Skull base 360°- Part ONE

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Published on March 9, 2014

Author: muralichandnallamothu

Source: slideshare.net

SKULL BASE 360°-ONE Endoscopic Lateral Skull base (Neuro-otology) Endoscopic Anterior skull base & Microscopic Lateral skull base & Middle cranial fossa skull base & Open skull base approaches [ Dated: 9-3-14 ] I will update continuosly with date tag at the end as I am getting more & more information Art & Presentation by Dr. N. Murali Chand DLO FHM Fellowship in HIV medicine, MAMC, New Delhi My website = www.integratedmedicine.co.in Cell= +91 99496 77605

Great teachers – All this is their work . I am just the reader of their books . Prof. Paolo castelnuovo Prof. Aldo Stamm Prof. Magnan Prof. Mario Sanna

Approach

Only to lesion lateral to meridian of pupil in frontal sinus we have to do osteoplastic flap The landmarks for canine fossa puncture/trephine are the intersection between a vertical line through the pupil and a horizontal line drawn through the floor of the nose.

Enhanced T1-weighted magnetic resonance imaging (MRI), coronal section demonstrates a right nasoethmoidal lesion (adenocarcinoma) with an “hourglass” intradural extension through the ethmoidal roof. Diffuse enhancement of the dural layer (arrowheads) over the orbital roof is suspicious for neoplastic spread. The vertical lines limit the area of the dura safely resectable by a pure endoscopic approach.

“Up & below” approach to frontal sinus

Illustration of the septal incisions necessary to achieve good access to the entire anterior wall of the maxillary sinus for tumors either originating from this region or with a significant anterior wall attachment. (B) Cadaveric image demonstrating the access to the anterior wall (AW) of the maxillary sinus with a 70-degree diamond drill (D).

(A) The microdebrider blade has been passed through an inferior meatal antrostomy. Note the anterior fulcrum (nasal vestibule, broken white arrow) and the posterior fulcrum (inferior meatal antrostomy, white arrow). The region of the maxillary sinus that can be cleared through this access is shaded. This shaded region is smaller with a middle meatal antrostomy. The single fulcrum of the canine fossa puncture is indicated (white arrow) (B,C,D), illustrating how the entire maxillary sinus can be accessed as the blade only has a single fulcrum.Medial , posterior & Lateral walls approached through Caldwel-luc

The red arrows demonstrate the endonasal approach, and the green arrows represents the transmaxillary approach. The blue rectangle shows the parasellar structures. A more perpendicular angle of attack is achieved in the transmaxillary approach, and the distance to the target from this route is equal to or smaller than that in the endonasal approach. Temp.: temporal.

Note that in the transmaxillary approach the structures in the lateral wall of the sphenoid sinus are seen in a more perpendicular way, facilitating dissection of this region.

Close-up view of the cavernous sinus through the transmaxillary approach. Gasser.: gasserian.

The pink and orange lines demonstrate the possible angles of maneuver in transmaxillary approach. In green is emphasized the possibilities of resection through transmaxillary approach.

General view of the radial endoscopic accesses to the skull base --- The green arrows represent the endonasal approaches, the red arrows represent the transmaxillary approaches, and the purple arrows represent the subtemporal approaches. Note the multiple possibilities of combination of these approaches.

Modified denkers approach - Blue dotted line shows the medial maxillary wall. (B) Panoramic view after removing the medial maxillary wall. Yellow dotted line shows the connected nasal cavity with maxillary sinus the maxillary sinus.

Schematic demonstrating how the removal of the lateral aspect of the piriform overture (in the red circle) enables a wider approach (the green cone compared with the yellow cone) to the lateral regions (pterygopalatine and infratemporal fossa).

Use combination of approaches when ever it is necessary Combined Transmastoid Middle Cranial Fossa Approach

Rt lower cranial nerve shwannoma, which approach will be better ,which approach will be better considering this side is dominant sinus.

Answer • Amit Keshri says - eight nerve was normal,so was 7th,removed tumor completely with retrolab approach and to get space,the sigmoid plate was decompressed and sinus retracted posteriorly after RMSO [ Retro mastoid sub-occipital ] craniotomy without opening dura posteriorioly. • Murali Chand Nallamothu For lower cranial nerve schawnnoma POTS approach is the best - but here you are saying it is dominent sinus , no need to sacrifice sigmoid sinus -- so in this case we can use extended translabyrinthine approach for the AFB area part & at carotid canal area part of the tumor can be removed by externally which is included in the lower C - shaped incision • Murali Chand Nallamothu if the 8 th nerve is good we can try retrolabyrinthinne & retrosigmoid approach & take the help of endoscope. • Post-op :

Posterior wall of maxillary sinus Periosteum after removal of posterior bony wall of maxillary sinus – this periosteum must be removed in JNA

MPP/VN LPP/V2

Anteriorly MPP & LPP are fused & posterioly only they are divided .

Anteriorly MPP & LPP are fused & posterioly only they are divided .

Medial pterygoid is in line with lateral wall of Sphenoid

Lateral part of Posterior choanae is MPP

Lateral part of Posterior choanae is MPP

Medial pterygoid is in line with Paraclival carotid

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 ]

Zygomatic nerve [ ZN ]

Infraorbital groove near inferior orbital fissure – If we drill supero-lateral to infraorbital nerve it is nothing but Inferior orbital fissure .

Infraorbital groove near inferior orbital fissure – If we drill supero-lateral to infraorbital nerve it is nothing but Inferior orbital fissure .

Red ring = V2

Inferior orbital foramen continues as pterygomaxillary fissure .

One line along Vidian nerve & another line along V2

Lateral to LPP & infra-orbital nerve [ or V2 ] is Infratemporal fossa

One transverse line from Vidian nerve connecting vertical line of V 2 & another transverse line from V2

The space above transverse line of Vidian nerve is Pterygoid Recess of sphenoid – Read the CT – scan/ Plane the surgery by using these lines

The space above transverse line of V2 is Middle cranial fossa ( Meckel’s cave ) – Read the CT – scan/ Plane the surgery by using these lines

Pterygo-palatine fossa

Pterygopalatine fossa. A, V2 (blue dotted line) coming out from the foramen rotundum; B, green-yellow dotted line shows the pterygopalatine ganglion; C, yellow dotted line shows the vidian nerve; D, red dotted line shows the sphenopalatine artery; E, light blue dotted line shows the great palatine nerve; F, white dotted line showing the infraorbital artery.

EC – Ethmoidal crest – left nose

PVC , VC & FR are in 45 degree angle line

Endoscopic view of PPG

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 ]

Zygomatic nerve [ ZN ]

Endoscopic view of foramen rotundum area

Infratemporal fossa

Lateral pterygoid muscle devides internal maxillary artery into 3 parts

1. The maxillary artery & Buccal nerve enters the infratemporal fossa between the superior and inferior head of the lateral pterygoid muscles. 2. Lingual nerve & Inferior alveolar nerve comes between medial pterygoid & lateral pterygoid mucles .

Anteriorly lingual nerve & posteriorly Inferior Alveolar nerve coming lateral to medial pterygoid muscle

Forceps behind IAN Forceps behind LN

Triangle formed by temporalis muscle , MPM & LPM Mandibulotomy approach Endospic view

Post-maxillectomy “Fat pad” over temporalis muscle – which is seen as Fat Pad [ FP ] in the triangle formed by temporalis mucle , MTM & LPM endoscopically

Internal carotid artery going medial & posterior to medial pterygoid muscle into Parapharyngeal space & becoming Parapharyngeal carotid

Internal carotid artery going medial & posterior to medial pterygoid muscle into Parapharyngeal space & becoming Parapharyngeal carotid

After removing the LPM you will see Tensor veli palatini muscle (TVPM) coming vertically downwards from anterior surface of ET , protecting parapharyngeal carotid & after TVPM , thick Stylopharyngeal apneurosis (SPHA ) present ANTERIOR to Parapharyngeal carotid [ So 2 structures ( TVPM & SPHA ) protecting parapharyngeal carotid ]

After removing the LPM you will see Tensor veli palatini muscle (TVPM) coming vertically downwards from anterior surface of ET , protecting parapharyngeal carotid & after TVPM thick Stylopharyngeal apneurosis present ANTERIOR to Parapharyngeal carotid -- Attached to this ET cartilage [ TP/ET attachment ] is the tensor palatini (TP) fibrous aponeurosis (solid white line) with its muscle fibers seen below (broken white line).

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

Parapharyngeal space

Internal carotid artery going medial & posterior to medial pterygoid muscle into Parapharyngeal space & becoming Parapharyngeal carotid

Post-styloid compartment = carotid space

Sphenoid osteum

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

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

L-OCR & M-OCR

The bone of the anterior clinoid (AC) process has been left in place, positioned within the lateral opticocarotid recess. L-ocr is the space in Optic strut - not the space in Anterior clinoid process

L-ocr is the space in Optic strut - not the space in Anterior clinoid process Note Optic strut Note Optic strut - Right Optic nerve Anterio-superior view

Pneumatization of anterior clinoid process – in various planes + onodi cell on both sides of sphenoid [ when transverse septum present in sphenoid it is onodi cell ] + sphenoid recess on left side between V2 & VN .

The same cadaver photo what you are seeing in CT scan above – Note the supraoptic pneumatisation [ present in anterior clinoid process ] in an onodi cell .

ICAcl clinoidal portion of the internal carotid artery , The clinoidal segment of the internal carotid artery faces the posterior aspect of the optic strut [L-OCR ]

Inferior boarder of L-OCR is by 6th nerve & V1

M-OCR

The mOCR is located just medial tothe paraclinoidal-supraclinoidal ICA transition and inferior to the distal cisternal segment of the ON(Labib et al. 2013 ). Cl clivus, ICAc cavernous portion of the internal carotid artery, ON optic nerve, PG pituitary gland, PS planum sphenoidale, TS tuberculum sellae, yellow asterisks upper dural ring, blue arrowheads lower dural ring, white asterisk lateral optico-carotid recess, white circle medial optico-carotid recess, white arrow ophthalmic artery, black arrows middle clinoid process, red arrows lateral tubercular crest, yellow arrows endocranial region corresponding to MCP

UDR = Upper dural ring

The mOCR is placed at the confluence of the sella, tuberculum sellae, carotid protuberance, optic canal and planum sphenoidale. The mOCR corresponds to the lateral extent of the tuberculum sellae. ---- white asterisk lateral opticocarotid recess, white circle medial opticocarotid recess

SIS & IIS

SIS – superior intercavernous sinus & IIS – inferior intercavernous sinus

1. Note ASIS & PSIS 2. Note Subarachnoid space at antero-superior area , which is the potential CSF leak area in pituitary surgery .

PSIS – Posterior superior intercavernous sinus ASIS & PSIS together called CIRCULAR SINUS

Clivus

Pneumatization of the sphenoid sinus

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

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

Transcochlear approach

Note CL [ clivus ] in these photos after drilling of cochlea

Note CL [ clivus ] in these photos after drilling of cochlea The clivus bone (CL) can be seen medial to the internal carotid artery (ICA). JB Jugular bulb In the lower part of the approach, the glossopharyngeal nerve (IX) can be seen. V Trigeminal nerve, VIII Cochlear nerve, AICA Anterior inferior cerebellar artery, CL Clivus bone, DV Dandy’s vein, FN Facial nerve, FN(m) Mastoid segment of the facial nerve, FN(t) Tympanic segment of the facial nerve, GG Geniculate ganglion, ICA Internal carotid artery, JB Jugular bulb, MFD Middle fossa dura, SCA Superior cerebellar artery, SS Sigmoid sinus

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

Note CL [ clivus ] in these photos after drilling of cochlea Note cochlear aqueduct [ CA ] Here ICA is vertical part of carotid infront to cochlea – this is not paraclival carotid

Note CL [ clivus ] in these photos after drilling of cochlea

Note CL [ clivus ] in these photos after drilling of cochlea Note the contralateral vertebral artery [ CVA ] in below photo

Clivus in Infratemporal fossa approach

PVC – is occupied by Ascending palatine artery (APA)

V3 & MMA

Endoscopically [ Anterior skull base ] if we follow upper end of LPT posteriorly we can reach V3 [ Posterior boarder of Lateral Pterygoid bone leads to Foramen Ovale – Dr.Kuriakose ]

MMA

My forceps touched the lingual nerve , posterior to this LN is Inferior alveolar nerve – These two nerves present in triangle formed by medial pterygoid , lateral pterygoid & temporalis muscle

Chorda[CT] attached to LN

Chorda[CT] attached to LN

Schematic diagram for infratemporal fossa approach

V3 & MMA

V3 & MMA

Posterior boarder of Lateral pterygoid bone leads to Foramen Ovale [ FO ] – Dr.Kuriakose

Posterior boarder of Lateral Pterygoid bone leads to Foramen Ovale [ FO ] – Dr.Kuriakose

Posterior boarder of Lateral Pterygoid bone leads to Foramen Ovale [ FO ] – Dr.Kuriakose , Endoscopically [ Anterior skull base ] also if you follow upper end of LPT posteriorly we can reach V3

In Infratemporal fossa approach- Posterior boarder of Lateral pterygoid bone leads to Foramen Ovale [ FO ] – Dr.Kuriakose

V3 is anterior (infront) to Horizontal carotid (= Petrous carotid ) & ET – It cause indentation on the ET also .

In open approaches in maxillary swing approach as long as you stay lateral to ET you will not injure the horizontal part of carotid

Petrous carotid & paraclival carotid is SADDLE shape – LEG of the rider is V3

V3 is an important landmark to locate the post-styloid compartment, as it is anterior to this space (Falcon et al. 2011 ) .

TP & LP

Dhingra photos of TP & LP

Eustachian tube

ET is pointing like an ARROW the posterior genu of internal carotid [ ICAp & CF is parapharyngeal carotid ]

black asterisks medial corridor to ICAp – TVPM attached to anterior surface of ET – so if we go inbetween MPM & TVPM we reach to ICAp

Bony-cartilagenous junction of ET tube is at posterior genu of carotid - ET is pointing like an ARROW the posterior genu of internal carotid

Yellow arrow - Bony-cartilagenous junction of ET tube is at posterior genu of carotid - ET is pointing like an ARROW the posterior genu of internal carotid

ET tube in SPF [Spheno-petrosal fissure]

At bony-cartilagenous junction of ET tube – Horizonal carotid & Parapharyngeal carotid is above & below ET My understanding

In open approaches in maxillary swing approach as long as you stay lateral to ET you will not injure the horizontal part of carotid

pharyngeal recess (fossa of Rosenmüller), which projects laterally from the posterolateral corner of the nasopharynx with its lateral apex facing the internal carotid artery laterally and the foramen lacerum above;

endonasal approaches to expose the area between the ICAs belong to the sagittal plane, and the approaches around the ICA define the coronal plane modules.

Note that the eustachian tube indicates the carotid canal only approximately. In other words, it lies on a different CORONAL plane in respect of the vessel, and from an anterior viewpoint, it covers the vessel for all its length. -- Medially the space between these two CORONAL planes is nothing but Fossa of Rosenmuller [ My understanding ]

Note that the eustachian tube indicates the carotid canal only approximately. In other words, it lies on a different CORONAL plane in respect of the vessel, and from an anterior viewpoint, it covers the vessel for all its length. -- Medially the space between these two CORONAL planes is nothing but Fossa of Rosenmuller [ My understanding ]

Surgeons should have in mind that the external orifi ce of the carotid canal is not on the same coronal plane of the foramen lacerum (anterior genu). It is by far more posteriorly located.

SOF [ Superior Orbital Fissure ]

SOF is the space between two Structs – Superiorly OS [ Optic Strut ] & Inferiorly MS [ Maxillary Strut ]

SOF is the space between two Structs – Superiorly OS [ Optic Strut ] & Inferiorly MS [ Maxillary Strut ]

SOF is the space between two Structs – Superiorly OS [ Optic Strut ] & Inferiorly MS [ Maxillary Strut ] Anterior view of SOF Posterior view of SOF

Yellow line = “nasal” part of SOF Clinically, the SOF and CS apex represents a continuum.

endoscopic endonasal viewpoint the nasal window to SOF is above V2, and below the lateral optico-carotid recess. blue-sky arrows SOF ; MS-Maxillary strut ; MP-Maxillary prominence

The structure Infero-lateral to SOF is – Horizontal part of carotid

One boundary of L-OCR is Superior Orbital Fissure – My Observation

SOF - Anterior

SOF - Posterior

MS- Maxillary strut /// Average distance from the FR at PPF and the vertical segment of ICAc is 35 mm [ 3.5cm ] (Amin et al. 2010 ) .

SOF , Middle Fossa , V3 in line vertically

GSPN-VIDIAN NERVE

GSPN passes above Horizontal [=petrous] carotid & passes underneath V3 & crosses petro-paraclival carotid junction at foramen lacerum before becoming vidian nerve

The bone overlying the internal auditory canal has been removed and the dura of the canal has been removed near the fundus. The facial nerve (FN) can be seen entering its labyrinthine segment to form the geniculate ganglion (GG) more laterally. V Trigeminal nerve, < Acousticofacial bundle, C Cochlea, ET Eustachian tube, GPN Greater petrosal nerve, I Incus, IAC Internal auditory canal, ICA Internal carotid artery, M Malleus, SSC Superior semicircular canal, SV Superior vestibular nerve Observe the relationship between GSPN & horizontal carotid

Fig. 2.62 The course of the horizontal segment of the internal carotid artery (ICAh), as seen from the middle cranial fossa of a left temporal bone. VI Abducent nerve, C Cochlea, GPN Greater petrosal nerve, IAC Internal auditory canal, ICA(ic) Intracranial internal carotid, M Mandibular nerve, MMA Middle meningeal artery, MX Maxillary nerve

Fig. 5.47 The view after completion of the middle crannial fossa approach. AE Arcuate eminence, BB Bill’s bar, C Cochlea, FN(iac) Internal auditory canal segment of the facial nerve, FN(t) Tympanic segment of the facial nerve, G Geniculate ganglion, GPN Greater petrosal nerve, I Body of the incus, L Labyrinthine segment of the facial nerve, M Head of the malleus, MFD Middle fossa dura, SVN Superior vestibular nerve

In Infratemporal fossa - Note that the greater petrosal nerve (GPN) is adherent to the dura, and that retracting the dura will lead to stress on the facial nerve at the geniculate ganglion (GG) level. Thus, if dural retraction is needed, cutting the petrosal nerve will prevent this injury. In middle cranial fossa – same point

After elevating V3 anterior[infront] to ET & petrous carotid observe -- GSPN continues as VN [ VN is lateral to paraclival carotid ]

Vidian nerve is formed by GSPN & Deep petrosal nerve – so GSPN (passes underneath V3) crosses laterally the Horizontal carotid and paraclival carotid junction (Prof.Kassam) & continues as Vidian nerve Blue arrow – LPN & Yellow arrow – GPN

Trans-pterygoid approch-- Vidian Artery present in 60% & enters at the junction of Horizontal carotid & paraclival carotid – it is present above the Vidian nerve so while drilling vidian canal in JNA first we have to drill inferior half and then upper half

Vidian nerve - lateral to paraclival carotid & medial to FO [ Foramen Ovale ]- actually it is GSPN

Vidian canal & Spheno-palatine foramen are in 90 degrees

Vidian nerve - lateral to paraclival carotid

Vidian nerve - lateral to paraclival carotid

Vidian nerve - lateral to paraclival carotid

Vidian nerve - lateral to paraclival carotid Close vision of the middle cranial fossa. The gasserian ganglion has been removed

Vidian nerve - lateral to paraclival carotid

Axial T2-weighted magnetic resonance imaging (MRI) sequence at the level of the vidian canal: 1, clivus; 2, pterygoid; 3, horizontal tract of the internal carotid artery (ICA); 4, vidian canal.

Infratemporal fossa approach type C

Vidian artery – origin from Laceral segment

Lateral Recess is the space between V2 & Vidian nerve .

Lateral Recess is the space between V2 & Vidian nerve .

LRSS = Lateral recess of the sphenoid sinus

Floor of Lateral recess is by ET ---BS basisphenoid, ET eustachian tube, LRSS lateral recess of the sphenoid sinus, OPPB orbital process of the palatine bone, PVA(s) palatovaginal artery(ies), RPm rhinopharyngeal mucosa, SPAib inferior branch of the sphenopalatine artery, SPPB sphenoidal process of the palatine bone, SS sphenoid sinus, RS rostrum sphenoidale, VN vidian nerve

Surpra petrous window ET eustachian tube, GPN greater petrosal nerve, MCFd dura of the middle cranial fossa, MMA middle meningeal artery, SPS superior petrosal surface, TI trigeminal impression, V3 third branch of the trigeminal nerve, yellow arrow accessory middle meningeal artery, white asterisks greater petrosal nerve groove

Carotid nerve

Middle cranial fossa approach

The middle fossa retractor is fixed at the petrous ridge (PR). AE Arcuate eminence, GPN Greater petrosal nerve, M Middle meningeal artery The expected location of the internal auditory canal (IAC). The bar-shaded areas are the locations for drilling. A Anterior, AE Arcuate eminence, GPN Greater petrosal nerve, MMA Middle meningeal artery, P Posterior

Petrous apex bone

Petrous apex - Quadrangular area

Petrous apex – Triangular area

Triangles

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

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

CAROTID

Looping / Kinking of Parapharyngeal carotid

kinking or looping of the ICAp - when looping present para-pharyngeal carotid comes to pre-styloid compartment – previously thought that para-pharyngeal carotid never comes anterior to styloid mucles – which is UNTRUE

The stylopharyngeus and styloglossus muscles are critical landmarks, being usually placed anterior to the great vessels (Dallan et al. 2011 ). Note that the presence of kinking or looping of the ICAp could make this statement untrue.

In this kinking of ICA also Prof.Mario Sanna uses very flexible ICA stents

Relation of Eustachian tube & looping of parapharyngeal carotid & styloid process

The external carotid artery passes deeply to the digastric and stylohyoid muscles, but super fi cially to the stylopharyngeus and styloglossal muscle when running toward the parotid gland (Janfaza et al. 2001 ) .

Intratemporal carotid = Horizontal carotid[= Petrous carotid] + Vertical carotid

In Infra-temporal fossa approach The full course of the intratemporal internal carotid artery has been freed. AFL Anterior foramen lacerum, CF Carotid foramen, CL Dura overlying the clivus area, ICA(h) Horizontal segment of the internal carotid artery, ICA(v) Vertical segment of the internal carotid artery, MN Stump of the mandibular nerve Drilling of the clivus has been completed. C Basal turn of the cochlea (promontory), FN(m) Mastoid segment of the facial nerve, FN(t) Tympanic segment of the facial nerve, GG Geniculate ganglion, GPN Greater petrosal nerve, ICA Internal carotid artery, RW Round window

Note the Cochlea basal turn anterior wall in left photo

Note that the basal turn of the cochlea (BT) starts to curve superiorly near the internal carotid artery (ICA), a short distance from the level of the round window.

In most cases, the medial aspect of the horizontal portion of the internal carotid artery is not covered by bone, but simply by dura.

In most cases, the medial aspect of the horizontal portion of the internal carotid artery is not covered by bone, but simply by dura.

In most cases, the medial aspect of the horizontal portion of the internal carotid artery is not covered by bone, but simply by dura.

Post-operative vasospasm of laceral segment [ carotid mobilization done for tumor removal ]

Paraclival carotid

TG ( Trigeminal ganglion ) is lateral to Paraclival carotid

Trigeminal notch at petrous apex

Carotid nerve

PLL- Petrolingual ligament

PLL- Petrolingual ligament - considered as a continuation of the periostium of the carotid canal (Osawa et al. 2008 ) .

“Front door” to Meckel’s cave PLL - It can be considered the border between the horizontal and cavernous portions of the internal carotid artery.

1. The foramen lacerum (FL) is located lateral to the floor of the sphenoid sinus at the level of the spheno-petro-clival confuence. 2. In respect to the FL, the JT is postero-medially located. Therefore to access the jugular tubercle from anteriorly a complete exposure of the foramen lacerum is needed. black asterisk foramen lacerum , JT jugular tubercle, HC hypoglossal canal

PLL = INFERIOR SPHENOPETROSAL LIGAMENT ACP anterior clinoid process, APCF anterior petroclinoid fold, DS dorsum sellae, ICF interclinoid fold, PF pituitary fossa, PLL petrolingual ligament (inferior sphenopetrosal ligament), PPCF posterior petroclinoid fold, PS planum sphenoidale, SSPL superior sphenopetrosal ligament (Gruber’s ligament), TS tuberculum sellae, black asterisk middle clinoid process

Parasellar carotid

Parasellar carotid – shrimp shaped

Retro, Infra, Presellar prominences

Branches of cavernous carotid 1. Meningohypophyseal trunk 2. Inferolateral trunk

Meningohypophyseal trunk

The MHT is traditionally described as having three branches: 1. the inferior hypophyseal artery, IHA 2. the dorsal meningeal artery (also called the dorsal clival artery) DMA, and 3. the tentorial artery (also called the Bernasconi-Cassinari artery) BCA .

Inferolateral trunk

Inferolateral trunk

Cholesterol granuloma

cholesterol granuloma immediately behind the ICA

ICA Clin.: clinoid, clinoidal

Dural rings – the ICA between upper & lower dural ring is Clinoidal ICA

blue-sky arrow = upper dural ring,

Cl clivus, ICAc cavernous portion of the internal carotid artery, ON optic nerve, PG pituitary gland, PS planum sphenoidale, TS tuberculum sellae, yellow asterisks upper dural ring, blue arrowheads lower dural ring, white asterisk lateral optico-carotid recess, white circle medial optico-carotid recess, white arrow ophthalmic artery, black arrows middle clinoid process, red arrows lateral tubercular crest, yellow arrows endocranial region corresponding to MCP

ICAcl clinoidal portion of the internal carotid artery , The clinoidal segment of the internal carotid artery faces the posterior aspect of the optic strut. white arrowhead - paraclinoid portion of the internal carotid artery – after removal of anterior clinoidal process

ICA Clin.: clinoid, clinoidal [ Observe here also – posterior border of Opticocarotid recess is Clinoidal ICA ]

ICA Clin.: clinoid, clinoidal

ICA Clin.: clinoid, clinoidal

ICA Clin.: clinoid, clinoidal

ICA Clin.: clinoid, clinoidal

Intracranial portion of ICA [ICA i]

In the lateral border of the chiasmatic cistern the first part of the ICAi is visible.

APAs anterior perforating arteries, ICAi intracranial portion of the internal carotid artery, OT optic tract, SF Sylvian fi ssure,

ACA anterior cerebral artery, APAs anterior perforating arteries, FOA fronto-orbital artery, FOV fronto-orbital vein, FPA fronto-polar artery, ICAi intracranial segment of the internal carotid artery, MCA middle cerebral artery, OlfT olfactory tract, OlfV olfactory vein, ON optic nerve, PS pituitary stalk, TL temporal lobe, black asterisk anterior communicating artery

ICA dividing into ACA and MCA

Carotid artery bleeding

Surpra petrous window

Surpra petrous window ET eustachian tube, GPN greater petrosal nerve, MCFd dura of the middle cranial fossa, MMA middle meningeal artery, SPS superior petrosal surface, TI trigeminal impression, V3 third branch of the trigeminal nerve, yellow arrow accessory middle meningeal artery, white asterisks greater petrosal nerve groove

Infrapetrous approach

OPTIC NERVE DECOMPRESSION

Optic tubercle

In 83% the OA passes around the lateral aspect of the optic nerve (b, left); in the remaining cases the OA stays medial to the optic nerve, 17% - this point important in optic nerve decompression

One artery in the head which we can’t move – is OA – Central retinal artery is avulsed

Relation of PEA & ON

The sphenoid ostium (SO) is first opened inferiorly (black arrow, 1) then laterally (black arrow, 2). This should afford a clear view into the sphenoid sinus and the remaining anterior face of the sphenoid can be removed up toward the optic tubercle (OT) but usually stopping short of the tubercle to lessen the potential risk to the optic nerve.

Branches of the cavernous internal carotid artery ( ICA ), a rare variation: ophthalmic artery passing through the superior orbital fissure

Various relations of OA [ Opthalmic artery ] to ON

The dura over the ACP passes over the ON, giving the falciform ligament

Fibrous tissue

FCB-Fibrocartilago basalis at junction of petrous & paraclival carotid Fibrous tissue surrounds the entrance of the vertebral artery into the CPA.

Fibrous tissue surrounds the entrance of the vertebral artery into the CPA. Left side. Combined transsigmoid, suboccipital and extreme lateral approaches provide an overview off the craniocervical junction, the foramen magnum area, and the surrounding structures of the medullary stem.

Note Fibrocartilagenous basalis at laceral segment in both photos

A nontoothed forceps is used to hold the soft tissues (ST) surrounding the nerve at the level of the stylomastoid foramen (SMF), and sharp scissors are used to dissect the soft tissues from the bone at that level. C Cochlea, FN(m) Mastoid segment of the facial nerve, LSC Lateral semicircular canal, NC New canal, SS Sigmoid sinus

Rerouting of the facial nerve. FN(m) Mastoid segment of the facial nerve, FN(p) Intraparotid facial nerve, SM Facial nerve at the stylomastoid level, ST Soft tissues The facial nerve has been rerouted into the new canal (*). FC Fallopian canal, FN(p) Rerouted part of the intratemporal facial nerve, FN(t) Rerouted part of the tympanic segment of the facial nerve, ST Soft tissues

Styloid process

Styloid apparatus – superior view Styloid apparatus – lateral view

After the attached muscles have been dissected away, the styloid process (SP) is fractured using a rongeur. FC Fallopian canal, FN Facial nerve, FN(p) Rerouted part of the intraparotid facial nerve, TB Temporal bone

Fig. 9.21 To obtain control over the vascular structures as they enter the temporal bone, the tympanic bone (TB), the fallopian canal remnants (FC), and the infralabyrinthine air cells are all to be removed. C Basal turn of the cochlea (promontory), IJV Internal jugular vein, JB Jugular bulb, SS Sigmoid sinus

The view after completely uncovering the lateral surfaces of the vascular structures. C Basal turn of the cochlea (promontory), ICA Internal carotid artery, IJV Internal jugular vein, JB Jugular bulb, SS Sigmoid sinus

Fig. 9.29 The plane of dissection between the internal carotid artery (ICA) and the overlying periosteum (P) is best developed at the entrance of the artery into its canal. C Basal turn of the cochlea (promontory)

Internal carotid artery is deeper to styloid process when we see from laterally & medial to styloid process when we see from anteriorly – [SP- Styloid process]

Two things protect the parapharyngeal carotid anteriorly 1. Tensor veli palatini & 2. SPHA [ = stylopharyngeal aponeurosis ]

Inferior petrosal sinus

HVP hypoglossal venous plexus

Inferior petrosal sinus

In Transcochlear approach

In infratemporal fossa type B approach

NOTE Inferior petrosal sinus at CLIVUS ICAc cavernous portion of the internal carotid artery, IPS inferior petrosal sinus, PAp petrous apex, SPCG sphenopetroclival gulf, cVIcn cisternal segment of the abducens nerve, gVIcn gulfar segment of the abducens nerve, pVIcn petrosal segment of the abducens nerve, white asterisks dura of the posterior cranial fossa

In middle cranial fossa approach

In middle cranial fossa approach

rd 3 nerve

3rd nerve is sandwiched between posterior cerebral artery & superior cerebellar artery

3rd nerve is sandwiched between posterior cerebral artery & superior cerebellar artery

3rd nerve is sandwiched between posterior cerebral artery & superior cerebellar artery Through endoscopic lateral skull base Through endoscopic anterior skull base

3rd nerve is sandwiched between posterior cerebral artery & superior cerebellar artery Through endoscopic lateral skull base Through endoscopic anterior skull base

P1 in relation to 3rd nerve P2 in relation to 3rd nerve

Relationship of posterior communicating artery & 3rd nerve

Relationship of posterior communicating artery & 3rd nerve

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

Oculomotor cistern Cranial nerve III enters the roof included in its own cistern (oculomotor cistern).

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

Fronto-temporal orbitozygomatic transcavernous approach COM= Caratico-occulomotor membrane , DR = dural ring

The oculomotor nerve divides into a small superior and large inferior division just before passing through the superior orbital fi ssure.

th 4 nerve

Endoscopic lateral skull base

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

1. The trochlear nerve, within the cavernous sinus, passes upward the oculomotor nerve (more or less at the level of the optic strut) and becomes the most superior structure of the CS (Iaconetta et al. 2012). 2. trochlear nerve is always superior to V1.

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

th 6 nerve

The pontomedullary junction. 1. The exit zones of the hypoglossal and abducent nerves are at the same level. 2. The abducent nerve exits from the pontomedullary junction, and ascends in a rostral and lateral direction toward the clivus.

6th nerve origin is above or below AICA or has two rootlets of origin

6th is appresiated in TA-II [ Transapical type II ] approach when 360 degrees IAC drilled

6th nerve – enters the dorellos canal – Intradural course

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

The DMA is in close relationship with the abducens nerve at the level of petrous apex (Cavallo et al. 2011 ) . The DMA is the main feeder of the Dorello’s segment of Vicn (Martins et al. 2011 ) . DMA & 6TH NERVE DMA & 6TH NERVE

When we are doing clival chordoma we have to anticipate 6th nerve medial to paraclival carotid which is present in dorellos canal

Courtesy Dr. Tomasz Skibinski

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

Gulfar segment of 6th nerve (GS in left picture ) ( gVIcn in right picture )

ICAc cavernous portion of the internal carotid artery, IPS inferior petrosal sinus, PAp petrous apex, SPCG sphenopetroclival gulf, cVIcn cisternal segment of the abducens nerve, gVIcn gulfar segment of the abducens nerve, pVIcn petrosal segment of the abducens nerve, white asterisks dura of the posterior cranial fossa

6th N. crossing carotid at Petro-clival junction when viewing in lateral skull base

Inferior boarder of L-OCR is by 6th nerve & V1

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

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

6th nerve passing below gruber’s ligament

ACP anterior clinoid process, APCF anterior petroclinoid fold, DS dorsum sellae, ICF interclinoid fold, PF pituitary fossa, PLL petrolingual ligament (inferior sphenopetrosal ligament), PPCF posterior petroclinoid fold, PS planum sphenoidale, SSPL superior sphenopetrosal ligament (Gruber’s ligament), TS tuberculum sellae, black asterisk middle clinoid process

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

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

6th nerve is freely hanging in the cavernous injury when compared to 3rd & 4th nerve – so postential for injury in tumor dissection

th 7 nerve

Vertical part of 7th nerve bissects the jugular bulb

In 50% of the cases mastoid segment of Facial nerve travels lateral to level of annulus – This is important while removing the 1. EAC in temporal bone malignancy 2. while decompressing the nerve in malignant otitis externa 3. very careful in children Click http://www.youtube.com/ watch?v=f0cblTWJQ4k

3rd GENU When facial nerve exists the temporal bone , the main trunk of the facial nerve is the perpendicular bisection of a line joining the cartilagenous pointer to the mastoid tip – some surgeons call this bend as 3rd genu.

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