The term hydrocephalus implies an increase in the volume of cerebrospinal fluid (CSF) occupying the cerebral ventricles. This is usually as a result of impaired absorption but it may occasionally be due to excessive secretion.Hydrocephalus may be categorised in various ways but all forms are considered essentially to be disorders of CSF hydrodynamics.
In the presence of increased CSF (due to reduced flow or absorption), there is ventricular dilatation and, subsequently, CSF permeates through the ependymal lining into the periventricular white matter. This results in white matter damage and gliotic scarring. Untreated hydrocephalus may result in death.
'Arrested' hydrocephalus is said to have occurred when the intracranial pressure (ICP) returns to normal, despite the ventricles remaining dilated. The CSF absorption appears to have balanced production. In the infant, normal development resumes but any pre-existing damage remains.
See separate Raised Intracranial Pressure article.
- Non-communicating/obstructive - the flow of CSF is obstructed within the ventricles or between the ventricles and the subarachnoid space.
- Communicating - there is communication between the ventricles and the subarachnoid space and the problem lies outside of the ventricular system (eg, due to reduced absorption or blockage of the venous drainage system). It may also be due to increased CSF production.
Other terms connected with hydrocephalus are:
- Normal pressure hydrocephalus - the CSF pressure remains normal or is only intermittently raised. See separate Normal Pressure Hydrocephalus article.
- Hydrocephalus ex vacuo - this describes ventricular expansion secondary to brain atrophy and shrinkage, such as in Alzheimer's disease and Pick's disease. There is no increase in CSF pressure.
There is some evidence that the incidence of paediatric hydrocephalus has declined in many developed countries. However, there are others citing improved survival of premature infants as a cause of increased rates. Higher rates of neonatal infection and neural tube defects in developing countries are linked to higher rates of hydrocephalus.
- One Swedish study of congenital hydrocephalus found over a ten-year period a prevalence of hydrocephalus was 0.82 per 1,000 live births, 0.49 for children with infantile hydrocephalus and 0.33 for children with myelomeningocele.
- The incidence of acquired hydrocephalus is unknown, but about 100,000 patients a year have shunts inserted in the developed world.
- Risk factors for congenital hydrocephalus include:
- Absence of any antenatal care.
- Maternal hypertension during pregnancy.
- Alcohol use during pregnancy.
- Maternal chronic hypertension (to a lesser extent).
Obstructive - congenital
- Bickers-Adams syndrome (stenosis of the aqueduct of Sylvius, characterised by severe learning difficulties; there may also be an adduction-flexion deformity of the thumb.
- Dandy-Walker malformation (atresia of the foramina of Magendie and Luschka).
- Arnold-Chiari malformation type 1 and type 2.
- Agenesis of the foramen of Monro.
- Vein of Galen aneurysm.
- Congenital toxoplasmosis.
Obstructive - acquired
- Acquired aqueduct stenosis (following infection or haemorrhage).
- Supratentorial masses causing tentorial herniation.
- Intraventricular haematoma.
- Tumours - ventricular, pineal tumours and tumours of the posterior fossa - eg, ependymoma, subependymal giant cell astrocytoma, choroid plexus papilloma, craniopharyngioma, pituitary adenoma, hypothalamic or optic nerve glioma, hamartoma, metastatic tumours.
- Any thickening of the leptomeninges ± involvement of the arachnoid granulations - eg, infection, subarachnoid haemorrhage (spontaneous, trauma, postoperative), carcinomatous meningitis.
- Any increase in CSF viscosity - eg, due to a high protein count.
- Excessive CSF production - eg, due to a choroid plexus papilloma.
Acquired causes in infants and children
- Mass lesions - eg, medulloblastoma, astrocytoma.
- Intraventricular haemorrhage (eg, prematurity, head injury, or rupture of a vascular malformation).
- Infections - meningitis, cysticercosis in some areas.
- Increased venous sinus pressure - can be related to achondroplasia, some craniostenoses, venous thrombosis.
- Iatrogenic - eg, hypervitaminosis A.
Other causes of hydrocephalus in adults
- Idiopathic (one third of cases).
- Iatrogenic - posterior fossa surgery.
- Normal pressure hydrocephalus.
- All causes of hydrocephalus described in infants and children.
Presenting symptoms depend on age, disease progression and individual differences in tolerance to CSF pressure changes.
Features in infants
Presentation varies depending on whether the hydrocephalus is of acute or gradual onset. The former tends to present with irritability, vomiting and impaired conscious level. The latter manifests itself as failure to thrive and developmental delays. Other signs include:
- Rapid increase in head circumference or head circumference is in the 98th percentile for the age or greater.
- Dysjunction of sutures, dilated scalp veins, tense fontanelle.
- Setting-sun sign (both ocular globes are deviated downward, the upper lids are retracted and the white sclerae may be visible above the iris).
- Macewen's sign (a 'cracked pot' sound on percussing the head).
- Increased limb tone.
Features in older children and adults
- Headache and vomiting.
- Papilloedema and impaired upward gaze.
- Unsteady gait due to spasticity in the legs.
- Large head (although the sutures are closed, the skull still enlarges due to chronic increased ICP.
- Unilateral or bilateral sixth nerve palsy secondary to increased ICP.
Other features specific to adults
- Cognitive deterioration
- Neck pain
- Nausea and vomiting
- Blurred and double vision
These individuals remain asymptomatic on the whole but a rapid return of further pressure symptoms can occur following minor injury or infection, suggesting an inherent instability of CSF dynamics.
- Tumours; brainstem gliomas, craniopharyngioma, glioblastoma multiforme, meningioma, oligodendroglioma, pituitary tumours, primary CNS lymphoma, pseudotumour cerebri.
- Causes of sudden visual loss.
- Types of childhood migraine.
- Bleeding; epidural haematoma, intracranial haemorrhage, subdural haematoma.
- Frontal lobe syndromes or epilepsy.
- Frontal and temporal lobe dementia.
- Infection; intracranial epidural abscess, subdural empyema.
CT scanning with or without contrast is considered to be adequate for the diagnosis of hydrocephalus. The pattern of ventricular enlargement helps to determine the cause:
- Dilated lateral + 3rd ventricle:
- With normal 4th ventricle - aqueduct stenosis.
- With abnormal 4th ventricle - posterior fossa mass.
- Generalised ventricular dilatation suggests a communicating hydrocephalus.
MRI may be required to demonstrate periventricular abnormalities or a neoplastic cause of the obstruction more clearly.
Scans through the anterior fontanelle are occasionally used in infants to demonstrate ventricular enlargement, instead of CT scanning.
- Management is dictated by the severity of the deterioration..
- Drugs are usually used as a holding measure until the appropriate intervention can be carried out.
- A lumbar puncture may be used in the management of acute deterioration if there is a communicating hydrocephalus. Repeated lumbar punctures may avoid neurosurgery if the condition is likely to resolve spontaneously.
- Gradual deterioration allows for a more ample assessment and careful consideration of options. Underlying causes such as tumours need to be identified and addressed.
- 'Arrested' hydrocephalus needs no treatment if it remains asymptomatic but the patient will benefit from regular developmental or psychometric assessments to catch any ill effects early.
Medication may help to defer surgery in order to stabilise the patient but medical treatment alone is generally unsuccessful in long-term control of ICP. Furosemide and acetazolamide inhibit secretion of CSF by the choroid plexus. Isosorbide promotes reabsorption.
- Insertion of an external ventricular drain.This allows for the temporary drainage of the CSF into an external collecting system. It can be created by externalising an existing system in situ or by creating a new system.
- Insertion of a shunt. This is performed in the majority of cases. A ventricular catheter drains the CSF through a small reservoir (placed on the surface of the scalp, to enable CSF aspiration for analysis) down to either the right atrium of the heart (ventriculoatrial (VA) shunt) or into the peritoneal cavity (ventriculoperitoneal (VP) shunt) - the latter being the most common. A catheter can also drain the distal CSF in the lumbar area into the peritoneum (lumboperitoneal (LP) shunt).
- Other surgical procedures - choroid plexectomy, choroid plexus coagulation and endoscopic cerebral aqueductoplasty have all been helpful in some cases. Endoscopic fenestration of the floor of the third ventricle may be effective in non-communicating hydrocephalus but is contra-indicated in communicating hydrocephalus.
Untreated congenital hydrocephalus is often fatal within the first four years of life. Epilepsy, and learning and developmental difficulties are some of the more common complications encountered. However, if treatment precedes irreversible brain damage, the outlook is good. The prognosis in other conditions depends on the underlying cause.
Of shunt surgery
- Infection (3-27%)
- Subdural haematoma
- Shunt obstruction
- Low pressure state
Some congenital conditions can be diagnosed antenatally and managed early in life to avoid complications. Preventative strategies for certain causes of hydrocephalus can also be implemented - eg, to prevent trauma in high-risk occupations or sports. However, most cannot be anticipated and it is the early detection and rapid intervention that underpins the management of these patients.
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