• Clinical science



Hydrocephalus refers to the abnormal enlargement of cerebral ventricles and/or subarachnoid space as a result of excess cerebrospinal fluid (CSF) accumulation. There are four types, which include communicating hydrocephalus, non-communicating hydrocephalus, normal pressure hydrocephalus (NPH), and hydrocephalus ex vacuo. Communicating hydrocephalus typically occurs as a result of decreased CSF absorption or increased CSF production, whereas non-communicating hydrocephalus is due to the obstructed passage of CSF from the ventricles to the subarachnoidal space. Both forms lead to an elevated intracranial pressure (ICP), which leads to headache, nausea, and/or vomiting. These symptoms are often accompanied by specific clinical manifestations, such as macrocephaly in congenital hydrocephalus, or changes in vital signs resulting from brainstem compression. In contrast, normal pressure hydrocephalus, which is usually due to decreased CSF absorption in the elderly, manifests with normal ICP because of effective compensation by ventricular dilation. This ventricular distension leads to the classic presentation of urinary incontinence, dementia, and abnormal gait. In hydrocephalus ex vacuo, CSF extension occurs secondary to loss of brain tissue (e.g., cerebral atrophy); this type of hydrocephalus is actually a misnomer as it is not a true hydrocephalus. CT or MRI (and ultrasound for infants) are important diagnostic procedures. Treatment involves surgical insertion of a shunt, which drains excess CSF into another area of the body – usually the peritoneum.


Abnormal enlargement of cerebral ventricles and/or subarachnoid space as a result of excess cerebrospinal fluid (CSF) accumulation

Types of hydrocephalus

Type of hydrocephalus


Pathophysiology Symptoms/Clinical findings Diagnosis
Non-communicating hydrocephalus
  • Ultrasonography
    • Indication: clinical suspicion during antenatal period or in infants < 6 months of age (through the anterior fontanelle when it is still open)
    • Findings: enlarged lateral ventricles
  • MRI (preferred for children) or CT
    • Indication: older infants (when fontanelle is already closed, typically > 6 months of age) or adults
    • Features of acute hydrocephalus: enlarged ventricles
      • Temporal horn dilation > 2 mm
      • Evans ratio > 30%
      • Sulcal enlargement
      • Mickey Mouse ventricles
      • Upward bowing of the corpus callosum

Communicating hydrocephalus

  • Inflammatory diseases of the central nervous system (CNS) → inflamed arachnoid villi
  • Subarachnoidal or intraventricular hemorrhage → inflammatory response → fibrosis
  • CSF absorption
  • CSF production

Normal pressure hydrocephalus

  • CSF absorption
  • Secondary: impaired CSF absorption caused by inflammation and subsequent fibrosis of the subarachnoid villi
  • Classic Triad
    • Wet: urinary incontinence
      • Initially, only ↑ urgency and frequency of micturition urge incontinence → later in the disease, incontinence worsens due to indifference of the patient to their recurrent urinary symptoms
      • Additionally, the gait disturbances can make the way to the toilet more difficult, leading to further incontinence related issues
    • Wacky: dementia
    • Wobbly: frequent falls, broad-based gait with short steps (ataxic gait)
  • Rule out other causes of symptoms:
  • MRI (initial test), CT
    • Ventriculomegaly without sulcal enlargement
    • Periventricular hypodensity due to periventricular edema
  • CSF tap test: confirmatory test
    • Note severity of symptoms before the test
    • Opening pressure is normal or slightly elevated
    • Remove a small amount of CSF fluid (30–50 mL)
    • Improvement of symptoms after CSF removal confirms NPH
    • Lumbar puncture is both diagnostic and therapeutic
Hydrocephalus ex vacuo
  • Occurs in primary cerebral atrophy or cerebral destructive lesions
  • Actually a misnomer; not a true hydrocephalus
  • Symptoms of the underlying condition
  • Resembles hydrocephalus on imaging
  • Cortical atrophy may be prominent

Because the fontanelles of infants are still open, the accumulation of CSF can lead to macrocephaly, which may offset elevations in ICP and delay neurological symptoms!References:[1][2][3][4][5][6]


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
    • Indications: hydrocephalus, syringomyelia
    • Important components
      • Inflow catheter
      • Adjustable one-way pressure valves
      • Outflow catheter
      • Reservoir
    • Complications
      • Underdrainage ↑ ICP
      • Overdrainage
        • Symptoms: see intracranial hypotension syndrome
        • Variant: Slit ventricle syndrome
          • Pathophysiology: Ventricular walls are pulled into the catheter slit by suction and permanently close the slit.
      • Shunt infection (∼ 5% of cases)
        • Bacterial contamination (e.g., Staphylococcus epidermidis), often associated with biofilm formation
        • Therapy: shunt explantation surgery
  • Possible interim therapy: diuretics, fibrinolysis, serial lumbar punctures, (acetazolamide)
  • Alternative surgical procedures
    • Endoscopic third ventriculostomy
    • Choroid plexectomy (or coagulation)
    • Cerebral aqueductoplasty