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Hydrocephalus is an increase in total cerebrospinal fluid (CSF) volume or a nonphysiologic distribution of cerebrospinal fluid. Hydrocephalus can be classified as communicating (non-obstructive), noncommunicating (obstructive) or normal pressure.


Hydrocephalus can occur when there is:

  • Increased production of CSF. This is rare and occurs typically in the setting of choroid plexus tumor.
  • Obstruction of the ventricular system secondary to aqueduct stenosis or mass lesion such as tumor. This is the most common type in congenital hydrocephalus.
  • Inadequate reabsorption of CSF. Reabsorption of CSF by the arachnoid granulations is blocked by blood products (e.g., sub-arachnoid hemorrhage [SAH]) or infectious material (e.g., meningitis). This is the most common type of post-traumatic hydrocephalus.

Ex vacuo hydrocephalus occurs when the ventricular space is enlarged due to loss of brain parenchyma, typically after trauma or stroke. This is a descriptive term and does not imply the patient has clinical findings of hydrocephalus.

Epidemiology including risk factors and primary prevention

The estimated incidence of congenital hydrocephalus varies by region of the world. It was previously reported as lowest in the United States and Canada at 68 per 100,00 births and highest in Latin America at 316 per 100,000 births. About 15% of children with myelomeningocele are born with significant hydrocephalus, and up to 80-90% eventually develop it due to deformities associated with the associated Chiari II malformation that obstruct CSF flow.

Ventricular dilation has been noted in 40-45% of patients with severe brain injury. Clinically significant hydrocephalus following TBI greatly varies in the literature. It is important to note that some patients have ex vacuo changes without clinical findings.

Up to 20% of patients with subarachnoid hemorrhage will develop hydrocephalus. The risk is highest in those with hemorrhage due to an aneurysm.

Normal pressure hydrocephalus typically occurs in adults older than 60 years. The incidence has been reported between 1.1 to 5.5 newly affected individuals per 100,000 persons.

Hydrocephalus is relatively common and reversible cause of disorders of consciousness (DOC). An incidence rate of 38.4% has been reported in patients presenting with DOC.


CSF is normally produced at a rate of 25 cc/hr by the choroid plexus in the lateral ventricles and reabsorbed by the arachnoid granulations in the sagittal sinus at the same rate. The volume of CSF is between 125-150 cc, of which ~20% is contained in the ventricles.

Acutely after injury, blood products within the ventricular system can block the foramen of Sylvius or the 4th ventricle and cause an outflow obstruction, which results in hydrocephalus. Aqueduct stenosis or Chiari malformation may be decompensated by traumatic brain injury (TBI) resulting in a relative CSF outflow blockage or obstructive hydrocephalus.

Post-traumatic hydrocephalus may also be of the communicating type due to blood products and proteins accumulating in the arachnoid granulations, preventing reabsorption of CSF.

Normal pressure hydrocephalus may develop after trauma but may also be idiopathic. Decreased turgor in the aging brain may allow normal pressures to produce hydrocephalus.

Hydrocephalus ex vacuo occurs due to loss of brain parenchyma after injury, which allows the CSF space to enlarge.

Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)

Historically, patients with congenital or pediatric hydrocephalus would develop unremitting head enlargement followed by several physical and neurobehavioral complications. Introduction of shunting or CSF diversion has improved outcomes in this population.

Disease progression in TBI patients is variable, depending on whether it is an acute or chronic presentation. Acute hydrocephalus may present with headache, nausea, vomiting, lethargy, and/or change in mental status and may progress to coma and death if untreated. In the subacute or chronic state, failure to progress with rehabilitation or a decline in cognition or behavior may indicate hydrocephalus. Earlier shunting has been associated with improved outcomes in TBI patients.

The natural course of NPH is progression of symptoms over time. The deterioration is only partially reversible leading to recommendations for earlier surgical management.

As previously mentioned, hydrocephalus is a potential reversible cause of disorders of consciousness.

Essentials of Assessment


History of trauma, central nervous system disease, or central congenital malformations should be elicited.

Acute hydrocephalus can present with headache, visual changes, nausea, vomiting, a decline in mental status, or lethargy, indicating increased intracranial pressure.

In patients with TBI, there may be the additional symptoms of failure to progress with rehabilitation therapies or a decline in performance. Other subtle signs may also be indicative of hydrocephalus including: abulia, perseveration, emotional lability, mutism, apraxia, decreased initiation or changes in bowel and bladder in the absence of infection.

Normal pressure hydrocephalus presents in the elderly with dementia, including memory loss and forgetfulness, gait ataxia and urinary incontinence. Gait is typically bradykinetic, wide-based with short steps and has been described as “magnetic.”

Physical examination

Physical examination should include vital signs, mental status exam, behavioral observation, cranial nerve exam including fundoscopic evaluation, speech and language, motor and sensory testing, reflexes, and gait assessment. Observation of craniectomy site should be included as appropriate.

Cushing’s triad of hypertension, bradycardia and hypoventilation may be present.

Enlarged head circumference and firm fontanelles can occur in infants with hydrocephalus.

Papilledema or a bulging of a craniectomy site may occur.

Frontal and subcortical deficits including forgetfulness and decreased attention are present in NPH. The presence of aphasia or agnosia are not typically seen in with NPH. The typical gait pattern seen in patients with NPH is bradykinetic, broad-based, magnetic, and shuffling. Unlike Parkinson’s, tremor and rigidity are not characteristic of NPH.

For a patient with a shunt in place, abdominal pain or palpable pseudocyst may be present when the distal shunt is occluded.

Functional assessment

Gait and balance should be assessed, including base of support and step length. Mental status exam should include comparison to previous evaluations if available.

Laboratory studies

Laboratory studies to rule out other etiologies contributing or causing a decline in cognition and gait should include evaluation for infection and electrolyte abnormalities.

Lumbar puncture or shunt tap (if present) with CSF analysis should be performed if meningitis is suspected.


Computerized tomography (CT) scan will show ventricular dilation and is helpful in identifying the existence and nature of the CSF obstruction.

Magnetic resonance imaging (MRI) offers more structural information of potential pathologic cause of hydrocephalus. MRI also provides imaging of the Sylvian aqueduct and foramen of Monro. Decreased signal in the Sylvian aqueduct indicates hydrocephalus.

Ex vacuo hydrocephalus due to injury-related atrophy results in sulcal prominence. As previously mentioned, this is a descriptive term and does not imply the patient has clinical findings of hydrocephalus.

There are several morphological changes which can be observed on CT or MRI. This includes an increased Evan’s index>0.3. The Evan’s index is the ratio of the maximum width of the frontal horns of the lateral ventricles and the maximal internal diameter of the skull at the same level. This index is particularly useful in patients with suspected NPH.

Shunt series is a set of radiographic images to assess for mechanical causes of shunt failure.

Nuclear medicine shunt patency studies determine if CSF is flowing through the shunt system by injection a small volume of radiotracer in the shunt reservoir. This allows for measurement of flow through the catheters and valve.

Supplemental assessment tools

CSF tap test can be performed to evaluate for normal pressure hydrocephalus. Prior to removal of 50 ml of CSF, neurologic status is evaluated. After CSF removal, the patient’s neurological and functional status is reassessed. If improvement is seen after CSF removal, shunting may be helpful.

The tap test can be extended to prolonged drainage by catheter for 3-5 days. This has been shown to be more sensitive and predictive of shunt success.

Early predictions of outcomes

Patients with longer duration of coma, increased age, decompressive craniectomy and subarachnoid hemorrhage (SAH) are reported to be at increased risk of developing post-traumatic hydrocephalus.

Patients who are treated with craniectomy have worse functional outcomes than patient treated with craniotomy. Following craniectomy, there is disruption of intracranial pressure dynamics resulting in decreased CSF outflow.

Flattening of the sulci with ventriculomegaly and periventricular lucencies on CT indicate that the response to shunting is typically favorable.

Untreated, acute hydrocephalus can progress to coma and death. External ventriculostomy is used to prevent this progression. Delayed treatment can slow or disrupt neuroplasticity, repair and recovery.

When shunting is performed for normal pressure hydrocephalus (NPH), slowness of gait rather than disequilibrium is more likely to improve. Significant improvement in cognitive function may occur after shunting for NPH as well.

Social role and social support system

Family members may report changes in cognition or behavior in their loved one that may warrant investigation for hydrocephalus or for malfunction of a shunt that is already in place.

Professional issues

For the low-level brain-injured patient with hydrocephalus, the decision to place a shunt should be considered in the context of other life-sustaining, quality of life measures. Expectations of outcomes following shunting should be discussed with family members.

Rehabilitation Management and Treatments

Available or current treatment guidelines

Medical management targets decreasing the rate of CSF formation or increasing CSF reabsorption. Carbonic anhydrase inhibitors, such as acetazolamide, decrease CSF production. It has been used in combination with furosemide, a loop diuretic, however, its efficacy and safety have been questioned. Isosorbide, a hypertonic osmotic agent, increases CSF reabsorption. Medical treatments are used as a temporary measure prior to more definitive management.

External ventriculostomy is recommended for the treatment of acute hydrocephalus. If the obstruction persists ventriculo-peritoneal shunt (VP shunt) may be needed for long-term management.

A typical VP shunt consists of a proximal catheter, which is usually placed in the frontal horn of the lateral ventricle, a valve that regulates the pressure and prevents retrograde flow of the shunted CSF, and distal tubing that is usually placed in the peritoneal space.

Membrane fenestration, which creates a hole in the floor of the third ventricle, allowing communication with the underlying cisterns and subarachnoid space, has been successful when obstruction such as aqueductal stenosis is present in the posterior fossa.

At different disease stages

  • If shunt failure is clinically suspected, radiographic evaluation is warranted. Plain radiography is recommended to check for disconnection and catheter kinking, breakage or migration. CT of the head is recommended to evaluate ventricular size. Nuclear medicine shunt patency studies evaluate the patency with radiotracer. Sonography can be used to evaluate the patency of the peritoneal end of the shunt. MRI evaluates for infection or hemorrhage.
  • Replacement or revision of the shunt may be necessary if shunt occlusion or disconnection is present.
  • Shunt infection occurs in 7-29% of cases and most commonly is related to Staphylococcus. Low-grade fever, malaise, irritability and nausea are presenting features. Diagnosis is made by shunt tap and is based on culture results. Shunt removal or externalization in combination with antibiotics is recommended.
  • Shunt overdrainage may result in orthostatic hypotension, dizziness, nausea, vomiting and diplopia. Overdrainage can also lead to hygromas or hematomas. Antisiphon devices and valves have been developed to counteract negative standing intracranial pressure.
  • Programmable valves can be adjusted to maximize optimal CSF pressure balance. Of note, shunts with programmable valves require checking the settings before and after MRI to ensure there was no inadvertent shunt readjustment.

Patient & family education

Family education should be provided so that any change in mental status, behavior, mobility, or bladder function prompts them to seek medical evaluation for possible hydrocephalus or shunt malfunction.

Emerging/unique interventions

Routine imaging of patients with shunts is not recommended and should be based on a change in mental status, physical exam, or performance in rehabilitation therapies.

In patients where definitive placement of a shunt is not recommended, routine large volume lumbar punctures may also be effective in managing symptoms.

Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills

It is important to note that hydrocephalus is a clinical diagnosis and should not be diagnosed or excluded by imaging alone.

A high index of suspicion should be maintained by clinicians treating patients at risk for hydrocephalus. In the context of neurotrauma or neurologic disease, subtle changes in cognition and behavior should prompt consideration of hydrocephalus.

In patients with posttraumatic hydrocephalus, earlier shunting predicted improved recovery.

In persons presenting with a disorder of consciousness, hydrocephalus should be excluded before a diagnosis of permanent vegetative state.

Cutting Edge/ Emerging and Unique Concepts and Practice

Research shows that traumatic brain injury may cause ependymal ciliary loss which decreased CSF flow and increase the likelihood of hydrocephalus.

Recent data is increasing our knowledge of the molecular mechanisms by which inflammation contributes to the pathogenesis of hydrocephalus. This includes TLR4-regulated CSF cytokines, immune cells, and signaling pathways that can lead to choroid plexus hypersecretion, ependymal denudation, and scarring of CSF pathways. These may be potential targets for therapeutic intervention.

The recently discovered glymphatic system plays a role in CSF regulation, however, the extent remains unclear. An imaging study in patients with idiopathic normal pressure hydrocephalus revealed significant suppression of glymphatic clearance.

Deferoxamine has been shown to decrease acute hydrocephalus after traumatic brain injury in animal studies.

Gaps in the Evidence-Based Knowledge

There is a lack of understanding of exact pathophysiology underlying hydrocephalus.  This has led to gaps in evidence-based knowledge involving primary and secondary prevention of hydrocephalus.


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Original Version of the Topic

Carolyn Geis, MD. Hydrocephalus. 6/07/2013

Previous Revision(s) of the Topic

Mary Russell, MD. Hydrocephalus. 3/29/2017

Author Disclosure

Jacob Jeffers, MD
Nothing to Disclose

Mary Russell, MD
Allergan; Honorarium; Speaker’s Bureau