Pathology and Management Planning

Many disorders can affect the cranial base. Disorders in which surgery has played a significant therapeutic role include basicranial trauma; craniofacial anomalies; congenital syndromes (e.g., hypertelorism, Crouzon’s syndrome); spontaneous cerebrospinal fluid fistulas; vascular problems (e.g., petrous carotid artery aneurysms); infectious diseases (e.g., petrositis, malignant external otitis); and neoplasms. Perhaps the widest acceptance and application of cranial base surgery has been in the management of neoplasms, in which the effectiveness of other modalities is limited.

Benign tumors and related lesions affecting the skull base have been reviewed by several authors and are summarized in Box 174-1.^9–11 In general, benign cranial base neoplasms are managed surgically. The surgical technique often involves “piecemeal” removal, with careful progression from one surgical landmark to the next, to permit the maximal preservation of functionally important structures. For larger tumors or those for which removal carries a high risk of damage to neighboring structures, incomplete resection with postoperative irradiation may be indicated.¹²

Malignant skull base lesions are listed in Box 174-2.¹⁰ With some notable exceptions (i.e., leukemia, lymphoma, myeloma, metastases), malignant neoplasms are managed surgically, although in most cases surgery will not be used as the sole modality. Adjuvant management with radiation (by external beam, implantation, or brachytherapy) or chemotherapy is usually included in the therapeutic plan. Single-modality radiation therapy, including sterotactic radiotherapy, has been recommended by some investigators for certain smaller lesions.¹³ Malignant lesions are surgically removed en bloc, with margins of uninvolved tissue after broad circumferential exposure whenever possible.¹⁴

When surgery is considered for tumors and tumor-like disorders of the cranial base, the first question that should be answered involves the biologic behavior of the lesion. As mentioned, an accurate clinical diagnosis often can be made on the basis of information obtained from the history, physical examination, and imaging studies. Whenever possible, this should be supplemented by a histologic diagnosis before definitive management is carried out.

When tumor is present within the nose, paranasal sinuses, middle ear, mastoid, oral cavity, pharynx, or neck, direct biopsy can be performed using standard techniques. When direct biopsy is not feasible, CT-guided needle biopsy may be done in selected cases (e.g., tumors of the infratemporal fossa). Occasionally a tumor may be inaccessible by either of these routes, or biopsy without adequate skull base exposure may be judged to be unsafe because of concerns about injury to nearby critical structures or because of vascularity of the lesion. In these situations, the surgeon should proceed with an operative approach to the skull base that is designed to provide access to the tumor for safe biopsy before any irreversible ablative steps are taken. Then, if the frozen-section biopsy result contraindicates resection or is questionable, an alternative management plan may be made. On the basis of histologic criteria, extirpative surgery is usually not performed when one of the following conditions is present: (1) a malignant lesion is metastatic from a distant source; or (2) a malignancy is of a type that responds well to other management modalities (e.g., lymphoma).

Overview of Approaches

Surgical treatment of lesions involving the anterior skull base, nasal cavity, and paranasal sinuses has evolved into a single category of craniofacial approaches. A myriad of surgical approaches have been developed for exposure of the anterior and middle cranial base regions; these range from purely intracranial to purely extracranial. However, most approaches for dealing with lesions of the skull base use combined intracranial and extracranial methods. For anterior cranial base lesions, the most commonly used approaches combine frontal craniotomy with some form of transfacial (transnasal, transmaxillary, or transorbital) exposure. Most commonly, a team of neurosurgeons and otolaryngologists performs this procedure resulting in a bifrontal craniotomy from above and a transfacial approach from below. The transfacial approach often involves midfacial degloving, and facial disassembly, requiring facial incisions and facial osteotomies. Lateral rhinotomy, removal of the frontonasal unit, Le Fort I and II osteotomies, and splitting of the maxilla have been described as means of accessing lesions of the anterior cranial base. Janecka and coworkers¹⁷ described the facial translocation approach, which also involves an extensive facial incision and facial disassembly for access to tumors in the anterior cranial base, cavernous sinus, clivus, and infratemporal fossa.

Since the 1990s, endoscopic sinus surgery has virtually replaced the conventional open techniques used by otolaryngologists in treating sinonasal disorders and is discussed in detail in Chapter 175. Use of the endoscope as a supplement to the surgical approaches can alleviate the need for some facial incisions by allowing the surgeon to observe areas hidden from the field of view of the microscope. For those tumors that invade the anterior cranial base, the endoscope may be utilized as an adjunct to the standard bifrontal craniotomy by allowing visualization of paranasal extension into the sphenoid, ethmoid, frontal, and maxillary sinuses. From nasal or maxillary portals, the endoscope allows visualization of all of the paranasal sinuses. As the technology of endoscope optics and video systems improves, the role of endoscopic cranial base surgery will augment and supplement current microsurgical techniques. Intraorbital lesions may be approached by frontal craniotomy or subcranial approaches, often combined with transfacial approaches.¹⁸

For middle cranial base lesions, access is most often provided by combining temporal or frontotemporal craniotomy with infratemporal fossa dissection, transfacial exposure, or transtemporal techniques. In addition, endoscope-assisted and image-guided navigational approaches are increasingly being applied (see Chapter 177). In anterior and middle cranial base approaches, craniofacial disassembly techniques have been widely used.

Implicit in the term craniofacial disassembly is the concept of the systematic, stepwise dissection of cranial and facial soft tissues on the basis of the knowledge of regional vascular territories and functional anatomy, followed by osteotomies and dismantling of the craniofacial skeleton. Some of these techniques, which were developed originally by plastic and reconstructive surgeons for the correction of congenital craniofacial deformities, are of major importance in cranial base surgery, because they allow wide exposure of the skull base through temporary displacement of the viscerocranium.^19,20 The enhanced exposure of the skull base from below the neuraxis significantly reduces the need for brain retraction and therefore helps minimize postoperative neurologic dysfunction. It also allows the surgeon greater oncologic precision during the extirpative phase, with preservation of the functional and aesthetic units of the face for reconstruction.⁵⁸

Planning the Operative Approach

Whether the surgery is being performed for a benign tumor, a malignancy, or other indications (e.g., inflammatory or vascular lesions, CSF fistula), the approach should be planned and executed to accomplish the four specific goals that are applicable to all cranial base operations, summarized in Box 174-3.

GOAL 1

The approach should provide adequate exposure to allow extirpation of the disease process. To a large extent, the degree of needed exposure is based on information obtained from the physical examination and imaging studies.

GOAL 2

The approach should be designed to protect critical structures near the lesion. Traditionally, the safest way to protect critical structures has been to achieve surgical access beyond the boundaries of the lesion itself to allow for direct visualization and control over the structures of interest. For example, surgical exposure around a tumor would be broadened to identify, dissect, and perhaps displace nearby cranial nerves or the carotid artery. Although obtaining this additional exposure may increase the operative time, it can be a major factor in the reduction of postoperative morbidity.

More recently, the introduction and increased application of two major technical advances have given the surgeon additional options for the protection of critical structures, often without the need for increased surgical exposure: image-guided computer-assisted surgery and endoscopic surgery.

Image-guided (stereotactic) computer-assisted surgery has become a very useful alternative—or adjunct—to wide surgical exposure in selected cases.^21–26 Such “navigational surgery” employs one of a variety of referencing systems that can assimilate preoperative imaging studies into a computer-based algorithm that allows image reformatting in three dimensions (The preoperative reference images may be CT- or magnetic resonance imaging [MRI]-based, or they may be a “fusion study” that takes advantage of both types of studies). The reformatted images then serve as the basis for intraoperative navigation, which involves the use of an interactive probe that transmits spatial-orientation information back to the computer via transmitters; these can be either electromagnetic or optical. The computer screen then displays the appropriate preoperative images with the location of the probe superimposed, thus “targeting” the area of interest (Figure 174-11). With navigational systems, structures that are anatomically fixed (i.e., orbital walls, carotid canal, optic canal) can be precisely located, and the risk of injury can be minimized.

Figure 174-11. Navigational images as seen on intraoperative computer display. The patient’s computed tomography images are displayed in the coronal (top left), axial (bottom left), and sagittal (top right) planes, and a three-dimensional cutaway view (bottom right) also is shown. On each image, the intersection of the crosshairs indicates the position of the navigational probe. As the probe is moved within the operative field, the images change to reflect the probe’s precise location. In this case, a lesion that was both osteoblastic and osteolytic and that involved the occipital condyle was approached endoscopically through the nasal cavity without the need for an extensive disassembly approach. The lesion turned out to be a metastasis from a previous renal cell carcinoma.

Reported uses of image-guided surgery include primary and revision endoscopic sinus surgery, osteoplastic frontal sinusotomy, transsphenoidal hypophysectomy, endoscopic cerebrospinal fluid leak and encephalocele or meningocele repair, endoscopic skull base tumor resection, orbital surgery, and endoscopic pterygomaxillary fossa biopsy.^27,28

The American Academy of Otolaryngology–Head and Neck Surgery endorses use of computer-aided surgery for the following specific procedures or conditions²⁹:

• Revision sinus surgery

• Distorted sinus anatomy of development, postoperative, or traumatic origin

• Extensive sinonasal polyposis

• Pathology involving the frontal, posterior ethmoid, and sphenoid sinuses

• Disease abutting the skull base, orbit, optic nerve, or carotid artery

• CSF rhinorrhea or conditions that feature a skull base defect

• Benign and malignant sinonasal neoplasms

Intraoperative MRI or CT also has been proposed as a useful adjunct in skull base surgery. Proponents advocate the improved ability to detect residual tumor and evaluate for intraoperative complications, however, limitations of time and cost have prevented its widespread use outside of certain academic centers.³⁰

Although large, multi-institutional prospective studies are yet to be accomplished, smaller studies and anecdotal reports demonstrate the efficacy of endoscope-assisted approaches for the treatment of selected skull base problems, most notably sinonasal neoplasms, pituitary tumors, and CSF leaks.^31–37

Stamm³⁸ classifies endoscopic skull base approaches as follows:

1. Transnasal direct

2. Transethmoidal

3. Transseptal

4. Transplanum

5. Transsphenoidal-transpterygoid

6. Transsphenoidal-transclival

7. Transnasal-transpharyngeal (cranial-cervical junction)

8. Combined

The location and suspected pathology dictate the selection of approach.

Endoscopy-based approaches to the nasal cavity, olfactory groove, nasopharynx, ethmoid roof (anterior skull base), orbit and orbital apex, sphenoid sinus and sellar and parasellar areas, clivus, cavernous sinus, optic chiasm, pterygopalatine and infratemporal fossae, parapharyngeal space, craniocervical junction, petrous apex, and jugular foramen all have been described. In short, access to the central skull base from the frontal sinus to C2 and from the sella to the jugular foramen is now possible using the expanded endonasal approach.^39–43

The endoscopic approach to the orbital apex and optic canal for orbital decompression in fibrous dysplasia, Graves’ orbitopathy, compressive or traumatic optic neuropathy has been described. Of note, decompression is indicated only in patients with fibrous dysplasia with continuous deterioration of vision or undergoing removal of neighboring bone, but not as a prophylactic procedure.^44,45 This approach also is used in the management of clival lesions, anterior skull base tumors, and vascular malformations of the skull base.^46,47

Kassam and associates described an approach to identify the petrous portion of the carotid artery following identification and retrograde dissection of the vidian artery. They found this to be a consistent landmark radiographically and intraoperatively.⁴⁸

Endoscopic approaches to pituitary surgery offer benefits of improved cosmesis, decreased recovery time, and fewer complications. Three approaches exist: transnasal-transethmoid, transnasal-transseptal, and direct transnasal. The direct transnasal approach has been touted because of the advantages of avoiding the ethmoid complex, decreased operative time, and improved visualization.² Although endoscopic skull base surgery has been more extensively described for the anterior cranial base, endoscopic-assisted approaches to the middle cranial base also have been described.⁴⁹

The protection of critical structures at the cranial base also is enhanced by the appropriate use of electrophysiologic monitoring, including intraoperative somatosensory evoked potentials, auditory brainstem evoked response, and EMG.¹⁴ The injection of low-dose intrathecal fluorescein has been shown to be a useful adjunct intraoperatively to decrease the CSF leak rate and, when appropriate medication is provided, has been proven safe and without significant adverse effects.⁵⁰

GOAL 3

The approach should be designed so that, at the completion of the extirpative phase, critical barriers between the neurocranium and viscerocranium can be reliably restored. These barriers, particularly the dura and subjacent soft tissues, normally serve to effectively insulate the intracranial contents and the ICA from exposure to the aerodigestive tract below, including the nasal cavity, sinuses, eustachian tube, and pneumatic spaces within the temporal bone. After they have been disturbed, the barriers should be restored to reduce the potential for such consequences as CSF fistula, meningitis, and septic carotid artery rupture. Also, an approach should respect the vascular territories of local tissues (i.e., the temporalis muscle, galea, and pericranium), which can then be used for the reconstruction.

Such vascularized local flaps are preferable to free flaps or nonvascularized grafts when available, however others have displayed excellent closure rates with materials ranging from acellular dermis to free microvascular transfers.^51,52 In general, smaller defects (less than 2 cm) are less likely to require vascularized tissue to achieve closure.^53,54

Robotic endoscopic skull base surgery and transoral robotic surgery have been advocated by some researchers for the advantages of improved visualization, access, precise technique, and improved watertight closure following endoscopic skull base surgery. Although promising, more clinical investigation is needed before widespread acceptance of these techniques.^55,56

GOAL 4

The choice of operative approach should reflect consideration for functional and aesthetic reconstruction, and it should include the placement of incisions within natural skin lines that respect aesthetic units of the face. The soft tissue closure should follow plastic surgery principles. Excellent skull base exposure usually can be achieved by elective osteotomies and the temporary removal of craniofacial bone segments, which are subsequently replaced, thereby preserving facial contour.^{17,51,57–59} Even in cases in which aesthetically important segments should be removed for oncologic reasons, acceptable cosmesis can usually be accomplished through the judicious use of bone grafts and soft tissue flaps or through surgical closures designed to support alloplastic or prosthetic materials.

Technical Note: The Bicoronal Incision

The bicoronal incision should be in the true coronal plane at the level of the top of the helix of the ear or slightly anterior to it (Fig. 174-12). A short, forward-directed, preauricular extension can be made on both sides to enhance scalp flap rotation. This coronal placement of the incision preserves the anterior branches of the superficial temporal artery, enhancing viability of the scalp flap. In addition, it substantially increases the length of vascularized galea and pericranium available for reconstruction as compared with incisions along the anterior hairline, the midforehead crease, or the brow. Additional length can be gained by back-elevating the scalp flap before division and elevation of the pericranial flap.

Figure 174-12. Bicoronal incision shown from the patient’s left and demonstrating proper placement to allow for preservation of anterior branches of the superficial temporal artery. This incision design permits the use of a long pericranial or galeal flap (based on supraorbital vessels), which is important for the reconstruction of anterior cranial base defects.

The central portion of the anterior scalp flap (i.e., the portion between the two superior temporal lines) is elevated in the subgaleal plane if a pericranial flap may be used and in the subperiosteal (subpericranial) plane if not. Lateral to the two superior temporal lines, it is elevated in the plane just above the deep temporal fascia. Therefore, at the temporal lines, the pericranium should be sharply incised to separate it from the origin of the deep temporal fascia (see Fig. 174-15). The pericranium is divided far enough posteriorly to provide sufficient length to the flap; then the dissection is carried forward in the subperiosteal plane as described earlier.

This deep temporal fascia begins to split into superficial and deep layers, beginning at approximately the level of the superior orbital rim.⁶² These fascial layers diverge to envelop the lateral and medial surfaces of the zygomatic arch inferiorly; between the layers is the temporal fat pad. The frontal (temporal) branches of the facial nerve course just superficial to the zygoma along the superficial temporal fascia (temporoparietal fascia) and are prone to injury if the dissection is done at that level (Fig. 174-13A). Often these injuries can be avoided by maintaining the plane of dissection at the level of the deep layer of the deep temporal fascia (i.e., at the surface of the temporalis muscle itself). This deep plane of exposure essentially elevates the fat pad along with the superficial fascia and the superficial layer of the deep temporal fascia, thereby protecting the facial nerve branches (see Fig. 174-13B).^63,64 After the dissection reaches the level of the zygomatic arch, the arch is palpated, and its superior surface is directly exposed by sharply incising the fat pad and periosteum.

Figure 174-13. Relationship of the frontal branch of the facial nerve to layers of the temporal fascia. A, Anatomic dissection showing superficial temporal fascia (temporoparietal fascia), through which the nerve courses; attempts at surgery to elevate this relatively thin fascial layer alone may injure the nerve. B, Surgical dissection showing a deeper plane of fascial elevation that is less likely to cause injury to the frontal branch of the facial nerve.

(From Stuzin JM, Wagstrom L, Kawamoto HK, Wolfe SA. Anatomy of the frontal branch of the facial nerve: the significance of the temporal fat pad. Plast Reconstr Surg. 1989;83:265-271.)

Further medially, flap elevation proceeds down the frontal area toward the supraorbital rims. Care should be taken to preserve the supraorbital supply of the galea and pericranium. This is best performed with elevation of the supraorbital rim periosteum that begins laterally and proceeds medially. A fine elevator is used first to palpate the supraorbital foramen (or notch) and then to expose its margins. If the pedicle is completely surrounded by bone, a 3-mm osteotome is used to fracture the inferior margin of the foramen, thereby liberating the pedicle and allowing it to be elevated intact, along with the remaining pericranium and underlying periorbita (Fig. 174-14). If the entire scalp flap is difficult to rotate inferiorly, the preauricular parts of the incision can be extended to as low as the tragus (without danger to the facial nerve trunk) or anteriorly (as far as the temporal hairline) to further enhance flap rotation.

Figure 174-14. Technique for preserving the supraorbital neurovascular pedicle. A, After the foramen has been identified, a 3-mm osteotome is inserted along its lower border. B, A small segment of bone along the inferior rim of the foramen is fractured to liberate the nerve and vessels, which are reflected downward, along with soft tissues of the bicoronal flap.

Anterior Craniofacial Resection

Anterior craniofacial resection (Fig. 174-15) combines bifrontal craniotomy with transfacial exposure of the nasal cavity, ethmoid, maxillary, and orbital areas, usually by modifications of lateral rhinotomy, midfacial degloving, or other transfacial approaches.^65–67 Anterior craniofacial resection most often is used for removal of neoplasms that originate in the sinonasal tract and invade the anterior cranial fossa floor, such as squamous cell carcinoma, esthesioneuroblastoma, and adenocarcinoma. For cases in which tumor frankly invades the soft tissues of the orbit, the approach is extended to include orbital exenteration.⁶⁸

Figure 174-15. Anterior craniofacial resection. A, Incisions. High bicoronal incision preserves the optimal length of the galea and the pericranium for use as a reconstructive flap. Facial incisions usually include lateral rhinotomy and contralateral Lynch incisions, but these may be modified to suit the clinical situation. B, Elevation of the bicoronal scalp flap. The pericranium has been incised bilaterally at the superior temporal lines to separate it from the deep temporal fascia. Supraorbital vessels have been released from the supraorbital foramina to allow for the exposure of the superior orbital rims (zygomatic arches may be exposed using bicoronal incision by dissecting further laterally, as may be required for extended anterolateral craniofacial resections). C, Bifrontal craniotomy. Dashed lines represent the outline of the planned craniotomy. Temporalis muscles have been partially elevated so that burr holes may be placed below the temporal lines; superior burr holes are placed above the level of the frontal hairline. Such placement helps minimize postoperative cosmetic deformity. Paramedian positioning of superior burr holes aids in protection of superior sagittal (venous) sinus while the bone flap is being cut. D, Intracranial exposure. The frontal lobes have been retracted, and the dura has been incised, thereby leaving olfactory nerves and the margin of the dura to be resected en bloc, along with the cribriform plate and the ethmoid labyrinth (dotted line). The amount of dura and anterior cranial fossa floor resected will depend on the extent of tumor. To enhance exposure and direct visualization, the supraorbital bar (dashed lines) may be included in the resected specimen; after resection margins have been verified, this portion of bone is detached from the tumor-bearing part of the specimen and replaced. E, Osteotomies as seen from transfacial exposure. Dashed lines illustrate bone cuts used for en bloc ethmoidectomy, which result in the obtaining of a specimen (left). Dotted lines indicate additional osteotomies to be used when total maxillectomy (with or without orbital exenteration) also is performed, thereby resulting in the obtaining of a specimen (right). In both cases, resection encompasses part of the anterior cranial fossa floor. The extent of anterior fossa floor resection varies and should be modified as required by the extent of tumor. F, Operative defect and preparation for closure. Large communication between the anterior cranial fossa and nasal cavity is closed by an inset of vascularized pericranial flap (shown here partially elevated from the galea). A dural defect created by resection of the olfactory nerves and surrounding dura has been closed with free graft of the pericranium taken from the posterior scalp (dotted lines). Frontal sinuses have been stripped of mucosa and filled with autogenous fat after obliterating the frontonasal ducts. G, Cranial base defect repaired. A pericranial flap has been turned intracranially to line the anterior cranial fossa floor. Release of the frontal lobe retraction and clamping of the spinal drain have allowed for reexpansion of the brain and obliteration of the epidural dead space. The frontal bone flap is replaced and secured, with care taken to avoid compression of the pericranial flap. H, Cutaway view of final closure, showing the position of the pericranial flap relative to the brain and the cranial base.

(A to G, Adapted from Schramm VL. Craniofacial resection. In: Sasaki CT, McCabe BF, Kirchner JA, eds. Surgery of the Skull Base. Philadelphia: JB Lippincott; 1984.)

The operation begins with transfacial exposure, which is followed by bifrontal craniotomy performed by the neurosurgeon. If the patient has a large frontal sinus, an osteoplastic flap may be elevated to avoid burr holes in the forehead area, which could later become aesthetically unsatisfactory. In such cases, the thin posterior table of the frontal sinus is opened with a diamond burr to expose the dura and then removed. If the frontal sinus is small, a frontal bone flap is developed using a guarded craniotome introduced through burr holes placed above the hairline or in the temporal areas. Near the midline, care is taken to separate the dural fold containing the sagittal sinus away from the bone to protect it before the craniotome is allowed to cross the sagittal plane. The lower horizontal bone cut should be kept low (within 1 cm of the superior orbital rims) to lessen the need for subsequent brain retraction. Withdrawing 25 to 50 mL of CSF from the lumbar subarachnoid catheter, lowering PCO₂ through controlled hyperventilation, and occasionally administering mannitol or corticosteroids will further reduce the need for mechanical frontal lobe retraction.

Next, the frontal lobes are elevated from the anterior cranial fossa floor by incising the dura and severing the olfactory nerves at the cribriform plate. This always results in some leakage of CSF, which is controlled by direct dural suture or a dural patch (from temporal fascia, fascia lata, or pericranium). The dural closure should be as watertight as possible. Dura is further elevated to expose the orbital roofs and planum sphenoidale and finally the base of the anterior clinoid processes.

If disease extirpation mandates the removal of the planum, the intracranial portions of the optic nerves should be exposed through the unroofing of the optic canal to protect them from injury at the time of sphenoid osteotomy.¹⁴ If the disease is confined to the cribriform area, however, the planum may be entered with a cutting burr or osteotome⁶⁶ to establish the posterior bony margin without optic nerve decompression. This completes the intracranial portion of the exposure for anterior craniofacial resection.

The transfacial exposure often involves modifications of a lateral rhinotomy incision, which may transect the upper lip; this depends on whether a total maxillectomy will be done in conjunction with the resection. The periosteum is elevated from the nasal bone and from the medial and inferior surfaces of the orbit, and the nasolacrimal duct is identified and transected distally. The anterior and posterior ethmoid arteries are identified and cauterized or clipped. In most cases, it is necessary to perform a complete en bloc ethmoidectomy. For this purpose, a contralateral Lynch incision is made to elevate the contralateral periorbita, cauterize the anterior and posterior ethmoid vessels, and make the appropriate osteotomies using a sagittal saw. If preoperative imaging studies or intraoperative observations confirm the presence of tumor within the soft tissues of the orbit, then orbital exenteration may be performed after extending the skin incision laterally to include a portion of the eyelids. Depending on the nature and extent of the tumor, osteotomies also may be made to include part or all of the maxilla.

At this point, a reciprocating saw or cutting drill bit is used to create the osteotomies of the cranial floor. The frontal lobes are retracted or protected from the cutting instrument by inserting an appropriate malleable retractor. The reciprocating saw or cutting drill bit is introduced through the nasal and ethmoid exposures, and, under direct vision, osteotomies are created from the planum sphenoidale, along the ethmoid roof, and forward to the front of the cribriform plate. These osteotomies may or may not include the supraorbital bar of bone, which is a portion of the frontal bone between the supraorbital rims (see Fig. 174-15D). If the tumor extends anteriorly to a significant degree, this supraorbital bar is removed with it as a single specimen, which can be closely inspected. If the supraorbital bar is not actually involved by tumor, it may be detached from the specimen and replaced for reconstruction at the completion of the operation.

After the resection margins have been verified by frozen section and are negative, reconstruction begins. As mentioned, it is critical that the dura be closed in a watertight fashion. This usually involves the placement of a patch of pericranium, temporal fascia, or fascia lata, followed by the placement of a vascularized pericranial flap over the defect in the floor of the anterior cranial fossa. The pericranial flap is developed by sharp dissection from the previously reflected scalp flap (see Fig. 174-15F).⁶⁹ Elevation of this flap of pericranium is continued down to the level of the glabella, with care taken to not injure its vascular pedicles. It is then rotated intracranially and positioned to form a bridge of soft tissue across the orbital roofs and back to the planum sphenoidale. If necessary, the distal end of the pericranial flap may be sutured to the dura over the planum for security; this provides a vascularized tissue barrier between the dura above and the nasal cavity below (see Fig. 174-15G and H). Unless a large amount of anterior cranial fossa bone has been resected and concern for brain herniation exists, it is usually not necessary to place a bone graft across the bony defect. Also, it is not necessary to place a skin graft on the undersurface of the pericranium (facing the nasal cavity), because this tissue mucosalizes readily on its nasal surface. After the pericranial flap is in place, the spinal drain is clamped so that no further intraoperative CSF decompression will take place. This will allow the gradual reexpansion of the brain to make contact with the pericranial flap, thereby obliterating any residual dead space. Because the pericranial flap traverses the frontal sinus, it is necessary to obliterate the frontonasal ducts and to remove all mucosa from within the sinus. A small amount of fat or free muscle may be packed into the ducts to obliterate any dead space inferiorly. The flap covers the frontonasal duct orifices and sinus floor. If the sinus is small, it may be obliterated by packing it with abdominal fat. If the sinus is large, however, removing the posterior table completely and allowing the brain and dura to expand and fill the space (cranialization of the frontal sinus) may be advisable.

In closing the facial incision, the medial canthal ligament is identified and secured to the remaining medial orbital wall. The upper and lower lid canaliculi may be intubated with a canalicular stent to prevent dacryostenosis. Before further closure, several tacking sutures are placed to secure the frontal dura to the margins of the craniotomy site; this will help in the prevention of postoperative epidural fluid and blood collections. The bifrontal craniotomy bone flap is then replaced and secured according to the surgeon’s preference; this may be done with wires, plates, or sutures.

Basal Subfrontal Approach

The basal subfrontal approach or transbasal approach (Fig. 174-16)^14,70 is in many ways similar to the anterior craniofacial resection operation, except that the transfacial exposure is less extensive. Because the target area in this approach is more posterior (sphenoid and clivus) than that in the anterior craniofacial resection (ethmoids and cribriform), the craniotomy bone flap generally is somewhat larger and the orbital bone cuts are broader. This approach is used for lesions that primarily or secondarily involve the bony cranial base in the regions of the sphenoid body and upper clivus (e.g., meningiomas, fibrous dysplasia, chordomas, chondrosarcomas, ossifying fibromas).⁶³

Figure 174-16. Basal subfrontal approach to the cranial base. A, Outlines of bifrontal craniotomy and bilateral orbital osteotomies. B, Surgeon’s view from above after the removal of cranial and orbital bone segments. Olfactory nerves have been transected to allow sufficient brain retraction for exposure of the anterior fossa floor and decompression of the optic nerves. The sphenoid sinus has been widely opened.

(From Sekhar LN, Janecka IP. Intracranial extension of cranial base tumors and combined resection: the neurosurgical perspective. In: Jackson CG, ed. Surgery of Skull Base Tumors. New York: Churchill Livingstone; 1991.)

This approach also begins with a bicoronal incision. After exposing the orbital rims, periorbita is elevated from beneath the orbital roofs and medial walls in preparation for osteotomy. The anterior and posterior ethmoid arteries are identified bilaterally as landmarks, but they need not be divided because the axial ethmoid osteotomy can be made just above this level. Bifrontal craniotomy is then performed, and dura is elevated from above the orbital roofs and cribriform areas, as described. Using malleable retractors to protect the orbital contents and the brain, the reciprocating saw is used to create osteotomies that result in the temporary removal of both orbital roofs and the supraorbital bar (see Fig. 174-16A).

The coronal osteotomies along the posterior orbital roof should be made as far posteriorly as possible to simplify reconstruction, to conserve orbital contour, and to prevent postoperative pulsatile exophthalmos. These orbital cuts can be made as far back as the posterior ethmoid foramen but should be made only under direct vision from intra- and extracranial perspectives. With the use of these osteotomies, a very broad and basal exposure of the entire anterior cranial base is achieved (see Fig. 174-16B).

Working with the aid of the microscope, the approach is completed by rongeuring or drilling a small amount of bone remaining posteriorly to unroof the optic nerves, the superior orbital fissures, and the sphenoid sinus. Extirpation proceeds as required by the tumor and is followed by reconstruction, which is similar to that done for anterior craniofacial resection.

Raveh and colleagues^71–73 have described and refined an approach, now generally referred to as the subcranial approach, that offers significant advantages over the traditional anterior craniofacial resection and the basal subfrontal approach while combining elements of each. In the subcranial approach, facial incisions are not used; instead, the bicoronal scalp flap is reflected much further inferiorly to more completely expose both orbits and the nasomaxillary bony framework (Fig. 174-17). Extensive access along the entire anterior cranial base is possible as far back as the sella, the orbital apices, and the upper clivus. Advantages of the subcranial approach include minimal brain retraction, wide exposure, and the absence of facial scars.

Figure 174-17. Subcranial approach to the anterior cranial base as described by Raveh.^71–73 A, Sagittal schematic showing the osteotomized frontonasal segment (FS), which is removed to allow access to deeper structures and then later replaced. B, Initial exposure afforded by the removal of the frontonasal bony segment; note the protection of the dura by a malleable retractor. C, Extent of exposure after lesion extirpation, with sphenoid sinus, sella, and orbital apices visible at the depth of the wound. Note that the bicoronal scalp flap has been elevated quite extensively along the lateral and medial orbital rims and nose to permt the frontonasal osteotomies and to compensate for the very low plane of access to the anterior cranial base while avoiding facial incisions (see text).

(From Raveh J, Laedrach K, Ilzuka T, et al. Subcranial extended anterior approach for skull base tumors: surgical procedure and reconstruction. In: Donald PJ, ed. Surgery of the Skull Base. Philadelphia: Lippincott-Raven; 1998. With permission.)

Division into Central and Lateral Compartments

When considering surgical approaches to the middle cranial base, it is helpful to subdivide the region into a single central compartment and paired lateral compartments (Fig. 174-18).⁷⁴ When viewing the skull from the inferior perspective, the central compartment may be defined as that area between two parasagittal lines drawn from the medial pterygoid plate to the occipital condyle on each side. These lines correspond approximately to the pathways of the ICAs through the skull base. Thus, the central compartment consists of the pituitary fossa, the sphenoid rostrum and lower sphenoid sinus, the nasopharynx, the pterygopalatine fossa, and the lower portion of the clivus. (The lower clivus actually is part of the occipital bone and not technically part of the middle cranial base. However, the surgical approaches to this area and also to the craniovertebral junction and upper cervical spine are essentially extensions of the approaches to the central compartment.)

Figure 174-18. Compartments of the middle cranial base. The pathways of the internal carotid arteries as they traverse the middle cranial base region divide the region into one central and two lateral compartments.

(From Krespi YP, Sisson GA. Transmandibular exposure of the skull base. Am J Surg. 1984;148:534-538.)

The lateral compartment includes the entire infratemporal fossa, the parapharyngeal space, and the petrous portion of the temporal bone. This area is important because of the high density of neural and vascular structures within, including, extratemporally, the ICA; the internal jugular vein; the maxillary nerve (V2); the mandibular nerve (V3); the facial nerve (VII); cranial nerves IX, X, XI, and XII; the sympathetic nerves; and major branches of the external carotid artery, and, intratemporally, the cochlea, the vestibule, and cranial nerve VIII.

These distinctions between central and lateral compartments are valid in the sense that limited lesions within their respective boundaries will clearly be more amenable to resection using one type of approach vs another. However, it is not unusual for advanced lesions to extend beyond the line that separates the central from the lateral compartment; therefore, the surgical approach should be tailored to suit each clinical situation.

Approaches to the Central Compartment

The major surgical approaches to the central compartment of the middle cranial base are listed in Table 174-1, along with the anatomic areas for which they provide useful exposure. Except for pituitary surgery, these approaches are used primarily for the management of extradural lesions along the skull base.

Although most central compartment approaches in the literature can give access to the sphenoid sinus, not all are suitable for pituitary or parasellar surgery because of indirect exposure or oblique angle of entry into the sinus, which increases the risk of injury to adjacent neurovascular structures. When lesions are limited to the sphenoid sinus or the pituitary fossa, the transethmoidal sphenoidotomy (Fig. 174-19)^75,76 and the transseptal sphenoidotomy (Fig. 174-20)^77,78 are usually satisfactory, safe, and effective. These approaches are useful for obtaining biopsy specimens of more extensive lesions that involve that region. For larger lesions that involve adjacent areas, however, the exposure is inadequate, because the operative field is deep and narrow, thus requiring the use of the operating microscope in most cases.

Figure 174-19. Transethmoidal-transsphenoidal approach to the cranial base. A, Incision. B, Retraction of orbital contents exposes the ethmoid labyrinth. C, Axial section at the level of the ethmoid and sphenoid sinuses. Progressive removal of ethmoidal air cells allows for entry into the sphenoid sinus and pituitary fossa.

(A and C, From Sasaki CT. Pituitary ablation for carcinoma of the breast: transethmoidal approach to the sella. Otolaryngol Clin North Am. 1981;14:391; B, from Kirchner JA. Transethmoidal approach to the sella. In: Sasaki CT, McCabe BF, Kirchner JA, eds. Surgery of the Skull Base. Philadelphia: JB Lippincott; 1984.)

Figure 174-20. Transseptal-transsphenoidal approach to the cranial base. A, A sublabial incision is used to gain access to the premaxilla and to the nasal septum, which is exposed from the anterior nasal spine to the sphenoid rostrum in the subperichondrial-superiosteal plane. B, Lateral view of exposed area, showing a self-retaining speculum in position at the sphenoid rostrum. C, Sphenoid sinus is opened. A transseptal-transsphenoidal approach may be used for pituitary fossa surgery, for the removal of limited lesions of sphenoid region, or for the biopsy of tumors that involve the area.

(From Sasaki CT. Transseptal-transsphenoidal approach to the sella. In: Sasaki CT, McCabe BF, Kirchner JA, eds. Surgery of the Skull Base. Philadelphia: JB Lippincott; 1984.)

With trends toward less invasive surgical techniques, endoscopic procedures are gaining popularity as primary or adjuvant approaches in cranial base surgery. For tumors of the pituitary gland, endoscopic transnasal-transsphenoidal resection is another valuable option. Proponents of endoscopic pituitary surgery report fewer complications of facial swelling, septal perforations, nasal septal deviation or synechia formation, and numbness of the upper incisors; they also report a shorter hospital stay.^79,80 The surgery is performed with the patient under general anesthesia in the supine position with the head elevated 10 degrees. In most cases, the operation can be performed through one nostril, the choice of which depends on the width of the nasal cavity and the laterality of the pituitary tumor. The nose is decongested topically, and further vasoconstriction is achieved by infiltrating the mucosa over the rostrum of the sphenoid, the middle turbinate, and the posterior septum with lidocaine hydrochloride 1% with epinephrine 1 : 100,000.

Using a rigid zero-degree endoscope, the sphenoid ostium is identified, and its position may be confirmed by the use of C-arm fluoroscopy or image-guided navigation. The middle turbinate can be outfractured or removed to provide increased exposure to the sphenoid rostrum. The sphenoid ostia are identified and fractured inferomedially. Kerrison rongeurs or Hardy punches are used to widen the sphenoidotomy and to remove the sphenoid rostrum. The posterior septum may be rongeured to provide wide visualization, including that of the contralateral sphenoid sinus cavity. The 30-degree endoscope is inserted into both sides of the sphenoid sinus for identification of the optic and carotid protuberance, the opticocarotid recess, the clival indentation, and the anterior wall of the sella⁸¹ (Fig. 174-21). After removal of the intersinus septum, the sella and dura are exposed and entered in the standard fashion. For resection of macroadenomas, insertion of the 30-degree endoscope allows the surgeon to follow intrasellar and extrasellar extension of the tumor and to identify and preserve the arachnoid membrane⁸¹ (Fig. 174-22). The ability to directly visualize tumor and healthy pituitary gland through the endoscope is a major advantage over the operating microscope. This increased visualization may allow for more complete tumor resection, while limiting the potential complications associated with blind curettage of the superior and lateral sella contents.

Figure 174-21. A, Endoscopic view of the sphenoid sinus after the completion of anterior sphenoidotomy and resection of the sphenoidal septum. B, Left: View with a zero-degree endoscope reveals the carotico-optic recesses, carotid protuberances, and clival indentation to the anterior wall of the sella. Right: A 30-degree endoscope provides a better panoramic view of the optic protuberances, the carotico-optic recesses, the carotid protuberances, and the upper portion of the anterior wall of the sella.

(From Jho HD, Carrau RL, Ko Y. Endoscopic pituitary surgery. In: Rengachary SS, Wilkins RH, eds. Neurosurgical Operative Atlas. Vol 5. Park Ridge, Ill: AANS; 1996. Copyright by the American Association of Neurological Surgeons.)

Figure 174-22. A, Sagittal view of the sella. B, 30-Degree endoscopic view of the suprasellar tumor. The suprasellar portion of the tumor is removed with a curved suction cannula beginning around the edge of the diaphragma sella circumferentially and heading toward the center of the tumor gradually. The healthy pituitary gland tissue is preserved, if possible. C, The arachnoid membrane will herniate down gradually when the suprasellar portion of the tumor has been completely removed. The center of the flower-shaped arachnoid membrane will be the pituitary stalk. Any healthy-looking pituitary gland tissue is preserved. When the 30-degree–angled endoscope placed inside the sella is rotated, it will reveal the suprasellar region superiorly, the lateral wall of the sella laterally, and the floor of the sella inferiorly. Residual tumor is removed from all corners by rotating the 30-degree endoscope.

(From Jho HD, Carrau RL, Ko Y. Endoscopic pituitary surgery. In: Rengachary SS, Wilkins RH, eds. Neurosurgical Operative Atlas. Vol 5. Park Ridge, Ill: AANS; 1996. Copyright by the American Association of Neurological Surgeons.)

The lateral rhinotomy (Fig. 174-23)⁸² and transantral (Fig. 174-24)⁸³ procedures afford wider access to the anterior sphenoid and adjacent nasopharynx, the pterygopalatine fossa, the maxilla, and the ethmoid regions. However, they generally are unsatisfactory for extirpation of any but the smallest lesions situated in the sphenoidal-clival area. The midfacial degloving approach (Fig. 174-25)⁸⁴ is more suitable for dealing with larger central compartment lesions, because it allows for improved midline access through the nose and both maxillary sinuses. Medial maxillectomy and resection of the ascending process of the palatine bone are included, if necessary, giving the surgeon good visualization of the nasopharynx and the adjacent skull base. The Le Fort I osteotomy (Fig. 174-26)^85,86 can be an alternative method for reaching these areas from a slightly more inferior angle, or it may be used as an adjunct to midface degloving, offering additional access to the oronasopharynx and clivus by displacing the hard and soft palate inferiorly.

Figure 174-23. Lateral rhinotomy. Top left, Incision and soft tissue exposure followed by maxillary antrostomy. Top right, Osteotomies of the orbit and maxilla. Bottom, Anterior (1) and sagittal (2 and 3) views of posterior osteotomies and soft tissue cuts to remove medial portions of the orbit and maxilla. Such exposure can provide access to the face of the sphenoid, nasopharynx, pterygopalatine fossa, and ethmoid regions.

(From Schramm VL, Myers EN. “How I do it”—head and neck. A targeted problem and its solution. Lateral rhinotomy. Laryngoscope. 1978;88:1042-1045.)

Figure 174-24. Transantral (transantrosphenoidal) approach to the cranial base as used for hypophysectomy. A, Near-sagittal section through the skull base and midface showing surgical route to the sphenoid region via the maxillary antrum. B, Oblique section in plane of the dotted line shown in A demonstrating the relationship among the maxillary sinus, the ethmoid air cells, and the sphenoid sinus. C, Partial medial maxillectomy performed to facilitate access. D, Ethmoidectomy and removal of the anterior wall of the sphenoid sinus. E, Exposure within the sphenoid sinus and pituitary fossa after partial submucous resection of the nasal septum.

(From Hamberger CA, Hammer G, Norlen G, Sjogren B. Transantrosphenoidal hypophysectomy. Arch Otolaryngol. 1961;74:2-8.)

Figure 174-25. Midfacial degloving approach. Intranasal and sublabial incisions are used to elevate skin and soft tissues from the anterior facial skeleton (degloving). Subsequent bone removal and skull base exposure are similar to that shown for lateral rhinotomy, with an added benefit of bilateral access.

(From Casson PR, Bonanno PC, Converse JM. The midface degloving procedure. Plast Reconstr Surg. 1974;53:102-103.)

Figure 174-26. Le Fort I osteotomy approach. A, Lateral view of proposed osteotomy site just above the level of the nasal floor. B and C, Incisions and bone cuts along the anterolateral maxillary surface. D, Separation of the nasal septum with an osteotome. E, Separation of the maxilla from the pterygoid plate with a curved osteotome. F, Down-fracture of the maxilla to allow access to the maxillary sinuses, nasopharynx, and adjacent skull base.

(From Bell WH. Le Fort I osteotomy for correction of maxillary deformities. J Oral Surg. 1975;33:412-426.)

For lesions of the clivus that also involve the upper cervical vertebrae (the craniovertebral junction), mandibulotomy (Fig. 174-27)^74,87,88 will afford a paramedian route to reach the lower areas of extension. The transpalatal (Fig. 174-28)^89,90 and transoral (Fig. 174-29)^91,92 approaches are also used for the management of lesions at the craniovertebral junction and may be used concomitantly with mandibulotomy, if necessary. A significant benefit of such a combined approach is that, with mandibulotomy, it is also possible to expose the parapharyngeal space and therefore to safely dissect along the ICA from the neck up to its entrance into the temporal bone.^74,87,88 This advantage is important when removing tumors that arise primarily in the central compartment but that have extended laterally. Conversely, for lesions that originate in the lateral compartment and extend centrally, the infratemporal fossa approach or one of its modifications can be used.⁹³ These approaches and the facial translocation approach,¹⁷ which is suitable for lesions in both compartments, will be discussed in the following section.

Figure 174-27. Mandibulotomy or transmandibular approach to the cranial base. A, Incision. B, Identification of major vessels and nerves in the neck. C, Paramedian mandibulotomy and intraoral incisions of the gingivolingual and palatal areas. D, After retraction of the mandible, tongue, and suprahyoid structures, major vessels may be dissected up to the skull base. Hard and soft palates are displaced to expose the nasopharynx and clivus, and upper cervical vertebrae are likewise accessible. Such an approach is useful for the management of tumors of the parapharyngeal space and the craniocervical junction.

(From Krespi YP, Cusumano RJ. Transpalatal and transmandibular approaches to the skull base. In: Jackson CG, ed. Surgery of Skull Base Tumors. New York: Churchill Livingstone; 1991:185-193.)

Figure 174-28. Transpalatal approach to the cranial base. A, A U-shaped incision has been made in the palatal mucoperiosteum, which has been elevated with care taken to preserve the greater palatine arteries bilaterally. The posterior portion of the bone of the hard palate has been removed to expose the nasal cavity and the tumor within. B, Sagittal view of the exposure obtained with a transpalatal approach.

(From Jenkins HA, Canalis RF. Transpalatal approach to the skull base. In: Sasaki CT, McCabe BF, Kirchner JA, eds. Surgery of the Skull Base. Philadelphia: JB Lippincott; 1984.)

Figure 174-29. Transoral approach to the cranial base, showing access to the craniocervical junction through the open mouth, with retraction of the soft palate. Light orange represents a tumor of the clivus, with concomitant compression of the brainstem.

(From Crockard HA, Bradford R. Transoral transclival removal of a schwannoma anterior to the craniocervical junction. Case report. J Neurosurg. 1985;62:293.)

An alternative approach for the removal of extensive lesions of the clivus and craniovertebral junction is the extended maxillotomy operation or its modification, the subtotal maxillectomy (Fig. 174-30).⁹⁴ In general, these innovative techniques combine the advantages of many approaches. They afford wide exposure of the central compartment by unilaterally displacing or resecting the hemimaxilla.

Figure 174-30. Extended maxillotomy; subtotal maxillectomy approach to the cranial base. A, Maxillectomy variation. Modified Weber-Fergusson incision followed by osteotomies to remove the hemimaxilla: a, masseter muscle divided; b, coronoidectomy defect; c, lateral pterygoid plate. B, Maxillectomy; defects: a, maxillary roof; b, infratemporal fossa; c, sinonasal defect; d, nasal septum; e, clivus tumor; f, C1 vertebra; g, lateral pharyngeal wall; h, pharyngeal wall incision; i, mucoperiosteum of hard palate; j, soft palate. C, Maxillotomy variation in which the hemimaxilla (j) is preserved but temporarily translocated, based on mucoperiosteum of the hard palate. See key in B for other lettered structures. Exposure is otherwise similar to that shown for maxillectomy. D, Temporalis muscle transferred into operative defect for reconstruction: a, sinonasal defect; b, fat graft; c, temporalis muscle flap; d, mucoperiosteum of hard palate; e, occipital condyle. E, Closure of the oral cavity and lip after subtotal maxillectomy.

(From Cocke EW Jr, Robertson JH, Robertson JT, Crook JP Jr. The extended maxillotomy and subtotal maxillectomy for excision of skull base tumors. Arch Otolaryngol Head Neck Surg. 1992;116:92-104.)

For very extensive clival and craniovertebral junction tumors, when bilateral transmaxillary access is needed, the midfacial split approach (Fig. 174-31) can be used.^51,57 This approach provides access to the entire central skull base in a unified surgical field that can extend vertically from the anterior fossa floor to the level of the second cervical vertebra (and lower, if combined with mandibulotomy) and horizontally from jugular fossa to jugular fossa. This exposure is achieved using craniofacial disassembly to completely displace the midfacial skeleton, including both maxillae, the orbital floors, and the palate. It is especially useful for the management of large tumors that originate in the central compartment and that have also involved the adjacent anterior cranial base, the craniovertebral junction, or the lateral compartment.

Figure 174-31. Midfacial split approach to the cranial base. A, Incisions. Horizontal incision across the nasion allows access to the upper orbits. Midline nasal incision divides skin and separates upper and lower lateral cartilage to expose septum; it is carried inferiorly along one side of the philtrum, splitting the upper lip. Gingivolabial incision (dotted line) facilitates exposure of the maxilla bilaterally. B, Partially developed facial soft tissue flaps, with attached nasal cartilages. C, Soft tissue flaps fully developed and reflected laterally to expose the orbitonasomaxillary skeleton. Proposed osteotomy sites are indicated by dotted lines. D, Midfacial exposure after osteotomies and temporary removal of bone segments, including portions of the medial and inferior orbital walls, the anterior maxilla, and the nasal bones. When necessary, osteotomies also may include the hard palate, which gives additional access to the oropharynx, the nasopharynx, and the clivus. In this example, tumor fills the posterior nasal cavity and nasopharynx and extends into the sphenoid sinus. E, After removal of the tumor, which included the nasal septum, the medial maxillae, and the sphenoid rostrum. F, Final closure. Orbitonasomaxillary bone segments are replaced and secured using microplates, and soft tissues are primarily repaired. Adhesive strips are applied, and silicone nasal stents are used for 1 week postoperatively.

Approaches to the Lateral Compartment

Numerous approaches have been developed and advocated for obtaining surgical access to the lateral compartment of the cranial base. Despite this apparent diversity of techniques and the sometimes confusing terminology by which they are described, considerable overlap exists. Most of the currently used approaches arrive at the cranial base through one (or more) of four main avenues: transtemporal, infratemporal, transfacial, or intracranial. These avenues refer to the primary direction or orientation from which the surgical exposure is ultimately achieved. In most cases, this orientation will influence the usefulness and morbidity of the operation. The cranial base surgeon should be familiar with the advantages and limitations of each of these four routes. For extensive lesions, it often becomes necessary to combine approaches.

Infratemporal Approaches

The infratemporal routes to the lateral compartment include the infratemporal fossa, lateral transparotid, extended rhytidectomy, lateral transtemporal-sphenoid, lateral facial, and subtemporal-infratemporal approaches.

The infratemporal fossa approach of Fisch and colleagues^93,98,99 encompasses three variations for use in specific clinical situations (Fig. 174-32). The type A approach provides exposure between the sigmoid sinus and the condylar fossa, and it is designed to reach to the petrous apex and infralabyrinthine areas. It is most useful for the management of cholesteatomas, meningiomas, and glomus tumors of those regions. The type B approach allows access from the sigmoid sinus to the petrous tip (including exposure of the horizontal ICA and foramen ovale) to reach lesions of the clivus, such as chordomas, meningiomas, and extensive apex cholesteatomas. The type C approach expands this access to include the parasellar region, the cavernous sinus, the foramen rotundum, and the foramen lacerum. Removal of the pterygoid plates in this approach also facilitates access to the nasopharynx. This approach is used in the resection of small nasopharyngeal carcinomas, adenoid cystic carcinomas, and angiofibromas. All three variations of the infratemporal fossa approach involve mastoidectomy, facial nerve dissection (and transposition), and obliteration of the eustachian tube, middle ear, and external auditory canal with resultant permanent conductive hearing deficit. Thus, types A, B, and C infratemporal fossa approaches share some features of the basic transtemporal approaches and yet extend the field of access anteriorly to reach the middle cranial base by virtue of exposing and controlling the petrous ICA (see Chapter 176).

Figure 174-32. Infratemporal approach to the cranial base. A, Areas of the skull base accessible by each of the variations of the infratemporal approach: a, jugular foramen and petrous apex; b, clivus; c, parasellar and parasphenoid compartments. B, Postauricular incision with extensions into the scalp and neck. Sternocleidomastoid and digastric muscles have been divided at the mastoid tip, thereby allowing access to the carotid artery and the internal jugular vein. The facial nerve has been identified extratemporally. The external auditory canal has been closed by turning the musculoperiosteal flap. C, Radical mastoidectomy has exposed the sigmoid sinus (which has been ligated) and the middle fossa dura. The tympanic membrane and ossicles have been removed. The facial nerve has been unroofed and transposed anteriorly. By progressive drilling, the internal carotid artery can be traced distally through its petrous course to reach the cavernous sinus. Similarly, additional bone removal anteriorly will allow access to the parasellar region and the nasopharynx.

(From Fisch U, Pillsbury HC, Sasaki CT. Infratemporal approach to the skull base. In: Sasaki CT, McCabe BF, Kirchner JA, eds. Surgery of the Skull Base. Philadelphia: JB Lippincott; 1984.)

For lesions of the middle cranial base that involve the infratemporal fossa, the upper pterygomaxillary space, the lateral orbit, and the orbital apex, the lateral facial approach¹⁰⁰ (Fig. 174-33) and the lateral transtemporal sphenoid approach¹⁰¹ (Fig. 174-34) have been described. These procedures reach the infratemporal fossa from a slightly more superior direction by displacing the zygomatic arch inferiorly and reflecting the temporalis muscle. The greater wing of the sphenoid is followed to the lateral pterygoid plate, which is used as a surgical landmark, as outlined earlier. These approaches also incorporate partial removal of the greater wing of the sphenoid, which means that they include subtemporal craniectomy and extradural dissection. The advantages of these procedures are that they require no facial nerve dissection (the temporal branch of cranial nerve VII is retracted inferiorly with the skin flap), and they allow some access to the cranial base from both intracranial and extracranial perspectives.

Figure 174-33. Lateral facial approach to the cranial base. A, A temporal and preauricular incision is used to expose the temporalis muscle and the zygomatic arch. The zygoma is sectioned to allow access to the insertion of the temporalis at the coronoid process. The frontal branch of the facial nerve is preserved within the skin flap. B, With the temporalis muscle retracted, the greater wing of the sphenoid is partially removed (subtemporal craniectomy). Retraction of the temporal lobe dura reveals branches of the trigeminal nerve and attachment of the pterygoid plate at the base of the sphenoid bone. C, Division of the maxillary nerve (V2) and resection of the pterygoid plate expose the nasopharynx.

(From Gates GA. The lateral facial approach to the nasopharynx and infratemporal fossa. Otolaryngol Head Neck Surg. 1988;99:321-325.)

Figure 174-34. Lateral transtemporal sphenoid approach to the cranial base. A, Incision. B, Retraction of the temporalis muscle to expose the greater wing of the sphenoid. This muscle should be preserved intact and reflected inferiorly if muscle flap reconstruction of a skull base defect is anticipated. The zygomatic arch has been temporarily removed. C, Subtemporal craniectomy exposes the orbital apex and the floor of the middle cranial fossa.

(From Holliday MJ. Lateral transtemporal-sphenoid approach to the skull base. Ear Nose Throat J. 1986;65:153-162.)

The lateral facial approach is useful as a straightforward approach to a limited area of the middle cranial base that is technically simple to perform (after the anatomy is well understood) and that incurs relatively little morbidity. It is applicable in the management of small- to medium-sized benign tumors with limited intracranial extension, such as that which occurs with some angiofibromas. The similarly oriented lateral transtemporal sphenoid approach can be extended so that it is significantly more complex than the lateral facial approach but affords additional exposure, thus making it useful for the management of lesions in the clivus, the parasellar region, the nasopharynx, the petrous apex, and the infratemporal fossa. As the name implies, the lateral transtemporal sphenoid approach is a combination of techniques. It is similar to the infratemporal fossa approaches of Fisch except that it does not usually result in permanent conductive hearing loss, and it does not require rerouting of the facial nerve.

The subtemporal-preauricular infratemporal approach (Fig. 174-35)^14,102 is a combination of the transparotid and lateral transtemporal sphenoid procedures in addition to temporal craniotomy. It provides excellent exposure of much of the middle cranial base and allows for improved access for intracranial dissection when necessary. The orientation of the exposure begins laterally and progresses medially so that it is useful for the management of lesions of the greater sphenoid wing, the petrous apex, and the middle and lower clivus. This approach is used extensively for the resection of tumors such as meningiomas, chondrosarcomas, chordomas, and petrous apex cholesteatomas. It illustrates many important techniques used in surgery of the middle cranial base.

Figure 174-35. Subtemporal-preauricular and infratemporal approach to the cranial base. A, Initial exposure. Distal branches of the facial nerve are for demonstration only; in most cases they are not dissected. The frontal branch is included with the skin flap and retracted inferiorly. B, The temporalis muscle has been reflected inferiorly (bottom left) after temporarily removing the zygomatic arch, the mandibular condyle has been resected, and a subtemporal craniectomy has been performed. After dividing the styloid complex, the carotid artery is traced distally through part of its course within the temporal bone to separate it from the tumor. The facial nerve need not be transposed, and the conducting mechanism of the middle ear remains undisturbed in this approach. C, Progressive dissection exposes the clivus, the sphenoid sinus, the superior orbital fissure, and the adjacent neural and vascular structures.

(From Sekhar LN, Janecka IP. Intracranial extension of cranial base tumors and combined resection: the neurosurgical perspective. In: Jackson CG, ed. Surgery of Skull Base Tumors. New York: Churchill Livingstone; 1991.)

A hemicoronal or curved temporal incision is extended into the preauricular and cervical regions to expose the temporalis muscle, the zygomatic arch, the parotid gland, and the upper neck. (As discussed in the description of the bicoronal incision, the temporal fascia and fat pad are elevated with the skin flap, thereby protecting the frontal branch of the facial nerve). The cervical extension is used to gain access to the ICA, the internal jugular vein, and cranial nerves IX through XII, and to help identify the facial nerve extratemporally. The parotid gland is mobilized away from the sternocleidomastoid muscle, and the underlying styloid complex is divided, revealing the high cervical ICA, the internal jugular vein, and cranial nerves IX to XII. Next, the zygomatic arch is osteotomized with a reciprocating saw and removed temporarily, thereby allowing the temporalis muscle to be reflected inferiorly to expose the greater wing of the sphenoid and the underlying infratemporal fossa. In cases in which the lesion also involves the orbit (e.g., sphenoid wing meningiomas), the lateral orbital wall and rim may also be osteotomized and removed along with the zygoma. The condyle of the mandible may be retracted or resected to expose the spine of the sphenoid and its nearby structures, including the middle meningeal artery, cranial nerve division V3, and the ICA at its entrance into the carotid canal. More medially, V2 can be identified just anterior to the lateral pterygoid plate.

A low temporal craniotomy is performed, and, by extradural dissection, the temporal lobe is elevated off of the middle fossa floor, thereby revealing the intracranial landmarks: the GSPN, the middle meningeal artery, and cranial nerve divisions V2 and V3.

By progressive removal of the greater wing of the sphenoid, cranial nerve divisions V3 and V2 may be completely unroofed. If necessary, the sphenoid sinus may be opened by removing the bone between V2 and V3 and the base of the pterygoid plates. The superior orbital fissure may be unroofed in the same way.

The intrapetrous course of the ICA may be exposed, beginning at the infratemporal opening of the carotid canal and extending to just above the foramen lacerum (where the ICA enters the cavernous sinus). This is accomplished with a high-speed drill and a diamond burr using a technique analogous to that used for facial nerve decompression. To facilitate this exposure, the middle meningeal artery and the GSPN should first be divided, and the high cervical ICA with its fibrous periosteal sheath should be rendered accessible by removal of the styloid process and the surrounding bone. The ICA may be displaced forward out of its bony canal; this is useful whenever the lesion involves the clivus medial to the ICA or the petrous part of the temporal bone posterior to the ICA. The inferior aspect of the cavernous sinus may also be approached from this exposure.⁷

The sequence and extent of exposure at the skull base depend on the nature of the lesion to be extirpated. Certain steps in the procedure may be eliminated or modified to suit the needs of the particular case. For example, it is only necessary to dissect the neck if the procedure will benefit from proximal control of the ICA or from low exposure of the internal jugular vein or cranial nerves IX through XII. Otherwise, the cervical extension may be avoided.

After the lesion has been extirpated, the wound is irrigated with antibiotic solution and carefully inspected. Any dural openings are meticulously repaired primarily or by using grafts of pericranium, temporalis fascia, or fascia lata. In addition to repairing dura, every effort is made to reconstitute a functional barrier between the intracranial compartment and the visceral spaces of the head and neck. Usually this does not include any attempt to rebuild the bony basicranium. Instead, efforts are focused on the interposition of reconstructive soft tissues—vascularized tissues, whenever possible—into the surgical defect.

Any communications with the aerodigestive tract are identified. These most often include the sphenoid sinus, the nasopharynx, and the eustachian tube. If the sphenoid sinus has been opened, its mucosa is removed, and it is obliterated with autogenous fat or by the transfer of vascularized temporalis muscle medially. If the eustachian tube has been entered, it is denuded of mucosa, packed with fat or muscle, sutured closed, and covered with vascularized temporalis muscle. If the nasopharynx has been violated, the opening is filled with a temporalis muscle flap or a free microvascular flap (e.g., rectus abdominis), depending on the size of the defect. Special care is taken to ensure that the ICA is covered with vascularized tissue throughout its course, particularly in cases in which the nasopharynx has been entered. Failure to protect the ICA in this way may result in continued exposure of the artery to bacterial contamination from the upper aerodigestive tract, with subsequent carotid rupture.

Finally, the zygomatic and craniotomy bone segments, which were previously displaced by osteotomy, are returned to their anatomic positions and secured appropriately. If the temporalis muscle has not been used as a reconstructive flap, it is returned to the temporal fossa. If a temporalis flap has been used, the temporal fossa may be filled with autologous fat from the abdomen or thigh to minimize the temporal fossa depression. Soft tissue closure then follows.

Transfacial Approaches

Transfacial exposure of the cranial base, particularly of the lateral compartment (middle cranial base region), is not a new concept. Operative procedures for the removal of neoplasms from this region were described by several authors in the 1960s.^103,104 These early procedures, which were used initially for the radical resection of malignant tumors, resulted in unacceptably high morbidity and mortality rates and considerable deformity, largely because methods to adequately reconstruct major cranial base defects were not yet available. With the introduction of craniofacial disassembly techniques and vascularized reconstructive flaps, it has become possible to dismantle the facial skeleton, to extirpate deep-seated lesions, and to perform functional reconstruction to a greater extent than ever. Accordingly, lesions of the lateral and central compartments are more amenable to surgery.

A transfacial approach to this region is desirable because it eliminates the viscerocranial skeleton as an obstacle to exposure, thereby opening up the entire infratemporal fossa and the nasal cavity, the nasopharynx, the pterygopalatine fossa, and the sphenoid region to direct access all at once. The facial translocation approach (Fig. 174-36)¹⁷ is such a procedure.

Figure 174-36. Facial translocation approach to the cranial base. A, Incisions. Infraorbital portion of an incision is made in the inferior fornix of the conjunctiva. The lip-splitting portion may be omitted in many cases in which low maxillary exposure is not needed. B, Facial soft tissue flaps fully developed and reflected to expose the craniofacial skeleton. C, Outline of osteotomies of the orbitozygomaticomaxillary skeleton. D, Exposure after temporary removal (translocation) of the orbitozygomaticomaxillary segment. E, Inferior reflection of the temporalis muscle—enhanced by outfracture of the coronoid process—gives access to the pterygoid region and the nasopharynx. F, Subtemporal craniectomy allows exposure of the middle fossa floor, the sphenoid sinus, and the adjacent neural and vascular structures. ICA, internal carotid artery.

(From Janecka IP, Sen CN, Sekhar LN, Arriaga M. Facial translocation: new approach to cranial base. Otolaryngol Head Neck Surg. 1990;103:413-419.)

Incisions are made in the face and scalp as shown in Figure 174-36A. The horizontal incision connects a lateral rhinotomy with a hemicoronal incision to create superior and inferior soft tissue flaps. (At this stage, the frontal branches of the facial nerve are identified using evoked EMG, tagged, and divided to be reconnected later on during the procedure. This horizontal incision is a key element in the exposure because it allows a single, unified surgical field that is unhampered by the need to work alternatively from separate cranial and facial incisions that limit the surgeon’s ability to develop three-dimensional exposure at the cranial base.) The soft tissue flaps are then elevated in the subperiosteal plane from the zygoma and maxilla. Periorbita is likewise elevated from the lateral, inferior, and medial orbital rims and walls. A reciprocating saw is used to create osteotomies, and the orbitozygomaticomaxillary skeletal segment is temporarily removed.

After the temporalis muscle is reflected inferiorly, the subtemporal skull base is fully exposed, and further dissection proceeds as dictated by the lesion, using the same skull base landmarks as for other approaches. Intracranial exposure is readily obtained, if needed, by subtemporal craniectomy or by frontal or temporal craniotomy. Similarly, the pterygoid plates and muscles may be removed, thus revealing the nasopharynx, the sphenoid sinus, and the clivus. As mentioned previously, facial translocation may therefore be used as an approach to the central compartment of the middle cranial base; it provides a unified surgical field with access to both compartments.

At the completion of the extirpation, reconstruction follows the same principles as discussed. After dural repair, the temporalis muscle is used to fill the skull base defect. Because of its appreciable soft tissue bulk, the muscle also is useful for obliterating the maxillary sinus space. There it serves as a vascularized tissue bed for the orbitozygomaticomaxillary bone segment, which is replaced and secured as a free bone graft. Bony stabilization is achieved with sutures or miniplates. If it has not been resected for oncologic reasons, the infraorbital nerve (which was transected during the development of the lower facial soft tissue flap) is rerouted through its maxillary canal and reconnected to its distal trunk by suture neurorrhaphy. The frontal branches of the facial nerve also are repaired. The nasolacrimal system is stented to prevent dacryostenosis, and the medial canthal ligament is secured to the lacrimal crest. Temporary tarsorrhaphy helps support this repair during the early postoperative period. Closure of skin incisions completes the procedure.

Postoperatively, tarsorrhaphy sutures may be removed within 1 week; nasolacrimal stents remain in place for 6 to 8 weeks. In most patients, infraorbital sensation returns within 3 to 6 months, and frontalis muscle function resumes in 6 to 9 months.

The facial translocation technique is valuable for obtaining the broad exposure needed when managing large or advanced lesions of the lateral and central compartments of the middle cranial base, especially those in which much of the lesion is extracranial. Because of its modular nature, it also can be applied in various scaled-down versions that are tailored for dealing with smaller cranial base lesions.