Line diagrams - skull base 360 - part 1

Dr.B.D.CHAURASIA - Great anatomist of
india whose books inspired me to take
up surgical field . Simplified the
anatomy with line diagrams .
Line diagrams - Skull
base 360°- Part 1
9-5-2017
12.43 pm

Chaurasia book weblink
http://www.amazon.in/s/?ie=UTF8&keywords=human+anatomy+by+chaurasia&tag=googinhydr1-
21&index=aps&hvadid=64937120410&hvpos=1t1&hvexid=&hvnetw=g&hvrand=13828071178419120710&hvpone=&h
vptwo=&hvqmt=b&hvdev=c&ref=pd_sl_1zkx9qygk2_b

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
- you have to login to slideshare.net with Facebook
account for downloading.

Anterior skull base line diagram
video – updated further time to time
– click
https://www.youtube.com/watch?v=
cLxLSyAo-KY

ORBIT
• 1. Two Ice cream cones in orbit -mnemonic - SOF
& IOF - superior orbital fissure & inferior orbital
fissure.
• 2. Bone between OC ( optic canal ) & SOF is optic
strut ( OS)
• 3. Bone between SOF & V2 ( foramen rotundum )
is MS ( maxillary strut ) - front door of cavernous
sinus
• 4. So SOF is presents between two struts - OS &
MS
• 5. Bone above SOF is LWS ( leader wing of
sphenoid )
• 6. Bone between SOF & IOF is GWS ( greater
wing of sphenoid )
• 7. Four semilunar lines 1, 2, 3, 4 are - orbital
surface of frontal bone , orbital surface of
zygomatic none , orbital surface of maxillary
none , laminae papyracea resp.
• 8. Medial wall of SOF is nothing but nasal surface
of SOF which is just anterior to cavernous sinus

Two bisections in whole skull
base

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

Two bissections in whole skull base
1. facial nerve bissects jugular bulb
2. GSPN bissects V3 & Petrous carotid

Posterior wall of maxilla & pterygoid
process is curved anteriorly

PPF is at supero-medial area of
posterior wall of maxilla

Lateral to infraorbital nerve & V2 is Infratemporal fossa
, Medial to ION & V2 is Pterygopalatine fossa

Pterygopalatine ganglion in PPF

Tracking of infraorbital nerve leads to V2 & tracking of V2 leads to Trigeminal ganglion/ Middle
cranial fossa [ one of the best way to track middle crannial fossa is to track V 2 ]

Medial wall of PPF is perpendicular plate of palatine bone –
foramen in it is sphenopalatine foramen

foramen rotandum is 5 mm to middle cranial fossa dura
where as vidian nerve from vidial canal to laceral carotid is 2 cm
– listen 4.00 time in this video
https://www.youtube.com/watch?v=Uk57MEgkde8

PPF extended into orbital apex

The PPF extended to superior orbital fissure ( SOF ) /
Orbital apex , inferior to the cavernous sinus and
Muller’s muscle. – anterior skull base view

The PPF extended to superior orbital fissure ( SOF ) /
Orbital apex , inferior to the cavernous sinus and
Muller’s muscle. – Lateral skull base view

The PPF extended to superior orbital fissure ( SOF ) / Orbital
apex , inferior to the cavernous sinus and Muller’s muscle.
Anterior skull base Lateral skull base

INFRA-TEMPORAL FOSSA ANATOMY in both anterior & lateral skull
base
1. When you go from MPP to jugular bulb it is anterior skull base
2 . When you go from jugular bulb to MPP it is lateral skull base
In CT - scan
1. The space below transverse line of V2 & lateral to LPP is infra-
temporal fossa
2 . The upper half of space between MPP & LPP is pterygo-palatine
fossa .
3. The space above transverse line of V2 is MCF ( middle cranial fossa )
4. The space above transverse line of VN is pterygoid recess

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

I Max = Internal maxillary artery

Temporalis
muscle flap is
based on
posterior (
PDTA ) &
anterior deep
temporal
arteries
(ADTA)

Anteior skull base Lateral skull base

1 = Nasal component , 2 = Infratemporal fossa component , 3 = Parapharyngeal component -
for nasal & Infratemporal component of JNA we don’t need external carotid artery control ,
just coblator is enough . Where as parapharyngeal part of JNA we need external carotid artery
control because the vascularity comes posteriorly from external carotid arterial system

The position of MA in respect to the LPM is hightly variable – Paolo
Castelnuovo
Photo Courtesy – Dr.Janakiram

1. One line along Vidian nerve & another line along V2
2. Lateral to LPP & infra-orbital nerve [ or V2 ] is Infratemporal fossa
3. One transverse line from Vidian nerve connecting vertical line of V 2 & another
transverse line from V2
4. The space above transverse line of Vidian nerve is Pterygoid Recess of sphenoid
5. The space above transverse line of V2 is Middle cranial fossa ( Meckel’s cave )

1. Pterygoid recess [= sphenoid recess ] is pneumatisation of pterygoid
trigone – spac between V2 & VN [ Vidian nerve ]
2. The space above transverse line of Vidian nerve is Pterygoid Recess
of sphenoid

LACERAL CAROTID in relation to PTERYGOID RECESS -Both diagrams right side
1. VN inline with MPP ( Medial pterygoid plate )
2. V2 inline with LPP ( lateral pterygoid plate )
3. Pterygoid recess present inbetween V2 & VN endoscopically
4. Laceral carotid present just behind the posterior wall of pterygoid recess (
sphenoid recess ) - very important vital structure in clearing pterygoid recess
pathology

Pvc, vc, FR are in a 45 degree angle

SOF also comes in the 45 degree angle – my observation

MPP[ medial pterygoid plate ] present at lateral surface of
posterior choana – which is in line with paraclival carotid

1. V1,V2,V3 of 5th nerve – V3 is 90° to V1 & V2 and anterior to
petrous carotid like horse rider leg [ V3 ] [ mneumonic ] on saddle
of horse [ petrous carotid & paraclival carotid junction ]
2. Vidian nerve is continuation of GSPN crosses laterally the laceral
carotid

V1,V2,V3 of 5th nerve – V3 is 90° to V1 & V2 and anterior to
petrous carotid like horse rider leg [ V3 ] [ mneumonic ] on
saddle of horse [ petrous carotid & paraclival carotid junction ]

LPP if you look anteriorly (radiologically ) is in line with FR (V2) , if you look laterally posterior
border of LPP leads to V3 . So when you are removing recurrent nasopharyngeal carcinoma
transnasally you can observe LPP leads to V3 . This V3 seperates pre & post styloid
compartments.

Posterior boarder of lateral pterygoid
plate leads to foramen ovale

GSPN bisects V3 & petrous carotid

Petrous bone has three surfaces with three boarders &
divided into three 1/3rds

In the floor of sphenoid sinus you will get Vidian
nerve when you approach by antero-lateral triangle

Hand model --
left hand = medial & lateral pterygoid
right hand = index is parapharyngeal
carotid , middle is IJV , ring is styloid &
stylopharyngeal muscles , thumb is
horizontal carotid

IAN = inferior alveolar nerve , LN = lingual nerve , MPM = medial
pterygoid muscle , LPM = lateral pterygoid muscle
Different layers of
muscles & aponeurosis
protecting great vessels
in infratemporal fossa –
Main protectors are
medial & lateral
pterygoid mucles &
temporalis muscle -
great vessels are
posterior to these 3
muscles –
small contribution of
protection of great
vessels are done by
tensor veli palatini &
styloid muscles &
stylopharyngeal
aponeurosis

IAN = inferior alveolar nerve , LN = lingual nerve , MPM = medial
pterygoid muscle , LPM = lateral pterygoid muscle

TVPM is triangular muscle , LVPM is
cylindrical muscle

SPM attached
to superior
constrictor ,
SGM attached
to tongue ,
SHM attached
to lesser cornu
of hyoid bone

After drilling LPP & MPP longissmus capitis & superior
constrictor seen .

Incision anterior to anterior to anterior
pillar of tonsil for “Trans - Oral
approach to infratemporal fossa”

Two planes posterior to MPM which have greater surgical importance ...... …..1. Nasopharyngeal
carcinoma/JNA excision - plane between medial pterygoid muscle ( MPM ) & ET tube/TVPM ( tensor veli
palatini muscle)........ 2 . Trans-oral exposure of Infratemporal fossa (ITF) - incision anterior to anterior pillar
of tonsil - leads to - plane between MPM & superior constrictor / styloid muscles............In the below
diagrams MPM reflected back for understanding purpose

Two planes posterior to MPM which have greater surgical importance ...... …..1. Nasopharyngeal
carcinoma/JNA excision - plane between medial pterygoid muscle ( MPM ) & ET tube/TVPM ( tensor veli
palatini muscle)........ 2 . Trans-oral exposure of Infratemporal fossa (ITF) - incision anterior to anterior pillar of
tonsil - leads to - plane between MPM & superior constrictor / styloid muscles............In the below diagrams
MPM reflected back for understanding purpose

1. Each styloid muscle accompanied by one nerve – SPM by 9th nerve ,
SGM by lingual nerve , SHM by 12th nerve
2. SPM & SGM protects ICA whereas SHM protects both ECA & ICA
3. ECA & ICA & CCA are like tuning fork – caricature diagram

Each styloid muscle accompanied by one nerve – SPM by 9th
nerve , SGM by lingual nerve , SHM by 12th nerve

MPM is reflected back – which shows the structures seen in trans-oral
approach of ITF – incision anterior to anterior pillar of tonsil

Schematic diagram for infratemporal fossa approach –
MMA & V3 & pterygoid plate from posterior to anterior

V3[MN] & MMA & ET in lateral & Anterior skull base – see the
relationship of ET tube which is medial to V3 & MMA

V3 & mma are together
2. V3 accompanied by mma whereas IAN [ inferior
alveolar nerve ] is accompanied by PSAA [ postero-
superior alveolar artery ]
Lateral skull base Anterior skull base

After drilling the tympanic bone & styloid process
inbetween jugular bulb & carotid , 9th nerve is seen

Cochlear aqueduct is a pyramidal shape structure present in between
round window & jugular bulb – which is an important landmark for
identification of 9th nerve in retrofacial mastoid air cells area .

The cochlear
aqueduct: An
important
landmark in
lateral skull base
surgery
http://booksc.or
g/book/1766130
2
EO [ external
opening of
cochlear
aqueduct ]

Complete exposure of CA in its entire length (right side). Lateral walls of jugular bulb
(JB) and IPS were removed. In this case IPS is only structure crossing external opening of
CA. Ninth nerve is located slightly anterior and inferior to opening. ICA is seen anterolateral
to CA.

Sympathetic trunk is posterior to vagus
– below photo right side

SCG anastamosed with all the lower
cranial nerves – below photo right side

Superior cervical ganglion is posterior to inferior ganglion of
vagus – SCG lies over prevertebral facia over longus capitis
– below photo left side

11th nerve present in between vertebral artery & IJV

11th nerve is postero-medial & antero-
lateral to IJV
Postero-medial to IJV Antero-lateral to IJV

1. Anterior to IPS - 9th nerve seen , posterior IPS - 10th & 11th seen
2. 12th nerve crosses 10th nerve laterally

1. 9th & 12th nerves crosses parapharyngeal carotid above & below
2. supracondylar groove leads to Hypoglossal canal

12th nerve seen in infra-petrous
approach in anterior skull base

9th & 12th nerves
Anterior skull base Lateral skull base

9th nerve is the most lateral nerve & 12th nerve is most medial nerve in
skull base

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
Lateral skull base Anterior skull base

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. 9th & 12th nerves crosses parapharyngeal carotid above & below
2. 12th nerves originates medial to apex of parapharyngeal carotid
3. 11th nerve hinges the transverse process of C 1
4. 11 th nerve between vertebral artery & IJV
5. 9th nerve anterior to origin of IPS whereas 10th & 11th nerve posterior to origin of IPS
6. superior ganglion of vagus [ SGV ] is inside the jugular foramen where as inferior ganglion of
vagus [ IGV ] is outside skull base

1. 9th & 12th nerves
crosses parapharyngeal
carotid above & below
2. 12th nerves originates
medial to apex of
parapharyngeal carotid
3. 11th nerve hinges the
transverse process of C 1
4. 11th nerve between
vertebral artery & IJV
5. 9th nerve anterior to
origin of IPS whereas 10th
& 11th nerve posterior to
origin of IPS
6. superior ganglion of
vagus [ SGV ] is inside the
jugular foramen where as
inferior ganglion of vagus
[ IGV ] is outside skull
base

Incision anterior to anterior pillar of
tonsil for “Trans - Oral approach of
infratemporal fossa”

Incision of trans-oral approach of ITF is – anterior to anterior
pillar of tonsil – pathway is between MPM & superior constrictor

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

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 anatom
y. Automatically you can
individualize the approach for
the tumor .

PARISIER'S TRIANGLE
(DANGEROUS TRIANGLE)
Perisier's triangle is very important triangle in endoscopic ear surgery
1) Superior limb is formed by inferior part of HFN
2) The apex is formed by the geniculate ganglion
3) The base is formed by the anterior commissure (end) of oval window
4) Inferior limb is formed by tunning point of jocobson's nerve to the the
geniculate ganglion.

PARISIER'S TRIANGLE (DANGEROUS TRIANGLE)

Iatrogenic chances of injury of cochlea in
infratemporal fossa transpetrous approach ,
kawase approach & anterior skull base approach.
For better understanding visit
www.skullbase360.in -- Here the cochlea is actually
postero-medial to vertical part of carotid – wrongly
depicted here medial to pre-cochlear carotid

ORBITAL APEX [ SOF = ALSC
+ Orbital apex]
Extraconal & intraconal
compartmements

A - trajectory leads to middle cranial fossa
B - trajectory leads to infra-temporal fossa

GWS=Greater wing of sphenoid
LWS = Lesser wing of sphenoid

All odd numbers of the carotid are VERTICAL
C7 = Parapharyngeal carotid
C6 = petrous carotid
C5 = paraclival carotid
C4 = lower horizontal part of parasellar carotid
C3 = vertical part of parasellar carotid
C2 = upper horizontal part of parasellar carotid
C1 = intracerebral carotid

Endoscopic view of the
internal carotid artery
showing 3 types of angles
(black lines) between the
posterior ascending and
horizontal portions of the
C4 segment. (A) angle
<80; (B) angle >100; and
(C) angle between 80 and
100. PG, pituitary gland;
ON, optic nerve. *C4
bend. (Printed with
permission from Mayfield
Clinic.)

See video lecture at https://www.youtube.com/watch?v=4tiRfPLYkBo

Transnasal transsphenoidal endoscopic view of the parasellar region illustrate that types I- III are
symmetric and type IV is asymmetric. (A) Type I angle between the posterior ascending and
horizontal portions of C4 segment is <80, resulting in direct contact between the pituitary gland
and the internal carotid artery (ICA) and a tortuous ICA configuration. (B) Type II angle between
the posterior ascending and the horizontal portions of the C4 segment is between 80 and 100. (C)
Type III angle between the posterior ascending and the horizontal portions of the C4 segment is
>100. ICA appears slightly curvilinear and less tortuous than the type I or the type II. (D) Type IV
angles of the left and right ICAs are asymmetric. PG, pituitary gland; ON, optic nerve. *C4 bend.
(Printed with
permission from Mayfield Clinic.)

Authors speculate that type I presents the highest risk for
vascular injury based on its contact between the ICA and
pituitary gland. In 50% of our specimens, the C4 bend was
behind the pituitary gland (Figure 4A). Risk of potential vascular
injury decreases in types II and III. – Get paper at
http://dx.doi.org.sci-hub.cc/10.1016/j.wneu.2014.09.021

core diagram of anterior skull base
If we don't know these diagrams posterior genu carotid blowout happens in
pituitary & anterior skull base surgery especially when the angle between
paraclival carotid & horizontal part of the parasellar carotid is < 80 degrees
where pituitary is very adhere to posterior genu

Transnasal transsphenoidal endoscopic view of a type II angle (between 80
and 100) that has no contact with the pituitary gland. Angle allows a corridor
to the posterior aspect of the cavernous sinus and the oculomotor nerve
without retraction of the internal carotid artery or the pituitary
gland. CN III, oculomotor nerve; CS, cavernous sinus; PG, pituitary gland.
(Printed with permission from Mayfield Clinic.)

Transnasal transsphenoidal endoscopic view between
the C3 and the C4 segments of the internal carotid
artery at the lacerum and clivus levels. Two distinct
shapes (green) were identified as trapezoid (A) in
80%or hourglass (B) in20%of specimens. (Printed with
permission from Mayfield Clinic.)

Conceptual illustration of the endoscopic perspective depicts the various internal
carotid artery (ICA) classifications. (Left) Bouthillier et al. (2) used 7 segments: C1 ¼
cervical, C2 ¼ petrous, C3 ¼ lacerum, C4 ¼ cavernous, C5 ¼ clinoid, C6 ¼ ophthalmic,
and C7 ¼ communicating. (Right) De Powell et al. (5) modification includes C3-C4 bend,
C4 bend, and C4-C5 bend. Depending on the angle of the C4 bend (green plane), a
potential corridor between the ICA and the pituitary allows access to the posterior
cavernous sinus (yellow arrow). SOF, superior orbital fissure; OS, optic strut; OCR,
opticocarotid recess; TS, tuberculum sellae. (Printed with permission Mayfield Clinic.)

Anatomic measurements between the internal carotid arteries and the pituitary gland
in 20 specimens. (A) (aee) Intercarotid distances between the left and right ICAs. (B)
Measurements (a’, b’, c’) of the space between the ICA and the pituitary gland at 3
levels (cephalic, middle, caudal). (Printed with permission from Mayfield Clinic.)

Sphenoid bone
LWS = lesser wing of sphenoid , GWS = greater wing of sphenoid

1. Vertical part of facial nerve bissects jugular bulb .
2. Both facial nerve & temporal part of carotid has vertical & horizontal ( Petrous
carotid ) parts .
3. horizontal & labyrinthine part of facial nerve junction [ 1st genu ] is V-shaped while
vertical part of facial nerve & diagastric tendon junction is U-shaped

Paraphayngeal carotid behind
adenoids
Paraphayngeal carotid behind
tonsils

Petrous carotid & paraclival carotid junction is saddle shapped – not
perpendicular to each other – This is where the carotid-clival window –
infra-petrous approach

1. Vidian artery ( VA ) is branch of laceral carotid . The bone around the vidian canal ( VC ) is drilled along
its inferior half (from 3 o’clock to 9 o’clock) until the carotid artery is identified at the lacerum segment .
VC is funnel shapped .
2. You have to simply cauterize VA to stop bleeding . If bleeding not controlled keep muscle plug in VA
3. VN is lateral to laceral carotid which is continuation of GSPN.
PCC = Paraclival carotid , PC = Petrous carotid , VN = vidian nerve

Anterior skull base view Lateral skull base view

Vidian canal is funnel shapped

1. Both sides 6th nerves in dorello’s canals present medial to para-clival carotids in mid-clivus &
2. 6th nerve crosses Para-clival & Para-sellar carotids juction in AI [ antero-inferior ] virtual
compartment of cavernous sinus

1. MPP & ET opening is
in line with paraclival
carotid .
2. Laceral carotid is in
posterior wall of
pterygoid recess /
sphenoid recess.
3. Transpyerygoid
approach is needed to
reach parasellar area.
4. Area between LPP &
MPP extrapolated lines is
cavernous sinus .
5. LPP in line with FR
6. Traiangle between FR
& VC is pterygoid trigone
or Pterygoid recess /
sphenoid recess

Sternberg canal – this
figure is not final – still
literature has to be
searched ------
actually sternberg canal is
lateral to V2 – Satish Jain

1. SHA supplies anterior pituitary originates from first part of intracerebral carotid
2. IHA supplies posterior pituitary , branch of MHT originates from posterior genu of carotid
3. ILT arises from horizontal carotid in parkinsons triangle
4. Strong opponents of extracapsular dissection of pituitary surgery argument is IHA is
damaged sothat posterior pituitary compromised & diabetes insipidus develops .

Vasculature of the Brain
and Cranial Base – book
name
Superior hypo-physeal
artery
CL anterior clinoid
DX distal ring
IC internal carotid artery
ON optic nerve
PK pituitary stalk
SH superior hypophyseal
artery

B, endonasal cadaveric
dissection using a zero-degree
endoscope after
releasing the pituitary gland from
the dural fold (DF)
that forms the aperture is shown.
The SHa runs above
the DF, and care should be taken
at the last cut when
opening the sellar aperture to
avoid damaging the
SHa. The CS, the IHa, the dorsum
sellae (DS), and the
clivus (C) are shown. The pituitary
stalk (S) can be
seen moved to the right side with
the pituitary gland
(PG) still being tethered by several
PLs, preventing
complete mobilization.

intraoperative suprasellar view with a zero-degree endoscope
showing the pituitary gland (PG) and the pituitary stalk (S) after the opening
of the suprasellar and sellar dura, ligation of the SIS, and complete excision of
the anterior dural fold (DF) that forms the pituitary aperture. The chiasm (Ch)
is visualized superiorly and anteriorly. A small subchiasmatic perforator (SP)
branch of the superior hypophyseal artery is shown.

Posterior genu is the most
common area of
iatrogenic injury of carotid
The parasellar carotid
protuberance is a C- shaped
bone protuberance with the
convexity of the C facing
anterolaterally. It covers four
segments of the ICA: (1) the
hidden segment / Posteriori
genu ; (2) the inferior
horizontal segment; (3) the
anterior vertical segment, and
(4) the superior horizontal
segment. The hidden segment
is located at the level of the
posterior sellar floor and
includes the posterior bend of
the ICA.

IATROGENIC CAROTID INJURE AREAS -
1. Upper & Lower point of C-shape of parasellar
carotid - mnemonic
2. Upper point is m-OCR ( optico - carotid recess ) -
junction of para seller & intra-cerebral carotid
3. Lower point is posterior genu - junction of
paraclival & parasellar carotid

Two potential iatrogenic carotid injury areas
We have to very careful at m-OCR in
transtubercular & transplanum drilling
because praclinoidal & supraclinoidal
junction is exactly m-OCR
Posterior genu is the most common
area of iatrogenic injury of carotid

Upper & lower points of C-shaped Parasellar carotid are origins of SHA & MHT --
These two potential iatrogenic carotid injury areas are origins of SHA ( Superior
hypophyseal artery ) & MHT ( Meningo-hypophyseal trunk ) ; IHA ( Inferior
hypophyseal artery is branch of MHT

Upper half of paraclival carotid is intracavernous while lower half is
extracavernous .
1. caudal part, the lacerum segment of the artery corresponding to the
extracavernous portion of the vessel, and
2. rostral part, the trigeminal, intracavernous portion of the artery, so- called
because the Gasserian ganglion is posterior to it and the trigeminal
divisions are lateral to it.

Branches of ICA – only retrograde artery is opthalmic artery
originates above the upper dural ring

1. After removing TS ( Tuberculam sellae ) you will appreciate SIS ( Superior
intercavernous sinus ) ;
2. SIS & IIS & Right cavernous & Left cavernous is called FOUR blues .
IIS = Inferior intercavernous sinus

SHA ( Superior hypophyseal artery )
1. SHA arises in carotid cave from
paraclival carotid or from intracerebral
carotid in sub-chiasmatic cistern .
2. UDR little bit exagerated for better
understanding of carotid cave
3. Opthalmic artery ,only retrograde
artery of carotid arises above the UDR
4. SHA present above the diaphragm (
cut anteriorly in diagram )
5. Protection of SHA is utmost important
in suprasellar tumors &
craniopharyngiomas
6. SHA gives upper chiasmatic branches (
injury causes scotomas ) & lower
pituitary branches mainly supplying
anterior pituitary .
7. SHA may present infero-medial aspect
of cisternal part of optic nerve in
subchiasmatic cistern .
8. Ophthalmic artery & SHA arises from
carotid cave

Vasculature of the Brain and
Cranial Base – from this book
Superior view of the right
internal carotid (IC) artery
with the roof of the cavernous
sinus dura removed. Part of
the anterior clinoid tip has
been removed.
III third nerve
21 anterior clinoid
DX distal ring
ON optic nerve
OP ophthalmic artery
PX proximal ring

Superior view of the internal
carotid artery with more
extensive removal of the
anterior clinoid exposing the
relationship of the third nerve
sheath to the proximal ring. A
thin veil of dura extends from
the third nerve sheath to the
lateral internal carotid artery.
Also note the at tachment of
the third nerve sheath to the
proximal ring.
III third nerve
IIIs third nerve sheath
21 anterior clinoid
DX distal ring
ON optic nerve
OP ophthalmic artery
PX proximal ring
IC internal carotid artery

1. Virtual compartments of cavernous sinus – parasellar carotid virtually devides cavernous sinus into
L,M,AI,PS compartments
2. 3rd , 4th , 6th , V1 nerves in lateral compartment [ V1 & 6th nerves are in parallel ]
3. 6th nerve in antero-inferior & lateral compartments . Only 6th nerve is freely present in cavernous , that is
the reason for high chances of injury to 6th nerve in cavernous surgery .
4. 3rd nerve in postero-superior compartment
5. there is no vital [ nerves or vessesl ] in medial compartment
6. medial & postero-superior compartment are in continuity .
7. 3rd nerve & pcom are in parallel. In the same way V1 & 6th nerve are in parallel

Actually FCB is filled in foramen
lacerum

Thick fibrous tissue attached to carotid present at carotid canal &
foramen lacerum [ called FCB – fibrocartilagenous basalis ]
In all the skull base foramena vital structure (vessel or nerve ) passes through
respective foramena. But laceral carotid NOT passing through foramen lacerum .
Laceral carotid stays ABOVE the foramen lacerum & fibrocartilageno basalis ( thick
fibrocartilagenous tissue ) . Actually FCB fills the foramen lacerum . This point useful in
infrapetrous approach in anterior skull base .For details see " carotid 360 " PPT at
www.skullbase360.in
Lateral skull base view Anterior skull base view

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

In FTOZ paraclival carotid looks horizontal while in
anterior skull base paraclival carotid looks vertical –
because of angle of view /angle of approach
FTOZ view Anterior skull base view

Observe the posterior genu & anterior genu [ parasellar carotid ] of
carotid is S-shaped in both anterior & FTOZ view – This posterior
genu is most common cause of iatrogenic injury
Anterior skull base view FTOZ view

Observe the posterior genu & anterior genu [ parasellar carotid ]
of carotid is S-shaped in both anterior & FTOZ view – This
posterior genu is most common cause of iatrogenic injury
Anterior skull base view Anterior skull base view

Eustachian tube points like an ARROW the APEX of parapharyngeal
carotid – infact bony part of ET tube is above the junction of vertical
part & horizontal part [ petrous carotid ] of temporal carotid [ in
middle ear carotid seen below the ET ]
Here the cochlea is actually postero-
medial to vertical part of carotid –
wrongly depicted here laterally

1. Cadaveric dissection demonstrating the osteotomies at the base of the posterior clinoids (PC) for
separation with the body of the dorsum sella (DS).
2. 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

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.

1. PCOM & 3RD nerve parallel to each other .
2. Relationship of PcomA & 3rd nerve – parallel or cross each other
in Kernochan's Notch diagram
http://en.wikipedia.org/wiki/Kernohan%27s_notch
In parasellar pituitary 3rd n & 4th n & Pcom
present in Postero-superior cavernous
compartment

Relationship of PcomA & 3rd nerve – parallel or cross each other
in Kernochan's Notch diagram
http://en.wikipedia.org/wiki/Kernohan%27s_notch
In parasellar pituitary 3rd n & 4th n
& Pcom present in Postero-
superior cavernous compartment

Schematic diagram of cavernous sinus roof

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

" Lateral limit of
subchiasmatic cistern is -
First part of intracerebral
ICA " - This is useful when
the tumor fills the whole
sphenoid cavity & has no
landmarks - then we
dissect/drill at planum
area & slow identify the
optic nerve - so just below
the optic nerve laterally [
in subchiasmatic cistern ]
you will encounter the First
part of intracerebral ICA -
ONE OF THE KEY POINT IN
ANTERIOR SKULL BASE

Don’t touch these chiasmatic vessels – scotomas develops

Outer wall of cochlea seperates from vertical part of
intratemporal carotid

Parapharyngeal carotid is at the same coronal place of anterior
arch of atlas – Satish Jain Dr

PARACLIVAL CAROTIDS
1. In 80% cases the space between paraclival carotids is
TRAPEZOID & in 20% the space between paraclival
carotids is HOURGLASS
2. Laceral carotid area ( paraclival & petrous carotid
junction ) is saddle shapped. It is not 90 degrees
3. Paraclival carotid is inline with MPP ( Medial
pterygoid plate )
4. Paraclival carotid can be pushed medially , laterally ,
anteriorly or posteriorly by the tumor at laceral
carotid area . Sometimes total paraclival carotid is
encircled by the tumor .

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

Pituitary is yellow in color like Jack fruit pulp ; spikes on fruit are
pituitary ligaments

Pituitary
1. Jackfruit analogous to pituitary
2. Normal pituitary is yellow in color .
Preserve it in surgery . Unless DI /
panhypo comes .
3. Jackfruit surface has spikes .
Analogous to Pituitary Ligaments
which is plane for extracapsular
pituitary - between pituitary capsule
& meningeal layer .
4. Jackfruit peel is pituitary capsule
after periosteal layer & meningeal
layer of dura . So total 3 layers to
enter into pituitary yellow mass from
sphenoid sellar bone. Endosteal layer
& Meningeal layer are fused to each
other at all places except where the
cranial venous sinuses are enclosed
between them .
5 . Superior & inferior intercavernous
sinus present between periosteal &
meningeal layer of dura

Endosteal layer & Meningeal layer are
fused to each other at all places
except where the cranial venous
sinuses are enclosed between them .

Endosteal layer
& Meningeal
layer are fused
to each other
at all places
except where
the cranial
venous sinuses
are enclosed
between them

Therefore, in regions of
the cranial base where the dura is not covered by overlying bone, the
periosteal layer is absent. This is best exemplified along the superior
and lateral portions of the sella, where the lack of bone creates a very
unique morphological arrangement of the dura mater.
Over the lateral portion of the cavernous sinus, on each side, there
is a meningeal layer along the sphenoid ridge. As this then spans medially
traveling along the roof of the cavernous sinus and toward the sellar
roof, the meningeal layer invaginates into the sella, forming a pouch.
As the meningeal layer from both sides progresses centrally and begins
to invaginate, a central oval aperture is formed through which the stalk
eventually runs (46). Now given that the sella, is completely covered by
bone anteriorly, posteriorly, and inferiorly along the sellar floor, the
invaginating meningeal layer encounters the periosteal layer in these
regions forming the dense double-layered dura mater of the sellar face,
which often is interpreted as a single layer (46). Laterally, by virtue of
the fact that there is no bone separating the pituitary fossa from the cavernous
sinus, the periosteal layer is absent and therefore the meningeal
layer alone separates the pituitary gland from the cavernous sinus.

Lateral wall of cavernous sinus has 2 layers –
there is clear cut plain between dura propria &
inner membranous layer .
1. outer meningeal layer is also called Dura
propria which we elevate in dolenc approach .
2. inner membranous layer formed by sheats of
nerves of 3 , 4 , V1 .

G & H are present observations

Artist's drawings of different types of cavernous sinus. Left. Normal cavernous sinus. The whole
cavernous sinus is enveloped by a thin membranous layer that separates the contents of the lateral wall (third
(III), fourth (IV), and ophthalmic division (V~) of the fifth cranial nerves) from the venous channels of the
cavernous sinus proper. The abducens nerve (VI) is the only intracavemous cranial nerve. The internal carotid
artery (ICA) and second division of the trigeminal nerve (V2) are also depicted. Center: Intracavemous (Type
I) tumors (for example, meningiomas) arise within the cavernous sinus, encircle and displace the cranial nerves
laterally, and tend to encase and narrow the ICA. Right; Interdural (Type II) tumors (tumors of the lateral
wall of the cavernous sinus) arise and remain between the two layers of the lateral wall. The deep membranous
layer separates these tumors from the venous channels of the cavernous sinus. The ICA is displaced medially,
but not encased or narrowed.

yellow arrow inferior part ( Sphenoidal part ) of the medial wall of the cavernous sinus (
yellow line ), blue-sky arrow superior ( Sellar part ) of the medial wall of the cavernous
sinus ( blue-sky line )
In the upper part, the medial wall is given by the meningeal layer, that is a continuation of the
diaphragma sellae, which surrounds the pituitary capsule inferiorly (Yasuda et al. 2005 ; Martins
et al. 2011 ) . In the inferior part, the medial wall is given by the endosteal layer that covers the
body of the sphenoid bone.

3 layers anteriorly, posteriorly, and inferiorly along the
sellar floor
1. periosteal dura [ PD ]
2. meningeal dura [ MD ]
3. pituitary capsule [ PC ]
Intraoperative view with a zero-
degree endoscope showing the two
components of the dura mater
located along the face and floor of
the sella. The dura here is formed by
an inner meningeal dura (MD) and
an outer periosteal dura (PD). The
intercavernous sinuses run in
between both layers as the IIS shown
in the picture. Once these layers
reach the cavernous sinus, they
bifurcate and only the meningeal
layer forms the medial wall of the
cavernous sinus (CS) along the
lateral border of the sella. The
pituitary gland is shown with a
preserved pituitary capsule (PC).

A, schematic drawing showing the sellar
region in a frontal view. The pituitary gland (P) is
demonstrated in the center attached to the medial
wall of the cavernous sinus (CS) by the pituitary
ligaments
(PLs). The anterior dura covering the pituitary
gland
was removed, and the pituitary stalk was freed
under
the chiasm (Ch). The internal carotid arteries are
shown on both sides. The inferior hypophyseal
arteries
(IHa) originate from the meningohypophyseal
trunk of
the ICA within the CS, and they travel medially and
posteriorly to vascularize the inferior posterior
third of
the gland. The inferior hypophyseal arteries are
ligated
and cut along with the IIS and the PLs to allow
the gland to be mobilized superiorly. The superior
hypophyseal arteries (SHa) are preserved, and
care
should be taken when opening the dural fold of
the
aperture to avoid injuring them.

From paper DOI 10.1007/s00701-011-0961-1 – “Transsphenoidal pseudocapsule-
based extracapsular resection for pituitary adenomas ” - Xin Qu - – get paper from
www.sci-hub.cc or www.sci-hub.bz
Diagrams illustrating the pseudocapsule-based intracapsular (a) and extracapsular (b)
resection approaches for large pituitary adenomas. A, adenoma; B, pseudocapsule; C,
normal pituitary gland; D, pituitary capsule; E, dural envelope

1. Mid clivus – from floor of pituitary 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

Just adding two triangles of petrous bone base around foramen magnum ,
your lower clivus / foramen magnum area completes -- just as simple as that

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

Cranio-vertebral junction in
anterior skull base

RCLM = rectus capitis lateral muscle , RCAM = rectus capitis anterior muscle , AIM =
anterior intertrasversarius muscle , Lcap = Longus capitis , Lcol = Longus coli – longus
capitis anterior to longus coli

1. Vertebral artery ( VA ) is medial to AIM in between C1 & C2 transverse process
2. ICA anterior to longus capitis . Lcap = Longus capitis , Lcol = Longus coli – longus
capitis anterior to longus coli

Jugular foramen is postero-lateral to hypoglossal canal . IJV is posterior to ICA
RCLM = rectus capitis lateral muscle , RCAM = rectus capitis anterior muscle , HC =
hypoglossal canal , IJV = internal juvular vein , S = styloid process , ICA = internal
carotid artery , VA = vertebral artery , AIM = anterior intertrasversarius muscle

Jugular foramen is postero-lateral to hypoglossal canal . IJV is
posterior to ICA

Anteior longitudinal ligament attached to PT ( Pharyngeal tubercle ) . AAOM
& AAAM present between lower clivus –C1 & C1–C2 respectively

In between eustachian tubes AAA ( anterior arch of atlas )
present .

1. In between eustachian tubes AAA ( anterior arch of atlas ) present
2. Floor of nasal cavity in line with AAA
FM = foramen magnum , MPP = medial pterygoid plate , LPP =
lateral pterygoid plate

After drilling AAA ( Anterior arch of
atlas ) dens seen .

After dens drilling- cruciate ligament seen - Transverse
fibres of cruciate ligament is transverse ligament which
embraces dens to prevent it dislocation

After anterior arch of atlas , dens drilling & cruciate ligament
removal – tentorial membrane seen – tentorial membrane is
upward continuation of posterior longitudinal ligament .
Tentorial ligament not attached to dens

After opening dura . Dura present after removal of posterior
longitudinal ligament & tentorial membrane .
Note two ASAs ( Anterior spinal arteries )

Cranio-vertebral junction in
lateral skull base

OC ( occipital condyle ) present at the back side angle
of jugular bulb

2 openings in medial wall of jugular bulb – anterior is IPS
opening & posterior is PCV opening

1. 12th nerve between JT & OC
2. vertebral artery below OC

Vertebral artery present in between
SO & IO triangle

Hypoglossal canal at anterior 1/3rd &
posterior 2/3rd junction of OC

HC ( hypoglossal canal ) present between JT ( Jugular tubercle ) & OC (
Occipital condyle ) - JT & OC drilled in below diagram in infrapetrous
approach

HC ( hypoglossal canal ) present between JT ( Jugular
tubercle ) & OC ( Occipital condyle )
; FM = foramen magnum

HC present between JT & OC approached in
behind jugular bulb in lateral skull base ( far
lateral approach ) & anterior skull base

Trasnasal endoscopic view
FPA = Fronto-polar artery ; FOA = Fronto-orbital artery

Trascranial view

FPA = Fronto-polar artery ; FOA =
Fronto-orbital artery
Transnasal endoscopic view Trascranial view

Bifrontal craniotomy view

Superior & inferior orbital fissure

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

Anterior wall of
Cavernous sinus
, SOF , Orbital
apex in
continnum
[ SOF = ALSC +
Orbital apex]

The term cavernous sinus addresses only the venous aspect, neglecting the neural and
soft tissue components. A more comprehensive and rational term is lateral sellar
compartment (Parkinson 1990 ) .
• Lateral sellar compartment ( =
Cavernous sinus ) is in
continuation with SOF & Orbit
• SOF devided into
[ SOF = ALSC + Orbital apex]
1. ALSC = Anterior lateral sellar
compartment – Located
anterior to the anterior loop
of the cavernous portion of
the internal carotid artery.
2. Orbital apex

Anterior lateral sellar compartment [ ALSC ]
[ SOF = ALSC + Orbital apex]
An important
vein travelling the
SOF is quite
constant. It is
immediately under
the periorbit,
outside the
muscular cone, and
reaches the
cavernous venous
compartment. This
vein can be a
limiting factor for
drilling the SOF area
(Dallan et al. 2013 ).

Parts of ALSC ( Anterior lateral sellar
compartment )
1. Superior Part – Nervous compartment
a. Lateral Group of nerves - from lateral to medial - LFT[ Liver
functional tests ] Menumonic – Lacrimal N., Frontal N.,TrochlearN.
b. Middle Group of nerves - 3rd , 6th , Nasocilliary N.
2. Inferior part – Venous compartment - Inferior Opthalmic vein – The
inferior venous compartment is given by the confluence of the superior
ophthalmic vein ( SOV ) and inferior ophthalmic vein ( IOV ), which drain
into the cavernous sinus (Froelich et al. 2009 ) .

ORBITAL APEX
[ SOF = ALSC +
Orbital apex]
Orbital apex is divided into the
1. intraconal compartment
2. extraconal compartments
- passed by the lacrimal,
trochlear, and frontal
nerves. The frontal and
trochlear nerves ascend
above the Levator muscle &
superior rectus muscle.
Within the intraconal space,
the
1. superomedial
foramen - optic nerve and
the ophthalmic artery pass.
2. superolateral
foramen - oculomotor, nasociliary,
and abducens nerves pass.

Parts of Orbital Apex
Orbital apex is divided into the
– intraconal compartment
– extraconal compartments - passed by the lacrimal,
trochlear, and frontal nerves. The frontal and trochlear
nerves ascend above the Levator muscle & superior
rectus muscle.
Within the intraconal space, the
1. superomedial foramen - optic nerve and the
ophthalmic artery pass.
2. superolateral foramen - oculomotor, nasociliary,
and abducens nerves pass.

Anterior wall of
Cavernous sinus ,
SOF , Orbital apex
in continnum
[ SOF = ALSC +
Orbital apex]

1. 3rd nerve supplies to the muscles from medially – so when you are doing principle of
divergence [ to separate the ocular muscles ] to remove the intraconal tumors , don’t stretch
too much , chances of nerve avulsion from the muscle is there sothat muscle palsy
2. SO4 LR6 – all muscles by 3rd nerve , super oblique by 4th nerve , lateral rectus by 6th nerve
3. MG = medial group of nerves – 3rd, 6rth , nasociliary ; LG = lateral group of nerves – LFT [
mneumonic = Lacrimal , frontal , trochlear ]
Orbital
apex
[ SOF = ALSC +
Orbital apex]

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

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

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

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

Carotid is usually not injured in ACP drilling because ICA
turns backwards poterior /behind OS ( Optic strut )
Before ACP drilling After ACP drilling

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

Compare the optic struct/ UDR/LDR/SOF in neurosurgical &
anterior skull base
3rd & 6th nerve in SOF

1. Upper thinner & lower thicker divisions of 3rd nerve
2. 6th nerve is lateral to nasociliary nerve in between two divisisons of 3rd nerve
because it has to supply lateral rectus .

Line diagrams - skull base 360 - part 1

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Line diagrams - skull base 360 - part 1