Hydrocephalus

The term hydrocephalus implies an increase in the volume of cerebrospinal fluid (CSF) occupying the cerebral ventricles. This is usually s 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 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.

You may find our record on Rising Intracranial Pressure of relevance.

Classification

• 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 (e.g. due to reduced absorption or blockage of the venous drainage system²). 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. Go to our dedicated record for more information.
• 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.

• One Swedish study of congenital hydrocephalus found over a ten year period found a prevalence of hydrocephalus was 0.82 per 1000 live births, 0.49 for children with infantile hydrocephalus and 0.33 for children with myelomeningocoele.³
• The incidence of acquired hydrocephalus is unknown, but about 100,000 patients a year have shunts inserted every year in the developed world.²
• Risk factors for congenital hydrocephalus include:⁴
  • Absence of any ante-natal care
  • Maternal hypertension during pregnancy
  • Pre-eclampsia
  • Alcohol use during pregnancy
  • Maternal chronic hypertension (to a lesser extent)
  There may be a hereditary component too.

Obstructive - congenital

• Bickers-Adams syndrome (stenosis of the aqueduct of Sylvius, characterised by severe learning difficulties and in 50% by 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 - acquired¹

• Acquired aqueduct stenosis (following infection or haemorrhage)
• Supratentorial masses causing tentorial herniation
• Intraventricular haematoma
• Tumours - ventricular, pineal tumours and tumours of the posterior fossa e.g. ependymoma, subependymal giant cell astrocytoma, choroid plexus papilloma, craniopharyngioma, pituitary adenoma, hypothalamic or optic nerve glioma, hamartoma, metastatic tumours

Communicating

• Any thickening of the leptomeninges ± involvement of the arachnoid granulations e.g. infection, subarachnoid haemorrhage (spontaneous, trauma, postoperative), carcinomatous meningitis
• Any increase in CSF viscosity e.g. due to a high protein count
• Excessive CSF production e.g. due to a choroid plexus papilloma

Acquired causes in infants and children

• Mass lesions (20% of all cases in children e.g. medulloblastoma, astrocytoma)
• Intraventricular haemorrhage (e.g. 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 - e.g. hypervitaminosis A
• Idiopathic

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 sign (a "cracked pot" sound on percussing the head)
• Increased limb tone

Features in older children and adults

Acute onset:

• Headache and vomiting
• Papilloedema and impaired upward gaze

Gradual onset:

• Unsteady gait due to spasticity in the legs
• Large head (although the sutures are closed, the skull still enlarges due to chronic increased intra-cranial pressure (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
• Incontinence

'Arrested' hydrocephalus

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.

• Brainstem gliomas
• Causes of sudden visual loss
• Childhood migraine variants
• Craniopharyngioma
• Epidural haematoma
• Frontal lobe epilepsy
• Frontal lobe syndromes
• Frontal and temporal lobe dementia
• Glioblastoma multiforme
• Intracranial epidural abscess
• Intracranial haemorrhage
• Meningioma
• Oligodendroglioma
• Pituitary tumours
• Primary CNS lymphoma
• Pseudotumour cerebri
• Subdural empyema
• Subdural haematoma

Skull X-ray

The skull may appear generally enlarged and there may be signs of raised ICP such as suture diastasis and erosion of the posterior clinoids. Associated defects such as basilar invagination (when the top of the second vertebra moves upwards) may be seen.

Neuroradiology

CT scanning with or without contrast is considered to be adequate for the diagnosis of hydrocephalus. The pattern of ventricular enlargement help to determine the causes:

• 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 more clearly demonstrate periventricular abnormalities or a neoplastic cause of the obstruction.⁵

Ultrasound

Scans through the anterior fontanelle is occasionally used in infants to demonstrate ventricular enlargement instead of CT scanning.

General principles

• Management depends on how acute the deterioration is.
• 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.

Drugs

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.²

Neurosurgery

• Insertion of an external ventricular drain⁶ - 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 shunt - VA shunt) or into the peritoneal cavity (ventriculoperitoneal shunt - VP shunt), the latter being the commonest. A catheter can also drain the distal CSF in the lumbar area into the peritoneum (lumboperitoneal shunt).
• Other surgical procedures - choroid plexectomy, choroid plexus coagulation and endoscopic cerebral aquaductoplasty 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.

Of hydrocephalus

Untreated congenital hydrocephalus is often fatal within the first four years of life. Epilepsy, 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 surgery¹

• Infection
• Subdural haematoma
• Shunt obstruction
• Low pressure state

Some congenital conditions can be suspected antenatally and managed early in life to avoid the above complications. Preventative strategies for certain causes of hydrocephalus can also be implemented e.g. to prevent trauma in high risk occupations or sports. However, most of the above causes cannot be anticipated and it is the early detection and rapid intervention that underpins the management of these patients.