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

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For Other powerpoint presentatioins of “ Skull base 360° ”

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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

Total anterior skull base

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

Pterygo-palatine fossa

Posterior wall of maxilla & pterygoid process is curved anteriorly

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

PPF & palatine bone relation

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

Infratemporal fossa

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

1st & 2nd & 3rd part

of I-MAX

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

Anteior skull base Lateral skull base

Anterior skull base view

Lateral skull base view

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 V22. 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

Vidian canal is funnel shaped

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

Apex of infratemporal fossa

V3 & mma are together

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.org/book/17661302

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. 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 & below2. 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. 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

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

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

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 anatomy. Automatically you can individualize the approach for the tumor .

PARISIER'S TRIANGLE (DANGEROUS TRIANGLE)

Perisier's triangle is very important triangle in endoscopic ear surgery1) 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 cochlear injury

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

Orbit

Orbital apex

ORBITAL APEX [ SOF = ALSC + Orbital apex]

Extraconal & intraconal compartmements

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

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

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

Carotid

All odd numbers of the carotid are VERTICALC7 = Parapharyngeal carotid

C6 = petrous carotidC5 = paraclival carotid

C4 = lower horizontal part of parasellar carotidC3 = vertical part of parasellar carotid

C2 = upper horizontal part of parasellar carotidC1 = 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 withpermission 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

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

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

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

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 clinoidDX distal ringIC internal carotid arteryON optic nervePK pituitary stalkSH superior hypophyseal artery

B, endonasal cadavericdissection using a zero-degree endoscope afterreleasing the pituitary gland from the dural fold (DF)that forms the aperture is shown. The SHa runs abovethe DF, and care should be taken at

the last cut whenopening the sellar aperture to avoid damaging theSHa. The CS, the IHa, the dorsum sellae (DS), and theclivus (C) are shown. The pituitary stalk (S) can beseen moved to the right side with the pituitary gland(PG) still being tethered by several PLs, preventingcomplete mobilization.

intraoperative suprasellar view with a zero-degree endoscopeshowing 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 ofthe 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.

PLL = petro-lingual ligament

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 cave3. Opthalmic artery ,only retrograde artery of carotid arises above the UDR4. SHA present above the diaphragm ( cut anteriorly in diagram )5. Protection of SHA is utmost important in suprasellar tumors & craniopharyngiomas6. 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

Carotid cave

Vasculature of the Brain and Cranial Base – from this book

Superior view of the right internal carotid (IC) arterywith the roof of the cavernous sinus dura removed. Part of the anterior clinoid tip has been removed.

III third nerve21 anterior clinoidDX distal ringON optic nerveOP ophthalmic arteryPX 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 nerveIIIs third nerve sheath21 anterior clinoidDX distal ringON optic nerveOP ophthalmic arteryPX proximal ringIC 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 clivusa. 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 diagramhttp://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

PARACLIVAL CAROTIDS1. 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 .

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 clivusa. Petrosal face

b.Clival face

Circle of willis

Circle of willis in anterior & lateral skull base view

??? is intracerebral carotid

Pituitary

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

Saggital section

Therefore, in regions ofthe cranial base where the dura is not covered by overlying bone, theperiosteal layer is absent. This is best exemplified along the superiorand lateral portions of the sella, where the lack of bone creates a veryunique morphological arrangement of the dura mater.Over the lateral portion of the cavernous sinus, on each side, thereis a meningeal layer along the sphenoid ridge. As this then spans mediallytraveling along the roof of the cavernous sinus and toward the sellarroof, the meningeal layer invaginates into the sella, forming a pouch.As the meningeal layer from both sides progresses centrally and beginsto invaginate, a central oval aperture is formed through which the stalkeventually runs (46). Now given that the sella, is completely covered bybone anteriorly, posteriorly, and inferiorly along the sellar floor, theinvaginating meningeal layer encounters the periosteal layer in theseregions forming the dense double-layered dura mater of the sellar face,which often is interpreted as a single layer (46). Laterally, by virtue ofthe fact that there is no bone separating the pituitary fossa from the cavernoussinus, the periosteal layer is absent and therefore the meningeallayer 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 wholecavernous 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 thecavernous sinus proper. The abducens nerve (VI) is the only intracavemous cranial nerve. The internal carotidartery (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 nerveslaterally, 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 membranouslayer 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 sellarregion in a frontal view. The pituitary gland (P) isdemonstrated in the center attached to the medial wall of the cavernous sinus (CS) by the pituitary ligaments(PLs). The anterior dura covering the pituitary glandwas removed, and the pituitary stalk was freed underthe chiasm (Ch). The internal carotid arteries areshown on both sides. The inferior hypophyseal arteries(IHa) originate from the meningohypophyseal trunk ofthe ICA within the CS, and they travel medially andposteriorly to vascularize the inferior posterior third ofthe gland. The inferior hypophyseal arteries are ligatedand cut along with the IIS and the PLs to allowthe gland to be mobilized superiorly. The superiorhypophyseal arteries (SHa) are preserved, and careshould be taken when opening the dural fold of theaperture 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

Clivus

Mid clivus

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

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

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

Lower clivus

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 process2. 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

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

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

Vertebral artery present in between SO & IO triangle

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

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

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

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

lateral approach ) & anterior skull base

ACA complex

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

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

FPA = Fronto-polar artery ; FOA = Fronto-orbital artery

Transnasal endoscopic view Trascranial view

Bifrontal craniotomy view FPA = Fronto-polar artery ; FOA = Fronto-orbital artery

Superior & inferior orbital fissure

1. SOF present between two structs2. OS [ optic struct separates optic canal from SOF ]

1. SOF present between two structs2. 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 importantvein travelling the

SOF is quite constant. It is

immediately under the periorbit, outside the

muscular cone, andreaches 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 compartment2. 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.

ORBITAL APEX [ SOF = ALSC + Orbital apex]

Extraconal & intraconal compartmements

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]

ORBITAL APEX [ SOF = ALSC + Orbital apex]

Orbital apex is divided into the 1. intraconal compartment2. 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.

ORBITAL APEX [ SOF = ALSC + Orbital apex]

Extraconal & intraconal compartmements

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]

Nasal part of SOF

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

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-OCR3. 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=wO2cWHiOdO02. https://www.youtube.com/watch?v=4dkQY3zxJHU3. https://www.youtube.com/watch?v=vd4_lPVIUvE4. https://www.youtube.com/watch?v=_dvYB1InGMc5. https://www.youtube.com/watch?v=83_VuKHXOmQ6. https://www.youtube.com/watch?v=0KwBhTqNXA47. https://www.youtube.com/watch?v=pCURjQ83HzU8. https://www.youtube.com/watch?v=DNIy0L3oFgY9. https://www.youtube.com/watch?v=GT4eBB2x58Q10. https://www.youtube.com/watch?v=OS4Mc0X8tlU11. https://www.youtube.com/watch?v=_xq9e3p1cc4

Compare the optic struct/ UDR/LDR/SOF in neurosurgical & anterior skull base

3rd & 6th nerve in SOF

Vasculature of the Brain and Cranial Base – from this book

Superior view of the right internal carotid (IC) arterywith the roof of the cavernous sinus dura removed. Part of the anterior clinoid tip has been removed.

III third nerve21 anterior clinoidDX distal ringON optic nerveOP ophthalmic arteryPX 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 nerveIIIs third nerve sheath21 anterior clinoidDX distal ringON optic nerveOP ophthalmic arteryPX proximal ringIC internal carotid artery

1. Upper thinner & lower thicker divisions of 3rd nerve2. 6th nerve is lateral to nasociliary nerve in between two divisisons of 3rd nerve

because it has to supply lateral rectus .