Anatomy of the anterior cerebral artery (ACA)

anatomy of the anterior cerebral artery (ACA) from the neuroradiology point of view. Important for neuroradiologists and neurointerventioalists.

1. Interventional Neuroradiology
Anatomy
Anterior Cerebral Artery (ACA)
Mohamed M.A. Zaitoun, MD
Interventional Radiology Consultant, Zagazig University Hospitals, Egypt
FINR-Switzerland
[email protected]
Interventional Radiology Unit,
Zagazig University, Egypt

3. Knowing as much as possible
about your enemy precedes
successful battle and learning
about the disease process
precedes successful
management.

4. Anterior Cerebral Artery
a) Origin
b) Course
c) Segmental Anatomy
d) Variants
e) Branches

5. a) Origin :
-The ACA originates below the anterior
perforating substance , lateral to the optic
chiasm as one of the terminal branches of
ICA

7. -Frontal view of the anterior (carotid)
intracranial circulation
1 internal carotid artery -cervical segment
2 internal carotid artery -vertical petrous
segment
3 internal carotid artery –horizontal petrous
segment
4 presellar segment (C5) internal carotid artery
9 ophthalmic artery
10 and 11 supraclinoid segment internal
carotid artery
13 anterior choroidal artery
14 internal carotid artery bifurcation
15 A1 segment of anterior cerebral artery
16 medial lenticulostriate arteries
17 recurrent artery of Heubner
18 A1-A2 junction anterior cerebral artery
19 anterior communicating artery
20 proximal A2 segment anterior cerebral
artery
21 callosomarginal branch of anterior cerebral
artery
28 pericallosal branch of anterior cerebral
artery
31 M1 segment of middle cerebral artery
32 lateral lenticulostriate arteries
33 bifurcation/trifurcation of middle cerebral
artery
34 anterior temporal lobe branches of middle
cerebral
43 sylvian point
44 opercular branches of middle cerebral
artery
45 sylvian(insular) branches of middle cerebral
artery

8. -Top down view (superior to inferior) of
the skull base
BLACK KEY
5 meningohypophyseal trunk
6 horizontal (C4) intracavernous ICA
7 inferolateral trunk
9 ophthalmic artery
12 PCOM
13 anterior choroidal artery
14 ICA bifurcation
15 A1 segment of ACA
19 ACOM
20 proximal A2 segment ACA
21 callosomarginal branch of ACA
28 pericallosal branch of anterior cerebral
31 M1 segment of MCA
33 bifurcation/trifurcation of MCA
34 anterior temporal lobe branches of
MCA
35 orbitofrontal branch of MCA
45 sylvian(insular) branches of MCA
RED KEY
1 vertebral artery
2 PICA
3 basilar artery
4 AICA
5 superior cerebellar artery
6.1 P1 segment PCA
6.2 P2 segment PCA
8 posterior temporal branch of PCA
9 parieto-occipital branch of PCA
10 calcarine branch of PCA
14 vertebral-basilar junction
16 pontine perforators
17 anterior spinal artery

9. b) Course :
-The A1 section runs horizontally forwards and
medially , crossing above the optic nerve to the
anterior interhemispheric fissure where it
communicates with its counterpart via the
anterior communicating artery (ACOM)
-The ACA then changes direction and the A2
section runs upwards and forwards in the fissure
to reach the genu of the corpus callosum

10. -It passes superior to the genu and the A3
section follows the corpus callosum
posteriorly either on its surface or in the
cingulate sulcus convexity
-It terminates as the posterior pericallosal
artery which passes along the body of the
corpus callosum to the splenium for a
variable distance which may extend to the
region of the pineal body

11. 1-ICA , 2-MCA ,3-ACA (A1) , 4-ACA (A2) , Arrow : ACOM

12. 1-Straight sinus , 2-Internal cerebral vein , 3-ACA (A2) , 4-ACA (A3) , 5-
Callosomarginal artery , 6-Pericallosal artery , 7-Corpus callosum

13. 1-ICA , 2-Vertebral artery , 3-Cavernous Sinus , 4-Carotid canal , 5-
ACA , 6-PCA

14. c) Segmental Anatomy :
-A1 segment: from the ICA bifurcation to the ACOM
14mm in length
-A2 segment: from ACOM to the origin of the
callosomarginal artery (the junction of the rostrum
and genu of the corpus callosum)
-A3 segment: distal to the origin of the
callosomarginal artery“a.k.a. pericallosal artery “
(extends around the genu until the artery turns
sharply posteriorly)
-A4 and A5 segments: above the corpus callosum
are separated by the plane of the coronal fissure

16. d) Variants :
1-Long or redundant A1
2-Fenestrations or duplications of the A1
3-Infraoptic course of the A1 segment
4-Variations in the relative size of the A1
segments and the ACOM
5-Fenestration or triplication of the anterior
communicating artery

17. 6-Persistent olfactory artery
7-Azygous ACA
8-Absent ACOM
9-ACA trifurcation
10-Bihemispheric ACA

18. 1-Long or redundant A1 :
-ACA joins the ACOM superior to the optic chiasm
(70%) , when the A1 segments are longer or
redundant , this union may occur more anteriorly
above the optic nerves
2-Fenestrations or duplications of the A1
3-Interoptic or infraoptic course of the A1
segment :
-Or even perforation of the optic nerve by the A1
segment
-Very rare

19. -A1 fenestration with associated aneurysm , a 3 mm ruptured aneurysm
extends from the proximal end of a fenestration of the right A1 segment (A) ,
evidence of mild intracranial vasospasm is seen in the distal anterior
cerebral artery circulation (B)

20. Fenestrated A1 (bilateral)

22. 4-Variations in the relative size of the A1
segments and the ACOM :
-Common , using a diameter of 1.5 mm or
smaller as a definition for hypoplasia ,
approximately 10% of brains demonstrate
hypoplastic A1 segments
-A1 segment absence / hypoplasia leads to
contralateral A1 segment dominance and
supply to ipsilateral A2 segment by a large
anterior communicating artery

23. -Asymmetry of the A1 segments has an important
impact on the likelihood of aneurysm formation in
the anterior communicating artery region , the end-
on hemodynamic impact of pulsatile flow in the
larger A1 segment directed against the anterior
wall of the anterior communicating artery is
thought to explain the higher rate of aneurysm
formation under these circumstances
-Up to 80% of anterior communicating artery
aneurysms have significant A1 asymmetry , this
hemodynamic force also explains why
approximately 70% of such aneurysms here
project anteriorly

24. -2D frontal view following left ICA injection
, there is severe
developmental hypoplasia (a normal
variant) of the A1 segment of the
ACA allowing for the visualization of only
the MCA territory
1 ICA –cervical segment
2 ICA –vertical petrous segment
3 ICA –horizontal petrous segment
4 presellar (Fischer C5) ICA
6 horizontal (Fischer C4) intracavernous
ICA
8 anterior genu (Fischer C3)
intracavernous ICA
9 ophthalmic artery
10 & 11 proximal and distal supraclinoid
segment ICA
13 anterior choroidal artery
31 M1 segment of MCA
32 lateral lenticulostriate arteries
33 bifurcation/trifurcation of MCA
35 orbitofrontal branch of MCA
39 parietal branch of MCA
40 angular artery
41 temporo-occipital branch of MCA
43 sylvian point
44 opercular branches of MCA
45 sylvian (insular) branches of MCA
* truncated lateral lenticulostriate arteries

25. A1 asymmetry associated with an aneurysm of the anterior
communicating artery complex , up to 80% of aneurysms in the
region of the anterior communicating artery are associated with
asymmetry of the A1 segments

26. -2D frontal view following right ICA
injection , there is an aneurysm in the
region of the ACOM
1 ICA –cervical segment
2 ICA –vertical petrous segment
3 ICA –horizontal petrous segment
4 presellar (Fischer C5) ICA
6 horizontal (Fischer C4)
intracavernous ICA
10 & 11 proximal and distal
supraclinoid
segment ICA
14 ICA bifurcation
15 A1 segment of ACA
18 A1-A2 junction ACA
19 anterior communicating artery
20 proximal A2 segment ACA
21 callosomarginal branch of ACA
22 orbitofrontal branch of ACA
28 pericallosal branch of ACA
32 lateral lenticulostriate arteries
33 bifurcation/trifurcation of MCA
34 anterior temporal lobe branches of
MCA
43 sylvian point
44 opercular branches of MCA
45 sylvian (insular) branches MCA

27. 5-Fenestration or triplication of the
ACOM :
-Other common variations include the
presence of two or more anterior
communicating arteries in 11% to 43% of
brains , this may take the form of a
fenestration of the anterior communicating
artery or complete duplication or
triplication

28. Single or duplicated ACOM forms a bridge between the
ACAs

29. Fenestration of the anterior communicating artery (arrow)

30. 6-Persistent olfactory artery :
-A rare variant of the proximal ACA
-It runs anteriorly from the internal carotid artery
bifurcation along the olfactory groove
-It may supply the territory of the anterior cerebral
artery distally
-Fenestrations of the distal A1 segment , an
anomaly that is embryologically difficult to
explain in this location , may represent an
incomplete fusion of the anterior cerebral artery
with the primitive olfactory artery

31. 7-Azygous ACA :
-An azygos ACA is an uncommon to rare variant
seen in approximately 0.4-1% of the population ,
in which the two A1 segments of the ACA join to
form a single A2 trunk , ACA territories supplied
by a single A2 trunk as a result no ACOM is
present
8-Absent ACOM :
-Absent ACOM and the two ACAs join together
directly

32. Azygous ACA

33. Azygous anterior cerebral artery variant , (a) LT ICA injection in a patient
with a LT MCA bifurcation aneurysm demonstrates prominent cross
flow to the right A1 segment , only one vessel (arrowheads) arises from
the midline to supply both hemisphere , note the bone subtraction
artifact from having the orbital rims superimposed on the M1 and A1
segments , (b) RT ICA injection in the same patient confirms the
azygous nature of the A2 segment , an internal frontal branch (double
arrow) arises from the right A1 segment proximal to the midline

34. Absent ACOM

35. 9-ACA trifurcation :
-Three A2 segments , incidence : 7.5 %
10-Bihemispheric ACA :
-Hypoplastic A2 segment with contralateral A2
segment dominance supplying both ACA
territories
-More commonly in situations of bihemispheric
supply , one anterior cerebral artery will be
dominant and a pericallosal branch of one
anterior cerebral artery will have bilateral supply
in its distal aspect

36. Bihemispheric anterior cerebral artery , LT ICA injection
opacifies a right hemispheric AVM , supply to the AVM is via a
right pericallosal branch of the left A2 artery

37. e) Branches :
1-A1 Section
2-A2 Section
3-A3 Section
4-A4 & A5 Sections

39. 1-A1 Section :Precommunicating Artery
a) Lenticulostriate Arteries
b) Recurrent Artery of Heubner
c) Anterior Communicating Artery

41. a) Lenticulostriate Arteries :
-The medial group of lenticulostriate arteries arise
from the proximal A1 section
-The majority are short central or diencephalic
arteries which arise from the superior surface
close to the origin of the ACA ad run into the
anterior perforating substance to supply the
anterior basal ganglion and anterior commissure
-Medial branches pass to the lamina terminalis to
supply the anterior aspect of the lateral wall of
the 3
rd
ventricle , the anterior hypothalamus and
septum pellucidum
-Inferiorly directed branches supply the optic nerve
and chiasm

43. b) Recurrent Artery of Heubner :
-This vessel represents a long central artery which
arises either proximal or distal to the origin of A2
section of the ACA (rarely from the ACOM) and
terminates by supplying part of the caudate
nucleus , the anterior portion of lentiform
nucleus and the neighbouring portion of the
internal capsule
-It usually runs parallel and above the A1 section
but may be long and prominent vessel (or a
duplicated trunk) and run more posteriorly in the
anterior perforating substance

44. Anterior circle of Willis showing lenticulostriate arteries arising from the anterior
cerebral arteries (M medial group) and middle cerebral artery (L lateral
group) , On the left , the anterior choroidal (AChA) and on the right the
recurrent artery of Heubner (RaH) , note that anterior perforating arteries
also arise from the anterior communicating artery

45. (a) Right internal carotid angiogram shows the recurrent artery of Heubner
arising from the A2 ( arrowed) , (b) Internal carotid DSA in the frontal
projections showing the anterior choroidal artery ( arrow on the left ) with
absent anterior cerebral artery

47. c) Anterior Communicating Artery :
-Arises from theACA and acts as an
anastomosis between the left and right
anterior cerebral circulation , it is about
4mm in length and demarcates the
junction between the A1 and A2 segments
of the ACA
-It is estimated than only 30-40 % of adults
have a single communicating artery and
two or more connections are present in the
majority

50. 2-A2 Section : Distal ACA
-The distal ACA is the pericallosal artery which
runs on the corpus callosum and can be divided
into A2 , A3 , etc
-In the case of the distal ACA , the next major
branch point is the origin of the calloso-marginal
artery
-A solution is to define the junction as the point at
which the course of the pericallosal artery turns
posterior over the genu of the corpus callosum
and so , the A3 is the section at the genu and
the A4 that over the body of the corpus callosum

51. -The main branches arise from this section are :
1-Orbitofrontal artery of the ACA :
-Runs forwards in the inferior inter-hemispheric
fissure & supplies the gyrus rectus , olfactory
bulb & the medial inferior frontal lobe
2-Frontopolar Artery :
-This artery arises at some point below the genu of
the corpus callosum to supply frontal cortex , it
may arise as more than one vessels

53. 1-Orbitofrontal
artery
2-Frontopolar
artery
3Callosomarginal
artery
4-Pericallosal
artery

54. 3-A3 Section :Distal to the origin of the
callosomarginal artery or the genu , if the
callosomarginal artery can’t be identified
-The callosomarginal artery classically arises at
the level of the genu of the corpus callosum and
runs parallel to the pericallosal artery in the
cingulate sulcus
-Its size is inversely related to the size of the
pericallosal artery and it is frequently larger

55. -It givesa group of four arterial branches :
1-Anterior internal frontal
2-Middle internal frontal
3-Posterior internal frontal
4-Paracentral artery

56. (1) Orbitofronal , (2) Frontopolar , (3) Anterior internal forntal , (4)
Middle internal frontal , (5) Posterior internal frontal , (6) paracentral
, (7) Superior parietal , (8) Inferior frontal , (9) Callosomarginal , (10)
Pericallosal

57. 4-A4 & A5 Sections :
-In its A4 (or A5) final section , the
pericallosal artery runs posteriorly over the
body of the corpus callosum in the cistern
of that name
-It terminates & anastomoses with the
posterior pericallosal artery that arises
from the PCA

58. -It gives :
1-Short callosal perforating arteries that piece the corpus
callosum and supply the pillars of the fornix & anterior
commissure
2-Long callosal arteries that run parallel to the main trunk
for a variable distance , supplying the adjacent cortex
and may participate in the anastomoses at the splenium
3-Parietal arteries :
-These are terminal cortical branches to the medial parietal
lobe
-They may be separable as a superior parietal artery and
an inferior parietal artery which arise posterior to the
callosomarginal artery and distribute to the cortex via
their respective sulci

59. -The ACOM provides collateral blood flow to
the contralateral hemisphere , the cortical
branches of the ACA border the MCA and
the ipsilateral PCA territories , the latter
can provide efficient collateral support in
cases of proximal carotid occlusion with an
ineffective or only partially effective ACOM
or in cases of occlusion of the ACA distal
to the ACOM

60. -Lateral view following CCA injection ,
non-filling of the MCA from
atherosclerotic occlusion allows
unobtrusive view of the ACA territory
4 presellar (Fischer C5) segment ICA
6 horizontal (Fischer C4)
intracavernous ICA
8 anterior genu (Fischer C3)
intracavernous ICA
9 ophthalmic artery
10 & 11 proximal and distal supraclinoid
segment ICA
12 PCOM
13 anterior choroidal artery
16 medial lenticulostriate arteries
21 callosomarginal branch ACA
22 orbitofrontal branch of ACA
23 frontopolar branch of ACA
24 anterior internal frontal branch of
ACA
25 middle internal frontal branch ACA
26 posterior internal frontal branch of
ACA
27 paracentral lobule artery branch of
ACA
28 pericallosal branch of ACA
29 superior internal parietal branch of
ACA
30 inferior internal parietal branch of
ACA