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27 Endoscopic Skull Base Reconstruction
27. Kuan EC, Palmer KN.Epistaxis. In: Flint PW, Haughey BH, Lund VJ, Thomas JR, Robbins
KT, Francis HW, editors. Cummings otolaryngology: head and neck surgery, 7th ed. Elsevier;
2020. p.733–744.
28. Choby GW, Pinheiro-Neto CD, de Almeida JR, etal. Extended inferior turbinate ap for endoscopic reconstruction of skull base defects. J Neurol Surg B Skull Base. 2014;75(4):225–30.
https://doi.org/10.1055/s- 0033- 1358791.
29. Yip J, Macdonald KI, Lee J, Witterick IJ, Zadeh G, Gentili F, Vescan AD.The inferior turbinate ap in skull base reconstruction. J Otolaryngol Head Neck Surg. 2013;42(1):6. https://doi.
org/10.1186/1916- 0216- 42- 6.
30. Hachem RA, Beer-Furlan A, Jamshidi A, ElKhatib A, Carrau RL, Prevedello DM.Skull base
reconstruction following resection of skull base chordomas and chondrosarcoma. In: Harsh IV
GR, Vaz-Guimaraes F, editors. Chordomas and chondrosarcomas of the skull base and spine,
2nd ed. Academic; 2017. p.259–270.
31. Kennedy D.Rhinology: diseases of the nose, sinuses, and skull base. NewYork: Thieme
Medical Publishers; 2012. p.699.
32. Kim GG, Hang AX, Mitchell CA, Zanation AM.Pedicled extranasal aps in skull base reconstruction. Adv Otorhinolaryngol. 2013;74:71–80. https://doi.org/10.1159/000342282.
33. Tien DA, Stokken JK, Recinos PF, Woodard TD, Sindwani R. Comprehensive postoperative management after endoscopic skull base surgery. Otolaryngol Clin North Am.
2016;49(1):253–63. https://doi.org/10.1016/j.otc.2015.09.015.
34. Fang CH, Hawn VS, Agarwal V, et al. Antibiotic prophylaxis in anterior skull-base surgery: a survey of the North American Skull Base Society. Int Forum Allergy Rhinol.
2019;9(10):1196–204. https://doi.org/10.1002/alr.22396.
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Open (Anterior) Skull Base Repair
28
YusufM.Agamawi, FiyinSokoya, andYadrankoDucic
Introduction
The development of interdisciplinary skull base surgery started with the collaboration between otolaryngology and neurosurgery, and it has continued to change with
the advancement in technology and techniques from ablative and reconstructive
skull base surgeries [1]. These advancements have caused a paradigm shift from
open techniques to endoscopic techniques, becoming the standard for skull base
surgery. However, it is crucial not to let open skull base surgery become a “lost art”
because open skull base reconstruction techniques for certain malignant tumors,
larger composite defects, major craniofacial trauma, osteoradionecrosis, and failed
previous endoscopic reconstructions are still often indicated [1].
The main goals of skull base reconstruction are to recreate a water-tight seal and
separation between the intracranial and extracranial contents while also eliminating
dead space and restoring reasonable form and function [1]. Anterior skull base
reconstruction can be done with grafting of local tissues (e.g., free mucosal graft)
and/or manufactured products (e.g., acellular matrices) in conjunction with or without local vascularized ap (e.g., pedicle-based nasoseptal ap) for minor defects
that generally coincide with endoscopic skull base surgery. For larger skull base
defects, the reconstructions can range from the minor ones mentioned above in
Y. M. Agamawi (*)
Department of Otolaryngology—Head and Neck Surgery, Saint Louis University School of
Medicine, Saint Louis, MO, USA
Otolaryngology and Facial Plastic Surgery Associates, Fort Worth, TX, USA
F. Sokoya
Wellstar Health Systems, Atlanta, GA, USA
Y. Ducic
Otolaryngology and Facial Plastic Surgery Associates, Atlanta, GA, 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_28
395
396
Y. M. Agamawi et al.
combination with larger pedicled muscle and/or fascia aps (e.g., pericranium or
temporalis muscle) and/or free tissue transfer or free ap.
Anatomy
Skull base surgery offers a unique “bi-approach” capability with the option to
approach endoscopically through the sinonasal cavities from below and/or approach
externally or open through the skin via the scalp and/or forehead from above the
skull base. To operate at full capacity, it is necessary to understand the anatomy and
its relations when approaching from above and below the skull base.
The anterior skull base is composed of the frontal, ethmoid, and sphenoid bones,
and this thin osseous structure separates the intracranial contents from the sinonasal
and orbital contents. The frontal bone contributes to the posterior wall of the frontal
sinus and the roof of the orbits, the ethmoid bone forms the ethmoid sinus roof and
cribriform plate, and lastly, the posterior portion of the skull base is made up of the
planum sphenoidale and anterior clinoid processes of the sphenoid bone (Fig.28.1)
[1]. Briey in regards to sinonasal anatomy from below or inferior to the skull base,
the anterior border is frontal sinus and/or agger nasi cell, the lateral border is the
lateral sinonasal wall and medial orbital wall/orbit, the posterior border is the posterior sphenoid wall and/or sella turcica, and when unilateral the medial border is
nasal septum and cribriform plate of the ethmoid bone. From the transnasal endoscopic approach, the oversimplied anatomical skull base layering is mucosa,
Frontal
Ethmoid
Sphenoid
Fig. 28.1 Skull base bony anatomy
Te mporal
Parietal
Occipital
Zygomatic
28 Open (Anterior) Skull Base Repair
397
periosteum, bone, meninges (dura mater, arachnoid, cerebrospinal uid (CSF), pia
mater), and then brain tissue.
For open skull base surgery, it is critical to understand scalp and forehead anatomy. The anatomic layers of the scalp, from supercial to deep, are the (S)kin,
sub(C)cutaneous tissue, galea (A)poneurosis, (L)oose areolar tissue, and (P)ericranium, which form the mnemonic “SCALP” (Fig. 28.2) [2]. In regards to scalp
reconstruction, there are “loose areas” of the scalp, which allow great mobility of
the scalp for local tissue rearrangement, and there are “tight areas” with little to
give. The area with the greatest mobility is at the temporoparietal fascia overlying
the temporalis fascia, and the area with the least mobility is at the temporal line
where the galea is adherent to the pericranium. However, this may be released to
increase mobility [2]. Blood vessels and nerves that supply the skin of the scalp run
supercially to the galea aponeurosis and frontalis muscle within the subcutaneous
tissue layer [2].
The vasculature of the scalp and forehead originates from both the internal and
external carotid arteries with an extensive network of terminal branches and the
formation of collaterals to aid in redundant blood supply to the areas (Fig.28.3).
The forehead and anterior scalp blood supply comes from the supraorbital (laterally) and supratrochlear (medially) artery branches from the ophthalmic artery via
the internal carotid artery. The lateral temporal and parietal scalp areas are supplied
by the branches from the supercial temporal artery (STA) via the external
carotid artery.
Skin and Dense Connective Tissue
Fig. 28.2 Scalp tissue anatomy
Epicranial Aponeurosis (Galea)
Loose areolar connective tissue
Periosteum
Cranium
398
Deep t
Descending palatine a.
Superior thyroid a.
ngeal a.
Frontal branch of
superficial temporal a.
Zygomatico-orbital a.
emporal arteries
Sphenopalatine a.
Posterior superior
alveolar a.
Angular a.
Infraorbital a.
Superior labial a.
Buccal a.
Transverse facial a.
Middle meningeal a.
Inferior labial a.
Mental branch of
inferior alveolar a.
Facial a.
Submental a.
Inferior alveolar a.
Ascending palatine a.
Facial a.
Lingual a.
Fig. 28.3 Vasculature anatomy of scalp and forehead
Y. M. Agamawi et al.
Parietal branch of
superficial temporal a.
Middle temporal a.
Occipital branches
of occipital a.
Anastomosis of
auricular branch with
posterior auricular a.
Occipital a.
Meningeal branch
Occipital branch
Descending branch
Stylomastoid a.
Posterior auricular a.
Occipital a.
Maxillary artery
Ascending phary
External carotid a.
Internal carotid a.
Common carotid a.
The temporal region is more anatomically complex given the more soft tissue
covering layers of the temporal calvarium and clinical importance in regards to
cranial nerve (CN) VII (facial nerve). The soft tissue layers from supercial to deep
are the skin, subcutaneous tissue, supercial temporal fascia (temporoparietal fascia), supercial layer of the deep temporal fascia, temporal fat pad, deep layer of
deep temporal fascia, temporalis muscle, and periosteum/pericranium. The classic
path of the frontotemporal (frontal) branch of the facial nerve traverses along
Pitanguy’s Line, which is generally from the tragal pointer (1cm anterior, inferior,
and deep to tragus; approximates the location of CV VII trunk where it exits the
stylomastoid foramen) to about 1.5–2cm above the lateral brow (Fig.28.4) [2, 3].
There are several other intracranial and extracranial neurovascular structures traversing the bony skeleton of the anterior skull base. In the midline between the
crista galli and frontal bone is the foramen cecum, which transmits nasal venous
drainage to the superior sagittal sinus. Smell bers or olfactory neurons of CN I
travel superiorly through multiple holes of the olfactory foramina in the cribriform
plate to the olfactory bulb above the anterior and posterior ethmoid arteries. Orbital
contents laterally travel posteriorly and medially in the optic canal (CN II, ophthalmic artery), superior orbital ssure (CN III, CN IV, CN V1, superior ophthalmic
vein), and inferior orbital ssure (inferior ophthalmic vein) to converge toward the
internal carotid arteries, cavernous sinus, and optic chiasm at the anterior clinoid
process, which is the border between the anterior and middle cranial fossae.
28 Open (Anterior) Skull Base Repair
Fig. 28.4 Pitanguy’s line
1.5 cm
1.5 cm
1.0 cm
1.0 cm
1.0 cm
1.0 cm
399
Planning
The primary objective of skull base reconstruction is to recreate a durable watertight seal separating the intradural contents from external exposure [1]. This facilitates the prevention/reduction of possible high-risk complications from persistent
CSF leak/stula, such as meningitis, pneumocephalus, and the associated morbidity
and mortality that increase over time [1]. The secondary objective is to eliminate
dead space, return function, and restore cosmesis [1, 4]. The reconstruction strategy
to attain these objectives requires careful consideration of various anatomic and
patient-related factors. Furthermore, the strategy must incorporate multiple reconstruction options, including free tissue transfer or free aps, to account for the
unpredictability of ablative skull base surgery.
The utilization of three-dimensional (3D) reconstructions from ne-cut computed tomography (CT) and magnetic resonance imaging (MRI) for virtual surgical
planning (VSP) is becoming more pronounced, especially with extensive defects,
and the application of multiplanar imaging for surgical navigation is considered the
standard of care [1, 5, 6]. VSP may help better dene the extent of the tumor and/or
defect to aid in reconstruction planning and prefabrication of customized hardware,
implants, and prostheses [1, 7–11].
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Y. M. Agamawi et al.
Anatomic Factors
Anatomic factors to consider mainly pertain to the defect’s location, size/volume,
and the associated extent of the communication between the intradural and extradural spaces. Persistent CSF leaks have been associated with intraoperative CSF leaks,
clival defects, and large dural openings [1, 12–15]. To minimize complications, the
integrity of the dural reconstruction and eliminating dead space are critical. For
anterior defects of the anterior skull base with small dural defect and/or intact bony
ledge, underlay grafts or aps with multilayered acellular alloplastic materials and
free grafts may be adequate reconstruction, and potentially, the weight of the anterior intracranial contents may help seal the reconstruction [1, 16]. For large posteriorly portioned defects with signicant dura defect and/or bony loss, vascularized
tissue is often required along with postoperative medical management of CSF pressure with or without CSF diversion [1]. If there is persistent dead space along the
skull base tissue reconstruction, dural expansion via duraplasty should be considered [1]. Skull base defects that are very large involve signicant bone loss (especially orbitocranial and/or extend to middle cranial fossa), include orbital
exenteration, and/or have high-ow CSF leaks likely to require free ap(s) for volume and allow for more anatomically analogous tissue reconstructions [1].
Patient Factors
Patient factors to evaluate are history of radiation therapy, prior surgeries and reconstruction attempts, and availability of local tissues for reconstruction [1]. Radiation
therapy prior to surgery has been associated with poor wound healing and central
nervous complications (e.g., CSF leak and meningitis) in skull base reconstruction
[1, 12, 17–19]. Prior head and neck surgeries and/or reconstruction attempts may
have disrupted the local vasculature and subsequently lessened the reliability and/or
availability of local or pedicled aps. This, coupled with the unpredictability of
ablative skull base surgery, further highlights the need to strategize multiple reconstruction options.
Instruments andEquipment Setup
Facial trauma and plastic and/or head and neck basic tray(s) with varying-sized
toothed pickups, dissecting scissors, scalpels, osteotomes, periosteal elevators,
bipolar cautery, saw, and attachments.
Fixation system with appropriate drills, drill bits and attachments, various plate
sizes/shapes, and associated screws. Consider having a Mitek mini bone anchor
system, external nasal splints/casts (e.g., Aquaplast) and K-wire available for nasoorbitoethmoid (naso-orbital-ethmoid; NOE) complex reconstruction.
28 Open (Anterior) Skull Base Repair
401
Surgical Technique
Open skull base reconstruction is performed under general anesthesia with the
patient/operative table turned 180° to allow the surgeon(s) full and uninhibited
access to the patient’s head, as well as to be sure that other potential tissue donor
sites remain accessible if needed. Suppose the reconstruction is in coordination with
ablation, and it is a two-team approach. In that case, the reconstruction team/
surgeon(s) should routinely check in with the ablative team/surgeon(s) to assess the
progress of the defect so that the reconstructive plan can be adjusted if needed.
Reconstructive options range from nonvascular grafts and manufactured materials,
local and regional aps, and free tissue transfer or free aps. It is critical to reestablish that water-tight seal between the intradural and extradural compartments and
eliminate dead space, as well as a tension-free repair for locoregional and free ap
reconstructions.
The main approach utilized for open skull base surgery is the coronal approach.
For the coronal incisional approach, the patient’s head is generally shaved, or a
1–2cm width strip is shaved along the proposed incision(s). Local anesthetic (1%
lidocaine with 1:100,000 epinephrine) is inltrated along the proposed incision(s).
Surgical sites, including all potential reconstructive donor sites, are then prepped
(betadine paint) and draped sterilely. It is critical to be continuously cautious and
cognizant of the eyes and to place eye corneal shields at the beginning of the case to
protect the eyes and vision of the patients.
Nonvascular andManufactured Grafts
There are a wide variety of nonvascular autologous tissue grafts (e.g., nasal mucoperichondrium and mucoperiosteum, tensor fascia lata, temporoparietal fascia, calvarial bone, and abdominal adipose tissue) and acellular manufactured materials
(e.g., DuraGen (Integra LifeSciences), AlloDerm (Allergan), DuraSeal (Integra
LifeSciences), and hydroxyapatite cement) [1, 20–25]. They have been successfully
used for skull base repair in combination with multiple layers, gasket-seal conguration, button, and/or underlay grafting. However, the defects are relatively small,
with bony ledge present as described in endoscopic skull base surgery and commonly used in combination with vascularized aps [1, 13, 26, 27].
Local andRegional Flaps
The main pillar of anterior skull base reconstruction is vascularized locoregional
aps [1]. The nasal septal or Hadad-Bassagasteguy ap base off of the posterior
septal artery is the main go-to ap in endoscopic reconstruction with decreased CSF
leak rates [1, 12, 28]. However, the nasal septal ap has limited use for the reconstruction of large skull base defects and may not be an option with advanced tumors
requiring resection of the nasal septum.
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Y. M. Agamawi et al.
The pericranial ap is the workhorse for open craniofacial and skull base reconstruction surgery because of its wide surface area, signicant length, and reliable
vascularity [1, 29]. This ap receives its blood supply from the supratrochlear and
supraorbital blood vessels and is ideal for patients with a history of and/or anticipating radiation therapy [1, 29]. Depending on the defect, the pericranial ap can be
harvested unilaterally or bilaterally, and because of its thinness and pliability, it is a
very functional option to restore a dural lining that will be used with other soft tissue
or bony reconstructions [1, 30]. An osteo-pericranial composite ap using split calvarial bone grafts has been described to reconstruct defects needing a more rigid
structure [1, 31].
The temporoparietal fascia ap (TPFF) has similar characteristics to the pericranial ap, which makes it an excellent choice in skull base reconstruction, especially
for more lateral defects. The TPFF is supercial to the supercial layer of the deep
temporalis fascia, and it is continuity with the adjacent and medial galea aponeurosis [32]. The supercial temporal artery (STA) from the external carotid system is
the blood supply for the TPFF.The main trunk of the STA divides into multiple
branches about 3cm above the level of the zygomatic arch [32]. The STA also gives
rise to the middle temporal artery and, if dissected with the STA, allows concomitant harvesting of deep temporal fascia, temporalis muscle, and/or adjacent calvarial
bone [32–34]. Similar to pericranium with its versatility and pliability, TPFF may
be tunneled through “keyholes” into the skull base [1].
The fan-shaped temporalis muscle transposition ap is another commonly used
option for skull base reconstruction. It has a robust blood supply, mainly from the
anterior and posterior deep temporal artery branches off of the internal maxillary
artery from the external carotid artery, as well as an accessory supply from the
middle temporal artery [35]. The temporal muscle spans the temporal fossa from the
inferior temporal line superiorly to under the zygomatic arch to the coronoid process and ascending ramus of the mandible inferiorly [35, 36]. This muscle ap
inherently provides more bulk than the pericranium and TPFF, which is useful for
lling dead space, and muscle tissue has been shown to have improved healing
properties [1, 37]. A composite ap with attached calvarial bone may be harvested
to aid in bony reconstruction [1, 38, 39]. Skull base defects with orbital exenteration
are excellent candidates for reconstruction with temporalis muscle ap because this
ap can be tunneled through the lateral orbital wall or via the sphenoid keyhole
technique [1, 35]. Because of its attachment at the coronoid process and ascending
ramus of the mandible and its proximal blood supply, the reach/coverage of the
temporalis muscle ap is somewhat limited and not ideal for medial or contralateral
defects [1]. Other notable fasciocutaneous or myocutaneous regional aps, but less
commonly used due to reach/coverage limitations, are median or paramedian forehead aps (supratrochlear artery) as local ap options, and trapezius, pectoralis, and
latissimus as regional ap options [1].
28 Open (Anterior) Skull Base Repair
403
Free Tissue Transfer
Free tissue transfer or free aps are a mainstay in anterior skull base reconstruction
given the versatility with size (surface area, volume), composition (soft tissue and/
or bony), and ability to shape. Free aps provide a superior capacity to obliterate
signicant dead space and have been shown to reduce the risk of serious postoperative complications such as CSF leak, meningitis, and pneumocephalus [1, 40–42].
For substantial skull base dural defects and salvage cases, particularly with a history
of extensive surgery and/or radiation therapy, free aps are being considered the
standard for reconstruction [1]. Soft tissue-free ap options include rectus abdominis, latissimus dorsi, anterolateral thigh (ALT), vastus lateralis, vascularized tensor
fascia lata, and radial forearm. Bony-free ap options include bula and scapula.
Coronal Approach andPericranial Flap
Prior to incision, the planned/marked incision is inltrated subcutaneously with
local anesthetic containing epinephrine (e.g., 0.5–2% lidocaine with 1:100,000 or
1:200,000 epinephrine).
For the coronal approach, incision placement and design will vary depending on
the patient’s hairline and/or balding pattern. Generally, most incisions will be from
one superior helical root region to the other to allow adequate exposure, and the
incisions will be a wave or zigzag/sawtooth geometric pattern rather than the traditional bow-like incision to better camouage the incision scar [43]. Incisions can be
extended inferiorly into the preauricular region bilaterally to allow for further exposure to the superior half of the maxilla if needed [44].
The initial incision should be between the upper origins of the temporal muscles,
extending from one temporal line to the other and down to, but not through, the
pericranium at the subgaleal plane [43, 44]. From the superior temporal line, the
subgaleal plane continues deep to the temporoparietal fascia (supercial temporal
fascia) but above the deep temporal fascia. The skin incision is continued laterally
and inferiorly to the superior helical root or insertion area of the zygomatic arch. If
considering TPFF, be cognizant of the STA and stay supercial to temporoparietal
fascia in the subcutaneous layer. As a way to avoid incising the deep temporal fascia
and temporalis muscle, which may cause brisk bleeding, undermining the skin soft
tissue with scissors in the subgaleal plane on the deep temporal fascia can be done
prior to incising the skin soft tissue [43]. The incision can then be further extended
inferiorly into the preauricular region within a preauricular skin crease at the same
subgaleal plane on the deep temporalis fascia. The coronal ap is then raised anteriorly in the subgaleal plane (within loose areolar tissue) above the pericranium and
deep temporal fascia, with the dissection starting midline and then going out laterally on both sides to create a broad ap. The broad anterior dissection and raising of
the coronal ap should be continued to the level of the supraorbital rims. The pericranium must be incised to develop and elevate the pericranial ap to expose the
bony supraorbital rims and foramina with associated neurovascular bundles.