The following excerpt is taken from Chapter One of Hydrocephalus: A
Guide for Patients, Families, and Friends by Chuck Toporek & Kellie
Robinson, copyright 1999 by O'Reilly & Associates, Inc. For book
orders/information, call 1-800-998-9938. Permission is granted to
print and distribute this excerpt for noncommercial use as long as the
above source is included. The information in this article is meant to
educate and should not be used as an alternative for professional
The word hydrocephalus is derived from the Greekhydro means
water, and cephalus means head. It is a neurological condition
that occurs when there is an abnormal accumulation of cerebrospinal
fluid (CSF) within the ventricles and/or subarachnoid space of the
brain. The increase of intracranial pressure (ICP) can either be the
result of an overproduction of CSF (a condition known as choroid
plexus papilloma), an obstruction of the flow of CSF, or a failure of
the structures of the brain to reabsorb the fluid. Although there is
little public awareness about hydrocephalus, according to recent
statistics from the U.S. Centers for Disease Control and Prevention,
hydrocephalus affects approximately 1 out of every 1,000 children born
each year. Hydrocephalus can also be acquired after birth from a
variety of causes.
Hydrocephalus is a condition where the normal drainage of CSF in the
brain is blocked in some way. Neurosurgeons classify hydrocephalus
according to when the condition was developed (congenital or
acquired), and whether it was caused by a reabsorption problem or a
blockage somewhere within the ventricles (communicating or
non-communicating). Another type of hydrocephalusnormal pressure
hydrocephalusis when the ventricles are enlarged, but there is
little or no increase in intracranial pressure. These terms are often
combined when referring to a particular type of hydrocephalus. For
example, if you have a condition known as aqueductal stenosis (a
blockage of the aqueduct of Sylvius) caused by an intraventricular
cyst, then your diagnosis would be "acquired, non-communicating
Hydrocephalus is considered congenital when its origin can be
traced to a birth defect or brain malformation that causes an
increased resistance to the drainage of CSF. A variety of factors can
cause congenital hydrocephalus. Among the possible causes:
- Toxoplasmosis, or T gondii, is a type of organism that can
be transmitted by eating undercooked meat, contact with contaminated
soil, or by direct contact with an animal or bird that already has the
- Cytomegalovirus (CMV) belongs to the herpes family of viruses, and
normally produces symptoms that resemble that of the common cold.
- Rubella, or German measles, is known to cause fetal malformations
during pregnancy, one of which is hydrocephalus.
- X-linked hydrocephalus is almost exclusively a genetic disorder
passed from mother to son on the X chromosome. It is inherited only
through the mother, and is predominantly seen in males (approximately
one in 20). There is also a small chance that first cousins of
children with uncomplicated congenital hydrocephalus can also inherit
Congenital hydrocephalus can be linked to other complications. A
17-year study that concluded in 1987 tracked four major congenital
neurological malformations: anencephaly, spina bifida, encephaloceles
and hydrocephalus. Of 370 births with these defects, 10.5 percent (39)
resulted in stillbirths. Although a majority of live-born infants with
hydrocephalus were free of other complications, 37 percent had
congenital malformations which were unrelated to the hydrocephalus. Of
those, the most common malformations were tracheoesophageal fistula
(an abnormal communication between the trachea, or windpipe, and the
esophagus), and anomalies with the reproductive, urinary, and cardiac
systems (Thomas E. Wiswell et al., "Major congenital neurologic
malformations: a 17-year study," American Journal of Diseases in
Children 144, no. 1, January 1990: 61-7).
Hydrocephalus can be acquired later in life if something
causes an increase in the resistance to the drainage of CSF, such as
an obstruction. Acquired hydrocephalus can also be caused by brain
tumor, arachnoid cyst, intracranial or intraventricular hemorrhaging
(IVH), trauma to the head, or by infections such as meningitis.
At the age of six weeks, my mom noticed that my head was unusually
large, and she could lay a finger between the bones in my skull. She
called the neurosurgeon, and met him in the emergency room. He saw me
from across the examination room, proceeded to the phone, and reserved
time in the operating room. To him, it was very apparent that I was in
dire need of a shunt. My head was about the size of the rest of my
In 1983, at the age of thirteen, I acquired hydrocephalus when I was
hit in the head by a baseball. It was a freak accident. I was a good
player, and could hit and field well. Unfortunately, that one time
the ball was thrown to me, I looked up and lost it in the sun. My
nose bled and immediately swelled; my family and I just assumed that I
broke my nose again. Only later did we realize the true complications
I went to the doctor and he confirmed that my nose was
broken. However, there was nothing he could do at that time. It would
have to just heal on its own. Approximately a month later, I missed
school because I was very lethargic and had excruciating headaches. At
first, they thought that it might be migraine headaches, however, as I
grew more lethargic and bright lights started to bother me, my family
grew very concerned.
Since it was at the end of my freshman year in high school, I did not
want to miss much school, so I tried to work through the
illness. However, when the nausea increased and my vision doubled, I
went to my pediatrician, who sent me to the hospital for tests and a
CT scan. As the result of my scans, I was sent to the Children's
Hospital in Boston. It was there that I was diagnosed with
Bacterial meningitis is an inflammation of the meninges, the
protective layering that surrounds the brain and spinal
cord. Hydrocephalus develops when scarring of the meninges restricts
the flow of CSF in the subarachnoid space, when it passes through the
aqueduct of the ventricular system, or affects the absorption of CSF
at the arachnoid villi.
If left untreated, bacterial meningitis can cause death within
days. Signs and symptoms of meningitis include: severe headaches, high
fever, loss of appetite, light and sound sensitivity, and tension in
the muscles of the neck and shoulders. In extreme cases, symptoms of
meningitis can include vomiting, convulsions or seizures, and
delirium. Once detected, bacterial meningitis can be treated with high
doses of antibiotics.
Brain tumors and cysts
Hydrocephalus may also be acquired as a result of brain tumors or
cysts. Most brain tumors are detected in children between the ages of
five and ten years old. Seventy-five percent of these tumors occur in
an area at the back of the brain, known as the posterior fossa. Other
types of brain tumors that can cause hydrocephalus include
intraventricular tumors, and in extremely rare cases, tumors of the
choroid plexus (including papilloma and carcinoma).
As the tumor grows in mass, it creates a form of non-communicating
hydrocephalus by reducing the flow of CSF within the
ventricles. Tumors that are located in the back of the brain most
commonly obstruct the flow of CSF through and out of the fourth
ventricle. In most cases, the best way to treat hydrocephalus related
to a tumor is to remove (excise) the tumor causing the
obstruction. However, hydrocephalus does persist in approximately 20
to 40 percent of patients after the tumor is removed.
Cysts are benign sacs or closed cavities that are filled with
fluid. Cysts can occur anywhere in the body. With arachnoid cysts, the
sacs are filled with CSF and are lined with tissue from the arachnoid
membrane. Cysts are commonly found in children, and are located both
within the ventricles and on the surface of the brain, or in the
subarachnoid spaces. Arachnoid cysts can cause a form of
non-communicating hydrocephalus by restricting the flow of CSF within
the ventricular systemparticularly in the third ventricle. Cysts
can also be found in the subarachnoid space.
Depending on the location of the cyst, the neurosurgeon may be able
to excise the cyst wall and drain the cyst's fluid. If the cyst is
located in an inoperable location (e.g., near the brain stem), the
neurosurgeon might decide to place a shunt catheter in the cyst. This
catheter is then connected to a shunt system to allow the fluid to be
drained. This stops the growth of the cyst and protects the brain
Intraventricular hemorrhages (IVH)
A common complication with premature births is the risk of an
intracranial or intraventricular hemorrhage (IVH), bleeding within the
ventricles of the brain. IVHs can be found in approximately 40 percent
of premature infants. If the IVH is severe enough, it could compromise
the ventricles, allowing blood to flow into surrounding brain tissues
and lead to neurological changes. The possibility of hydrocephalus
developing as a result of an IVH depends largely on the severity of
the bleed, and whether or not blood and debris have caused an
obstruction in the CSF pathways, or reduced the brain's ability to
reabsorb the CSF. In many cases, however, hydrocephalus is mild and
tends to stabilize. Thus, not all infants who have an IVH will need a
Severe head trauma can also cause hydrocephalus, although it is
uncommon. The hydrocephalic condition occurs as a result of bleeding
into the subarachnoid spaces. Scarring of the drainage pathways from
the resulting intracranial bleed can cause a partial obstruction of
the flow of CSF.
The term "communicating hydrocephalus" means that the site of
increased resistance to CSF drainage resides outside of the
ventricular system in the subarachnoid space. Communicating
hydrocephalus is caused one of three ways:
- An overproduction of CSF (a rare condition associated with a
choroid plexus papilloma).
- A venous obstruction (a rare condition known as Otitic hydrocephalus).
- An increased resistance to the drainage of CSF from the subarachnoid space.
"Communicating" means the ventricles of the brain communicate,
or pass along, the CSF to the surface of the brain. The obstruction of
CSF flow occurs not within the ventricles, but within the subarachnoid
spaces of the brain. Communicating hydrocephalus can also be the
result of a meningeal inflammation, such as an infection, or by blood
or tumor cells in the subarachnoid spaces.
Non-communicating, or obstructive, hydrocephalus is caused
when there is an obstruction in the flow of CSF within the ventricular
system of the brain, including the outlets of the fourth ventricle
(the foramina of Luschke and Magendie). The most common place for the
non- communicating CSF obstruction is in the aqueduct of Sylvius (also
known as aqueductal stenosis). However, the obstruction can also
occur in the outlets of the fourth ventricle and from the lateral
ventricles into the third ventricle at the foramina of Monro.
An example of non-communicating hydrocephalus is stenosis (or
blockage) of the aqueduct of Sylvius. This blockage causes
non-communicating hydrocephalus by not permitting CSF to flow from the
third to the fourth ventricle. When the obstruction is located in the
ventricular system, it causes the ventricles to expand as a result of
the accumulation of CSF. Non-communicating hydrocephalus is the most
common form of hydrocephalus in fetuses.
Normal-pressure hydrocephalus (NPH)
A person can be diagnosed as having normal pressure hydrocephalus
(NPH) when the ventricles of the brain are enlarged, but there is
little or no increase in the pressure within the ventricles. NPH is
normally seen in elderly patients, and is most likely caused by an
obstruction of the CSF pathways and abnormal brain compliance.
NPH can be divided into two classifications: those where the cause of
the hydrocephalus is known, such as a previous history of meningitis
or a subarachnoid hemorrhage, and
idiopathic, where the cause of NPH is not known.
Management of NPH can often be tricky, as the neurosurgeon must try
to find the right shunt to treat the condition. If the shunt
overdrains, it could result in a subdural accumulation, or pocket, of
CSF and/or blood between the dura and arachnoid mater of the
meninges. If the shunt doesn't drain enough CSF (known as
undershunting), the ventricles may not be allowed to reduce in size.
Also, shunting may not improve the situation.
Although hydrocephalus can develop for a variety of reasons,
congenital hydrocephalus is often a part of other neurological
conditions and congenital malformations. Other conditions that
hydrocephalus is often associated with include, from most to least
- Dandy-Walker syndrome.
- Neural tube defects (NTDs).
- Spina bifida.
- Chiari malformations.
- Vein of Galen malformations.
This section briefly describes these disorders and explains how they
can cause hydrocephalus, as well as symptoms, treatments and
prognosis. For more detailed information, talk with your doctor or
neurosurgeon, as she can provide more detailed information as it
pertains to your child.
Dandy-Walker syndrome is a congenital brain malformation that
involves the fourth ventricle and the cerebellum. It is defined as an
enlargement of the fourth ventricle, and is accompanied by an absence
(partial or complete) of the cerebellar vermis (the narrow middle area
between the hemispheres of the brain). The combination of these
malformations is what causes hydrocephalus in patients with
Symptoms that often occur in early infancy include slow motor
development and progressive macrocephaly (an abnormally enlarged
skull). In older children, symptoms of increased intracranial pressure
such as irritability, vomiting, and/or signs of cerebellar dysfunction
such as ataxia (unsteady gait) and nystagmus (jerky eyes) may occur.
Symptoms of Dandy-Walker syndrome include increased head
circumference, bulging occiput (the back of the head), cranial nerve
dysfunction, and abnormal breathing patterns. Dandy-Walker syndrome
can be associated with other central nervous system structural
abnormalities, including malformations of the heart and an absence of
the corpus callosum.
In cases where increased intracranial pressure is present, a shunt
will most likely be placed to control the hydrocephalus. Even when
hydrocephalus is treated early, patients with Dandy-Walker syndrome
often face other problems. Prognosis for normal intellectual
development is variable depending on the severity of the syndrome and
its associated malformations.
Neural tube defects
Spina bifida (SB) is a general term that denotes failure of normal
formation of midline structuresin this case, the spinal cord and
the spinal column. Those conditions that are of clinical importance
include only the neural tube and are collectively referred to as
neural tube defects (NTDs). NTDs are best divided into two groups:
open and closed.
- Open NTDs. These are found in infants with
myelomeningoceles. The spinal cord is open and is continuously or
intermittently leaking CSF. The entire CNS is malformed, and the
myelomeningoceles is likened to the tip of the iceberg above the
These infants have a partial or complete paralysis of the lower
extremities, which may also be deformed. Bladder and bowel function
are almost always severely affected with the infant never becoming
continent for urine or stool. The vast majority of infants develop
progressive hydrocephalus and will need to be shunted. Because of
cortical disorganization, the majority of children will have learning
disorders that vary from mild to severe. The medical care required is
complex and lifelong.
- Closed NTDs. The spinal cord is not exposed, but is covered
by skin. CSF leakage is not present. The abnormality is confined to
the lower end of the spinal cord, and there is no malformation of the
brain. Thus, the Chiari malformation, hydrocephalus, and learning
disorders are not a consideration. These infants can develop bladder
and/or bowel dysfunction and a mild motor/sensory loss that normally
involves only one lower extremity.
At present, there is no cure for myelomeningoceles because the nerve
tissue cannot be replaced or repaired. Surgery to close the
newborn's spinal opening is generally performed within two days of
birth to minimize the risk of infection and to preserve existing
function in the spinal cord. Ongoing therapy, medical care, and
surgical treatments may be necessary to prevent and manage
complications throughout the person's life. Many individuals with
myelomeningoceles will need assisting devices such as braces,
crutches, or wheelchairs.
The prognosis for children with myelomeningoceles depends on the
number and severity of other abnormalities. Prognosis is poorer for
those with complete paralysis, hydrocephalus, and other congenital
defects. With proper medical care, most children with
myelomeningoceles live well into adulthood.
Chiari malformation (CM)
A Chiari malformation (CM; formerly referred to as Arnold-Chiari
malformation, or ACM) is a rare congenital anomaly in which two parts
of the brainthe brain stem and the cerebellumare longer than
normal and protrude down into the spinal canal. Chiari malformations
are divided into two groups:
- Type I. A mild form with the cerebellar tonsils protruding
into the spinal cord. This may be asymptomatic or be associated with
cranial nerve dysfunction or fluid build-up in the spinal cord
- Type II. A more severe form with an extensive malformation
of the cerebellum and brain stem that is seen almost exclusively with
an open NTD (i.e., myelomeningoceles). Hydrocephalus is usually
present. Some infants may develop difficulty with breathing,
swallowing, feeding, etc., as a result of this malformation.
Most patients who have surgery experience an improvement of symptoms
almost immediately, and may experience prolonged periods of relative
stability, while others may continue to have neurological
deterioration. Infants with severe malformations may have
Vein of Galen malformation (VGM)
The vein of Galen malformation (VGM) is a rare vascular disorder that
is present at birth, but normally isn't detected until the child is
a few months old. VGMs occur when the vein of Galen, which runs above
the aqueduct of Sylvius, balloons to create an aneurysimal sac. This
aneurysm often compresses the aqueduct of Sylvius, causing
Vein of Galen malformations are commonly diagnosed in infants by a
cardiologist, as the infant often suffers heart failure (a heart
attack) because of the rapid rate of heart circulation. Another
symptom that aids in the detection and diagnosis of a VGM is
macrocrania (an enlarged skull). Macrocrania is caused when the
ventricles enlarge due to the obstruction of CSF flow, causing
increased intracranial pressure.
Symptoms often include headache (due to increased intracranial
pressure), lethargy (due to an enlarged heart), and vomiting. One of
the primary concerns in the diagnosis of a VGM is the enlarged heart,
which may lead to heart failure. VGMs are easily diagnosed with
contrast- enhanced CT or MRI. X-rays of the chest will confirm whether
the heart is enlarged or not.
Shunting is often required to treat the hydrocephalus, but may not be
necessary if ICP is reduced when the VGM is treated.
Hydranencephaly is a rare condition in which the brain's cerebral
hemispheres are absent and are replaced by sacs filled with
cerebrospinal fluid. An infant with hydranencephaly may appear normal
at birth. The infant's head size and spontaneous reflexes, such as
sucking, swallowing, crying, and moving the arms and legs may all be
Due to the lack of cerebral hemispheres, there is no significant
neurological development, with the infant's function remaining at
the newborn level forever. Hydrocephalus frequently develops, and a
shunt is inserted to keep the child's head from becoming abnormally
Diagnosis may be delayed for several months because early behavior
appears to be relatively normal. Some infants may have additional
abnormalities at birth, including seizures, myoclonus (spasm or
twitching of a muscle or group of muscles), and respiratory
problems. There is no definitive treatment for hydranencephaly other
than to place a shunt to prevent the head from becoming large, and
surgery to treat other malformations.
Craniosynostosis is a congenital anomaly which is characterized by the
premature closure of one or more cranial sutures before the brain has
fully grown. The disorder results in an abnormal head shape, and may
be a feature of a chromosomal or genetic syndrome or
abnormality. Treatment for craniosynostosis generally consists of
surgery, usually performed early in life. This allows the skull to
accommodate brain growth, and improves the appearance of the
Prognosis for craniosynostosis varies depending on whether single or
multiple sutures are involved and the presence of associated
abnormalities. The prognosis is generally better for patients with
single suture involvement and no associated
abnormalities. Hydrocephalus is rarely present with single-suture
involvement, and is occasionally seen with some other forms of
Schizencephaly is an extremely rare developmental disorder
characterized by abnormal slits, or clefts, in the brain's cerebral
hemispheres. Individuals with clefts in both hemispheres (bilateral
clefts) are commonly developmentally delayed, and have delayed speech
and language skills. Individuals with smaller, unilateral clefts
(clefts in only one hemisphere) are often paralyzed on one side of the
body and may have normal intelligence. Patients with schizencephaly
may also have varying degrees of microcephaly, mental retardation,
hemiparesis or quadriparesis, reduced muscle tone, and
hydrocephalus. Most patients with schizencephaly experience seizures.
Individuals with schizencephaly are generally treated with physical
therapy, prescribed anti- convulsants to control seizures, and
placement of a shunt for hydrocephalus.
Cerebrospinal fluid (CSF) is a clear, colorless fluid that surrounds
the brain and spinal cord, protecting them from injury. CSF is mostly
made up of water with a few trace proteins, electrolytes, and
nutrients that are needed for the nourishment and normal function of
your brain. CSF also serves the brain by carrying away waste products
from surrounding tissue.
Cerebrospinal fluid production and absorption
Under normal conditions, the brain produces an amount of CSF equal to
what is absorbed by the body each day. Approximately 80 to 90 percent
of CSF is produced by the choroid plexus. The choroid plexusfound
in the lateral, third and fourth, ventriclesis a network of blood
vessels covered by a tissue membrane that secretes newly formed
CSF. The average person, including older infants, produces
approximately 20 milliliters (ml) of CSF per hour (about 500 ml, or a
pint, per day).
The average volume of intracranial CSF (the fluid that is within the
brain at any one time) is 125 to 150 ml, of which approximately 90 to
100 ml can be found in the subarachnoid space which surrounds the
brain and spinal cord.
CSF is constantly being produced, flowing through, bathing,
protecting, and cleansing the structures of your brain before it is
reabsorbed into the bloodstream. There is a threefold turnover of CSF
within a 24-hour period.
Flow of cerebrospinal fluid
The flow of CSF follows a somewhat predictable pattern throughout the
brain and spinal column. Cerebrospinal fluid is produced mainly by
the choroid plexus of the lateral ventricles. CSF flows from the
lateral ventricles of the brain through the foramen of Monro (a short
passageway that extends down from the lateral ventricles) on its way
to the third ventricle. From there, the CSF passes through the narrow
passageway of the cerebral aqueduct on its way to the fourth
ventricle. The cerebral aqueduct is also known as the aqueduct of
Sylvius. It is here that the most common cause of hydrocephalus can be
CSF exits the fourth ventricle by way of the foramina of Luschke and
Magendie, where it enters the subarachnoid spaces. The fluid continues
to flow over the brain to the arachnoid granulations (or villi) in the
superior sagittal sinus where it is reabsorbed. The superior sagittal
sinus is a venous channel that runs between the left and right
hemispheres of the brain. It extends down to the back of the head
where it splits in two, creating the transverse sinuses, which then
turn into the internal jugular veins that return blood to the right
atrium of the heart. Arachnoid villi, located in the subarachnoid
space, permit the flow of CSF from that space to the superior sagittal
sinus, as well as other large channels.
The brain is the nerve center and is by far the most complex organ in
the human body. The primary function of the brain is to control the
body. It regulates breathing and circulation, and controls the
functions of the body's vital organs. The brain is also responsible
for analyzing and remembering everything that you see, touch, hear,
taste, and smell. For instance, when you reach down to touch a flower,
the nerves in your fingertips send an impulse to the parietal lobe of
your brain, which identifies the sensation.
To communicate effectively with neurosurgeons, patients who have
hydrocephalus need to become familiar with the basic structures of the
brain. Your neurosurgeon will talk about the various structures of the
brain, and by being familiar with their location and functions, you
will better understand what she is talking about. Learning about some
of the terms and functions of the brain will allow you to more
actively participate in your care. After some experience with the
condition, you will find yourself talking about ventricles,
hemispheres, lobes, the cerebellum, cranial nerves, and possibly other
parts of the brain you didn\306t know existed.
The brain is divided into sections that control different bodily
functions. The effect that hydrocephalus has on an area of the body
greatly depends on where the blockage or abnormal accumulation of CSF
is located. If there is a build-up of fluid near the frontal lobes of
the brain, you could experience difficulty with motor skills, since
the frontal lobe houses the motor cortex. Likewise, if there is a
arachnoidal cyst that is placing pressure on the occipital lobe, your
vision might be affected.
Responses on one side of the brain control actions on the opposite
side of the body. For example, if you want to move your right arm, a
signal is sent to the motor cortex of your left frontal lobe. This
signal is then sent to the muscles of your arm to perform and control
the movement. If there is a cyst or tumor placing pressure on the
right side of the brain, it will affect the functions of the left side
of the body controlled by the area where the cyst or tumor is located.
This article gives you an overview of the structures of the brain and
discusses some of their functions. It first looks at the outermost
structures of the brain, the meninges, then at the middle of the brain
where the ventricles are located, and finally moves inside to the core
of the brain, the brain stem.
The meningeal layer surrounds the brain and spinal cord and protects
them from injury. CSF acts as a cushioning device between the
meninges, gray matter, and the inside of the skull. The meninges
consist of three separate layers: the dura, arachnoid, and pia mater.
The outermost meningeal layer is the dura mater. The dura mater is a
tough, inelastic membrane that consists of two layers fused
together. The outer layer of the dura mater is similar to the
periostium, and the inner layer is called the dura.
The area between the dura and arachnoid layers is known as the
subdural space. When a shunt overdrains, it reduces the volume of CSF
within the ventricles, causing the brain to move inward away from the
meninges. As the brain moves inward, blood vessels in the arachnoid
layer of the meninges are torn, forming a subdural hematoma (a pocket
of blood) between the arachnoid and dura layers. Overdraining of the
ventricles and subdural hematomas are just one of many possible
complications of having a shunt.
The next meningeal layer is the arachnoid. This fine, cobweb-like
layer covers the brain and spinal cord, and contains many large blood
vessels. Unlike the dura, the arachnoid mater has an elastic
quality. The area between the arachnoid layer and the next, the pia
mater, is known as the subarachnoid space. CSF flows through the
subarachnoid space, over the surface of the brain and spinal cord.
The innermost meningeal layer is known as the pia mater. The pia mater
hugs the surface of the brain and spinal cord, and is filled with
blood vessels that supply the nerve tissue below.
The meninges extend downward between the cerebral hemispheres (the
cerebrum) to create the falx cerebri, and between the occipital lobes
of the cerebrum and cerebellum to form the tentorium. The falx cerebri
is what divides the left and right hemispheres of the brain, while the
tentorium is what separates the upper and lower sections of the brain.
The brain is divided into two cerebral hemispheres, which are commonly
referred to as the left and right hemispheres. When combined, the
cerebral hemispheres make up the cerebrum, which is the largest and
most highly developed part of the brain.
The left and right hemispheres are separated by the longitudinal
fissure, where the falx cerebri of the dura is located. The left and
right cerebral hemispheres are joined together at the center of the
brain by the corpus callosum. The corpus callosum is a broad band of
fibers which allows one side of the brain to communicate with the
other. The cerebral hemispheres are each made up of four pairs of
lobes: frontal, temporal, parietal and occipital.
The frontal lobes are located at the front part of each cerebral
hemisphere and extend back to about the middle of the brain. The
frontal lobes make up approximately one-third of each hemisphere of
the brain. The lower region of the left frontal lobe, known as
Broca's area, is responsible for initiating speech. The prefrontal
cortex, which is located at the front of each frontal lobe, plays a
role in memory, social behavior, learning, judgment and personality.
Just forward of the central sulcus, located at the posterior margin of
the frontal lobe, is the motor cortex. The motor cortex is responsible
for controlling voluntary movements of the muscles and limbs of the
body. The central sulcus, which separates the frontal and parietal
lobes, begins at the top of the hemisphere and extends downward until
it reaches the lateral sulcus.
The temporal lobes are located at the side of the brain, within the
temple of the cranium. They are separated from the frontal lobes by a
cleft called the lateral fissure. The lateral fissure is an in-
folding of the frontal lobe that runs laterally between the frontal
and temporal lobes. The upper region of the temporal lobe is
associated with the sense of hearing. The inner region of the temporal
lobe is responsible for memory.
The parietal lobes are situated above the temporal lobes and between
the frontal and occipital lobes. Located within the parietal lobe is
the primary sensory area, which is responsible for receiving
sensations from the body. Abnormalities in this area of the brain can
be associated with reading and learning disabilities.
The occipital lobe is located in the back of the brain, behind the
parietal and temporal lobes and above the cerebellum. The occipital
lobe is responsible for interpreting what is seen with the eyes.
The ventricular system of the brain is made up of four chambers, or
ventricles, which are connected to each other by way of narrow
passages, called foramen. As mentioned earlier, CSF is produced in the
ventricular system by the choroid plexus. The CSF flows from the
ventricles into the subarachnoid space, and over the surface of the
brain and spinal column. Hydrocephalus occurs when there is an
obstruction of one of the ventricles or ventricular foramina (CSF
passageways) that restricts the flow of CSF either within the
ventricular system, the subarachnoid space, or the cisterns
(reservoirs for CSF). The ventricular foramina consist of the
intraventricular foramina (or the foramen of Monro), which connect the
lateral ventricles with the third ventricle, and the foramina of
Luschke and Magendie (located in the fourth ventricle) which provide a
means for CSF to exit the ventricular system. (Foramina is the
plural of foramen.)
The third and fourth ventricles are connected to each other by the
cerebral aqueduct, also known as the aqueduct of Sylvius. This is the
most common place for non-communicating hydrocephalus to occur, as it
is the smallest passageway in the ventricular system. The foramina of
Luschke and Magendie are also found in the fourth ventricle. The
foramen of Magendie protrudes from the back, and the foramina of
Luschke extend from each side of the fourth ventricle. The foramina of
Luschke and Magendie are passages where CSF exits the ventricular
system over the cerebellum into the subarachnoid space and down to the
The two largest ventricles are known as the lateral ventricles. They
are commonly referred to by their left-right position (i.e., left
lateral ventricle or right lateral ventricle). The lateral ventricles
can also be referred to as the first (left lateral) and second (right
lateral) ventricles. Each lateral ventricle lies within its respective
cerebral hemisphere (i.e., the left lateral ventricle lies within the
left hemisphere of the brain, and the right lateral ventricle lies
within the right hemisphere).
The lateral ventricles, although one structure, have three different
horns which extend into different lobes of the brain. The anterior
horns extend forward into the frontal lobes. The posterior horns
extend backward into the occipital lobes, and the inferior horns
project downward into the temporal lobes. The area between the
posterior and inferior horns of the lateral ventricles is known as the
atrium, or trigone, located within the parietal lobes. The structure
of the lobes and how they fit together create the chambers of the
The lateral ventricles are connected to the third ventricle by the
interventricular foramen (more commonly known as the foramen of
Monro). The third ventricle is located at the center of the brain,
which is also home to the hypothalamus and the thalamus. The
hypothalamus regulates body temperature, thirst, emotions, sleep,
hunger, water balance and sexual behavior. The thalamus is the relay
station of the brain. All incoming messages to the brain, with the
exception of the sense of smell, enter the thalamus before being
transmitted to the primary sensory cortex in the parietal lobe.
The fourth ventricle is bordered by the medulla and the pons in the
front, and the cerebellum behind, with the aqueduct of Sylvius
extending upward into the third ventricle.
Located below the occipital lobes and behind the brain stem, the
cerebellum is made up of two distinct-looking hemispheres. The
cerebellum is primarily responsible for coordinating movements and
muscle tone, and controlling the body's sense of balance.
Hydrocephalus can be caused near the cerebellum when there is an
increase of intracranial pressure (ICP) that forces the tonsil of the
cerebellum down onto the foramen magnum. The tonsil of the cerebellum
is located near the base of the cerebellum. Raised ICP forces the
tonsil against the brain stem and can cause an obstruction of CSF flow
from the fourth ventricle. This form of non-communicating
hydrocephalus can result in severe respiratory and cardiac distress,
due to its pressure on the lower region of the medulla.
The structure that connects the brain with the spinal cord is called
the brain stem. The brain stem is made up of three sections: the pons,
the medulla, and the midbrain. The pons is responsible for control of
facial movement, as well as some eye movements, while the medulla
controls heart rate and breathing.