Tumours of the posterior fossa intrinsic

HAEMANGIOBLASTOMA (contd) Clinical features

Cerebellar signs and symptoms or the effects of CSF obstruction usually develop insidiously. Occasionally subarachnoid haemorrhage occurs. In female patients, symptoms often appear during pregnancy. Polycythaemia due to increased erythropoietin production is common.

Investigations

CT scan shows a well defined low density cyctic region in the cerebellum with a strongly enhancing nodule in the wall. Occasionally, multiple lesions are evident. MR I gives more anatomical detail (see pages 39-41).

nodule cyst nodule cyst

Management

In most patients operative removal of the tumour nodule is straightforward, but recurrences (or further tumours at other sites, e.g. spine) develop in 20%.

MEDULLOBLASTOMA

Medulloblastomas occur predominantly in childhood, with a peak age incidence of about 5 years. They arise in the cerebellar vermis and usually extend into the 4th ventricle. All are highly malignant and spread readily throughout the CSF pathways, often seeding to the lateral ventricles or the spinal theca. The origin is uncertain but appears to arise from primitive embryonic cells.

Clinical features

Destruction of the cerebellar vermis causes truncal and gait ataxia often developing over a few weeks.

Alternatively, the patient presents with signs and symptoms of raised intracranial pressure due to blockage of CSF drainage. In the very young, failure to recognise these features has resulted in permanent visual loss from severe papilledema.

Investigations

CT scan shows an isodense midline lesion in the cerebellar vermis, compressing and displacing the 4th ventricle and enhancing strongly with contrast.

Higher cuts shows dilated ventricles, sometimes containing CSF tumour seedlings.

318 MRl may provide more anatomical detail

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