Ventricles, CSF Flow, Ventricles, CSF Flow, Meninges and HerniationsMeninges and Herniations

Dr. BenazirDr. Benazir

2020thth August, 2008 August, 2008

Ventricles of the brain 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 ventriclesThe lateral ventriclesThere 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 callosumMedially: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 Choroid plexus of the lateral ventriclesventriclesIs 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 ventricleThe third ventricle

Is a slit like space between the thalami. Width is between 2 and 10mm and increases with age.

Lateral walls: thalamiInferiorly: 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 ventricleThe fourth ventriclePosterior 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 MRICT and MRIThe 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 cisternsThe subarachnoid cisternsCisterna 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 flowCSF production and flow

Total volume: 150 ml25 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.

HydrocephalusHydrocephalus

Abnormal increase in the volume of the CSF within the skull. It can beCommunicating: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.

MeningesMeningesDura 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 materArachnoid 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 materPia 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 HaematomaExtradural Haematoma

Occurs when vessel (middle meningeal artery)in the extradural space is torn by trauma.

Subdural HaematomaSubdural HaematomaAlso 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 HaemorrhageSubarachnoid HaemorrhageOccurs 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 herniationsBrain herniationsCranium is essentially a rigid box filled with incompressible Cranium is essentially a rigid box filled with incompressible

contents.contents.Total volume of brain tissue, CSF, and blood must exist in Total volume of brain tissue, CSF, and blood must exist in

equillibrium.equillibrium.Increased ICP is one of the most important causes of secondary Increased ICP is one of the most important causes of secondary

brain injury. brain injury.

Compensatory mechanismsCompensatory mechanisms: : 1/ CSF homeostatic mechanisms1/ CSF homeostatic mechanisms2/ Cerebral blood flow (first venous and then arterial)2/ Cerebral blood flow (first venous and then arterial)

Increased ICP causesIncreased ICP causes::1/ focal mass lesion ( hematoma, abcess, tumor)1/ focal mass lesion ( hematoma, abcess, tumor)2/ diffuse cerebral swelling ( cerebral hyperemia or cerebral 2/ diffuse cerebral swelling ( cerebral hyperemia or cerebral

edema) 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 Diffuse cerebral swelling is occasionally difficult to diagnose because there is no region of normal diagnose because there is no region of normal brain available for comparison.brain available for comparison.

• By definition brain herniation represents By definition brain herniation represents displacement of tissue from one compartment to displacement of tissue from one compartment to another. The intracranial compartmentalization is another. The intracranial compartmentalization is defined by the dural partitions. ( e.g. falx, defined by the dural partitions. ( e.g. falx, tentorium)tentorium)

• The internal dural compartments, in conjuntion The internal dural compartments, in conjuntion with bony openings in the skull provides a basis for with bony openings in the skull provides a basis for the classification of brain herniation into six types:the classification of brain herniation into six types:

• SubfacialSubfacial herniationherniation: results in displacement of : results in displacement of part or all of the cingulate gyrus beneath the falx part or all of the cingulate gyrus beneath the falx cerebri and above the cerebri and above the

Corpus collosum. as the cingulate gyrus Corpus collosum. as the cingulate gyrus herniates beneath the falx, the collosal sulcus herniates beneath the falx, the collosal sulcus and corpus callosum are tilted and displaced and corpus callosum are tilted and displaced inferiorly. The ipsilateral frontal horn is usually inferiorly. The ipsilateral frontal horn is usually compressed. Contralateral displacemecnt of compressed. Contralateral displacemecnt of the pericollosal arteries is readily identified on the pericollosal arteries is readily identified on CT scans, MRI, and angiography. When the CT scans, MRI, and angiography. When the cingulate gyrus is forced under the falx, the cingulate gyrus is forced under the falx, the patient is predisposd to compression of patient is predisposd to compression of anterior cerebral artery against the margin of anterior cerebral artery against the margin of the falx.the falx.

• Uncal herniationUncal herniation: : the the imaging appearance of imaging appearance of uncal herniation depends uncal herniation depends on two major factors: the on two major factors: the size and shape of the size and shape of the tentorial incisura and the tentorial incisura and the size and location of size and location of offending mass.. Unilateral offending mass.. Unilateral or bilateral herniation is or bilateral herniation is more common with a more common with a congenitally large incisura. congenitally large incisura. Unilateral type is usuaaly Unilateral type is usuaaly secondary to a temporal secondary to a temporal lobe mass. Bilateral can be lobe mass. Bilateral can be due to mass lesions within due to mass lesions within both temporal lobes, large both temporal lobes, large supratentorial lesions, supratentorial lesions, diffuse cerbral edema, ordiffuse cerbral edema, or

• Bilateral enlargement Bilateral enlargement of the lateral ventricles.of the lateral ventricles.

• One of the earliest One of the earliest imaging manifestations imaging manifestations is subtle effacement of is subtle effacement of the lateral aspect of the lateral aspect of the suprasellar and the suprasellar and ambient cisterns.ambient cisterns.

• Less commonly, the Less commonly, the cerebral peduncle cerebral peduncle contralateral to the contralateral to the cerebral mass is cerebral mass is compressed acompressed 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 herniationTonsillar herniation:d also :d also known as foraminal known as foraminal impaction and cerebral cone. impaction and cerebral cone. When cerebellar tissue When cerebellar tissue herniates inferiorly, tongues herniates inferiorly, tongues of compressed tonsillar folia of compressed tonsillar folia extend through the foramen extend through the foramen magnum for a variable magnum for a variable distance into the upper distance into the upper cervical spinal canal.in cervical spinal canal.in severe cases tonsil can be so severe cases tonsil can be so displaced that their cortex displaced that their cortex becomes necrotic and becomes necrotic and subsequently sclerotic.subsequently sclerotic.

• Tonsillar herniation can also Tonsillar herniation can also occur with diffuse cerebral occur with diffuse cerebral swelling which causes swelling which causes downward displacement of downward displacement of the Tentorium and the Tentorium and compression of the compression of the cerebellum.cerebellum.

On CT and MRI tonsillar herniation causes effacement of On CT and MRI tonsillar herniation causes effacement of cisterna magna. When sudden and severe, it can also cisterna magna. When sudden and severe, it can also cause compression of the posterior inferior cerebellar cause compression of the posterior inferior cerebellar artery (PICA).artery (PICA).

Distances below the foramen magnum were Distances below the foramen magnum were recommended as criteria for tonsillar ectopia: first recommended as criteria for tonsillar ectopia: first decade of life (6mm), second-third decades (5mm), decade of life (6mm), second-third decades (5mm), fourth-eighth decades (4mm), and ninth decade (3mm).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 On CT scans, inferior displacement of the pineal gland relative to the calcification within the gland relative to the calcification within the choroid plexus of the trigones has been described choroid plexus of the trigones has been described as a manifestation of downward herniation.as a manifestation of downward herniation.

• Sever cases obliterates the ambient, Sever cases obliterates the ambient, guadrigeminal, interpeduncular, pontine, superior guadrigeminal, interpeduncular, pontine, superior cerebellar, supracellar, and chiasmatic cisterns. It cerebellar, supracellar, and chiasmatic cisterns. It compresses the diencephalon and displaces the compresses the diencephalon and displaces the mamillary bodies caudally.mamillary bodies caudally.

• Vascular compromise is a common sequela of Vascular compromise is a common sequela of downward herniation. The PCA is most commonly downward herniation. The PCA is most commonly affected.affected.

• Upward herniationUpward herniation: also known as ascending transtentorial : also known as ascending transtentorial herniation. Occurs when an expanding mass within the herniation. Occurs when an expanding mass within the posterior fossa causes the cerebellum to be displaced posterior fossa causes the cerebellum to be displaced superiorly through the tentorial incisura. Stretching, superiorly through the tentorial incisura. Stretching, displacement, and compression of the superior cerebellar displacement, and compression of the superior cerebellar artery can occur.artery can occur.

• The imaging findings in upward herniation include the The imaging findings in upward herniation include the flattening of the posterior guadrigeminal plate cistern and flattening of the posterior guadrigeminal plate cistern and effacement of the ambient and superior cerebellar cisterns by effacement of the ambient and superior cerebellar cisterns by the herniated cerebellar vermis.the herniated cerebellar vermis.

• Upward herniation is invariably associated with Upward herniation is invariably associated with nonvisualization of the fourth ventricle.nonvisualization of the fourth ventricle.

• Hydrocephalus is extremely common for two reasons: Hydrocephalus is extremely common for two reasons: aqueductal obstruction prevents the exit of CSF from the aqueductal obstruction prevents the exit of CSF from the lateral ventricles and effacement of pontine and ambient lateral ventricles and effacement of pontine and ambient cistern impedes the rostral flow of the CSF from the posterior cistern impedes the rostral flow of the CSF from the posterior to anterior aspects of brain surface. to anterior aspects of brain surface.

http://www.cmaj.ca/cgi/content/full/177/3/247/F213

• External herniationExternal herniation: also known as transcalvarial : also known as transcalvarial herniation, is relatively rare. Occurs when an elevation herniation, is relatively rare. Occurs when an elevation in ICP is combined with a skull opening.in ICP is combined with a skull opening.

• On CT and MRI it appears as a region of cerebral On CT and MRI it appears as a region of cerebral parenchyma ‘mushrooming’ through the calvarial parenchyma ‘mushrooming’ through the calvarial defect.defect.

• One of the potential complications is development of One of the potential complications is development of venous congestion which results in hemorrhagic venous venous congestion which results in hemorrhagic venous infarction.infarction.

• Nonenhanced computed Nonenhanced computed tomography (CT) scan of the tomography (CT) scan of the brain at the level of the body brain at the level of the body of the lateral ventricles was of the lateral ventricles was obtained in a 37-year-old man obtained in a 37-year-old man who underwent a right who underwent a right frontotemporal frontotemporal decompression craniectomy decompression craniectomy for a large right frontal for a large right frontal hematoma after a skiing hematoma after a skiing accident. A focal accident. A focal hypoattenuating infarct is hypoattenuating infarct is seen in the right frontal lobe, seen in the right frontal lobe, with an adjacent edematous with an adjacent edematous brain parenchyma herniating brain parenchyma herniating through the right through the right frontotemporal craniectomy frontotemporal craniectomy defect. The patient had defect. The patient had communicating hydrocephalus communicating hydrocephalus with dilatation of the lateral with dilatation of the lateral ventricles.ventricles.

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