hydrocephalis
The term hydrocephalus is derived from the Greek words "hydro" meaning
water and "cephalus" meaning head. As its name implies, it is a condition
in which the primary characteristic is excessive accumulation of fluid in
the brain. Although hydrocephalus was once known as "water on the brain,"
the "water" is actually cerebrospinal fluid (CSF) - a clear fluid
surrounding the brain and spinal cord. The excessive accumulation of CSF
results in an abnormal dilation of the spaces in the brain called
ventricles. This dilation causes potentially harmful pressure on the
tissues of the brain.
The ventricular system is made up of four ventricles connected by
narrow pathways. Normally, CSF flows through the ventricles, exits into
cisterns (closed spaces that serve as reservoirs) at the base of the
brain, bathes the surfaces of the brain and spinal cord, and then is
absorbed into the bloodstream.
CSF has three important life-sustaining functions: 1) to keep the brain
tissue buoyant, acting as a cushion or "shock absorber"; 2) to act as the
vehicle for delivering nutrients to the brain and removing waste; and 3)
to flow between the cranium and spine to compensate for changes in
intracranial blood volume (the amount of blood within the brain).
The balance between production and absorption of CSF is critically
important. Ideally, the fluid is almost completely absorbed into the
bloodstream as it circulates; however, there are circumstances which, when
present, will prevent or disturb the production or absorption of CSF, or
which will inhibit its normal flow. When this balance is disturbed,
hydrocephalus is the result.
Hydrocephalus may be congenital or acquired. Congenital hydrocephalus
is present at birth, and may be caused by either environmental influences
during fetal development or genetic predisposition. 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.
Hydrocephalus may also be communicating or non-communicating.
Communicating hydrocephalus occurs when the flow of CSF is blocked after
it exits from 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
pathways 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 passageway
between the third and fourth ventricles in the middle of the brain.
There are two other forms of hydrocephalus which do not fit distinctly
into the categories mentioned above and primarily affect adults:
hydrocephalus ex-vacuo and normal pressure hydrocephalus.
Hydrocephalus ex-vacuo occurs when there is damage to the brain caused
by stroke or traumatic injury. In these cases, there may be actual
shrinkage (atrophy or wasting) of brain tissue. Normal pressure
hydrocephalus commonly occurs in the elderly and is characterized by many
of the same symptoms associated with other conditions that occur more
often in the elderly, such as memory loss, dementia, gait disorder,
urinary incontinence, and a general slowing of activity.
Incidence and prevalence data are difficult to establish as there is no
existing national registry or database of people with hydrocephalus and
closely associated disorders; however, hydrocephalus is believed to affect
approximately 1 in every 500 children. At present, most of these cases are
diagnosed prenatally, at the time of delivery, or in early childhood.
Advances in diagnostic imaging technology allow more accurate diagnoses in
individuals with atypical presentations, including adults with conditions
such as normal pressure hydrocephalus.
The causes of hydrocephalus are not all well understood. Hydrocephalus
may result from genetic inheritance (aqueductal stenosis) or developmental
disorders such as those associated with neural tube defects including
spina bifida and encephalocele. Other possible causes include
complications of premature birth such as intraventricular hemorrhage,
diseases such as meningitis, tumors, traumatic head injury, or
subarachnoid hemorrhage blocking the exit from the ventricles to the
cisterns and eliminating the cisterns themselves.
Symptoms of hydrocephalus vary with age, disease progression, and
individual differences in tolerance to CSF. For example, an infant's
ability to tolerate CSF pressure differs from an adult's. The infant skull
can expand to accommodate the buildup of CSF because the sutures (the
fibrous joints that connect the bones of the skull) have not yet closed.
In infancy, the most obvious indication of hydrocephalus is often the
rapid increase in head circumference or an unusually large head size.
Other symptoms may include vomiting, sleepiness, irritability, downward
deviation of the eyes (also called "sunsetting"), and seizures.
Older children and adults may experience different symptoms because
their skulls cannot expand to accommodate the buildup of CSF. In older
children or adults, symptoms may include headache followed by vomiting,
nausea, papilledema (swelling of the optic disk which is part of the optic
nerve), blurred vision, diplopia (double vision), sunsetting of the eyes,
problems with balance, poor coordination, gait disturbance, urinary
incontinence, slowing or loss of development, lethargy, drowsiness,
irritability, or other changes in personality or cognition including
memory loss.
The symptoms described in this section account for the most typical
ways in which progressive hydrocephalus manifests itself; it is, however,
important to remember that symptoms vary significantly from individual to
individual.
Hydrocephalus is diagnosed through clinical neurological evaluation and
by using cranial imaging techniques such as ultrasonography, computed
tomography (CT), magnetic resonance imaging (MRI), or pressure-monitoring
techniques. A physician selects the appropriate diagnostic tool based on
the patient's age, clinical presentation, and the presence of known or
suspected abnormalities of the brain or spinal cord.
Hydrocephalus is most often treated with the surgical placement of a
shunt system. This system diverts the flow of CSF from a site within the
central nervous system (CNS) to another area of the body where it can be
absorbed as part of the circulatory process.
A shunt is a flexible but sturdy silastic tube. A shunt system consists
of the shunt, a catheter, and a valve. One end of the catheter is placed
in the CNS - most usually within a ventricle inside the brain, but also
potentially within a cyst or in a site close to the spinal cord. The other
end of the catheter is commonly placed within the peritoneal (abdominal)
cavity, but may also be placed at other sites within the body such as a
chamber of the heart or a cavity in the lung where the CSF can drain and
be absorbed. A valve located along the catheter maintains one-way flow and
regulates the rate of CSF flow.
A limited number of patients can be treated with an alternative
procedure called third ventriculostomy. In this procedure, a
neuroendoscope - a small camera designed to visualize small and difficult
to reach surgical areas - allows a doctor to view the ventricular surface
using fiber optic technology. The scope is guided into position so that a
small hole can be made in the floor of the third ventricle, allowing the
CSF to bypass the obstruction and flow toward the site of resorption
around the surface of the brain.
Shunt systems are not perfect devices. Complications may include
mechanical failure, infections, obstructions, and the need to lengthen or
replace the catheter. Generally, shunt systems require monitoring and
regular medical followup. When complications do occur, usually the shunt
system will require some type of revision.
Some complications can lead to other problems such as overdraining or
underdraining. Overdraining occurs when the shunt allows CSF to drain from
the ventricles more quickly than it is produced. This overdraining can
cause the ventricles to collapse, tearing blood vessels and causing
headache, hemorrhage (subdural hematoma), or slit-like ventricles (slit
ventricle syndrome). Underdraining occurs when CSF is not removed quickly
enough and the symptoms of hydrocephalus recur (see "What are the symptoms
of hydrocephalus?"). In addition to the common symptoms of hydrocephalus,
infections from a shunt may also produce symptoms such as a low-grade
fever, soreness of the neck or shoulder muscles, and redness or tenderness
along the shunt tract. When there is reason to suspect that a shunt system
is not functioning properly (for example, if the symptoms of hydrocephalus
return), medical attention should be sought immediately.
The prognosis for patients diagnosed with hydrocephalus is difficult to
predict, although there is some correlation between the specific cause of
the hydrocephalus and the patient's outcome. Prognosis is further
complicated by the presence of associated disorders, the timeliness of
diagnosis, and the success of treatment. The degree to which decompression
(relief of CSF pressure or buildup) following shunt surgery can minimize
or reverse damage to the brain is not well understood.
Affected individuals and their families should be aware that
hydrocephalus poses risks to both cognitive and physical development.
However, many children diagnosed with the disorder benefit from
rehabilitation therapies and educational interventions, and go on to lead
normal lives with few limitations. Treatment by an interdisciplinary team
of medical professionals, rehabilitation specialists, and educational
experts is critical to a positive outcome.
Treatment of patients with hydrocephalus is life-saving and
life-sustaining. Left untreated, progressive hydrocephalus is, with rare
exceptions, fatal.
Within the Federal government, the leading supporter of research on
hydrocephalus is the National Institute of Neurological Disorders and
Stroke (NINDS). The NINDS, a part of the National Institutes of Health
(NIH), is responsible for supporting and conducting research on the brain
and the central nervous system. NINDS conducts research in its
laboratories at NIH and also supports studies through grants to major
medical institutions across the country.
One NINDS-supported study examined cognitive development, academic
achievement, and behavioral adjustment in children with hydrocephalus.
With further research, investigators hope to shed new light on the
influence of hydrocephalus on development as well as the more general
issue of the effect of early brain injury.
The NINDS also conducts and supports a wide range of fundamental
studies that explore the complex mechanisms of normal brain development.
The knowledge gained from these studies provides the foundation for
understanding how this process can go awry and, thus, offers hope for new
means to treat and prevent developmental brain disorders such as
hydrocephalus.
Keeping on Top of Your Condition
Keeping in tune with your disease or condition not only makes treatment less intimidating but also increases its chance of success, and has been shown to lower a patients risk of complications. As well, as an informed patient, you are better able to discuss your condition and treatment options with your physician.
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Private, voluntary organizations that offer information and services to
those affected by hydrocephalus include the following:
Guardians of Hydrocephalus Research Foundation, Inc.
2618 Avenue
Z
Brooklyn, New York 11235-2023
718-743-GHRF (4473)
718-743-1171
(fax)
GHRF2618@aol.com
http://ghrf.Homestead.com/ghrf.html
Hydrocephalus Association, Inc.
870 Market Street
Suite
705
San Francisco, California
94102
415-732-7040
888-598-3789
415-732-7044
(fax)
hydroassoc@aol.com
http://www.hydroassoc.org/
Hydrocephalus Support Group
PO Box 4236
Chesterfield, Missouri
63006-4236
636-532-8228
dhydrobuff@aol.com
National Hydrocephalus Foundation
12413 Centralia Road
Lakewood,
CA 90715-1623
562-402-3523
888-857-3434
562-924-6666
(fax)
hydrobrat@earthlink.net
http://nhfonline.org/
BRAIN
P.O. Box 5801
Bethesda, Maryland 20824
(800)
352-9424
http://www.ninds.nih.gov/
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