Hydrocephalus means that there is an excessive amountof CSF within the cranium. Although this also occurs in cerebral atrophy, in practice the term hydrocephalus is used to describe different syndromes in which there is, or has been, obstruction to CSF outflow with consequent high pressure and dilatation of the cerebral ventricles. Exceptionally an increase in CSF production occurs.
• Infantile hydrocephalus
Enlargement of the head in infancy is diagnosed in about 1 in 2000 live births. There are several causes: ARNOLD-CHIARI MALFORMATION. There is elongation of the medulla and abnormal cerebellar tissue
(the tonsils) in the cervical canal. Associated spina bifida is common. Syringomyelia may develop. DANDy-WALKER SYNDROME. There is cerebellar hypoplasia and obstruction to the outflow foramina of the fourth ventricle.
STENOSIS OF THE AQUEDUCT OF SYLVIUS (Fig. 18.21). This may be either congenital or acquired following neonatal meningitis or haemorrhage.
Hydrocephalus in adult life
Infantile hydrocephalus not infrequently becomes symptomaticonly in adult life. The features are of headache, vomiting, papilloedema , ataxia and bilateral pyramidal signs.
Hydrocephalus in adults also occurs with:
TUMOURS OF THE POSTERIOR FOSSA AND BRAIN STEM. These obstruct the aqueduct or fourth ventricular outflow.
SUBARACHNOID HAEMORRHAGE, HEAD INJURY OR MENINGITIS (PARTICULARLY TUBERCULOUS). The ydrocephalus is often a transient phenomenon.
TUMOURS OF THE THIRD VENTRICLE. A colloid cyst of the third ventricle causes enlargement of the lateral entricles, headache and papilloedema.
NORMAL-PRESSURE HYDROCEPHALUS. In this syndrome enlarged cerebral ventricles occur without cortical atrophy. It presents with dementia, urinary incontinence and apraxia, usually in the elderly. The
CSF pressure is characteristically normal. It is currently thought that this syndrome is the late result of previous episodes of high pressure, though usually of unknown cause.
PAPILLOMA OF THE CHOROID PLEXUS. This is an extremely rare neoplasm that secretes CSF. Ventriculo-atrial or ventriculo-peritoneal shunting may be necessary when hydrocephalus is diagnosed.
Idiopathic (or benign) intracranial hypertension
This syndrome consists of marked papilloedema without other signs in patients who are subsequently shown to have neither a mass lesion nor an increase in ventricular size. It occurs mainly in obese young women with vague menstrual irregularities. Steroid therapy is sometimes thought to be a cause and many other drugs have seen occasionally implicated. Other causes of papilloedema should be excluded. The condition is benign only in that it is not fatal. Infarction of the optic nerve occurs (with consequent blindness) when the papilloedema is severe and longstanding. Surgical decompression or shunting may be necessary. Thiazide diuretics appear to reduce the intracranial pressure in this condition. Weight reduction is important.