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This article was provided to us by David Schiff, MD, Associate Professor of Neurology, Neurosurgery,
and Medicine at University of Virginia, Charlottesville. We appreciate his generous donation of time
in preparing this material.

Just like a cyst elsewhere in your body, a cyst in the brain is a sphere filled with fluid, similar
to a miniature balloon filled with water. Cysts may contain fluid, blood, minerals, or tissue.
Although cysts tend to be benign growths, they are sometimes found in parts of the brain that
control vital functions, or they may be found inside malignant tumors.

The symptoms associated with a cyst in the brain depend on where the cyst is located. Each
part of the brain controls a function somewhere in the body. Some parts of the brain are
relatively “silent,” allowing a cyst to grow quite large before it causes symptoms. Other parts
of the brain control functions such as swallowing, dexterity, or balance; a cyst growing in those
locations may be noticed sooner than other locations. We offer extensive information about
each part of the brain, what it controls, and what you might see when a tumor or cyst is present.
If you would like that information, please visit our web site at or call us at 800-

CT and MRI scans are used to diagnose brain cysts. CT scans show the detail of the skull
bones, and provides a visual image of mineral content in or around these masses. MRI scans
complement CT scanning by providing a picture of the location of the cyst in relation to the
blood vessels and vital structures of the brain. When a cyst is found in the brain, there is
usually only one; however, multiple tiny cysts may be found inside a malignant tumor. On a
scan, a cyst has well-defined edges, as opposed to malignant tumors which have irregular

There are specific types of cysts. They are named for the type of tissue from which they arise
and for their contents. The most common cysts found in the brain are arachnoid, colloid,
dermoid, epidermoid, and pineal cysts. Each is described below.

Arachnoid Cyst
also called Leptomeningeal Cyst

An arachnoid cyst is an enlarged sphere containing cerebrospinal fluid. Arachnoid cysts are
found in the “subarachnoid space” -- the space between the arachnoid and pia mater layers of
the meninges. Those layers form a membrane-like covering around the brain and spinal cord.
Arachnoid cysts are thought to represent a duplication or split in these normal membranes,
which creates a localized pouch of trapped cerebrospinal fluid. Arachnoid cysts can occur in

both adults and children, but are most often found in infants and adolescents. They affect more
males than females. Arachnoid cysts tend to be located in the area of the Sylvian fissure (a
deep fold which separates the frontal, temporal and parietal lobes of the brain), the
cerebellopontine angle (the “corner” at which the upper parts of the brain meet the lower
parts), the cisterna magna (a fluid-containing space near the brain stem) or the suprasellar
region (the area above the “sella” – a bony pouch near the center of the skull).

Treatment for an arachnoid cyst may be “watchful waiting,” or it may be surgery. If the cyst is
small and is not causing problems, your doctor may suggest “watching” the cyst for a while to
see if it grows. During that time, it is important to keep your appointments for follow-up scans
on a regular basis, as these cysts may slowly continue to enlarge. After each scan, your doctor
will compare the new scan to the old scan to monitor the size of the cyst. Some arachnoid cysts
never enlarge.

If the cyst is causing symptoms or is located in a part of the brain where continued growth
would cause a problem, your doctor may suggest surgery to remove the cyst. The usual
procedure is to drain and attempt to remove the entire cyst, including its outermost lining.
Sometimes, when this is not feasible, the surgeon will open the cyst wall to drain the contents
into the normal cerebrospinal fluid pathways. If the cyst is blocking the flow of cerebrospinal
fluid through the brain, a shunt may be used to help move the fluid and open these
passageways. If the fluid in the cyst is aspirated through a needle, without the cyst wall being
addressed, the fluid generally reaccumulates rapidly.

Colloid Cyst

Although scientists are not sure exactly which cells give rise to colloid cysts, they do agree that
this type of cyst begins during the embryonic formation of the central nervous system. These
grape-like spheres contain a thick, gelatinous substance called colloid. As the colloid filling of
the sphere increases, the size of the cyst increases. These cysts may quietly sit in the brain
during childhood, not making their presence known until the adult years when they finally
reach a large enough size to cause symptoms. In addition to the colloid filling, they may also
contain blood, minerals, or cholesterol crystals.

Colloid cysts are typically found growing along the roof of the third ventricle (a space in the
center of the brain which holds spinal fluid) or in the choroid plexus (the lining of the third
ventricle). Cysts in these locations may block the flow of fluid through the brain, causing a
fluid backup called hydrocephalus. As the fluid builds up in the ventricles, increased pressure
occurs and causes headaches. Other symptoms may include confusion, difficulty walking, and
brief interruption of consciousness.

Continued, untreated pressure from a cyst in this location may cause brain herniation or sudden
death. For that reason, the first goal of therapy for a colloid cyst will be to relieve the pressure
buildup. A shunt may be used to drain fluid, or surgery may be done to remove or drain the

cyst. Removing the entire cyst can be challenging because of its location on/near the third
ventricle. Some surgeons are exploring the use of endoscopes for operating in the ventricles;
others are exploring computer-assisted surgical navigation tools for tumor removal in this area.
The "best" treatment is still under discussion and study.

Dermoid Cyst
also called Dermoid

Dermoid cysts most likely form during the very early weeks of fetal growth. As an embryo is
developing, the neural tube – the cells which eventually form the brain and spine - separate
from the cells destined to become the skin and bones of the face, nose, and vertebrae. A
dermoid cyst results when cells predestined for the face become entrapped in the brain or the
spinal cord. Consequently, the inside of a dermoid cyst often contains hair follicles, bits of
cartilage, or glands which produce skin oils and fats. On very rare occasions, a dermoid cyst
may spontaneously open, releasing these oils into the brain or spinal cord. This event can cause
a situation called chemical meningitis, in which the released contents irritate the meninges.

Dermoid cysts located in the brain are relatively rare; more often, they are found in the ovaries,
spine, face, neck, or scalp. Outside the brain, they are sometimes referred to as sebaceous
cysts. In the brain, these benign masses tend to be located in the posterior fossa (the lower back
portion of the brain) or the neighboring meninges (the thin membranes which form the
covering of the brain and spinal cord).

Dermoid cysts in the brain tend to be found in children under 10 years old. In older children
and young adults, they are usually located at the lower end of the spine. The cavity of the
fourth ventricle and the base of the brain, under the surface of the frontal lobes, are also
common sites.

The standard treatment for a dermoid cyst is surgical removal. If the lining of the cyst (the
complete outer wall of the sphere) is unable to be completely removed, it will likely regrow.
But that growth may be very slow, and it could be years before symptoms again return.

Epidermoid Cyst
also called Epidermoid, or Epidermoid Tumor

Epidermoid cysts, also referred to as epidermoid tumors, develop in the same manner as
dermoid cysts. These masses arise when embryonic cells meant to be skin, hair or nail tissue
become entrapped in the cells forming the brain and spinal cord. The distinction between
dermoid cysts (discussed above) and epidermoids is that epidermoid cysts do not contain hair
or sebaceous glands. These cysts contain a thick yellow substance that may also contain hair,
skin oils, or cholesterol crystals. As with dermoid cysts, on very rare occasions, an epidermoid
cyst may spontaneously open, releasing these contents into the brain or spinal cord.

Epidermoid cysts are benign masses, occurring more frequently in the brain than in the spine.
They are most often found in middle-aged adults. These cysts tend to be located near the
cerebellopontine angle (the area where the top part of the brain meets the brain stem), near the
pituitary gland, or along the skull where they may actually grow through the skull bone.

Standard treatment of epidermoid cysts is surgical removal. If the complete cyst (including the
sac-like lining of the cyst) is able to be removed, the cyst may be considered cured. If the
complete lining cannot be removed, however, the cyst may begin to grow. Regrowth tends to
occur slowly, often with years passing before symptoms again return. There are a few, albeit
extremely rare, cases of these benign tumors transforming themselves into squamous cell
cancer. If this were to occur, surgery and radiation therapy may be suggested.

Pineal Cysts
Cysts in the pineal gland are found in 1-4% of people undergoing MRI for other causes. Why
they develop remains unclear. They may be developmental in origin, or they may arise when
the pineal gland begins the normal process of shrinkage following puberty. It is rare for pineal
cysts to cause neurologic problems. When this does occur, problems arise either because there
has been increased cerebrospinal fluid production or bleeding into the cyst. Symptoms may
include headache and difficulty looking upwards; if hydrocephalus (blockage of fluid pathways
in the brain) occurs, patients may experience sleepiness, confusion, trouble walking, and
double vision. Most patients with asymptomatic pineal cysts (cysts not causing symptoms) will
never experience cyst enlargement or the development of symptoms. Pineal cysts are rarely
associated with underlying tumors, and typically an associated tumor is readily identified with
MRI scanning. Some doctors obtain repeat scans of pineal cysts over time to make sure there is
no associated tumor or cyst enlargement. Once it has been determined that there is no
associated tumor, some doctors continue to recommend periodic scans to look for cyst growth.
Others advocate getting further scans if, and only if, the person develops symptoms.

Tumor-Associated Cysts
The cysts discussed above are generally not considered “neoplasms” or “tumors” because they
originate as developmental abnormalities. Both benign and malignant tumors, however, may be
associated with cysts (sometimes known as “tumor cysts”). When a cyst is associated with an
underlying tumor, the tumor is usually obvious because CT or MRI scan shows a nodule or
lump adjoining the cyst. Certain benign tumors -- including hemangioblastomas, pilocytic
astrocytomas, and gangliogliomas -- are commonly associated with cysts and are usually
treated with surgery. Malignant tumors may also be associated with cysts; these tumors may
require radiation and/or chemotherapy in addition to surgery, when feasible.

Frequently Asked Questions About Cysts

I’ve been told to wait to see if my cyst grows. Should I worry about this?
Very often, cysts do not produce any symptoms and do not enlarge over time. If a cyst is not

causing symptoms and is not thought to be associated with a tumor, that patient might never
develop a problem from the cyst. An operation to remove the cyst might carry a greater risk
than living with the cyst. Your doctor can help you weigh the risks of “watching and waiting”
with the risks of undergoing surgery.

Can my cyst explode if it isn’t removed?
Cysts rarely produce explosive symptoms; much more commonly, a gradual increase in fluid
inside a cyst leads to progressive symptoms. As mentioned above, some cysts (such as
dermoids and epidermoids) contain fluid that if released may be irritating to the brain or
meninges. On the rare occasions that such cysts spontaneously burst and release their contents,
patients may experience fever, headache, or neck stiffness.

How can the doctors tell this is a cyst, and not some type of cancerous brain tumor?
A CT, or particularly, an MRI scan of a cyst generally shows no solid or nodular components
which could suggest an associated malignant tumor. Sometimes, when a cyst appears benign
but the doctor cannot be 100% certain, repeated radiological studies over time will be
recommended. A malignant tumor would be expected to grow over time, whereas a benign cyst
might not.

What is the difference between a cyst and a tumor? Why are epidermoid cysts also called
epidermoid tumors?
The term “cyst” refers to a fluid-filled structure, whereas a tumor consists of a mass of
abnormal cells with abnormal growth potential. Cysts not associated with tumors typically
have a very thin rim surrounding the fluid. When a tumor has an associated cyst, there is
generally a mass, or at least a thickening of the rim, visible on CT or MRI scan. Since the
growth rate of the skin cells in an epidermoid cyst is generally the same as that of normal skin,
from a technical standpoint, epidermoids are more accurately classified as cysts than tumors.

It appears that surgery may, or may not, be suggested. What are the guidelines a
neurosurgeon uses to make this decision?
There are no rigorous guidelines. If the cyst is causing symptoms, or it is a size that it is likely
soon to cause symptoms, surgery will generally be recommended. If the cyst is associated with
an undiagnosed tumor, this may be grounds for surgery. If a cyst is asymptomatic (the patient
has no symptoms) and the neurosurgeon believes growth potential is low, the surgeon may
recommend observation with surveillance brain scanning.

Is radiation therapy ever used to treat a cyst?
In general, radiation is used to kill dividing cells. The fluid inside a cyst does not contain
dividing cells, and the cells forming the walls of most cysts (including arachnoid, colloid,
dermoid, epidermoid, and pineal cysts) are not dividing. Targeting the fluid or the cyst walls
would therefore not be of use.

If the cyst is associated with a tumor, radiation is sometimes directed (usually from outside the

body) at the tumor plus or minus the cyst wall. Rarely, in tumor-associated cysts such as
craniopharyngiomas, particles emitting radiation may be injected into the cyst fluid to deliver a
very high dose of radiation to the cells comprising the wall of the cyst.

What are the odds of a cyst regrowing?
It depends on what is causing the cyst. In general, if the wall of the cyst is completely
removed, the chance of cyst recurrence is quite low. If the cyst is drained but the wall is left
intact, the odds of fluid reaccumulating are much higher.

Can cysts be prevented?
There is nothing specifically to be done to prevent development of cysts.

What does it mean when a cyst is an “incidental finding” ?
This means that the cyst is unlikely to be causing any symptoms, and the cyst is unrelated to
what the doctor who ordered the brain scan was looking for.

Can a cyst affect your white blood cell count?
As a general rule, it would not.

Can you tell a cyst from a tumor on MRI?
A cyst may be part of a tumor, or it may exist without a tumor. Sometimes it is easy to tell if a
cyst is associated with a tumor, particularly if there is a lump of excess, abnormal tissue next to
a cyst. Sometimes it is very clear that a cyst is not associated with a tumor. Occasionally, it is
hard to be sure-- even with an MRI.

Current as of November, 2006

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