Meninges, CSF & Ventricular system

Objectives

• Describe the arrangement of the meninges and their relationship to brain and spinal cord.

• Explain the occurrence of epidural, subdural and subarachnoid spaces.

• Locate the principal subarachnoid cisterns, and arachnoid granulations.

• Describe the ventricles of brain and importance of their choroids plexus.

• Summarize the pathway of cerebrospinal fluid (CSF) circulation

• Identify brain ventricles in CT scan, MRI .

MENINGES• The brain and spinal cord are invested by

three concentric membranes ;• The outermost layer is the dura matter.• The middle layer is the arachnoid matter.• The innermost layer is the pia matter.

1. Dura Mater - Composed of two layersa) Periosteal – outer layer,

attaches to bone.b) Meningeal – inner layer,

closer to brain.Two layers fused, except to

enclose the dural sinuses

2. Arachnoid Layer - ‘spider’ web like.

3. Pia Mater - delicate, follows convolutions.

Cranial Meninges - 3 layer protective membrane

Cranial Meningeal Spaces

Epidural spacePotential space superior to dura.

Subdural space Potential space between

dura and arachnoid mater.Subarachnoid space Filled with CSF Contains the blood

vessels supplying brain.

In the cranial vault, the epidural space is normally closed since the dura is attached to the periosteum which is attached to the inner surface of the skull

In the spinal cord the epidural space is filled with adipose tissue.

DURA MATERThe cranial dura is a two layered tough, fibrous membrane that surrounds the brain.It is formed of two layers; periosteal and meningeal.The periosteal layer is attached to the skull.The meningeal layer is folded forming the dural folds; falx cerebri, and tentoriam cerebelli.Sensory innervation of the dura is mostly from the three branches of the trigeminal and vagus nerves & C1 to C3.

DURA MATERTwo large reflection of dura extend into the cranial cavity 1.The falx cerebri, In the midline, It is a vertical sickle shaped sheet of dura, extends from the cranial roof into the great longitudinal fissure between the two cerebral hemispheres.It has an attached border adherent to the skull.And a free border lies above the corpus callosum.

DURA MATER2. A horizontal shelf of

dura, The tentorium cerebelli,

It lies between the posterior part of the cerebral hemispheres and the cerebellum.

It has a free border that encircles the midbrain.

In the middle line it is continuous with the falx cerebri,

Arachnoid Mater& Pia MaterThe arachnoid mater is a soft, translucent membrane loosely envelops the brain. The arachnoid mater is separated from the dura by a narrow subdural space.The pia mater is the innermost, thin, delicate & highly vascular membrane that is closely adherent to the gyri and fitted into the sulci. Between the pia and arachnoid mater lies the subarachnoid space which contains; fibrous trabeculae, main blood vessels and CSF.

Subarachnoid SpaceIt is varied in depth forming; subarachnoid cisterns. The cisterna magna, or cerebllomedullary cistern which lies between the inferior surface of the cerebellum and the back of the medulla. At this cistern CSF flows

out of the fourth ventricle.

Subarachnoid SpaceThe interpeduncular cistern, which is located at the base of the brain, where the arachnoid spans the space between the two cerebral peduncles. This cistern contains the optic chiasma & circulus arteriosus of Willis.

• Pontine cistern(Prepontine cistern or cisterna pontis). Surrounds the ventral aspect of the pons. It contains:

• The basilar artery and the origin of the anteroinferior cerebellar artery.

• The origin of the superior cerebellar arteries.

• The sixth (VI) cranial nerve

Subarachnoid Space

CSF• CSF is clear, colorless, and odorless fluid

• produced within the ventricles secreted by the Choroid plexus.Choroid plexuses are areas where the lining wall of the ventricle is very thin and has a profusion of capillaries

• provides mechanical support – protection from pressure changes.

• In adults, the total volume of CSF is about 150 ml

• Between 400 and 500 mL of CSF is produced and reabsorbed daily.

• Thus the CSF turns over about 3.7 times a day. This continuous flow into the venous system dilutes the concentration of larger, lipoid soluble molecules penetrating the brain and CSF.

Choroid Plexus• The lining ependyma

of each ventricle comes into contact with the surface pia mater allowing the invagination of a mass of blood capillaries --- combination of these capillaries, pia and ependyma constitutes the choroid plexus.

Pia and Ependyma

EpendymaPia

The “hollow” brain Diagrammatic Cross Section

Pia and Ependyma

In some locations pia mater and ependyma come together. A plexus of blood vessels “invaginates” the thin layer. Cerebrospinal fluid enters the ventricle across this membrane.

CSF Formation

• The cerebrospinal fluid is formed mainly in the choroid plexuses of the lateral, third, and fourth ventricles;

• Some originate from the ependymal cells lining the ventricles and from the brain substance through the perivascular spaces.

Choroid Plexus

• lateral ventricles– continuous through Interventricular foramen with

the small plexus in the third ventricle.– secretes the bulk of the CSF

• fourth ventricle

– separate from that in the third and lateral ventricles– only makes a small contribution to the total amount

of CSF

Circulation The circulation begins with its secretion from the choroid

plexuses in the ventricles The fluid passes from the lateral ventricles into the third

ventricle through the interventricular foramina It then passes into the fourth ventricle through the narrow

cerebral aqueduct. The circulation is aided by the arterial pulsations of the

choroid plexuses and by the cilia on the ependymal cells lining the ventricles.

From the fourth ventricle, the fluid passes slowly through the median aperture and the lateral foramina of the lateral recesses of the fourth ventricle and enters the subarachnoid space

CSF Drainage

• The CSF returns to the vascular system by entering the dural venous sinuses via the arachnoid granulations (or villi).

• The arachnoid villi act as one-way valves between the subarachnoid space and the dural sinuses. The rate of absorption correlates with the CSF pressure.

CSF Drainage

• Flows along the cranial nerves and spinal nerve roots into the lymphatic channels; this flow may play a substantial role in CSF reabsorption, in particular in the neonate, in which arachnoid granulations are sparsely distributed.

Summary• Filtered from blood in:

– Choroid plexuses• Circulates in through ventricles, canals, &

between meninges• Returned to blood at superior sagittal

sinus mainly in addition to other venous sinuses

• Along nerves to extra cranial lymphatics• Through venous plexuses in vertebral

canal and around spinal cord

VENTRICULAR SYSTEM• Comprises of:

– two lateral ventricles

– third ventricle

– cerebral aqueduct

– the fourth ventricle

VENTRICULAR SYSTEMfrom the right from above

Central canal

The Lateral Ventricle

• Is the cavity inside the cerebral hemisphere

• The 2 lateral ventricles are the largest of the ventricles.

• They are irregular in shape. • Each consists of a central part, with

anterior, posterior and inferior horns.

Lateral ventricles• C-shaped cavity

• within each cerebral hemisphere

• Consists of:

– anterior horn - frontal lobe

– body --- parietal lobe

– posterior horn ---- occipital lobe

– inferior horn ---- temporal lobe

Anterior horn (Frontal lobe)

Is anterior to the interventricular foramen(of Monro) .

Its roof and anterior border are formed by the corpus callosum,

Its vertical medial wall by the septum pellucidum. The floor is formed by the head of the caudate nucleus.

Central part• Triangular in shape,

having :• Roof: corpus

callosum; • Medial wall: by the

posterior part of the septum pellucidum

• Floor and inferolateral wall: by parts of the caudate nucleus, thalamus, choroid plexus and fornix.

Thalamus

Thalamus and Basal ganglia

Brain stem

Amygdaloid body

Thalamus

Tail of Caudate nucleus

Head of Caudate nucleusLentiform nucleus Body of Caudate nucleus

Posterior Horn

• Extends into the occipital lobe.• Its roof is formed by fibers of the corpus

callosum.• It is the most variably developed and may

even be absent.

Cingulate sulcus

Posterior horn of lateral

ventricle

Collateral eminence

Collateral sulcus

Splenium of corpus callosum

Tapetum of corpus callosum

Optic radiation

Callosal radiation

Inferior Horn• It traverses the temporal lobe. • Its roof is formed by the white substance

of the cerebral hemisphere.• Along the medial border is the stria

terminalis and the tail of the caudate nucleus.

• The floor and the medial wall are formed by the fimbria, the hippocampus and the collateral eminence.

• The amygdaloid nucleus bulges into the terminal part of the inferior horn.

Third Ventricle

• It is a narrow cavity between the 2 thalami. • is a narrow vertical cleft between the 2 lateral ventricles• It communicates with the 2 lateral ventricles through the

interventricular foramen and with the 4th ventricle through the cerebral aquiduct.

• Comprises of:

– Anterior wall– Two side walls– Floor– Roof

Third Ventricle• Anterior wall:

– lamina terminalis– anterior commissure

• Roof: The roof is formed by the tela choroidea• Floor:

– optic chiasma– tuber cinereum median eminence– infundibulum – mamillary bodies– posterior perforated substance– tegmentum of the cerebral peduncles

• Two side walls:– Thalamus Interthalamic adhesion (60% of brains)– Hypothalamus Supraoptic nucleus – ADH

Paraventricular nucleus – Vasopressin/Oxytocin– Subthalamus Subthalamic nucleus

Tela choroidea

• Reflection of two layers of pia matter

– Medially b/w interventricular foramina

– Laterally across the upper surface of thalamus

Tela choroidea (double fold of pia)

Third Ventricle

Third Ventricle

Third Ventricle

Aqueduct (of Sylvius)

• Cavity within midbrain

• Continuous above with third ventricle

• leads through the midbrain into the cavity of the fourth ventricle

Fourth ventricle• The fourth ventricle is a cavity

which lies posterior to the pons and upper half of the medulla oblongata and anterior to the cerebellum.

• It is continuous with the cerebral aqueduct (mesencephalic or Sylvius) above and the central canal of the spinal cord in the lower half of the medulla.

• On each side, a narrow prolongation, the lateral recess, projects around the brainstem; its lateral aperture (Foramen of Luschka) lies below the cerebellar flocculus.

Fourth ventricle• The fourth ventricle

has lateral boundaries, a roof and a floor.

• The lateral boundaries are formed on each side by the superior cerebellar peduncle, the inferior cerebellar peduncle and the cuneate and gracile tubercles.

• Roof of the fourth ventricle • The upper part is formed by the

superior medullary velum • The lower part is formed by the

inferior medullary velum

• The floor of the fourth ventricle,

• also known as rhomboid fossa, is formed by the dorsal surfaces of the pons and medulla oblongata

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Applied Anatomy

• TB meningitis – block of aqueduct of Sylvius - hydrocephalus

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Normal Brain

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Normal Ventricles

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Hydrocephalus

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Normal ventricles and hydrocephalus