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Conditions · Head and neck

Hydrocephalus !

Hydrocephalus is a build-up of cerebrospinal fluid in the brain's cavities, which widen and can raise pressure inside the skull.

Updated 2026-10-29

Structures involved

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Microorganisms that cause it

In histology

In embryology

In the clinical exam

In physiology

What it is

Abnormal build-up of cerebrospinal fluid in the ventricles of the brain, which enlarge and may raise intracranial pressure. It can be congenital or acquired, and obstructive or communicating.

Who gets it

Occurs from infancy to old age: congenital forms and those linked to prematurity and neural tube defects in children, and normal pressure hydrocephalus in older adults. In Colombia, neurocysticercosis and infections are important acquired causes.

Causes

  • Obstruction of flow: aqueductal stenosis, tumours (especially of the posterior fossa), cysts such as ventricular neurocysticercosis
  • Impaired absorption: after subarachnoid haemorrhage or meningitis
  • Congenital malformations: Chiari II with myelomeningocele, Dandy-Walker malformation
  • Intraventricular haemorrhage in premature infants
  • Rarely overproduction (choroid plexus papilloma)

Risk factors

  • Prematurity
  • Neural tube defects
  • Meningitis and neurocysticercosis
  • Subarachnoid or intraventricular haemorrhage
  • Brain tumours and head injury
  • Older age (normal pressure hydrocephalus)

Pathophysiology

CSF made by the choroid plexus flows from the lateral ventricles through the third ventricle, aqueduct and fourth ventricle to the subarachnoid space, then drains to the venous sinuses. Blocked flow within the ventricles causes obstructive hydrocephalus; impaired absorption causes communicating hydrocephalus. In infants with open sutures the head enlarges; in older patients pressure rises quickly.

Classification

  • Obstructive (non-communicating)
  • Communicating
  • Normal pressure hydrocephalus (older adults)
  • Congenital or acquired
  • Acute or chronic

Symptoms and signs

  • Infants: rapidly growing head circumference, bulging fontanelle, separated sutures, irritability, vomiting, sunset eyes
  • Older children and adults: headache worse in the morning, nausea, vomiting, drowsiness, papilloedema
  • Upward gaze palsy (Parinaud syndrome) with dorsal midbrain compression
  • Normal pressure hydrocephalus: gait disturbance, urinary incontinence and cognitive decline
  • Shunt malfunction: return of headache, vomiting and drowsiness

Diagnosis

Clinical
Head circumference charts and fontanelle examination in infants; symptoms of raised pressure and fundoscopy in older patients; the gait-incontinence-dementia triad in normal pressure hydrocephalus.
Tests
CSF studies when infection is suspected. In normal pressure hydrocephalus, a high-volume lumbar tap test or lumbar drainage to see whether gait improves.
Imaging
Cranial ultrasound through the fontanelle in infants. CT or MRI shows enlarged ventricles and the site of obstruction; MRI is better for aqueduct and posterior fossa lesions.

Differential diagnosis

  • Brain atrophy with ex vacuo ventricular enlargement
  • Benign enlargement of subarachnoid spaces in infancy
  • Idiopathic intracranial hypertension
  • Alzheimer disease and Parkinson disease (versus normal pressure hydrocephalus)
  • Brain tumour or abscess

Goal of treatment

Divert or restore CSF flow to relieve raised pressure and protect brain development and function, and treat the cause.

Treatment

Acute
Acute obstructive hydrocephalus with deterioration: emergency external ventricular drain.
Surgical
Ventricular shunt, usually ventriculoperitoneal, with a valve that controls drainage.
Surgical
Endoscopic third ventriculostomy for selected obstructive cases, avoiding a permanent shunt.
Surgical
Removal of the cause when possible: tumour resection, endoscopic removal of ventricular cysticerci.
Follow-up
Lifelong follow-up of shunted patients for malfunction or infection; developmental follow-up in children.

Complications

  • Shunt obstruction, infection or over-drainage
  • Brain herniation and death if untreated
  • Visual loss from chronic papilloedema
  • Developmental delay, learning difficulties and epilepsy
  • Subdural collections after drainage

Prognosis

Depends on the cause, age and speed of treatment. Many children reach good developmental outcomes, although shunt revisions are common. In normal pressure hydrocephalus, gait responds best to shunting.

Prevention

  • Folic acid before conception to reduce neural tube defects
  • Prenatal care to reduce prematurity
  • Prevention and treatment of neurocysticercosis and meningitis
  • Vaccination against meningitis-causing bacteria

Test yourself

Think of the answer, then tap the question to see it.

What is the difference between obstructive and communicating hydrocephalus?

Obstructive: flow is blocked within the ventricular system; communicating: CSF reaches the subarachnoid space but is poorly absorbed.

What is the triad of normal pressure hydrocephalus?

Gait disturbance, urinary incontinence and cognitive decline.

Why does the head enlarge in infants with hydrocephalus?

Their cranial sutures and fontanelles are still open, so the skull expands with the raised pressure.

Which parasitic infection is an important cause of hydrocephalus in Colombia?

Neurocysticercosis, through ventricular cysts or arachnoiditis.

What is the most common surgical treatment for hydrocephalus?

A ventriculoperitoneal shunt; endoscopic third ventriculostomy is an option in selected obstructive cases.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Hydrocephalus (StatPearls (NCBI Bookshelf), 2023).

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Representative model, for educational purposes only.

Lateral ventricles highlighted on the Durgical 3D model