Hydrocephalus

Definition

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.

Etiology

Hydrocephalus can occur when there is:

1. Increased production of CSF. This is rare and occurs typically in the setting of choroid plexus tumor.
2. Obstruction of the ventricular system. This is the most common form of hydrocephalus and occurs with aqueductal stenosis or mass lesion such as tumor.
3. 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).

Epidemiology including risk factors and primary prevention

Ventricular dilation has been noted in 40-45% of patient with severe brain injury. Up to 20% of patients with subarachnoid hemorrhage will develop hydrocephalus, especially if the hemorrhage is due to an aneurysm.

Trauma, brain tumor and central nervous system (CNS) infection can cause noncommunicating (obstructive) hydrocephalus due mechanical obstruction at or between ventricles.

Trauma may result in communicating hydrocephalus due to accumulation of blood products and proteins, which block the arachnoid granulations from absorbing CSF.

Ex vacuo hydrocephalus occurs when the ventricular space is enlarged due to loss of brain parenchyma, typically after trauma.

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.

Normal pressure hydrocephalus typically occurs in adults older than 60 years.

Patho-anatomy/physiology

CSF is normally produced at a rate of 150 cc/hr by the choroid plexus in the lateral ventricles and reabsorbed by the arachnoid granulations in the sagital sinus at the same rate.

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. Aqueductal 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. Decreasedturgorin 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)

1. Acute hydrocephalus may present with headache, nausea, vomiting, lethargy, and/or change in mental status and may progress to coma and death. Cushing’s triad of hypertension, bradycardia and hypoventilation may be seen.
2. In the subacute or chronic state, failure to progress with rehabilitation or a decline in cognition or behavior may indicate hydrocephalus.
3. The triad of dementia, decline in gait, and urinary incontinence in the elderly population is consistent with normal pressure hydrocephalus.

History

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.

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.”

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 initation or changes in bowel and bladder in the absence of infection.

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.

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 typically not 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 with CSF analysis should be performed if meningitis is suspected.

Imaging

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. Flattening of the sulci and periventricular lucencies indicates clinically significant hydrocephalus that typically responds to shunting.

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

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

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

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.

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.

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.

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. Specifically, after TBI, family members should understand that while shunting may be helpful, deficits from the brain injury will remain after the shunt has been placed.

Available or current treatment guidelines

Medical management targets decreasing the rate of CSF formation or increasing CSF reabsorption. Carbonic anhydrase inhibitors, such as acetozolamide, decrease CSF production. 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. Scintigraphy evaluates the patency of the shunt. Sonography can be used to evaluate the patency of the peritoneal end of the shunt. MRI evaluates for infection or hemorrhage.
• Injection of iodinated contrast material into the shunt system evaluates for CSF leakage or obstruction.
• 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. Antisiphon devices and valves have been developed to counteract negative standing intracranial pressure.
• Programmable valves can be adjusted to maximize optimal CSF pressure balance.

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

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

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

REFERENCES