Tumours of the posterior fossa intrinsic

MEDULLOBLASTOMA (contd) Management

Staging is essential because of the high incidence of leptomeningeal spread and bone marrow involvement. Assess this with spinal MR I with gadolinium, CSF analysis and bone marrow examination.

Operation: The aim is to remove as much tumour as possible, yet producing minimal damage to surrounding tissue, in particular crucial structures in the floor of the 4th ventricle. Some patients require a CSF shunt, although this provides a further potential route for tumour seeding.

Radiotherapy: Medulloblastomas are radiosensitive. Whole neural axis irradiation attempts to cover any CSF seeding.

Chemotherapy: Although medulloblastomas respond to chemotherapy and are routinely treated, the extent to which they alter the quality or duration of survival is far less certain.

Prognosis

Studies in the last decade show a 5-year survival of approximately 40-60%. With present treatment methods, it is hoped this figure will approach 70%.

CEREBELLAR ASTROCYTOMA

In contrast to astrocytomas of the cerebral hemispheres, cerebellar astrocytomas are usually low grade tumours of the fibrillary or pilocytic types. They are particularly common in children and carry an excellent prognosis. Occasionally a more diffuse or anaplastic type occurs with a less favourable outcome. They usually lie in the cerebellar hemisphere or vermis but occasionally extend through a peduncle into the brain stem. Many have cystic components.

Clinical features

Cerebellar signs and symptoms tend to develop gradually over many months; if CSF obstruction occurs, the patient may present acutely with headache, papilledema and deteriorating conscious level.

Investigations

CT scan - density changes and the degree of contrast enhancement are variable.

Management

Ideally, complete operative removal is attempted provided the brain stem is not involved. With 'juvenile' pilocytic tumours, long-term survival is likely. Even after partial removal 'cures' have been reported; although histologically similar to some supratentorial lesions, growth characteristics clearly differ. Persistent hydrocephalus may require a ventriculoperitoneal shunt. 319

Often a low density cystic area abuts or encircles the tumour mass

Displaced 4th ventricle

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