Anterior Skull Base Resection External Approaches

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OPEN ACCESS ATLAS OF OTOLARYNGOLOGY, HEAD & NECK OPERATIVE SURGERY

ANTERIOR SKULL BASE RESECTION: EXTERNAL APPROACHES Kyle VanKoevering, Daniel Prevedello, Ricardo Carrau

The sinonasal cavity and anterior cranial a fossa can be involved by a wide variety of diverse, rare neoplasms. Surgical extirpation of these lesions is often the mainstay of multimodal treatment for both benign and malignant diseases. However, these tumours pose a variety of challenges for surgical management, including complex anatomic considerations (Figures 1a-c).

Relevant Anatomy

Also refer to Chapter on FESS for surgical anatomy b Nasal Cavities and Sinuses

The nasal cavity can be imagined as a quadrangular corridor that is narrower at the top and divided into right and left compart- ments by a midline septum. It communi- cates with the exterior through anterior openings, the nares (nostrils). Posteriorly, it opens into the nasopharynx through the posterior choanae. Its external shape re- flects its skeletal support, which is com- posed of the paired nasal bones and the upper and lower lateral nasal cartilages as they surround the pyriform aperture. The c walls of each nasal fossa include the nasal septum medially, the horizontal portion of the maxillary bone and palatine bone inferiorly, and the inferior turbinates and ethmoid bones laterally.

Superiorly, the nasal fossae are confined by the cribriform plate and the rostrum of the sphenoid sinus as it slants posteroinferiorly toward the nasopharynx. The inferior turbinate is an independent bone, whereas the middle and superior turbinates are part of the ethmoid bone. Figures 1a-c: Preoperative images of a large heterogeneously enhancing chondro- sarcoma occupying the entire skull base with significant intracranial extension The ethmoid air-cell labyrinth consists of 3- may be found at the sphenoethmoidal recess 18 cells per side that are connected in the above and posterior to the middle turbinate. midline by the cribriform plate (Figure 2). Each side is divided into an anterior and posterior group of cells based on the attachment of the middle turbinate to the lateral nasal wall i.e. basal lamella. An Onodi cell represents a posterior ethmoid cell which is located superior or lateral to the sphenoid sinus and can occasionally contain the optic nerve or portions of the carotid artery. It may be bigger than the sphenoid sinus.

The roof of the ethmoid labyrinth comprises a portion of the anterior skull base. Late- rally, the ethmoid air cells are bound by the orbit (lamina papyracea), and along the roof of the ethmoid sinuses, the anterior and posterior ethmoid arteries can be found exiting the orbit and traversing the skull base toward the vertical lamella of the cribriform plate.

The frontal sinuses are paired cavities within the diploic frontal bone with frond- like pneumatisation and asymmetric shapes and sizes. The posterior wall is shared with the anterior cranial fossa. Their floors corre- spond to the roofs of the orbits and anterior ethmoid cells. The maxillary antrum is the largest of the paranasal sinuses and is situated lateral to the nasal cavity and inferior to the orbit. Its floor, which is formed by the alveolar process of the maxilla, lies 1-1.5 cm inferior to the nasal floor. The posterior and posterolateral walls of the maxillary sinus are contiguous with the pterygopalatine and infratemporal fossae, respectively. The medial wall of the antrum corresponds to the lateral wall of the nasal cavity and contains the drainage ostium. The sphenoid sinus lies in the center of the skull and is situated posterior to the nasal cavity cephalad to the nasopharynx. Its anterior wall bulges into the nasal cavity Figures 2a-c: Bony anatomy of anterior and contains the drainage ostium, which skull base

2 There is a wide variety in the degree of the vertical wall of the cribriform plate, the pneumatisation of the sphenoid sinuses weakest point of the anterior skull base. between patients and even from one side to Anterior to the cribriform, a bony promi- the other. Superiorly, the planum sphenoi- nence known as the crista galli is seen. The dale constitutes the posterior portion of the planum sphenoidale denotes the area poste- anterior skull base. The sella typically sits rior to the cribriform plate, and its posterior within the superior sphenoid sinus. aspect marks the posterior boundary of the anterior cranial fossa. Orbits

The orbit shares three of its walls with the Preoperative Workup paranasal sinuses. Its medial wall corresponds to the lateral wall of the ethmoid Workup of patients with any new sinonasal sinus. It bears, from anterior to posterior, or anterior skull base mass should include a the nasolacrimal sac lying on the lacrimal detailed examination, including cranial ner- bone (lacrimal fossa), the anterior and ve examination, and nasal endoscopic eva- posterior ethmoidal arteries, the trochlea, luation. Biopsy of the mass should be per- and the optic nerve with its foramen at the formed either in the clinic (if bleeding risk apex of the orbital cavity. Its inferior wall appears low and patient is amenable) or in corresponds to the roof of the maxillary the operating room. Definitive surgical sinus. The orbital cavity contains the infra- plans should not be executed without final orbital fissure and infraorbital neurovas- (permanent) pathologic diagnosis whenever cular bundle. The infraorbital fissure is con- possible. tinuous with the pterygomaxillary fissure. The superior wall is contiguous with the The extent of disease and hence the required ethmoid or frontal sinuses and with the extent of the resection is established endo- anterior cranial fossa. As previously stated, scopically and by imaging. Cross-sectional the superior orbital fissure serves as a imaging is imperative to ascertain the extent passage for CN V1, III, IV, and VI and of the disease, potential cranial nerve and represents a potential pathway to the middle internal carotid artery involvement, and cranial fossa. The lateral wall is contiguous resectability and potential for cure. Typi- with the temporal fossa anteriorly to cally, a CT scan is best to evaluate the bony laterally. anatomy (bony destruction or remodeling, intracranial extension) and is usually paired Anterior Cranial Fossa (Figure 2) with MRI (with and without contrast) to evaluate the soft tissue extent of disease, The floor of the anterior cranial fossa com- including orbital, dural, vascular, brain or prises the frontal, ethmoid, and sphenoid cranial nerve invasion (Figure 1). A proper bones. Laterally, the floor of the anterior staging workup for metastatic disease (PET cranial cavity corresponds to the roof of the scan, or CT of neck and chest or ultrasound orbits, while, centrally, it corresponds to the neck and chest x-ray) is critical in treatment vault of the nasal cavity and the roof of the planning. In the case of parameningeal ethmoid sinuses. At the central anterior sarcomas, MRI of the spine is indicated to skull base, the most prominent structure is ascertain the presence of “drop metastases”. the cribriform plate, which contains multiple foramina, through which the olfactory filaments pass into the nasal cavity. Bran- ches of the anterior ethmoid artery penetrate

3 Surgical Planning Open Craniofacial Approach: Surgical Technique Surgical planning must consider two key components: The open craniofacial approach is described • The surgical approach must facilitate a in the following steps: complete, oncologic resection of the • Access to the mid- and upper face and tumour, preserving normal tissue and cranium protecting neurovascular structures • Sinonasal approaches • The operative plan must include a ro- a. Lateral rhinotomy bust reconstructive algorithm to restore b. Midfacial degloving the separation of the cranial cavity and c. Expanded endonasal upper aerodigestive tract with adequate • Reconstruction cosmetic and functional outcomes • Closure

Two distinct surgical techniques should be Access to mid- and upper face and considered when planning surgery cranium

• Traditional open approaches involve a • Intraoperative navigation, though gen- transcranial subfrontal approach (most erally not critical, can be registered to frequently via coronal incisions) com- the preoperative imaging to assist with bined with a transfacial approach (late- intraoperative confirmation of surgical ral rhinotomy, midface degloving, landmarks Weber-Ferguson incisions) to facilitate • Make a straight scalp incision in a en bloc resection of the median anterior coronal plane of the skull from one cranial base (cribriform plate, roof of preauricular crease to the contralateral ethmoids), superior nasal septum, eth- preauricular crease moid sinuses and lateral wall(s) of the • Carry the incision down to the calva- nasal cavity (medial maxilla and lamina rium from temporal line to temporal papyracea). When needed, it may be line combined with orbital exenteration or a • At the temporal line, the dissection subtemporal approach to access the late- plane is transitioned to just above the ral skull base, orbit and infratemporal deep layer of the temporalis fascia fossa • Elevate the scalp in a subpericranial plane, transecting the attachments of • Endonasal endoscopic approaches the pericranium at its junction with the have evolved over the last 30 years and deep temporal fascia, around the supe- permit comprehensive sinonasal resec- rior border of the temporalis muscle tion and anterior skull base extirpation • It is imperative to preserve the in lieu of a traditional transfacial ap- pericranium, as this is typically proach. The endoscopic approach is utilised as the reconstructive layer that equivalent, both oncologically and will separate the intracranial space functionally to a traditional craniofacial from the sinonasal cavity (Figure 3) resection. Furthermore, the endoscopic • As the scalp is elevated anteriorly, the approach may be combined with a orbital rims and glabella are exposed subfrontal approach to avoid facial incisions. Each of these approaches is detailed below.

Figure 3: Elevating the scalp flap in a Figure 4: Pericranium is then incised and subgaleal plane. The rake is used to lift the mobilized off the skull, following the scalp while the loose areolar tissues and temporal lines laterally and the coronal pericranium are sharply dissected off the incision for the posterior cut. If needed, the galea. Alternatively, the scalp and peri- posterior cut can be extended several centi- cranium can be elevated as one flap meters further posteriorly, if additional initially, and the pericranium back-elevated length will be required for the recon- off the scalp later in the dissection if needed struction

• A 1cm incision over the periosteum of the zygomaticofrontal area serves as an internal relaxing incision, allowing mobilisation of the scalp flap with minimal retraction • Alternatively, the scalp flap and the pericranium can be elevated separately. To perform this manoeuvre, the standard coronal incision is performed but the scalp flap is elevated in a subgaleal plane, leaving the loose areolar tissue and pericranium attached Figure 5: The pericranium is fully mobili- to the skull (Figure 4). Laterally the sed for the reconstruction, either by back- deep temporalis fascia is left intact as elevating off the scalp flap or elevating the scalp is mobilised like the separately conventional flap elevation noted above. The dissection continues until a • The frontal branch of the facial nerve point 2cm above the supraorbital rims. lies just deep to the superficial tempo- At this point, the pericranium is ralis fascia (temporoparietal fascia) mobilised separately off the skull by inferior to an imaginary line extending incising along the temporal lines and from the root of the zygoma to the across the coronal line posteriorly superior orbital rim. It only comes into (Figure 5). play if the resection needs to be extended laterally to expose the middle cranial or infratemporal fossa. In such cases the frontal branch needs to be 5 preserved either by identifying and dissecting the nerve or dissecting in a plane that does not place the branch at risk. The deep temporalis fascia divides into a superficial and deep layer, con- taining between them a temporal fat pad. The superficial layer is incised superior to that imaginary line extending from the root of the zygoma to the superior orbital rim i.e. prior to encoun- tering the frontal branch, and the scalp flap is elevated in an interfascial plane between the superficial and deep layers Figure 6: The left supraorbital neuro- of the deep temporalis fasciae. This vascular bundle supplies sensation to the plane can be followed to the orbital rim left frontal region and serves as one of the and down to the zygoma, depending on key vascular pedicles to the pericranial the extent of exposure needed at the flap. Here the bundle is mobilised from the nasion, and will protect the frontal supraorbital notch (or foramen as needed) branch to maintain its integrity as it exits the • As the scalp flap is turned anteriorly periorbita and enters the pericranium and and inferiorly, the supraorbital rims are scalp. This allows bony osteotomies to be exposed, and the supraorbital neuro- made without compromising the peri- vascular bundles are dissected from cranium or sensation in the frontal region the supraorbital notches, as depicted in Figure 6. When a true supraorbital foramen is present, it may be opened inferiorly using a 3 - 6mm osteotome and mallet. This manoeuvre allows inferior mobilisation of the supraorbital neurovascular bundle and dissection of the periorbita from the superior and medial orbital walls. Notably, as the periorbita are dissected from the orbital rim, the orbital roof takes a superior trajectory around the orbital rim with an acute angle that must be anticipated or the periorbita will be violated. Al- though not critical, maintaining the integrity of the periorbita lessens trau- ma to the orbits and limits fat herniation into the surgical field. Any remaining periosteum is elevated to expose the Figure 7: Fully mobilising the superior nasal root and nasal bones (Figure 7). periorbita allows the scalp flap to be

further retracted as the entire nasal root and superior nasal bones are exposed. The purple line highlights the planned division between the frontal craniotomy and the orbital bar

6 • This coronal approach exposes the while minimizing the retraction of the superior cranium, frontal area, glabel- frontal lobes. It comprises removal of la, nasal bones, temporalis muscles the bone forming the superior orbital and temporal fossae, and the superior rims bilaterally, glabella and nasion, two thirds of the orbits down into the nasal bones (Figures 9, • A bifrontal craniotomy is next per- 10). The lateral bone cuts are placed at formed to expose the frontal lobes. It is the lateral orbital rims and a posterior typically performed in conjunction with cut joins these incisions by traversing the neurosurgical team (Figure 8). The the anterior orbital roofs (retracting the craniotomy typically encompasses the periorbita to protect the orbital con- frontal bone bilaterally from the key- tents) and across the frontoethmoidal hole pterional burr holes and down to junction just posterior to the frontal approximately 2cm from the orbital outflow tracts. A transverse incision rims (Figure 8). Typically, small burr across the nasion, or further inferiorly holes are placed on each side of the through the nasal bones, is then sagittal sinus; thus, facilitating its performed, often requiring a curved dissection and avoiding laceration. The osteotome to free the anterior superior frontal sinus is often transgressed with attachment of the nasal septum to the these cuts, and the posterior table is orbital bar to fully mobilise the graft usually removed from the frontal bone • Direct exposure of the anterior skull graft, with the remainder of the sinus base has now been achieved completely stripped of mucosa to • The subfrontal exposure limits the cranialise the sinus. These craniotomy need for frontal lobe retraction cuts also can be extended laterally for • The dura is elevated from the floor of tumours that extend into the orbit or the anterior skull base and is sharply infratemporal fossa. divided from the crista galli, which is removed

Figure 8: A bifrontal craniotomy, widely exposing the frontal lobes to limit brain Figure 9: Removal of the orbital bar after retraction the bifrontal craniotomy viewed from the patient’s left. It demonstrates the osteo- • Following the craniotomy, the sub- tomies required to mobilise the orbital bar, frontal approach is facilitated by including the lateral osteotomy through the removing the orbital bar (Figure 9). orbital rim, which is then carried down The subfrontal approach maximises along the roof of the orbit and into the root exposure of the anterior skull base of the nasal bones

Figure 10: This demonstrates en bloc Figure 11: Final exposure of the anterior removal of the orbital bar, exposing the skull base after removal of the tumour frontoethmoid region and superior orbits demonstrates how the left orbit is fully skeletonised (note the orbital fat) and the • Careful elevation of the frontal lobe entire nasal cavity has been removed. The dura from the roof of the orbits and frontal lobes have been decompressed after crista galli exposes the cribriform plate creating a CSF leak allowing wide expo- • The dural sleeves along the olfactory sure without significant brain retraction nerves are individually divided and ligated; however, multiple lacerations • In most instances the medial orbital of the dura often result around the walls are included in the resection to perforations of the olfactory nerves provide adequate margins and facilitate through the cribriform plate the control of the ethmoidal arteries • Intracranial tumour extension with • The intracranial exposure allows the dural involvement requires one to leave complete and often en bloc removal of a patch of involved dura attached to the the anterior cranial base with visuali- specimen and even to resect a portion sation and protection of the optic nerves of one or both frontal lobes to secure and the lateral walls of the sphenoid adequate tumour margins sinus including the internal carotid • Gently elevate the anterior fossa dura arteries in a posterior direction to identify the • At this point of the resection, the planum sphenoidale, the anterior cli- superior margins and exposure have noid processes and optic canals (Figure been achieved, and the tumour has 2c) been safely separated and removed • Drilling with a high-speed drill through from the cranial contents the planum sphenoidale exposes the sphenoid sinus allowing its inspection • A high-speed drill or reciprocating saw Sinonasal Approaches is then used to cut around the cribriform plate and through the floor of the A separate inferior (sinonasal) exposure is anterior cranial fossa often required to obtain adequate inferior • The anterior skull base can be fully and lateral margins, as the tumour typically mobilised with a high-speed drill limits visibility into the nasal cavity via a utilising this approach, from the frontal subfrontal approach. This can be performed sinus to the planum (Figure 11) through a variety of approaches, including lateral rhinotomy with medial maxillec-

8 tomy, midface degloving, or endoscopic and the sac is divided and marsupia- endonasal assistance. lised • The anterior and posterior ethmoid a. Lateral Rhinotomy Approach (See vessels are identified at the frontoeth- Medial maxillectomy chapter) moidal suture and controlled with bipolar electrocautery • A vertical skin incision is made along • Lateral elevation of the cheek flap the lateral nose, from the medial exposes the medial maxilla and infra- canthus to the nasal ala, then joining a orbital nerve, which is preserved curvilinear incision along the alar- • The anterior wall of the maxillary facial groove on the tumour side antrum is opened (Figure 12). The incision is carried • Osteotomies are performed through the through the muscular layer to the nasal process of the maxilla, through pyriform aperture. To prevent subse- the lacrimal fossa and the anterior quent alar retraction the incision around aspect of the lamina papyracea, con- the ala is carried vertically toward the necting to the previous osteotomies maxilla and not under the ala; further- • The medial wall of the maxilla is cut more, the medial aspect of the nasal ala with an osteotome or drill along the is not transected nasal floor • The remaining posterior aspect of the lateral nasal wall is cut in a posterior and cephalad direction using curved Mayo scissors from the nasal floor to the sphenoid rostrum • A septal incision is created along nasal floor and carried cephalad with curved Mayo scissors. A strut of nasal septum is preserved, if able, to support the external nasal framework • Transection of the attachment of the nasal septum to the rostrum of the sphenoid sinus allows the mobilization of the specimen • The defect is inspected, and additional Figure 12: Lateral rhinotomy incision bone or soft tissue margins are obtained under direct visualization. Exposure of • The nasal mucosa is incised along the the contralateral sinonasal cavity is piriform aperture through the lateral somewhat limited with this approach nasal vestibule avoiding the tip of the inferior turbinate b. Midface Degloving Approach • Detachment of the medial canthal ligament facilitates elevation of the To avoid facial incisions, the sinonasal periosteum of the medial wall of the tumour component may be resected and orbit, keeping the orbital contents mobilised via a sublabial approach. It within its periosteal sac provides wide exposure to the midface, • The nasolacrimal duct is transected at allowing for mobilisation of the periorbita, its junction with the nasolacrimal sac dividing the ascending process of the maxilla, septal incisions and medial maxil-

9 lectomy incisions to obtain clear tumour • Dissection of the paranasal sinuses fol- margins lows a technique similar to that used for the treatment of inflammatory disease • Make a wide sublabial incision (1st • Whenever necessary, debulk the molar to 1st molar) onto the bone of the tumour to provide an adequate working maxilla space and visualisation, identifying and • Dissect in a subperiosteal plane along maintaining the origin of the tumour the anterior maxilla up to the orbital rim and assessing its boundaries. The extent and infraorbital nerve of the tumour determines the need for • Expose the nasal cavity by incising the unilateral versus bilateral exposure mucoperiosteum around the piriform • Following an uncinectomy, create a aperture and elevating the now mobile wide medial maxillary antrostomy nose (lower lateral cartilage and nasal giving access to the posterior maxillary skin) and soft tissue envelope off the wall and providing orientation with remaining nasal framework respect to the medial and inferior • Incise the nasal mucosa along the floor orbital walls of the pyriform aperture • Complete anterior and posterior eth- • Gently elevate the medial crura of the moidectomies, middle turbinectomies, lower lateral cartilages off the septum and exposure of the nasofrontal with a full transfixion incision and con- recess t o define and expose the para- nected to an intercartilaginous incision median anterior skull base, including along the pyriform aperture the roof of the ethmoid sinuses, the • The soft tissue envelope is then eleva- vertical and horizontal lamellae of the ted with the lip and lower lateral cribriform plate, and the anterior and cartilages posterior ethmoidal artery canals • Wide bilateral exposure of the sphe- c. Expanded Endonasal Approach noid sinuses with complete removal of the rostrum provides unencumbered Endoscopic endonasal approaches (EEA), access to the planum sphenoidale and can be used to supplement traditional sub- defines the posterior tumour limit frontal approaches to avoid facial incisions • Similarly, a Draf III frontal sinuso- (combined open-endoscopic resections) or tomy (modified endoscopic Lothrop as an oncologically equivalent approach for procedure) provides access to the crib- the resection of the anterior cranial base. riform plate and posterior table of the EEA evolved following advances in rod- frontal sinus and defines the anterior lens endoscopy, improved digital camera limit and video monitor definition, customisation • At this point the reconstructive plan of surgical instruments, and refinements in should be considered. If a nasoseptal electrophysiological monitoring, jointly flap is available (it is often not due to with image-guided surgery equipment. oncologic involvement), it should be harvested at this point. Using mono- • Examine the nasal cavities with a zero- polar cautery, the superior incision is degree rigid endoscope placed along the superior septum • Depending on the bulk and origin of the beginning at the sphenoid ostium, to be tumour, dissection may commence carried anterior and cephalad towards either with tumour debulking or with the olfactory groove. Anterior to the traditional endoscopic sinus surgery anterior head of the middle turbinate the incision is carried along the

10 superior-most septum to reach the • These osteotomies are then connected mucocutaneous junction. The inferior bilaterally with osteotomies along the incision is typically performed across lateral aspect of the roof of the ethmoid the inferior choana and along the infe- sinuses (junction of the ethmoid sinus rior margin of the septum, at the roof and orbital roof junction with the nasal floor, and • These rectangular osteotomies incur- carried anteriorly to meet the anterior porate the cribriform plates, septum, incision. The flap is elevated in a sub- and portions of the planum sphenoidale mucoperichondrial plane, left pedicled and roof of the ethmoid sinuses and to the posterior septal branch of the surround the tumour sphenopalatine artery. The flap is then • Any remaining bone is thinned and tucked in the nasopharynx to complete elevated to expose the dura of the the resection ventral skull base and the crista galli, • A wide posterior septectomy is then which is resected performed, ensuring adequate preserva- • Olfactory filaments are cauterised tion of the anterior septal strut to main- and the bone of the anterior skull base tain nasal support. The contralateral is resected septal mucosa can be utilised as a • Dura can be opened or resected along reverse septal flap provided that there is the with olfactory bulbs (Figures no tumour invasion 14,15) as needed for tumour clearance • The sphenoidotomies are connected • Margins are sampled circumferen- and widened tially to ensure an adequate oncologic • This completes a wide exposure of the resection median anterior skull base, from orbit to orbit and from the sella turcica to the frontal sinus (Figure 13) • The lamina papyracea may be eggshell fractured and carefully removed as a lateral margin, if necessary, or to better identify and control the ethmoidal arteries. The integrity of the underlying periorbita should be preserved unless tumour invasion mandates its removal • Bone over the anterior and posterior ethmoidal canals may be removed by gentle curettage or drilling, exposing the ethmoidal arteries that then may be cauterised (bipolar electrocautery is Figure 13: Expanded endonasal ap- strongly recommended) proach for exposure of the anterior skull • Using a high-speed drill witha3 mm base. After total extirpation of the sinu- extended-tip coarse diamond or hybrid ses, nasoseptal flap harvest (if indicated) burr, a horizontal osteotomy is made and a posterior septectomy, the sphenoid through the planum sphenoidale several ostia are enlarged into a common sphe- millimeters anterior to the optic canals noid cavity, widely exposing the skull • Using the Draf III frontal sinusotomy, base from orbit to orbit. A Draf III frontal another horizontal osteotomy is made sinusotomy is helpful in joining and posterior to the frontal outflow to ex- defining the frontal exposure pose the crista galli

11 Reconstruction

The primary goal of reconstruction is to achieve a watertight dural closure to mini- mise the risk of a postoperative CSF leak and meningitis. • Small dural lacerations are closed primarily • Large defects require the use of a free tissue graft. Cadaveric dura, pericarp- dium, acellular dermis, and fascia lata can be used • Reconstruction of the skull base infra- Figure 14: The cribriform plate is drilled structure is best achieved with a and the anterior skull base can be resec- vascularised flap to ensure a durable ted to include the underlying dura watertight seal. This is typically completed with a pericranial or galeo- pericranial flap (open approach) or nasoseptal flap (endoscopic approach) (Figure 16)

Figure 15: As the cribriform and olfactory bulbs are being gently mobilised from the skull base in an anterior to posterior direction, the olfactory nerves Figure 16: After the resection is complete, can be identified, transected and sampled an inlay reconstruction is typically per- for a margin as indicated formed of the skull base (fat, fascia lata, or a collagen matrix). The nasoseptal flap is • Alternatively, the endoscopic drill is then rotated into place, widely covering the used to connect the endoscopic resec- defect with bony contact 360 degrees tion to the previously performed os- around the skull base defect teotomies done via the subfrontal approach, when being used in combina- Pericranial flap tion with open approaches. This allows complete mobilisation and en The pericranial flap is pedicled on the bloc removal of the tumour supraorbital neurovascular bundles (and sometimes supratrochlear neurovascular bundles and anterior branches of the superficial temporal artery) (Figures 4, 5,

12 6). A unilateral blood supply is sufficient • The nasoseptal flap is then rotated for the survival of the flap. extracranially into position to cover the defect (Figure 15). The flap should • The pericranium is elevated off the have adequate overlap circumferential- previously elevated scalp flap or is ly to the remaining bony surface elevated independently if a subgaleal • The flap is generally bolstered with scalp flap is performed (Figures 4, 5) sponge-type packing to secure the graft • The flap is elevated in a subgaleal plane tightly against the skull base but remains attached to the scalp flap 1- 2 cm above the orbital rims to prevent Closure injury to the supraorbital pedicles • The flap is then gently tucked in the • The supraorbital and craniotomy bone epidural space and below the orbital bar grafts are replaced into their anatomic and craniotomy bone grafts (Figure 17) position with adaptation miniplates (wires or even sutures may yield an adequate result) • The pericranial flap is typically placed between the supraorbital graft and the nasal bones • The scalp is then rotated back into position and the facial and scalp incisions are closed in standard fashion

Postoperative Care, Identification and Management of Complications

• The patient is typically extubated immediately postoperatively • It is imperative to communicate with Figure 17: The pericranium is tucked into the anaesthesia team, as with an open the epidural plane between the remnant skull base defect, the patient cannot be cribriform/orbital roof and the dura. This supported with positive pressure mask is typically done prior to replacing the ventilation, or significant pneumo- frontal bar or bifrontal bone flaps to create cephalus could result a watertight closure

• The patient is transferred to a moni- Endoscopic reconstruction tored intensive care setting for close neurologic monitoring, and a postoperative CT scan is routinely performed to • This is best completed with a naso- rule out intracranial haemorrhage, brain septal flap, although lateral wall flaps contusion or significant pneumocepha- are a viable alternative lus • Having elevated the flap earlier with • A lumbar spinal drain is not routinely the endoscopic approach, the open skull required but may be considered in base defect is cleared and exposed patients with a tenuous reconstruction. • Fat, fascia lata, Duragen or other free Alternatively, acetazolamide may be grafts can be used as inlay grafts for a administered to decrease the production multilayered reconstruction of CSF, in turn decreasing the pressure

13 and diminishing the potential for a Useful References postoperative CSF leak • The patient is checked daily for a CSF • Patel SG, Singh B, Polluri A, et al: leak by sitting the patient upright and Craniofacial surgery for malignant skull flexing the neck, monitoring for a base tumors: Report of an international steady drip of clear fluid from the nose collaborative study. Cancer 98:1179- (“tilt test”) 1187, 2003 • IV antibiotics are continued for 48 • Bhatki AM, Carrau RL, Snyderman hours and advanced to oral antibiotics CH, Prevedello DM, Gardner PA, with the patient’s diet. Antibiotics are Kassam AB. Endonasal Surgery of the continued until the nasal packing is Ventral Skull Base- Endoscopic Trans- removed, approximately 1 week post- cranial Surgery. Oral Maxillofac Surg operatively Clin North Am. 2010 Feb; 22(1): 157-68 • The patient usually remains in the • Kassam A, Thomas A, Carrau R, Sny- hospital for 3-5 days derman C, Vescan A, Prevedello D, • The patient is typically seen in the Mintz A, Gardner P. Endoscopic recon- clinic 1-2 weeks postoperatively. The struction of the cranial base using a nasal cavity is gently debrided and pedicled nasoseptal flap. Neurosurg, packing removed 2008 Jul;63(1) Suppl:44-52 • Saline irrigations are then initiated to • Blacklock JB, Weber RS, Lee YY, hydrate the raw mucosal surfaces and Goepfert H. Transcranial resection of gently hydrodebride residual packing tumors of the paranasal sinuses and and crusting nasal cavity. J Neurosurg. Jul 1989;71 • Multiple postoperative debridement (1):10-5 visits are typically required while the • Cheesman AD, Lund VJ, Howard DJ. nose is healing Craniofacial resection for tumors of the • The two most common major nasal cavity and paranasal sinuses. complications of anterior skull base Head Neck Surg. Jul-Aug 1986;8(6): resection are CSF leak and tension 429-35 pneumocephalus. Others include brain contusion, oedema, stroke, meningitis, Authors intracranial abscess, and osteomyelitis • Following a viable reconstruction, a Kyle K Van Koevering MD CSF leak may be managed conserva- Assistant Professor tively with lumbar spinal drainage, but Department of Otolaryngology – Head and a low threshold for surgical re- Neck Surgery exploration should be maintained University of Michigan Medical Center • Tension pneumocephalus is treated Ann Arbor, MI, USA with percutaneous aspiration through a [email protected] gap between the cranium and the craniotomy bone graft. Recurrent tension Daniel M Prevedello MD pneumocephalus may require diversion Professor, Department of Neurological of the nasal airway including endo- Surgery tracheal intubation, a nasal airway Co-Director of Comprehensive Skull Base (nasal trumpet), or a tracheotomy Surgery Program The Ohio State University Medical Center Columbus, Ohio, USA [email protected]

14 Ricardo L Carrau MD, F.A.C.S., MBA Professor and Lynne Shepard Jones Chair in Head and Neck Oncology Department of Otolaryngology-Head & Neck Surgery Co-Director of the Comprehensive Skull Base Surgery Program The Ohio State University Medical Center Columbus, Ohio, USA [email protected] [email protected]

Editor

Johan Fagan MBChB, FCS (ORL), MMed Professor and Chairman Division of Otolaryngology University of Cape Town Cape Town, South Africa [email protected]

Acknowledgment: Subcranial photographs from Erin L. McKean, MD.

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The Open Access Atlas of Otolaryngology, Head & Neck Operative Surgery by Johan Fagan (Editor) [email protected] is licensed under a Creative Commons Attribution - Non-Commercial 3.0 Unported License