Hydrocephalus is 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 is caused by decreased CSF resorption or increased CSF production in the absence of CSF flow obstruction, and noncommunicating hydrocephalus, which is caused by the obstructed passage of CSF from the ventricles to the subarachnoid space. Both forms typically manifest with signs of elevated intracranial pressure (ICP). Other clinical manifestations may include changes in vital signs resulting from brainstem compression and, in congenital hydrocephalus, macrocephaly. Normal pressure hydrocephalus (NPH) is a gradual-onset chronic form of communicating hydrocephalus that primarily occurs in adults > 60 years of age. ICP is normal or mildly elevated; manifestations include a classic triad of gait apraxia, dementia, and urinary incontinence. All types of hydrocephalus are diagnosed using MRI brain or CT head; ultrasound is used in children < 18 months of age with an open anterior fontanelle. A lumbar puncture may be required (once intracranial lesions with mass effect have been ruled out) to measure opening pressure, obtain CSF samples for analysis, and, if NPH is suspected, perform a CSF tap test. Temporizing measures to reduce CSF volume, such as external ventricular drain placement or serial lumbar punctures, may be used in the acute setting. Definitive treatment often involves surgical insertion of a shunt that drains excess CSF into another area of the body. Hydrocephalus ex vacuo is the enlargement of the ventricles and subarachnoid space due to loss of brain tissue (e.g., cerebral atrophy). It is not considered a true hydrocephalus because ventricular enlargement does not result from CSF accumulation and it does not affect ICP or CSF flow.
- Hydrocephalus is a condition in which CSF accumulates within the cerebral ventricles, causing their enlargement.
- In hydrocephalus, ICP can be elevated or normal.
|Overview of hydrocephalus|
|NPH) (|| |
|Hydrocephalus ex vacuo|| || |
- Prevalence: communicating hydrocephalus is more common than noncommunicating hydrocephalus
- Age 
- Sex: ♂ = ♀
Epidemiological data refers to the US, unless otherwise specified.
Etiology and pathophysiology
- ↓ CSF absorption
- ↑ CSF production
Noncommunicating hydrocephalus (obstructive hydrocephalus)
Obstruction of the obstructed passage of CSF from the ventricles to the subarachnoidal space., the , or the results in
Congenital: Noncommunicating hydrocephalus is the most common form of congenital hydrocephalus.
- Dandy-Walker malformation: congenital malformation caused by failure of the fourth ventricle to close, which leads to persistence of Blake's pouch (cyst in the 4th ventricle) and cerebellar vermis hypoplasia
- Intrauterine infections: e.g., congenital toxoplasmosis (see “”)
- Colloid cyst obstructing the interventricular foramen
- Congenital stenosis of the cerebral aqueduct of Sylvius
- Features of increased ICP
Clinical features in infants
- Macrocephaly: an enlarged head with a circumference greater than the average for age and sex by two standard deviations (as indicated by a percentile growth chart)
- Tense fontanelle
- Setting sun sign: persistent downward deviation of the eyes due to increased ICP in infants and young children
- Developmental delays (e.g., psychomotor delays)
- Behavioral changes (e.g., irritability)
- MacEwen sign (cracked pot sign): percussion of the skull near the junction of the frontal, temporal, and parietal bones evokes an unusually resonant sound
- Other findings
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 adults > 60 years of age
- Characterized by a distinct clinical triad (gait apraxia, dementia, and urinary incontinence) and normal or only mildly elevated ICP
- Idiopathic (iNPH, most common in adults > 60 years of age)
- Possible secondary causes that result in obstruction and/or fibrosis of subarachnoid villi
- ↓ CSF absorption → CSF accumulation → enlargement of the ventricle
- ICP: normal or only mildly elevated because ventricular dilation compensates for the slow accumulation of CSF
Clinical features 
A classic triad of:
- Gait abnormalities: frequent falls, broad-based gait with short shuffling steps (gait apraxia, also known as magnetic gait)
- Dementia: short attention span, loss of motivation, disturbances of spatial orientation 
- Initially, only increased urgency and frequency of micturition; later also urge incontinence
- Dilation of the lateral ventricles results in a distortion of the fibers of the corona radiata, which causes a loss of inhibition of detrusor activity.
- Incontinence worsens as cognitive impairment progresses.
- Gait disturbances can make reaching the toilet more difficult, leading to further incontinence-related issues.
- Imaging: MRI brain (preferred) ; , CT head
- CSF tap test: with measurement of opening pressure, followed by removal of 30–50 mL of CSF
- : to assess for causes of secondary NPH (e.g., )
For differential diagnoses based on the initial clinical presentation, see:
- Refer to neurosurgery for placement.
- Manage treatable causes of secondary NPH, if identified.
- Initiate .
- Ventriculomegaly without or out of proportion to sulcal enlargement
- Evans ratio (ratio of largest width of frontal horns to largest biparietal diameter): > 30%
- Findings of underlying cause, e.g., congenital malformations or tumors
Lumbar puncture 
Consider the following with specialist guidance if noare present:
- Opening pressure measurement: to estimate ICP
- : if NPH is suspected
- CSF analysis: e.g., to assess for evidence of meningitis or neoplastic seeding
Hydrocephalus ex vacuo
- Definition: 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.
- Clinical features
Other differential diagnoses
For differential diagnoses based on the initial clinical presentation, see:
- “Differential diagnoses of headache”
- “Causes of elevated ICP”
- “Causes of altered mental status and coma”
The differential diagnoses listed here are not exhaustive.
General principles 
- Management must be guided by neurosurgery.
- Temporizing CSF drainage and/or medications may be used in the acute setting for .
- Definitive treatment involves surgical intervention for permanent CSF drainage (e.g., through a ventriculoperitoneal shunt).
Initiate treatment promptly, as most types of hydrocephalus are progressive and can result in neurological damage if left untreated.
Temporizing measures 
Interim drainage procedures: typically used for acute posthemorrhagic hydrocephalus or if infection precludes definitive treatment
- Serial lumbar punctures or lumbar drain placement: for communicating hydrocephalus
- Ventricular tap: for preterm infants with intraventricular hemorrhage (performed through the open anterior fontanelle)
- External ventricular drain: for noncommunicating hydrocephalus (e.g., after subarachnoid hemorrhage)
- Pharmacotherapy: may be considered, although the benefit is likely limited 
Definitive treatment 
- Definition: a definitive treatment for hydrocephalus that diverts excess CSF from the ventricles to a body cavity where it is absorbed into the systemic circulation
- Inflow catheter
- Shunt valve
- Outflow catheter
- Most commonly with gram-positive bacteria (e.g., Staphylococcus epidermidis)
- Clinical features include fever, headache, and signs of elevated ICP.
- Initial diagnostics: CSF analysis with cultures , further as indicated
- Management: immediate neurosurgical consult for shunt removal and antibiotic therapy
- See also “Management of neurosurgical device-related infection.”
- Shunt obstruction
- A neurosurgical emergency that manifests with signs of elevated ICP
- Initial diagnostics: CT head to confirm shunt placement and integrity,
- Management: immediate neurosurgical consult for shunt revision
- Shunt overdrainage or underdrainage
- Underdrainage: can lead to
- Overdrainage: can lead to
- Slit ventricle syndrome: ventricular collapse and shunt obstruction due to chronic CSF overdrainage 
- Shunt infection
Shunt infection and obstruction are neurosurgical emergencies.
Other surgical procedures 
- Endoscopic third ventriculostomy: for hydrocephalus due to obstruction at or distal to the
- Cerebral aqueductoplasty: a procedure in which a stenotic or closed cerebral aqueduct is opened to allow adequate passage of CSF between the third and fourth ventricles
- Excision of obstructive lesion: e.g., posterior fossa tumor