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Ventricles, CSF Flow,
Meninges and Herniations
Dr. Benazir
20th August, 2008
Ventricles of the brain
These are fluid filled spaces within the brain related to the
development Of the nervous systems a tubular structure within the
central canal.
Lateral ventricles represent expansion of the most anterior part of the
Ventricular system into each cerebral hemisphere. The third ventricle,
the aqueduct and the fourth ventricle are midline in position and are
continuous with the central canal of the cord.
The lateral ventricles
There is a lateral ventricle within each cerebral hemisphere. Each is
C-shaped with the limbs of c facing anteriorly
Frontal (anterior) horn:
This extends into the frontal lobe. Its roof and anterior extremity
are formed by the corpus callosum.
Medial wall is formed by septum pellucidum. There is no choroid
plexus in the anterior horn.
Body:
This is within the parietal lobe.
Roof and lateral wall:corpus callosum
Medially:thalamus
Temporal horn:
Extends anteriorly into the temporal lobe.
Lateral wall is formed by the fibers of the tapetum.
The caudate nucleus lies in the floor of the anterior horn. The choroid
plexus of the body of the lateral ventricle is continuous with that of the
inferior horn.
Occipital horn:
The posterior convexity of the body from which it arises is called the
trigone of the lateral ventricle. This maybe absent or poorly developed
or may extend the full depth of the lobe. The posterior horns of two
lateral ventricles are often asymmetrical and are bilaterally well
developed in only 12% of the subjects. If it is present on one side, it is
usually the left. There is no choroid plexus in the occipital horn.
Choroid plexus of the lateral
ventricles
Is responsible for the production of most of the CSF.
Extends from the inferior horn through the body to the inter
ventricular foramen where it is continuous with that of the third
ventricle. The vessels supplying the choroid plexus are the anterior
and posterior choroid arteries.
The anterior choroid artery is a branch of internal carotid artery.
Posterior choroidal arteries are branches of posterior cerebral artery.
The vein draining the plexus unite to form the choroid vein, it joins
the thalamostriate vein to form the internal cerebral vein.
The third ventricle
Is a slit like space between the thalami. Width is between 2 and
10mm and increases with age.
Lateral walls: thalami
Inferiorly: subthalamic groove
Cerebral aqueduct:
A narrow channel connecting the posterior end of the third ventricle
with the superior end of the fourth ventricle.
The nuclei of the third fourth and fifth cranial nerves suround the
aqueduct and are called the periaqueductal grey matter
The fourth ventricle
Posterior to the pons the aqueduct widens as the fourth ventricle and
narrows again as the central canal of the medulla and of the spinal
cord.
The floor of the fourth ventricle is diamond shaped (the rhomboid
fossa) and is formed by the posterior surface of the pons and the
upper part of the medulla.
Roof is formed superiorly by superior cerebellar peduncles, with the
superior medullary velum between, and inferiorly by the inferior
cerebellar peduncles and the inferior medullary velum.
The fourth ventricle tends to be symmetrical in it’s
anatomy and minor asymmetry may be a sign of
pathology.
CT and MRI
The ventricular system can be visualized on axial CT and MR scans.
Starting on the lowest cuts. the fourth ventricle can be seen as a slit
like CSF-filled structure between the brainstemand the cerebellum.
• Sections taken through the midbrain may show the aqueduct with
high attenuation periaqueductal grey matter.
• The third ventricle becomes visible on higher cuts as a slit like
space between thalami.
• The posterior horns are visible also on this section and calcified
choroid plexus is commonly seen in the trigone of the lateral
ventricles. The temporal horns are small or not visible unless they
are dilated.
• Sagittal MR images show the third ventricle, aqueduct and fourth
ventricle in continuity with each other and with the central canal of
the medulla and of the spinal cord.
The subarachnoid cisterns
Cisterna magna:
This lies behind the medulla and below the cerebellar hemispheres.
It contains the vertebral artery and its posterior inferior cerebellar
branch.
Pontine cistern:
This lies between the pons and the clivus. It contains the basillar
artery.
Interpeduncular cistern:
This lies between the cerebral pedunclesof the midbrain and the
dorsum sellae. It contains the posterior part of the arterial circle of
willis.
Quadrigeminal cistern:
This lies posterior to the guardigeminal plate of the midbrain. It
contains the venous confluence of the internal cerebral veins and the
basal veins to form the great cerebral vein (of Galen)
Ambient cistern:
These extend around both sides of the midbrain between the
interpeduncular cistern anteriorly and the quadrigeminal cistern
posteriorly.
Suprasellar cisterns:
This cistern is above the pituitary fossa. The optic nerve pass to the
chiasm in the anterior part of the suprasellar cistern.
Pericallosal cistern:
Suprasellar and chiasmatic cisterns continue superiorly around the
superior surface of the corpus callosam as the pericallosal cistern. It
contains branches of anterior cerbral artery.
CSF production and flow
Total volume: 150 ml
25 ml of which is within and around the spinal cord. Production rate
is 0.4ml/min. independent of CSF pressure.
It flows through the interventricular foramen into the third ventricle
through the cerebral aqueduct to the fourth ventricle, via the midline
aperture into the cisterna magna and via the lateral apertures into
the pontine cisterns.
Absorbed through the arachnoid villi which are herniations of
arachnoid through holes in the dura into the venous sinuses.
Hydrocephalus
Abnormal increase in the volume of the CSF within the skull. It can
be
Communicating:
There is no obstruction within or to the outflow from the ventricular
system.
Non communicating:
Raised pressure of the CSF is due to blockage at some point between
it’s formation at the choroid plexus and it’s exit through the foramina
in the roof of the fourth ventricle.
Meninges
Dura mater:
This is a tough membrane having two layers.
Outer layer:
Periosteum of the inner aspect of the skull and is continous through
all the foramina and suture of the skull with the periosteum on the
outside of the skull.
Inner layer:
Dura mater proper, is adherent to the outer layer in all places except
where the layer separate around the dural venous sinuses.
Falx cerebri is a sickle shaped dural septum in the median sagittal
plane.
Attachments:
Cisterna galli in the midline of floor of anterior cranial fossa and
along the midline along the inner aspect of the vault of skull.
Posteriorly:
It is attached with the upper surface of the tentorium cerebelli
enclosing the straight sinus. Its lower free edge contains the inferior
sagittal sinus.
Diaphragma sellae:
Fold of dura that almost completely covers the pituitary fossa.
Tentorium cerebelli:
It seperates the occipital lobes from the superior surface of
cerebellum.
Attachments:
To the occipital bone along margins of the transverse sinuses to the
internal occipital protuberance.
Anterior free edge, the tentorial notch is attached to the anterior
clenoid process and surrounds the midbrain.
Uncus of the temporal lobe and the posterior cerebral
artery lie close to the free edge of the tentorium and
may be compressed against it if there is increased
pressure in the supra tentorial part of the brain.
Arachnoid mater
A delicate membrane which is impermeable to CSF.
separated from pia mater via the subarachnoid space which contains
the CSF.
It projects into the inter hemispheric fissure and into the root of the
sylvian fissure.
It surrounds the cranial and spinal nerves as far as their exit from
the skull and the vertebral canal.
It herniates through holes in the dura into the venous sinuses and
venous lakes as arachnoid villi.
Pia mater
It is closely adherent to the brain surface and dips into all the sulci.
Continues around all the cranial and spinal nerves.
It is also invaginated into the surface of the brain by the entering
cerebral arteries.
Extradural Haematoma
Occurs when vessel (middle meningeal artery)in the extradural space
is torn by trauma.
Subdural Haematoma
Also due to traumatic bleed into potential space between the dura
and arachnoid mater, when a bridging vein is torn.
Can extend into the interhemispheric fissure and the root of the
sylvian fissure but not into other sulci.
Subarachnoid Haemorrhage
Occurs into the subarachnoid space from spontaneous or traumatic
rupture of, usually an artery, in this space.
Blood can then be seen in the cisterns and extending into the sulci
and fissures on the brain surface close to the site of bleeding.
Brain herniations
Cranium is essentially a rigid box filled with incompressible contents.
Total volume of brain tissue, CSF, and blood must exist in
equillibrium.
Increased ICP is one of the most important causes of secondary
brain injury.
Compensatory mechanisms:
1/ CSF homeostatic mechanisms
2/ Cerebral blood flow (first venous and then arterial)
Increased ICP causes:
1/ focal mass lesion ( hematoma, abcess, tumor)
2/ diffuse cerebral swelling ( cerebral hyperemia or cerebral edema)
Causes of cerebral edema:
1/ vasogenic: water that accumulates within extracellular space
owing to a loss of osmotic buffering from a disrupted BBB.it has
predilection for cerebral white matter.
2/ cytotoxic: water that accumulates within the cells because of
faliure of sodium potassium pump and other transport mechanisms.
it has predilection for cerebral grey matter.
3/ interstitial: periventricular edema due to obstructive
hydrocephalus.
4/ hydrostatic: edema caused by abrupt decompression of a focal
mass.
5/ hypo-osmotic: edema secondary to decreased serum osmolality.
• Diffuse cerebral swelling is occasionally difficult to
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diagnose because there is no region of normal brain
available for comparison.
By definition brain herniation represents displacement
of tissue from one compartment to another. The
intracranial compartmentalization is defined by the
dural partitions. ( e.g. falx, tentorium)
The internal dural compartments, in conjuntion with
bony openings in the skull provides a basis for the
classification of brain herniation into six types:
Subfacial herniation: results in displacement of
part or all of the cingulate gyrus beneath the falx
cerebri and above the
Corpus collosum. as the cingulate gyrus herniates
beneath the falx, the collosal sulcus and corpus
callosum are tilted and displaced inferiorly. The
ipsilateral frontal horn is usually compressed.
Contralateral displacemecnt of the pericollosal
arteries is readily identified on CT scans, MRI, and
angiography. When the cingulate gyrus is forced
under the falx, the patient is predisposd to
compression of anterior cerebral artery against the
margin of the falx.
• Uncal herniation: the
imaging appearance of uncal
herniation depends on two
major factors: the size and
shape of the tentorial incisura
and the size and location of
offending mass.. Unilateral or
bilateral herniation is more
common with a congenitally
large incisura. Unilateral type
is usuaaly secondary to a
temporal lobe mass. Bilateral
can be due to mass lesions
within both temporal lobes,
large supratentorial lesions,
diffuse cerbral edema, or
• Bilateral enlargement of
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the lateral ventricles.
One of the earliest
imaging manifestations is
subtle effacement of the
lateral aspect of the
suprasellar and ambient
cisterns.
Less commonly, the
cerebral peduncle
contralateral to the
cerebral mass is
compressed against the
margin of the tentorium.
As the brainstem is displaced to the opposite side, the ipsilateral
cerbellopontine angle cistern widens and the contralateral temporal
horn dilates.
Enlargement of the temporal horn contralateral to the mass lesion is
an extremely common finding in uncal herniation. Earliest clinical
manifestation is unilaterally fixed and dilated pupil due to mass effect
on occulomotor nerve.
Mass effect on ipsilateral cerebral peduncle usually results in a
contralateral hemiplegia.
Pressure can also be exerted on branches of PCA.
• Tonsillar herniation:d also
known as foraminal impaction
and cerebral cone. When
cerebellar tissue herniates
inferiorly, tongues of
compressed tonsillar folia
extend through the foramen
magnum for a variable distance
into the upper cervical spinal
canal.in severe cases tonsil can
be so displaced that their
cortex becomes necrotic and
subsequently sclerotic.
• Tonsillar herniation can also
occur with diffuse cerebral
swelling which causes
downward displacement of the
Tentorium and compression of
the cerebellum.
On CT and MRI tonsillar herniation causes effacement of
cisterna magna. When sudden and severe, it can also cause
compression of the posterior inferior cerebellar artery (PICA).
Distances below the foramen magnum were recommended as
criteria for tonsillar ectopia: first decade of life (6mm), secondthird decades (5mm), fourth-eighth decades (4mm), and ninth
decade (3mm).
Downward herniation: also known as descending transtentorial,
central and diencephalic herniation. It is usually caused by
parasagittal masses that caudally displace the hemispheres, basal
ganglia, and eventually the diencephalon and adjoining
mesencephalon through the tentorial incisura. When the brainstem is
suddenly displaced caudally, secondary brainstem hemorrhage can
occur.
• On CT scans, inferior displacement of the pineal
gland relative to the calcification within the choroid
plexus of the trigones has been described as a
manifestation of downward herniation.
• Sever cases obliterates the ambient, guadrigeminal,
interpeduncular, pontine, superior cerebellar,
supracellar, and chiasmatic cisterns. It compresses
the diencephalon and displaces the mamillary bodies
caudally.
• Vascular compromise is a common sequela of
downward herniation. The PCA is most commonly
affected.
• Upward herniation: also known as ascending transtentorial
herniation. Occurs when an expanding mass within the posterior fossa
causes the cerebellum to be displaced superiorly through the tentorial
incisura. Stretching, displacement, and compression of the superior
cerebellar artery can occur.
• The imaging findings in upward herniation include the flattening of the
posterior guadrigeminal plate cistern and effacement of the ambient
and superior cerebellar cisterns by the herniated cerebellar vermis.
• Upward herniation is invariably associated with nonvisualization of the
fourth ventricle.
• Hydrocephalus is extremely common for two reasons: aqueductal
obstruction prevents the exit of CSF from the lateral ventricles and
effacement of pontine and ambient cistern impedes the rostral flow of
the CSF from the posterior to anterior aspects of brain surface.
• External herniation: also known as transcalvarial herniation,
is relatively rare. Occurs when an elevation in ICP is combined
with a skull opening.
• On CT and MRI it appears as a region of cerebral parenchyma
‘mushrooming’ through the calvarial defect.
• One of the potential complications is development of venous
congestion which results in hemorrhagic venous infarction.
• Nonenhanced computed
tomography (CT) scan of the
brain at the level of the body of
the lateral ventricles was
obtained in a 37-year-old man
who underwent a right
frontotemporal decompression
craniectomy for a large right
frontal hematoma after a skiing
accident. A focal hypoattenuating
infarct is seen in the right frontal
lobe, with an adjacent edematous
brain parenchyma herniating
through the right frontotemporal
craniectomy defect. The patient
had communicating
hydrocephalus with dilatation of
the lateral ventricles.
Thank You