22A. Hydrocephalus

Definition

Hydrocephalus is a condition where there is an increased amount of CSF, often causing increased ICP. There are four types:

  • Obstructive (non-communicating) hydrocephalus = increased CSF due to mechanical blockage of CSF flow within the ventricular system
  • Communicating (non-obstructive) hydrocephalus = increased CSF due to impaired absorption of CSF or due to increased CSF production
  • Normal pressure hydrocephalus
  • Hydrocephalus ex vacuo = not a true hydrocephalus, only there is brain atrophy which makes the ventricles appear dilated

Normal pressure hydrocephalus is a subtype of communicating hydrocephalus where the ICP is normal.

Etiology

  • Obstructive hydrocephalus
    • CNS tumour
    • Congenital stenosis of cerebral aqueduct
  • Communicating hydrocephalus
    • Choroid plexus tumour
    • Genetic syndromes (trisomies, triploidy, etc.)
  • Either or both obstructive and communicating hydrocephalus
    • Subarachnoid haemorrhage
    • Intraventricular haemorrhage
    • CNS infection (bacterial meningitis, etc.)
    • Neural tube defect -> Chiari II malformation

Clinical features

Hydrocephalus causes symptoms of ICP and potentially herniation, see topic 24B.

Normal pressure hydrocephalus is the exception, where there is no ICP but instead a classical triad of wet, wacky, and wobbly:

  • Urinary incontinence
  • Dementia
  • Ataxic gait, frequent falls

Diagnosis and evaluation

MRi or CT shows dilated ventricles. If the hydrocephalus is communicating, all ventricles are dilated. If it’s obstructive, only the ventricles upstream of the obstruction are dilated.

In normal pressure hydrocephalus, cortical atrophy is also present.

Treatment

Treatment requires drainage of CSF, often with a ventriculoperitoneal (VP) shunt. This shunt unfortunately frequently has complications. Another option is third ventriculostomy, where an opening is made in the floor of the third ventricle.

While waiting for surgery, the patient may receive diuretics or acetazolamide to decrease the ICP.


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