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Endoscopic Skull Base Reconstruction
27
BritneyScott, CollinSmith, LukaBahra, RicardoL.Carrau,
andSameepP.Kadakia
Introduction
Advancements in transnasal endoscopic surgery of the skull base have allowed for
safe and effective management of both benign and malignant lesions of the skull
base. With the help of technological advances, improvements in surgical techniques,
and the use of multidisciplinary teams, endoscopic surgery of the skull base has
seen rapid development over the last several decades [1]. Beginning with purely
pituitary and sellar approaches, surgical resection has expanded to include suprasellar lesions, as well as a myriad of lesions extending from the cribriform plate to C2
and laterally out to the infratemporal fossa and petrous apex [2]. With the development of expanded ablative techniques, the surgeon is often left with large skull base
defects that require reconstruction to separate the cranial cavity from the sinonasal
cavity and obliterate the remaining dead space. Today, endoscopic reconstruction
using local and regional vascularized grafts has allowed for successful reconstruction of the skull base with a reduction in postoperative complications such as CSF
leaks and meningitis. This chapter is intended to review the key principles of
B. Scott · C. Smith
Department of Otolaryngology—Head and Neck Surgery, Kettering Health,
Kettering, OH, USA
L. Bahra
College of Osteopathic Medicine, Rocky Vista University, Englewood, CO, USA
e-mail: luka.bahra@rvu.edu
R. L. Carrau
Department of Otolaryngology—Head and Neck Surgery, The Ohio State University Wexner
Medical Center, Columbus, OH, USA
S. P. Kadakia (*)
Department of Plastic and Reconstructive Surgery, Wright State University Boonshoft
College of Medicine, Dayton, OH, USA
© The Author(s), under exclusive license to Springer Nature
Switzerland AG 2024
F. Sokoya, A. G. Vincent (eds.), Manual of Head and Neck Reconstruction,
https://doi.org/10.1007/978-3-031-65999-7_27
373
374
B. Scott et al.
endoscopic skull base reconstruction as well as describe endoscopic surgical reconstructive techniques using local and regional vascularized aps. The primary goal is
to provide a framework to help guide selection for skull base reconstruction and to
allow for successful outcomes while minimizing morbidity to the patient.
Endoscopic Anatomy oftheSkull Base
An understanding of skull base anatomy is critical to the success of both its resection and reconstruction. Historically, certain anatomical areas were thought to only
be accessible via an open transcranial and/or external approach. Over time, expanded
endonasal approaches (EEA) developed, leading to advancements in techniques,
allowing for safe and reliable surgical resection and reconstruction with limited
need for open approaches. By providing a minimally invasive option, the surgeon
has the opportunity for safe surgical resection and reconstruction, minimizing the
tissue disruption, brain retraction, and neurovascular manipulation that come along
with many open approaches [3]. Using a rod-lens endoscope, the surgeon has access
and high-quality visualization of several distinct anatomic regions of the skull base,
allowing for a safe and successful endoscopic skull base surgery. These areas
include the anterior cranial fossa, sella/suprasellar regions, clivus/posterior cranial
fossa, cavernous sinus, and the petrous apex. The anatomy of these regions is briey
reviewed below.
Endoscopic Anatomy oftheAnterior Cranial Fossa
Transnasal endoscopic access to the anterior skull base allows the resection of a
variety of anterior skull base tumors. A purely endoscopic anterior skull base resection is ideal for malignancies conned to the area between the orbits and benign
lesions of the anterior cranial fossa. Larger tumors require the use of endoscopicassisted approaches in combination with external craniofacial approaches. Important
anatomical landmarks include the frontal recess anteriorly, the planum sphenoidale
posteriorly, and the lamina papyracea laterally. To expose the anterior skull base
bilaterally, removal of the middle turbinate, anterior and posterior ethmoid air cells,
and the superior part of the nasal septum are required until a rectangular area of the
cranial base is exposed limited by the lamina papyracea laterally, the planum sphenoidale posteriorly, and the frontal recess anteriorly [4]. Superiorly in the midline is
the cribiform plate, along with the small olfactory nerves extending from the olfactory bulb. Key vascular structures in this region include the anterior and posterior
ethmoid arteries, which can be identied and isolated along the ethmoid roof.
Removing the bone of the anterior skull base between the orbits exposes the dura
and, if needed, the intracranial contents.
27 Endoscopic Skull Base Reconstruction
375
Endoscopic Anatomy oftheSella/Suprasellar Region
The sellar and suprasellar regions encompass the midline portion of the middle
cranial fossa. The sella is housed within the sphenoid bone that contains the pituitary gland and is covered superiorly in a thin dural layer known as the diaphragma
sellae. The anterior boundary is made up of a portion of the sphenoid bone known
as the tuberculum sellae and posteriorly by the bony dorsum sellae. Endoscopic
surgical access to these areas is achieved through the transsphenoidal approach.
This approach requires wide removal of the anterior face of the sphenoid sinus
along with any intersinus septa. Once removed, exposure of the posterior and lateral
walls of the sphenoid sinus allows identication of the rostrum and oor of the sella,
most commonly within the midline central portion of the posterior wall but can vary
depending on the degree of pneumatization (i.e., sellar, presellar, and conchal)
within the sphenoid sinuses [5]. Superior to the sellar oor lies the planum sphenoidale, and inferiorly lies the superior portion of the clivus. Within the lateral walls,
the bony protuberances of the optic nerves superiorly, and inferiorly the intracavernous portion of the internal carotid arteries. Between these two projections is the
optico-carotid recess [6]. The removal of the upper half of the sella, tuberculum
sellae, and the posterior portion of the planum sphenoidale offers the possibility of
exploring the suprasellar region [5]. This region contains key neurovascular structures, including the pituitary stalk, the optic chiasm, the medial portion of bilateral
optic nerves, along with the anterior cerebral artery.
Endoscopic Anatomy oftheClivus andPosterior Cranial Fossa
When viewing the posterior wall of the sphenoid sinus, immediately below the sellar oor lies the anterior surface of the clivus. From an endoscopic view, the clivus
is located along the inferior portion of the sphenoid sinus and represents the posterior cranial fossa. The bony landmark acts to separate the nasopharynx from the
posterior cranial fossa. Extending inferiorly, the clivus transitions into the craniocervical junction. Endoscopic access to the clivus is achieved via the removal of the
inferior portion of the sphenoid sinus down to the sphenoid-vomer junction. The
junction, including the sphenoid rostrum and vomer, is removed. This is carried out
laterally until the vidian nerves are identied at the oor of the sphenoid sinus. Once
identied, the vidian nerves represent the lateral and inferior limit of the bony resection and serve as useful landmarks to prevent injury to the intrapetrous portion of
the carotid artery [7]. Further access to the craniocervical junction is achieved by
the downward extension of the dissection from the clivus. When the clival bone is
fully removed, the dura covering the posterior cranial fossa is exposed and can be
opened to allow access to key structures such as the basilar artery, brain stem, and
upper cranial nerves.
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B. Scott et al.
Endoscopic Anatomy oftheCavernous Sinus
The cavernous sinuses are paired structures located lateral to the sella turcica bilaterally. They form the parasellar region and extend from the superior orbital ssure
anteriorly to the petrous part of the temporal bone posteriorly [8]. Housed within
these venous sinuses are a number of important neurovascular structures, including
the intracavernous portion of the internal carotid artery and cranial nerves III, IV,
V1, V2, and VI.Endoscopic access to this region can be achieved through a transsphenoidal route with wide removal of the anterior face of the sphenoid sinus. This
exposure is then extended to include removal of the bony coverings of the lateral
wall of the sphenoid sinus and carotid protuberances. Key structures helping to
guide dissection in this area are the paraclival and intracavernous portions of the
internal carotid artery, V2, and the vidian canal [9].
Endoscopic Anatomy ofthePetrous Apex
The petrous apex forms a portion of the medial temporal bone and is the area housed
between the inner ear laterally, the oor of the middle fossa superiorly, the posterior
cranial fossa posteriorly, and the clivus medially. Anatomically, this area is a pyramidal shape and develops with a variable degree of pneumatization. The orientation
of the petrous apex lies in an oblique plane with the apex positioned anteromedially
and its base located posterolaterally [10]. It is divided into an anterior and posterior
portion by the internal auditory canal. Key anatomical landmarks to endoscopic
surgery of the petrous apex include the petrous carotid canal, Dorello’s canal housing the abducens nerve, Meckel’s cave contains the trigeminal ganglion and is associated with the vidian canal, and vidian artery (quadrangular space). Endoscopic
access to this area involves expert techniques and anatomical knowledge of these
key landmarks.
Indications andContraindications
The minimal access nature of endoscopic endonasal approaches to the skull base
provides inherent advantages over open approaches. Although technically different,
the fundamentals are universal, including surgical access that delivers maximal
visualization of the lesion, tumor resection occurs in accordance with oncological
principles, and conservation of key neurovascular elements [11]. The surgeon must
be aware of the indications and contraindications, advantages and disadvantages of
each approach, and the degree of tumor involvement with surrounding anatomical
structures. If the most direct path to the lesion is impeded by critical neurovascular
components and signicant manipulation of these components is required, other
surgical approaches should be considered in the surgical decision-making [12].
Both benign and malignant pathologies can warrant the need for resection and
reconstruction of the skull base, and their extent depends on the nature and spread
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
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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B. Scott et al.
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
27 Endoscopic Skull Base Reconstruction
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].
381
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.
382
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)