Hydrocephalus

The term hydrocephalus implies an increase in the volume of cerebrospinal fluid (CSF) occupying the cerebral ventricles. Hydrocephalus may be categorised in various ways, but all forms are now considered essentially to be disorders of CSF hydrodynamics, more commonly resulting from impaired absorption than increased production of fluid.

Terms Used When Describing Hydrocephalus¹

• Communicating This implies communication between the ventricles and the subarachnoid space. It is usually due to increased CSF production, but occasionally may be due to reduced absorption or blockage of the venous drainage system.²
• Non-communicating The flow of CSF is obstructed within the ventricles or between the ventricles and the subarachnoid space. Congenital causes include Arnold-Chiari³ and Dandy Walker syndromes.⁴
• Normal pressure hydrocephalus The CSF pressure remains normal or is only intermittently raised. Failure to reabsorb the CSF is compensated by reduced production. The condition may be congenital or acquired. There are two types of congenital hydrocephalus, that associated with myelomeningocoele and that occurring without (also known as infantile hydrocephalus).
• Hydrocephalus ex vacuo This is seen in conditions associated with cerebral atrophy and shrinkage, such as Alzheimer's Disease and Pick's Disease. The ventricles expand and 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.⁵ The incidence of acquired hydrocephalus is unknown, but about 100,000 patients a year have shunts inserted every year in the developed world.²

Congenital causes in infants and children

• Stenosis of the aqueduct of Sylvius
• Dandy-Walker malformation/Arnold-Chiari malformation type 1 and type 2
• Agenesis of the foramen of Monro
• Congenital toxoplasmosis
• Bickers-Adams syndrome (stenosis of the aqueduct of Sylvius, severe mental retardation, and in 50% by an adduction-flexion deformity of the thumb)

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

Causes of hydrocephalus in adults

• Subarachnoid haemorrhage
• Idiopathic (one third of cases)
• Head injury
• Tumours (e.g. ependymoma, subependymal giant cell astrocytoma, choroid plexus papilloma, craniopharyngioma, pituitary adenoma, hypothalamic or optic nerve glioma, hamartoma, metastatic tumors)
• Iatrogenic - posterior fossa surgery
• Congenital aqueductal stenosis (may not be symptomatic until adulthood)
• Meningitis, especially bacterial
• 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

• Poor feeding, irritability, reduced activity, vomiting
• Rapid increase in head circumstance 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)
• Increased limb tone

Features in Older Children and Adults

• Papilloedema
• Failure of upward gaze
• Macewen sign (a "cracked pot" sound on percussing the head)
• 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

• 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
• Mental retardation
• Oligodendroglioma
• Pituitary tumours
• Primary CNS lymphoma
• Pseudotumor 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.⁷ Associated defects such as basilar invagination (when the top of the second vertebra moves upwards) may be seen.⁸

Neuroradiology

CT scanning with or without contrast is considered to be adequate for the diagnosis of hydrocephalus although MRI scanning is occasionally required.⁹ Generalised dilation of the ventricles suggests a communicating hydrocephalus. Dilation of the lateral and 3rd ventricles suggests an aqueduct stenosis (if the fourth ventricles are normal) or a posterior fossa mass (if the fourth ventricles are absent or deviated).¹

Ultrasound

Scans through the anterior fontanelle is occasionally used in infants to demonstrate ventricular enlargement instead of CT scanning.¹

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

Surgery^1,2

• Treat the underlying cause The cure rate is 80% if a tumour can be identified (e.g. meningioma).
• Repeated lumbar punctures - this approach is only valid in communicating hydrocephalus, but may avoid shunting if the condition is likely to resolve spontaneously (e.g. intraventricular haemorrhage).
• Insertion of a shunt This is performed in the majority of cases. Various shunts may be used, of which the ventriculoperitoneal shunt is the commonest. This drains fluid from the lateral ventricle to the peritoneal cavity.
• 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.

Untreated congenital hydrocephalus is often fatal within the first four years of life. The prognosis in other conditions depends on the underlying cause.