Ventricular Anatomy And Csf Physiology

Anatomy of the Ventricles and CSF Physiology Dr F Taleb

Ventricles of the Brain  CNS is hollow  Develops from a NEURAL TUBE whose

cavity persists  Lined with single Epithelial-like layer of cells – Ependyma (cuboidal)  Ventricles

Ventricles of the Brain  Ventricles contain CSF  Secreted in ventricles by choroid plexus  CSF necessary for brain development –

Reasons ??

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Normal brain- 4 ventricles 2 lateral - Cerebal hemispheres 3rd ventricle – Diencephalon 4th Pons and Medullasharing connnections – FOM and AS

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Lateral ventricles C shaped structure Around the caudate nucleus and white matter of the internal capsule

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Lateral Ventricles 5 Parts Frontal(anterior) Horn Body Atrium(Trigone) Occipital(posterior) Temporal(inferior)

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Frontal Horn Anterior to Foramen of Monro Corpus Callosum – roof, anterior part and part of the floor Bulbous head of the caudate nucleus forms the rest of the floor

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Lateral wall – Caudate nucleus Meets the roof at an angle Medial wall – septum pellucidum- (4 layers 2 pia 2 ependyma) and anterior column of fornix No choroid plexus

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BODY Behind FOM Floor – Thalamus and body of the caudate nucleus Grove – thalamostriate vein and Stria medullaris (amygdala to ant perf subs)

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Roof - Corpus Callosum Medial wall – crus and body of the fornix Choroid plexus invaginates between thalamus and fornix – choroid fisssure Covered with 2 layers –pia and ependyma

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Lateral wall – essentially caudate body Note: the genu of the internal capsule touches the lateral wall lateral to FoM between tha caudate and thalamus

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Cavity arches downwards and forwards into the Temporal horn and backwards into the occipital horn Atrium/trigone

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Occipital Horn Most variable Can be absent Floor: collateral eminence – collateral sulcus Medial wall: 2 convexities Upper – bulb – fibres of forceps major

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Lower - calca avis – calcarine sulcus Can obliterate the occiptal horn when well developed Roof - tapetum of corpus callosum Lateral wall – optic radiation NO choroid plexus

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Temporal Horn ? Largest Medial part of temporal lobe Ends blindly posterior to amygdaloid body

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Floor – Hipppocampus medially Collateral eminence laterally

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Roof – Tail of caudate continuous anteriorly with the amygdaloid boby – lateral to anterior perforated substance Prominence at tip above pes hippo Laterally tapetum

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Lateral wall – Tapetum

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Medially – Choroid fissure Lower lip - fimbria Upper lip – tail of caudate

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Trigone Body - temporal occipital horns converge Base on pulvinar Glomus – tuft of choroid plexus Calcified

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THIRD VENTRICLE Slit like space in sagital plane Lateral wall thalamus mainly

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Thalamus bulge of grey matter Interthalamic adhesion(massa intermedia) in 60% of brains only Not a comissure

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Hypothalamic grove from FoM to AS Hypothalamus below grove including floor Subthalamus caudally merges with midbrain Hypothalamus – supraoptic and paraventricular nuclei

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Stria meditullaris – runs along superomedial border of thalamus White matter band from piriform area U loop posteriorly habenular comissure Olfactory(like ant commissure)

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Columns of fornix – prominence from FoM blends in the lateral wall

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Roof – From FoM to supra pineal recess 4 layers Fornix body 2 layers of pia( tela choroida) Vascular layer between the tela (velum interpositum)

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Habenular comm.

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Choroid plexus hanging from roof in pairs Continuous with choroid plexus of lateral ventricles through FoM and temporal horns(eshaped)

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Anterior wall – Optic chiasm to FoM Optic chiasm Supra optic recess Lamina terminalis Anterior commissure Columns of fornix

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Floor – From Optic chiasm to AS Ant ½ diencephalic Post ½ mesencephalic

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Ant – post Optic chiasm Infundibulum Tuber cinereum(grey)– median eminence – no blood/brain barrier Mamillary bodies (external) Posterior perforated substance

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Floor Tegmentum AS

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Posterior wall From supra pineal recess to AS Superior – inferior Supra pineal recess – slack roof pia + ependyma Habenular comm. Pineal body and recess Posterior comm. -Sup colliculi

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AS Through midbrain Into 4th ventricle

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FOURTH VENTRICLE Extends from the AS to the central canal Rhomboid shaped cavity over pons and medulla Roof is tent shaped Mainly ependyma

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Covered by the cerebellum Upper part – over pons – thin sheet of white matter – superior medullary velum Bounded by superior cerebellar peduncles

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Lower part – over medulla Superiorly Ependyma + white matter from base of flocculus –Inferior medullllary velum Inferiorly Only ependyma and pia Attached to margins of cuneate and gacile nuclei

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Midline slit Foramen of Magendie Comunicates with cerebellomedullary cistern

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Lateral recess – laterally Around and behind the inferior cerebellar peduncle Narrow and tubular Opening – lateral aperture-foramen of Luschka

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Opens anteriorly just behind the VIII nerve Into pontine cistern These are the only exits from the ventricles

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Choroid plexus is separate Small L – shaped Indents the medullary part of the roof Starts at the lateral aperture from a branch of PICA Lies below flocculus

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Passes medially Meets the opposite choroid plexus Run down as parallel structures to foramen of Magendie Drains into occipital sinus

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The Floor Diamond shaped – Rhomboid fossa Upper boundaries – superior and inferior cerebellar peduncles Lower boundaries – gracile and cuneate nucleus

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Median sulcus – deep grove from AS to central canal Floor symetrical on each side Medullary striae – crosses the floor at its widest part aberrant fibres from pontine nuclei to cerebellum via inferior peduncle

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Demarcates medullary and pontine parts Overly vestibular area at lateral angle

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Pontine Part Vestibular area Median eminence insignificant Lower part – bulge – Facial collliculus Overly the recurving fibres of CN VII and the underlying CN VI nucleus

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Superior fovea – between vestibular area and facial colliculus Locus caerulus – bluish colour due to noradrenergic pigmented cells – part of Reticular Formation

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Medullary part Smaller than Pontine part Vestibular area Inferior fovea divides the floor into 2 smaller traingles Superior triangle – hypoglossal triangle CN XII nucleus

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Inferior/lateral triangle – Vagal triangle

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Entire CNS cavity – Brain and spine 1600 to1700ml 150ml CSF Ventricles Cisterns Subarachnoid space – brain and cord All connected and pressure regulated

CSF Physiology  Formation  500 ml/day – 3 to 4 times total vol  2/3 from choroid plexuses  Rest

mostly from ependymal surfaces and arachnoidal membranes  Small amount from brain itself, through the perivascular spaces  Outflow – arachnoid villi in the venous sinuses

CSF Physiology  Secretion by the Choroid Plexus  Depends on active transport of sodium

ions through the epithelial cells that line the plexus  Chloride follows  Water follows by osmosis  Also small amount of glucose is pumped out and potassium and bicarbonate into the capillaries

CSF Physiology  CSF –  Osmotic pressure =plasma  Sodium conc = plasma  Cl 15% > plasma  K 40% < plasma  Glucose 30%< plasma

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Absorption Arachnoid villi – microscopic fingerlike projections of the arachnoid membrane into the venous sinuses Conglomerates – macroscopic arachnoid granulations

CSF physiology  Endothelial cells -

Large holes through the bodies of the cell  Free flow of prot red and white cells into venous sinus  Some absorbtion around the spinal nerve roots

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Perivascular spaces Blood vessels penetrate the brain parenchyma carying a layer of pia mater Loosely packed around – perivascular space Up to arterioles and venules Not capillaries

CSF Physiology  Lymphatic Funtion of Perivascular Space  No lymphatics in brain  Protein leaks into

brain tissue  Leaves brain tissue into perivasc spaces then subarachnoid space  Thus the protein is scavenged into the CSF.  Also removes debris – dead white cells etc

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CSF pressure Normal 13 mm Hg – lying down(5 – 20 mmHg) Regulation of pressure by absorption by the arachnoid villi mainly Production is fairly constant Villi functions as valves No back flow of blood ‘Opening pressure’ of 1.5mmHg

CSF Physiology  Blood / fibrosis / particles / proteins can

block the villi  Also mechanical blockage around incisura  Hydrocephalus

CSF physiology  Blood-brain barrier and blood-CSF barrier  CSF and brain interstitial fluid different  Tight junctions – only selective diffusion  Permeable to water, carbon dioxide,

oxygen, and most lipid soluble substances(alcohol and anaesthetic drugs)  Slightly permeable to electrolytes  Impermeable to protein and hydrophillics

CSF physiology  Pia and ependyma are permeable  Most substances in the CSF can diffuse

into the brain parenchyma  Drugs that do not cross the blood-brain barrier can be injected intrathecally

CSF Physiology  Mechanical Cushioning  Major function of CSF !  Brain and CSF have the same SG(4%diff)  Brain is ‘suspended’ in the vault  A blow to the head moves the entire brain

simultaneously

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Contrecoup Severe blow – cause damage on the opposite side How? Rapid acceleration and deccelration Due to inertia On the initial mvt the brain is cushioned (momentum is diffused) by the CSF – crumple zone Due to the inertia relative CSF deficiency at opposite end. On decceleration brain hits vault with no CSF cushion – No crumple zone - CONTUSION