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Last updated: December 5, 2019


Hydrocephalus refers to the abnormal enlargement of cerebral ventricles and/or subarachnoid space as a result of excess cerebrospinal fluid (CSF) accumulation. There are two types of true hydrocephalus: communicating hydrocephalus, which occurs due to decreased CSF absorption or increased CSF production in absence of any CSF-flow obstruction, and noncommunicating hydrocephalus, which occurs due to the obstructed passage of CSF from the ventricles to the subarachnoidal space. Both forms cause elevated intracranial pressure (ICP), which leads to headache, nausea, and/or vomiting. Specific clinical manifestations include changes in vital signs resulting from brainstem compression and, in congenital hydrocephalus, macrocephaly. Normal pressure hydrocephalus (NPH) is a chronic form of communicating hydrocephalus that occurs in older individuals (> 60 years of age). NPH occurs due to decreased CSF absorption and manifests with normal ICP because of effective compensation to the slow CSF accumulation by ventricular dilation. This ventricular distension leads to the classic presentation of urinary incontinence, dementia, and ataxic gait. Hydrocephalus ex vacuo is the enlargement of the ventricles and subarachnoid space due to loss of brain tissue (e.g., cerebral atrophy) and the subsequent filling of the void with CSF. It is not considered a true hydrocephalus since ventricular enlargement does not result from CSF accumulation and, accordingly, does not affect intracranial pressure or flow of cerebrospinal fluid. CT or MRI (and ultrasound for infants) are important diagnostic procedures for all types of hydrocephalus. A CSF tap test confirms the diagnosis of NPH. Treatment involves surgical insertion of a shunt, which drains excess CSF into another area of the body (usually the peritoneum).


Pathophysiology Clinical features Diagnosis
Communicating hydrocephalus
  • CSF production
  • CSF absorption
Noncommunicating hydrocephalus
  • Obstructed passage of CSF from the ventricles to the subarachnoidal space
Normal pressure hydrocephalus (NPH)
  • CSF absorption


Epidemiological data refers to the US, unless otherwise specified.

Etiology and pathogenesis

Communicating hydrocephalus

Dysfunction of subarachnoid cisterns or arachnoid villi resulting in decreased CSF absorption or increased CSF production.

Noncommunicating hydrocephalus

Obstruction of the cerebral aqueduct of Sylvius, the lateral foramen of Luschka, or the median foramen of Magendi results in obstructed passage of CSF from the ventricles to the subarachnoidal space.

Clinical features

Because the fontanelles of infants are still open, the accumulation of CSF can lead to macrocephaly; this accommodation offsets the elevation in ICP, meaning that neurological symptoms often develop later than in older patients whose fontanelles are closed!

Subtypes and variants

Normal pressure hydrocephalus

A form of chronic communicating hydrocephalus that primarily affects elderly individuals (> 60 years) and is characterized by a distinct clinical triad (urinary incontinence, dementia, ataxic gait) and normal or episodic increase in ICP.

Etiology and pathogenesis

Impaired CSF absorption results in CSF accumulation

Clinical features

  • Classic triad
    • Urinary incontinence
      • Initially, only increased urgency and frequency of micturition , later also urge incontinence.
      • Incontinence worsens as dementia progresses.
      • Gait disturbances can make the way to the toilet more difficult, leading to further incontinence related issues
    • Dementia
    • Frequent falls, broad-based gait with short steps (ataxic gait)

Normal pressure hydrocephalus does not manifest with signs of increased ICP (e.g., headache, papilledema).

Patients present with the classic triad of wet, wacky, and wobbly.



Differential diagnoses

Hydrocephalus ex vacuo

Hydrocephalus ex vacuo is often classified as a form of hydrocephalus, however, this is a misnomer as it is not a true hydrocephalus. The ventricles and subarachnoid space appear enlarged secondary to loss of brain tissue; however, intracranial pressure and flow of cerebrospinal fluid are normal.

Etiology and pathogenesis

Loss of brain tissue results in the expansion of the subarachnoid space filled with CSF. The ventricles appear dilated as well, with an apparent increase in CSF because of reduced brain tissue. However, there is no increase in CSF production, decreased CSF absorption, or obstruction.

Clinical features

  • Usually asymptomatic
  • Symptoms of the underlying condition (see “Etiology and pathogenesis” above)


  • Resembles hydrocephalus on imaging (i.e., enlarged CSF spaces, especially lateral ventricles)
  • Cortical atrophy may be prominent
  • ICP is normal

References: [3]

The differential diagnoses listed here are not exhaustive.


Most types of hydrocephalus are progressive and present a risk of neurological damage. Definitive treatment of hydrocephalus involves the drainage of excess CSF via a cerebral shunt, usually into the peritoneum (e.g., ventriculoperitoneal or VP shunt).

Cerebral shunt

  • Important components
    • Inflow catheter
    • Adjustable one-way pressure valves
    • Outflow catheter
    • Reservoir
  • Complications
    • Underdrainage ↑ ICP
    • Overdrainage
    • Shunt infection (∼ 5% of cases)
    • Slit ventricle syndrome
      • Symptoms:
        • Chronic intermittent headache
        • Nausea/vomiting
        • Altered mental status
        • Cranial neuropathies
      • Pathophysiology: the exact mechanisms underlying this syndrome are still debated. One hypothesis states that the overdrainage of one ventricle results in the collapse of its walls and occlusion of the shunt catheter. This, in turn, leads to underdrainage of the contralateral ventricle.

Possible interim therapy

Diuretics, fibrinolysis, serial lumbar punctures, (acetazolamide)



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