ENDOSCOPIC SKULL BASE SURGERY-LEVEL III

DR.SHUBHANGI

LEVELS OF SKULL BASE SURGERYLevel 1 • Sinonasal surgeryLevel 2 • Pituitary surgery • CSF leaksLevel 3 • Extradural • Transcribriform • Transplanum • Transorbital (extraconal) • Transclival • Transodontoid

Level 4 • Intradural A. With cortical cuff • Transplanum • Transcribriform • Type I craniopharyngiomas B. Lack of cortical cuff • Transorbital (intraconal) • Transplanum • Transcribriform • Type II/III craniopharyngiomas • Transclival intraduralLevel 5 • Cerebrovascular surgery A. Middle and posterior coronal planes B. AVM/Aneurysms

Illustration showing the skull base in an inferior view. Eachcolored area represents a module of expanded endonasal approach at the skull base. CP-AF = coronal plane anterior fossa; CP-MF = coronalplane middle fossa; CP-PF = coronal plane posterior fossa; TC = transclival (pink area); TC = transcribriform (white area);TO = transodontoid;TP/T = transplanum/transtuberculum; TS = transsellar.

Distribution of EEA surgical approaches. Some of the surgicalapproaches are grouped. 1: transfrontal; 2:transcribriform;3: transplanum; 4: transsellar; 5: transclival; 6:transodontoid

TRANSCRIBRIFORM APPROACH• Defined by the removal of the cribriform plate to approach

skull base.

• This module extends anteriorly from the posterior ethmoidal arteries upto the level of the crista galli and frontal sinus.

• The limits of this module are both laminae papyraceae laterally, the frontal sinus anteriorly the transition with the planum sphenoidale posteriorly at

the level of the posterior ethmoidal arteries

TRANSCRIBRIFORM APPROACH• INDICATIONS1. Anterior skull base meningiomas including those

originating at the olfactory groove, planum sphenoidale & tuberculum sellae

2. Esthiseoneuroblastomas3. Invasive sinonasal malignancies

CONTRAINDICATIONS There are potential surgical limits laterally,posteriorly, and superiorly.

LATERALLY- the midorbital plane -Removal of the lamina papyracea enables the displacement of the orbital soft tissues to provide access to the orbital roof

laterally. Lesions that present a lateral extension beyond the midorbit meridian should not be accessed with a pure endonasal approach.

POSTERIORLY—the optic chiasm and anterior cerebral circulation. Tumors lateral to the optic nerves should not be resected from a midline

endonasal approach. Very tall tumors-difficult to access and care must be taken not to remove too

much of the inferior and anterior capsule before the apex of the tumor has been debulked.

DIAGNOSTIC WORK UP

• Physical examination-neurologic assessment with special focus on cranial nerve function

• Endoscopic assessment of the nasal cavity- to visualize any nasal lesions and document septal integrity, septal deviations,and any other anatomical findings.

• A complete ophthalmologic examination & visual fields examination.

• Signs of intracranial hypertension detected by papilledema should be addressed preoperatively [external ventricular drainage (EVD) or ventriculoperitoneal (VP) shunt ]

SURGERY High-concentration adrenaline soaked cottonoids (1:1000) are placed

in the nasal cavity for 10 minutes before the surgical procedure begins. The septum is infiltrated with lidocaine with adrenaline 1:100,000.

Nasoseptal flap created & preserved First, the intranasal portion of the tumor - debulked to the plane of the

skull base to define the attachment to the cribriform plate, and this attachment is cauterized with bipolar electrocautery.

Complete sphenoethmoidectomy performed bilaterally Draf 3 procedure performed to define the anterior resection margin. Nasal septum transected along the sagittal plane from the crista galli to

the sphenoid rostrum approximately 1 cm inferior to the tumor attachment to the septum.

This defines the inferior resection margin.

The tumor-devascularized by cauterizing and transecting the anterior and posterior ethmoidal arteries , along the fovea ethmoidalis, midway along its course from the orbital margin and lateral lamella

The bone of the anterior cranial base in the periphery of the tumor – thinned to the resection margins, anteriorly to the posterior table of frontal sinus, posteriorly to the planum sphenoidale, and laterally to the medial orbital walls. The thinned bone-gently fractured and elevated inferiorly off the overlying dura.

Dural incision along its posterior margin allows removal of the entire dural specimen en bloc . When indicated, the olfactory bulbs and nerves are elevated inferiorly off the overlying brain and transected at the level of the posterior dural margin. Surgical defect extends from the posterior table of the frontal sinus to the planum sphenoidale & to the medial wall of the orbit on either side. Surgical defect closed by nasoseptal flapSmall ipsilateral tumors- ipsilateral resection of the anterior cranial base with preservation of olfaction on the contralateral side can be done.

•The dura - cauterized and incised longitudinally along the lateral orbital margins, taking care to avoid injury to cortical vessels. The crista galli – removed , & attached falx cauterized and transected- facilitates rotating the dural specimen posteriorly

Large olfactory groove meningioma. (A) Preoperative (coronal)

(B) Axial section close relation of tumor to anterior cerebral arteries at the proximal A2 segment.

(C) Intraoperative- The right lamina papyracea removed to expose the periorbita and provide access to the orbital roof. The anterior and posterior ethmoidal arteries coagulated and sectioned to expose the anterior skull base and provide early devascularization of the tumor. (D) Intraoperative- Once the tumor has been extensively debulked, gentle extracapsular dissection is performed.

(E) Postoperative-T1-weighted MRI (coronal section) complete resectionof the tumor, cribriform plate, and crista galli. The anterior skullbase reconstructed with the nasoseptal flap. (F) Postoperative FLAIR sequence MRI (axial section) showing nearly complete resolution of the signal changes and minimal encephalomalacia.

COMPLICATIONS• Worsening of vision.• Intraoperative injury to A2 - it eventually led to a subsequent

pseudoaneurysm• Bleeding associated with permanent neurologic deficits.• CSF leak- decreased significantly as a vascularized nasoseptal flap

used for reconstruction. • Pulmonary embolus/deep venous thrombosis • Seizures• Pituitary dysfunction • Bacterial meningitis • Myocardial infarction • Loss of olfaction (preserved in cases of unilateral resections )

• Defined by the removal of the planum sphenoidale and tuberculum sellae to reach skull base.

• SURGICAL LIMITS- Laterally-The optic canals Anteriorly, the posterior ethmoidal arteries. • The critical anatomic landmark is the medial optic carotid

recess. • The most important vital• structures related - the optic nerve - ICAs - the anterior cerebral arteries (A1,

Huebner’s, Anterior communicating and perforators).

TRANSPLANUM APPROACH

TRANSPLANUM /TRANSTUBERCULUM APPROACH

INDICATIONS Lesions involving the posterior aspect of the anterior skull base and the suprasellar region. Tuberculum sellae meningiomas Giant pituitary adenomas Craniopharyngiomas Epidermoid tumors Rathke cleft cysts

(A) Pituitary macroadenoma with significant suprasellar extension. (B) Craniopharyngioma with large suprasellar cyst above a normal sized sella. (C) Meningioma of the planumsphenoidale. (D) Meningioma of the tuberculum sellae.

ADVANTAGESProvides the most direct route to midline lesions of the suprasellar cisternDo not place critical neurovascular structures between surgeon & lesionObviates the need of brain retractionFacilitates complete , b/l optic canal decompresssion without manipulation of compressed optic nerveEnables surgeon to remove bone from base of tumor –site for meningioma recurrenceAllow surgeon to interrupt blood supply early in operation

DIAGNOSTIC WORK UP• Detailed history and physical examination- -cranial nerve examination -

-ophthalmologic evaluation -visual field testing -assessment of cognitive function -comprehensive endocrine workup -endoscopic examination of the nasal cavity.• CT/MRI• Angiography ( if carotid artery compromise is suspected or the

functional integrity of the circle of Willis requires assessment)

CONTRAINDICATIONS• Tumor extending beyond lateral limit of this module• Patient comorbidities that preclude prolonged anaesthesia• Encasement of critical neurovascular structures- not an absolute c/I

but surgeon should proceed only if he/she can safely dissect from these structures & has the ability to address surgial emergency (ICA injury)

SURGERY• High-concentration adrenaline soaked cottonoids (1:1000) are

placed in the nasal cavity for 10 minutes before the surgical procedure begins. The septum is infiltrated with lidocaine with adrenaline 1:100,000.

• Nasoseptal flap created & preserved• The posterior third of the bony septum is resected and a piece of

vomeric bone is harvested as a rigid buttress for reconstruction of the skull base.

• The sphenoid rostrum opened widely • Bilateral posterior ethmoidectomies done• Sphenoid ostia identified & opened widely• Mucosa of the sphenoid sinus removed• identification of the sella, optic nerves, and ICA is verified with

frameless stereotactic image guidance

• The tuberculum sellae is thinned with a high-speed diamond drill under constant irrigation till halfway down into the sella

• The thinned bone removed & continued along the planum sphenoidale until the underlying dura is exposed.

• The anterior limit of resection is the fovea overlying the posterior ethmoid sinuses and cribriform plates.

• The superior intercavernous sinus is transected to open the suprasellar area and visualize the pituitary stalk and optic chiasm when necessary.

•The dura cauterized to interrupt the blood supply to the tumor.• Dural and bony attachments of the meningioma resected to prevent recurrence

•Internal decompression•The tumor capsule sharply dissected away methodically starting with the optic nerve .•ICA identified ( just lateral and inferior to the optic nerve) and tumor traced to the chiasm, along the contralateral optic nerve until the associated ICA is identified and free of tumor.•Important structures such as the ACA complex,recurrent artery of Heubner, subchiasmal perforating vessels,optic nerves, and pituitary stalk preserved by sharp dissection off the tumor capsule. •Arteries that may appear to be encased can often be dissected free of the tumor•The resection bed is examined using angled endoscopes, with special attention paid to ensuring that the optic nerves and canals are free of tumor

is performed

Four corridors -to address lesions of the suprasellar cistern.

• The first corridor - passes in front of the optic chiasm - for meningiomas of the planum and tuberculum sellae. •The second corridor - a prechiasmal approach to the third ventricle. ( between the chiasm and the ACA ) - for pathology high in the third ventricle. •The third corridor - below the chiasm and above the pituitary gland. - for cystic lesions arising from the infundibulum that extend into the third ventricle.• The fourth corridor- beneath the pituitary gland (requires superior mobilization of the gland), - for lesions such as craniopharyngiomas,chordomas, and petroclival meningiomas located behind the pituitary gland and infundibulum

Surgical defect reconstructed with fat to prevent pooling of cerebrospinal fluid (CSF) at the bony defect- a “gasketseal” closure done – nasoseptal flap then rotated to cover the defect, and a tissue sealant (DuraSeal) is used to secure the multilayer graft in place

COMPLICATIONS INTRAOPERATIVE• Arterial / venous bleeding• Cranial nerve injury• Damage to pituitary gland , stalk

& hypothalamus POSTOPERATIVE• CSF leak• Meningitis• Hematoma formation• Sinusitis• Synechia formation

TRANSCLIVAL APPROACH

• The clivus extends from the dorsum sellae to the foramen magnum.

• Transclival approaches - divided into partial (superior, middle, inferior) & complete clivus removal.

• A transclival approach provides direct access to the brainstem and vertebrobasilar arterial system.

INDICATIONS

• Meningiomas• Chordomas.• Chondrosarcomas• Cholesterol granulomas• Mucocele• Rarely, an aneurysm that cannot be treated by

endovascular means or with significant mass effect may be accessed via this approach and clipped

• The upper third - related to the dorsum sellae in the midline and the posterior clinoids in the paramedian region-removed either intradurally via a transsellar approach or extradurally via a subsellar corridor by first performing a superior pituitary transposition

• Removal of these structures can provide access to the basilar artery and interpeduncular cistern

•The middle clivus - directly accessed at the posterior aspect of the sphenoid sinus and its resection is limited laterally by both ICAs ascending in the paraclival areas. •The lower third of the clivus- bone drilling continues inferiorly- limited laterally by the fossa of Rosenmuller and the torus tubarius.• A panclivectomy can extend all the way from the dorsum sellae and posterior clinoids up to the basion at the foramen magnum.•The most germane structures for this module - the brain stem, cranial nerves II, III and VI, basilar and vertebral arteries, superior cerebellar arteries, posterior cerebral arteries & respective perforators

ADVANTAGES

• Avoid any cerebral retraction• To decrease the incidence of injury to the lower

cranial nerves.

CONTRAINDICATIONS

• Patient comorbidities that might preclude them from prolonged general anesthesia;

• Unfavorable anatomy, such as small sphenoid sinus or diminished space between the internal carotid arteries-makes drilling the clival bone more difficult and risky

• Lack of multidisciplinary team cooperation and interaction• Lack of specialized equipment/instruments

DIAGNOSTIC WORKUP The physical examination- neurologic assessment with a

special focus on cranial nerve function. Endoscopic assessment of the nasal cavity- to visualize

any nasal lesions and document septal integrity, deviations, and other anatomical findings.

An ophthalmologic examination including a visual field examination

IMAGING• Coronal, axial, and parasagittal CT of the paranasal sinuses and skull

base - preoperative assessment for surgery , evaluate the size of the sphenoid sinus, the position of the internal carotid artery, especially its paraclival portion, and the thickness of the clivus in the sagittal plane.

• MRI - to demonstrate the morphology of the soft tissues , for involvement of the carotid artery , vertebrobasilar system & dural sinuses

• Magnetic resonance angiography (MRA) or CT angiography(CTA)- to assess relationship between the basilar and internal carotid arteries and the pathology

• to verify the functional integrity of the circle of Willis and the extent of any carotid artery compromise, and to differentiate an aneurysm from a tumor

SURGERY High-concentration adrenaline soaked cottonoids (1:1000) are placed

in the nasal cavity for10 minutes before the surgical procedure begins. The septum is infiltrated with lidocaine with adrenaline 1:100,000

Nasoseptal flap created and preserved• B/l ethmoidectomy performed• The sphenoid rostrum and anterior wall of the sphenoid sinus

exposed.• The mucosal flap is lifted until both natural sphenoid ostia are in view. • A wide opening of the anterior sphenoid sinus wall created

The sinus mucosa that lines the clival area reflected , exposing the clival bone. Care is taken to ensure complete hemostasis at this point in the procedure. The field should be completely dry before proceeding to the next stage of the procedureClival bone fully exposed, and removed by drilling The limits of the clival bone removal are the floor of the sella superiorly, the foramen magnum inferiorly, and the internal carotid arteries and occipital condyles laterally.

Exposure at the start of drilling the clival bone. The distance between the internal carotid arteries is an important factor in determining surgical access to this area

For intradural exposure, the external layer of the dura is first incised with a No. 11 blade. Bleeding in the basilar plexus not cauterized but packed with hemostatic material

The opening of the internal layer of the dura at the level of the middle and superior clivus must be accomplished with great care to avoid injury to the underlying basilar artery.Once the dura opened, minor bleeding is stopped by bipolar coagulation, and finally the 0-degree endoscope carefully introduced into the intradural space.

Once the anatomy is appreciated, identify the major vessels of the posterior fossa (basilar artery and branches, anterior inferior cerebellar artery [AICA], vertebral arteries, superior cerebellar and posterior cerebral arteries); the intradural course of cranial nerves III, IV, V, and VI; the brainstem; and the mamillary bodies.The cerebellopontine angle, cranial nerves VII through XII, and retrosellar regions are best visualized with the 45-degree endoscope

Meticulous dissection is required to remove the lesion.At the end of the procedure, the dural defect is sealed with fat and fascia lata, and covered with the flap. The packing is positionedand stays for as long as necessary.

Endoscopic anatomy following clival resection. (A) Anatomicalspecimen demonstrating midline structures. (B) Corresponding intraoperativeview. (C) Anatomical specimen demonstrating left cerebellopontineangle (CPA) using a 45-degree endoscope. (D) Correspondingintraoperative view of the left CPA.

COMPLICATIONS• Cerebrospinal fluid (CSF) leakage• Nasal bleeding• Bleeding from internal carotid artery, intracranial bleeding, venous

bleeding,• Cranial nerve injuries• Infections• Orbital hematoma• Nasal synechia• Nasal infection.

•Used for resection of the odontoid process in degenerative / inflammatory diseases or to allow for exposure of the ventral medulla and upper cervical spinal cord.• INDICATIONSForamen magnum meningiomas To decompress the brainstem in rheumatoid arthritis patients with degeneration of the upper cervical spine due to compressive pannus

•It is defined by the removal of the odontoid process of the axis (second vertebra) . This approach is an extension of the transclival approach. •The lower third of the clivus is exposed as well as the anterior arch of C1 after dissection of the nasopharyngeal mucosa and the rectus capitis anterior muscle.• The arch of C1 is drilled and the odontoid process is exposed and drilled out.•Pannus removed by sharp and blunt dissection

TRANSODONTOID APPROACH

•The most vital neurovascular structures for this module arethe vertebral arteries, posterior inferior cerebellar arteries (PICAs),brain stem lower cranial nerves. The ICAs have to be considered as a risk factor as well because occasionally they can be positioned close to the midline in their parapharyngeal segment under the mucosa

Preoperative CT scan of a patient with brainstem compression secondary to rheumatoid degeneration (arrow). Decompression is achieved with removal of the odontoid process to the body of C2 and pannus resection

TRANSORBITAL APPROACH

• A transorbital approach may be used for access to tumors located within the orbit. The dissection can be extraconal or intraconal.

INDICATIONS

• Resection of sinonasal lesions that are invadingthe medial wall of the orbit as sinonasal malignances • To decompress the optic nerves in the presence of

unresectable intraconal pathologies • To access intraconal diseases with the goal of

resection as for schwannomas, cavernomas and meningiomas.

ADVANTAGES

• Posterior access to pathology near the orbital apex is excellent via an endoscopic approach.

• The near vision easy identification of the optic nerve transition to the orbit apex and fibrous annulus.

• Avoid disruption of the orbicularis oculi, lacrimal pump, or canthal ligament disruption.

CONTRAINDICATIONS

• ABSOLUTE pathology lateral to the neural axis a lack of specialized equipment and expertise• RELATIVE Presence of acute/ subacute sinusitis

SURGERY• It is defined by the removal of the lamina papyracea or the medial optic canals.• Requires a wide resection of the anterior and posterior ethmoid cells to expose the

lateral wall of the sinonasal cavity. • The surgical field is limited laterally by the lamina papyracea and orbital apex

deeply • The most important vital structures related to this module are the optic nerves, the

anterior and posterior ethmoidal arteries and the ophthalmic artery with its central retina artery branch.

• The ocular muscles must be well identified during surgery and dissection can be performed in between them.

• Subconjunctival localization and mobilization of eye muscles are extremely helpful during endonasal endoscopic procedures.

ENDOSCOPIC OPTIC NERVE DECOMPRESSION

• The most common indication for endoscopic optic nerve decompression is traumatic optic neuropathy

• Medical Therapy for Traumatic Optic Nerve Injury-Methylprednisolone 30 mg/kg intravenous (IV) loading dose is given followed by an infusion of 5.4 mg/kg/hour thereafter

Surgical intervention is considered if thepatient fills any of the criteria listed below:

Fracture of optic canal on CT scan with vision less than 6/60 Fracture of the optic canal with vision . 6/60 but the patient’svision deteriorates on steroids Vision is , 6/60 (or there is a deterioration of vision) after48 hours of steroid treatment with probable canal injury

PROCEDURE• Cotton pledgets containing adrenaline 1:1000 are placed in the nasal cavity

over the areas of surgical access for 10 minutes before the surgical procedure.

• The lateral nasal wall and septum are infiltrated with 1% Naropin with adrenaline 1:100.000.

• An uncinectomy, wide antrostomy combined with anterior and posterior ethmoidectomy is performed.

• The antrostomy is widened superiorly to ensure that the maxillary sinus roof can be easily seen. This defines the orbital floor, allows easier skeletonization of the medial orbital wall, places the infraorbital canal on view, and is an important landmark for defining the level of the skull base posteriorly

• Sphenoidotomy performed• The sphenoid should be inspected and the optic nerve, carotid artery and pituitary fossa identified.

Cadaveric dissection image taken of the left sphenoid sinusdemonstrating the fovea ethmoidalis (FE) and lamina papyracea (LP).ON, optic nerve; CCA, anterior genu of the intracavernous carotidartery; L. OCR, lateral opticocarotid recess; ISS, sphenoid intersinus septum;SS, sphenoid sinus; MS, maxillary sinus; MT, middle turbinate

•The thick bone overlying the junction of the orbital apex and sphenoid sinus known as the optic tubercle is thinned out with burr•blunt Freer elevator is pushed through the lamina papyracea ,1.5 cm anterior to the junction of the posterior ethmoids air cell(s) and the sphenoid •The bone of the posterior orbital apex flaked off•Once the bone over the orbital apex is removed the bone of the optic canal is approached.

•Once all the bone has been cleared off the optic canal and the underlying optic nerve sheath is clearly visible, the sheath is incised • The location of the ophthalmic artery should be kept in mind. The ophthalmic artery usually runs in the posteroinferior quadrant of the nerve.

•Therefore , the nerve is incised in the upper medial quadrant

•This incision is continued onto the orbital periosteum of the posterior orbital apex with resultant protrusion of orbital fat • The orbital fat covering this area of the medial rectus muscle is thin and care should be taken to avoid injuring this muscle •No packs are placed on the nerve or in the sinuses.

COMPLICATIONS•CSF LEAKS•Internal carotid artery injury

Cadaveric dissection image of the left sphenoid sinus.The anterior face of the sphenoid has been removed so that the roof of the sphenoid and posterior ethmoids is continuous. A diamond burr has been used to allow the removal of bone at the junction of the orbital apex and sphenoid sinus (the optic tubercle). The lamina papyracea (LP) has been removed 1.5 cm from the junction of the posterior ethmoids with the sphenoid sinus, exposing periorbita (PO

The thin bone overlying the orbital apex and optic nerve is gently flaked off

The optic nerve sheath (ONS) is incised to release the optic nerve. PO, periorbita; ISS, intersinus septum.

Cadaveric dissection of the lateral wall of the left sphenoid sinus. The optic sheath and periorbita (PO) of the orbital apex has been incised. PS, planum sphenoidale; CCA, anterior genu of the intracavernous carotid artery; L. OCR, lateral opticocarotid recess; OS, optic sheath