CP angle 360°

CP angle 360°
6-6-2016
7.07 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

For Other powerpoint presentatioins
of
“ Skull base 360° ”
I will update continuosly with date tag at the end as I am
getting more & more information
click
www.skullbase360.in
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account after clicking www.skullbase360.in

Approaches to the brainstem –
Rhoton
https://www.youtube.com/watch?v=
K-42KXujh0o

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

Superior anatomical view of the left
cerebellopontine angle (CPA): The CPA is defined
as the angle formed in the horizontal section by the
pons and the cerebellum in which the trigeminal (V)
and acousticofacial nerve bundle (VIII) are located.
The angle is bordered laterally and anteriorly by the
posterior face of the petrous temporal bone. The
tip of the endoscope (4 mm diameter) is facing the
acousticofacial nerve bundle which is the reference
level, crossing the middle of the CPA from the
brainstem to the internal auditory meatus (IAM), and
separating it into two anatomical areas. Superiorly
and
anteriorly, the trigeminal area is usually inspected for
the management of trigeminal neuralgia. Inferiorly,
the
lower cranial nerve area is inspected for treatment of
hemifacial spasm and glossopharyngeal neuralgia.
aica indicates anterior-inferior cerebellar artery;
m, malleus; i, incus.

Posterior view of CP angle
1. level 1 = Trigeminal area
2. Level 2 = AFB area
3. Level 3 = Lower cranial nerve area
4. Level 4 = Foramen magnum area

The petrosal or anterior surface of the cerebellum faces the posterior surface of the temporal
bone and the brain stem. The neurovascular bundles define four levels from superior to inferior:
trigeminal, acousticofacial, lower cranial, and foramen magnum.

Right retrosigmoid approach under the operating
microscope. The acousticofacial nerve bundle crosses the
middle
of the cerebellopontine angle (CPA). Its entrance into the
porus acusticus provides an unquestionable
identification.
The flocculus overlies the root entry zone of the
cochleovestibular and facial nerves. Superiorly, the
trigeminal nerve exits the pons and travels obliquely in
an anterosuperior
direction toward the petrous apex. Interiorly, the
posterior
inferior cerebellar artery and the glossopharyngeal nerve
are
seen.
Right retrosigmoid approach under the operating
microscope. The acousticofacial nerve bundle crosses the
middle
of the cerebellopontine angle (CPA). Its entrance into the
porus acusticus provides an unquestionable
identification.
The flocculus overlies the root entry zone of the
cochleovestibular and facial nerves. Superiorly, the
trigeminal
nerve exits the pons and travels obliquely in an
anterosuperior
direction toward the petrous apex. Interiorly, the
posterior
inferior cerebellar artery and the glossopharyngeal nerve
are
seen.

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.

The trigeminal nerve from the poms to the Meckel
cavity (trigeminal cavity). Posterior to the trigeminal
nerve lies
the superior petrosal vein (Dandy vein). Superior to the
trigeminal nerve the superior cerebellar artery. In the
background
and inferiorly, the abducent nerve and basilar artery
are seen. In the background and superiorly, the free
border of
the tentorium and the mesencephalic area are seen.
The entrance of the trigeminal nerve
into the
Meckel cavity. The superior petrosal
vein prior to its entrance
into the superior petrosal sinus is
seen.

Closer view of the superior area of the left CPA:
tip of the 30° endoscope is above the acousticofacial nerve
bundle (VIII-VII) and its entrance in the internal auditory
meatus (IAM). The trigeminal nerve (V) runs obliquely upward
from the lateral part of the pons toward the petrous apex. It exits the posterior fossa to enter the middle fossa by passing
beneath the tentorial attachment to enter Meckel’s cave.
Posterior to the trigeminal nerve lies the superior petrosal vein or Dandy’s vein (DV) entering the superior petrosal sinus.
The trochlear nerve (IV) is seen in the background passing
underneath the tentorium.

Here, the tip of the endoscope is positioned at
the level of the posterior margin of the trigeminal nerve in
order to carry out an inspection above it, visualizing the rostral
and cranial branches of the superior cerebellar artery and
the trochlear nerve. The trochlear nerve disappears under the
free margin of the tentorium. The point of entrance is just
before the cavernous sinus. In the background, the oculomotor
nerve and the posterior cerebral artery, are seen, as well as the free border of the
tentorium and the uncus of the
temporal lobe.

The endoscope is positioned between the trigeminal
nerve and the tentorium. The superior cerebellar
artery
encircles the brain stem above the trigeminal nerve
and below
the trochlear nerve. The superior cerebellar artery,
arising as a
single trunk, bifurcates into rostral and caudal trunks.
The pontomesencephalic incisure, with the third
cranial nerve, lies between the uncus and the
trochlear nerve. The posterior
cerebral artery and a branch passing to the
mesencephalon
are seen.
Arterial relationships around the
oculomotor nerve.
The superior cerebellar artery lies
interiorly, and the posterior
cerebral artery superiorly. The
exit zone of the third cranial
nerve between the superior
cerebellar artery and the
posterior
cerebral artery is seen.

Left side. The trigeminal nerve
and Dandy vein are
seen entering the superior
petrosal sinus.
Left side. The trigeminal nerve
and Dandy vein are
seen entering the superior
petrosal sinus.

using the 30° angled endoscope, the
Meckel cavity and the intradural course
of the abducent nerve are seen
delimiting the petrociival area. After
piercing the inner layer of the dura
mater, the nerve changes direction and
courses medially toward the petrous
apex.
The upper major sensory fibres
& lower less motor fibres

From CP angle book – see other
photos – fig 9

Left side. The acousticofacial nerve bundle runs
obliquely from the pons to the internal acoustic meatus in
asuperolateral direction. Its length between the entry zone
of the nerves and the porus of the internal acoustic meatus
varies from 8 mm to 14 mm. A groove or raphe on the
posterior surface of the cochleovestibular nerves indicates
the division of the cochlear segment interiorly and the
vestibular segment superiorly. A labyrinthine artery arises
from the loop of the anterior inferior cerebellar artery. The
fifth nerve lies in
the background.
Left side. The acousticofacial nerve bundle runs
obliquely from the pons to the internal acoustic meatus in a
superolateral direction. Its length between the entry zone of
the nerves and the porus of the internal acoustic meatus
varies from 8 mm to 14 mm. A groove or raphe on the
posterior surface of the cochleovestibular nerves indicates
the division of the cochlear segment interiorly and the
vestibular segment superiorly. A labyrinthine artery arises
from the loop of the anterior inferior cerebellar artery. The
fifth nerve lies in the background.

FN & SVN converge as they pass toward the fundus , while the CN & IVN can
be seen diverging from each other as they pass laterally to the fundus - ---
Basal turn of cochlea pushing away IVN from CN
See the cochlea in below photo

7up- 7th is above
Coca cola – cochlear n. is cola[=lower]

Add other slides of Retrosigmoid &
retrolabyrinthine approach

Posterior semicircular canal is
aligned with axis of petrous bone

Add middle cranial fossa photos
Fig. 5.30 A simple middle cranial fossa approach has been
established,
and the internal auditory canal dura has been opened. A Anterior, B
Bill’s
bar, FN Facial nerve, P Posterior, SSC Superior semicircular canal,
SV Superior vestibular nerve

The acousticofacial bundle components have been separated.
Both the facial nerve (FN) cochlear nerve (CN) can now be seen.
AICA Anterior inferior cerebellar artery

Keep sashidhar tatavarthy post vertigo MRI pictures & mario sanna facial
nerve or vestibular schawannoma book -- crossing of vestibular & cochlear
nerves as we go from medial to lateral direction

Left Ménière disease: In around 40% of cases,
the anterior inferior cerebellar artery (aica)
forms a vascular
loop running toward the porus acusticus,
usually inferior to the
vestibulocochlear nerve bundle. Within the
vestibulocochlear nerve,
the vestibular fibers (Ve) are more superior
(rostral) and close to the
trigeminal nerve, and the cochlear nerve (Co)
is inferior (caudal)
and close to the lower cranial nerves (LCN).
Left Ménière disease: A small
dissector is inserted
into the inter-vestibulocochlear
cleavage plane to divide the
vestibulocochlear nerve into its
two parts.

Mneumonic is Circle inspector of Police [ CI ] – Cochlear nerve is inferior
In cisternal AFB cochlear nerve is
inferior to vestibular nerve
In IAC cochlear nerve is anterio-
inferior quadrant
At the end of tumor
removal, the most
lateral fundus part
of the internal
auditory meatus is
checked with an
endoscope. Often
there is residual
tumor (T) in the
fundus. Fn indicates
facial nerve; Cn,
cochlear nerve; Vn,
residual vestibular
nerve.

Vestibular neurotomy is
progressively performed with
microsurgical scissors.
Left endoscopic vestibular
neurotomy is complete.
The facial nerve located
anteroinferior to the vestibular nerve
is now
visible.

Left microsurgical vestibular neurotomy with terminal
fibers being dissected by blunt probe. co indicates the cochlear
nerve; ve, sectioned vestibular nerve; aica, anterior inferior
cerebellar artery.

Anterior to the Acoustico facial Nerve
Bundle

The abducent nerve. In the background, the vertebral
and basilar arteries are first visualized. The origin of the
anterior inferior cerebellar artery is clearly seen.

Inferior to the Acousticofacial Nerve
BundleA closer view of the CPA from the porus acusticus.
The root exit zones of the facial nerve and the abducent
nerve
are seen. Note the relationships between the loop of the
anterior inferior cerebellar artery and the acousticofacial
nerve
bundle. The lower cranial nerves are seen in the
background.
A deeper view, showing the relationships
between
the vertebral artery and the lower clivus;
the flocculus lobe
and the anterior inferior cerebellar artery
are seen.

The vertebral artery joins its fellow on the
opposite
side and gives off several perforating
arteries to the spinal
cord.
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.

Microvascular Decompression (MVD) Surgery for Unilateral
Disabling Tinnitus
Subarcuate artery (red arrow)
causing compression
of the cochlear nerve.
Subarcuate artery is gently displaced from the
cochlear nerve and coagulated. The
demyelinized zone on the cochlear nerve is
visible as a grayish discoloration and
narrowing of the nerve in contact area (yellow
arrow).

The AICA forms collateral branches along its path, in padicular in the area of its loop. Recurrent
arteries for the cerebral trunk and the origin of the facial nerve, the internal auditory artery and
the subarcual artery, the purpose of which is vascularization of the inner ear (Fig. 3).
Anatomy of the AICA branches
1. Labyrinthine artery
2. Subarcual artery
3. Recurrent artery for the cerebral trunk

Level 3 = Lower cranial nerve
area

Right side. The acousticofacial nerve
bundle, posterior
inferior cerebellar artery, and lower cranial
nerves are seen
in the lower part. The inferior cerebellar
vein (not constant)
enters the jugular bulb. As the posterior
fossa is approached
from behind the sigmoid sinus, the jugular
dural fold appears
as a white linear structure overlying the
lower cranial nerves.
Right side. The acousticofacial nerve
bundle, posterior
inferior cerebellar artery, and lower
cranial nerves are seen
in the lower part. The inferior
cerebellar vein (not constant)
enters the jugular bulb. As the
posterior fossa is approached
from behind the sigmoid sinus, the
jugular dural fold appears
as a white linear structure overlying
the lower cranial nerves.

A closer view of the pars nervosa of
the jugular foramen. The
glossopharyngeal nerve has its own
dural porus, which is situated 0-3
mm upwards from the dural
porus of the tenth cranial nerve. The
vagus and the accessory
nerve exit the posterior fossa
together in a sleeve of dura
through the jugular foramen.
Closer view of the inferior area of the left CPA, with
the tip of the endoscope just over the flocculus. The
vagus nerve
(X) and spinal accessory nerve (XI) arise as a widely
separatedseries of rootlets that originate from the lower
medulla and from theupper cervical cord. The rootlets of
the hypoglossal nerve (XII) runhorizontally and are
displaced and stretched by the curved vertebral
artery (VA). The posterior-inferior cerebellar artery (PICA)
arisesfrom the vertebral artery and forms a vascular loop
inferior to the
root exit /entry zone of the acoustic-facial nerve bundle
(VII/ VIII).

The right side of the
bulbomedullary junction. It is the
lowermost and narrowest part of
the posterior fossa. This area
requires special dissection prior
to endoscopic investigation
between the pontomedullary
stem and the jugular foramen.

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.
10 Vagus nerve
11 Accessory nerve
12 Hypoglossal nerve
PICA Posterior inferior cerebellar
artery
Vert. A Vertebral artery

The posterior inferior cerebellar artery travels
through the nerve fiber roots of the accessory
nerve and
encircles the brain stem. The course of the
vertebral artery is
inferior and anterior to the lower cranial nerves
and the
hypoglossal nerve. Fibrous tissue surrounds the
entrance of
the vertebral artery into the CPA.
9 Glossopharyngeal nerve
10 Vagus nerve
11 Accessory nerve
12 Hypoglossal nerve
PICA Posterior inferior cerebellar
artery
Vert. A Vertebral artery

Left side. The lower cranial
nerves, with the poste-rior
inferior cerebellar artery
arising from the vertebral
artery in the background.
Neurovascular relationships
between the exit zone of the root
fiber bundles of the eleventh and
twelfth nerves, the posterior
inferior cerebellar and vertebral
arteries. Fibrous tissue is seen
around the vertebral artery.

The root fibers of the spinal
accessory nerve and the fibers of C1
and C2. The entrance of the vertebral
artery is the boundary between the
foramen magnum and the spinal part
of the accessory nerve.
A 30° endoscope provides an
overview of the medullary canal,

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.
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.

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.

PICA passes between two bundles of 12th nerve &
between two roots of 11th 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.
The posterior inferior cerebellar
artery travels through the nerve
fiber roots of the accessory nerve

Closer view of the inferior area of the left CPA, with
tip of the endoscope between the acousticofacial nerve bundle and lower cranial nerves. PICA
originating from the vertebral arterycan be seen forming a loop near the REZ of the facial nerve.
AICA arises from the more medial basilar artery and traverses under the acousticofacial nerve
bundle to supply the anterior surface of cerebellum. Abducens nerve (VI) is occasionally formed
by two different nerve bundles as seen here.

Middle cranial fossa
Transpetrous ( = Transapical )

A right-sided skin incision for the
middle cranial fossa approach.

The skin and subcutaneous tissues
have been elevated as one flap.

The temporalis fascia has been harvested and the
temporalis muscle cut using monopolar diathermy.

The temporalis muscle and periosteum
have been elevated as one flap.

The craniotomy has been performed
using a small drill.

The craniotomy flap has been elevated and
the middle fossa (MFD) can be seen.
The branches of the trigeminal nerve (V1, V2, V3) can be
identified at the anterior part of the approach.

The Fukushima middle cranial fossa retractor has
been applied to maintain the elevated dura.
Three-quarters of the canal circumference is
skeletonized, leaving a thin shell of bone over it.

The different areas of access for the middle fossa approaches.
a Classic middle fossa approach to the internal auditory canal.
b Enlarged middle fossa approach for tumor removal. c−e The middle
fossa transpetrous approach.

The landmarks for the internal
auditory canal (arrow) in middle
fossa approach. AE, arcuate
eminence; gspn, greater
superficial petrosal nerve; MMA,
middle meningeal artery.
A schematic representation of the
position of the internal audi tory
canal in middle cranial fossa
approach. EAC, external auditory
canal; IAC, internal auditory
canal; SSC, superior semicircular
canal; SPS, superior petrosal
sinus.

An anatomical dissection carried out
through the middle fossa,
illustrating the relationships between
the various structures in this area.
A closer view of the lateral end of
the internal auditory canal.

The posterior rhomboidal area
(Q) of the anterior petrous apex.
The anterior triangular area
has been uncovered by
sectioning the mandibular
nerve (V3) and reflecting the
gasserian ganglion.

The amount of circumferential
exposure of the internal auditory
canal near the fundus is only 180°.
Kawase approach
The quadrangular area of the
petrous apex anterior to the internal
auditory canal is drilled and the
horizontal segment of the internal
carotid artery (ICA) is exposed.

the anterior petrosectomy with preoperative embolization of the inferior
petrosal sinus is a time-conserving approach giving one of the best routes to
reach the ventral brainstem while working in front of the cranial nerves and
preserving hearing.
http://www.worldneurosurgery.org/article/S0090-3019(00)00271-8/fulltext

Videos of kawase approach or
Anterior Transpetrosal approach
– click
http://aiimsnets.org/AnteriorTranspe
trosalapproach.asp#

The whole length of the horizontal
portion of the internal carotid artery
(ICA) is exposed up to the anterior
foramen lacerum (AFL).
The dura is opened by creating
an inferiorly based flap, the
dashed lines.

Surgical Anatomy after Opening of the Dura
The middle fossa transpetrous approach.

The anterior inferior cerebellar
artery is seen looping around the
acousticofacial bundle (AFB).
At a higher magnification a
prominent flocculus (Fl) is observed.

The distal part of the vertebral
artery (VA) can be seen.
The distal part of the vertebral
artery (VA) can be seen.

After removing the remaining
bone of the petrous apex, the
basilar artery (BA) can be seen in
the prepontine cistern.
Opening the dura of the middle
cranial fossa exposes the third nerve
(III) and intracavernous portion of
the internal carotid artery (ICA).

A closer view at the level of the fundus of
the internal
auditory canal. The facial nerve lies
anteriorly and superiorly. The vestibular
nerve posteriorly is separated from the
facial nerve by a plane of cleavage. The
cochlear nerve is
located inferior to the facial nerve.
The cochlear nerve travels along an inferior
course
in the internal auditory canal. Inferior to the
vestibular nerve
at the porus acusticus, it becomes inferior to the
facial nerve
at the lateral end of the internal auditory canal.
There is a
labyrinthine artery coursing between the
cochlear and facial
nerves.

A closer view at the level of the porus acusticus. The anterior inferior cerebellar artery forms a
vascular loop and gives off labyrinthine arteries, which fix the contact between the artery and
the inferior surface of the acousticofacial nerve bundle at the inferior lip of the meatus.

The root exit zone of the facial nerve
is anterior to the root of the cochlear
nerve and superior to the rootlets of
the lower cranial nerves.
7 Facial nerve
8 Vestibulocochlear nerve
9 Glossopharyngeal nerve
10 Vagus nerve
AICA Anterior inferior cerebellar artery
IAC Internal auditory canal
PICA Posterior inferior cerebellar artery

The pontobulbar junction and the roots of the
lower cranial nerves are visualized. The loop of the posterior
inferior cerebellar artery is seen in the background.

Right enlarged middle fossa approach. The internal
auditory canal has been opened, revealing the acousticofacial
Perve bundle contained within it. The facial nerve runs anteriorly,
and the superior vestibular nerve lies posteriorly. The
loop of the anterior inferior cerebellar artery runs near the
Meatus, below the acousticofacial nerve bundle.

Various Transpetrous approaches to get lateral view of CP angle
( = to reach Lateral part of Posterior cranial fossa dura )
predominently to reach Level 1 = Trigeminal nerve
area & Level 2 = AFB area
1. Retrolabyrinthine Transpetrous ( =
Transapical )
2. Translabyrinthine Transpetrous ( =
Transapical )
3. Transcochlear Transpetrous ( = Transapical )
predominently to reach Level 3 = Lower cranial
nerve area
4. POTS = Petro-Occipital Trans-Sigmoid
approach
5. Infralabyrinthine Transpetrous ( =
Transapical ) -- which is nothing but IFTA-A ,
PONS , IFTA-B Transpetrous approach
[ IFTA-A,B = Infratemporal fossa approach A , B /
PONS = petro-occipital trans-sigmoid approach ]
predominently to reach
Level 4 = Foramen magnum area
6. Exrtreme lateral or Far lateral or
Transcondylar approach

Photograph of a cadaveric dissection showing an overview of the temporal bone and depicting the posterior
surface of the petrous part. The sphenoid bone, which articulates anteriorly with the petrous and squamous
temporal bone, has been removed in this specimen. The pyramidal petrous part, located between the sphenoid
and occipital bones, has a base, apex, and three surfaces. The sigmoid sinus descends along the posterior
surface of the mastoid part and turns anteriorly toward the jugular foramen. The posterior transpetrosal
approaches involve progressive degrees of resection of the petrous temporal bone. The retrolabyrinthine
(green outline) dissection exposes the area between the superior petrosal sinus, the sigmoid sinus, and the
posterior semicircular canal. The translabyrinthine approach (pink outline) extends more anteriorly to remove
all three semicircular canals and to expose the anterior wall of the IAC. The transcochlear (blue outline)
dissection extends even more anteriorly to the petrous apex, resulting in an almost complete petrosectomy
with the widest and most direct exposure of all the posterior transpetrosal approaches. PET. =
petrous/petrosal; POST. = posterior; RETROLAB = retrolabyrinthine; S.C. = semicircular canal; SIG. = sigmoid;
SUP. = superior; TRANSLAB = translabyrinthine.

Middle cranial fossa Transpetrous approach - the anterior
petrosectomy with preoperative embolization of the inferior petrosal sinus is
a time-conserving approach giving one of the best routes to reach the ventral
brainstem while working in front of the cranial nerves and preserving hearing.
http://www.worldneurosurgery.org/article/S0090-3019(00)00271-8/fulltext

Retrolabyrinthine Transpetrous (
= Transapical )

Retrolabyrinthine Transpetrous ( =
Transapical ) &
Translabyrinthine Transpetrous ( =
Transapical ) &
Transcochlear Transpetrous ( =
Transapical )
Level 1 = Trigeminal nerve area &
Level 2 = AFB area

COMBINED APPROACHES
Retrolabyrinthine Transpetrous ( = Transapical
)Subtemporal Approach
Retrolabyrinthine Transpetrous ( = Transapical
)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.

Endoscopic Retrolabyrinthine
approach – from Prof. Magnan book

Translabyrinthine Transpetrous (
= Transapical )

The Enlarged Translabyrinthine Approach with Transpetrous ( =
Transapical ) Extension
Schematic drawings showing the amount of bone removal
around the internal auditory canal in the different variants of the
translabyrinthine approach. Note that in the transapical modification the
exposure is 320° and about 360° in types I and II, respectively. Abbreviations
as in Fig. 5.1. cn, cranial nerve; CN, cochlear nerve; FN, facial nerve;
IV, inferior vestibular nerve; SV, superior vestibular nerve.

Drilling inferior to the right
internal auditory canal (IAC).
Further extensive drilling inferior to the internal auditory
canal (IAC) toward the petrous apex.

Extensive bone removal inferior and
superior to the internal auditory
canal (IAC). Bone superior to the
canal (*) is still to be removed.
The whole contents of the internal
auditory canal (IAC) are pushed
inferiorly to allow removal of the
remaining bone (*) superior to the
canal.

The whole contents of the canal are
displaced inferiorly to show the extent
of bone removal. The anterior wall of
the canal can also be drilled if needed.
Schematic drawing showing the technique and
extent of bone removal in the type I (green
line) and type II (red line) transapical
extension. F, facial nerve; C, cochlear nerve;
Vs, superior vestibular nerve; Vi, inferior
vestibular nerve.

Schematic drawing showing the technique and extent of bone removal in the type I
(green line) and type II (red line) transapical extension. F, facial nerve; C, cochlear
nerve; Vs, superior vestibular nerve; Vi, inferior vestibular nerve.

General view of the structures in the
cerebellopontine angle
after opening the dura. Note the enhanced
exposure of the angle and
the excellent exposure of the trigeminal
nerve (V).
The trigeminal nerve (V) is
pushed superiorly. The basilar
artery (BA) in the prepontine
cistern can be seen well.

With more traction of the tentorium, a panoramic view of the
structures in the angle is available. The trochlear nerve (IV) is
seen before piercing the tentorium to gain access to the middle
fossa.

Transcochlear Transpetrous ( =
Transapical )

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 .

An extended mastoidectomy,
labyrinthectomy, identification
of the internal auditory canal, and
drilling of the cochlea has been
performed.
The facial nerve (FN) has been
skeletonized.
The facial nerve (FN) has been skeletonized.

Using a diamond burr to uncover
the labyrinthine segment of
the facial nerve (FN).
The facial nerve (FN) is completely uncovered. Note Bill’s
bar
(BB) separating the nerve from the superior vestibular
nerve (SVN) at the
level of the fundus of the internal auditory canal.

Identification of the greater
superficial petrosal nerve (gspn).
The greater superficial petrosal
nerve is (gspn) cut.

The geniculate ganglion (GG) and
the labyrinthine portion of
the facial nerve (FN) are elevated.
The tympanic segment is freed.

A beaver knife is used to free the
mastoid segment.
The superior vestibular nerve (SVN)
is detached from its attachment.

The whole contents of the internal
auditory canal are transposed
posteriorly with the facial nerve (FN).
New position of the facial nerve
(FN) after posterior rerouting

Removal of the fallopian canal
with a rongeur.

Surgical Anatomy after Opening the
posterior cranial fossa dura
Drilling of the cochlea (Co). Drilling of the petrous apex (PA).

View after complete performance of
the approach. The
dashed lines represent the dural
incision.
View after opening the dura, showing
excellent control of the
basilar artery (BA) and prepontine cistern.

Tilting the microscope downward,
both the ipsilateral (VA)
and contralateral (VAc) vertebral
arteries come into view.
With a slight retraction of the middle fossa dura,
the origin of
the superior cerebellar artery at the basilar artery
(BA) can be seen. Note
the excellent control of the trigeminal nerve (V).

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

Mild retraction of the tentorium (Ten)
provides a good view of
the oculomotor nerve (III) and its relation
to the superior cerebellar
artery (SCA) lying inferiorly and the
posterior cerebral artery (PCA) lying
superiorly. The trochlear nerve (IV) is seen
running on the undersurface
of the tentorium.
Meckel’s cave (MC) can be
opened when necessary.

The 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

POTS = Petro-Occipital Trans-
sigmoid approach

POTS = Petro-Occipital Trans-sigmoid
approach predominently to reach
Level 3 = Lower cranial nerve area

The C-shaped skin incision. A skin flap is raised.

A U-shaped musculoperiosteal
flap is outlined.

Bone exposure. Note that no
retractors are used.
The internal jugular vein (IJV) is
identified.

The internal jugular vein is
liberated.
An extended mastoidectomy has
been performed.

A wide retrosigmoid craniotomy.
The sigmoid sinus (SS) is uncovered.
Note that the bone overlying
the genu from the lateral to the
sigmoid sinus is intact (arrowhead).

The dura is separated from the
overlying bone.
The dura is separated from the
overlying bone.

The endolymphatic sac (ELS) is
identified.
Further separation of dura from
the overlying bone.

Placement of aluminum to
protect the dura from injury.
The cochlear aqueduct (CAq)is
identified.

Complete drilling of the
retrofacial air cells.
The approach has been completed.
The dotted line representsthe dural
incision.

The dura has been opened and
the tumor (T) can be seen.
Closure of the dura. The remaining
defect (white arrowheads), together
with the operative cavity, is
obliterated with abdominal fat.

Surgical Anatomy after Opening the
posterior cranial fossa dura
General view of the structures that can
be visualized after opening the dura. At the superior aspect of the approach,
the fourth (IV) and fifth (V) cranial
nerves can be appreciated.

The facial nerve can be clearly seen
in the middle part of the approach
after retracting the posteriorly lying
cochlear nerve. Separation of the
glossopharyngeal nerve (IX) from the
vagus (X) and accessory (XI) nerves
at the medial aspect of the jugular
foramen.
Further inferiorly, the ninth (IX),
tenth (X), and eleventh (XI) cranial
nerves can be seen exiting the skull
through the jugular foramen

At the inferior part of the
approach the lower cranial nerves
can be appreciated.
The relation between the inferior
petrosal sinus (ips) and the lower
cranial nerves.

The origin of the hypoglossal nerve (XII).
.
The drilled occipital condyle (OC) and
the hypoglossal canal (HC).

Exrtreme lateral or Far lateral or

Exrtreme lateral or Far lateral or
Level 4 = Foramen magnum area

Patient placed in the lateral decubitus
position.

The levator scapulae (LS) and the splenius capitis (SpC)
muscles are identified.
Detaching the splenius capitis (SpC),
longissimus capitis (LC) and levator
scapulae muscles reveals the inferior and
superior oblique muscles. More posteriorly,
the semispinalis capitis muscle (SsC) can be
seen.

Subperiosteal separation of the suboccipital
muscles identifies the vertebral artery (VA).
The foramen transversarium has
been opened to better expose
the vertebral artery (VA).

Dissection of the right side. The
sternomastoid muscle (StM) has
been retracted anteriorly. The
levator scapulae (LS) and the
splenius capitis (SpC) muscles can
be identified at a superficial level.
Reflecting the splenius capitis
(SpC) muscle together with the
slender, deeply attached
longissimus capitis (LC) muscle
reveals the deep inferior (IO) and
superior (SO) oblique muscles.

The transverse process of the atlas (TPC1)
forms an important landmark in this region.
Course of the vertebral artery
(VA) after leaving the transverse
process of the axis. The foramen
transversarium of the atlas
(hatched lines) has been opened.
Pa, posterior arch of the atlas.

At a higher magnification, the C2 nerve root
is seen crossing the vertebral artery (VA).
The point where the vertebral
artery (VA) pierces the dura.

A presigmoid craniotomy has been partially
performed, exposing the sigmoid sinus
(SS). A suboccipital craniotomy (*)
extending caudal to the level of the
foramen magnum is performed.
The occipital condyle (OC) is
partially drilled.

Opening the dura posterior and
parallel to the sigmoid sinus.

Surgical Anatomy after Opening the Dura
A general view showing the different structures exposed after opening the dura. A cuff of
adherent dura is left attached to the vertebral artery (VA). Note the close proximity of the spinal
accessory nerve (XIs) to the artery and the dura at this level. The lower cranial nerves in relation
to the posterior inferior cerebellar artery are appreciated. The cerebellum is gently retracted to
expose the different structures at the cerebellopontine angle.
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.

At a higher magnification, the nerves
IX−XI are seen coursing toward the
jugular foramen. The two bundles of
the hypoglossal nerve (XII) are
closely related to the vertebral artery
(VA) before they unite to course in
the hypoglossal canal in the partially
drilled occipital condyle (OC). XIs,
spinal accessory nerve.
Changing the tilt of the microscope,
the two vertebral arteries
and the vertebrobasilar junction
(VBJ) are exposed. Note the control
of the ventrolateral surface of the
medulla (Med). VA, vertebral artery;
VAc, contralateral vertebral artery.

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

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.

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

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.

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.

With a more downward angulation of the microscope, the upper part of the
spinal cord (SpC) is well controlled. The posterior spinal artery (PSA) is also
seen.

Endoscopic transcochlear
approach

DEAR SURGEONS these are pictures of C PAngle
It is transmeatal endoscopic cadaveric dissection of c p angle
45 70 degrees of endoscopes are used through transmeatal transinternal
auditory canal route is used . We can see the anterior face of cp angle
here . All other procedures like retro sigmoid retrolab translab . We see
posterior face here infront of us 7th nerve comes first in other
procedures the vestibulo cochlear nerve bundle hides facial nerve
So here facial nerve is clearly vaisible from porus to pons
Surgical implications
1) endoscopic exposure to all pathological lesions of c p angle
2) Intra cranial grafting of facial nerve we are directly visualising the
intracranial portion of nerve
3) other pathologies of Meckles cave
4) No much bone drilling no brain retraction it is keyhole surgery for
future endoscopic lateral skull Base surgeons
5) The endoscopic otologist should be thorough with endoscopic
anatomy of this region before applying these type of procedures

Vcn ) Vestibulocochlear nerve
6th) 6th cranial nerve
Dc) Durello canal
P) Pons
Ica) Internal carotid artery
Iac) Anterior wall of internal auditory canal
Dv) Dandy vein
Sca) Superior cerebellar vein
Ten) Tentorium

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. BA, basilar artery; PCA, posterior cerebral artery;
SCA, superior cerebellar artery; CN III, occulomotor nerve; CN IV, trochlear nerve; CN
V, trigeminal nerve; TM, tentorial membrane; PComA, posterior communicating
artery; MB, mamillary body.

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 ).

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 ).

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.

Cadaveric dissection image on the right side with retraction inferiorly of the
glossopharyngeal and vagus nerves to reveal the choroid plexus (CP) as it spills out of
the foramen of Luschka. The folliculus (F) can also be visualized laterally, just behind
the facial (CN VII) and vestibulocochlear nerves (CN VIII). AICA, anterior inferior
cerebellar artery; PICA, posterior inferior cerebellar artery.

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.

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

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.

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.

CP angle 360°

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CP angle 360°