ENDOSCOPIC SKULL BASE
LEVELS OF SKULL BASE SURGERY
Level 1 • Sinonasal surgery
Level 2 • Pituitary surgery
• CSF leaks
Level 3 • Extradural • Transcribriform
• Transorbital (extraconal)
Level 4 • Intradural A. With cortical cuff • Transplanum
• Type I craniopharyngiomas
B. Lack of cortical cuff • Transorbital (intraconal)
• Type II/III craniopharyngiomas
• Transclival intradural
Level 5 • Cerebrovascular surgery A. Middle and posterior coronal
Illustration showing the skull
base in an inferior view. Each
colored area represents a
module of expanded endonasal
approach at the skull base.
CP-AF = coronal plane anterior
fossa; CP-MF = coronal
plane middle fossa; CP-PF =
coronal plane posterior fossa;
TC = transclival (pink area);
TC = transcribriform (white
TO = transodontoid;
TS = transsellar.
Distribution of EEA surgical
approaches. Some of the
approaches are grouped. 1:
3: transplanum; 4: transsellar;
5: transclival; 6:transodontoid
• Defined by the removal of the cribriform plate to approach
• This module extends anteriorly from the posterior
ethmoidal arteries upto the level of the crista galli and
• 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
1. Anterior skull base meningiomas including those
originating at the olfactory groove, planum
sphenoidale & tuberculum sellae
3. Invasive sinonasal malignancies
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
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
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
• Signs of intracranial hypertension detected by
papilledema should be addressed preoperatively
[external ventricular drainage (EVD) or
ventriculoperitoneal (VP) shunt ]
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
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
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 flap
Small 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
(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 resection
of the tumor, cribriform plate, and crista galli. The anterior skull
base reconstructed with the nasoseptal flap.
(F) Postoperative FLAIR sequence MRI (axial section) showing nearly complete
resolution of the signal changes and minimal encephalomalacia.
• Worsening of vision.
• Intraoperative injury to A2 - it eventually led to a subsequent
• Bleeding associated with permanent neurologic deficits.
• CSF leak- decreased significantly as a vascularized nasoseptal flap
used for reconstruction.
• Pulmonary embolus/deep venous thrombosis
• 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
• The most important vital
• structures related - the optic nerve
- the anterior cerebral arteries (A1,
Huebner’s, Anterior communicating and perforators).
Lesions involving the posterior aspect of the anterior skull base and
the suprasellar region.
Tuberculum sellae meningiomas
Giant pituitary adenomas
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 planum
sphenoidale. (D) Meningioma of the tuberculum sellae.
Provides the most direct route to midline lesions of the suprasellar
Do not place critical neurovascular structures between surgeon &
Obviates the need of brain retraction
Facilitates complete , b/l optic canal decompresssion without
manipulation of compressed optic nerve
Enables surgeon to remove bone from base of tumor –site for
Allow surgeon to interrupt blood supply early in operation
DIAGNOSTIC WORK UP
• Detailed history and physical examination-
-cranial nerve examination -
-visual field testing
-assessment of cognitive function
-comprehensive endocrine workup
-endoscopic examination of the nasal cavity.
• Angiography ( if carotid artery compromise is suspected or the
functional integrity of the circle of Willis requires assessment)
• 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
• 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 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
•The tumor capsule sharply dissected away methodically starting with the optic
•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
•The resection bed is examined using angled endoscopes, with special attention
paid to ensuring that the optic nerves and canals are free of tumor
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
• The clivus extends from the dorsum sellae to the foramen
• Transclival approaches - divided into partial (superior,
middle, inferior) & complete clivus removal.
• A transclival approach provides direct access to the
brainstem and vertebrobasilar arterial system.
• Cholesterol granulomas
• 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
•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
• Avoid any cerebral retraction
• To decrease the incidence of injury to the lower
• 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
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
• 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
• MRI - to demonstrate the morphology of the soft tissues , for
involvement of the carotid artery , vertebrobasilar system & dural
• 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
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
Nasoseptal flap created and preserved
• B/l ethmoidectomy performed
• The sphenoid rostrum and anterior wall of the sphenoid sinus
• 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
Clival 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
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.
Bleeding in the basilar plexus not cauterized but packed with hemostatic
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
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 positioned
and stays for as long as necessary.
view. (C) Anatomical
angle (CPA) using a
intraoperative view of
the left CPA.
•Used for resection of the odontoid process in degenerative / inflammatory
diseases or to allow for exposure of the ventral medulla and upper cervical
Foramen 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
•The most vital neurovascular structures for this module are
the vertebral arteries,
posterior inferior cerebellar arteries (PICAs),
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
Decompression is achieved with
removal of the odontoid process to
the body of C2 and pannus
• A transorbital approach may be used for access to
tumors located within the orbit. The dissection can
be extraconal or intraconal.
• Resection of sinonasal lesions that are invading
the 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
• 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.
pathology lateral to the neural axis
a lack of specialized equipment and expertise
Presence of acute/ subacute sinusitis
• It is defined by the removal of the lamina papyracea or the medial optic
• 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
• 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
• 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
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’s
vision deteriorates on steroids
Vision is , 6/60 (or there is a deterioration of vision) after
48 hours of steroid treatment with probable canal injury
• Cotton pledgets containing adrenaline 1:1000 are placed in the nasal cavity
over the areas of surgical access for 10 minutes before the surgical
• The lateral nasal wall and septum are infiltrated with 1% Naropin with
• 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 sinus
demonstrating the fovea
ethmoidalis (FE) and lamina
ON, optic nerve; CCA, anterior
genu of the intracavernous
artery; L. OCR, lateral
opticocarotid recess; ISS,
sphenoid intersinus septum;
SS, sphenoid sinus; MS,
maxillary sinus; MT, middle
•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
•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.
•Internal carotid artery injury
Cadaveric dissection image of the left
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