What is hydrocephalus?
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 of hydrocephalus 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, 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 is normal pressure hydrocephalus?
Normal pressure hydrocephalus (NPH) is an accumulation of CSF that causes the ventricles in the brain to become enlarged, sometimes with little or intermittent increases in intracranial pressure (ICP). It is most commonly seen in older adults, and is accompanied by some or all of the following symptoms: gait disturbance, mild dementia and impaired bladder control.
What causes normal pressure hydrocephalus?
The majority of cases of NPH have no known cause. It can develop as the result of a head injury, cranial surgery, subarachnoid hemorrhage, tumor or cysts, as well as subdural hematomas , meningitis and other brain infections.
What are the symptoms of hydrocephalus?
NPH is usually characterized by a triad of symptoms: complaints of gait disturbance (difficulty walking), mild dementia and 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. The cognitive deficits of NPH can resemble those associated with Alzheimer’s and the gait disturbances of NPH can look similar to those of Parkinson’s disease. In some cases NPH can occur in combination with these diseases. Symptoms of hydrocephalus seem to progress with time, but the rate is variable. As a general rule, the earlier the diagnosis, the better the chance for successful treatment; however some patients who have had symptoms for years may improve with treatment.
How is normal pressure hydrocephalus diagnosed?
Once NPH 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
What treatment is available?
The only available treatment for NPH 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.
Who is a likely candidate for shunting?
The answer to this question is still uncertain. No one single factor is reliable in predicting success from implantation of a shunt. The following findings are generally associated with a better outcome following shunt placement:
- The onset of gait disturbance as the first and most prominent symptom
- A known cause for NPH, such as a trauma or hemorrhage
- The scan shows the ventricle size to be disproportionately larger than the CSF in the subarachnoid space
- Removal of spinal fluid via lumbar puncture or lumbar catheter gives dramatic, temporary relief of symptoms
- ICP or spinal fluid pressure monitoring shows an abnormal range or pattern of spinal fluid pressure or an elevated CSF outflow resistance
Although everyone hopes for a complete recovery, it is not often seen. Many individuals and their families are satisfied when shunt surgery results in reduced disability or dependence than he or she had before surgery, or prevention of further neurological deterioration. People with NPH, their families and their physicians need to be supportive and hopeful, but they should also know the possible complications, risks and realities of shunt implantation.
How can I consult a Johns Hopkins specialist for assessment of possible NPH?
There are several neurologic conditions that can mimic NPH. Obtaining a CT or MRI of the Brain is helpful in narrowing the possibilities and is often the first step in the diagnosis. If the symptoms and scans are consistent with NPH your primary care physician or neurologist can refer you to our center for further assessment. To arrange for a personal appointment to discuss hydrocephalus diagnosis and treatment options with a specialist at the Johns Hopkins Normal Pressure Hydrocephalus Center, please call 410-955-7482. We will need you to fill a detailed questionnaire and review your medical notes and actual scans before your appointment, for optimal assessment at your clinic visit.