Blood Supply of the Brain

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INTRODUCTION

 About 18% of the total blood volume in the body circulates in the
brain, which accounts for about 2% of the body weight.

 Loss of consciousness occurs in less than 15 seconds after blood

flow to the brain has stopped, and irreparable damage to the
brain tissue occurs within 5 minutes.

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INTRODUCTION

 The brain is richly supplied with blood through the

vertebrobasilar and internal carotid arteries.

 The common causes of cerebral hemorrhage are

aneurysm of major arteries, small arteriolar aneurysms
due to hypertension and arteriovenous malformations.

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INTRODUCTION

 Cerebrovascular disease or stroke, occurs as a result of

vascular compromise or haemorrhage and is one of the most
frequent sources of neurologic disability.

 Nearly half of the admissions to many busy neurologic services

are because of strokes.

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Arteries of brain

Two sources
 Internal carotid artery:
supplies anterior 2/3 of cerebral
hemisphere and parts of
diencephalon
 Vertebral artery: supplies
posterior 1/3 of cerebral
hemisphere and parts of
diencephalon, brain stem and
cerebellum

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 INTRODUCTION

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INTERNAL CAROTID ARTERY
 Intracranial Course of Internal
Carotid Artery
 The intracranial course of the artery
is subdivided into intrapetrous,
Intracavernous and supraclinoid
parts.
 Intrapetrous Part
 The internal carotid artery (ICA)
ascends in the carotid canal and
enters the middle cranial fossa
through the upper opening of the
foramen lacerum

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INTERNAL CAROTID ARTERY
 Intracavernous Part
 From foramen lacerum the artery
courses forwards in the floor of
the cavernous sinus, where it is
in close relation to the abducent
nerve.

Ant. Post.

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INTERNAL CAROTID ARTERY
 Supraclinoid Part
 After the artery pierces the dural
roof of the cavernous sinus it
bends sharply backwards and
upwards to terminate by dividing
into middle and anterior cerebral
arteries.

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 INTERNAL CAROTID ARTERY
 Carotid Siphon
 The internal carotid artery shows multiple
bends, which produce S-shaped shadow
called the carotid siphon on an angiogram.
The carotid siphon helps in damping down
its pulsations in the cranial cavity.
 The carotid siphon is a U or S-shaped part to
the ICA that varies with age. It begins at the
posterior bend of the cavernous part of ICA and
ends at the cerebral part, at ICA bifurcation
The term carotid siphon was introduced by Moniz in 1927 to describe the
radiographic appearance of the intracranial internal carotid artery (ICA
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 Carotid Siphon

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INTERNAL CAROTID ARTERY

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 INTERNAL CAROTID
ARTERY
 They arise from the common carotid
arteries where these bifurcate into the
internal and external carotid
arteries at cervical vertebral level 3
or 4 .
 Internal carotid artery at the
bifurcation from the common
carotid is Lateral to the external
carotid.

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BRANCHES:
1. Cervical part in the neck
2. Petrous part in the petrous
temporal bone
3. Cavernous part in the
cavernous sinus
4. Cerebral part in relation to
base of brain

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1. Cervical Part:
 It ascends vertically in the neck
from its origin to the base of skull to
reach the lower end of the carotid
canal.
 This part is enclosed in carotid sheath
along with internal jugular and vagus
nerve.
 No branches arises from the internal
carotid artery in the neck.
 Its initial part shows slight
dilation, carotid sinus, which acts as
a baroreceptor.

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1. Cervical Part:

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2. Petrous Part
 Within the petrous part of the
temporal bone, in the carotid
canal runs upward forward &
medially at rt. Angle.
 Branches (2):
 Caroticotympanic– enter middle
ear & anastomose with ant. & post.
Tympanic branches
 Artery of the Pterygoid Canal–
anastomose with greater palatine
artery

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3. The Intracavernous part
 Within the Cavernous Sinus
 Branches (4):
 Cavernous branch
 Superior & inferior Hypophyseal
artery
 Meningeal branch

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 4. Cerebral Part-
 Lies at the base of the brain after
emerging from the cavernous sinus.
 Largest
 Branches (5):
 Ophthalmic Artery
 Anterior Cerebral Artery
 Middle Cerebral Artery
 Posterior Communicating Artery
 Anterior choroidal Artery

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OPHTHALMIC ARTERY
 The ophthalmic
artery (latin: arteria ophthalmica)
is a branch of the internal carotid
artery that supplies all structures in
the orbit, also structures of the
nose, face and meninges.
 It enters orbit through optic
canal lying inferolateral to optic
nerve.

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OPHTHALMIC ARTERY
 Both artery & nerve lie in a
common dural sheath.
 The ophthalmic artery arises in the
cavernous sinus, enters the orbit via
the optic canal, then turns medially
and continues along the medial wall
of the orbit, dividing at the medial
end of the upper eyelid into terminal
branches - supratrochlear artery
and dorsal nasal branches.

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 OPHTHALMIC ARTERY
 It gives following branches:
 1. Central artery of retina →an end artery: Central
artery of the retina (first and most essential). It
supplies the optic nerve and inner 6/7 layers of the
retina.
 2. Lacrimal artery: originates from ophthalmic artery
just before it crosses the optic nerve. It gives
following branches-
 Glandular branches to lacrimal gland.
 2 lateral palpebral arteries-1 to every eyelid.
 2 zygomatic branches: zygomaticofacial and
zygomaticotemporal.
 Recurrent meningeal branch runs backwards to
goes into the middle cranial fossa via the superior
orbital fissure.
 ⦁ Muscular branches.
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OPHTHALMIC ARTERY
 Ciliary arteries (usually two,
sometimes three),
 Ethmoid arteries (usually two),
 Supraorbital artery,
 Muscular arteries (usually two),
 Medial palpebral arteries
(superior and inferior),
 Supratrochlear artery, and
 Dorsonasal artery.

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Branches of Int. Carotid Artery
• Anterior cerebral arteries
– smaller terminal branch of the ICA
– enters longitudinal fissure
– connected to the opposite anterior
cerebral artery by anterior
communicating artery (part of the
Circle of Willis)
– central branch supply deep masses
of gray matter within the cerebral
hemisphere

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 Anterior cerebral
arteries
– Supply:
• Cortical branches supply all medial
surface of cerebral cortex up to
parieto-occipital sulcus
• Corpus callosum
• Approximately 1 inch of the frontal
and parietal cortex on the superior
aspect of their lateral surface (this
include the leg area of the
precentral gyrus)
• Anterior portions of the basal
ganglia and internal capsule
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Effects of Occlusion of Anterior Cerebral Artery

 The loss of cortical supply to

paracentral lobule results in
contralateral spastic
monoplegia (lower limb),
altered sensorium in lower
limb and urinary incontinence.
 There may be gradual change
in personality due to damage
to orbital cortex of prefrontal
lobe
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 Branches of Int. Carotid Artery
 Middle Cerebral Arteries:
largest branch.
 runs laterally in the lateral sulcus .
 cortical branches supply entire
lateral surface of the hemisphere
EXCEPT
 area supplied by anterior cerebral
artery
 inferolateral surface supplied by
posterior cerebral artery
 occipital pole

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Supply
 The middle cerebral arteries supply the majority of the lateral
surface of the hemisphere, except the superior portion of
the parietal lobe (via the ACA) and the inferior portion of
the temporal lobe and occipital lobe (via the PCA).
 Inaddition, they supply part of the internal capsule and basal
ganglia.
 In its territory lie the motor and sensory areas excluding leg
and perineum and auditory and speech areas.
Middle Cerebral Arteries:
– CENTRAL BRANCH supply
deep masses of gray matter
within the cerebral hemisphere
– Supply:
 Supply all motor area except
“leg area”
 Supply parts of the internal
capsule and basal ganglia
 Central branches supply deep
masses of gray matter within
the cerebral hemisphere
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 MCA segments
 The MCA is angiographically
subdivided into four segments.
The M1 segment, also called
the horizontal segment,
originates at the carotid M1 Branches
bifurcation and terminates as 1. Medial lenticulostriate penetrating arteries
2. Lateral lenticulostriate penetrating arteries
the middle cerebral artery, and 3. Anterior temporal artery
its branches turn superiorly into 4. Polar temporal artery
the area between the temporal 5. Uncal artery (which may branch from the
anterior choroidal artery)
lobe and the insula.
 MCA segments
 The M2 segment (the
insular segment)
originates as the artery
enters between the
temporal lobe and the
insula and ascends along  M2 Branches
 78% bifurcate into superior and inferior
the insular cleft before divisions
making a hairpin turn at  12% trifurcate into superior, middle and inferior
the sulcus of the insula. divisions
 10% branch into many smaller branches
 MCA segments
 The M3 segment (the opercular
segment) begins at the apex of the
hairpin turn in the sulcus of the
insula and terminates as the
branches reach the lateral
convexity of the hemisphere.
 The M4 segment (the cortical  Superior terminal branch
segment) is visible on the lateral  lateral frontobasal artery
convexity of the hemisphere as the  prefrontal sulcal artery
 pre-Rolandic (precentral) and Rolandic (central) sulcal arteries
artery arises between the frontal,
parietal, and temporal lobes  Inferior terminal branch
 three temporal branches (anterior, middle, posterior)
 branch to the angular gyrus
 two parietal branches (anterior, posterior)
 Middle Cerebral Arteries: branches
• Posterior communicating
artery
– runs backward to join posterior
cerebral artery at interpeduncular
fossa
• deep depression on inferior of
midbrain between cerebral peduncles
• part of the circle of Willis
• Choroidal artery
– enter inferior horn of lateral
ventricle to supply choroid plexus
– branches may help supply the optic
tract, LGB, internal capsule and
crus cerebri
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Effects of Occlusion of Middle Cerebral Artery
 The loss of cortical supply to precentral gyrus results in
contralateral spastic paralysis of trunk, upper limb and lower
part of face with altered sensorium and conjugate deviation of
the eyes to the side of the lesion (due to involvement of
posterior part of middle frontal gyrus).
 There will be global aphasia (if dominant hemisphere is
affected).
 Loss of blood supply to prefrontal lobe results in gradual
changes in personality.

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Effects of Occlusion of Middle Cerebral Artery
VERTEBRAL ARTERY
• Branch of the 1st part of the
subclavian artery
• ascends the neck through the
transverse foramina of upper
6 cervical vertebrae
• Enters skull through foramen
magnum

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Vertebrobasilar Arteries
 The right and left vertebral
arteries unite with each other
at the lower margin of pons to
form the basilar artery.

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 VERTEBRAL ARTERY
• Cranial branches
– meningeal arteries
– anterior and posterior spinal arteries
– posteroinferior cerebellar artery
• largest branch of the vertebral artery and
supplies parts of the cerebellum and the
dorsolateral portion of the rostral medulla
• Occlusion: lateral medullary syndrome
– medullary arteries
• along with posteroinferior cerebellar artery,
supply most of the medulla

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Branches contd.
 BASILAR ARTERY:
ascends along the ventral
midline of the pons and
terminates near the
rostral border of pons by
dividing into 2 posterior
cerebral arteries

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  The vertebral arteries are the
Branches contd. main source of blood to
the spinal cord. However, the
following arteries branch from
the vertebral arteries to
directly supply the spinal cord
itself:
 one anterior spinal artery
 two posterior spinal arteries
 The anterior and two posterior
spinal arteries are direct
branches of the two vertebral
arteries which merge rostrally
to form a single artery -
the basilar artery
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Branches contd.
 Branches: to pons, cerebellum, internal
ear
 labyrinthine artery: follows the course
o the CN VIII and supplies inner ear
 anterior inferior cerebellar artery:
supplies part of the pons and the
anterior and inferior regions of the
cerebellum
 superior cerebellar artery: supplies
part of the rostral pons and superior
region of the cerebellum
 pontine branches : supply most of
pons
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Branches contd.
 Posterior cerebral arteries
 formed by the terminal
bifurcation of the basilar
artery
 anastomoses with the
posterior communicating
artery in the Circle of Willis
 Supply: lateral surface of the
hemisphere – occipital pole
and inferior temporal lobe
 medial surface of the
hemisphere – occipital lobe
and posterior 2/3 of temporal
lobe
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 Effects of Occlusion of Posterior Cerebral
Artery
 The loss of cortical supply
results in contralateral
homonymous hemianopia
with macular sparing.
 Damage to association cortex
of visual area causes visual
hallucinations (distortion of
color vision).

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Circle of Willis (circulus arteriosus)
 Formation
 The circle of Willis is formed by two group of arteries - the
internal carotid arteries and two vertebral arteries. These
arteries provide the anterior and posterior circulation of the
brain respectively.
 The arterial circle at the base of the brain is an anastomosis
between the internal carotid and the vertebrobasilar system of
arteries. It is polygonal in shape and is located in the
interpeduncular cistern.
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Circle of Willis (circulos arteriosus)
 The circle of Willis is a
confluence of vessels that
gives rise to all of the major
cerebral arteries.
 When the circle is complete, it
contains a posterior
communicating artery on each
side and an anterior
communicating artery.
 The circle of Willis shows
many variations among
individuals.
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A ferocious spider lives in the brain. His name is Willis! Note that
he has a nose, angry eyebrows, two suckers, eyes that look
outward, a crew cut, antennae, a fuzzy beard, 8 legs, a belly that,
according to your point of view, is either thin (basilar artery) or fat
(the pons, which lies from one end of the basilar artery to the
other), two feelers on his rear legs, and male genitalia

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SUMMARY
 The CIRCLE OF WILLIS is
therefore formed by
 2 internal carotid arteries
 2 anterior cerebral arteries
 2 posterior cerebral
arteries
 1 anterior communicating
artery
 2 posterior communicating
arteries
 1 Basilar artery
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Carotid Angiogram
 The carotid angiography is
performed by direct needle
puncture into the carotid
arteries to inject radio-opaque
dye.
 This cerebral angiogram
demonstrates a berry
aneurysm jutting from the top
of the basilar artery of the
circle of Willis at the base of
the brain.
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 Berry Aneurysm
 The berry aneurysm is a localized
dilatation on one of the arteries of
the circle of Willis due to congenital
muscular weakness.
 The most common sites of berry
aneurysm are the junction of anterior
cerebral and anterior communicating
arteries and at the bifurcation of
internal carotid arteries.
 Rupture of berry aneurysm may
cause life-threatening subarachnoid
hemorrhage.
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VENOUS DRAINAGE
 The venous drainage of the brain and coverings includes:
the veins of the brain itself,
the dural venous sinuses,
the dura's meningeal veins,
and the diploic veins between the tables of the skull.

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Venous Drainage of Cerebrum
 The veins of the cerebrum are divided into external
(superficial) and internal (deep) sets.
 The veins of the superficial set drain the surface of the
cerebrum while those of deep set drain the interior of the
cerebrum.

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 VENOUS DRAINAGE OF BRAIN
• Superficial veins
– drain the cortex and the
more superficial hemispheric
white mater mainly into the
superior sagittal and
cavernous sinuses
• Deep or internal veins
– drain the deep hemispheric
white mater and basal
ganglia into the 2 internal
cerebral veins w/c unite to
form the great cerebral vein
• Great cerebral vein
– formed by the union of 2
internal cerebral veins and
drains into the straight sinus 58
Veins of brain
Superficial cerebral veins
 Drain blood from cortex and
subcortical medullary substance
and empty into adjacent sinuses
of dura mater

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 Veins of brain
 Deep cerebral veins: drain
deeper parts of hemispheres,
basal nuclei, internal
capsule, diencephalon and
choroid plexus. The two
internal cerebral veins and
the basal veins of
Rosenthal join below or
behind the splenium of
the corpus callosum to form
the great cerebral vein of
Galen. which enter straight
sinus

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 Superficial System
 The superficial system of
veins is largely responsible for
draining the cerebral cortex:
 Superior cerebral veins:
Drain the superior surface,
carrying blood to the superior
sagittal sinus.
 Superficial middle cerebral
vein: Drains the lateral
surface of each hemisphere,
carrying blood to the
cavernous or sphenopalatine
sinuses.
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Superficial System
 Inferior cerebral veins:
Drain the inferior aspect of
each cerebral hemisphere,
depositing blood into
cavernous and transverse
sinuses.
 Superior anastomotic
vein (Trolard): Connects the
superficial middle cerebral
vein to the superior sagittal
sinus.
 Inferior anastomotic
vein (Labbé): Connects the
superficial middle cerebral
vein to the transverse sinus.
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Deep System
 Subependymal veins – There are numerous subependymal veins.
These receive blood from the medullary veins and carry it to the
dural venous sinuses.
 Subependymal regions of the central nervous system drain venous
blood into the inferior sagittal sinus superiorly or into the great
cerebral vein of Galen inferiorly, both of which drain into the straight
sinus
 Medullary veins: Originate 1-2cm below the cortical grey matter,
and drain into subependymal veins. These drain the deep areas of
the brain.

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VENOUS DRAINAGE OF BRAIN
• Veins of the brain have no muscular tissue in the wall and no
valves
• Venous sinuses – located between 2 layers of the dura
• Superficial and deep veins of the brain drain into the dural venous
sinuses (which in turn drain into the internal jugular veins)
• The venous blood from the deep areas of the brain is collected
into channels called the venous sinuses.

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 Clinical significance (Subdural
hemorrhage)
 It occurs due to rupture of cerebral veins in the subdural
space. The cerebral veins are while traversing the subdural
space en-route to drain into the dural venous sinuses have
little support.
 The superior cerebral veins are most generally torn at the
point where they go into the superior sagittal sinus.
 The reason is generally a strike on the front or rear of the
head, leading to excessive anteroposterior displacement of
the brain inside the skull