BLOOD SUPPLY OF BRAIN

Dr Srikanth

Normal vascular anatomy of brain Comprises of 1.Arterial supply 2.Venous drainage

Carotid artery External carotid artery Superior thyroid artery Ascending pharyngeal

artery Lingual artery Occipital artery Posterior auricular artery Superficial temporal artery Internal maxillary artery

Internal carotid artery Carotid bulb Cervical segment Petrous segment Lacerum segment Cavernous segment Clinoid segment Ophthalmic segment Post communicating

artery

Internal carotid artery

CIRCLE OF WILLIS

Anterior cerebral artery :-

The anterior cerebral artery is the more medial branch of supraclinoid ICA.the ACA runs mostly in the interhemispheric fissure and has three distinct segments.

A1.(HORIZONAL)ACA SEGMENT

Branches: MEDIAL LENTICULOSTRIATE ARTERY-pass superiorly

through anterior perforated substance to supply medial basal ganglia

RECURRENT ARTERY OF HEUBNER-arise from distal A1 or promixal A2 and curves backward above horizontal ACA,joins medial lenticulostriate arteries to supply inferomedial basal ganglia,and anterior limb of internal capsule.

ACA SEGMENTS cont…. A2(vertical)segment-courses superiorly in the

interhemispherical fissure extending from A1-AcoA junction to corpus callosum rostrum .

It has two cortical branches,the orbitofrontal and frontopolar that supply the undersurface and inferomedial aspect of frontal lobe.

A3(callosal)segment curves anteriorly around

corpus callosum genu Divides into two

terminal ACA branches 1.pericallosal-larger one

,runs posteriorly between dorsal surface of corpus callosum and cingulate gyrus.

2.callosomarginal arteries-courses over the cingulate gyrus within cingulate sulcus.

Vascular territory of ACA cortical branches supply

anterior two thirds of medial hemisphere and cc,the inferomedial suface of frontal lobe and the anterior two thirds of cerebral convexity adj to the interhemispheric fissure.

The penintrating ACA branches (mainly the medial lenticulostriate arteries)supply the medial basal ganglia,cc genu anterior limb of internal capsule

Middle cerebral artery Large ,more lateral terminal branch of

supraclinoid ICA 4 segments:-(1) Horizontal segment(M1)-extends laterally from

ICA bifurcation towards sylvian fissure (lateral cerebral) fissure.it bifurcates or trifurcates before entering sylvian fissure.

Branches-1.Lateral lenticulostriate arteries-supply lateral

putamen,caudate nucleus and external capsule2. anterior temporal artery-supply tip of temporal

lobe.

Middle cerebral artery cont…. M2(INSULAR)segment- The post bifurcation MCA

trunk turn posterosuperiorly in sylvian fissure following a gentle curve or genu(knee)

Arise from post bifurcation trunks and sweep upward over the surface of insula.

M3(opercular)segment-branches loop at the top of sylvian fissure then course laterally under the parts (opercula)of the frontal ,parietal and temporal lobes that hang over and enclose the sylvian fissure

M4(CORTICAL)segment-MCA becomes M4 when it exits the sylvian fissure and ramify over the lateral surface of cerebral hemisphere

Vascular territories of MCA MCA supplies most of

lateral surface of cerebral hemisphere ,only a small thin strip at the vertex is supplied by ACA,and occipital and posteroinferior parietal lobes supplied by PCA .its penintrating branch supply mostly lateral basal brain structure.

Posterior cerebral artery The two posterior cerebral arteries are two major

terminal branches of distal basilar artery 4 segments P1(precommunicating)segment 1.the thalamoperforating arteries Corses posterosuperiorly in the interpeduncular

fossa to enter the underface of midbrain

Posterior cerebral artery cont P2 (ambient)

Two major cortical branches – Anterior temporal artery Posterior temporal artery These arise from P2 segment and pass laterally

towards inferior surface of temporal lobe. Small branches- Thalmoperforating artery Peduncular perforating artery

P2 segment cont…. Medial posterior

choroidal artery(PchA) Curves around

brainstem courses superomedially to enter tela choroidea and roof of 3rd ventricle

Lateral posterior choroidal artery(PchA) enters lateral ventricle and travels with choroid plexus curves around pulvinar of thalamus

P3(QUADRIGEMINAL)SEGMENT-.it begins behind the midbrain and ends where the PCA enters the callcarine fissure of occipital lobe

P4 (calcarine)segment-terminates within the calcarine fissure where it divides into two terminal PCA trunks.

the medial trunk gives off the medial occipital artery ,calcarine artery posterior splenial artery The lateral trunk – Lateral occipital artery

Vascular territory of PCA Supplies most of inferior

surface of cerebral hemisphere with the exception of the temporal tip and frontal lobe

Also supplies occipital lobe ,posterior one third of the medial hemisphere and corpus callosum and most of choroid plexus

Penintrating PCA branches are the major vascular supply of mid brain and posterior thalami.

Vertebrobasilar system Vertebro basilar system consists of:- 2 vertebral arteries The basilar artery

Vertebral Artery Anatomy

Vertebral Artery extend - First branch of the Subclavian

Arises from the upper and back of the first part of the Subclavian Artery

Ascends in foramina in the transverse processes of the upper six cervical vertebrae

Winds behind the superior articulating surface of the atlas

Enters the skull through the foramen magnum

Unites at the lower border of the pons with the artery of the opposite side to form the Basilar artery

Vertebral Artery (V1,V2,v3,v4 segments)Divided into 4 segments

V1(extraosseous): unnamed segmental arteries V2(foraminal): anterior meningeal artery aries from it V3(extraspinal ): posterior meningeal artery arises from it V4 (intradural)segment Branches 1.Anterior spinal artery 2.posterior spinal arteries 3.medullary perforating branchesThe posterior inferior cerebellar artery (PICA)arise from distal VA

curves around over the tonsil and gives off perforating branches like-

MedullaryTonsillarInferior cerebellar

Basilar arteryBasilar Artery

Formed by the junction of the two vertebral arteries at pontomedullary junction

BA courses superiorly in prepontine cistern lying between clivus in front and pons behind

Tereminates in interpeduncular fossa by dividing into the two posterior cerebral arteries

Basilar artery branches BRANCHES: Anterior inferior cerebellar artery(AICA) Superior cerebellar arteries Pontine labyrnthine Vascular territory The vertobasilar system supplies all the

posterior surface fossa structure as well as midbrain ,posterior thalami,occipital lobes,most of the inferior and posterolateral surface of the temporal lobe and upper cervical spinal cord .

l

Circle of willis Arterial anastomostic ring that surrounds the basal brain

structure and connects the anterior and posterior circulation with each other

10 components-Two ICATwo proximal or horizontal (A1)anterior cerebral

artery(ACA)segment.Anterior communicating artery (AcoA)Two post communicating arteries (PcoA)The basilar artery(BA)Two proximal or horizontal (P1)segments of the(PCA)

End of arterial system

Venous drainage of brain Intracranial venous system has Two components Dural venous sinuses The cerebral veins

Dural venous system

Anteroinferior group• Cavernous sinuses• Superior petrosal

sinuses• Inferior petrosal

sinuses• Clival venous plexus• Sphenoparietal sinus

Posterosuperior group• Superior sagittal sinus• Inferior sagittal sinus • Straight sinus • Sinus confluence

(torcular herophili)• Transverse sinus • Sigmoid sinus• jugular bulbs

Dural sinus cont… Dural sinuses and venous plexuses Endothelium lined channels

contained between the outer(periosteal)

And inner (meningeal)dural layers. Contains arachnoids

granulations(AG) also known as pacchionian granulations and contains CSF

A central core of CSF extends from subarachnoid space (SAS) into the granulations covered by an apical cap of arachnoid cells

Multiple small channels extend through full thickness of the cap to sinus endothilium and drains CSF into venous circulation

Superior sagittal sinus Large ,curvilinear sinus parallels the inner

calvarial vault. Originates from ascending frontal veins

anteriorly and runs in midline at the junction of falx cerebri with calvaria ,its diameter increases posteriorly,and associated with no of superficial cortical veins that drains into diploic space ,and large anastomosing vein of trolard

Coronal section –appears triangular vascular channel contains between dural leaves of falx cerebri

Inferior sagittal sinus Smaller than sss.lies bottom of falx cerebri And abv corpus callosum and cingulate

gyrus ,collecting small tributaries as it curves posteriorly along inferior free margin of falx

The ISS terminates at the falcotentorial junction where it joins with great vein of galen to form straight sinus

Transverse sinus Contained between attachment of tentorium

cerebelli to inner table of skull. curve laterally from trocular to posterior

border of petrous temporal bone where they turn inferiorly and become sigmoid sinus

Straight sinus Straight sinus formed by ISS and great

cerebral vein of galen. Runs posteroinferiorly from origin at

falcotentorial apex.recieves tributaries from falx cerebri and tentorium cerebelli.

Terminates by joining superior sagittal and transverse sinuses to form venous sinus confluence(torcular herophili)

Sigmoid sinuses and jugular bulbs Inferior continuations of the two transverse

sinuses.(s shape curve)descending behing petrous temporal bone to terminate becoming internal jugular veins

The jugular bulbs are focal venous dilation at the skull base between sigmoid sinuses and extracranial internal jugular veins(IJV)

Cavernous sinus Irregularly shaped heavily

trabeculated/compartmentalized venous sinuses lie along the side of sella turcica ,extending from superior orbital fissure anteriorly to clivus and petrous apex posteriorly.

Formed by a thin medial dural wall contains- Two cavernous internal carotid arteries(ICA) And abducens( CN VI) CN III,IV,V1,V2 are actually within lateral dural wall and

not inside CS proper. Major tributaries draining Ophthalmic vein Sphenoparietal sinuses

The cs communicates with each other by intercavernous venous plexuses.

Drain inferiorly through foramen ovale into pterygoid venous plexus

Posteriorly clival venous plexus also superior and inferior petrosal sinus

Superior and inferior petrosal sinus Superior petrosal sinus-courses

posterolaterally along top of petrous temporal bone extending from CS to sigmoid sinus

Inferior petrosal sinus –courses just abv petrooccipital fissure from inferior aspect of clival venous plexus to jugular bulb

Clival venous plexus It’s a network of connected venous channels

extends along dorsum sellae superiorly to foramen magnum.it connects cavernous and petrosal sinuses with each other with suboccipital veins around foramen magnum.

Sphenoparietal sinus Courses around lesser sphenoid wing at rim of

middle cranial fossa .receives superficial veins from anterior temporal lobe and drains into cavernous or inferior petrosal sinus.

CEREBRAL VEINS Subdivided into three groups1)superficial/ cortical/ external veins2) deep/internal veins3) Brain stem/posterior fossa veins

Superficial cortical veins It consists of 1)Superior group2) Middle group3) Inferior group

Superior cortical veins Superior cortical veins 8 to 12 superficial veins

course over upper surface of cerebral hemisphere following convexity sulci,cross subarachnoid space pierce arachnoid and inner dura before draining SSS.

A dominant superior cortical vein the vein of trolard courses upward from sylvian fissure to join SSS

Middle cortical vein Prominent is the superficial middle cerebral

vein.begins over sylvian fissure and collects numerous small tributaries from temporal frontal,and parietal opercula that overhang the lat cerebral fissure

Inferior cortical vein Drain most of inferior frontal lobes and temporal

poles The deep middle cerebral vein collect tributaries

from insula ,basal ganglia,and parahippocampal gyrus then anastomoses with basal vein of rosenthal.

it courses postrosupereiorly in the ambient cistern curving around mid brain to drain into v of G

Posterior anastomosing vein i.e., vein of labbe courses inferolaterally over temporal lobe to drain into transverse sinus .

Deep cerebral vein Divided into 3 groups 1. medullary veins 2.subependymal veins 3.deep paramedian vein

Medullary vein Originate one or two cm below the cortex and course

straight through the white matter towards the ventricle where they terminate in subpendymal veins

Subependymal veins Course under ventricular ependyma,collecting blood from

basal ganglia and deep white matter(via medullary vein) Important subependymal veins are septal veins and

thalamostrate veins. Septal veins –curve around frontal horn of 4th

ventricle.courses posteriorly along septum pellucidi. Thalamostraite veins-receive tributaries from caudate

nuclei and thalami curving medially to unite with septal vein near foramen of monroe to form two internal cerebral vein.

Deep paramedian vein Internal cerebral vein(ICV)and vein of galen (VofG) Paired paramedian veins that courses posteriorly

in cavum velum interpositum ,the thin invagination of subarachnoid space lies between 3rd ventricle and fornices.the ICV s terminate in the rostral quadrigeminal cistern by uniting with each other to form of VofG.the vein of galen curves posterosuperiorly under corpus callosum splenium uniting with iss to form straight sinus.

Brainstem /posterior fossa veins Divided 1.SUPERIOR GALENIC GROUP 2.ANTERIOR(PETROSAL)GROUP 3.POSTERIOR GROUP Superior galenic group Drain sup into vein of galen Major vein of this group Precentral cerebellar vein The superior vermian vein Anterior pontomesencephalic vein

Precentral cerebellar vein Single midline vein lies between lingula and

central lobule of vermis terminates behind inferior colliculi by draining into VofG.the superior vermian vein runs over top of vermis,joining PCv and draining into VofG

Anterior pontomesencephalic vein Interconnected venous plexus covers the

cerebral peduncles and extends over anterior surface of pons

Anterior petrosal groupposterior (tentorial group) Large venous trunk lies in cerebellopontine

angle cistern collecting numerous tributaries from cerebellum ,pons and medulla

Posterior (tentorial group) Inferior vermian vein (the most prominent

vein).,paired paramedian structure that curve under the vermis and drain inferior surface of cerebellum.

Pattern of venous drainage1)Peripheral venous drainage Radical pattern Mid and upper surfaces of cerebral hemisphere together

with their subjacent white matter drain centrifugaly (outward)via cortical veins of SSS

2)Deep(central)brain damage Basal ganglia thalami,most of interspheric white matter

drain centripetally(inward)into deep cerebral veins.the internal cerebral vein ,vein of galen and straight sinus drain entire central core of brain.

Most area of temporal lobes the uncus and anteromedial hippocampus drain into galenic system via deep middle cerebral veins and basal veins of rosenthal.

3)Inferolateral(perisylvian)drainage Parenchyma surrounding sylvian(lateral

cerebral)fissure consist of frontal ,parietaland temporal opercula plus insula

This perisylvian drain via superficial middle cerebral vein into sphenoparietal sinus and cavernous sinus.

4) Posterolateral(temoroparietal)drainage The posterior temporal lobes and inferolateral

aspect of parietal lobes drain via superior petrosal sinuses and anastomosing vein of labbe into transverse sinuses.

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