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27 Endoscopic Skull Base Reconstruction
377
of the tumor. Nonhematopoietic malignancies usually mandate a surgical resection
if complete tumor extirpation can be achieved with satisfactory morbidity [13].
Benign lesions that often necessitate these practices include pituitary adenoma, craniopharyngioma, meningocele or encephalocele, arachnoid cyst, chordoma,
schwannoma, inverted papilloma, osteoma, and bro-ossifying lesions with skull
base involvement. It should be noted that with regards to craniopharyngiomas, a
nuanced surgical approach that considers the origin, lesion morphology (i.e., cystic
vs. solid), as well as pituitary function is required for successful treatment.
Additionally, the treatment planning is dependent on the craniopharyngioma subtype. In recent literature, craniopharyngiomas of the papillary type have been shown
to have a strong response to BRAF (e.g., vemurafenib, dabrafenib) and MEK inhibitors (e.g., trametinib, selumetinib) in the neoadjuvant setting. Contrarily, surgical
intervention remains the primary indication in the adamantinomatous subtype as
drugs targeting the WNT/CTNNB1 pathway remain largely in the in-vitro phase
[14]. Malignant lesions that warrant surgical resection include sinonasal malignancies such as esthesioneuroblastoma, adenocarcinoma, sinonasal undifferentiated
carcinoma, and neuroendocrine carcinoma, as well as intracranial lesions such as
anaplastic meningioma, chondrosarcoma, and malignant schwannoma [15].
Typically, the primary objective of skull base reconstruction is to prevent postoperative complications such as CSF leak and subsequent meningitis or pneumocephalus via separation of the intra- and extracranial spaces. Secondary objectives
include reconstructive efforts to promote efcient healing, protect neurovascular
elements, and reduce postoperative morbidity [16]. To determine if reconstruction
is indicated, the surgeon rst determines the extent of the defect and the presence of
the CSF leak. Second, the character of the leak is described—absent, low ow, or
high ow. In the absence of a CSF leak or intracranial opening, reconstruction is
typically not indicated. However, the repair and technique are at the acumen of the
surgeon. The surgeon may choose to repair with a simple epidural or subdural synthetic graft (with packing and sealant) that can be further augmented with a free
mucosal graft or a similar autograft [17]. The CSF leak classication system and the
algorithm for ap selection will be described in detail.
It is important to note that factors that increase the likelihood of postoperative
CSF leak indicate the use of vascularized aps. These include the pathologies previously described, as well as Cushing disease (reduced healing from hypercortisolemia) and morbid obesity (increased intracranial pressure). In the case of
extradural defects, especially those previously irradiated or that will undergo radiation therapy, vascularized aps have shown better reliability and resilience when
compared to nonvascularized aps. In this case, the primary objective would be to
provide coverage of the defect with enhanced healing [17, 18].
Tumor extirpation is dependent on its extent, aggressiveness, and involvement of
critical structures. Generally speaking, anatomic contraindications to skull base surgery are lesion involvement of the brainstem, specic areas of the cerebrum, superior sagittal sinus, both internal carotid arteries, both cavernous sinuses, and vital
bridging veins. Purely endoscopic approaches are contraindicated when the tumor
demonstrates extensive invasion of the nasal bones, lacrimal apparatus or structures
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B. Scott et al.
of the orbit, lateral recesses or anterior walls of the maxillary sinus, or dura overlying the roof of the orbit [12]. Other contraindications that are dependent on the
nature of the lesion include spread to distant locations. It should be noted that even
in cases with distant metastatic disease, it is appropriate to surgically decompress
neuroanatomical structures to preserve neurological function [19].
Preoperative Planning
Preoperative planning in endoscopic skull base reconstruction is of the utmost
importance in optimizing postoperative outcomes. As with most reconstructive surgeries, a thorough evaluation of past medical history and preexisting risk factors
should be assessed. This includes identifying risk factors such as obesity, diabetes
mellitus, cardiovascular disease and atherosclerosis, use of anticoagulation, hematologic malignancies such as leukemias or lymphomas, as well as overall functional
and nutritional status. A thorough social history should also be reviewed, including
smoking and alcohol consumption, as well as any nonprescription supplements
being used. Any prior nasal surgeries should also be reviewed, including prior septorhinoplasty or sphenopalatine artery ligation, as well as any prior internal maxillary artery embolization procedures, as this may inuence the reconstructive options
that are available. All these factors play a role in predicting success in reconstructive
surgery as they heavily impact the reconstructive options available to the surgeon as
well as the wound healing process.
In a recent retrospective study looking at patients who underwent endoscopic
endonasal approach for resection of intradural skull base tumors the risk factors
identied to increase the risk of postoperative CSF leak was BMI >25 and tumors
located in the posterior fossa. Sex and use of perioperative lumbar drain did not
affect CSF leak rates [20].
Additionally, any endoscopic skull base surgery is best executed as part of a
multidisciplinary team, often composed of a neurosurgeon and an otolaryngologist.
Transparency and open communication between the respective disciplines are
imperative to a successful surgery. This includes discussing preoperative imaging
and pathology to gain insight into the characteristics of the anticipated skull base
defect that will need to be repaired. The size and location of the defect, the potential
need for dural repair, the presence of a CSF leak, plans for a lumbar drain, as well
as the need for adjuvant postop treatment such as radiation to the newly reconstructed wound bed should also be communicated amongst disciplines preoperatively if possible, but certainly intra and postoperatively as appropriate.
The use of lumbar spinal drains remains controversial. Many studies show that
the use of lumbar drains does not decrease postoperative CSF leak rates and can
increase the risk of postoperative meningitis [20, 21]. While others have shown the
use of a short-term lumbar drain following endoscopic skull base surgery demonstrated CSF leak rates of 8.2% compared to 21.2% in patients who did not receive a
lumbar drain [22]. Nonetheless, a graded approach to skull base reconstruction
denoting the severity of the CSF leak has proven benecial in identifying the
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27 Endoscopic Skull Base Reconstruction
necessary components needed to increase the success of the repair [21]. This grading system and steps to repair will be outlined in further detail in the surgical technique section.
379
Instruments andEquipment
Endoscopic skull base reconstruction requires a broad skill set as well as a wide
range of instruments. A standard anterior skull base reconstruction will require an
endoscopic sinus tray with a variety of angled scopes and a septorhinoplasty tray.
Instruments of particular interest in these procedures include Kerrison rongeurs, a
sickle knife, microdebrider, Freer, suction Freer or Cottle dissectors, a septal scissor, a 15-blade scalpel, a curved beaver blade, and a Takahashi forceps. An endoscopic, high-speed, diamond-bit drill may also be needed to rene the bony defect.
An ultrasonic aspirator can also be helpful in removing additional bone if needed
based on the operating surgeon’s preference. An extended Colorado or insulated
needle-tip electrocautery has also been proven useful in these procedures. The ne
tip can be slightly bent with forceps and used to make mucosal incisions endoscopically within the nose. This technique provides a good balance between sharp dissection and hemostasis, minimizing the need for repetitive suctioning within the nasal
cavity. Suction cautery and/or endoscopic bipolar forceps are also excellent supportive instruments in the event that profuse intraoperative bleeding is encountered.
Aside from instrumentation, endoscopic skull base reconstruction also utilizes a
variety of synthetic materials that should be on hand for skull base repair. Commonly
used materials include collagen matrix and sealants, although some surgeons prefer
to avoid sealants because of the cost and potentially questionable efcacy.
Stereotactic CT or MRI navigation can also be quite helpful for the reconstructive
surgeon with respect to intraoperative orientation.
Surgical Technique: Endoscopic Skull Base Reconstruction
This section will outline the basics of skull base defect assessment and grading of
CSF leaks, as well as a stepwise approach to the planning and harvesting of vascularized pedicled aps that are commonly used in endoscopic skull base
reconstruction.
Assessment andSeverity ofCSF Leak
When technically executing skull base reconstruction, as with any reconstructive
case, it is important to have a good working knowledge of the reconstructive options
that are available and to have multiple options that can be reliably pursued in the
event that the defect evolves and certain reconstructive options become contraindicated or less feasible. As mentioned in the previous section, the major
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characteristics of a skull base defect that will need to be accounted for are the location and size of the defect as well as the presence and severity of a CSF leak. The
classication system and repair protocol for intraoperative CSF leaks were initially
described by Esposito etal. in 2007; it has since been updated following the adoption of endoscopic techniques and introduction of the pedicled nasoseptal ap. In
the updated system outlined by Conger etal., it is recommended that CSF leaks be
graded 0–3 with a stepwisereconstructive protocol for the respective grades. The
following algorithm for grading CSF leaks is adapted from Conger etal. and provides a good framework for assessing skull base defects. However, the authors
understand that variations in assessing skull base defects will exist on a case-bycase basis as well as between surgeons and institutions.
Grade 0
Grade 0 is the absence of a CSF leak, as conrmed by the intraoperative Valsalva
maneuver. This defect calls for an intrasellar fat graft in the setting of large sellar
dead space, collagen sponge on-lay, repositioning of sphenoid sinus mucosa, if
available, over sella and collagen, followed by a second layer of collagen sponge
over mucosa and posterior sphenoid. Finally, a layer of brin sealant is applied.
Grade 1
Grade 1 is dened by a small “weeping” CSF leak, conrmed by intraoperative
valsalva with small diaphragmatic or dural defect. Repair of this defect entails an
intrasellar fat graft in the setting of large sellar dead space and collagen sponge onlay, much like a grade 0. However, unlike grade 0, it is recommended that a bone or
synthetic buttress (intrasellar, extradural) be placed if it is safe to do so. Repositioning
of sphenoid mucosa over the sellar defect and buttress, followed by a second layer
of collagen sponge, then brin sealant. If it is not possible to bolster the defect with
bone within the sella then a unilateral or bilateral merocel nasal packing is recommended and left in place for 5days.
Grade 2
Grade 2 is classied as a moderate CSF leak with obvious dural defect. This repair
calls for an intrasellar fat graft in the setting of large sellar dead space, collagen
sponge on-lay, placement of intrasellar buttress using bone or other rigid synthetic
material, and repositioning of the sphenoid sinus mucosa over the defect with the
placement of additional fat within the sphenoid. A second layer of collagen sponge
over the fat graft and brin sealant is then placed. In the scenario where an intrasellar rigid buttress cannot be placed, a unilateral or bilateral merocel nasal packing is
positioned and left in place for 5days.
Grade 3
Grade 3 is dened as a large CSF leak that is usually the result of an extended transsphenoidal approach (transplanum or transclival). This repair calls for intrasellar,
suprasellar, or clival fat graft, collagen sponge on-lay, bone or synthetic buttress
wedged within the bony defect, a pedicled nasoseptal or other vascularized mucosal
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27 Endoscopic Skull Base Reconstruction
381
ap, as well as additional fat bolstering over the ap. Finally, a second layer of collagen sponge is applied with brin sealant, and bilateral merocel nasal packing is
placed on opposing the ap to the skull base.
Of note, all repairs necessitate a multilayer technique, but not all CSF leaks
require a pedicled vascularized ap for successful repair as the postoperative CSF
leak rates for grades 0, 1, 2, and 3 were 0%, 1.9%, 3.1%, and 4.8%, respectively
[22]. Nonetheless, it is important to note that these recommendations and outcomes
reect a particular study, and adaptations between cases, surgeons, and institutions
will exist. As such, vascularized pedicle aps can be utilized in grade 1 and 2 CSF
leaks based on surgeon preference. It is also worth mentioning that some authors
report the addition of a fascial inlay graft for larger transcribiform and transclival
dural defects. This graft is placed inside the dural defect between the brain parenchyma and dura in these scenarios. However, they do not recommend this modication for transplanum transtuberculum defects, especially tuberculum sella
meningiomas, as the optic nerve sheath is often exposed, and there is a risk of nerve
compression with inlay grafting [23].
Intranasal Vascularized Pedicled Flaps
Nasoseptal Flap (Hadad-Bassagasteguy Flap)
The nasoseptal ap is by far the most commonly used and well-documented in the
literature for endoscopic skull base repair. The posteriorly pedicled nasoseptal ap
was rst described in 2006 by Hadad etal. and named the Hadad-Bassagaisteguy
ap (HBF) after its co-creators [24]. It entails incising the nasal septal mucosa and
raising a mucoperichondrial ap that is pedicled posteriorly around the posterolateral nasal arteries of the sphenopalatine artery (Fig.27.1). In their original article
published in the Laryngoscope, they outline the steps to ap harvest and inset,
which are detailed below (Fig.27.2).
Flap Design andHarvest
• The inferior and middle turbinates are out fractured to allow for visualization of
the nasal septum from cribriform to nasal oor (to allow for bimanual technique
during endoscopic endonasal approaches one of the middle turbinates can be
removed; this also allows for visualization of the ap pedicle).
• The ap is designed based on the size and shape of the defect and is recom-
mended to overestimate the size needed as trimming can be performed later.
• Two parallel incisions are then made in the sagittal plane, one along the maxil-
lary crest and one superiorly below the olfactory epithelium (i.e., 1–2cm below
the most superior aspect of the septum).
• A vertical incision is then made connecting the two incisions at the mucocutane-
ous junction of the columella.
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Superior
turbinate
turbinate
l
l
Vomer
l
B. Scott et al.
a
Middle
Inferior
turbinate
turbinate
Nasosepta
flap
Nasoseptal
artery
b
Middle
resected
Inferior
turbinate
Superior
turbinate
Nasosepta
flap
Nasosepta
artery
Fig. 27.1 Vascular supply of the nasal septal mucosa. (This gure modied from Gutierrez etal.
by Springer Nature. Gutierrez WR, Bennion DM, Walsh JE, Owen SR.Vascular pedicled aps for
skull base defect reconstruction. Laryngoscope Investig Otolaryngol. 2020;5(6):1029-1038)
t.me/Dr_Mouayyad_AlbtousH
Anterior septal
superior labial
Posterior septal
27 Endoscopic Skull Base Reconstruction
383
branch of
anterior ethmoidal
artery
Nasal septal
branch of
branch of
facial artery
Greater
palatine artery
Fig. 27.2 Illustration showing harvest and inset of the nasoseptal ap. (This gure modied from
Laibangyang etal. by Springer Nature. Laibangyang A, Rodgers SD, Baron SL, etal. Pedicled
nasoseptal ap reconstruction for craniopharyngiomas in pediatric patients. Childs Nerv Syst.
2020;36(3):491-496)
Septal branch of
posterior ethmoidal
artery
branch of
sphenopalatine
artery
• At the posterior septum, the superior incision is extended laterally and with an
inferior slant over the rostrum of the sphenoid sinus and crossing it horizontally
at the level of the natural ostium.
• The inferior incision is then extended superiorly along the free posterior edge of
the nasal septum and then laterally to cross the posterior choana below the oor
of the sphenoid sinus.
• The ap is then elevated using a cottle dissector from anterior to posterior and
completed once the ap is raised off of the face of the sphenoid sinus with pres-
ervation of the posterolateral pedicle. (It is recommended to complete all inci-
sions prior to raising the ap because it is difcult to maintain orientation and
tension once the ap is elevated).
• The ap can then be rotated down into the nasopharynx or placed against the
lateral nasal wall until the ablative phase of the procedure is complete.
• The nal defect is then reconstructed in a multilayer fashion as described in the
previous section.
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B. Scott et al.
Flap Advantages andLimitations
This ap is highly modiable and can be sized to a varying degree of widths and
lengths depending on the defect to be reconstructed. These capabilities make the
nasoseptal ap the most versatile and superior vascularized pedicled ap for skull
base reconstruction. If needed, the entirety of the mucoperichondrium and mucoperiosteum can be elevated off the ipsilateral septum to cover anterior skull base
defects from the posterior frontal sinus to the sella turcica and span the orbits. It is
possible to extend the inferior incision along the oor of the nose to gain extra
width, and bilateral aps can be harvested and interposed [25]. Since the original
Hadad etal. article, other modications of this ap have been reported.
The nasoseptal ap is not limited to the nasal septal mucosa and nasal oor
either. In a recent study, a 360-degree nasoseptal ap, including the septum, nasal
oor, and entire mucosa of the lateral nasal wall, was successfully harvested and
used in ve patients to reconstruct extensive skull base defects caused by invasive
pituitary tumors. All aps harvested healed successfully with no persistence of CSF
rhinorrhea. However, because this modied ap includes the lateral nasal wall
mucosa, one patient experienced nasolacrimal duct obstruction requiring dacryocystorhinostomy [25].
Posterior Pedicle Inferior Turbinate Flap
The posterior pedicle inferior turbinate ap (PPITF), or inferior turbinate ap (ITF),
is a local intranasal ap that is pedicled on the inferior turbinate artery. It can be
used to repair the posterior aspect of the anterior cranial fossa for small-moderatesized sellar or clival defects or as a secondary reconstructive method when the vascular supply of the nasoseptal ap has been compromised. This can occur secondary
to tumor invasion and erosion of the vascular pedicle, previous septectomy, previous
widened sphenoidotomy, or radiation therapy. ITF consideration is dependent on
the anatomic location of the defect and the coverage required [18, 26]. Although it
provides a reliable alternative to the HBF, it is important to consider other free grafts
and local or regional reconstructive aps.
To review, the vascular origin and route of the pertinent arteries will be described.
The sphenopalatine artery is a terminal branch of the maxillary artery that leaves the
pterygopalatine fossa via the sphenopalatine foramen to access the nasal cavity.
Sphenopalatine artery branching is highly variable. The most clinically relevant pattern occurs as it bifurcates into the posterior lateral nasal artery and posterior septal
nasal artery; the former is relevant to this technique [27].
The posterior lateral nasal artery supplies the majority of the lateral nasal wall,
including the middle and inferior turbinates, by taking an anterior inferior route
over the palatine perpendicular plate, during which it provides a medial branch to
the middle turbinate. It descends on average 1.2cm before piercing the inferior
turbinate at the superior aspect of its lateral attachment 1.0–1.5cm from the posterior margin. The posterior lateral nasal artery typically terminates by providing two
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385
inferior turbinate arteries that ultimately form a robust anastomotic connection with
the anterior supply of the inferior turbinate [28].
Flap Design andHarvest
• 1% lidocaine with 1:100,000 epinephrine is injected into the lateral nasal wall
just anterior to the inferior turbinate to decongest the nasal cavity.
• After EEA has been completed, the inferior turbinate can be carefully medialized
to provide optimal exposure of its entire medial surface.
• The uncinate process and ethmoid bulla are then removed to visualize the maxil-
lary ostium. The sphenopalatine artery is visualized as it exits the sphenopalatine
foramen and is followed until the posterior lateral nasal artery is identied, as
this serves as the pedicle it is vital that it remains viable.
• The maxillary ostium can then be extended posteriorly; it is important to con-
sider variations in the course of the posterior lateral nasal artery, as it may lie
anterior to the posterior wall of the maxillary sinus.
• The submucoperiosteal mucosa is lifted from the anterior aspect of the palatine’s
ascending process posteriorly toward the crista ethmoidalis, sphenopalatine
artery, and foramen.
• Two parallel incisions are made in the sagittal plane. A superior incision is made
just above the inferior turbinate that extends from its posterior aspect, at the level
of the middle meatal antrostomy, over its attachment to the lateral nasal wall. An
inferior incision is made just below the inferior turbinate, along its caudal mar-
gin, in the posterior to anterior direction. A vertical incision is made connecting
these two along the anterior head of the inferior turbinate.
• The mucoperiosteum is elevated from the oor of the inferior turbinate in an
anteroposterior fashion. A variable amount of bone can be elevated depending on
the ease of dissection.
• The ap is carefully unrolled so that the mucosal side faces externally and that
the pedicle is free of kinks. After nonvascularized tissue, bone, and foreign body
have been cleared in between the ap and defect margins, it can then be placed
either directly to the dura, denuded bone or over a fat graft.
• After sealant or biological glue is applied over the ap, absorbable gelatin
sponges are placed. To press the ap gently against the defect, a sponge nasal
packing may be used. While a Foley catheter balloon can be used, some caution
against its use to prevent untoward damage to the ap pedicle. Finally, silicone
nasal splints are placed, and remain for 10–21days postoperatively to protect the
denuded lateral nasal wall [18, 26, 28, 29].
Surgical Challenges oftheITF
A common technical challenge is the often difcult elevation of the ITF, especially
after the inferior turbinate has been fractured. Additionally, because of the presence
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of the midline ridge overlying the mucosa of the inferior turbinate, the ap will
often retain its shape. It may be necessary to make a small Y-shaped incision in the
distal ap and atten it for it to t securely over the defect [26].
Flap Advantages andLimitations
The ITF is a reliable option when the HBF is contraindicated. It eliminates risks
associated with vascularized regional aps such as parietal and pericranial aps and
minimizes healing time because of rapid mucosalization [29]. However, inherent
limitations include shorter length, limited arc of coverage, and difculty rotating
the ap.
The estimated surface area provided by the ITF is not well described currently;
several sources, even in recent literature, cite the 1999 Murakami etal. analysis of
ve cadavers, in which an average ITF was reported to be 4.97cm2 [18, 29, 30].
Regardless, surgeons in the eld are aware of the limitations of the ITF and have
since elaborated upon its design and capabilities. The extended ITF (EITF),
described by Choby etal. 2014, incorporated nasal oor mucosa to supplement the
ITF; this was further expanded upon with the addition of septal mucosa. They
reported an EITF surface area of 27.26±3.65cm2 and 40.53±6.45cm2 with the
addition of septal mucosa. For reference, the reported HBF surface area was 25cm2.
The EITF also reduces the arc of rotation by providing a longer, further-reaching
ap [28]. Fortunately, like the HBF, the ITF is modiable, and its historical limitations are no longer absolute. The defects of the anterior skull base beyond the standard ITF’s capabilities can be repaired effectively.
Posterior Pedicle Middle Turbinate Flap
The posterior pedicle middle turbinate ap (PPMTF), or middle turbinate ap
(MTF), is a local intranasal ap based on the middle turbinate artery, a medial
branch of the posterior lateral nasal artery. The relevant vascular anatomy was
described previously; however, the middle turbinate artery lies inferior to the middle
turbinate and splits into anterior and posterior segments that vascularized the lateral
and medial mucosa, respectively. As the MTF surface area is comparable to that of
the ITF, similar limitations are found in both designs. However, the superior location of the vascular pedicle provides a means of reaching further into the anterior
skull base. As such the MTF is a reliable option for reconstruction of the small-tomoderate-size defects of the planum sphenoidale, cribriform plate, or sella. If necessary, the ap can be used to repair clival defects, but the ITF is still considered the
primary design if HBF is not an option [26, 30].
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