Circle of willis 360°

Circle of Willis 360°
24-4-2016
2.54 am

Great teachers – All this is their work .
I am just the reader of their books .
Prof. Paolo castelnuovo
Prof. Aldo Stamm Prof. Mario Sanna
Prof. Magnan

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Circle of willis in anterior & lateral skull base view
??? is intracerebral carotid

In anterior skull base approach

In anterior skull base approach - Type C Modified
Transcochlear Approach – after cutting the tentorium
With mild retraction of the temporal lobe, the bifurcation of the internal carotid artery (ICA) into
the anterior (ACA) and middle cerebral (MCA) arteries is seen. The ipsilateral (ON) and
contralateral (ONc) optic nerves are seen. The oculomotor nerve (III) is embraced by the
posterior cerebral artery (PCA) superiorly and the superior cerebellar artery (SCA) inferiorly

http://www.ajnr.org/content/27/8/1770/F2.expansion.html
Classification of the anatomic variations in the circle of Willis. In the “textbook” type, both the
precommunicating segment of the anterior cerebral artery (A1) and that of the posterior cerebral
artery (P1) were normal in size. The next group included both right and left A1 hypoplasia.
Because no significant difference between cerebral arteries on the right and left sides has been
established,5,18 we combined right and left A1 hypoplasia into A1 hypoplasia. The next group
included right and left P1 hypoplasia, which again were treated as a single category, P1
hypoplasia. “Other” type included a combination of A1 hypoplasia and P1 hypoplasia, bilateral P1
hypoplasia, as well as other unclassified variations. ACA indicates anterior cerebral artery; ACo,
anterior communicating artery; MCA, middle cerebral artery; ICA, internal cerebral artery; PCo,
posterior communicating artery; PCA, posterior cerebral artery; BA, basilar artery

http://www.ajnr.org/content/27/8/1770/F3.expansion.html
Relative contribution of proximal arteries to total volume flow in variations in the circle of Willis.
Values signify mean percentage ± SD. The upper left value corresponds to the relative
contribution of the right internal carotid artery in the “textbook” type or of the internal carotid
artery ipsilateral to hypoplastic A1 or P1 in the other variations. The upper right value
corresponds to the relative contribution of the left internal carotid artery in the “textbook” type,
or of the internal carotid artery contralateral to hypoplastic A1 or P1 in the other variations. The
value at the bottom corresponds to the relative contribution of the basilar artery.
* The value for A1 hypoplasia variation was significantly smaller than those for “textbook” type
and P1 hypoplasia variation. The value for P1 hypoplasia variation was significantly larger than
that for “textbook” type.
** The value for A1 hypoplasia variation was significantly larger than that for “textbook” type.
*** The value for P1 hypoplasia variation was significantly smaller than that for “textbook” type.

http://stroke.ahajournals.org/content/30/12/2671/F2.expansion.html
Scheme of anatomic variations of the posterior part of the CW: variant types a
through c are complete, whereas the remainder are incomplete. a, Bilateral PCoA
present. b, PCA originating predominantly from the ICA. This type is known as a
unilateral fetal-type PCA (FTP), indicated by the arrows; the PCoA on the other side is
present. c, Bilateral FTP, with both P1 segments patent. d, Unilateral PCoA present. e,
Hypoplasia or absence of both PCoAs, with isolation of the anterior and posterior
circle parts at this level. f, Unilateral FTP, with hypoplasia or absence of the P1
segment. g, Unilateral FTP, with hypoplasia or absence of the contralateral PCoA. h,
Unilateral FTP, with hypoplasia or absence of the P1 and PCoA. i, Bilateral FTP, with
hypoplasia or absence of both P1 segments. j, Bilateral FTP, with hypoplasia or
absence of one P1 segment.

Pcom absent in post-
craniopharyngioma case

http://www.anatomyatlases.org/AnatomicVariants/Cardiova
scular/Images0200/0294B.gif

Cisternal / Intracranial ICA [ICA i]

Anatomically speaking, the paraclinoid segment of the internal carotid artery is not fully
intracavernous, and it is separated from the cavernous sinus by the extension of the dura
covering the inferior surface of the anterior clinoid process (Reisch et al. 2002 ) .
Note carotid cave , cavernous
sinus , upper & lower dural rings

Oculomotor cistern
Cranial nerve III enters the roof included in its own cistern
(oculomotor cistern).
Oculomotor cistern goes upto
anterior clinoid tip

The mOCR is located just medial to the paraclinoidal-supraclinoidal ICA
transition and inferior to the distal cisternal segment of the ON(Labib et al. 2013 ).
Cl clivus, ICAc cavernous portion of the internal carotid artery, ON optic nerve, PG pituitary
gland, PS planum sphenoidale, TS tuberculum sellae, yellow asterisks upper dural ring, blue
arrowheads lower dural ring, white asterisk lateral optico-carotid recess, white circle medial
optico-carotid recess, white arrow ophthalmic artery, black arrows middle clinoid process, red
arrows lateral tubercular crest, yellow arrows endocranial region corresponding to MCP

Cadaveric dissection image demonstrating the close anatomical relationship
of the posterior clinoid (PC) with both the intracranial carotid artery (ICCA)
and the posterior genu of the intracavernous carotid artery (P. CCA). AL,
anterior lobe of the pituitary gland; PL, posterior lobe of the pituitary gland;
BA, basilar artery.
green dotted triangle area for entry
of the endoscope into the interpeduncular fossa

Posterior clinoidectomy in
cisternostomy in head injury video –
by Dr. Iype Cherian - click
https://www.youtube.com/watch?v
=vNaEFMrdgfw

Aneurysms of initial intracranial
carotid

Opthalmic artery – Retrograde branch of Intracranial carotid
Branches of the cavernous internal
carotid artery ( ICA ), a rare
variation: ophthalmic
artery passing through the superior
orbital fissure

In the lateral border of the chiasmatic cistern the first part of
the ICAi is visible.
Note Optic tract here which is above
Posterior clinoid process [ PCP ]

In the lateral border of the chiasmatic cistern the first part of
the ICAi is visible.
Dry bone dissection image taken with a 30-degree endoscope demonstrating the fovea
ethmoidalis (FE) and cribriform plate (CP) junction with the planum sphenoidale (PS). This is
marked approximately by the posterior ethmoidale artery (PEA). ISS, intersinus septum of
sphenoid sinus; ON, optic nerve; CCA, anterior genu of the intracavernous carotid artery.

Supra-clinoidal carotid=1st part of
intracranial carotid

APAs anterior perforating arteries, ICAi intracranial portion of
the internal carotid artery, OT optic tract, SF Sylvian fi ssure,

A 1 [ ACA ] crosses above the Optic
tract , not Optic nerve .
Left subchiasmatic cistern

ACA anterior cerebral artery, APAs anterior perforating arteries, FOA fronto-orbital artery,
FOV fronto-orbital vein, FPA fronto-polar artery, ICAi intracranial segment of the internal
carotid artery, MCA middle cerebral artery, OlfT olfactory tract, OlfV olfactory vein, ON optic
nerve, PS pituitary stalk, TL temporal lobe, black asterisk anterior communicating artery

Fig. 2.1 Drawing showing the skin incision (red line), the craniotomy
and the microsurgical intraoperative view of the subfrontal unilateral approach. This approach provides a
wide intracranial exposure of the frontal lobe and easy access to the optic nerves, the chiasm, the carotid
arteries and the anterior communicating complex

Fig. 2.4 Intraoperative microsurgical photograph showing contralateral
extension of the tumor (T) dissected via a unilateral subfrontal
approach. Note on the left side the falx cerebri (F) and
the mesial surface of the left frontal lobe (FL)

Fig. 2.5 Drawing showing the skin incision (red line), the craniotomy
and the microsurgical anatomic view of the subfrontal bilateral
route. This approach provides a wide symmetrical anterior
cranial fossa exposure and easy access to the optic nerves, the
chiasm, the carotid arteries and the anterior communicating arteries
complex

Supraorbital approach - Fig. 3.2 Illustrations comparing the incision and
bony exposure in a supraorbital craniotomy with those in a pterional craniotomy. a
The supraorbital craniotomy utilizes the subfrontal corridor and involves a frontobasal
burr hole and removal of a small window in the frontal bone. b The pterional
craniotomy utilizes a frontotemporal incision and removal of the frontal and temporal
bones andsphenoid wing. The pterional craniotomy primarily exploits the sylvian
fissure

Fig. 4.6 a Craniotomy. b When the flap has been removed the
lesser wing of the sphenoid is drilled down to optimize the most
basal trajectory to the skull base. c Dural opening. DM dura
mater, FL frontal lobe, MMA middle meningeal artery, LWSB
lesser wing of the sphenoid bone, SF sylvian fissure, TL temporal
lobe, TM temporal muscle, ZPFB zygomatic process of the frontal bone

Fig. 4.8 Intradural exposure; right approach. Before (a) and after (b) opening of the
Sylvian fissure. A1 first segment of the anterior cerebral artery, AC anterior clinoid, FL
frontal lobe, HA Heubner’s artery, I olfactory tract, III oculomotor nerve, ICA internal
carotid artery, LT lamina terminalis, M1 first segment of the middle cerebral artery,
MPAs perforating arteries, ON optic nerve, P2 second segment of the posterior
cerebral artery, PC posterior clinoid, PcoA posterior communicating artery, SF sylvian
fissure, TL temporal lobe, TS tuberculum sellae

Fig. 4.9 Intradural exposure; right approach. a Instruments enlarging the optocarotid
area. b Displacing medially the posterior communicating artery, exposing the
contents of the interpeduncular cistern. AC anterior clinoid, AchA anterior choroidal
artery, BA basilar artery, FL frontal lobe, ICA internal carotid artery, III oculomotor
nerve, OA left ophthalmic artery, ON optic nerve, OT optic tract, P2 second segment of
the posterior cerebral artery, PC posterior clinoid, PcoA posterior communicating
artery, Ps pituitary stalk, SCA superior cerebellar artery, SHA superior hypophyseal
artery, TE tentorial edge, TL temporal lobe

Fig. 4.10 Intradural exposure; right approach; enlarged view. A1 first segment of the anterior
cerebral artery, A2 second segment of the anterior cerebral artery, AC anterior clinoid, AcoA
anterior communicating artery, BA basilar artery, FL frontal lobe, HA Heubner’s artery, ICA
internal carotid artery, III oculomotor nerve, LT lamina terminalis, M1 first segment of the middle
cerebral artery, OA left ophthalmic artery, ON optic nerve, P2 second segment of the posterior
cerebral artery, PC posterior clinoid, PcoA posterior communicating artery, SCA superior cerebellar
artery, SHA superior hypophyseal artery, TE tentorial edge, TL temporal lobe, TS tuberculum sellae

Posteior clinoid can be approached in optico-carotid
triangle [ 3mm ] OR lateral carotid triangle

Posteior clinoid can be approached in optico-carotid triangle [
3mm ] OR lateral carotid triangle

Pcom is seen in optico-carotid triangle – can be injured
in cisternostomy while cutting lillequet membrane

Fig. 4.11 Intradural exposure; right approach; close-up view ofthe interpeduncular fossa. AchA
anterior choroidal artery, BAbasilar artery, DS dorsum sellae, III oculomotor nerve, IV
trochlear nerve, P1 first segment of the posterior cerebral artery,P2 second segment of the
posterior cerebral artery, PC posteriorclinoid, PcoA posterior communicating artery, Ps pituitary
stalk, SCA superior cerebellar artery, TE tentorial edge

Endoscope-assisted microsurgery [ 45° endoscope in a corridor
between the carotid artery and the oculomotor nerve ]-- Fig. 4.12
Intradural exposure; right approach; microsurgical (a) and endoscopic (b–d) views. AchA
anterior choroidal artery, BA basilar artery, C clivus, FL frontal lobe, ICA internal carotid artery, III
oculomotor nerve, ON optic nerve, P1 first segment of the posterior cerebral artery, P2 second
segment of the posterior cerebral artery, PC posterior clinoid, PCA posterior cerebral artery, PcoA
posterior communicating artery, SCA superior cerebellar artery, TE tentorial edge, TL temporal
lobe, Tu thalamoperforating artery; green dotted triangle area for entry of
the endoscope into the interpeduncular fossa

Fig. 4.12 Intradural exposure; right approach; microsurgical (a) and endoscopic (b–d) views.
AchA anterior choroidal artery, BA basilar artery, C clivus, FL frontal lobe, ICA internal carotid
artery, III oculomotor nerve, ON optic nerve, P1 first segment of the posterior cerebral artery, P2
second segment of the posterior cerebral artery, PC posterior clinoid, PCA posterior cerebral
artery, PcoA posterior communicating artery, SCA superior cerebellar artery, TE tentorial edge, TL
temporal lobe, Tu thalamoperforating artery; green dotted triangle area for entry of the
endoscope into the interpeduncular fossa

Fig. 4.13 Intradural exposure; right approach; microsurgical (a)
and endoscopic omolateral (b) and contralateral (c) views. A1 first segment of the anterior
cerebral artery, AC anterior clinoid, ICA internal carotid artery, FL frontal lobe, III oculomotor
nerve, LT lamina terminalis, M1 first segment of the middle cerebral artery, OA left ophthalmic
artery, ON optic nerve, PcoA posterior communicating artery, SHA superior hypophyseal artery, TE
tentorial edge, TS tuberculum sellae

Craniopharyngioma
https://www.facebook.com/groups/4
05175366256295/permalink/552393
251534505/?stream_ref=2

CRANIOPHARYNGIOMAS-Removal corridors.

https://www.scienceopen.com/document_file/84699ab2-4980-4f70-a5b0-
c8d95a1fb6a2/PubMedCentral/84699ab2-4980-4f70-a5b0-c8d95a1fb6a2.pdf
FIGURE 4. The capsule of the cystic craniopharyngioma was firmly attached to the left
hypothalamus, the stalk was dislocated to the right side (Patient 6). The outgrowth of the
craniopharyngioma from proximal stalk is recognizable A. Complete removal of the capsule was
possible, but produced subpial blood injection over the left hypothalamic surface B. MRI scan
revealed a small ischemic injury in the left hypothalamus C. This patient had transient sleep
disorder, moderate hyperphagia and memory problems (see also a supplemented video
material 1).

FIGURE 2. In this cystic craniopharyngioma (Patient 5), the stalk was centrally
infiltrated close to the pituitary and could not be preserved A. The incipient third
ventricle entrance is seen from intracavitary view. The slit into the third ventricle is
still covered with tumour capsule B. Complete removal of the capsule opened the
third ventricle C. Petehiae in the hypothalamus bilaterally resulted from apparently
gentle traction and blunt dissection of the capsule away from the hypothalamus
D. Psychoorganic change, disorientation and memory deficits were noticed in less
than a week after surgery, the transient sleep disorder become apparent in the
second week postoperatively (see also a supplemented video material 2).

FIGURE 3. Large craniopharyngioma (Patient 3) produced unilateral hydrocephalus
by obstructing the right formen of Monro A. The dome was filled with soft
cholesterine cristals B, which were easily removed. Lower limbus of the right foramen
of Monro is seen through the empty third ventricle D. Despite bilateral preservation
of anteromedial hypothalamus C and stalk preservation E, the patient developed
panhypopituitarism and diabetes insipidus with long lasting psychoorganic change

Fronto-temporal orbitozygomatic
transcavernous approach
COM= Caratico-occulomotor
membrane , DR = dural ring

Fig. 4.15 Microsurgical view; extradural anterior
clinoidectomy. a Exposure and drilling of the anterior clinoid process
and optic canal under microscope magnification. b Widened space after complete removal of
the AC. AC anterior clinoid, eON extracranial intracanalar optic nerve, FD frontal dura, ICA
internal carotid artery, iON intraorbital optic nerve, LWSB lesser wing of sphenoid bone, OC optic
canal, OR orbit roof, SOF superior orbital fissure, TD temporal dura

Fig. 4.16 Microsurgical view; intradural anterior clinoidectomy. a, b After the dura above the
anterior clinoid process has been transected in a “T” shape (a), we usually drill always parallel
tothe optic nerve and to the carotid artery (b). c The distal ring is finally exposed. A1
precommunicating anterior cerebral artery, AC anterior clinoid, AchA anterior choroid artery, Ch
optic chiasm, DR distal ring, fl falciform ligament, FL frontal lobe, ICA internal carotid artery, M1
first tract of the middle cerebral artery, ON optic nerve, PC posterior clinoid, PCOA posterior
communicating artery, TS tuberculum sellae

FTOZ – Fronto-temporal
orbitozygomatic approach

Fig. 7.13 a Intraoperative photograph shows good exposure of the left tentorial anterior and middle incisura
obtained through the pretemporal and subtemporal corridors. In this patient the
basilar apex is well above the superior margin of the dorsum sellae. b Same patient. A more lateral exposure
showing the pontomesencephalic junction surface and the neurovascular structures in the ambient cistern. c
Intraoperative photograph of another patient showing structures in the left lateral incisural space from the
subtemporal corridor. d Same patient. More lateral view. e Same patient. More posterior exposure. The lifting
of the free edge of the tentorium shows the trochlear nerve entering the tentorium. The junction between the
P2a and P2p segments (P2a, P2p) of the posterior cerebral artery is shown. ACA anterior cerebral artery, AChA
anterior choroidal artery and tiny perforating vessels, BA basilar artery, DS dorsum sellae, FET free edge of
tentorium, ICA internal carotid artery, LM Liliequist’s membrane, LON left optic nerve, ON oculomotor nerve, OT
optic tract, PCA posterior cerebral artery, PComA posterior communicating artery, PLChA posterolateral
choroidal artery arising from the P2a–P2p junction, PS pituitary stalk, RON right optic nerve, SCA superior
cerebellar artery, TN trochlear nerve in the arachnoidal covering

THE FULLY ENDOSCOPIC SUBTEMPORAL APPROACH [ from
Shahanian book ] - The traditional middle fossa subtemporal approach requires long-
standing placement of retractors on the temporal lobe; therefore, potential injury to the
temporal lobe can occur
(e.g., hematoma and edema resulting in aphasia, hemiparesis, or seizures). This concern should
not be a problem with the described approach because temporal lobe retractors are not used.
(L) a Epidermoid tumor. b Atraumatic
suction. c Brainstem. d Occulomotor (III)
nerve. e Posterior cerebral artery (PCA).
f Superior cerebellar artery (SCA). g
Trochlear (IV) nerve.
(N) a Epidermoid tumor. b Atraumatic suction. c
Left-curved tumor forceps. d Occulomotor (III)
nerve. e Posterior cerebral artery (PCA). f
Posterior communicating (PCOM) artery. g
Superior cerebellar artery (SCA).
h Brainstem. i Trochlear (IV) nerve.

Q) a Occulomotor (III) nerve. b
Internal carotid artery (ICA). c
Posterior cerebral artery (PCA).
d Superior cerebellar artery
(SCA).
(P) a Ipsilateral optic (II) nerve. b
Internal carotid artery (ICA). c
Occulomotor (III) nerve.
d Dura overlying anterior clinoid
process.

The recurrent artery of Heubner usually origins from the post-communicating segment of the anterior
cerebral artery (ACA). It doubles back the ACA to reach the medial part of the Sylvian fi ssure, below
the anterior perforated substance. Sometimes its path is so long that the artery loops below the basal
surface of the frontal lobes. Not frequently more than one recurrent arteries can be present (Rhoton
2003 ). According to Lang the artery is double in about 30% of cases (Lang 1995 ) .

3rd ventricle entry by - Supra optic chiasmic route – by
Lamina terminalis

Recurrent artery of heubner originates
near Acom
(A) The middle cerebral artery (MCA) gives rise to the lateral lenticulostriate arteries
(LLA) at the bifurcation complex. The medial lenticulostriate arteries (MLA) arise from
the proximal section of A1. At the juncture of A1-AComm-A2 the recurrent artery of
Heubner (RAH) is given off. AComm completes the anterior portion of the circle of
Willis and has several perforating vessels ( Acomm Perf) that head posteriorly. In the
first 5 mm of A2 the orbitofrontal ( OF) artery is given off with the frontopolar (FP)
artery staying more medial. (B) A clinical picture after removal of a tuberculum sella
meningioma with a well-defined display of the anterior cerebral arteries.

Recurrent artery of heubner [ R-RAH ]
originates near Acom

In parasellar pituitary 3rd n & 4th n & Pcom present
in Postero-superior cavernous compartment

a,b Intraoperative image of the fenestration of deep cystic membrane using different microsurgical
instruments (forceps and scissors). Asterisks posterior communicating artery and anterior choroidal
artery. c Fenestration of the cisternal layer (cross Liliequist’s membrane). d Intraoperative picture at the end
of the procedure
http://www.springerimages.com/Images/MedicineAndPublicHealth/1-10.1007_s00381-004-0940-4-0

ACA anterior cerebral artery, AchA anterior choroidal artery, BA basilar artery, Cl clivus, DS diaphragma
sellae, ICAi intracranial portion of the internal carotid artery, OA ophthalmic artery, ON optic nerve,
PcomAf posterior communicating artery (fetal configuration), PcomAn posterior communicating artery
(normal configuration), PG pituitary gland, PS pituitary stalk, P1 fi rst segment of the posterior cerebral
artery, SCA superior cerebellar artery, SHAs superior hypophyseal arteries, TS tuberculum sellae, IIIcn
oculomotor nerve
The PcomA is the most variable vessel of Willis’s circle. If PcomA is wider than P1, it is
said to be of the fetal type. This happens in about 20 % of cases. In 1 % of cases, it is
absent (Lang 1995 ) .

Relationship of PcomA & 3rd nerve –
parallel or cross each other

Relationship of PcomA & 3rd nerve – parallel or cross each other
in Kernochan's Notch diagram
http://en.wikipedia.org/wiki/Kernohan%27s_notch

Relationship of PcomA & 3rd nerve

Endoscopic third ventricle from
posteriorly -- a. Infundibular
recess b. tuber cinereum c.
mammillary bodies
left posterior communicating artery (a),
mammillary body (b), and right posterior
hypoplasic communicating artery (c) ---
measurement performed between the
posterior communicating arteries using
Geogebra software (a-b = 11.3 mm),

In the descriptive analysis of the 20 specimens, the PCoAs
distance was 9 to 18.9 mm, mean of 12.5 mm, median of 12.2
mm, standard deviation of 2.3 mm.

AchA anterior choroidal artery
Usually, the AchA arises from the ICA as a single artery, in most
cases close to the PcomA. In rare cases (2 %), it arises from the
PcomA or the MCA (Lang 1995 ; Rhoton 2003 ) . 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.

ACA anterior cerebral artery, AchA anterior choroidal artery, BA basilar artery, Cl clivus, DS diaphragma
sellae, ICAi intracranial portion of the internal carotid artery, OA ophthalmic artery, ON optic nerve,
PcomAf posterior communicating artery (fetal con fi guration), PcomAn posterior communicating artery
(normal con fi guration), PG pituitary gland, PS pituitary stalk, P1 fi rst segment of the posterior cerebral
artery, SCA superior cerebellar artery, SHAs superior hypophyseal arteries, TS tuberculum sellae, IIIcn
oculomotor nerve
The PcomA is the most variable vessel of Willis’s circle. If PcomA is wider than P1, it is
said to be of the fetal type. This happens in about 20 % of cases. In 1 % of cases, it is
absent (Lang 1995 ) .

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.

MINIMALLY INVASIVE RETROSIGMOID APPROACH (MIRA) -
Port of entry to Endoscopic Lateral Skull Base

Lilliquits membrane present over the
basillar artery & 3rd N. origin area

The basilar artery (BA) can be seen
very tortuous , not always straight

Cadaveric dissection image demonstrating structures seen
following dissection of the lower third of the clivus. Note how
the basilar arteries and vertebral arteries can be extremely
tortuous in their course.

Note
1. Basillar artery is kinky , not always straight
2. observe bilateral hypoglossal canals
Cadaveric dissection following the removal of the apical and alar ligaments, and the odontoid
process has been drilled away (OP). This re veals the strong and thick transverse portion of the
cruciform ligament (CL). Behind this is located the tectorial membrane (TM). ET, eustachian
tube; SP, soft palate; HC, hypoglossal canal; VA, vertebral artery; BA, basilar artery.

The pontomedullary junction.
1. The exit zones of the hypoglossal and abducent nerves are at
the same level [ same vertical line when view from Transclival
approah ( through lower clivus ) ]
2. The abducent nerve exits from the pontomedullary junction, and ascends
in a rostral and lateral direction toward the clivus.

A closer view of the anterior border
of the pontomedullary stem and the
vertebral artery junction and origin
of the basilar artery. Perforating
arteries arise from the vertebral and
basilar arteries.
The endoscope is focusing on the
hypoglossal nerve area. The
posterior inferior cerebellar artery
arises from the vertebral artery in
the background, and runs between
the two bundles of the hypoglossal
nerve.

Fig. 26a, b Right side. The root fibers of the hypoglossal
nerve (12) collect in two bundles, which pierce the dura in
two dural pori. The hypoglossal nerve is situated more anteriorly
and medially than the root fibers of the lower cranial
nerves. The arterial relationship is the vertebral artery, with
perforating arteries to the brain stem. The curved vertebral
artery displaces and stretches the hypoglossal nerve fibers.

Through lateral skull base - The
curved vertebral artery displaces
and stretches the hypoglossal
nerve fibers.
Through anterior skull base

Through lateral skull base - The curved
vertebral artery displaces and stretches the
hypoglossal nerve fibers.
Through lateral skull base - The opposite
vertebral artery exits from the dural porus
and stretches /raises the hypoglossal nerve.

Transcochlear approach leads to Lower
clivus
AAAM anterior atlanto-axial membrane, AAOM anterior atlanto-occipital membrane, AIM anterior intertrasversarius muscle, Cl clivus, C1
atlas, C1TP transverse process of C1, C2 axis, ET eustachian tube, JF jugular foramen, JT jugular tubercle, HC hypoglossal canal, ICAc cavernous
portion of the internal carotid artery, LCapM longus capitis muscle, LColM longus colli muscle, PG pituitary gland, RCAM rectus capitis
anterior muscle, RCLM rectus capitis lateralis muscle, blue-sky arrow apical ligament, green arrow external ori fi ce of the hypoglossal canal,
black arrow lateral atlanto-occipital ligament, black asterisk foramen lacerum

Note CL [Lower clivus ] in these photos after drilling of cochlea
The clivus bone (CL) can be seen
medial to the internal carotid
artery (ICA). JB Jugular bulb
In the lower part of the approach, the
glossopharyngeal nerve
(IX) can be seen. V Trigeminal nerve, VIII Cochlear
nerve, AICA Anterior
inferior cerebellar artery, CL Clivus bone, DV
Dandy’s vein, FN Facial
nerve, FN(m) Mastoid segment of the facial nerve,
FN(t) Tympanic segment
of the facial nerve, GG Geniculate ganglion, ICA
Internal carotid
artery, JB Jugular bulb, MFD Middle fossa dura, SCA
Superior cerebellar
artery, SS Sigmoid sinus

Note CL [Lower clivus ] in these photos
after drilling of cochlea
Note the contralateral vertebral
artery [ CVA ] in below photo

Two cerebellar lobes and the medullary stem. The
posterior inferior cerebellar artery encircles the medullary
stem. The opposite vertebral artery exits from the dural porus
and raises the hypoglossal nerve.

HC = hypoglossal canal , JT= Jugular Tubercle

COMBINED APPROACHES
1. Retrolabyrinthine Subtemporal Transapical Approach
2. Retrolabyrinthine Subtemporal Transtentorial Approach
Retrolabyrinthine Subtemporal
Transapical Approach
Transtentorial Approach

A view of the cerebellopontine angle
through the retrolabyrinthine
approach Note the narrow field and
limited control.
Posterior fossa dura (PFD) structures
exposed through the standard
retrolabyrinthine approach.
A view of the posterior fossa dura
through the combined
retrolabyrinthine subtemporal
transapical approach.

The middle fossa dura has
been cut. The oculomotor
nerve (III) is clearly seen.
With more retraction of the
temporal lobe and the tentorium
(*), the optic nerve (II) is seen.

Retrolabyrinthine Subtemporal Transapical
(Transpetrous Apex) Approach
Schematic drawing showing the
incision to be performed.
A retrolabyrinthine approach is
performed.

The dura of the middle fossa is
detached from the superior surface of
the temporal bone from posterior to
anterior.
With further detachment of the
dura, the middle meningeal
(MMA) artery is clearly identified.

The middle meningeal artery (MMA)
and the three branches
(V1, V2, V3) of the trigeminal nerve
are identified.
View after cutting the middle
meningeal artery (MMA) and
the mandibular branch of the
trigeminal nerve (V).

The internal auditory canal (IAC)
is identified.
A large diamond burr is used to
drill the petrous apex.

The petrous apex has been
drilled. The internal carotid artery
(ICA) is identified.
At higher magnification, the
abducent nerve (VI) is identified
at the level of the tip of the petrous
apex (PA).

Panoramic view showing the
structures after opening of the
posterior fossa dura.
At higher magnification, the anterior
inferior cerebellar artery (AICA)is
seen stemming from the basilar
artery (BA) at the prepontine cistern.
The artery is crossed by the
abducent nerve (VI). Note the good
control of the prepontine cistern
through this approach.

Tilting the microscope downward,
the lower cranial nerves
are well seen.

Transtentorial Approach
The retrolabyrinthine craniotomy
has been performed. The petrous
apex has been partially drilled.
The middle fossa dura (*) is
incised.

The tentorium (*) is cut, taking care not to injure the
trochlear nerve.
The tentorium is further cut until
the tentorial notch is
reached. With retraction of the
temporal lobe the optic (II),
oculomotor
(III) and contralateral oculomotor
(IIIc) nerves are seen.

Branches of the trigeminal nerve (V1, V2, V3) at the level of
the lateral wall of the cavernous sinus.

intra operative photograph through operating microscope during removal of posterior
fossa arachnoid cyst -showing medulla oblnagata-cervical spinal cord -cerebellar
tonsils-vertebral artery-hypoglossal nerve -accessory nerve -1st cervical nerve root -
PICA loope,after removal of cyst wall

Posterior view of the left CPA with a 30° angled
endoscope gives a view of CPA contents and permitsobservation of the blind spots by “looking
around the corner.” V indicates trigeminal nerve; VI, abducens nerve; IV, trochlear nerve; VII,
facial nerve anteriorly hidden by VIII; VIII, vestibulocochlear nerve; IX, glossopharyngeal nerve; X,
vagusnerve; XI, spinal accessory nerve; XII, hypoglossal nerve; aica, anterior-inferior cerebellar
artery; DV, Dandy’s vein or superior petrosal vein; SPS, superior petrosal sinus; Tent, tentorium.

6th nerve origin is above or below AICA or has two
rootlets of origin

Right sided anterior petrosectomy on a cadaver dissection: intradural exposure
and operative field. PCA Petrous carotid artery; DPA drilled petrous apex; IPS
inferior petrosal sinus; BA basilar artery; VI 6th cranial nerve; AICA anterior inferior
cerebellar artery; P pons; V 5th cranial nerve

Cadaveric dissection image taken with a 70-degree endoscope. The right internal
auditory canal (IAC) can be clearly visualized with the meatal segment of the anterior
inferior cerebellar artery (AICA) entering the meatus. This vessel then loops between
the facial (CN VII) and vestibulocochlear nerves. CN, cochlear nerve; CN V, trigeminal
nerve.

The anterior inferior cerebellar artery, lying between
the auditory and facial nerves, is found in 38% of cases.
5 Trigeminal nerve
7 Facial nerve
8 Vestibulocochlear nerve

Artist’s renderings showing posterior view of
the left IAM. ( a ) Subarcuate artery penetrates the dura of
the subarcuate fossa near the IAM. The labyrinthine artery
enters the meatus with the vestibulocochlear and the facial
nerves. ( b ) Laterally convex loop of the AICA is embedded
in the dura covering the subarcuate fossa, where it
gives off the subarcuate artery. ( c ) AICA loop is embedded
in the dura and bone ( arrow ) surrounding the subarcuate

fossa. ( d ) Dura over the subarcuate fossa has been incised,
and the dura with the adherent loop is dissected free from
the subarcuate fossa in preparation for opening the IAM.
( e ) Dura over the subarcuate fossa has been incised and
remains attached to the artery. The bone surrounding the
embedded AICA loop is removed with a 2-mm diamond
drill to displace the artery medially for exposure of the
IAM (From Tanriover and Rhoton [ 50 ] )

The LA usually originates from the
AICA, rarely directly from the BA.

https://www.facebook.com/entdissect
ionpg/posts/852889001461081
• The subarcuate artery arises from the anterior inferior cerebellar
artery(AICA-from the Basilar Artery) and does not supply the
labyrinth.
It is located between the anterior and posterior crura of the
superior semicircular canal passing through the petro mastoid
canal.
This endoscopic view shows the posterior relationship to the
AFB(acousticofacial bundle).
• On CT it can be easily be mistaken for a fracture line.
Radiologic classification (Migirov et al 2007):
type I - invisible
type II - less than 0.5 mm width
type III - 0.5-1 mm width
type IV - greater than 1 mm width
• This artery is commonly encountered during labyrinthectomy.

Labyrinthine artery / subarcuate artery
Labyrinthine artery Subarcuate artery

PICA passes between two bundles of 12th nerve
The endoscope is focusing on the hypoglossal nerve area. The posterior inferior cerebellar artery arises
from the vertebral artery in the background, and runs between the two bundles of the hypoglossal nerve.

PICA can be seen running between the vagus (CN X)

PICA can be seen running between spinal and cranial portions of the accessory
nerves (CN XI – S, CN XI – C).
Endoscopic lateral skull
base
Endoscopic anterior
skull base
Lateral skull base – far
lateral approach

PICA passes between two bundles of 12th nerve &
between two roots of 11th nerve
Cadaveric dissection image demonstrating the posterior inferior cerebellar artery (PICA) running
between the vagus (CN X) and the cranial accessory nerve rootlets (CN XI-C) at the position where
the nerves exit the brainstem. CN VII, facial nerve; CN VIII, vestibulocochlear nerve; NI, nervus
intermedius; CN IX, glossopharyngeal nerve; CN XI-S, spinal accessory nerve
The tip of the endoscope lies between the
acousticofacial nerve bundle and the anterior
inferior cerebellar artery. The posterior inferior
cerebellar artery arises from the vertebral artery,
runs between the root fibers of the hypoglossal
nerve, and forms a loop below the roots of the
lower cranial nerves, before coursing in a posterior
direction.

11th nerve behind left vertebral artery at cervico-medullary junction – listen
lecture at 23.25 min in this Prof. Amin Kassam video
https://www.youtube.com/watch?v=QoMCqwJ6Ke0
Through anterior skull base
approach
Through endoscopic lateral skull
base approach – The entrance of
the vertebral artery is the
boundary between the foramen
magnum and the spinal part of
the accessory nerve.

The accessory nerve (XI) is closely related to the vertebral artery (VA) at the point of
dural entrance. Note the dura attached to the artery at this level.
Endoscopic lateral skull base
approach

The accessory nerve (XI) is closely related to the vertebral artery (VA) at the
point of dural entrance. Note the dura attached to the artery at this level.
In far lateral approach

C2 nerve root below the 11th nerve
in posterior triangle clearance in SLD
the C2 nerve root is seen crossing
the vertebral artery (VA).

Superior Cerebellar Artery [ SCA ]

SCA in enlarged translabyrinthine
approach

Endoscopic lateral skull base [ note 2
branches of SCA – may present from
the origin itself ]

3rd nerve is sandwiched between posterior cerebral artery & superior
cerebellar artery [ note 2 branches of SCA – may present from the
origin itself ]
base
base

3rd nerve is sandwiched between posterior cerebral artery &
superior cerebellar artery
base
Through endoscopic anterior
skull base

3rd nerve is sandwiched between posterior cerebral
artery & superior cerebellar artery
base
Through endoscopic anterior
skull base

See the basilar artery, PCA,SCA.....through
endoscopic 3rd ventriculostomy

0° endoscope. In the next pictures the retrosellar area is
presented when an endoscope is inserted behind the pituitary
stalk and orientated downwards (arrows). The dorsum sellae is
outlined with a dotted line. - From Atlas of Endoscopic Anatomy
for Endonasal lntracranial Surgery ; Paolo Cappabianca

30° endoscope. After the introduction of a downward orientated
endoscope behind the dorsum sellae the basilar tip is visualized.
PCoA = posterior communicating artery, SCA = superior
cerebellar artery, P1-P2 = posterior cerebral artery.

30° endoscope. Right side. closer view. PCoA =
posterior communicating artery. SCA = superior
cerebellar artery. P1 = posterior cerebral artery.

30° endoscope. Left side. closer view. SCA = superior
cerebellar artery. P1-P2 = posterior cerebral artery.
PCoA = posterior communicating artery.

Posterior cerebral artery [ P1 & P 2 ]

P1 in relation to 3rd nerve P2 in relation to 3rd nerve

3rd nerve is sandwiched between posterior
cerebral artery [ PCA ] & superior
cerebellar artery [ SCA ]

Right supraorbital approach (0 optic). 1 Diaphragma sellae, 2 cn II, 3 optic
tract, 4 ICA, 5 A1, 6 M1, 7 C. N.III, 8 anterior petroclinoid fold, 9 anterior
clinoid process.
A Optocarotid window,
B window between ICA and cn III –I think B
is nothing but posterior clinoid process
C window lateral of cn III
Right supraorbital approach (30 optic).
Window between ICA and cn III : 1
tuber cinereum, 2 left P1, 3 left cn III, 4
BA, 5 right P1, 6 right SCA, 7 right cn III

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