arterial supply of brain

1. ARTERIAL SUPPLY OF BRAIN
Dr.D.Sunil Kumar

2. • The brain is a highly vascular organ, its profuse
blood supply characterized by a densely
branching arterial network. It has a high
metabolic rate that reflects the energy
requirements of constant neural activity.
• 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.
• Cerebrovascular disease or stroke, occurs as a
result of vascular compromise or haemorrhage
and is one of the most frequent sources of
neurologic disability.

3. • The brain is supplied by two internal carotid
arteries and two vertebral arteries that form a
complex anastomosis (circulus arteriosus, circle
of Willis) on the base of the brain.
• In general, the internal carotid arteries and the
vessels arising from them supply the forebrain,
with the exception of the occipital lobe of the
cerebral hemisphere, and the vertebral arteries
and their branches supply the occipital lobe, the
brain stem and the cerebellum.
ARTERIAL SUPPLY TO BRAIN

4. INTERNAL CAROTID ARTERY
• The internal carotid artery
arises from the bifurcation of
the common carotid
artery, most frequently
between C3 and C5 vertebral
level, ascends in the neck and
enters the carotid canal of the
temporal bone.
• Origin -Lateral to ECA.
• Can be divided into number of
segments between the bulb
and its bifurcation into MCA
and ACA

5. ECA
Internal carotid- carotid
bulb
Left CCA
3-D CTA

6. Bouthillier classification of ICA
segments
Bouthillier et al described a seven segment internal
carotid artery (ICA) classification system:
– cervical segment
– petrous segment
– lacerum segment
– cavernous segment
– clinoid segment
– ophthalmic (supraclinoid) segment
– communicating (terminal) segment

8. Cervical segment
• Cervical ICA extends from carotid bifurcation
to skull base.
– No narrowing
– No dilatation
– No branches
– No tapering
Course – crosses behind and medial to ECA

9. Variants – cervical segment
• 10%- ICA
originates medial
to ECA
ICA
ECA

10. • Anomalous ECA branches arises from cervical
ICA
– The ascending pharyngeal artery occasionally
takes off from the proximal ICA also, as does the
occipital.
• Persistent embryonic vesels may anastomose
with vertebrobasilar system.
– Persistent hypoglossal artery is one such branch.
The persistent hypoglossal artery originates from
the internal carotid artery at the levels of the C1
through C3 vertebral bodies, courses through the
hypoglossal canal, and anastomoses with the
basilar artery.

11. Persistent hypoglossal artery. Axial image from CT angiography shows an artery that
courses through the hypoglossal canal (arrows). CT angiogram depicts a hypoglossal
artery (arrowhead) that arises from the proximal internal carotid artery (arrow) at the
C2 vertebral level and anastomoses with the basilar artery.

12. • This is the ICA segment inside
the petrous bone and partially
within foramen lacerum.
• The artery enters the skull at
right angle and has an initially
ascending course (vertical
petrous subsegment), turning
anteromedially (horizontal
petrous subsegment) and exits
the petrous bone at foramen
lacerum.
Petrous segment

13. Vertical
•2 subsegments joined at genu
•Short vertical segment – anterior to IJV
•Genu – petrous ICA turns anteromedially in front of
cochlea
•Longer horizontal segment
Horizontal
Genu

14. DSA

15. MRA

18. 3D-DSA of petrous segment aneurysm

19. Variant
• Aberrant Carotid Artery
– This vessel is, in fact, not the “ICA”, but rather
ascending pharyngeal reconstitution of the true
ICA in the petrous segment, due to cervical ICA
agenesis.
– The aberrant carotid is made up of the ascending
pharyngeal artery, its inferior tympanic branch,
and the caroticotympanic branch of the ICA.

20. The vessel has a characteristic lateral swing within the petrous bone (red arrows),
bringing it into the middle ear cavity, which can be appreciated on MR, CT, and angio.

21. Note the posterior course of the intratympanic
segment ofthe aberrant carotid artery compared with the
normal.

22. •Reduced caliber
•Lateral sling

23. Variant -Aberrant
ICA
Aberrant course
•Posterolateral course thro temporal bone
•Reduced diameter of ICA
•Visible pulsatile mass in hypotympanum
•Bony plate separating ICA from tympanic cavity
absent
•Vertical segment of carotid canal absent
Normal course of ICA
•Anteromedial course thro temporal bone
•ICA anterior to IJV
•In front of cochlea
• 2 segments

24. Lacerum Segment
Small segment that extends from petrous apex, above foramen lacerum curving upwards
towards and lies extradurally until it reaches petrolingual ligament after this it becomes the
cavernous segment
Covered by trigeminal ganglion
No branches

26. • Defined as that portion of the ICA located
within the cavernous sinus.
Cavernous ICA

27. C4 segments
1. Ascending (posterior vertical )
2. Posterior genu
3. Horizontal
4. Anterior genu
5. Anterior vertical
1
Starts from petrous apex
Terminates at its entrance into
intracranial subarchnoid space
adjacent to anterior clinoid process.
Covered by trigeminal ganglion
posteriorly.
Has 5 segments

30. • The cavernous segment ends when the ICA
passes through an opening in the anterior
cavernous sinus wall called the “proximal
dural ring” (PDR).
• A short but very important segment, where
the ICA is sandwiched between the PDR and
the Distal Dural Ring, (which marks the
intradural transition), is neither
intracavernous nor intradural.
Clinoid segment C5

31. The anterior clinoid and sphenoid sinus position, is outlined in white. The proximal
ring (yellow line) extends from clinoid undersurface to medial ICA wall. The distal
ring (purple line) comes off the clinoid roof. The Clinoid segment is defined as the
space between the two rings.

33. Opthalmic
segment C6
Extends from distal dural
ring at superior clinoid to
just below posterior
communicating artery
(PCoA) origin
Branches –
•Opthalmic artery
ANT CLINOID
PROCESS C6
POST COMM
ARTERY

34. Mid arterial phase DSA
Lateral view MRA
Lateral DSA

35. Variations in Origin Of Opthalmic
Artery
In its “classic” location, the ophthalmic
ostium is located just distal (1mm) to the dural
ring and therefore intradural. However, the
vessel may arise either somewhat more distal
to the ring (as far up as the ACOM — ventral
ophthalmic variant), or somewhat proximal —
in which case it may be extradural – within
“transitional” or cavernous segments

36. lateral DSA of RT ICA injection, demonstrating ophthalmic artery origin from
anterior genu of the ICA, proximal to its usual location

37. •Extends from below PCoA to
terminal ICA bifurcation.
•Passes between optic and
occulumotor nerve.
C7 segment branches
Posterior communicating artery Anterior choroidal artery
Lateral DSA
AChA
PCoA
Communicating C7 Segment

38. Posterior communicating artery
•Arises – posterior aspect of
intradural ICA just below
anterior choroidal artery
•Course – posterolaterally
above the occulumotor nerve
to join posterior cerebral
artery
•Branches – anterior
thalamoperforating arteries
•Supplies – optic chiasma,
pituitary stalk , thalamus ,
hypothalamus.

39. Lateral late
arterial DSA
MRA

41. Computed tomography angiography
of the brain illustrating saccular
aneurysm (blue arrow) in the region
of the right posterior
communicating artery.

42. Posterior Communicating
Artery Anomalies
• Fetal Origin of the Posterior Cerebral Artery
– A fetal PCOM or fetal origin of the posterior cerebral
artery is a very common variant in the posterior
cerebral circulation.
– The posterior communicating artery (PCOM) is larger
than the P1 segment of the posterior cerebral artery
(PCA) and supplies the bulk of the blood to the PCA.
– The P1 can be small (hypoplastic) or absent. The
significance is in the stroke pattern, as the PCA will be
a part of the anterior circulation.

43. CT angiogram shows bilateral fetal posterior cerebral arteries
(arrows). Both P1 segments are absent.

44. • DWI in a Young
patient with
an internal carotid
artery occlusion
resulting in acute
MCA and PCA
territory infarcts
due to a fetal
origin of posterior
cerebral artery.

45. Posterior Communicating Artery
Infundibulum
• An infundibulum is a funnel shaped region of dilatation
at the origin of the posterior communicating artery
from the internal carotid artery.
• It may be round or conical, has a diameter of less than
2 mm, and is symmetric. The internal carotid artery is
at its base, and the posterior communicating artery
arises from its apex.
• An infundibulum must be distinguished from
aneurysms of the posterior communicating artery and
internal carotid artery

46. CT angiogram shows a posterior communicating artery (arrowhead) that arises
from the apex of a funnel-shaped infundibulum (arrow). The base of the
infundibulum is located at the origin of the posterior communicating artery

47. Terminal Branches of ICA
• Anterior Choroidal artery
• Middle cerebral artery
• Anterior cerebral artery

48. Segments
The ACA is divided into three segments:
A1 (horizontal): origin from the ICA to the anterior
communicating artery (ACOM). ~14 mm in length
A2 (vertical): from ACOM to the origin of
the callosomarginal artery
A3 (callosal): distal to the origin of the callosomarginal
artery
Anterior cerebral artery
The anterior cerebral artery along with the middle
cerebral artery, forms at the termination of the internal carotid
artery. It is the smaller of the two, and arches anteromedially to
pass anterior to genu of the corpus callosum, dividing as it does
so into its two major branches; pericallosal and callosomarginal
arteries

50. A1 (horizontal): origin from
the ICA to the anterior
communicating artery
(ACOM)

51. A2 (vertical): from ACOM to
the origin of
the callosomarginal artery

53. Arise from A1 segment-
perforating branches.
• Pass cephalad
thro anterior
perforated
substance.
• Supply head of
caudate nucleus
and anterior limb
of IC, putamen .
Medial lenticulostriate artery.

54. Recurrent Artery of Heubner
• Largest of the perforating
branches.
• May arise from A1 or A2
segment.
• A1 – 44%
• Proximal A2 – 50%
• ACoA – less common
• Derives its name from the fact
that it doubles back on its parent
artery at an acute angle to join
lenticulostriate vessel.
• Lies parallel to A1 .
• Supplies inferior part of anterior
limb of internal capsule

55. A2 segment- Interhemispheric segment
From ACoA junction
Ascend in front of 3rd ventricle in cistern
of lamina terminalis
Curves around corpus callosum genu
gives terminal branches
A2 terminal
branches-
Pericollasal
Collasomarginal

56. Cortical A3
segment
• Supply the anterior 2/3rds
of medial hemispheric
surface and small superior
area over the convexities.
• Callosomarginal a.– lies in
cingulate gyrus supplies
medial frontal lobe
• Pericallosal a.– course along
the posterior aspect of
corpus callosum and
supplies it and medial
parietal lobe

57. Callosomarginal
Pericallosal
A2 Segment

58. CT study of brain shows infarct involving right
para sagittal frontal lobe. Area of
involvement corresponds to right ACA
territory.

59. CT study of brain shows infarct involving left
para sagittal frontal lobe. Area of
involvement corresponds to left ACA territory.

60. ACA– ACoA complex
• ACoA -Part of COW -not a
true branch of ACA
• Branches – perforating
• Supply –Lamina terminalis ,
Hypothalamus , Anterior
commissure , Fornix, Septum
pellucidum , Para olfactory gyrus
, Subcellosal region , Anterior
part of cingulate gyrus

61. Variants ACA – ACoA Complex
• Azygos anterior cerebral artery
– It represents persistence of the embryonic median
artery of the corpus callosum .
– Bilaterally, the anterior cerebral artery territories
are supplied by a single midline A2 trunk.
– The anomaly is clinically relevant also because in
the event of anterior cerebral artery occlusion
secondary to thromboembolic disease or surgical
error, the resultant ischemia affects both
hemispheres

62. Azygos anterior cerebral artery. Multidetector CT angiogram
shows convergence of the A1 segments to form a single
midline A2 trunk.

63. • Anterior Cerebral Artery Trifurcation
• It is defined as the occurrence of three A2 segments.
Multidetector CT angiogram shows three A2 segments
(arrows) that arise from the anterior communicating artery.

64. Bihemispheric
Anterior Cerebral Artery
• This anomaly is characterized by hypoplasia of one A2 segment, with the
contralateral A2 segment providing the major arterial supply bilaterally to
the anterior cerebral artery territory
Multidetector CT angiogram
depicts a dominant or
bihemispheric
A2 segment (arrow) that
supplies bilateral
anterior cerebral artery
territories and a contralateral
nondominant A2 segment
(arrowhead).

65. A1 Segment Absence or Hypoplasia
• In the presence of either variant, the contralateral anterior cerebral
artery may supply part or all of the territory of the normal anterior
cerebral artery via a large anterior communicating artery
Absence of an A1 segment of the
anterior
cerebral artery. Multidetector CT
angiogram shows
the origin of both A2 segments
from a single, unilateral
A1 segment.

66. Absent Anterior
Communicating Artery
Absence of the anterior communicating artery. Multidetector CT angiogram
demonstrates absence of the anterior communicating artery and equal caliber
of the A1 segments

67. Middle cerebral artery
• The MCA arises from the internal carotid
artery (ICA) as the larger of the two main
terminal branches (MCA and anterior cerebral
artery) and continues into the lateral
sulcus where it branches and provides many
branches that supply the cerebral cortex.

68. Segments
• The MCA is divided into four segments:
– M1: from the origin to bifurcation/trifurcation
(the limen insulae); also known as horizontal or
sphenoidal segment
– M2: also known as insular segment, from
bi(tri)furcation to circular sulcus of insula where it
makes hairpin bend to continue as M3
– M3: opercular branches (those within the Sylvian
fissure); also known as opercular segment
– M4: branches emerging from the Sylvian fissure onto
the convex surface of the hemisphere; also known as
cortical segment

71. Lateral lenticulostriate arteries
• The lateral
lenticulostriate
arteries arise from
the proximal middle
cerebral artery
(MCA) and supply the
lateral portion of
the putamen
and external
capsule as well as
the upper internal
capsule.

72. Sylvian segment
[M3] territory
• Supplies
• Inferolateral frontal lobe
• Insular cortex
• Parietal lobe
• Temporal lobe
Cortical segment
territory [M4]
• Supplies –
• Lateral
cerebrum
• Insula
• Ant- lateral
temporal
lobe

73. MCA Territory infarct

74. Variant
• Accessory Middle Cerebral Artery
– An accessory middle cerebral artery is an artery that arises from
the anterior cerebral artery and courses parallel to the M1
segment of the middle cerebral artery, supplying the anterior-
inferiorregion of the frontal lobe
– It may be difficult to differentiate an accessory middle cerebral
artery from a duplicated middle cerebral artery.
– A smaller middle cerebral artery branch arising from the
anterior cerebral artery is designated as an accessory middle
cerebral artery, whereas a smaller middle cerebral artery branch
arising from the distal carotid artery is called a duplicated
middle cerebral Artery
– Comparison with the level of carotid bifurcation and the pattern
of branching on the opposite side may be helpful for identifying
this variant

75. Accessory middle cerebral artery. Multidetector
CT angiogram shows the main middle cerebral
artery (arrowhead) with a smaller-caliber
accessory middle cerebral artery (arrow) that
arises from the A1 segment.
Duplication of the middle cerebral artery.
Multidetector CT angiogram depicts the
main middle cerebral artery branch, which
arises directly from the distal internal
carotid artery (arrow), and a smaller-
caliber duplicate middle cerebral artery
that arises from a more proximal site
(arrowhead).

76. POSTERIOR CIRCULATION

77. Vetebral artery
• The vertebral artery (VA) arises from
the subclavian artery, ascends in the
neck to supply the posterior fossa and
occipital lobes as well as provides segmental
vertebral and spinal column blood supply.

78. • Origin
– The origin of the VA is
usually from the
posterior superior part
of the subclavian
arteries bilaterally,
although the origin can
be variable:
• brachiocephalic artery
(on the right)
• aortic arch: 6% of cases
– The VA is normally 3-5
mm in diameter and the
ostium is the most
common site of stenosis.

79. Segments
• The vertebral artery is
typically divided into 4
segments:
– V1: origin to transverse
foramen of C6
– V2: from the transverse
foramen of C6 to the
transverse foramen of C2
– V3: from C2 to the dura
– V4: from the dura to their
confluence to form the
basilar artery

81. Extracranial VA branches
1. V1-Small segmental spinal/
meningeal/ muscular
branches.
2. V2- Anterior Meningeal
artery , muscular branches.
3. V3 -Posterior Meningeal
artery
– Courses along posterior arch
of atlas.
– Supplies falx cerebri
– Variant – origin from ECA /
PICA.
– Greatly enlarged with
vascular malformations and
neoplasms
Posterior meningeal artery

82. Intracranial branches
• Anterior spinal artery
– Joins ASA from opposite VA along anteromedial sulcus of cervical
cord.
– Medial medullary syndrome [Dejerine syndrome]
• Posterior inferior cerebellar artery
– Arises from distal VA
– Lateral Medullary syndrome [Wallenberg syndrome]

83. • Abnormal
hyperintensity is
noted in the right
medial medulla on
both T2- and
diffusion-weighted
scans, which
corresponds to
vasogenic and
cytotoxic edema,
respectively
• Medial medullary
syndrome

84. FLAIR image showing
ischemic infarct in left
medulla.
Lateral Medullary
Syndrome

85. Variants –
• Persistent
vertebrobasilar
anastamosis
• Left VA – aortic
arch origin – 5%
• Hypolastic VA – 40
%
Hypoplastic VA

86. Posterior
inferior
cerebellar
artery
• Segments
• anterior medullary segment
– Front of medulla
• lateral medullary segment
– Along side of medulla caudally to level of CN 9-11
• posterior medullary segment
– ascends posterior to the medulla behind CN IX and CN X.
• supratonsillar segment

87. anterior medullary segment
lateral medullary segment
posterior medullary segment
supratonsillar segment

88. • Supply
• Has a variable
territory depending
on the size of
the AICA.
• Typically it may
supply:
– posteroinferior cer
ebellar hemisphere
s (up to the great
horizontal fissure)
– cerebellar tonsils:
85% of the time
– inferior portion of
the vermis
– lower part of the
medulla: 50%

89. Basilar Artery
• It artery arises from the confluence of
the left and right vertebral arteries at
the base of the pons as they rise
towards the base of the brain.
• The basilar artery runs cranially in the
central groove of the pons towards
the midbrain within the pontine
cistern.
• Terminates in the interpeduncular
cistern by dividing into posterior
cerebral arteries.

90. MRA

91. Branches
1. AICA – Anterior Inferior
Cerebellar Artery
– 1st major branch.
– Posterior laterally in
cerebellopontine angle cistern.
– Supplies-
• Inferolateral pons
• Middle cerebellar peduncle
• Flocculus
• Anterolateral cerebelllar
hemisphere

93. SCA- Superior
Cerebellar Artery –
– Arises from BA
apex.
– Supplies –
• Superior surface
of vermis n
cerebellar
hemisphere.
• Deep cerebellar
white matter.
• Dentate nucleus.

97. Posterior cerebral artery
• The posterior cerebral arteries (PCA) are the terminal
branches of the basilar artery and supply the occipital lobes
and posteromedial temporal lobes.
• Segments:
The PCA is divided into four segments:
– P1: from it origin at the termination of the basilar artery
to posterior communicating artery (PCOM), within
interpeduncular cistern.
– P2: from the PCOM around the mid-brain(lies in ambien cistern)
– P3: quadrigeminal segment (segment within the quadrigeminal
cistern)
– P4: cortical segment (e.g. calcarine artery, within the calcarine
fissure)

99. CT ANGIO

100. P1 precommunicating
/ peduncular
• Br –
• Posterior
thalamoperforating-
Thalamus , Midbrain
• Medial posterior choroidal
artery – anteromedially
along roof of 3rd ventricle –
tectal plate , midbrain ,
thalamus posterior , pineal
gland , tele choroidae of 3rd
ventricle.
P2 ambient / crural
• Br –
• Thalamogeniculate
arteries- MGB , pulvinar ,
brachium superior
colliculus , crus cerebri ,
LGB
• Lateral post choroidal
artery – over pulvinar of
thalamus – posterior
thalamus , lateral
ventricular choroid
plexus

101. P1 Segment
supplying
Thalamus and
Midbrain
P COM
P2 SUPPLYING
Crus Cerebri
Lateral post choroidal artery lateral ventricular choroid plexus

102. P3 quadrigeminal
Behind midbrain in quadrigeminal plate cistern
Inferior temporal artery
• Undersurface of temporal lobe
• Anastamose -MCA
Parietooccipital artery
• Posterior 1/3rd interhemispheric
surface
• Anastamose with ACA
Calcarine artery( P4 )
• Visual cortex
• Occipital pole
Posterior pericollasal artery
(splenial)
• Splenium of corpus callosum
• ACA

103. MRI Axial FLAIR images of Brain shows infarct involving right
thalamus, right medial occipital and medial temporal lobe. Area of
involvement corresponds to right proximal PCA territory.

104. Circle of Willis
• It is formed by an arterial polygon as the internal
carotid and vertebral systems anastomose around the optic
chiasm and infundibulum of the pituitary stalk.
• Vessels comprising the circle of Willis:
– left and right internal carotid arteries(ICA)
– horizontal (A1) segments of the left and right anterior cerebral
arteries (ACA)
– anterior communicating artery (ACOM)
– left and right posterior communicating arteries (PCOM)
– horizontal (P1) segments of left and right posterior cerebral
arteries (PCA)
– basilar artery(tip)

106. 3DVRT CTA MRA
CT MRA
1. A1
2. P1
3. PCoA
4. ACoA

107. Other Variants of the
Cerebral Circulation
• Duplications
– A duplication is defined as two distinct arteries
with separate origins and no distal arterial
convergence
Multidetector CT angiogram
clearly demonstrates
duplication of the anterior
communicating
artery (arrow), with each vessel
originating separately
from an anterior cerebral artery.

108. • Fenestration, by contrast, is defined as a division of the
arterial lumen into distinctly separate channels, each
with its own endothelial and muscularis layers, while
the adventitia may be shared.
• More common in the vertebrobasilar arteries than in
the arteries of the anterior circulation.
Multidetector CT angiogram
shows dual
channels with a common
origin from the anterior
cerebral
artery (arrow).

109. • An association has been observed between
fenestration and aneurysm formation.
• It has been postulated that turbulent flow
created by defects in the tunica media at the
proximal and distal ends of a fenestrated
segment leads to aneurysm formation.
• These gaps in the media, combined with
increased hemodynamic stress, are believed
to contribute to the increased prevalence of
aneurysms among patients with fenestration.