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 .
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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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