Approximately 0.5-1% of
all primary brain tumors and 15-20% of all intraventricular masses are
They may cause sudden
death or longstanding symptoms from obstructive hydrocephalus.They
are still associated with considerable morbidity and mortality.
In 1858, Wallman
first reported colloid cyst. Dandy accomplished the first successful
resection of a colloid cyst in 1921.
Although these tumors
are considered congenital, their presentation in childhood is rare. They
usually present in the middle age.
The origin of these
cysts continues to be uncertain. Remnants of paraphysis, diencephalic
ependyma, invagination of neuroepithelium of the ventricle, or the
respiratory epithelium of endodermal origin are other etiologic
Colloid cysts are thought to enlarge through increases in their
contents. This process is postulated to occur in several ways. The
epithelial lining of the cell wall secretes a mucinous fluid. In
addition, cyst cavities filled with blood degradation products and
cholesterol crystals have been reported.
are slowly growing lesions, probably of endodermal origin, and usually
founding the anterior third ventricle close to the foramen of Monro,
but other locations, such as, the roof of the third ventricle, the
columns of the fornix, or the choroid plexus, are possible.
Their fibrous walls
with simple or pseudostratified epithelial cells. Their shape is
either flattened cuboidal or low columnar, and they rest on a thin
capsule of collagen and fibroblasts. The cysts are mucin secreting and
Colloid cyst (H&E):
wall is lined by cuboidal to columnar epithelium(arrow),
supported by delicate collagenous stroma
The Cells are
periodic acid-Schiff (PAS) positive and stain positively for S100 and
negatively for glial fibrillary acidic protein (GFAP), vimentin, and
neurofilament. The stromal wall stains positively for vimentin. Contents
of the cyst are usually greenish and of variable viscosity.
Symptoms are usually
caused by constant or intermittent hydrocephalus. Headache related to
position of the head and sudden drop attacks are typical. Colloid cysts
have been the cause of sudden death due to obstruction of CSF flow or
hypothalamic disturbance of cardiovascular control.
The majority of colloid
cysts are detected in the work-up of milder symptoms: Headaches (68%),
Gait disturbances (47%), Disturbed mention (37%), Nausea (37%), Blurred
vision (24%), Incontinence (13%), Tinnitus (13%), Seizures (10%), Acute
deterioration (10%), Diplopia (8%)
include: papilloedema (47%), gait disturbance, hyperreflexia, positive
babinski sign (21-32%), 24% have a normal examination.
With the advent of MR
and CT imaging an increasing number of colloid cysts will be incidental
demonstrates a usually hyperdense (iso-and hypodense are also
possible), and may enhance with contrast.
visualization the same typical features, But with better anatomical
detail and with delineation of venous anatomy.
diagnosis includes other tumors in the region such as hamartomas,
astrocytomas and ependymomas, and benign cysts of the choroid plexus.
The latter are adjacent to the plexus, usually in the lateral
ventricles, hypodense and non-contrast enhancing on CT.
Common modes of
treatments are stereotactic aspiration, microsurgical extirpation and
endoscopic fenestration of the cysts.
For small (<0.5),
asymptomatic cysts that do not cause hydro-cephalus can probably be
followed without treatment, although data on possible deterioration are
lacking. This is, however. controversial. This approach does restrict the
patient to life long follow up.
shunts have been advocated. The rationale was an assumption that the cyst
occluded both foramina of Monro. It is, however, possible that CSF flow
is actually interfered with in the posterior part of the ventricle. A
single shunt would thus suffice. Shunting carries a risk of sudden
deterioration if dysfunction occurs, and does not alleviate symptoms
caused by pressure on the fornices or the hypothalamus. Shunt revisions
for infection or malfunction are common.
approaches are feasible with normal ventricles. The main risks are venous
infarction from interference with bridging veins, and damage to the
pericallosal arteries. Traction on the gyrus cinguli may produce (usually
transient) mutism. Disconnection syndromes are not detectable following a
small (<2.5 cm) callosotomy, which is made starting 1-2 cm behind the genu.
An operation can be carried out through a 1.5 cm callosotomy. Special
tests may, however, demonstrate minor deficits.
other approaches apart from the transcallosal that are available for
lesions in this area are the transcortical, transventricular and the
subfrontal. The subfrontal approach is used for tumors that arise
inferiorly and compress the third ventricle from below. The transcortical
approach involves doing a frontal craniotomy usually on the right side,
cortical incision down to the ventricle and then locating the foramen of
Monroe. The transcortical route cannot be used when the ventricles are
normal or narrow and requires a lot of brain incision and retraction. The
foramen of Monroe on both sides cannot be visualized if necessary.
transcallosal approach which was first employed by Dandy and later on
by others is a direct midline approach to either or both lateral
ventricles and the third ventricle. There is no cortical incision and
only retraction. The small opening made in the anterior part of the
corpus callosum (1.5 to 2.5 cms) does not cause any disconnection
syndromes. Occasionally a frontal cortical vein may have to be sacrificed
to get adequate retraction of the frontal lobe and this may lead to
convulsions or to venous infarction of the frontal lobe. The size of the
ventricle is inconsequential in this approach which can be used after the
patient has been shunted.
steps of the operation described is the way the author does and is most
patient is positioned supine with the head elevated 20 degrees. Three pin
fixation is not used, only a head ring is used. It should be made sure
that the head is not tilted to the left or right to a great extent. A
question mark skin flap is turned with the medial limb on the midline.
Two thirds of the medial limb is anterior to the coronal suture and one
third is behind it. The posterior end is curved downwards towards the
zygoma for 7 to 8 centimetres. The other skin flaps that may be used are
bicoronal and horseshoe.
bone flap is turned with the medial end on the midline to expose only the
lateral edge of the superior sagittal sinus (SSS). If there is a small
ridge of bone lateral to the sinus, this must be ronguered or a Kerrison
punch can be used to remove the inner table. This is necessary to avoid
excessive retraction of the frontal lobe and the need to work under a
ledge of bone. Some surgeons recommend going across the midline and
others do not. The advantage of going across the midline is that a little
more space may be available The author feels that the space available is
determined by the SSS rather than by the extent of bone removal. The
disadvantages are the potential injury to the SSS when the whole of it is
exposed and the chance of pressure on the sinus during retraction. This
pressure can lead to venous stasis and raised intracranial pressure during
surgery or venous infarction of either frontal lobe. The ledge of bone
left over the SSS prevents this pressure.
applying the hitch stitches on the dura, the dura is opened as a flap
hinged towards the sinus. The lateral extent of the dural opening should
be only about 2 cms from the midline so that the retracted frontal lobe
stays under the dura and does not get hitched against the cut dural
margin. In some, due to cortical veins entering the SSS, the entire
anteroposterior extent of the dura cannot be opened. The restriction is
usually posterior and the anterior two thirds of the dura can be
comfortably opened and this exposure is adequate. 3 to 4 cms of
longitudinal exposure of the frontal lobe is all that is necessary for
patients one or more cortical veins will be seen in the area exposed and
they will be entering the SSS. As far as possible, the retraction should
be done between these veins. An extra 3 to 5 mms of the vein can be
mobilized by dissecting the arachnoid around the vein in the cortex. If
absolutely essential the smallest vein may be sacrificed. The vein should
be anterior to the coronal suture. In the authorís experience sacrifice
of a vein has been seldom necessary.
gentle retraction of the frontal lobe, the falx will be seen. There may
be adhesions between arachnoid granulations and the falx or sinus and
these have to be released. In patients, in whom the brain is tight and
the ventricles are enlarged the right frontal horn can be tapped and CSF
let out. When the ventricles are normal in size 20% mannitol can be given
in a dose of 5 ml per kg body weight. It is advisable not to give
mannitol when the ventricles are enlarged as at the end of surgery there
will be excessive shrinkage of the brain due to a large quantity of CSF
being let out during surgery.
frontal lobe is retracted initially using a one cm retractor. The angle
of the microscope has to be changed to 60 degrees to the right during this
step till the falx is seen well. The microscope angle is then changed to
have direct vision of the interhemispheric fissure. The arachnoid in the
fissure is dissected and CSF is let out. Further retraction is carried
out only after letting out the CSF which leads to further relaxation of
the brain. A 2 cm retractor is now used. In most cases the two frontal
lobes are easily separable but in some sharp dissection may be required.
Sharp dissection lessens the chances of injury to the cortex. A branch of
the pericallosal artery may be seen coursing in the cortex on one or both
sides. The cingulate gyri may be densely adherent to each other and in
some the fissure may be angled to the left or right. It is extremely
important to identify the cingulate gyri and not mistake them for the
pericallosal arteries will now be seen. The arachnoid between and around
the arteries are dissected and the corpus callosum will come into view.
The pericallosal arteries can be displaced to one side or the dissection
can be carried out between the two arteries. This will depend on the
anatomy seen in each individual patient and there is no hard and fast
rule. Rarely a single pericallosal artery may be seen. Occasionally a
small cortical branch may have to be sacrificed in order to mobilise the
pericallosal arteries and get enough space to expose the corpus callosum.
corpus callosum will be white in color with a few small arteries and veins
coursing over it. The cingulate gyrus should not be mistaken for the
corpus callosum as then the entry into the ventricle becomes difficult and
confusing. An incision is made in the corpus callosum for a distance of
1.5 to 2.5 cms, depending on the type and size of the pathology in the
ventricle. The callosum is relatively avascular and the incision is
deepened the ependyma will come into view. A few small veins may be seen
coursing over the ependyma and these can be coagulated. Initially a
small opening is made in the ependyma in order to let out the CSF
slowly. The CSF should not be rapidly let out especially in patients
with dilated ventricles as this will collapse the brain and may lead to
the formation of a subdural haematoma. The ependyma is then opened to the
step is to determine whether the left or the right lateral ventricle has
been opened into. This is determined by locating the choroid plexus and
following it forwards. The choroid plexus as it is traced forwards curves
medially and enters the foramen of Munro. The thalamostriate and septal
veins will also be visible. In third ventricular tumors it really does
not matter which ventricle has been entered into.
approach to the third ventricle depends on the size and location of the
lesion and whether the lesion has enlarged the foramen of Munroe. When
the foramen of Monroe is enlarged which is so in the majority of the cases
that the author operated upon, the lesion can be removed by the
transforaminal approach. This is the ideal approach as there is no
destruction of neural tissue or sacrifice of veins. If in case, there is
necessity to enlarge the foramen of Monroe and this is not a common
occurrence, one anterior column of the fomix can be sacrificed and the
foramen enlarged anteriorly. This should be done preferable on the non
dominant side. The other way is to enlarge the foramen posteriorly by
sacrificing the thalamostriate vein. In many instances, it is possible
to enlarge the foramen posteriorly without sacrificing the vein. The
foramen of Monroe may appear narrow on first appearance and there may be a
bulge posteriorly. In these it is best to make a small incision in the
area of bulge, decompress the lesion and then the foramen of Monroe will
open out and the further dissection and removal of the tumor can be
carried out through the foramen of Munro.
corpus callosum and pericallosal art exposed
colloid cyst exposed
subchoroidal approach can be used in mid third ventricular tumors where
the foramen of Monroe is not enlarge and there is no obvious bulge. In
this approach, the choroid plexus is mobilized from the choroidal
fissure. This will require cauterization of the choroid plexus and
mobilizing the branches of the medial posterior choroidal arteries. A
microdissector passed under the tela chloridea will expose the plane of
cleavage between the medial wall of the thalamus and the roof of the third
ventricle. The internal cerebral vein in continuity with the septal vein
will dissect away from the ipsilateral dorsolateral thalamus and will
remain suspended in strands of arachnoid of the velum interposium. The
thalamostriate vein should be sacrificed only when absolutely essential.
interfomiceal approach is the other option available and should be used
only rarely and in specific instances. The approach should be strictly in
the midline with a midline callosotomy and dissecting between the two
fornices. The fornices are very delicate structures and can be damaged
easily leading to post operative problems. The ideal lesion in which
this can be used is where there is a direct upward extension of the tumor
and the fornices are spread apart by the tumor. The maximum neural
complications occur in the interforniceal approach and most neurosurgeons
do not use this approach except in rare instances. The complications that
can occur are memory disturbances and a state of mutism.
Complications: The complications that may specifically occur with the
transcallosal approach are (1) immediate post operative convulsions
especially if a cortical vein has been sacrificed. This is not often
seen. (2) Disconnection syndromes are extremely rare in anterior callosal
sections limited to 2.5 cms. (3) Transient lower limb weakness may occur
if there has been some pressure on the pericallosal artery during
retraction. The other complications like acute hydrocephalus, transient
mutism, memory disturbances and hypothalamic disturbances are related to
the surgical procedure in the lateral or third ventricle and are not
related to the transcallosal approach.
technique was originally claimed to have lower morbidity than
excision, but severe complications have been reported. Initial
success is achieved in approximately 50% of cysts. A 100% recurrence
rate has, however, been reported following aspiration procedures.
This was not surpirising since vital epithelium capable of producing
mucoid was left intact.
Endoscopy is a
minimally invasive means of operating in the ventricular system. Improved
instrumentation has allowed the use of flexible and non-flexible
endoscopes for fenestration and aspiration of colloid cysts, and lately,
aspiration remains a treatment with the drawbacks of simple aspiration.
Aspiration with a generous fenestration of the cyst was described
recently. A fenestration should allow continuous emptying of the colloid
produced and thereby avoiding recurrences.
These methods are
recent, and have not yet been available for long-term follow-up.
successful microsurgical removal is excellent. The risks of microsurgery
depend on the skills of the surgeon. Different results have been
Patients treated with
shunting carry a risk of deterioration when shunts malfunction and are at
risk of shunt infection.
Aspiration has an
unacceptable recurrence rate, and patients treated with aspiration
procedures need to be followed and re-operated when a recurrence appears.
Significant morbidity from recurrence following aspiration has been
The natural history of
colloid cysts is not well known. An increasing number of cysts are
incidental findings, and will be followed without surgical intervention.
The safety of conservative treatment and risks of deterioration remain to
Simple aspiration has
been challenged lately while endoscopy is becoming more of a routine tool
in many departments. Its use for colloid cyst surgery appears to become
established, but long term follow-up is necessary to evaluate its safety
in fenestration procedures.