including an interview with the family, will enable an accurate pathological and anatomical diagnosis to be made. This is vital for the appropriate management of these tumours.

CT scanning, with and without contrast enhancement will provide additional information about the site and size of the tumour to enable further treatment to be planned. A computer-derived lateral topogram will greatly assist in localization of the tumour and planning surgical approach. MRI with and without gadolinium enhancement is especially useful for visualizing and delineating the extent of low grade gliomas.

Management is dependent upon many factors, including the length of the history, age of the patient, presence or absence of focal signs, and the presence or absence of raised intracranial pressure. Treatment usually involves a combination of surgery and radiotherapy.

Surgery allows tissue to be obtained for confirmation of the diagnosis. Microscopic removal of tumour mass can be undertaken to reduce intracranial pressure and alleviate the focal signs. Surgical reduction of tumour mass may also be performed as a precursor to radiotherapy or other adjuvant therapy.

Radiotherapy may take the form external beam irradiation (5–6000 cGy over 5–6 weeks), stereotactic focal irradiation using a linear accelerator, gamma knife or proton beam, or brachytherapy (stereotactic implantation of radiation source).

Other therapy may be appropriate. Chemotherapy has limited application; either single drugs or a combination of agents may be used. Photodynamic therapy involves selective uptake of a sensitizer into tumour cells and subsequent destruction of that cell by light activation of the sensitizer. In view of the poor prognosis associated with high grade gliomas, conservative treatment (with or without biopsy) must be considered for selected patients.

Cerebral metastases are found in 30 per cent of patients with systemic cancer, and these account for 15 per cent of cerebral tumours. The common sites of origin are shown in Table 3 598. The majority of metastases occur in distal arterial fields, especially those of the middle cerebral artery and posterior fossa. They are usually multiple (Fig. 3) 2279 and no other evidence of systemic spread of disease can be found in 50 per cent of patients.

Metastases present in the same way as other central nervous system tumours, although often with a shorter history and with rapid elevation of intracranial pressure due to the intense steroid-sensitive oedema generated around the lesion. Metastatic melanoma and renal carcinoma often present with intracerebral haemorrhage.

CT scanning shows metastases as hypodense lesions which show uniform enhancement. Melanoma and gastrointestinal tract adenocarcinoma are often hyperdense prior to enhancement. MRI scanning often reveals multiple small metastatic deposits which may not be seen on CT scans. A chest radiograph is vital to enable either a primary source or other metastases to be identified.

Surgery is appropriate if the primary site is unknown and histological diagnosis is in doubt, or if the patient presents with a single intracranial lesion in an accessible site. Even if the primary tumour is poorly controlled, excision of the cerebral metastatic lesion may provide excellent symptomatic relief. Radiotherapy is used to treat multiple metastases and also after surgical excision of a solitary lesion (3000 cGy over 14 days).

Tumours of the central nervous system account for 20 per cent of childhood malignancies, and the majority of these (60 per cent) develop in the posterior fossa. Patients present with a history of raised intracranial pressure (headache, vomiting, papilloedema), together with focal signs which may include truncal and limb ataxia, brain-stem signs, head tilt, and neck stiffness. In infants the non-specific nature of early symptoms often leads to a delay in presentation; diagnosis depends upon a high clinical index of suspicion.

Cystic cerebellar astrocytomas (30 per cent), medulloblastomas (30 per cent) and ependymal tumours (20 per cent) are the most common, but other tumours should be considered. These include choroid plexus papillomas (irregular isodense or hyperdense, enhancing, partly calcified tumours in the region of the trigone or fourth ventricle, and associated with an increase in cerebrospinal fluid), haemangioblastomas, and chordomas.

These benign, slow growing, often cystic tumours present with a history of progressive raised pressure and associated focal signs. CT scan shows a large cystic or solid tumour with associated hydrocephalus (Fig 5) 2281. Immediate shunting may be required to relieve raised intracranial pressure prior to surgical excision of the solid tumour and drainage of the tumour cyst. Complete excision carries a good prognosis, and adjuvant radiotherapy is not usually required.

This is a malignant, small cell cerebellar tumour, usually in the midline, which presents with a short history of raised intracranial pressure, often without focal signs. CT scan shows an enhancing tumour, often filling the fourth ventricle; there is associated hydrocephalus. High signal intensity is seen on MRI scan, with variable gadolinium enhancement.

Treatment is by complete surgical excision followed by cranio-spinal irradiation after staging by myelography or MRI. Combination chemotherapy provides a valuable adjunct, especially in children under 2 years of age. Despite aggressive surgery, radiotherapy, and chemotherapy, patients treated for medulloblastoma have a survival rate of 65 per cent at 5 years, falling to 40 per cent at 10 years.

Ependymomas arise from the lining of the floor of the fourth ventricle. They present with raised intracranial pressure, together with focal and sometimes brain-stem signs. These tumours are clinically, and often radiologically, indistinguishable from medulloblastoma (Fig. 7) 2283. Treatment involves microscopic surgical excision with whole neuraxis radiotherapy. A boost dose of radiation is usually given to the site of origin of the tumour. Complete surgical excision is associated with a good prognosis.

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