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Hydrocephalus

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Overview

Hydrocephalus (‘water’ on the brain’) describes excessive cerebrospinal fluid (CSF) in the ventricular system of the brain due to an imbalance between CSF production and absorption.

Since the skull is a rigid structure, hydrocephalus can lead to elevated intracranial pressure. In infants, the skull sutures are not fused, and elevated intracranial pressure can lead to an increase in head circumference and a bulging anterior fontanelle.

Classification

Overview

Hydrocephalus can broadly be classified into the following:

  • Communicating (non-obstructive) hydrocephalus
  • Non-communicating (obstructive) hydrocephalus

Communicating hydrocephalus

Communicating (or non-obstructive) hydrocephalus occurs due to an imbalance of CSF production or absorption. This is most commonly due to:

  • Failure of reabsorption at the arachnoid granules – more common
  • Excess production of CSF – rare
    • An example cause is a tumour of the choroid plexus, which is very rare

Non-communicating hydrocephalus

Non-communicating (or obstructive) hydrocephalus is due to the blockage of CSF flow due to structural abnormalities. Causes include:

Normal pressure hydrocephalus

This is discussed in more detail here. Its pathogenesis is not entirely understood, however, normal pressure hydrocephalus (NPH) is a type of chronic communicating hydrocephalus characterised by large ventricles and only intermittently elevated CSF pressures and normal intracranial pressure.

Ordinarily, hydrocephalus and enlarged ventricles lead to elevated intracranial pressure. In NPH, there is increased CSF pressure and no elevated intracranial pressure, explaining why patients do not have classic signs of elevated intracranial pressure (such as nausea, vomiting, fluctuating consciousness, and headaches). This is because, in NPH, the disease is not caused by excess CSF production or impaired CSF flow.

Presentation

In infants

Features suggesting hydrocephalus in infants include:

  • Anterior bulging fontanelle
  • Increased head circumference
  • ‘Sunset eyes’ – eyes are in a downward gaze with the lower half of the eye covered by the lower eyelid. The upper eyelids are retracted and the sclerae are visible above the iris
  • Irritability
  • Vomiting
  • Reduced consciousness
  • Increased tone
  • Seizures

Investigations

Overview

  • CT head:
    • Used first-line and identifies ventricular dilation
  • MRI head:
    • Used to assess hydrocephalus in more detail and identify possible structural abnormalities
  • Lumbar puncture – avoid in obstructive hydrocephalus:
    • Is both diagnostic and therapeutic as it allows measurement of CSF pressure and drains CSF
    • Lumbar punctures should be avoided in obstructive hydrocephalus as reduced spinal CSF pressure compared to the brain CSF pressure causes the contents within the meninges to move downwards causing brain herniation

Management

Overview

Treatment depends on the timeline and severity of hydrocephalus. Options may include:

  • Insertion of an external ventricular drain:
    • Allows temporary CSF drainage into an external system
  • Insertion of a shunt:
    • Performed in most cases and redirects CSF from the ventricles into the peritoneal cavity
  • In non-communicating hydrocephalus, surgery may be necessary to treat the obstruction

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