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Intracranial Vascular Anatomy
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ppf
splICA
Fig. 31.2 Schematic representation of the transpterygoidal route to the supralacerum internal carotid artery and cavernous
paraclival internal carotid artery after radical ethmoidectomy and wide sphenoidotomy with opening of the pterygopalatine fossa.
cpcICA, cavernous paraclival internal carotid artery; cpsICA, cavernous parasellar internal carotid artery; ppf, pterygopalatine fossa;
splICA, supralacerum internal carotid artery; VC, vidian (pterygoid) canal.
PG
VC
ON
ppf
cpsICA
splICA
ACP
IIIcn
VIcn
V1
PG
cpsICA
cpcICA
IIIcn
VIcn
cpsICA
cpcICA
splICA
V1
V2
C
Fig. 31.3 Relationship between the vidian artery and anterior genu of the internal carotid artery. The vidian artery and nerve arising
from the lateral aspect of the anterior genu run through the vidian (pterygoid) canal to reach the pterygopalatine fossa where the
artery anastomoses with the same-named branch of the maxillary artery. ACP, anterior clinoid process; C, clivus; cpcICA, cavernous
paraclival internal carotid artery; cpsICA, cavernous parasellar internal carotid artery; IIIcn, oculomotor nerve; ON, optic nerve; PG,
pituitary gland; splICA, supralacerum internal carotid artery; VA, vidian artery; VC, vidian (pterygoid) canal; V1, ophthalmic branch of
trigeminal nerve; V2, maxillary branch of trigeminal nerve; VIcn, abducens nerve.
cpcICA
splICA
VA
31.1.3 Cavernous segment
Above the petrolingual ligament, the ICA can be
considered intracavernous. The petrolingual ligament
connects the petrous apex and the lingula of the sphenoid.
It can be considered the border between the horizontal
and cavernous portions of the ICA. From an endoscopic
anterior viewpoint, we can define two cavernous
segments: (1) paraclival segment and (2) parasellar
segment, both evident especially in well-pneumatized
sphenoid sinuses.
VC
V2
C
spIICA
VC
VA
Cavernous Paraclival Segment
Cavernous Paraclival Segment of ICA
via the Transpterygoidal Corridor
A wide bilateral sphenoidotomy allows good exposure
of the intrasphenoid landmarks (sellar floor, optic nerve,
medial and lateral opticocarotid recess, cavernous paraclival and parasellar ICA, vidian crest, V2, clivus) that
appear differently depending on whether the pneumatization of the sinus is presellar, sellar, or conchal type.
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Exposure of the posterior wall of the maxillary sinus
with section of the sphenopalatine, the descending palatine and palatovaginal arteries, allows dissection of the
medial portion of the pterygoid and identification of the
vidian foramen; thus, safety surgical landmarks can be
maintained. Drilling of the sphenoidal floor is then performed, identifying the middle pterygoid lamina, which
is also an essential landmark. In fact, if this lamina is
drilled perpendicularly to the clivus, it is possible to reach
the ICA at its anterior genu, where its petrous tract becomes vertical. Once identified, the paraclival ICA can be
skeletonized by thinning down and removing its overlying bone (Fig. 31.2).
The cavernous paraclival segment (posterior vertical
segment) of the ICA, endoscopically speaking, represents
the lateral border of the transclival corridor. This segment
runs upward, at a variable distance from the posterior clinoid process, and bends forward forming the posterior
bend of the cavernous segment of the ICA (ICAc). It must
be underlined that the configuration of the posterior
bend varies significantly and that sometimes it can bulge
upward into and deform the dura of the cavernous sinus
(CS) roof just lateral to the posterior clinoid process. The
meningohypophyseal trunk (MHT) is usually visible at the
posterior vertical segment of the ICA and usually arises at
the medial aspect of this. The branches of the MHT are the
inferior hypophyseal artery (IHA) for the pituitary gland,
the dorsal meningeal artery for the dura of the posterior
cranial fossa (PCF), and the Bernasconi–Cassinari artery
for the tentorium (Fig. 31.4).
Anatomy
Although there is a short paraclival-located supralacerum
portion, delimited inferiorly by the petrolingual ligament
and superiorly by the maxillary nerve (V2), which is extracavernous, we will consider for convenience the whole
paraclival segment as intracavernous.
The paraclival segment corresponds to the posterior
vertical segment of the ICAc, extending from the anterior
genu over the FL to the posterior bend of the parasellar
segment at the level of the posterior clinoid process. The
paraclival segment of the ICA presents constantly as a
branch, the MHT which typically arises from the posterior bend of the ICA. Two types of the vessel are described:
complete and incomplete. In the complete version, there
are three branches: the tentorial artery (also called the
Bernasconi–Cassinari artery), the dorsal meningeal artery (also called the dorsal clival artery),7 and the IHA
(Fig. 31.4).
more of these three vessels arising directly from the ICAc.
More often, it is the dorsal meningeal artery. Rarely, all
three vessels arise directly from the ICA. The IHA travels
superior and medially toward the pituitary gland and primarily to its posterior lobe. In some cases, the vessel supplies the anterior lobe, mainly on its periphery.
sel, when approaching the pituitary gland, bifurcates and
sometimes trifurcates.
arteries anastomose with one another on both sides, thus
forming a circulus arteriosus around the root of the dorsum sellae. The dorsal meningeal artery, or dorsal clival
artery, passes posterior toward Dorello’s canal and supplies the dura of the upper clivus and the proximal aspect
of the abducens nerve (Fig. 31.5). During its travelling, it
contributes, with the Bernasconi–Cassinari artery (which
supplies the tentorium), to the blood supply of the proximal part of the cranial nerves inside the CS.
8
The incomplete type demonstrates one or
6
The ves-
9
The IHA and the dorsal meningeal
326
DC
SPS
IHA
IPS
VIcn
spIICA
BCA
MHT
cpcICA
DMA
ACP
cpsICA
PG
SPS
BCA
IHA MHT
C
Fig. 31.4 The meningohypophyseal trunk arises from the posterior bend of the cavernous paraclival internal carotid artery (cpcICA).
The Dorello’s canal with the sixth cranial nerve passing through it (black arrow) can been seen medially after lateralization of the
cpcICA. ACP, anterior clinoid process; BCA, Bernasconi–Cassinari artery; C, clivus; cpsICA, cavernous parasellar internal carotid artery;
CS, cavernous sinus; DC, Dorello’s canal; DMA, dorsal meningeal artery, IHA, inferior hypophyseal artery; IIIcn, oculomotor nerve;
IPS, inferior petrosal sinus; MHT, meningohypophyseal trunk; PG, pituitary gland; splICA, supralacerum internal carotid artery; SPS,
superior petrosal sinus; VA, vidian artery; V2, maxillary branch of trigeminal nerve; VIcn, abducens nerve.
DMA
spIICA
cpcICA
VA
IIIcn
CS
VIcn
C
V2
SPS
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BCA
IPS
GL
VIcn
DC
DMA
cpcICA
Fig. 31.5 Endoscopic view of Dorello’s canal and sixth cranial
nerve. The internal carotid artery has been placed medially
and the endoscope has passed through the cavernous sinus.
BCA, Bernasconi–Cassinari artery; cpcICA, cavernous paraclival
internal carotid artery; DC, Dorello’s canal; DMA, dorsal
meningeal artery, GL, Gruber’s ligament; IPS, inferior petrosal
sinus; SPS, superior petrosal sinus; VIcn, abducens nerve.
Cavernous Parasellar Segment
Cavernous Parasellar Segment of ICA
via the Transpterygoidal Corridor
Removal of the anterior sphenoidal wall and drilling of the
sphenoidal floor and pterygoid allow exposure of the lateral recess of the sphenoid sinus (medial wall of the CS).
Complete exposure of the medial portion of the CS requires removal of the bony wall that covers the ICAc and
thereafter the lateral wall of the sphenoid as far as the
orbital apex. In very pneumatized sphenoid sinuses, removal may involve the medial portion of the great wing
of the sphenoid. To extend the access to the lateral portion of the CS and to the floor of the middle cranial fossa,
the removal of the medial portion of the posterior wall
of the maxillary sinus and lateralization of the contents
of the pterygoid-maxillary fossa are necessary to expose
the vidian canal (with cauterization of the vidian artery),
as well as the foramen rotundum (with the V2). At this
point in the dissection, drilling the pterygoid and sphenoid bases enables the view to be extended to the lateral
portion of the CS and to the floor of the middle cranial
fossa (Fig. 31.6).
A very close relationship between the cavernous
parasellar portion of the ICA and the pituitary gland is
present, and it is quite variable even in the absence of
pathology. Endoscopically, it is not easy to differentiate
the medial cavernous wall from the pituitary capsule, as
contrariwise reported in microscopic dissection.
the body of the pituitary gland, it is possible to see the
terminal ramification of the IHA of both sides.
The inferolateral trunk (ILT) is slightly more distal to the
MHT and nearly always passes above the abducens nerve
(VI cn), ending more or less in the Meckel’s cave area
10
Below
Intracranial Vascular Anatomy
(Fig. 31.7). Endoscopically, different fibrous–dural septations can be observed within the CS, thus apparently
creating a common space with different venous lacunae,
in which the terminal branches of the ILT run with variable shapes. While the ILT is easy to see, the McConnell’s
capsular artery, when present, is somewhat difficult to
identify. On the roof of the CS, the close relationship with
the optic nerve is very evident. The ophthalmic artery
usually arises at the supraclinoid portion of the ICA above
the dural roof of the CS, but in less than 10% of the cases,
it can originate from the cavernous parasellar portion.
Anatomy
The parasellar segment forms the shape of a C with medial concavity. Following the posterior bend of the ICAc,
the artery usually runs horizontally for a short distance
(horizontal segment) and curves upward, thus giving the
anterior bend that reaches the lower and upper dural
rings at the level of the anterior clinoid process (clinoid,
infraclinoid, or paraclinoid segment) and then turns to the
anterior vertical segment (cisternal or supraclinoid segment). Looking through a transsphenoidal corridor, the
parasellar ICA is positioned on the side of the pituitary
gland, thus producing the parasellar ICA prominence on
the sphenoid sinus wall. This prominence corresponds,
more or less, to the distal part of the horizontal segment,
the anterior bend, and the clinoid segment.
The parasellar segment of the ICA presents different
branches, the most constant being the ILT (also called the
artery of the inferior CS). The ILT arises from the central
one-third of the inferior or lateral surface of the horizontal segment of the ICAc, distal to the origin of the MHT
(3–13 mm; Fig. 31.7).
ducens nerve and then divides into two branches.
superior one curves posteriorly along the trochlear nerve
and the edge of the tentorium to supply the proximal portion of cranial nerves III, IV, and V1. The second branch is
the artery of the superior orbital fissure (SOF), which runs
under the first two trigeminal branches and provides
vascularization for the foramen ovale and rotundum. The
SOF artery is critical for the blood supply of the distal
portion of cranial nerves III, IV, ophthalmic (V1), and VI.
Other branches are the McConnell’s capsular artery, the
persistent trigeminal artery (PTA), the ophthalmic artery, the
superior hypophyseal artery (arteries) (SHAs), the recurrent
artery of the FL, and the artery of the Gasserian ganglion.
In more details:
• The McConnell’s capsular artery is not always present
(30–50% of the cases).
most superior segment of the parasellar ICAc. In less
than 10% of cases, it arises from the medial aspect of the
horizontal segment of the parasellar ICAc. When pres-
ent, it supplies the inferior and peripheral aspect of the
anterior lobe of the pituitary gland and the diaphragma
6
sellae.
McConnell’s arteries may give branches that penetrate the sella turcica to enter the sphenoid sinus via
the craniopharyngeal canal (when present).
• The PTA, when present, arises from the central middle
d of the posterior bend of the ICAc. Its incidence is
thir
described as between 0.06 and 0.6%.
half of the cases, the PTA penetrates the sella turcica
near the clivus to join the basilar artery (BA). In the
remaining cases, the artery travels lateral to the sella turcica.
16
There are two types of PTA, according to
the relationship to the abducens nerve: a lateral or
11
Usually, it crosses over the ab-
13
The vessel may come from the
14,15
In more than
12
The
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S
cpsICA
cpcICA
spIICA
cpsICA
Fig. 31.6 Schematic representation of the transpterygoidal route to the cavernous parasellar segment of the internal carotid artery
and to the cavernous sinus after radical ethmoidectomy and wide sphenoidotomy with opening of the pterygopalatine fossa. cpcICA,
cavernous paraclival internal carotid artery; cpsICA, cavernous parasellar segment of the internal carotid artery; splICA, supralacerum
internal carotid artery.
VIcn
cpsICA
Fig. 31.7 Endoscopic view of the inferolateral trunk in the
cavernous sinus. The cavernous sinus has been opened and the
cavernous parasellar internal carotid artery has been placed
medially to highlight the sixth cranial nerve and the inferolateral
trunk passing above it. cpcICA, cavernous paraclival internal
carotid artery; cpsICA, cavernous parasellar internal carotid
artery; CS, cavernous sinus; ILT, inferolateral trunk; V2,
maxillary branch of trigeminal nerve; VIcn, abducens nerve.
ILT
CS
V2
cpcICA
cpsICA
OA
VIcn
cpcICA
Fig. 31.8 Endoscopic view of the cavernous sinus. A rare
variation is evident: the ophthalmic artery arises from the
anterior bend of the cavernous parasellar internal carotid
artery and passes through the superior orbital fi ssure together
with the abducens nerve (VIcn). cpcICA, cavernous paraclival
internal carotid artery; cpsICA, cavernous parasellar internal
carotid artery; OA, ophthalmic artery.
petrosal and a medial or sphenoidal. If the artery arises from the posterolateral aspect of the ICAc, it runs
lateral to the abducens nerve intradurally and inferior
to it within the CS and thus displaces the nerve superiorly. When the PTA arises from the posteromedial
aspect of the ICAc, it pierces the dura over the dorsum
sellae and courses medial to the abducens nerve.
• The ophthalmic artery can arise from the cavernous
portion in 1 to 7.5% of cases.
328
18–20
When coming from
the parasellar segment, it arises from the anterior bend
(Fig. 31.8).
• In rare cases, the SHAs originate from the parasellar
segment of the ICA (more commonly from the paraclinoid segment). These are perforating branches for
17
the superior aspect of the pituitary gland. It is also
possible to observe several branches, some arising in
the intracavernous segment and others coming from
the cisternal one.
Intracranial Vascular Anatomy
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• The recurrent artery of the FL seems to supply the
pericarotid autonomic nervous plexus.
anastomosis with the ascending pharyngeal artery. It
can be considered a periosteal branch.
• The branches of the artery of the Gasserian ganglion
cross the abducens nerve within the CS as they travel
laterally.
21
It forms an
31.1.4 Supracavernous Segment
Above the inferior (also known as lower or proximal or
Perneczky’s) dural ring, the ICA can be considered to be
supracavernous. The dura lining the inferior aspect of the
anterior clinoid process forms the lower dural ring, which
can be considered the border between the intracavernous
and supracavernous portions of the ICA.22 From an endoscopic anterior viewpoint, we can define two segments
of the supracavernous ICA: (1) clinoidal segment and (2)
cisternal segment.
Clinoidal Segment
Supracavernous Clinoidal Segment of
ICA via the Transpterygoidal Corridor
The dura lining the upper and lower surface of the ACP
extends medially to form the upper (also known as superior or distal) and lower dural rings that border the
clinoidal segment of the ICA (Fig. 31.9). Note that the
clinoid segment of the ICA is against the optic strut. The
lateral opticocarotid recess (lOCR) corresponds to the
pneumatization of the optic strut.
inferior border of the lOCR identify the position of the
upper and lower dural rings.
by the extension of the dura just beneath the anterior
clinoid process. This dura forms the caroticoclinoid lig-
ament, lying between the anterior and middle clinoid
process. This ligament fixes the vessel to the carotid sulcus. So, the middle clinoid process can be considered as
marking the inferior border of the paraclinoid segment
on its medial wall. As a whole, the medial and anteroinferior venous compartments of the CS are separated
from the paraclinoid compartment. Just underneath the
proximal dural ring, III, IV, and V1 can be found running toward the SOF. The lower dural ring is often incomplete on the medial side and often a venous channel
can follow the paraclinoidal ICA to the superior dural
ring which is given by the extension of the dura covering the superior surface of the anterior clinoid process.
This ring is not closely attached to the ICA, and a small
cuff of arachnoid can surround the artery.
the upper dural ring joins the lower dural ring to form
the apex of the clinoidal triangle of the roof of the CS.
The dura of the upper ring leaves a small posteromedial
space called the carotid cave, and not rarely the SHA may
arise in this space.
22
The superior and
23
The roof of the CS is given
13
Posteriorly
24
Cisternal Segment
Supraclinoid Segment of the ICA via
(a) Transtuberculum–Transplanum
Suprasellar Corridor
The opening of the ethmoido-sphenoidal planum allows
access to the anterior skull base and the suprasellar cistern without passing through the sella turcica (Fig. 31.10).
In this case, the transsphenoid access is accompanied by
selective opening of the posterior ethmoid to reveal the
posterior ethmoidal arteries, which are considered the
anterior margins of this approach, to avoid damaging the
olfactory neuroepithelium. This is followed by the bony
removal between the lOCR, which corresponds to the tuberculum sellae area on the intracranial side. Opening of the
dura mater here enables control over the optic chiasm and,
thereafter, the pituitary stalk and the gland.
A rich arterial network coming from the internal carotid arteries is present all around the pituitary stalk. This
network is given by the SHAs, which usually arise from
the supraclinoid portion of the ICA (Fig. 31.11). Rarely,
these vessels can arise from the cavernous portion of the
ICA. Sometimes it is possible to see a “crown” of arteries
ON
OA
uDR
sccICA
Fig. 31.9 The sellar and suprasellar region. The clinoidal
segment of the internal carotid artery extends between the
upper and lower dural rings. The dural rings are formatted,
respectively, by the dura that lays on the superior and inferior
surface of the anterior clinoid process. A1, fi rst segment of
anterior cerebral artery; iDR, inferior dural ring; OA, ophthalmic
artery; OC, optic chiasma; ON, optic nerve; PG, pituitary gland;
PS, pituitary stalk; scciICA, supracavernous cisternal internal
carotid artery; sccICA, supracavernous clinoidal internal carotid
artery; SHA, superior hypophyseal artery; uDR, upper dural ring.
ON
iDR
cpcICA
A1
OC
SHA
PS
PG
OA
scciICA
uDR
sccICA
iDR
cpcICA
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Intracranial Vascular Anatomy
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fs
scICA
cpsICA
SS
it
scICA
Fig. 31.10 Schematic representation of the transtuberculum–transplanum suprasellar corridor to the supraclinoid segment of the
internal carotid artery after posterior ethmoidectomy and wide sphenoidotomy. Passing below the optic chiasma through a transplanum
supraretrosellar corridor is possible to reach also the basilar artery. cl, clivus; cpsICA, cavernous paraclival internal carotid artery; cpsICA,
cavernous parasellar internal carotid artery; fs, frontal sinus; it, inferior turbinate; scICA, supraclinoid segment of the internal carotid artery;
splICA, supralacerum internal carotid artery; SS, sphenoid sinus.
cpcICA
spIICA
cI
around the superior aspect of the pituitary stalk, from
which coaxial vessels run downward to reach the body of
the anterior lobe of the pituitary gland (Fig. 31.12). On the
inferomedial surface of the optic nerves, it is possible to
see the ophthalmic artery, which normally arises as the
first branch of the supraclinoid ICA, which enters the optic
canal and orbital cavity after a short distance (Fig. 31.13).
Superolaterally to the optic chiasm, the supraclinoid
segment of the ICA can be seen running upwards on the
lateral side of the optic tract, where it then divides into the
anterior cerebral artery (ACA) and the middle cerebral artery (MCA) just below the anterior perforate substance (Fig.
31.14). There is a large arterial complex at this level, where
the branches are overall known as anterior perforating arteries. By definition, this is a group of arteries that enter
the anterior perforate substance and they originate from
the ICA, the ACA, the MCA, and the anterior choroidal ar-
tery (AchA). The veins from the frontal lobes (such as the
olfactory veins and the orbital veins) converge here.
Above the chiasm, in the midline, the anterior commu-
nicating artery (AcomA) complex with the first segments
of ACA (A1 and A2) as well as the lamina terminalis can
be seen (Fig. 31.15). In a slightly more anterior position
lies the posterior portion of the olfactory tracts, as well as
the rectal gyrus. The olfactory vein is usually identifiable
close to the olfactory tract, while the anterior cerebral
vein, which has been joined by the paraterminal veins
coming from the interhemispheric fissure, is generally
visible over the chiasm. At this level, the anterior communicating vein can be seen as well.
25
A2
AcomA
A1
ON
SHA
ICA
Fig. 31.11 Endoscopic view of the suprasellar region.
The branches of the superior hypophyseal arteries supply
the pituitary stalk, optic nerves, and optic chiasm. A1,
fi rst segment of the anterior cerebral artery; A2, second
(postcommunicating) segment of the anterior cerebral artery;
AcomA, anterior communicating artery; BA, basilar artery; ICA,
internal carotid artery; OC, optic chiasma; ON, optic nerve; P1,
fi rst segment of the posterior cerebral artery; PcomA, posterior
communicating artery; PG, pituitary gland; PS, pituitary stalk;
SCA, superior cerebellar artery; SHA, superior hypophyseal
artery.
SHA
PcomA
P1
SCA
OC
BA
A1
P1
ON
SHA
PS
SCA
PG
(b) Transcribriform Corridor
By removing the bone of the anterior cranial base, in the
midline, from orbit to orbit and from the posterior wall
of the frontal sinus to planum sphenoidalis, the dura becomes apparent (Fig. 31.16). The crista galli in the midline
is also visible and can extend to a variable depth into the
330
cranial cavity, and is situated between the frontal bones.
Usually it is a thick bony structure and is rarely pneumatized. To remove the crista galli, it is necessary to drill internally until it becomes eggshell thin and can be removed
easily. The falx cerebri can be seen in close proximity to
the crista galli. This structure is a large fold of the dura in
OC
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Intracranial Vascular Anatomy
ON
CIP
CIP
Fig. 31.12 Endoscopic view of the complex vascular
network coming from the superior hypophyseal arteries
and surrounding the pituitary stalk and optic chiasm. CIP,
circuminfundibular plexus; OC, optic chiasma; ON, optic nerve;
PS, pituitary stalk.
PS
the sagittal plane, running in the midline between the cerebral hemispheres. As stated, it is attached anteriorly to
the crista galli, mainly on its posterior border, and to the
adjacent anterior skull base. At this level, the beginning of
the superior sagittal sinus is located just behind the frontal sinuses. When drilling the crista galli, venous bleeding
from the most inferior part of the superior sagittal sinus
or from the venous vessels lying on the cribriform plate
can take place. From this point, the superior sagittal sinus
runs superiorly in a shallow groove of the inner surface
of the calvaria, with its sidewalls given by two laminae of
the falx cerebri. In rare cases, it may communicate with
the veins of the nasal cavity through the foramen cecum.
At this level, it is sometimes possible to see the anterior
falcine artery, a branch of the anterior ethmoidal artery.
By removing the falx cerebri and the dural plane, the basal surface of the frontal lobes and the interhemispheric
fissure become evident. In the paramedian position, it is
possible to locate the olfactory bulbs and, more posteriorly, the olfactory tract (Fig. 31.17).
26
The basal surface of the
frontal lobes is divided by the olfactory sulcus into a medial compartment, the gyrus rectus, and a larger portion,
the orbital gyri. More laterally, the orbital sulcus divides
this latter portion into anterior, medial, lateral, and posterior groups. Endoscopically, this last division is of limited
significance. In close relationship to the olfactory bulb,
there is rich vascularization coming from the ACA. The latter supplies the medial part of the orbital gyri, the gyrus
rectus, and the olfactory bulb and tract on the basal sur-
27
face.
From an endoscopic point of view, only the orbitofrontal and frontopolar arteries are truly significant. These
vessels usually arise from A2. The orbitofrontal artery is
almost constantly present and arises usually from A2; it
seldom arises from A1. From its point of origin, it passes
down and forward toward the floor of the anterior cranial
A2
A1
AcomA
ON
OA
scciICA
Fig. 31.13 Endoscopic view of the sellar and suprasellar
region. The ophthalmic artery origins from the supraclinoidal
cisternal segment of the internal carotid artery and enters the
optic canal running below the optic nerve. A1, fi rst segment of
the anterior cerebral artery; A2, second (postcommunicating)
segment of the anterior cerebral artery; AcomA, anterior
communicating artery; BA, basilar artery; OA, ophthalmic
artery; OC, optic chiasma; ON, optic nerve; PG, pituitary gland;
PS, pituitary stalk; scciICA, supracavernous cisternal internal
carotid artery; SHA, superior hypophyseal artery.
OC
SHA
PS
Fig. 31.14 Endoscopic view of the internal carotid artery
dividing into anterior cerebral artery (ACA) and middle cerebral
artery (MCA). The ACA runs medially above the optic chiasm,
while the MCA runs lateral to the optic chiasm. AchA, anterior
choroidal artery; BA, basilar artery; OC, optic chiasma; PcomA,
posterior communicating artery; PS, pituitary stalk; P1,
fi rst segment of the posterior cerebral artery; SCA, superior
cerebellar artery; scciICA, supracavernous cisternal internal
carotid artery; SHA, superior hypophyseal artery.
BA
SHA
SCA
BA
P1
OC
SHA
PS
PG
ACA
PcomA
ON
OA
scciICA
MCA
scciICA
AchA
PcomA
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A2
A2
RAH
RAH
RAH
RAH
A2
ON
A2
AcomA
A1
LT
OC
scICA
cpsICA
SS
AcomA
ON
A1
LT
OC
Fig. 31.15 Endoscopic view of the suprachiasmatic region with the anterior communicating artery complex evident and the vascular
network given by the anterior cerebral arteries. A1, fi rst segment of the anterior cerebral artery; A2, second (postcommunicating)
segment of the anterior cerebral artery; AcomA, anterior communicating artery; LT, lamina terminalis; OC, optic chiasma; ON, optic
nerve; RAH, recurrent artery of Heubner.
OO
A1
fs
A1
ON
cpcICA
splICA
ms ms
Fig. 31.16 Schematic representation of the transcribriform corridor to the supraclinoid segment of the internal carotid artery after
radical ethmoidectomy with wide sphenoidotomy and Draf type III frontal sinusotomy. cl, clivus; cpcICA, cavernous paraclival internal
carotid artery; cpsICA, cavernous parasellar internal carotid artery; fs, frontal sinus; it, inferior turbinate; scICA, supraclinoid segment
of the internal carotid artery; splICA, supralacerum internal carotid artery; ss, sphenoid sinus.
it it
fossa to reach the level of the planum sphenoidalis. The
frontopolar artery arises usually from A2 and passes anteriorly along the medial surface of the hemisphere toward
the frontal pole. The venous vascular network develops in
a far less constant way. It is usually possible to recognize
the frontopolar, anterior and posterior orbitofrontal veins,
and the olfactory veins. All together, these veins drain the
basal surface of the frontal lobe. The anterior orbitofrontal
veins empty into the anterior part of the superior sagittal sinus. The posterior orbitofrontal veins empty into the
veins below the anterior perforated substance that converges on the anterior end of the basal vein.
332
cl
it
Anatomy
The supracavernous segment extends between the proximal dural ring and the carotid bifurcation, where the
artery divides into the ACA and MCA. It presents a posterosuperior direction and passes laterally to the optic chiasm
until it reaches the anterior perforate substance, where
it bifurcates. In this segment, the ICA usually gives some
branches/arteries: ophthalmic, AchA, posterior communi-
cating (PcomA), perforating branches, and SHAs. The oph-
27
thalmic artery presents a short intradural course, and it is
located under the optic nerve. The AchA passes laterally
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F
GR
FOA
Fig. 31.17 Endoscopic view of the anterior cranial fossa after
bilateral removal of the cribriform plate and ethmoidal roof. C,
clivus; FOA, orbitofrontal artery; GR, gyrus rectus; ICA, internal
carotid artery; OT, olfactory tract; S, sella.
FOA
OT
ICA
GR
OT
ICA
S
C
around the cerebral peduncle and into the temporal horn,
while the PcomA presents a posteromedial course parallel
to the oculomotor nerve. During its intracranial pathway,
the ICA gives off a series of perforating branches. The first
of these, in close proximity to the ophthalmic segment,
arises from the posterior and medial aspect of the artery
and supplies the pituitary stalk (SHAs), the optic chiasm,
and less frequently the optic nerve and optic tract. The
branches from the PcomA address the optic tract, floor of
the third ventricle, and the area around the mammillary
bodies. From the prebifurcation area, branches supplying
the anterior perforated substance, the optic tract, and the
uncus arise from the posterior aspect of the vessel.
In more detail:
• The SHAs usually arise from the first part of the
supraclinoid segment of the ICA and terminate on the
pituitary stalk and gland, but that can also send branches to the optic nerves and chiasm and the floor of the
third ventricle (Fig. 31.11). The infundibular arteries
originate from the PcomA and are mainly directed to
the infundibulum. Both the infundibular and the SHAs
pass medially, below the chiasm, to reach the tuber
cinereum. They form several anastomoses around the
pituitary stalk, creating the circuminfundibular plexus
(Fig. 31.12).
27
Secondary braches from this plexus are
directed to the anterior lobe of the pituitary gland, the
tuber cinereum, the optic chiasm, and nerves.
• Usually, the ophthalmic artery arises below the optic
nerve, above the dural roof of the CS (Fig. 31.13). Rarely,
it arises from the intracavernous segment (8%; Fig. 31.8),
clinoidal segment, or middle meningeal artery.
27
It can
branch meningeal rami, which, if present, go to the ventral aspect of the optic nerve and chiasm. The cisternal
segment of the ophthalmic artery is usually very short
and covered laterally by the anterior clinoid process.
siCS
OA
iiCS
ON
scciICA
PG
PS
SS
Fig. 31.18 Macroscopic sagittal view of the middle and
posterior cranial fossae. BA, basilar artery; BP, basilar plexus;
C, clivus; DS, Dorsum sellae; iiCS, inferior intercavernous
sinus; IIIcn, oculomotor nerve; IPS, inferior petrosal sinus;
OA, ophthalmic artery; ON, optic nerve; PcomA, posterior
communicating artery; PG, pituitary gland; PS, planum
sphenoidalis; PT, porus trigeminus; scciICA, supracavernous
cisternal internal carotid artery; siCS, superior intercavernous
sinus; SPS, superior petrosal sinus; SS, sphenoid sinus; Vcn,
trigeminal nerve; VIcn, abducens nerve.
DS
PcomA
IIIcn
BP
C
SPS
PT
VIcn
BA
Vcn
IPS
• The PcomA arises from the posterior surface of the
ternal segment of the ICA (Fig. 31.18). It runs back-
cis
ward and medially below the tuber cinereum, above
the sella turcica, and parallel and medial to the oculomotor nerve to connect with the posterior cerebral artery (PCA; Fig. 31.19). It gives rise to several branches,
mostly from the superior and lateral surfaces, that
reach the tuber cinereum (infundibular arteries), the
premammillary part of the floor of the third ventricle,
the posterior perforated substances, and the interpeduncular fossa. The largest branch to the premammillary region is called the premammillary artery and
ing arteries (TPAs).
27
• Usually, the AchA arises from the ICA as a single artery,
in most cases close to the PcomA (Fig. 31.20). In rare
cases (2%), it arises from the PcomA or the MCA.
27,28
In
the great majority of cases, it arises from the cisternal
segment of the ICA lateral to the optic tract and passes
below or along the optic tract (usually medially to it) to
get the lateral surface of the cerebral peduncle. It gives
rise to different perforating arteries, reaching the optic
tract, uncus, cerebral peduncle, and so on. The extreme
variability of this network makes any attempt of description of limited significance.
Regarding the terminal branches:
• The ACA is the smaller of the two terminal branches of
the ICA. It arises at the medial end of the Sylvian fissure,
below the anterior perforated substance and lateral to
the optic chiasm (Fig. 31.14). The artery courses antero-
333
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SHA
P1
PcomA
IIIcn
Fig. 31.19 Endoscopic view of the posterior communicating
artery connecting the internal carotid artery to the posterior
cerebral artery. To note how the artery runs parallel and
medial to the oculomotor nerve. BA, basilar artery; IIIcn,
oculomotor nerve; PcomA, posterior communicating artery;
P1, fi rst segment of the posterior cerebral artery; SCA, superior
cerebellar artery.
SCA
BA
medially above the optic chiasm and nerve to enter the
interhemispheric fissure. In front of the lamina terminalis, before entering the fissure, the ACA is connected
by means of the AcomA to the ACA of the contralateral
side (Fig. 31.15). The ACA–AcomA complex is usually above the optic chiasm (70% of cases).27 The AcomA
is similar to the textbook description in three-fourths
of the cases. In approximately 10% of cases, it can be
hypoplastic or even duplicated (30%) and triplicated
28,29
(10%).
The ACA, usually in proximity of the AcomA,
sends several perforating branches for the anterior part
of the diencephalon, the lateral regions of the lamina
terminalis, and surrounding regions (superior surface
of the optic chiasm).
27,28
The AcomA divides the ACA
into two parts, proximal (precommunicating) and distal
(postcommunicating). The precommunicating segment
(A1) extends from the origin to the AcomA. Usually, the
A1 courses above the optic chiasm and if is long, it can
present a tortuous course and may be in close proximity of the planum sphenoidale. The postcommunicating
segment (A2 through A5) begins at the AcomA and extends around the corpus callosum to its termination.
The A2 (infracallosal) enters the pericallosal cistern and
courses around the genu of the corpus callosum. The
A3 (precallosal) segment 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 that may extend to the region of the pineal body. The A4 (supracallosal) and A5 (postcallosal) segments are located above
the corpus callosum and are separated into an anterior
(A4) and posterior (A5) portion by a point bisected in
the lateral view close and behind the coronal suture.
27
SHA
ON
OC
P1
PS
Fig. 31.20 Endoscopic view of the posterior communicating
artery and anterior choroidal artery. The endoscope is passing
above the diaphragma sellae between the pituitary stalk
medially and the left internal carotid artery laterally. ACA,
anterior cerebral artery; AchA, anterior choroidal artery;
IIIcn, oculomotor nerve; OC, optic chiasma; ON, optic nerve;
PcomA, posterior communicating artery; PS, pituitary stalk;
P1, fi rst segment of the posterior cerebral artery; SCA, superior
cerebellar artery; scciICA, supracavernous cisternal internal
carotid artery; SHA, superior hypophyseal artery.
AchA
PcomA
SCA
ACA
PcomA
IIIcn
scciICA
AchA
The recurrent artery of Heubner (RAH) is a branch of the
ACA (in most cases from proximal A2) that doubles back
to the major artery and passes above the carotid bifurcation and MCA to feed the anterior perforated substance.
29
In two-thirds of the cases, given its long course, the RAH
participates in supplying the olfactory bulbs and tracts
and the orbital parts of the frontal lobes.
RAH presents a strict relationship with A1. In 30% of
cases, the vessel is double (Fig. 31.15),
than 70% of cases two to four arteries may be present.
28
Usually, the
28
while in more
29
The orbitofrontal and frontopolar arteries are almost always present and usually arise from A2. The orbitofrontal
artery runs down and forward toward the planum sphenoidale to reach the floor of the anterior cranial fossa
(Fig. 31.17). It supplies the gyrus rectus, olfactory bulb,
and tract, and the medial part of the orbital surface of the
frontal lobe. The frontopolar artery, from its origin, passes anteriorly along the medial surface of the hemisphere
toward the frontal pole. It crosses the subfrontal sulcus
and supplies portions of the medial and lateral surfaces
of the frontal pole.
27
The ACA–AcomA complex, the cisternal ICAs, the Pco-
mAs, and PCAs form the circle of Willis (Fig. 31.21).
• The MCA is considered the continuation of the ICA
(Fig. 31.22) and is rarely absent or duplicated.
cessory MCAs have been described as arising from the
28
ACA.
Its origin is at the medial end of the Sylvian fis-
28,30
Ac-
sure, lateral to the optic chiasm and below the anterior
perforated substance where it offers several branches,
the lenticulostriate arteries.
27
It runs horizontally and
laterally to its primary bifurcation at the limen insulae
334
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