Hydrocephalus is a condition characterized by an abnormal accumulation of cerebrospinal fluid (CSF) within the ventricles of the brain. CSF surrounds the brain and spinal cord.
When the circulatory path of the CSF is blocked, fluid begins to accumulate, causing the ventricles to enlarge and the pressure inside the head to increase, resulting in hydrocephalus.
What are the different types of hydrocephalus?
Hydrocephalus may be communicating or non-communicating. Communicating hydrocephalus occurs when the flow of CSF is blocked after it exits the ventricles. This form is called communicating because the CSF can still flow between the ventricles, which remain open.
Non-communicating hydrocephalus – also called “obstructive” hydrocephalus – occurs when the flow of CSF is blocked along one or more of the narrow passages connecting the ventricles.
One of the most common causes is “aqueductal stenosis.” In this case, hydrocephalus results from a narrowing of the aqueduct of Sylvius, a small passage between the third and fourth ventricles in the middle of the brain.
Normal pressure hydrocephalus (NPH), a form of communicating hydrocephalus, can happen to people at any age, but it is most common among the elderly. It may result from a subarachnoid hemorrhage, head trauma, infection, tumor, or complications of surgery.
However, many people develop normal pressure hydrocephalus even when none of these factors are present for reasons that are unknown. In that case it is called idiopathic normal pressure hydrocephalus.
Hydrocephalus may be also be classified as congenital or acquired. Congenital hydrocephalus is present at birth and may be caused by either events or influences that occur during fetal development, or genetic abnormalities.
Acquired hydrocephalus develops at the time of birth or at some point afterward.
This type of hydrocephalus can affect individuals of all ages and may be caused by injury or disease. Rarely congenital hydrocephalus may be compensated in childhood but only manifest in adulthood.
It often but not always associated with aqueductal stenosis. There is another form of hydrocephalus that does not fit exactly into the categories mentioned above and primarily affect adults: hydrocephalus ex-vacuo.
Hydrocephalus ex-vacuo occurs when stroke, degenerative diseases like Alzheimer’s disease or other dementias or traumatic injury cause damage to the brain. In these cases, brain tissue may actually shrink.
What are the symptoms of hydrocephalus?
The possible triad of symptoms typically present as follows:
gait disturbance and difficulty walking
impaired bladder control
These symptoms may not occur all at the same time, and sometimes only one or two symptoms are present. The triad of symptoms is often associated with the aging process and a majority of the NPH population is older than 60 years.
How is hydrocephalus diagnosed?
Once a type of hydrocephalus is suspected by a primary physician, one or more of the following tests are usually recommended to confirm the diagnosis and assess the person’s candidacy for shunt treatment.
It is important that at this point a neurosurgeon and/or neurologist become part of the medical team.
Their involvement is helpful not only in interpreting test results and selecting likely candidates for shunting, but also in discussing the actual surgery and follow-up care as well as expectations and risks of surgery.
Clinical Exams – consists of an interview and or a physical/neurologic examination
Brain images to detect enlarged ventricles
- CT or CAT scan
- CSF tests to predict shunt responsiveness and/or determine shunt pressure
- Lumbar or spinal tap – large volume
- External lumbar drainage
- Measurement of CSF outflow resistance
- Measurement of CSF outflow resistance
What treatment options are available?
The only available treatment for hydrocephalus is the surgical implantation of a shunt, a device that channels CSF sway from the brain to another part of the body where it can be absorbed. Most shunt systems consist of three components:
- A collection catheter situated within the cerebral ventricles
- A valve mechanism to control how much CFS flows
- An exit catheter to drain the CSF to another part of the body
After the surgery, all components of the shunt system are entirely under the skin, and nothing is exposed to the outside. A limited number of individuals can be treated with an alternative procedure called endoscopic third ventriculostomy.
In this procedure, a neuroendoscope — a small camera that uses fiber optic technology to visualize small and difficult to reach surgical areas — allows a doctor to view the ventricular surface.
Once the scope is guided into position, a small tool makes a tiny hole in the floor of the third ventricle, which allows the CSF to bypass the obstruction and flow toward the site of resorption around the surface of the brain.
Management depends on how acute the deterioration is.
Drugs are usually used as a holding measure until the appropriate intervention can be carried out.
A lumbar puncture may be used in the management of acute deterioration if there is a communicating hydrocephalus. Repeated lumbar punctures may avoid neurosurgery if the condition is likely to resolve spontaneously.
Gradual deterioration allows for a more ample assessment and careful consideration of options. Underlying causes such as tumours need to be identified and addressed.
‘Arrested’ hydrocephalus needs no treatment if it remains asymptomatic but the patient will benefit from regular developmental or psychometric assessments to catch any ill effects early.
Medication may help to defer surgery in order to stabilise the patient but medical treatment alone is generally unsuccessful in long-term control of ICP.
Furosemide and acetazolamide inhibit secretion of CSF by the choroid plexus. Isosorbide promotes reabsorption.
Insertion of an external ventricular drain- this allows for the temporary drainage of the CSF into an external collecting system. It can be created by externalising an existing system in situ or by creating a new system.
Insertion of a shunt – this is performed in the majority of cases. A ventricular catheter drains the CSF through a small reservoir (placed on the surface of the scalp, to enable CSF aspiration for analysis) down to either the right atrium of the heart (ventriculoatrial shunt (VA shunt)) or into the peritoneal cavity (ventriculoperitoneal shunt (VP shunt)) – the latter being the most common.
A catheter can also drain the distal CSF in the lumbar area into the peritoneum (lumboperitoneal shunt).
Other surgical procedures – choroid plexectomy, choroid plexus coagulation and endoscopic cerebral aqueductoplasty have all been helpful in some cases.
Endoscopic fenestration of the floor of the third ventricle may be effective in non-communicating hydrocephalus but is contra-indicated in communicating hydrocephalus.
Complications of hydrocephalus
Untreated congenital hydrocephalus is often fatal within the first four years of life. Epilepsy, and learning and developmental difficulties are some of the more common complications encountered.
However, if treatment precedes irreversible brain damage, the outlook is good. The prognosis in other conditions depends on the underlying cause.
- Of shunt surgery
- Infection (3-27%)
- Subdural haematoma
- Shunt obstruction
- Low pressure state
Some congenital conditions can be diagnosed antenatally and managed early in life to avoid complications. Preventative strategies for certain causes of hydrocephalus can also be implemented, eg to prevent trauma in high-risk occupations or sports.
However, most cannot be anticipated and it is the early detection and rapid intervention that underpins the management of these patients.