10 triangles 360°

10 Triangles 360°
26-11-2015
10.06pm

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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10 Triangles = 4 Cavernous Sinus Triangles + 6 Middle Fossa
Triangles
4 Cavernous Sinus Triangles
1. Clinoidal (Anteromedial) Triangle
2. Oculomotor (Medial or Hakuba's) Triangle
3. Supratrochlear (Paramedian) Triangle
4. Parkinson's (Infratrochlear) Triangle
6 Middle Fossa Triangles
1. Anteromedial (Mullan's) Triangle
2. Anterolateral Triangle
3. Posterolateral (Glasscock's) Triangle
4. Posteromedial (Kawase's) Triangle
5. Inferolateral Triangle
6. Inferomedial Triangle

Cavernous Sinus Triangles
1. Clinoidal (Anteromedial) Triangle
· Borders:
1. Optic Nerve
2. Occulomotor Nerve
3. Tentorial Edge
· Contents:
1. Anterior Clinoid Process
2. Clinoidal ICA
2. Oculomotor (Medial or Hakuba's) Triangle
· Borders:
1. Anterior petroclinoid dural fold.
2. Posterior petroclinoid dural fold.
3. Interclinoid dural fold.
· Contents:
2. Horizontal Segment of ICA

cavernous Roof has - two triangles:
1. clinoid (anterior)
2. oculomotor (posterior)
ACP anterior clinoid process, APCF anterior petroclinoid fold, DS dorsum sellae, ICF interclinoid
fold, PF pituitary fossa, PLL petrolingual ligament (inferior sphenopetrosal ligament),
PPCF posterior petroclinoid fold, PS planum sphenoidale, SSPL superior sphenopetrosal
ligament (Gruber’s ligament), TS tuberculum sellae, black asterisk middle clinoid process , CSR
cavernous sinus roof , white asterisk oculomotor nerve
If the Gruber’s ligament is ossificated it is called Wegener’s
bridge.

Schematic diagram of cavernous sinus roof

1. LDR=COM
2. 3rd nerve below COM after ACP drilling
3. COM present below ACP

Anterior clinoid drilling videos in FTOZ
[ neurosurgery skull base ]
1. https://www.youtube.com/watch?v=wO2cWHiOdO0
2. https://www.youtube.com/watch?v=4dkQY3zxJHU
3. https://www.youtube.com/watch?v=vd4_lPVIUvE
4. https://www.youtube.com/watch?v=_dvYB1InGMc
5. https://www.youtube.com/watch?v=83_VuKHXOmQ
6. https://www.youtube.com/watch?v=0KwBhTqNXA4
7. https://www.youtube.com/watch?v=pCURjQ83HzU
8. https://www.youtube.com/watch?v=DNIy0L3oFgY
9. https://www.youtube.com/watch?v=GT4eBB2x58Q
10. https://www.youtube.com/watch?v=OS4Mc0X8tlU
11. https://www.youtube.com/watch?v=_xq9e3p1cc4

Clinoid has three roots of attachment
1. Anteriror root = Anterior Clinoid process attachemnt to planum
2. Posterior root = Optic struct = L-OCR
3. 3rd root = Anterior Clinoid process attachment to Lesser wing of sphenoid

Three surgical attachments of the right anterior clinoid process.
(a, sphenoid ridge; b, roof of optic canal; c, optic strut.)

1. SOF present between two structs
2. OS [ optic struct separates optic canal from SOF ]

SOF & IOF are in C-shape when you
see through orbit /maxilla/nose

Anterior clinoid process [ ACP ] has 3 roots of attachements :
1. Anterior root – ACP attachment to sphenoid planum medial
to falciform ligament
2. posterior root = OS = L-OCR
3. 3rd root to lesser wing of sphenoid

Optic strut [ OS ] =
L-OCR
[ Pneumatisation
of OS ] =
Posterior root of
Anterior clinoid
process [ ACP ]
OS = L-OCR =
posterior root of
ACP

1. Surpa-optic pneumatisation starts from anterior root of ACP & goes to ACP
, infra-optic pneumatization starts in posterior root of ACP [ = OS = L-OCR ] &
may goes into ACP
2. In ACP drilling if there is pneumatization we will directly open into sphenoid
so we have to plug with fat after ACP drilling in neurosurgical skull base

Surpa-optic pneumatisation starts from anterior root of ACP & goes to
ACP , infra-optic pneumatization starts in posterior root of ACP [ = OS
= L-OCR ] & may goes into ACP

The lower dural ring is given by the COM, that lines the inferior surface of the ACP. It
can be visible, through a transcranial route, only by removing the ACP. The lower dural
ring is also called Perneczky’s ring. Medially the COM blends with the dura that lines
the carotid sulcus (Yasuda et al. 2005 )
Endoscopic supraorbital view of the anterior clinoid region. The right
portion of the planum sphenoidale is seen from above. The anterior clinoid process
has been removed. Vision obtained through a right supraorbital approach with a 30°
down-facing lens focusing on the cavernous sinus roof.
ACP anterior clinoid process (removed), COM carotid oculomotor membrane, ICAc
cavernous portion of the internal carotid artery, ICAi intracranial portion of the
internal carotid artery, OA ophthalmic artery, ON optic nerve, LWS lesser wing of the
sphenoid, IIIcn oculomotor nerve

The lower dural ring is given by the COM [ Carotid-oculomotor
membrane ] , that lines the inferior surface of the ACP. It can be visible, through a
transcranial route, only by removing the ACP. The lower dural ring is also called
Perneczky’s ring. Medially the COM blends with the dura that lines the carotid sulcus
(Yasuda et al. 2005 )
Endoscopic supraorbital view with a 30°
down-facing lens -The right portion of the
planum sphenoidale is seen from above.
Right side

COM = carotico–oculomotor
membrane
Superior view of the right
ophthalmic artery in the right paraclinoid area. The anterior
clinoid process, which is situated on the lateral side of the
optic nerve, has been removed. The optic canal has been
unroofed, the optic sheath opened, and the optic nerve elevated
to expose the origin of the ophthalmic artery under the
medial half of the optic nerve. In the optic canal, the ophthalmic
artery courses within the dural sheath of the optic
nerve. It exits the optic canal and the optic sheath to enter the
orbital apex on the inferolateral aspect of the optic nerve.
The oculomotor nerve courses just below the dura covering
the lower margin of the anterior clinoid process. The clinoid
segment of the internal carotid artery is the segment that
courses on the medial side of the anterior clinoid process and
is exposed by removing the anterior clinoid process. The
upper edge of the clinoid segment is defined by a dural ring,
called the upper dural ring, formed by the dura, which
extends medially from the upper surface of the anterior clinoid
process. The lower edge of the clinoid segment is
defined by the lower dural ring, which is formed by the dura
that line1 the lower surface of the anterior clinoid process and
separates the clinoid process from the upper surface of the
oculomotor nerve and continues medially as the carotid-
oculomotor membrane to surround the carotid artery The
ophthalmic
artery usually arises just above the clinoid segmenl
However, it may infrequently arise from the clinoid segment.

Fig. 22.31 Clinoidal and oculomotor triangles
have been opened and the anterior clinoid removed
up to the optic strut, exposing the carotido-
oculomotor membrane. The optic strut has two
neural-facing surfaces( yellow dotted lines) and one
vascular-facing surface (red dotted line). CN: cranial
nerve; Falc.: falciform; ICA: internal carotid artery;
Inf.:inferior; Lig.: ligament; Pet.: petrosal; V1: first
division; V2: second division; V3: third division of
trigeminal nerve.
ACP anterior clinoid process, APCF anterior
petroclinoid fold, DS dorsum sellae, ICF
interclinoid fold, PF pituitary fossa, PLL
petrolingual ligament (inferior sphenopetrosal
ligament), PPCF posterior petroclinoid fold, PS
planum sphenoidale, SSPL superior
sphenopetrosal ligament (Gruber’s ligament), TS
tuberculum sellae, black asterisk middle clinoid
process

The optic strut has two neural-
facing surfaces( yellow dotted
lines) and one vascular-facing
surface (red dotted line).
[ COM= Lower dural ring – Carotico-
Occulomotor membrane seperates
3rd N from Clinoidal carotid ]

3rd & 4th nerves below optic nerve

Roof - two triangles:
1. clinoid (anterior)
2. oculomotor (posterior)
Anterior skull base approach – see
clinoid triangle in below photo

Oculomotor triangle [ 3rd N. , 4th N. & Pcom ] is seen in Posterosuperior
compartment [ virtual compartment ] of cavernous sinus –better
understanding see cavernous sinus PPT
http://www.slideshare.net/muralichandnallamothu/cavernous-sinus-360

Note the aperture for 3rd nerve & 4th nerve anterior & posterior to
posterior petro-clival fold [ PPCF ]

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

The trochlear nerve in 80 % of cases enters at the posterior end
of the roof of the cavernous sinus ( CS ) and in 20 % at the lower
surface of the TC (Lang 1995 ) .
80 % of cases enters at the posterior end
of the roof of the cavernous sinus ( CS ) ---
---Note the aperture for 3rd nerve & 4th
nerve anterior & posterior to posterior
petro-clival fold [ PPCF ]
in 20 % at the lower surface of
the TC (Lang 1995 )

The trochlear nerve is divided into 5 segments: cisternal, tentorial,
cavernous, fissural ( in superior orbital fissure ) and orbital.
The cisternal segment exits the midbrain and courses through the
quadrigeminal and ambiens cisterns towards the TC. The tentorial segment
starts when the nerve pierces the TC, usually posterior to the postero-lateral
margin of the oculomotor triangle. This segment ends at the level of the
anterior petroclinoid fold. This portion is in close relationship with the
spheno-petro-clival venous gulf and the petrous apex (Iaconetta et al. 2012 ).

The TC [ tentorium cerebelli ], with the trochlear nerve inside,
can be visualized passing inferiorly to the IIIcn.
endoscopic transclival view

1. In the posterior part of the CS the trochlear nerve is below the oculomotor nerve,
while anteriorly it turns upward and becomes the most superior structure of the CS
(at the level of the optic strut) (Iaconetta et al. 2012 ) .
2. Trochlear nerve is always
superior to V1.

L-OCR – Triangle
1. Upper boarder – Optic nerve & Opthalmic artery
2. Posterior boarder – Clinoidal carotid
3. Lower boarder – 3rd N. [ COM – Carotico-Occulomotor
membrane seperates 3rd N from Clinoidal carotid ]
[ 6th N. & 4th N. & V1 present inferior to 3rd N. ]

Oculomotor triangle is seen [ 3rd N. , 4th N. & Pcom ] seen in
Posterosuperior compartment [ virtual compartment ] of cavernous sinus –
better understanding see cavernous sinus PPT

Antero-inferior compartment [ virtual compartment ] of cavernous sinus
– for better understanding see cavernous sinus PPT
1. The abducens nerve and the sympathetic plexus around the intracavernous carotid artery are the only
nerves which have a real intracavernous course.
2. The anteroinferior and lateral compartments contain the abducens nerve and, as surgical corridors, they
are exposed to the risk of injury to the VIth nerve.
BS basisphenoid, CS cavernous sinus, CSd dura of the cavernous sinus, ET eustachian tube, ICAc cavernous portion of the internal carotid
artery, ICAh horizontal portion of the internal carotid artery, ICAp parapharyngeal portion of the internal carotid artery, ILT inferolateral
trunk, LVPM levator veli palatini muscle, MHT meningohypophyseal trunk, PAp petrous apex, PCFd posterior cranial fossa dura and
periosteum, PG pituitary gland, TVPM tensor veli palatini muscle, VN vidian nerve, IIIcn oculomotor nerve, IVcn trochlear nerve, V1 fi rst
branch of the trigeminal nerve, V2 second branch of the trigeminal nerve, V3 third branch of the trigeminal nerve, VIcn abducens nerve,
XIIcn hypoglossal nerve, white asterisks sympathetic fi bres
connecting the VIcn

Cavernous Sinus Triangles
3. Supratrochlear (Paramedian) Triangle
· Borders:
2. Trochlear Nerve
3. Tentorial Edge
· Contents:
1. Meningohypophyseal Trunk
4. Parkinson's (Infratrochlear) Triangle
· Borders:
1. Trochelar Nerve
Middle_fossa_triangles
Clinoidal (Anteromedial) Triangle 2
2. Opthalmic Division (V1)
3. Tentorial Edge
· Contents:
1. Cavernous ICA
2. Abducens Nerve

Supra-trochlear triangle Infra-trochlear triangle

http://www.slideshare.net/INUB/endoscopic-anatomy-and-approaches-of-the-cavernous-sinus-
cadaver-study - Endoscopic view of the right cavernous sinus and neurovascular relations,
demonstrating the ‘S’ shaped configuration formed by the oculomotor, the abducens and the
vidian nerves. III oculomotor nerve, V1 ophthalmic nerve, V2 maxillary nerve, V3 mandibular nerve, VI
abducens nerve, C clivus, ICA-Sa anterior bend of the internal carotid artery–parasellar segment, ICA-Sp
posterior bend of the internal carotid artery–parasellar segment, ICA-C paraclival segment of the
internal carotid artery, ICA-L lacerum segment of the internal carotid artery, ICA-P petrous segment of
the internal carotid artery, PG pituitary gland, VC vidian canal, VN vidian nerve
6th nerve is parallel to V1 – in the
same direction of V1

6th nerve is parallel to V1 – in the same direction of V1

STA is devided into 1. Supra-Trochlear triangle
2. Infra-Trochlear triangle

http://www.slideshare.net/INUB/endoscopic-anatomy-and-approaches-of-the-
cavernous-sinus-cadaver-study- Endoscopic view of the right cavernous sinus and its
neurovascular relations, demonstrating the triangular area formed by the medial
pterygoid process laterally, the parasellar ICA medially and the vidian nerve inferiorly
at the base. III oculomotor nerve, V1 ophthalmic nerve, V2 maxillary nerve, V3
mandibular nerve, VI abducens nerve, C clivus, ICA-Sa anterior bend of the internal
carotid artery–parasellar segment, ICA-Sp posterior bend of the internal carotid
artery–parasellar segment, ICA-C paraclival segment of the internal carotid artery, ICA-
L lacerum segment of the internal carotid artery, ICA-P petrous segment of the
internal carotid artery, PG pituitary gland, VC vidian canal, VN vidian nerve

1.Supra Trochanteric & Infratrochanteric Triangles
2. Upper & lower dural rings

http://www.slideshare.net/INUB/endoscopic-anatomy-and-approaches-of-the-cavernous-
sinus-cadaver-study -Endoscopic view of the right cavernous sinus showing its neurovascular
relations and the main anatomic areas. III oculomotor nerve, V1 ophthalmic nerve, V2
maxillary nerve, V3 mandibular nerve, VI abducens nerve, C clivus, ICA-Sa anterior bend of
the internal carotid artery–parasellar segment, ICA Sp posterior bend of the internal carotid
artery–parasellar segment, ICA-C paraclival segment of the internal carotid artery, ICA-L
lacerum segment of the internal carotid artery, ICA-P petrous segment of the internal carotid
artery, PG pituitary gland, VC vidian canal, VN vidian nerve, STA superior triangular area, SQA
superior quadrangular area, IQA inferior quadrangular area

http://www.slideshare.net/INUB/endoscopic-anatomy-and-approaches-of-the-
cavernous-sinus-cadaver-study - Endoscopic view (a), and a drawing (b) of the right
cavernous sinus demonstrating its neurovascular relations. c A drawing of the right
cavernous sinus demonstrating the exposure of the trochlear nerve after retracting
the oculomotor nerve. III oculomotor nerve, IV trochlear nerve, V1 ophthalmic nerve,
VI abducens nerve, ICA internal carotid artery, OA ophthalmic artery, OCh optic
chiasm, ON optic nerve, PG pituitary gland

http://www.slideshare.net/INUB/endoscopic-anatomy-and-approaches-of-the-cavernous-sinus-
cadaver-study - Endoscopic view of the right cavernous sinus and neurovascular relations,
demonstrating the ‘S’ shaped configuration formed by the oculomotor, the
abducens , carotid nerve ( paraclival carotid ) and the vidian nerves.
III oculomotor nerve, V1 ophthalmic nerve, V2 maxillary nerve, V3 mandibular nerve, VI abducens
nerve, C clivus, ICA-Sa anterior bend of the internal carotid artery–parasellar segment, ICA-Sp posterior
bend of the internal carotid artery–parasellar segment, ICA-C paraclival segment of the internal carotid
artery, ICA-L lacerum segment of the internal carotid artery, ICA-P petrous segment of the internal
carotid artery, PG pituitary gland, VC vidian canal, VN vidian nerve
VI nerve is parallel & medial to V1 –
in the same direction of V1 [
Mneumonic – VI & V1 in same
direction ]

Meningo-hypophyseal trunk & carotid nerve

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 ).

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 ).

Carotid nerve –
part of S’ shaped configuration formed by the
oculomotor, the abducens , carotid nerve (
paraclival carotid ) and the vidian nerves.

VI nerve is parallel & medial to V1 – in the same direction of V1 [ Mneumonic – VI &
V1 in same direction ]

3. lower dural ring is COM ( Carotico-Oculomotor Membrane )
In the below picture superior
cerebellar artery mislabelled as
meningohypophyseal trunk .

3. lower dural ring is COM ( Carotico-Oculomotor Membrane )
Right lateral view of the inferolateral trunk or artery of the inferior
cavernous sinus, a branch of the horizontal part of the internal carotid
artery (ICA) that provides blood to the dura of the lateral wall of the
cavernous sinus as well as to the cranial nerves running along the lateral
wall of the cavernous sinus. The trochlear nerve has been displaced
inferiorly and the oculomotor nerve has been displaced superiorly. A
recurrent branch from the inferolateral trunk is observed in this specimen.
This branch heads back toward the tentorium cerebelli forming the so-
called marginal tentorial artery. 1=horizontal segment of cavernous ICA,
2=clinoid segment of ICA, 3=supraclinoid ICA, 4=inferolateral trunk or
artery of the inferior cavernous sinus, 5=marginal tentorial artery, 6=optic
nerve, 7=oculomotor nerve, 8=trochlear nerve, 9=ophthalmic nerve,
10=abducent nerve, and 11=sphenoid sinus.

1. In the posterior part of the CS the trochlear nerve is below the oculomotor nerve, while
anteriorly it turns upward and becomes the most superior structure of the CS (at the level of
the optic strut) (Iaconetta et al. 2012 ) .
2. Trochlear nerve is always superior to V1.

From lateral skull base - The lateral aspect of the parasellar &
paraclival carotid junction is crossed by the abducent nerve (VI)

The abducens nerve in most case is a single trunk throughout its entire course (Zhang et al. 2012 ) . There
are some variants, and one should be aware that the nerve can fuse with the oculomotor nerve for all its
course (Zhang et al. 2012 ) . The surgeon must be prepared to face other rare variations, such as different
fasciculi within the CS. Globally, the incidence of a duplicated abducens nerve has been reported, ranging
from 8 % to 18 % (Nathan et al. 1974 ; Iaconetta et al. 2001 ; Ozveren et al. 2003 ) . In the prepontine cistern,
when the duplication is present, AICA passes through the bundles. Furthermore, the incidence of a
bilaterally duplicated nerve has been reported as frequently as 8 % of the time (Nathan et al. 1974 ; Ozveren
et al. 2003 ) . The abducens nerve can pass above the Gruber’s ligament in 12 % of cases (Lang 1995 ) .
Endoscopic vision of the cavernous sinus. Vision obtained through a right supraorbital
approach with a 30° down-facing lens focusing on the cavernous sinus
ICAc cavernous portion of the internal carotid artery, lwCS lateral wall of the cavernous sinus, SCA
superior cerebellar artery, IIIcn oculomotor nerve, IVcn trochlear nerve, Vcn root of the trigeminal nerve,
VIcn abducens nerve, blue arrow Gruber’s ligament, white asterisk Dorello’s canal.

Blue arrow in Left picture ; * in Right
picture - Gruber’s ligament

Middle Fossa Triangles
5. Anteromedial (Mullan's) Triangle
· Borders:
1. Opthalmic Nerve (V1)
2. Maxillary Nerve (V2)
3. A line connecting Superior Orbital Fissure and Foramen Rotundum
· Contents:
1. Sphenoid Sinus
2. Opthalmic Vein
3. Abducens Nerve
6. Anterolateral Triangle
· Borders:
1. Maxillary Nerve (V2)
2. Mandibular Nerve (V3)
3. A line connecting Foramen Rotundum and Foramen Ovale
· Contents:
1. Lateral sphenoid wing
2. Spenoid emmissary vein
3. Cavernous-Pterygoid Venous Anastamosis

The space between V1 & V 2 and V2 & V3
is sphenoid sinus
Middle cranial fossa approach –
the nerve between V2 & V3 is VN
Anaterior skull base

JNA DISSECTION IN ANTEROLATERAL TRIANGLE .. NOTE V3

VI nerve is parallel & medial to V1 – in the same
direction of V1 [ Mneumonic – VI & V1 in same
direction ]

7. Posterolateral (Glasscock's) Triangle
· Borders:
2. Greater Superficial Petrosal Nerve
3. A line from Foramen Spinosum to Arcuate Eminence
· Contents:
1. Foramen Spinosum
2. Horizontal Petrous ICA (for anastamosis)
3. Infratemporal Fossa
8. Posteromedial (Kawase's) Triangle
This area is also known as The Rhomboid. Removal of the petrous bone within this triangle/quadrangle is an
anterior petrosectomy.
· Borders:
2. GSPN
3. Arcuate Eminence
4. Superior Petrosal Sinus
-or-
1. GSPN
2. Arcuate Eminence
3. A line connecting the hiatus fallopii and Meckel's Cave
· Contents:
1. Petrous Apex
2. IAC
3. Vertebrobasilar Junction
Contains cochlea

Posterolateral (Glasscock's)
Triangle

Posterolateral (Glasscock's) Triangle approach in
Trans-temporal skull base approaches is called “ Infra-
temporal fossa B approach “ by Prof. Mario sanna
The petrous apex as viewed through the
infratemporal fossa type B approach.
Structures lying lateral to the internal carotid artery
(ICA). The mandibular nerve (V3) and the middle
meningeal artery have been cut. The instrument points
to the position of the already drilled bony
eustachian tube (ET).

Infratemporal fossa anatomy
line diagram in both anterior
& lateral skull base (
Infratemporal fossa approach
A, B, C , D )

Iatrogenic chances of injury of cochlea
in infratemporal fossa transpetrous
approach

The skin incision.
The external auditory canal
(arrow) is closed as cul-de-sac.

The temporalis muscle is
detached anteriorly.
The zygomatic arch is transected.
Arrows point to the transection sites.

Subtotal petrosectomy. The facial nerve (FN) is skeletonized and the
vertical internal carotid artery (ICA) is identified.

A minicraniotomy helps positioning
the infratemporal fossa retractor.
Identification of the middle meningeal artery (MMA)
crossing lateral to the eustachian tube (ET).

Coagulation of the middle
meningeal artery (MMA).
Cutting the middle meningeal
artery (MMA).

Identification of the mandibular
nerve (V3). The mandibular nerve (V3) is cut.

Suturing the eustachian tube (ET)
at the end of the procedure. Closure and drain insertion.

Infratemporal fossa approach B
in cadaver

The temporalis muscle (TM ) of a left temporal
bone has been
reflected anteriorly after it has been dissected
from the squamous bone
(S). TL Temporalis line, ZR Root of the zygomatic
process

The periosteum (P) overlying the
zygomatic arch (ZA) is
being dissected away. This step helps
avoid the laterally lying frontal
branch of the facial nerve. SB
Squamous bone
The view after dissection of the
periosteum (P) from the
zygomatic
arch (ZA). SB Squamous bone, TM
Temporalis muscle

The zygomatic arch has been
transected. EAC External auditory
canal, SB Squamous bone, TM
Temporalis muscle, ZR Zygomatic
root
The skin of the external auditory
canal (S) is being dissected
away under the microscope. TM
Tympanic membrane

After complete removal of the external
auditory canal skin
and tympanic membrane, the
incudostapedial joint is disarticulated in
order to remove the ossicular chain. C
Chorda tympani, I Incus, M Malleus,
S Stapes
The mastoid cavity and the posterior
and superior walls of the
external auditory canal have been
partially drilled. FB Facial bridge,
FR Facial ridge, MFP Middle fossa
plate, SS Sigmoid sinus

A radical mastoidectomy has been carried out, and the facial
nerve has been skeletonized. AR Anterior attic recess, C Basal turn
of the
cochlea (promontory), DR Digastric ridge, FN(m) Mastoid segment
of
the facial nerve, FN(t) Tympanic segment of the facial nerve, LSC
Lateral
semicircular canal, MFP Middle fossa plate, PSC Posterior
semicircular
canal, RW Round window, S Stapes, SS Sigmoid sinus, SSC Superior
semicircular canal, TT Tensor tympani
The retrofacial and infralabyrinthine air cells are
being drilled
using an appropriately sized diamond drill.
Attention must be paid
during this step to avoid injuring the laterally
lying facial nerve with the
burr or the shaft. ELS Endolymphatic sac, FN(m)
Mastoid segment of the
facial nerve, ICA Internal carotid artery, SS
Sigmoid sinus

The anterior wall of the external auditory
canal has been partially
drilled, and the vertical segment of the
internal carotid artery (ICA)
has been identified. FN(m) Mastoid
segment of the facial nerve,
FN(t) Tympanic segment of the facial nerve,
JB Jugular bulb, LSC Lateral
semicircular canal, S Stapes, SS Sigmoid
sinus, TT Tensor tympani
Dissecting the articular disk (AD)
of the temporomandibular
joint. ACWAnterior canal wall, SB
Squamous bone, ZR Zygomatic
root

A small craniotomy (CT) has
been created in the squamous
bone. ACWAnterior canal wall,
AD Articular disk
A self-retaining retractor is used
to keep the mandible retracted
inferiorly. ACWAnterior canal
wall, AZT Anterior zygomatic
tubercle, GF Glenoid fossa

The rest of the anterior canal wall has been
drilled away, and
the internal carotid artery is better
skeletonized. C Basal turn of the
cochlea (promontory), ET Eustachian tube,
FN(m) Mastoid segment of
the facial nerve. G Genu of the internal
carotid artery, ICA(v) Vertical
segment of the internal carotid artery
To obtain control of the horizontal segment
of the internal
carotid artery, the eustachian tube (ET),
glenoid fossa bone (GF), and the
anterior zygomatic tubercle (AZT) have to
be carefully drilled away.
ICA Vertical segment of the internal carotid
artery

In live surgery, the middle meningeal
artery (MMA) should be
coagulated to prevent bleeding. ICA
Internal carotid artery, MFP Middle
fossa plate
The middle meningeal artery
(MMA) is being sharply cut.
ET Eustachian tube, ICA Internal
carotid artery, MFP Middle fossa
plate

Further anterior drilling uncovers the
mandibular nerve (MN).
This nerve also has to be coagulated
in live surgery before it is cut.
ET Eustachian tube, ICA Internal
carotid artery, MFP Middle fossa
plate
Sharply cutting the mandibular
nerve (MN). ET Eustachian
tube, ICA Internal carotid
artery, MFP Middle fossa plate

The stumps of the mandibular
nerve (*). ET Eustachian tube,
ICA Internal carotid artery,
MFP Middle fossa plate
The eustachian tube (ET) and tensor
tympani muscles (TT)
are the last structures lying lateral to the
horizontal segment of the facial
nerve and should be removed. ICA Internal
carotid artery, JB Jugular
bulb, MN The cut end of the mandibular
nerve

The lateral, thin part of the
eustachian tube (ET) that remains
can be removed with forceps. C Basal
turn of the cochlea (promontory),
ICA Internal carotid artery, MFP
Middle fossa plate
The tensor tympani muscle has
been dissected away from its
canal (TTC). ET Medial wall of the
eustachian tube, ICA Internal
carotid
artery, MFP Middle fossa plate

A large diamond burr is used to remove the remaining
bone
overlying the horizontal segment of the internal carotid
artery. C Basal
turn of the cochlea (promontory), ICA Vertical segment
of the internal
carotid artery, MFP Middle fossa plate, MMA Stump of
the middle
meningeal artery, MN Stump of the mandibular nerve
The horizontal segment of the internal carotid artery
(ICAh)
has been skeletonized. Note that the greater petrosal
nerve (GPN) is adherent
to the dura, and that retracting the dura will lead to
stress on the
facial nerve at the geniculate ganglion (GG) level. Thus, if
dural retraction
is needed, cutting the petrosal nerve will prevent this
injury. C Basal turn
of the cochlea (promontory), CL Clivus bone, G Genu,
ICA(v) Vertical
segment of the internal carotid artery

The tip of the suction is used to displace the internal
carotid
artery (ICA) laterally while the medially lying bone is
being drilled.
C Basal turn of the cochlea (promontory), FN(m) Mastoid
segment of
the facial nerve, FN(t) Tympanic segment of the facial
nerve,
GPN Greater petrosal nerve, MFP Middle fossa plate,
MMA middle
meningeal artery stump
Drilling of the clivus has been
completed. C Basal turn of the
cochlea (promontory), FN(m) Mastoid
segment of the facial nerve,
FN(t) Tympanic segment of the facial
nerve, GG Geniculate ganglion,
GPN Greater petrosal nerve, ICA
Internal carotid artery, RW Round
window

The full course of the intratemporal internal
carotid artery has
been freed. AFL Anterior foramen lacerum,
CF Carotid foramen, CL Dura
overlying the clivus area, ICA(h) Horizontal
segment of the internal
carotid artery, ICA(v) Vertical segment of
the internal carotid artery,
MN Stump of the mandibular nerve
The view after completion of the
approach.

The relationship of the internal carotid artery (ICA) to the
tympanic membrane (TM) and middle ear in a right temporal bone.
A Annulus, FN(m) Mastoid segment of the facial nerve, I Incus, JB Jugular
bulb, LSC Lateral semicircular canal, M Malleus, MFD Middle fossa
dura, PSC Posterior semicircular canal, SSC Superior semicircular canal

Two bissections in skull base
1. vertical part of facial nerve bisects jugular bulb
2. GSPN bisects V3& petrous carotid
Vertical part of facial nerve
bisects jugular bulb
GSPN bisects V3 & petrous
carotid

Triangles of Middle cranial fossa – see Ant. Medial & Ant. Lateral triangles in both photos.
http://www.eneurosurgery.com/surgicaltrianglesofthecavernoussinus.html
Postero-medial Triangle = KAWASE triangle [Prof.KAWASE , JAPAN Neurosurgeon -below photo]

Neurosurgeons are doing FTOZ + kawase approach to
get control of middle cranial fossa & posterior cranial
fossa respectively
For FTOZ + Kawase approach click
1. https://www.youtube.com/watch?v=qgItZDwRYjk
2. https://www.youtube.com/watch?v=M89uijtuzQA
3. https://www.youtube.com/watch?v=es-U3QitxdY
4. https://www.youtube.com/watch?v=vDGO4kVy0Gc
5. http://www.aiimsnets.org/skull_base_tumors.asp
6. http://aiimsnets.org/AnteriorTranspetrosalapproach.asp#
others
https://www.youtube.com/results?search_query=frontotemporal+orbitozygo
matic+approach
https://www.youtube.com/results?search_query=kawase+approach

FTOZ + kawase approch cadaver
albums
• https://www.facebook.com/groups/38350835
5070291/permalink/896897763731345/
• https://www.facebook.com/groups/38350835
5070291/permalink/897122833708838/

Modified Anterior Transpetrosal Posterior Cavernous Posteromedial
Rhomboid (Dolenc-Kawase Rhomboid) Approach to Posterior Cavernous
and Petroclival Lesions –AIIMS , INDIA
https://www.thieme-
connect.com/products/ejournals/abstract/10.10
55/s-0034-1370530

The same approach what you get in
FTOZ + KAWASE approach , you get
in Type C Modified transcochlear
approach without any brain
retraction

Various types of Modified
transcochlear approach
Don't give too much
importance to the jargon
of approaches .
Approaches developed
from anatomy . Anatomy
not developed from
approaches. Know the
www.skullbase360.in anat
omy. Automatically you
can individualize the
approach for the tumor .

a Schematic drawing showing the extent of the modified
transcochlear type C approach. Note the superior extent of the craniotomy
and the cut of the tentorium. b The markings of the skin incision
to be made.

Drawing showing the structures
exposed.
Incision of the middle fossa dura. The vein of Labbé (vL)
is
clearly seen.

Cutting the tentorium (Ten).
The last part of the tentorium is still to
be cut to reach the tentorial notch.

The different structures seen
after completion of the approach.
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.

Petroclival meningiomas surgery by
Modified transcochlear approach
Click video
https://www.youtube.com/watch?v=
kUa9fQ4_aQY

• 9. Inferolateral Triangle
· Borders:
1. A line from the dural entries of the Trochlear and Abducens Nerve
2. A line from the dural entries of the Abducens Nerve and the Petrosal Vein
3. The petrous apex
Posterolateral (Glasscock's) Triangle
· Contents:
1. Porous Trigeminii (Dural opening into Meckel's Cave)
10. Inferomedial Triangle
· Borders:
1. A line from the dural entries of the Trochlear and Abducens Nerve
2. A line from the dural entries of the Abducens Nerve and the Posterior Clinoid
3. The petrous apex
· Contents:
1. Porous Abducens (Dural opening into Dorello's Canal)
2. Gruber's Ligament

inferomedial triangle – remember that 6th nerve below the
grubers ligament passes in this triangle
· Borders:
1. A line from the dural
entries of the Trochlear and
Abducens Nerve
entries of the Abducens
Nerve and the Posterior
Clinoid
3. The petrous apex
· Contents:
1. Porous Abducens (Dural
opening into Dorello's Canal)
2. Gruber's Ligament

Anterior skull base view of Inferomedial triangle - 6th
nerve – enters the dorellos canal – Intradural course
clinical importance = Gradenigo Syndrome - Infection & inflammation of petrous apex involves
6th cranial nerve at the Dorello's canal and 5th cranial nerve in the Meckel's cave

The basilar artery (BA) can be seen
very tortuous.

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.

Gulfar segment of 6th nerve (GS in left picture ) ( gVIcn in right picture ) - 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 ).
6th nerve enters dorello’s canal between
the meningeal layer of dura and the
periosteal layer of dura (POD).

AICA anterior-inferior cerebellar artery, Cl clivus, CS cavernous sinus, ICAc cavernous portion
of the internal carotid artery, IPS inferior petrosal sinus, LPMVN lateropontomesencephalic
venous network, PBs pontine branches, PG pituitary gland, TPV transverse pontine vein, VA
vertebral artery, VN vidian nerve (bordered in yellow ), Vcn trigeminal nerve, VIcn abducens
nerve, yellow arrow cavernous portion of the abducens nerve

inferolateral triangle – remember that 5th nerve
passes in this triangle
· Borders:
entries of the Trochlear and
Abducens Nerve
entries of the Abducens
Nerve and the Petrosal Vein
3. The petrous apex
Posterolateral (Glasscock's)
Triangle
· Contents:
1. Porous Trigeminii (Dural
opening into Meckel's Cave)

Anterior skull base view of Inferolateral triangle -“Front door” to
Meckel’s cave – the space between trigeminal ganglion & laceral carotid is
called quadrangular space – suprapetrous approach
PLL - It can be considered the border between the horizontal and cavernous
portions of the internal carotid artery.

10 triangles 360°

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