Interventional Neuroradiology: Anatomy of the internal carotid artery (ICA)

Interventional Neuroradiology
Anatomy
Internal Carotid Artery (ICA)
Mohamed M.A. Zaitoun, MD
Interventional Radiology Consultant, Zagazig University Hospitals, Egypt
FINR-Switzerland
zaitoun82@gmail.com
Interventional Radiology Unit,
Zagazig University, Egypt

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

Internal Carotid Artery (ICA)
a) Origin
b) Cervical Portion
c) Petrous Portion
d) Cavernous Portion
e) Intradural Portion

a) Origin :
-ICA originates in the neck as a terminal
branch of the common carotid artery
(CCA) at the level of the thyroid cartilage
(i.e. C3 or C4 vertebrae)
-It terminates intracranially at the inferior
surface of the brain by dividing into
anterior & middle cerebral arteries

-Lateral 2D view
following left common
carotid artery injection
, note the
atherosclerotic plaque
involving the proximal
internal carotid artery
1-Common carotid A.
2-Internal carotid A.
3-External carotid A.
5-Occipital artery
7-Superior thyroid A.
8-Lingual-facial artery
trunk

b) Cervical Portion :
-Extends from the bifurcation of the CCA to the
skull base
-In this section , the artery lies in the carotid sheath
with the internal jugular vein (IJV) laterally , the
vagus nerve & the cranial root of the accessory
nerve “XIth” (which travels with Xth) run
posteriorly & between these vessels
-The sheath , which is compromised of all three
layers of the deep cervical fascia , also contains
lymph nodes & postganglionic sympathetic fibers
which run with the artery into its petrous portion

-The internal diameter is about 4-5 mm
throughout , except at the carotid sinus
(carotid bulb) where the artery is 7.5 mm
wide for a distance of 15-25 mm
-The ICA normally (in 80 % of individuals)
lies initially behind & lateral to the ECA ,
but as this arteries run cranially , the ECA
inclines superficially to lie lateral to the ICA
on a frontal angiogram

-The wall of the carotid sinus contains
baroreceptors and the carotid body which
monitor systemic blood pressure and
blood oxygen , CO2 & PH levels
respectively
-These receptors are connected via nerve
fibers of Xth & XIth to the cardiovascular
center in the medulla oblongata and nerve
endings in the carotid sinus connected to
the inferior ganglion of the vagus

-The parasympathetic nervous system modulates
systemic blood pressure and endovascular
manipulation of the sinus may simulate its
physiological response to increases in pressure
by signalling to reduce heart rate and by
inhibiting the vasoconstrictor center of the
medulla oblongata causing peripheral
vasodilatation
-The carotid body tumor is a chemoreceptor that
monitors blood oxygen and CO2 levels and
stimulates respiration and heart rate in response
to detected hypoxia

1-Common Carotid Artery
2-Internal Carotid Artery
3-Ascending pharyngeal Artery
4-Occipital Artery
5-Superficial Temporal Artery
6-Middle cerebral Artery
7-Anterior cerebral Artery
8-Middle meningeal Artery
9-Maxillary Artery
10-Facial Artery
11-Lingual Artery
12-External Carotid Artery
13-Superior Thyroid Artery

-No named branches arise from the cervical
portion of the ICA
-The most common variant is that the
ascending pharyngeal artery arises from
the proximal internal carotid artery
-Other external carotid artery branches may
arise from the ICA & agenesis or
hypoplasia may occur

c) Petrous Portion :
-The petrous segment of the internal carotid
artery consists of a vertical and a horizontal
portion
-It enters the skull base at the exocranial
opening of the carotid canal , ascends
approximately 1 cm (vertical portion) and
then turns anteromedially until it enters the
intracranial space at the foramen lacerum
(horizontal portion)
-The laceral segment is a continuation of the
petrous segment ending at the petrolingual
ligament where it turns upwards into the
cavernous sinus

1=vertical portion of petrous ICA
2=horizontal portion of petrous
ICA
3=middle meningeal artery
4=tympanic cavity and ossicles of
the middle ear
5=otic capsule , 6=eustachian tube
7=geniculate ganglion
8=GSPN , 9=deep petrosal nerve
10=lesser petrosal nerve
11=mandibular nerve
12=maxillary nerve
13=ophthalmic nerve
14=trochlear nerve
15=oculomotor nerve
16=optic nerve
17=lateral rectus muscle
18=superior petrosal sinus

-Transition between the petrous and
cavernous segments of the internal
carotid artery (ICA) , the transition
occurs at the level of the
petrolingual ligament
1=horizontal segment of petrous ICA
2=petrolingual ligament
3=posterior vertical segment of
cavernous ICA
4=posterior bend of ICA
5=horizontal segment of cavernous ICA
6=anterior bend of cavernous ICA
7=clinoid ICA , 8=supraclinoid ICA
9=ophthalmic artery , 10=optic nerve
11=oculomotor nerve
12=trigeminal nerve
13=abducent nerve
14=ophthalmic nerve
15=maxillary nerve
16=mandibular nerve

-Branches :
Angiographically , branches of the petrous
internal carotid artery are uncommon but
at least three possible branches are worth
remembering :
1-Caroticotympanic Branch
2-Mandibulovidian Trunk
3-Variant Stapedial Artery

1-Caroticotympanic Branch :
-Arise from the horizontal segment and
gives the tympanic artery which supplies
the middle ear
-The importance of the caroticotympanic artery
lies in its potential supply to vascular tumors
of the middle ear

2-Mandibulovidian Trunk :
-Arises from the ICA in the foramen lacerum
-It gives the artery of the pterygoid canal (or vidian
artery) which supplies the sphenoid sinus and
anastomoses with the vidian artery arising from
the proximal portion of the internal maxillary
artery and the mandibular artery
-The mandibular artery take part in the
anastomoses around the eustachian tube

-This artery is usually too small to see but
may enlarge quickly in the setting of
occlusive disease
-It is rare to see this artery in adults , when
seen it is usually in children with a
vascular mass of the nasopharynx (for
example , juvenile angiofibroma)

3-Variant Stapedial Artery :
a) Incidence
b) Anatomy
c) Radiographic Findings

a) Incidence :
-PSA is a rare congenital vascular anomaly of the
middle ear
-Usually manifests as a pulsatile mass in the
middle ear cavity , an incidental finding during
middle ear surgery or pulsatile tinnitus
-Can be associated with an aberrant internal
carotid artery or other middle ear anomalies

b) Anatomy :
-The stapedial artery is transiently present in fetal
life and connects the branches of the future
external carotid artery to the internal carotid
artery
-The stapedial artery arises at 4-5 weeks of fetal
life from the hyoid artery which is a derivative of
the second branchial arch , near its origin from
the proximal internal carotid artery (third
branchial arch)

-The stapedial artery gives rise to two branches
after entering the cranial cavity :
1-The upper , or supraorbital branch becomes the
middle meningeal artery and also transiently
anastomoses with the ophthalmic artery
2-The lower , or maxillomandibular division has
two branches , a mandibular branch and an
infraorbital branch which persist in adult life as
inferior alveolar and infraorbital arteries
respectively
-Anastomosis forms between ventral pharyngeal
artery (precursor of external carotid artery) and
lower division of stapedial artery

-As the ventral pharyngeal artery supplies flow to middle
meningeal artery , stapedial artery regresses leaving
small caroticotympanic artery
-Persistence of the stapedial artery in postnatal life leads to
the middle meningeal artery typically arising from it , the
foramen spinosum remains hypoplastic or aplastic which
is an indirect sign of PSA
-Variant stapedial remnants giving rise to distal external
branches with significant input to the ophthalmic artery
are important to recognize before undertaking what
would be otherwise routine external carotid
embolizations (as embolizations of a tumor supplied by
the external carotid artery “ e.g. meningioma or
hemangiopericytoma ” can result in blindness)

A , The hyoid artery arises from the
ICA , the stapedial artery arises
from the hyoid artery near its
origin , the stapedial artery
branches into upper and lower
divisions after passing through the
stapes , the ventral pharyngeal
arteries are the precursors of the
definitive ECA , the stapedial
artery is the only supply to the
upper and lower divisions
B, Anastomosis forms between the
ventral pharyngeal artery and the
lower division branches
C, The stapedial artery decreases in
size
D, Normal adult anatomy with
involution of the stapedial artery
E, Anatomic configuration of typical
PSA

Axial HRCT image showing absence of foramen spinosum
on the left side compared to the normal right

-The PSA arises from the petrous part of the internal
carotid artery , enters the anteromedial hypotympanum
and is contained in the Jacobson canal
-After leaving the osseous canal , it crosses the cochlear
promontory and passes through the obturator foramen of
the stapes
-It then enters the fallopian canal through a dehiscence just
behind the cochleariform process and travels anteriorly
in the anterior facial canal
-This leads to prominence of the tympanic part of the facial
nerve , another indirect imaging sign of PSA
-Finally , the PSA exits just before the geniculate ganglion
entering into the extradural space of the middle cranial
fossa

-Axial Images (A-H) from superior to
inferior
-The small vascular channel can be
seen leaving the vertical carotid
at G (arrow) and can be followed
along the lower medial wall of the
middle ear (D-F) (arrows)
-Level C is at the plane of the
stapedial crura
-The vessel cannot be clearly
separated from the anterior crus
of the stapes
-After following the facial nerve canal
, the small vascular channel
reaches the middle cranial fossa
at level B (arrowhead)
-Level A represents the position of
the geniculate ganglion turn of
the facial nerve canal

-Coronal images (A–D) , from
posterior to anterior
-The narrow presumed vascular
structure is seen at B (arrowheads)
coursing along the promontory
-At level A , the small vascular
structure (arrows) crosses the oval
window niche to end in the lower
inferomedial aspect of the
tympanic segment of the facial
nerve canal
-This small channel is also seen at B
(arrow)
-More anteriorly (C and D) , the small
canal (arrows) courses just inferior
to the tympanic segment of the
facial nerve canal in a separate
channel as it passes toward the
floor of the middle cranial fossa
-The small soft-tissue structure
immediately inferior to this canal is
the tensor tympani muscle within
its semicanal

Axial and coronal CT showing the intracranial course of the stapedial
artery in the bony ridge to the promontary

Coronal image showing enlarged right facial nerve (yellow arrow)
compared to normal (blue arrow)

Sagittal image on the left side showing course of persistent stapedial
artery traversing through the canaliculus to enter the cranial cavity

c) Radiographic Findings :
-Small canaliculus originating from petrous
segment of ICA
-Linear soft tissue density crossing over
cochlear promontory
-Enlarged facial nerve canal or separate
canal parallel to facial nerve
-Aplastic or hypoplastic foramen spinosum

(a) Transverse CT of the left skull base shows absence of the foramen
spinosum posterolateral to the foramen ovale (arrow) ,
(b) Transverse CT of the right skull base shows the normal foramen
spinosum (arrowhead) posterolateral to the foramen ovale (arrow)

A, Axial CT scan of skull base shows a normal left foramen spinosum (straight arrow) ,
the right foramen spinosum is absent , the right ICA is laterally displaced into the
middle ear (curved arrow) , the left ICA is in a normal position
B, Coronal CT scan through right middle ear shows the ICA in the middle ear cavity
(straight arrow) , the soft tissue at the tympanic segment of the facial nerve is
prominent because of the presence of a stapedial artery (curved arrow)

A, Axial CT scan shows a normal right foramen spinosum (arrow) and
absence of the left foramen spinosum
B, Coronal CT scan shows the aberrant ICA on the left (straight arrow)
and the soft-tissue density of a PSA (curved arrow)

C, Left carotid arteriogram , lateral view shows a PSA arising from the
aberrant ICA (arrow)
D, Left carotid arteriogram , frontal view shows a PSA arising from the
aberrant ICA (arrow)

A, Axial CT scan shows a normal left foramen spinosum (arrow) and absence of the right
foramen spinosum
B, Axial CT scan through middle ear shows prominent soft tissue representing facial
nerve and PSA (arrow)
C, Coronal CT scan through middle ear shows prominent soft tissue representing facial
nerve and PSA (arrow)

A, Axial CT scan shows a normal left foramen spinosum (arrow) and absence of the right
foramen spinosum
B, Coronal CT scan through right middle ear shows the soft tissue at the tympanic
segment of the facial nerve is prominent because of the presence of a stapedial
artery (arrow)
C, Coronal CT scan through left middle ear shows the tympanic facial nerve is normal in
size (arrow)

Carotid arteriogram , lateral view shows a PSA (curved arrow) arising
from the aberrant ICA which represents the inferior tympanic branch
of the ascending pharyngeal artery assuming the role of the ICA
(straight arrow)

Lateral internal carotid angiogram shows the persistent stapedial artery
arises from the proximal internal carotid artery and ends as the
middle meningeal artery , the middle meningeal artery anastomoses
with the ophthalmic artery

AP internal carotid angiogram shows connection between the
persistent stapedial artery , middle meningeal artery and ophthalmic
artery is demonstrated , when the middle meningeal artery arises in
this manner , it does not enter the skull base in the usual fashion

Lateral internal carotid angiogram shows the persistent stapedial artery
arises from the proximal internal carotid artery and ends as the
middle meningeal artery

AP internal carotid angiogram shows the origin of the persistent stapedial artery
from the proximal intracranial internal carotid is again seen , the persistent
stapedial artery continues as the middle meningeal artery , the middle
meningeal artery lacks its characteristic curve as it does not enter the skull
base in the usual fashion

A, Axial CT scan shows a normal right foramen spinosum (arrow)
and absence of the left foramen spinosum
B, Coronal CT scan shows the aberrant ICA on the left (straight
arrow) and the soft-tissue density of a PSA (curved arrow)

C, Coronal CT scan through left middle ear shows the ICA in a normal position below the
cochlea (straight arrow) , the tympanic facial nerve is normal in size (curved arrow)
D, Coronal CT scan at level of vestibule shows the entrance of the aberrant ICA into the
right middle ear (arrow)

d) Cavernous Portion :
-Following its petrous passage , the ICA enters the
cavernous sinus and lies medial to the Gasserian
ganglion , the ophthalmic division of the trigeminal nerve
and the oculomotor , trochlear and abducens cranial
nerves
-It runs horizontally forwards and then turns superiorly and
medial to the anterior clinoid process , passes through
the dural ring and enters its final intradural and
supraclinoid course
-The branches that arise in this portion of the ICA are small
and difficult to identify individually on angiography but
nevertheless are as important to the endovascular
therapist as to pituitary surgeon

-Branches : 3 Groups
1-The Meningohypophyseal Trunk (MHT)
2-The Inferolateral Trunk (ILT)
3-The Capsular Arteries of McConnell

1-The Meningohypophyseal Trunk (MHT) :
-Also known as the posterior trunk
-The MHT and posterior inferior hypophyseal
artery (PIHA) form the remnant of the first
branchial arch artery and arise from the proximal
portion of the cavernous portion of the ICA
-These small branches may arise from a common
trunk or separately as three arteries :
a) Marginal tentorial artery & basal tentorial artery
b) Lateral clival artery
c) Posterior hypophyseal artery (PIHA)

**This figure shows :
-A: MHT , The classical main branches of the MHT
-B: Lateral Tentorial Artery along the lateral edge of the tentorium and in
hemodynamic balance with petrosquamosal branches (L) of the MMA and
Occipital Artery (O)
-C: Marginal Tentorial Artery
-D: Inferior Hypophyseal Artery, branching into :
-E: Hypophyseal branches supplying the posterior and parts of anterior pituitary
and anastomosing with each other
-F: Inferior Clival Branch descending along the dorsum sella where it is in
hemodynamic balance with the ascending clival braches (K) of the
Ascending Pharyngeal
-G: Lateral Clival artery branching into:
-H: Lateral Branch of the Lateral Clival artery which runs alongside the Superior
Petrosal Sinus
-I: Medial Branch of the Lateral Clival Artery which runs alongside the Inferior
Petrosal Sinus and is in balance with Jugular branches (J) of the Ascending
Pharyngeal
-The checkered vessel connecting MHT with the Basilar Artery (P) is the
Trigeminal Artery , which may come off the MHT or ILT
-Most MHT will not look anything like this. Variation is the rule and most of
these branches are too small to see in normal state anyway , important
anastomoses also include branches of the ILT (N) such as recurrent
marginal artery , the foramen lacerum branch of the Middle Meningeal
Artery (M) and Occipital Artery (O)

-2D frontal view following right CCA
injection , this view shows the normal
appearance of the intracranial ICA
circulation with filling of the ACA &
MCA branches
-There is filling of both sides from a
patent ACOM
-There is also a small clival branch of
the meningohypophyseal trunk
providing flow to the left ICA (4)
2 ICA – vertical petrous segment
3 ICA – horizontal petrous segment
4 presellar (Fischer C5) segment ICA
5 meningohypophyseal trunk
9 ophthalmic artery
10 & 11 proximal and distal
supraclinoid segment ICA
14 internal carotid artery bifurcation
15 A1 segment ACA
20 proximal A2 segment ACA
21 callosomarginal branch of ACA
28 pericallosal branch of ACA
31 M1 segment of MCA
32 lateral lenticulostriate arteries
33 bifurcation/trifurcation of MCA
35 orbitofrontal branch MCA
43 sylvian point
44 opercular branches of MCA
45 sylvian (insular) branches of MCA

-Meningohypophyseal Trunk Origin (white arrow )
and course (black arrows) of the
meningohypophyseal trunk

a) Marginal tentorial artery & basal tentorial
artery :
-These usually arise as a common trunk (called
the dorsal meningeal artery)
-The marginal (or medial) tentorial artery (named
as the artery of Bernasconi & Cassinari) follows
the free edge of the tentorium posteriorly and is
therefore medial to the basal branch
-The basal branch follows the tentorial attachment
to the petrous ridge and runs laterally to
anastomose with the posterior branch of the
middle meningeal artery

- A , B : Basal tentorial artery
-PA view and lateral views of the right internal carotid artery
in a patient with a symptomatic dural arteriovenous
malformation in the region of the right sigmoid and
transverse sinuses
-The basal tentorial artery (arrowheads) extends laterally
and horizontally along the petrous ridge , this could be
confirmed by looking at the course of the artery on a
nonsubtracted image
-C , D : Marginal tentorial artery
-PA and lateral views of the right internal carotid artery in a
different patient being studied for symptoms related to a
cavernous internal carotid artery aneurysm

-Tentorial branches of the internal
carotid artery
-In this patient , a large tentorial
meningioma is announced
early in the arterial phase on
this lateral view with a
hypervascular pattern
(arrowheads)
-Two tentorial arteries are running
posteriorly from the carotid to
the mass , the uppermost
vessel (double arrow) likely
being along the tentorial
incisura, thus representing the
marginal artery
-As is commonly the case , even
when this vessel is
pathologically enlarged , it
tends to be very tortuous and
difficult to catheterize

b) Lateral clival artery :
-The lateral clival artery supplies the dura of
the clivus
-Gives lateral and inferomedial branches
along the course of the superior and
inferior petrosal sinuses respectively

-Meningohypophyseal trunk
of the internal carotid
artery , a lateral
projection of the left
internal carotid artery in a
60-year-old female with a
large meningioma of the
tentorium and petrous
region , part of the
vascular supply to the
tumor derives from the
meningohypophyseal
trunk (MHT) , which
supplies the tumor via the
lateral clival branch

c) Posterior hypophyseal artery (PIHA) :
-PIHA supplies the posterior lobe of the pituitary and
anastomoses with the capsular arteries of McConnell as
well as its contralateral counterpart , these branches
cause a characteristic early neurohypophyseal blush on
carotid angiography
-It gives a medial clival branch which anastomoses with the
clival meningeal branches of the hypoglossal artery
(another ascending pharyngeal artery branch) , this
connection explains the occasional visualization of the
pituitary blush on ascending pharyngeal artery injections

Pituitary blush , lateral view of selective ICA injection shows a prominent but
normal posterior pituitary vascular blush (arrow)

2-The Inferolateral Trunk (ILT) :
-Was previously known as the inferior cavernous
sinus artery
-Arising laterally from the cavernous segment and
is directed inferiorly (thus inferolateral trunk)
-Crosses the VIth cranial nerve to divide into three
principal branches :
a) Superior Branch
b) Anterior Branch
c) Posterior Branch

**In this figure , Post-traumatic
pseudoaneurysm of the left
internal carotid artery , a young
adult underwent emergency
embolization of the left ECA
following a shotgun blast to the
face and neck
-The ECA distal to the origin of
the superior thyroidal artery
(s.thy.a.) is occluded , there is
enlargement of the ipsilateral
inferolateral trunk (i.l.t.) from
the cavernous internal carotid
artery which is participating in
collateral flow to the territory of
the occluded external carotid
artery
-On this follow-up angiogram 10
days after the initial
embolization , a developing
pseudoaneurysm of the
cervical internal carotid artery
is identified (arrow)

-Enlarged extracranial branches of the
cavernous ICA ,this teenager
presented with nasal stuffiness and
was found to have a hypervascular
mass arising from the
pterygomaxillary fissure with
prominent vascularity demonstrated
on the ipsilateral ECA injection (not
shown) , the ICA injection provided
here shows a prominent vessel from
the cavernous segment most likely
an inferolateral trunk (ilt) which
contributes substantially to the
posterior aspect of the tumor
(arrowhead) , the importance of this
finding is of some interest to the
operating surgeon for prediction of
bleeding
-However , it is very important for
planned embolization of the ECA as
well because a large connector to
the ICA can be the source of
retrograde embolization into the ICA
, if the embolic material is pushed
too hard in the ECA branches which
invariably interconnect within or
around the tumor with ILT branches
, this is termed intratumoral
anastomosis of feeding vessels and
is a common phenomenon in all
types of hypervascular lesions

-Lateral DSA after injection
of the CCA in a patient
treated for a giant
aneurysm with a high-
flow surgical bypass , the
proximal ECA was ligated
at surgery and collateral
branches of the
inferolateral trunk (*) fill
the internal maxillary
artery (arrowheads) via
the accessory meningeal
artery (white arrow) and
artery of the foramen
rotundum (small arrow)

a) Superior Branch :
-Returns medially towards the roof of the
cavernous sinus which it supplies together
with the IIIrd & IVth cranial nerves as they
lie in the wall of the sinus

b) Anterior Branch :
-Runs forwards in the cavernous sinus and supplies the
IIIrd , IVth & VIth cranial nerves
-Branches :
1-Brach which traverse the superior ophthalmic fissure to
anastomose with the deep recurrent ophthalmic artery
(i.e. the remnant of the embryonic dorsal ophthalmic
artery) , (this is an important consideration during
embolization)
2-Branch which traverse the foramen rotundum to
anastomose with the artery of the foramen rotundum (a
branch of the internal maxillary artery) , (this is the most
frequently seen branch on angiography , the artery of the
foramen rotundum consistently has a characteristic
tortuous and near horizontal appearance which allows
ready recognition on the lateral view)
3-A further branch to the foramen ovale which anastomose
with the accessory meningeal artery , which if the ILT is
small , may become the dominant vessel supplying the
territory

-Very rarely , the dorsal ophthalmic artery
may persist beyond embryonic life and
be the dominant arterial supply to the
orbit
-Persistent dorsal ophthalmic artery , a
persistent primitive dorsal ophthalmic
artery is present in this middle-aged
female who presented with headaches
related to a dural arteriovenous
malformation of the anterior cranial
fossa , the origin of this unusual vessel
from the horizontal cavernous internal
carotid artery corresponds with that of
the inferolateral trunk
-Most commonly , the dorsal ophthalmic
artery regresses to become an
anastomotic twig , the deep recurrent
ophthalmic artery , between the
ophthalmic artery and the inferolateral
trunk , dural arteriovenous
malformations of the anterior cranial
fossa in this location are typically
supplied by ethmoidal branches of the
ophthalmic arteries , because of a
propensity for subarachnoid or cortical
venous drainage, they are thought to
have a high risk of becoming
complicated early by subarachnoid
hemorrhage

- Enlarged artery of the foramen
rotundum , this patient has a
large facial arteriovenous
malformation , several years
previously an attempt at
treatment included ligation of
the ipsilateral branches of the
external carotid artery , this
stratagem did not work well for
the patient because it was
ineffective for eliminating the
AVM but blocked subsequent
endovascular access to the
AVM , the AVM is now deriving
prominent supply from the
ipsilateral internal carotid
artery via the inferolateral trunk
via the artery of the foramen
rotundum (arrowhead) and the
ophthalmic artery (oph)

c) Posterior Branch :
-Follows the VIth nerve posteriorly and supplies it as well
as the maxillary division of the trigeminal nerve and the
Gasserian ganglion
-It gives dural branches which anastomoses with the
marginal tentorial artery and with the middle meningeal
laterally in the middle cranial fossa
-The recurrent artery of the foramen lacerum usually arises
with the branches of the ILT but may arise as a branch of
MHT , it takes part in the anastomosis with the superior
pharyngeal branch of the ascending pharyngeal artery
around the foramen lacerum

A) ILT
B) Recurrent branch of the ILT courses along CN IV and collateralizes
with branches of the MHT , not rarely it annexes the territory of
marginal tentorial (G) or lateral tentorial (F) arteries which more
commonly come off the ILT
C) Anteromedial branch , a very important branch , this is a vestige of the
primitive dorsal ophthalmic artery which in very early embryonic life
supplied the orbit together with primitive ventral ophthalmic artery , this
artery is hemodynamic balance with the recurrent meningeal branch (N)
of the ophthalmic artery (M) , very rarely , when proximal ophthalmic
(M) is absent , this branch (C) can reconstitute the ophthalmic artery ,
although more commonly the middle meningeal artery fulfills this role
through its ophthalmic branch (K)
D) Artery to the foramen rotundum , another very important vessel
supplying the nerve of the same foramen , It collateralizes with foramen
rotundum branch of the IMAX (L) and is the primary route of ICA
reconstitution via the IMAX
E) Foramen ovale branch , yet another important branch which supplies
the appropriate foramen ovale nerve and collateralizes with the
accessory meningeal artery (J) and also with carotid branch of the
ascending pharyngeal artery (H) coming up through foramen ovale and
cavernous branch (I) of the middle meningeal artery
The checkered vessel anastomosing with the basilar artery (N) is the
trigeminal artery , which sometimes originates from the region of the ILT

3-The Capsular Arteries of McConnell :
-These are a series of small arteries providing a
systemic (rather than portal) supply to the
anterior lobe of the pituitary gland and the sella
dura
-They have been implicated in the formation of the
uncommon medially directed aneurysm of the
cavernous ICA
-If the ILT is absent , the MHT will supply most of
its territory and if a persistent trigeminal artery
occurs , its carotid connection is at the level of
the MHT

-Intrasellar aneurysm from the
cavernous internal carotid artery
-PA angiographic view (A) of a right
internal carotid artery injection in a
middle-aged female with multiple
aneurysms
-A medially directed aneurysm from
the cavernous internal carotid
artery is present (arrow) ,
aneurysms in this location are
thought to correspond with the
hypophyseal or capsular branches
, the intrasellar location was
confirmed on a coronal T1-
weighted, gadolinium enhanced
MRI study (B)
-Although this particular aneurysm
was asymptomatic, endovascular
treatment was recommended ,
intrasellar aneurysms that rupture
can leak into the subarachnoid
space causing significantly greater
morbidity than rupture of
cavernous aneurysms in other
positions

e) Intradural Portion :
-The supraclinoid portion of the ICA is intradural , the artery
having entered the subarachnoid space after crossing
the dural ring medial to the anterior clinoid process
-It turns posteriorly and runs lateral to the optic nerve to
terminate by dividing into anterior and middle cerebral
arteries
-From this portion originates successfully : the ophthalmic
artery , the superior hypophyseal artery , the PCOM and
the anterior choroidal arteries
-The level of the ophthalmic artery origin varies and some
authors describe a clinoid portion to the ICA between the
proximal and distal dural rings

Intracranial superior view of the right sellar and parasellar region , AC: anterior
clinoid process , ICA: internal carotid artery , LT: lamina terminalis , ON:
optic nerve , OlN: olfatory nerve , SW: sphenoid wing , TS: tubercullum
sellae

-Branches :
1-Ophthalmic Artery
2-Superior Hypophyseal Artery
3-Posterior Communicating Artery
4-Anterior Choroidal Artery

1-Ophthalmic Artery :
-Originates from the anterior surface , passes
forwards into the orbit through the optic canal
initially lateral and then above the optic nerve
-In the orbit , it runs medially along the upper
border of the medial rectus muscle and
terminates by dividing into the dorsonasal artery
(or dorsal artery of the nose) and supratrochlear
artery

-Branches :
a) Central Artery of the Retina
b) Lacrimal Artery
c) Anterior & Posterior Ethmoidal Arteries
d) Supratrochlear Artery
e) Dorsonasal Artery

The black arrow identifies the course of the ophthalmic artery as it passes
superior to the optic nerve , significant terminal branches are noted , the
PCOM and anterior choroidal arteries are also easily seen in this view ,
abbreviations: ICA , internal carotid artery ; AchA, anterior choroidal artery;
PCOM, posterior communicating artery; LA, lacrimal artery; CrA, central
retinal artery; PeA, posterior ethmoidal artery; AeA, anterior ethmoidal
artery

a) Central Artery of the Retina :
-May arise within the optic canal and
penetrates the dural sheath of the optic
nerve to supply the retina
b) Lacrimal Artery :
-Gives the recurrent meningeal artery and
distributes to the lacrimal gland , lateral
extraocular muscles and lateral eyelids

-Sphenoid wing meningioma , a
middle-aged female with a
symptomatic large left sphenoid
wing meningioma , on the PA view
(A) , there is marked mass effect
on the course of the middle
cerebral artery (small arrows) and
shift of the anterior cerebral artery
(long arrows)
-On the lateral view (B) , a
characteristic blush of the
meningioma is seen on the
internal carotid artery injection ,
the predominant supply to the
tumor is via the recurrent
meningeal branch of the
ophthalmic artery (men.br.)
reaching the tumor via the
superior orbital fissure

c) Anterior & Posterior Ethmoidal Arteries :
-Are potential collateral arteries between the ophthalmic
artery and the internal maxillary artery systems
-The anterior ethmoidal artery gives off anterior meningeal
branches (as the anterior artery of the falx) and supplies
the mucosa of the superior nasal septum
-The posterior ethmoidal artery supplies the posterior
ethmoid sinus and part of the posterosuperior aspect of
the nasal mucosa
-The proximity of the territories of these branches and
those of the internal maxillary artery (in particular , the
sphenopalatine artery and middle meningeal artery)
makes the study of the vascular anatomy of this region
so important

-Ethmoidal branches of the
ophthalmic artery , unusually
prominent ethmoidal
branches (eth.br.) of the
ophthalmic artery are seen
on this right internal carotid
artery injection , these
vessels have large
anastomoses along the nasal
septum with the long
sphenopalatine arteries ,
therefore , a route of potential
hazard to the ophthalmic
artery exists through these
vessels during embolization
of the internal maxillary artery
and its branches

d) Supratrochlear Artery :
-Runs forwards to the supraorbital notch and
is distributed as the supraorbital artery to
the skin of the forehead
e) Dorsonasal Artery :
-Terminal branch of the ophthalmic artery

A) Main Ophthalmic Artery
B) Lacrimal branch (actually many small branches by the
time it gets to the lacrimal gland) which will
collateralize with IMAX anterior deep temporal
branches (K) through transosseous (M) or muscular
(L) routes , this is a very common pathway of
ophthalmic / ICA reconstitution via the IMAX
C) Medial division which gives off important anterior (G) and
posterior (H) ethmoidal arteries , these enter the anterior
cranial fossa through respective foramina and supply
regions of the cribriform plate and anterior falx , the
anterior falcine artery can be particularly prominent
especially after pterional craniotomies or other
destructive processes of the middle meningeal artery ,
the ethmoid arteries also send branches into the nasal
cavity
D) Central retinal artery: a true end-artery with NO collaterals ,
occlusion results in irreversible permanent loss of vision
, aside from the central retinal artery , the other
ophthalmic branches supply muscle and other orbital
tissue.
E) Recurrent tentorial branch , an important collateral pathway
connecting orbit to middle cranial fossa , collateralizing
with anteromedial branch (I) of the ILT , both (E) and (I)
are vestiges of the primitive dorsal ophthalmic artery
F) Recurrent meningeal branch : important branch from the
lateral (lacrimal) division which can collateralize with
ophthalmic branch (J) of the middle meningeal artery
and is a potential MMA to ophthalmic connection, often
visualized in setting of main ophthalmic or ICA
occlusions , this artery tends to exit the orbit through its
own foramen which when large enough carries a name
of Foramen of Hyrtl
F1) Anterior Frontal Meningeal Branch : vascularises
dura of the frontal convexity , can be prominent in
setting of meningiomas, etc.
N) Inferior branches supplying muscle and other tissue ,
which can collateralize with distal inferior orbital
branch (O) of the IMAX exiting through the
infraorbital foramen and angular branch (P) of the
facial artery

2-Superior Hypophyseal Artery :
-Infrequently identified on angiograms since
it is small and may arise as a single
branch or as several small branches
-It supplies the pituitary gland and part of the
optic chiasm and intracranial optic nerve

3-Posterior Communicating Artery : (PCOM)
-Is an anastomotic artery with the vertebrobasilar
network and part of the circle of Willis
-It joins the posterior cerebral artery (PCA)
between the P1 and P2 segments of that artery
-It runs posteromedially above the oculomotor
nerve to reach the PCA
-It gives small perforators arteries from its superior
surface that supply the pituitary stalk , optic tract
, chiasm and the floor of the third ventricle

1, optic nerve
2, internal carotid artery
3, PComA
4, AChA
5, uncal artery
6, oculomotor nerve
7, posterior cerebral artery
8, tip of the basilar artery
9, mesencephalon
10, aqueduct of Sylvius
11, cerebellum
12, uncus of the temporal lobe
13, choroidal fissure

Lateral projection of a left common carotid artery injection that displays
the order of branching in the intracranial carotid including 1:
ophthalmic , 2: posterior communicating , 3: anterior choroidal and
4: anterior cerebral arteries

Black Key
1 internal carotid artery , cervical segment
2 internal carotid artery , vertical petrous
segment
3 internal carotid artery , horizontal
petrous segment
4 presellar segment (C5) ICA
6 horizontal (C4) intracavernous ICA
7 inferolateral trunk
8 anterior genu (C3) intracavernous ICA
9 ophthalmic artery
10 supraclinoid (C2) segment ICA
11 supraclinoid (C1) segment ICA
12 PCOM
13 anterior choroidal artery
15 A1 segment of ACA
21 callosomarginal
22 orbitofrontal branch of ACA
23 frontopolar branch of ACA
24 anterior internal frontal branch of ACA
25 middle internal frontal branch of 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

Red Key
1 vertebral artery
2 PICA
3 basilar artery
4 AICA
5 SCA
6.1 P1 segment of PCA
6.2 P2 segment of PCA
8 posterior temporal branch of PCA
9 parieto-occipital branch of PCA
10 calcarine branch of PCA
11 anterior thalamoperforators
12 posterior thalamoperforators
13m medial posterior choroidal artery
13L lateral posterior choroidal artery
14 vertebral-basilar junction
15 posterior pericallosal artery (splenial
artery)
16 pontine perforator
17 anterior spinal artery
AT anterior temporal branches of PCA
MT mid-temporal branches of PCA

BLACK KEY
10 supraclinoid (C2) segment internal carotid
11 supraclinoid (C1) segment internal carotid
12 posterior communicating artery
15 A1 segment of anterior cerebral artery
18 A1-A2 junction anterior cerebral artery
19 anterior communicating artery
31 M1 segment of middle cerebral artery
33 bifurcation/trifurcation of middle cerebral
34 anterior temporal lobe branches of middle cerebral
35 orbitofrontal branch of middle cerebral
44 opercular branches of middle cerebral
45 sylvian (insular) branches of middle
RED KEY
1 vertebral artery
2 posterior inferior cerebellar artery
3 basilar artery
4 anterior inferior cerebellar artery
5 superior cerebellar artery
6.1 P1 segment of posterior cerebral artery
8 posterior temporal branch of posterior cerebral artery
9 parieto-occipital branch of posterior
cerebral artery
10 calcarine branch of posterior cerebral artery
11 anterior thalamoperforators
12 posterior thalamoperforators
13L lateral posterior choroidal arteries
MT mid-temporal branches of posterior cerebral artery

-Lateral view of the posterior (vertebralbasilar)
Circulation
BLACK KEY
1 vertebral artery
2 posterior inferior cerebellar artery
3 basilar artery
4 anterior inferior cerebellar artery
5h hemispheric branch of superior cerebellar
8 posterior temporal branch of posterior cerebral artery
9 parieto-occipital branch of posterior cerebral
10 calcarine branch of posterior cerebral
13m medial posterior choroidal artery
13L lateral posterior choroidal artery
15 posterior pericallosal artery(splenial artery)
RED KEY
10 supraclinoid (C2) segment internal carotid artery
12 posterior communicating artery
45 sylvian(insular) branches of middle cerebral artery

-The Anterior Group of Thalamoperforator
Arteries :
*Seven to ten in number , arise from the
superolateral aspect of the PCOM , a
prominently visible artery from among this
number directed to the base of the brain
between the optic chiasm and the mamillary
bodies is sometimes referred to as the
premamillary artery or the thalamotuberal artery
*The anterior group of thalamoperforator arteries
supplies the thalamic nuclei , posterior aspect of
the optic chiasm , proximal part of the optic
radiations , posterior hypothalamus and part of
the cerebral peduncle

PCOM (asterisk) is in its normal configuration joining to the PCA , P1 is the segment
before the PComA and P2 is the segment after the PComA , note the premamillary
artery (arrow head) , (CP: cerebral peduncle , OcM: oculomotor nerve , ON: optic
nerve , ICA: internal carotid artery)

4-Anterior Choroidal Artery : (AchA)
a) Origin
b) Course
c) Branches

a) Origin :
-The anterior choroidal artery arises from the
posterior wall of the internal carotid artery as the
most consistently identifiable branch between
the posterior communicating artery and the
internal carotid bifurcation , it arises most
commonly 2 to 4 mm distal to the origin of the
posterior communicating artery , It measures
1mm in diameter

(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

(A) Pericallosal Artery•, (B) ACA , (C) MCA , (D) Anterior Choroidal Artery ,
(E) Ophthalmic Artery , (F) ICA , (G) PCA

-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
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

-Top down view (superior to inferior) of
the skull base
BLACK KEY
6 horizontal (C4) intracavernous ICA
7 inferolateral trunk
9 ophthalmic artery
12 PCOM
14 ICA bifurcation
15 A1 segment of ACA
19 ACOM
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
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
16 pontine perforators

b) Course :
-The course can be divided into two segments , the
cisternal and the intraventricular
1-Cisternal segment :
-The length of the cisternal segment ranges from 15 to 35
mm (mean 26 mm)
-In this segment , it has a complex relationship to the optic
tract , which changes along its course , at its origin , it is
located lateral to the optic tract , then it curves medially
to the inferomedial surface , to curve again laterally
running along the lateral aspect of the optic tract to reach
the lateral geniculate body

The right AChA arises as a single trunk from the ICA and then crosses
the optic tract (OT) from lateral to medial direction , it courses along
the OT to reach the crural cistern and it then enters choroidal fissure
, note the branch arising from the AChA (uncohippocampal artery)
(arrow)

Axial cut through the midbrain , the AChA (4)
originates from the internal carotid artery
(2) , runs toward the medial aspect of the
uncus (12) and then curves laterally
along the medial aspect of the temporal
lobe through the ambient cistern to the
choroidal fissure (13) , the uncal artery
on the left has a common origin with the
AChA
1, optic nerve
2, internal carotid artery
3, PComA
4, AChA
5, uncal artery
6, oculomotor nerve
7, posterior cerebral artery
8, tip of the basilar artery
9, mesencephalon
10, aqueduct of Sylvius
11, cerebellum
12, uncus of the temporal lobe
13, choroidal fissure

2-Intraventricular segment :
-It then passes through the choroidal fissure to
reach the choroid plexus of the temporal horn ,
the terms plexal point or ventral choroidal point
have been proposed to describe the point of
entry of the AChA into the lateral ventricle at the
choroidal fissure
-It passes over the medial surface of the temporal
horn , curving around the atrium to the floor of
the body of the lateral ventricle , within the
collateral trigone the anterior choroidal artery
anastomoses with the posterior choroid artery

Red=A. Choroidal ; Purple=plexal point ; Yellow=choroidal
segment

c) Branches :
-It gives a series of perforator arteries which
supply the posterior limb of the internal capsule ,
in particular , its inferior level and part of the
retrolenticular segment
-It gives small branches to the optic radiation , the
lateral geniculate body , the angle of the
hippocampus and the amygdala as well as part
of the globus pallidum and thalamus

Interventional Neuroradiology: Anatomy of the internal carotid artery (ICA)

Interventional Neuroradiology: Anatomy of the internal carotid artery (ICA)

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