Clivus 360°

Clivus 360°
21-12-2016
10.51 pm

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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Sphenoid osteum present at the juction of upper 2/3rd
& lower 1/3rd junction of Superior turbinate – this
became very useful to me in extensive fungal sinusitis
with polyposis & bleeding.

Three sequential indentations are made with the blunt end of the 4-mm
microdebrider blade starting at the medial upper limit of
the posterior bony choana and moving directly superiorly medial to the cut
edge of the superior turbinate.

Both clivus & petrous bone devided
into three 1/3rds

Clivus
1. Upper Clivus
2. Mid Clivus
3. Lower Clivus

One neurosurgeon classified into 4 quadrants like this

The “Ventral” Rule of Three - 3 turbinates codes to
upper,middle, lower Clivus ...

Pneumatization of the sphenoid sinus

In conchal sphenoid surgical landmarks –
1. posterior end of vomer or
keel of sphenoid tells about
the position of pituitary
2. lateral boarder of
posterior choana [ or MPP
]tells about paraclival carotid
& sellar carotid C-SHAPE
convex is lateral to this line
3. posterior lower boarder of
vomer is at the junction of
middle & lower 1/3rd clivus &
it is exactly at foramen
lacerum –my understanding

Accoding to literature of lateral skull base - by Prof. Mario sanna -
1. Upper clivus – Upto 6th nerve entry dorello’s canal (petro-clival junction)
2. Middle clivus – from 6th nerve to jugular foramen
3. Lower clivus – from jugular foramen to foramen magnum
Lateral skull base Anterior skull base

According to literature of anterior skull base –
The middle third clivus (M. 1/3rd) begins at the sella floor (SF) and extends to
the floor of the sphenoid sinus (SSF), and the lower third (L. 1/3rd) extends
from the floor of the sphenoid sinus to the foramen magnum (FM).

Mid clivus is from “Floor of sella to Floor of sphenoid” – best
Mneumonic – is nothing but clivus between paraclival carotids

Cadaveric dissection demonstrating that instrumentation without adequate removal of the floor
of the sphenoid sinus results in a straight instrument being driven high into the middle third of
the clivus beneath the pituitary fossa. Removal of the floor of the sphenoid sinus (SS) will allow
access to the junction of the posterior sphenoid floor and adjacent clivus.

Cadaveric dissection in the plane between the periosteal layer of dura and
the meningeal layer of dura (MD) covering the right side of the pituitary
gland. The pituitary dentate ligaments (DL) can be clearly visualized. CS,
cavernous sinus.

Pituitary Translocation for Access to the Upper Third of the
Clivus
Cadaveric dissection of the sphenoid sinus
demonstrating the removal of bone over the
anterior genu of the intracavernous
carotid arteries, sella, tuberculum sella, and the
posterior half of the planum sphenoidale (PS).
CCA, anterior genu of the intracavernous
carotid artery; IIS, inferior intercavernous sinus;
SIS, superior intercavernous sinus; P, pituitary
gland.
Fig. 19.23 Cadaveric dissection demonstrating the
osteotomies at the base of the posterior clinoids (PC) for
separation with the body of
the dorsum sella (DS). P. CCA , posterior genu of the
intracavernous carotid artery; PCA, paraclival carotid
artery; ICCA, intracranial
carotid artery; BA, basilar artery; PL, posterior lobe of the
pituitary gland; AL, anterior lobe of the pituitary gland.

Cadaveric dissection demonstrating the osteotomies at the base of the posterior
clinoids (PC) for separation with the body of the dorsum sella (DS). P. CCA , posterior
genu of the intracavernous carotid artery; PCA, paraclival carotid artery; ICCA,
intracranial carotid artery; BA, basilar artery; PL, posterior lobe of the pituitary gland;
AL, anterior lobe of the pituitary gland.

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

Normal pituitary YELLOW in color
• Anterior & posterior lobe of pituitary

ICAc cavernous portion of the internal
carotid artery, IPS inferior petrosal sinus,
PAp petrous apex, SPCG sphenopetroclival
gulf, cVIcn cisternal segment of the
abducens nerve, gVIcn gulfar segment of
the abducens nerve, pVIcn petrosal
segment of the abducens nerve, white
asterisks dura of the posterior cranial fossa
– The gulfar segment can be identified at the
intersection of the sellar floor and the
proximal parasellar internal carotid artery
(ICA) (Barges-Coll et al. 2010 ).
Upper clivus – Upto 6th nerve entry dorello’s canal (petro-clival junction)

1. 6th N. crossing carotid at Petro-clival junction when viewing in lateral skull base - The
lateral aspect of the parasellar & paraclival carotid junction is crossed by the
abducent nerve (VI) at the entrance of both [ 6th nerve & carotid ] structures into the
cavernous sinus.
2. The gulfar segment can be identified at the intersection of the sellar floor and the
proximal parasellar internal carotid artery (ICA) (Barges-Coll et al. 2010 ).

Pregnant of upper clivus is Sella

Endoscopic view of the fl oor of the third ventricle. The dorsum sellae and the
upper premesencephalic (mammillary bodies) region are evident.
DS dorsum sellae, IR infundibular region (infundibulum), MBs mammillary
bodies, PS pituitary stalk, ThV fl fl oor of the third ventricle

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.

ENDOSCOPIC ENDONASAL PITUITARY TRANSPOSITION APPROACH TO THE
SUPERIOR CLIVUS - Rare basilar or PCA aneurysms could be accessed as well ,
though this requires significant experience and very careful patient selection.
A. Preoperative CTA showing a three-dimensional reconstruction view of a large PCA aneurysm causing
an oculomotor nerve palsy. B. Intraoperative view of the aneurysm before clipping. C. Intraoperative
view of the aneurysm after clipping. Intraoperative angiogram showing complete obliteration of the
aneurysm and patency of normal basilar apex branches.

A. Preoperative CTA showing a three-dimensional reconstruction view of a large
PCA aneurysm causing an oculomotor nerve palsy. B. Intraoperative view of the aneurysm before
clipping. C. Intraoperative view of the aneurysm after clipping. Intraoperative angiogram showing
complete obliteration of the aneurysm and patency of normal basilar apex branches.

Cadaveric dissection image taken with a 30-degree endoscope following removal of
the superior third of the clivus, visualizing the small trochlear nerve seen running
along the tentorial membrane edge.

Pituitary transposition (Upper
clivus): Take special care to identify
and preserve the
superior hypophyseal arteries.
(SHA)
Extradural:
Dissect the pituitary gland from the
remainingsellar floor and posterior
wall.
Lift the pituitary gland, expose and
drill out theposterior clinoids.
Intradural:
Open the sellar dura anteriorly and
dissect the dura from the tunica.
Transect the ligaments that join
these two layers and the inferior
hypophyseal arteries. Divide the
diahragm exposing the stalk of the
pituitary.Transpose the gland
superiorly over the chiasm.

Endoscopic view with 45º lens after pituitary transposition. MB:
mammillary bodies; PCA: posterior cerebral artery; PCoA: posterior communicating
artery; SCA: superior cerebellar artery; VA: vertebral artery; III: third cranial nerve

Lower half of paraclival carotid - caudal part, the lacerum segment of
the paraclival carotid
”The unsolved surgical problem remains the medial wall of the ICA at the level of the
anterior foramen lacerum, until now unreachable with the available surgical
approaches." - In lateral skull base by Prof. Mario sanna – this unreachable is Carotid-
Clival window which is accessable in Anterior skull base
Infrapetrous Approach
Carotid-Clival window – Mid clivus
a. Petrosal face
b.Clival face

1. Mid clivus – from floor of sella to floor of sphenoid sinus
2. From carotid-clival window we can reach petrous apex by infra-petrous approach
3. Mid clivus is in between paraclival carotids

JT = jugular tubercle separates the hypoglossal
canal from Jugular foramen

Jugular tubercle [ JT ]
AICA antero-inferior cerebellar artery, ASC anterior semicircular canal, BA basilar artery, HC
hypoglossal canal, IAC internal acoustic canal, ICAh horizontal portion of the internal carotid
artery, JT jugular tubercle, LCNs lower cranial nerves, LSC lateral semicircular canal, P pons,
PICA postero-inferior cerebellar artery, PSC posterior semicircular canal, VIcn abducens nerve,
VIIcn facial nerve, white arrow vestibolocochlear nerve

The foramen lacerum (FL) is located lateral to the floor of the sphenoid sinus
at the level of the spheno-petro-clival confuence.
JT jugular tubercle, HC hypoglossal canal –
addFig 3.78 also

Pontomedullary junction = Vertebro-basillar junction =
Junction of Mid clivus & Lower clivus = foramen lacerum area
The pontomedullary junction. The vertebral artery junction is at the level of the
junction of the inferior and midclivus. The basilar artery runs in a straight line on the
surface of the pons. The exit zones of the hypoglossal and abducent nerves are at the
same level. The abducent nerve exits from the pontomedullary junction, and ascends
in a rostral and lateral direction toward the clivus.

Very rare specimen..The vbj is far
inferior to floor of sphenoid sinus

Cadaveric dissection of the middle third of the clivus with removal of the basilar
plexus and exposing the dura. The abducens
nerves (CN VI) can be seen bilaterally as they perforate the meningeal dura and
become the interdural segments of CN VI. CS,
cavernous sinus; PCA, paraclival carotid arteries; P, pituitary gland.

See the relationship between lower boarder of posterior end of vomer &
clivus – vomer lower boarder is at junction of mid & lower clivus – my
understanding

http://www.neurosurgicalapproaches.
com/2013/08/25/

Anterior cranial fossa dura Posterior cranial fossa dura

Groove for medulla on Lower Clivus [ =
Basi Occiput ]

1. The HC divides the condylar region into the tubercular compartment
(superior) and the condylar compartment (inferior).
Tubercular compartment contains LPT lateral pharyngeal tubercle, PT
pharyngeal tubercle,
2. The SCG [Supracondylar groove] represents a reliable landmark for hypoglossal
canal (HC) identification (red arrow) (Morera et al. 2010 ) .

The tubercular compartment corresponds to the Jugular tubercle ( JT )
Line along the lateral pharyngeal tubercle [ LPT ] passes through
Jugular tubercle [ JT ] – so when you are drilling LPT in anterior skull
base you will land up on JT .
LPT lateral pharyngeal tubercle, OC
occipital condyle, PT pharyngeal
tubercle, SCG supracondylar groove
Jugular tubercle ( JT )

Line along the lateral pharyngeal tubercle [ LPT ] passes through Jugular tubercle [ JT
] – so when you are drilling LPT in anterior skull base you will land up on JT .
Red rings = hypoglossal canals , yellow
ring = pharyngeal tubercle [ PT ] , blue
rings = lateral pharyngeal tubercle [
LPT]

Line along the lateral pharyngeal tubercle [ LPT ] passes through Jugular
tubercle [ JT ] – so when you are drilling LPT in anterior skull base you will
land up on JT .
yellow ring = pharyngeal tubercle [ PT ] , blue rings = lateral pharyngeal
tubercle [ LPT] , green ring = Jugular tubercle

Hypoglossal canals
From front – through nose From back

Lower clivus devided into
1. tubercular compartment [ Above red line ]
2. condylar compartment [ Below red line ]
Hypoglossal canal present at the junction of anterior 1/3rd & posterior 2/3rd

Lower clivus + petrous bone [ base ]
Petrous
bone
devided
into three
1/3rds

Lower clivus + petrous bone [ base ] + Zygomatic bone
Petrous bone devided
into three 1/3rds

Lateral skull base view – observe the
petrous apex

Lower clivus + petrous apex in anterior skull base
1. observe the petrous apex in both views
2. hypoglossal canal medial to parapharyngeal carotid & jugular fossa

1. 3th nerve between PCA & SCA
2. 4th nerve coming from dorsal
brain stem passes above SCA [ some
times SCA has two branches]
3. 6th nerve originates at VBJ [
Vertebro-basillar junction ] . 6th
nerve may have two rootlets of
origin , one above & one below the
AICA
4. In 30 % of cases AICA passes in
between 7th & 8th nerves
5. PICA passes between two bundles
of 12th nerve & between two roots
of 11th nerve [ 11c = 11th cervical ,
11s = 11th spinal root ]
6. The exit zones of the 6th and 12th
nerves are at the same level [ same
vertical line when view from
Transclival approah ( through lower
clivus ) ]
7. 11th nerve behind left vertebral
artery at cervico-medullary junction
. 11th is closely related to the
vertebral artery (VA) at the point of
dural entrance

2. 4th nerve coming from dorsal brain
stem passes above SCA [ some times SCA
has two branches]
3. 6th nerve originates at VBJ [ Vertebro-
basillar junction ] . 6th nerve may have
two rootlets of origin , one above & one
below the AICA
4. In 30 % of cases AICA passes in
between 7th & 8th nerves
5. PICA passes between two bundles of
12th nerve & between two roots of 11th
nerve [ 11c = 11th cervical , 11s = 11th
spinal root ]
6. The exit zones of the 6th and 12th nerves
are at the same level [ same vertical line
when view from Transclival approah (
through lower clivus ) ]
7. 11th nerve behind left vertebral artery
at cervico-medullary junction . 11th is
closely related to the vertebral artery (VA)
at the point of dural entrance

2. 4th nerve coming from dorsal brain stem passes above SCA [ some times SCA has two branches]
3. 6th nerve originates at VBJ [ Vertebro-basillar junction ] . 6th nerve may have two rootlets of origin , one above & one below the AICA
4. In 30 % of cases AICA passes in between 7th & 8th nerves
5. PICA passes between two bundles of 12th nerve & between two roots of 11th nerve [ 11c = 11th cervical , 11s = 11th spinal root ]
6. The exit zones of the 6th and 12th nerves are at the same level [ same vertical line when view from Transclival approah ( through lower
clivus ) ]
7. 11th nerve behind left vertebral artery at cervico-medullary junction . 11th is closely related to the vertebral artery (VA) at the point of dural
entrance

1. Laceral carotid & jugular
tubercle & lower cranial
nerves 9th ,10th ,11th are in
the same line .
2. hypoglossal canal present
between occipital
condyle/foramen magnum &
jugular tubercle

1. Laceral carotid & jugular tubercle & lower cranial nerves 9th ,10th ,11th are in the same
saggital line .
2. hypoglossal canal present between occipital condyle/foramen magnum & jugular tubercle
3. PICA passes between two bundles of 12th nerve & between two roots of 11th nerve [ 11c =
11th cervical , 11s = 11th spinal root ] & encirlces lower cranial nerves 9th ,10th ,11th

Trans clival trans odontoid trans tubercular view of brainstem and cranial
nerves....note sharp oblique course of 6 nerve and two trunks of 12 nerve
which joins to form single trunk in hypoglossal canal...a dorsal clival branch of
meningohypophyseal trunk is seen along six nerve close to dorello
canal...AICA is seen going towards IAM.

Coronal cut – hypoglossal canal

Inferior clival line (Fernandez-Miranda et al. 2012 )
The longus capitis and rectus capitis anterior muscle attach on the inferior surface of the clivus.
Below the RCAM the occipito-cervical joint capsule lies. The area of attachement of the RCAM
has been named inferior clival line (Fernandez-Miranda et al. 2012 ) and correspond to the
SCG [supracondylar groove ] (that is a landmark for the hypoglossal canal).
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

The area of attachement of the RCAM has been named inferior clival line
(Fernandez-Miranda et al. 2012 ) and correspond to the SCG [supracondylar
groove ] (that is a landmark for the hypoglossal canal).
SCG = Supracondylar groove – is an important landmark to hypoglossal canal

When we are drilling lower clivus – lateral to
hypoglossal canal we get Jugular fossa

Jugular fossa is just lateral to
hypoglossal canal

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.

Cadaveric dissection image showing the hypoglossal nerve
exiting the hypoglossal foramen with its corresponding vein that
communicates the internal jugular vein with the basilar plexus.
HC, hypoglossal canal; CN XII, hypoglossal nerve and rootlets;
FM, foramen magnum; VA, vertebral artery; PICA, posterior
inferior cerebellar artery; BA, basilar artery; CN X, vagus nerve.

Cadaveric dissection with image taken just above the skeletonized hypoglossal canal
(HC) at the cerebellopontine angle. The anterior inferior cerebellar artery (AICA) can
be seen intimately associated with the vestibulocochlear nerve (CN VIII), facial nerve
(CN VII), and the nervus intermedius (NI). The posterior inferior cerebellar artery
(PICA) can be seen running between the vagus (CN X) and spinal and cranial portions
of the accessory nerves (CN XI – S, CN XI – C).

Cadaveric dissection image taken following dissection of the right lower third of the
clivus. As the posterior inferior cerebellar artery (PICA) courses from the vertebral
artery (VA) it frequently runs through the rootlets that make up the hypoglossal nerve
(CN XII). It may tent these rootlets as it courses to the cerebellomedullary fissure to
run intimately with the cranial nerves IX – XI. CN X, vagus nerve; HC, hypoglossal canal;
IPS, inferior petrosal sinus; BA, basilar artery; FM, foramen magnum; A. AOM, anterior
atlanto-occipital membrane.

The hypoglossal nerve do not exit with VA. It can have maximum
3 outlets. On the contrary, C1 roots exit with the VA.

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

HC = hypoglossal canal , JT= Jugular Tubercle

Transoral approach to SUPERO-MEDIAL Parapharyngeal
tumors – incision anterior to anterior pillar of tonsil

Hypoglossal is just behind the upper end of
parapharyngel carotid – very easy way to
identify 12th nerve in paraphayrngeal space
– Dr.Satish jain

FCB & JT & LCNs are at same level from anterior
to posterior
FCB = Fibrocartilago basalis , JT = Jugular tubercle , LCNs
Lower cranial nerves ( = 9th , 10th, 11th )

In infrapetrous approach there are chances of injury to 6th nerve [ in dorello’s
canal medial to paraclival carotid ] & 12th nerve

Posterior cranial fossa (jugular and hypoglossal areas); vision obtained with a 45° endoscope
through a clival window
AICA anteroinferior cerebellar artery, BA basilar artery, IO inferior olive, LA labyrinthine artery, PCA posterior cerebral artery, PcomA
posterior communicating artery, PICA posteroinferior cerebellar artery, POV preolivary vein, RPA recurrent perforating artery, SCA
superior cerebellar artery, SPV superior petrosal vein, VA vertebral artery, IIIcn oculomotor nerve, Vcn trigeminal nerve, VIcn abducens
nerve, VIIcn facial nerve, VIIIcn vestiboloacoustic (statoacoustic) nerve, IXcn glossopharyngeal nerve, Xcn vagus nerve, XIIcn hypoglossal
nerve
The LA usually originates from the AICA, rarely directly from the BA. It feeds the inner ear. AICA and SCA course through the
cerebellopontine cistern. AICA enters the lower part of cerebellopontine cistern and it usually bifurcates into its rostral and caudal trunks
within the cistern. PICA origins from the VA, near the inferior olive, and passes posteriorly around the medulla. It could pass rostral, caudal
or even between the rootlets of the hypoglossal nerve. RPA(s) are arteries that present a recurrent course and reach the root entry zone of
the VII and VIII cns. They send branches to these nerves and to the brainsterm around the root entry zone.

Intracranial hypoglossal region. Anterior endoscopic transnasal-transclival vision is
compared with a posterior retrosigmoid endoscopic one
JF jugular foramen, JT jugular tubercle, IO inferior olive, PICA posteroinferior cerebellar artery, VA vertebral artery, IXcn
glossopharygeal nerve, Xcn vagus nerve, XIcnCR cervical roots of accessory nerve, XIcnSR spinal roots of accessory nerve,
XIIcn hypoglossal nerve
Cranial nerves IX and X present a close relationship with the fi rst portion of the PICA. They are protected by the arachnoid
membrane (Roche et al. 2008 ) . The roots of cranial nerve XIcn from the spine pass through the foramen magnum posterior
to the vertebral artery. Within the hypoglossal canal, XIIcn is surrounded by a venous plexus and dural and arachnoid
sheets. Branches of the ascending pharyngeal artery coursing through the hypoglossal canal are seen in about 50 % of cases
(Lang 1995 ) . Also branches from the posterior meningeal artery have been described (Janfaza and Nadol 2001 ). The
transcisternal vein to the area of the JF can be seen. Also, veins to the hypoglossal canal can be present. The hypoglossal
nerve do not exit with VA. It can have maximum 3 outlets. On the contrary, C1 roots exit with the VA.

Nerves and vessels of the posterior cranial fossa. (a) Basilar tip region, endoscopic view (b) Right cerebellopontine angle, endoscopic view from
anterior. (c) Right laterobulbar region, endoscopic intracranial view. (d) Three-dimensional reconstruction of the posterior cranial fossa. AICA,
anteroinferior cerebellar artery; BA, basilar artery; DV, Dandy’s vein; Fl, flocculus; IIIcn (CS), intracavernous portion of the oculomotor nerve; IIIcn,
oculomotor nerve; IO, inferior olive; IXcn, glossopharyngeal nerve; IX–X, glossopharyngeal and vagus nerves; LA, labyrinthic artery; LPMVN,
lateropontomesencephalic vein network; P1, posterior cerebral artery (first segment); P2, posterior cerebral artery (second segment); PcomA,
posterior communicating artery; PICA, posteroinferior cerebellar artery; POV, preolivary vein; PV, peduncular vein; RPA, recurrent perforating
artery; SCA, superior cerebellar artery; SPV, superior petrosal vein; TGAs, thalamogeniculate arteries; TPAs, thalamoperforating arteries; VA,
vertebral artery; Vcn, trigeminal nerve; VIcn, abducens nerve;
VII–VIIIcn, facial nerve and vestibuloacoustic nerve; VIIcn, facial nerve; VIIIcn, vestibuloacoustic nerve; X/XIcn, vagus and accessory nerves; XIcn,
accessory nerve; XIIcn, hypoglossal nerve.

TPV & LAPMVs , PMedSV unite to form SPV
AICA anteroinferior cerebellar artery, BA basilar artery, LPMVN
lateropontomesencephalic venous network, PBs pontine branches, PcomA posterior
communicating artery, PICA posteroinferior cerebellar artery, PMedSV
pontomedullary sulcus vein, SCA superior cerebellar artery, SPV superior petrosal
vein, TPAs talamoperforating arteries, TPV transverse pontine vein, IIIcn oculomotor
nerve, Vcn trigeminal nerve, VIcn abducens nerve, VIIcn facial nerve, VIIIcn vestibulo-
cochlear (statoacoustic) nerve

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.

Transcochlear approach leads to Mid clivus above foramen
lacerum [ FL ] & lower clivus below foramen lacerum [ FL ]
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 [ Mid clivus above FL & lower clivus below FL ] in these
photos after drilling of cochlea

Note CL [Mid clivus above FL & lower clivus below FL ] 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 [Mid clivus above FL & lower
clivus below FL ] in these photos after
drilling of cochlea
BT- basal turn of the cochlea Fig. 8.34 The bone medial to the
internal carotid artery (ICA) has been
drilled and the clivus bone (CL) has
been reached. FN Facial nerve,
JB Jugular bulb

drilling of cochlea
Note cochlear aqueduct [ CA ]
Here ICA is vertical part of carotid infront
to cochlea – this is not paraclival carotid

drilling of cochlea

drilling of cochleaNote the contralateral vertebral
artery [ CVA ] in below photo

Mid clivus above FL & lower clivus [ CL ]
below FL in Infratemporal fossa approach

ITFA with Transcondylar [ = TC ]
Transtubercular [ = TT ] approach
Here Transcondylar is through Occipital Condyle ;
Transtubercular is through Jugular tubercle &
lateral pharyngeal tubercle

Endoscopic endonasal view of a cadaveric dissection showing transection of the right eustachian tube (ET)
attachment to foramen lacerum (FL). The hypoglossal nerve (XII) enters the hypoglossal canal just deep to
the ET and separates the occipital condyle (OC) and the jugular tubercle (JT). (BA, basilar artery; ICA,
internal carotid artery [paraclival segment]; IPS, inferior petrosal sinus; VN, vidian nerve.) B. Endoscopic
endonasal view of cadaveric dissection showing the parapharyngeal internal carotid artery (ICA) and
jugular foramen (JF) following transection and removal of the eustachian tube. (BA, basilar artery; IPS,
inferior petrosal sinus; FL, foramen lacerum; JT, jugular tubercle; OC, occipital condyle; XII, hypoglossal
nerve.)

Note 12th nerve in between JT ( Jugular tubercle ) & OC
( Occipital condyle ) in both lateral & anterior skull base

ITF-A + Transcondylar, transtubercular extension improves
posteroinferolateral and medial exposure.

Comparison of classic ITFA (zone delimited by the red line) and ITFA with
transcondylar–transtubercular extension (zone delimited by the blue line). * jugular
process of the occipital condyle , CF carotid foramen , DR digastric ridge , JF jugular
foramen , MT mastoid tip . Note hypoglossal nerve at anterior 1/3rd & middle 1/3rd
junction .

Extreme lateral extension [ Far-lateral – Transcondylar ]
approach
AFL anterior foramen lacerum , C1 atlas , CO cochlea , ICA internal carotid artery , IJV internal
jugular vein , Lv vein of Labbé , M mandible , mma middle meningeal artery
OC occipital condyle , pc clinoid process , pp pterygoid plate , sph sphenoid sinus , sps superior
petrosal sinus , TA transverse process of the atlas , TS transverse sinus , V2 maxillary branch of
the trigeminal nerve , V3 mandibular branch of the trigeminal nerve , za zygomatic arch , VA
vertebral artery , VII facial nerve , IX glossopharyngeal nerve , XI spinal accessory nerve , XII
hypoglossal nerve
Far-lateral approach further extends
posteroinferolateral exposure
Schematic illustration of the
extreme lateral approach (ELA)

For mid clivus – transcochlear
approah
&
For lower clivus – far lateral /
transcondylar approach OR
ITF-A + TC + TT
From decision making of Mario sanna lateral
skull base book

The 6 linear landmarks of the PCF superimposed on a midsagittal T1-weighted MR
imaging from a patient with CMI: herniation (HR), McRae line (MC), clivus (CL), Twining
line (TW), cerebellum (CR), and supraocciput (SO).
http://www.ajnr.org/content/34/9/1758.figures-
only?cited-by=yes&legid=ajnr;34/9/1758

Clivus 360°

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Clivus 360°