22A. Hydrocephalus

Hydrocephalus

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 (see next section)
• Hydrocephalus ex vacuo = not a true hydrocephalus, ventricles appear enlarged because there is brain atrophy

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 in adults causes symptoms of ICP and potentially herniation, see topic 24B. In children whose cranium is not yet completely ossified, the head may become enlarged, the sutures split and the fontanelles bulging.

Diagnosis and evaluation

MRI or CT shows dilated ventricles and shrunk subarachnoid space. If the hydrocephalus is communicating, all ventricles are dilated. If it’s obstructive, only the ventricles upstream of the obstruction are dilated.

Treatment

Treatment requires drainage of CSF, often with a ventriculoperitoneal (VP) shunt. This shunt unfortunately frequently has complications, including infection, shunt failure, and overdrainage of the CSF.

Another option is third ventriculostomy, where an opening is made in the floor of the third ventricle.

While waiting for surgery, the patient may require treatment to decrease the ICP (topic 24B).

Normal pressure hydrocephalus

Normal pressure hydrocephalus is a subtype of communicating hydrocephalus where the ICP is normal on when measured during spinal puncture. It mostly affects elderly and is idiopathic, but it may also develop secondary to intracranial bleeding, TBI, etc.

Normal pressure hydrocephalus is characterised by a classical triad of wet, wacky, and wobbly:

• Urinary incontinence
• Dementia
• Ataxic gait, frequent falls

The gait is sometimes described as “magnetic” due to how the patient’s feet look as though they’re glued to the floor while walking.

On MRI the subarachnoid space is normal, and the ICP (as measured by lumbar puncture) is normal. Cortical atrophy is often present.

The intracranial pressure can be measured by an intraventricular catheter or by lumbar puncture. A manometer is connected to the lumbar puncture needle or catheter. Normal ICP is 8 – 20 cmH2O.

The tap test can be used to aid the diagnosis. During this test, 20 – 50 ml CSF is drained though a lumbar puncture. The patient’s gait or cognitive symptoms are then assessed afterward. In NPH drainage of CSF usually improves the symptoms.

Treatment is as for other hydrocephalus, with a VP shunt.