Imaging

In most patients, magnetic resonance imaging (MRI) is performed preoperatively to determine the suspected diagnosis, extent of disease, and status of surrounding anatomical structures. Computed tomography (CT) with bone windows is often useful for visualizing the extent of bony skull base involvement by tumor. Major arterial involvement by tumor should prompt diagnostic cerebral angiography with possible test occlusion. For internal carotid artery (ICA) involvement, the contralateral ICA is injected, as are the vertebral arteries to assess collateral supply. For venous sinus involvement, the pattern of venous drainage and patency of venous structures needs to be determined, including any collateralization. If there is arterial involvement with poor collateral supply or a failed occlusion test, preoperative evaluation of donor vessels for likely bypass needs to be performed. Finally, especially for dura-based tumors, preoperative angiography can be performed to embolize feeding vessels.

Selection of Approach

The choice of approach is dependent on the goals of the operation (total versus subtotal resection), the areas of invasion, major arteries involved, and access to the tumor blood supply (tentorium, clinoid carotid, etc.). Previous treatments, including surgery and radiation therapy, can affect the choice of surgical approach from the perspective of wound healing and surgical scar from a certain trajectory. Finally, assistance from other specialties (neuro-otology, plastic surgery) may be required, as is the support of neurointensivists for the immediate postoperative care.

Anesthesia and Intraoperative Monitoring

For cranial base operations, the neuroanesthesiologist maintains blood pressure and oxygenation within normal limits. Arterial line, central venous catheter, and in some cases jugular bulb oximetry are utilized. Brain relaxation is achieved with modest hyperventilation, diuretics, and in some cases, lumbar cerebrospinal fluid (CSF) drainage or ventriculostomy. For prolonged skull base tumor operations, infusions of tranexamic or aminocaproic acid are run to promote hemostasis.

In most cases, transcranial cortically evoked motor evoked potentials (MEPs) and somatosensory evoked potentials (SSEPs) provide information regarding the integrity of the long tracts during the procedure. For this reason, total intravenous anesthetics are often required, consisting typically of propofol and remifentanil. When needed, electrodes are placed in the target muscles of cranial nerves V, VII, IX, X, XI, and XII for intraoperative mapping and assessment of functional continuity.

Transsphenoidal Approach

The primary indication for the transsphenoidal approach is midline sellar and suprasellar lesions, and it is the workhorse approach for most pituitary adenomas. Several authors have reported endonasal techniques of resection of other lesions, such as tuberculum sellae meningiomas and craniopharyngiomas.⁶ This approach is limited laterally by the internal carotid arteries; therefore, lesions extending laterally to this point cannot be resected completely. Either the microscope or the endoscope (either as the primary or assistive device) may be used for visualization. Current transsphenoidal instruments remain limited in the ability to apply standard microsurgical techniques of sharp dissection for intradural lesions, and intraoperative complications such as arterial injury are difficult to repair for this reason. Selected intradural lesions, such as tuberculum sellae meningiomas and craniopharyngiomas, may be removed via an extended transsphenoidal approach, provided an adequate arachnoid plane is visualized on preoperative imaging, and the tumor is primarily midline with no lateral extension beyond the carotid arteries or optic nerves. The caveat of an extended approach is an increased risk of postoperative CSF rhinorrhea, given the inherent difficulty of primarily repairing dural or bony openings in a watertight fashion. Dural substitutes, fibrin glue, postoperative lumbar CSF diversion, and nasoseptal mucosal flaps are useful adjuncts to prevent CSF leakage.

The patient is positioned supine with the head elevated above the body to reduce venous pressure and turned slightly to the left for a right-handed surgeon, who operates from the patient’s right side. Intraoperative neuronavigation is preferred over C-arm fluoroscopy to assist in localizing the anatomy, particularly the position of the cavernous carotid arteries. Either a sublabial or a purely endonasal approach may be used. For a sublabial approach, the upper gingival mucosa is infiltrated with local anesthetic and incised transversely. A periosteal elevator is used to expose the cartilaginous and then nasal septum, down to the vomer. The cartilaginous septum is fractured from the bony septum, exposing the anterior wall of the sphenoid sinus. The sinus is then opened using Kerrison rongeurs inserted into either sphenoid ostia, or using a microdrill or pituitary rongeurs. At this point, the pituitary fossa and optic and carotid prominences are identified. The bone overlying the pituitary fossa is removed, exposing the sellar dura. For more extensive lesions, bony resection is extended to incorporate the planum and tuberculum sellae.

For a purely endonasal approach, the nasal cavity is first treated with cocaine-soaked cottonoids. The nasal cavity is then entered, with or without the use of a nasal speculum, and the inferior and middle turbinates as well as the choana are used as landmarks until the ipsilateral sphenoid ostium is reached. The middle turbinate is either temporarily outfractured to increase the working space, or resected either with scissors or a microdébrider. If a mucosal flap is not harvested, a small incision is made in the septal mucosa at the junction of the bony and cartilaginous septum, which is outfractured. Submucosal dissection of the contralateral bony septum and vomer is performed, exposing the contralateral sphenoid ostium. Removal of the anterior wall of the sphenoid sinus proceeds as for the sublabial approach described earlier, and the remainder of the surgery proceeds in a similar fashion as well.

For closure, if no CSF leak is apparent, a small piece of Duragen or other dural substitute is tucked under the bony edges of the sellar opening and secured with fibrin glue. The closure may be augmented with Nasopore packing. In cases of intraoperative CSF leak, fat is harvested from the abdomen and placed within the sphenoid sinus to augment the closure, followed by placement of a lumbar drain in the operating room. Occasionally, a Foley catheter may be inflated to secure the nasal packing postoperatively. For larger osteodural defects, bone substitute such as Medpor (Porex Technologies, Fairburn, GA) may be used, or bony septum harvested from the initial exposure, as well as a mucosal flap, which is rotated on its pedicle to provide vascularized tissue coverage.

Currently, our practice has been to use the endoscopic transsphenoidal approach for most pituitary tumors that appear to have reasonable dissection planes from surrounding neurovascular structures. More invasive tumors with irregular suprasellar involvement or with extensive clival involvement are removed with either a cranial or transmaxillary approach.

Extended Subfrontal Approach

This versatile approach is useful for intra- and extradural lesions of the anterior skull base, paranasal sinuses, as well as the sella, and midline clivus down to the foramen magnum. It is also better suited than the transmaxillary approach for intradural lesions in these areas. Furthermore, it can be adapted for more lateral exposure, including the cavernous sinus and frontotemporal area as needed. As such, it is useful for purely extradural lesions, such as for craniofacial resection of sinonasal malignancies, and for mixed intra- and extradural lesions such as esthesioneuroblastomas, chordomas, and chondrosarcomas (Fig. 43.1).

FIGURE 43.1 Extended subfrontal approach. A, Craniotomy and orbital osteotomy. B, Superior view of osteotomy and area of planum sphenoidale that is removed with a high-speed drill. C, View after planum drilled and optic nerves unroofed. Note cavernous carotid arteries bilaterally. D, Reconstruction of the anterior cranial base with autologous fat and pericranial grafts.

The patient is positioned supine with the head neutral and the body secured for tilting as required during the procedure for contralateral exposure. Brain relaxation and CSF diversion are facilitated by intraoperative placement of a lumbar drain. A bicoronal incision is performed behind the hairline and reflected anteriorly. A pericranial incision is made from behind the skin incision to maximize the available graft and the pericranium is reflected anteriorly as a separate layer to repair the frontal and ethmoid sinuses as well as the dura at the end of the surgery. Care is taken to preserve the supratrochlear and supraorbital bundles, which may emerge either from a notch or true foramen from above the orbital rim. In the case of a foramen, they are osteotomized with a small straight osteotome and outfractured with the scalp flap. The periorbita is dissected for a distance of approximately 3 cm to allow the orbitofrontal osteotomy to be sufficiently posterior, and the frontonasal suture is also exposed. At this point a low bifrontal craniotomy is performed, taking care not to lacerate the dura or the superior sagittal sinus. The subfrontal dura is mobilized off the orbital roofs bilaterally, sparing the cribriform plate region. A bilateral orbitofrontal osteotomy is then performed using the reciprocating saw, incorporating the orbital bar and through the nasoethmoidal complex in the midline, and circumventing the cribriform plate in order to spare the olfactory dura. The remaining cribriform plate is drilled until the olfactory dural sheath is exposed. Depending on the pathology and the preoperative state of the patient’s olfaction, the olfactory nerves can be preserved during this approach, particularly for when the pathology is primarily intradural. Following an osteotomy circumventing the cribriform plate, the dura is opened, and the olfactory tract and sulcus are identified. Arachnoid dissection is used to mobilize the olfactory tracts off their sulci, allowing the basal frontal lobes to relax without transmitting traction on the olfactory tracts. In more extensive primarily extradural lesions, particularly if the patient is anosmic, the entire complex can then be suture-ligated and divided from within the nasal cavity, allowing the frontal lobes to relax superiorly. The anterior and posterior ethmoidal arteries are divided.

At this point the optic canals are unroofed using an irrigating microdrilled or ultrasonic curet under microscope visualization. The planum down to the tuberculum sellae is drilled as well, leading into the sphenoid sinus, the pituitary fossa, and the medial cavernous sinus walls bilaterally. Extradural exposure of the cavernous carotid artery is performed if required. Venous bleeding from the cavernous sinus is controlled by filling of the bleeding point with oxidized cellulose followed by fibrin glue, which is very efficacious. From the sphenoid sinus, the sella and clivus are exposed extradurally, and the entire clivus can be drilled if needed down to the foramen magnum, achieving an exposure in this area similar to that obtained with the extended maxillotomy approach. The lateral limits of this clival exposure include the cavernous sinuses, petrous apices, and hypoglossal canals.

Reconstruction involves suturing the pericranial flap to repair all dura defects in a watertight fashion. Mucosal tissue is resected from the exposed sinus and on the craniotomy flap, and the sinus opening and any dead space are obliterated with fat harvested from the abdomen and the pericranial flap as a second layer. The olfactory dural sheaths are also sutured closed in watertight fashion. For larger bony defects along the planum or clivus, structural support is achieved with either a split-thickness bone graft or titanium plate, with screw fixation when possible. The fronto-orbital osteotomy is reaffixed over the pericranial repair and the entire closure is injected with fibrin glue to promote a watertight seal. In occasional cases, a lumbar drain is placed for postoperative CSF diversion. For significant splaying of the eyes secondary to the tumor, a medial orbital canthopexy is performed.

Transmaxillary and Extended Transmaxillary Approaches

This approach is best suited for midline extradural lesions centered on the midportion of the clivus, such as chordomas and chondrosarcomas (Fig. 43.2). The exposure is also well suited for lesions extended superiorly up to the sella turcica. The lateral limits of this exposure include the cavernous sinus and carotid arteries, and the pterygoid space. Depending on the extent of disease, however, the lower clivus, anterior cervical spine, or lateral infratemporal space may be accessed via extended maxillotomy approaches.

FIGURE 43.2 Transmaxillary and extended transmaxillary approaches. A and B, Schematic lateral and anterior views, respectively, of the transmaxillary approach, demonstrating the extent of exposure of the sella and mid and upper clivus. C and D, Exposure is extended caudally down to the upper cervical spine with the extended maxillotomy approach.

We generally prefer a sublabial gingival incision for cosmesis; however, a Weber-Ferguson facial incision or a facial degloving approach may be employed as well. Laterally the maxilla is dissected in a subperiosteal fashion toward the pterygoid plates, as far as the infraorbital foramina and bundles bilaterally. Superiorly, the dissection is carried toward the frontonasal suture and, if required, the periorbital is dissected from the inferomedial orbital walls. A LeFort I osteotomy is planned. Perfect reapposition of the osteotomy is important to prevent malocclusion, hyperphonia, or dysphagia; therefore, plating systems are marked and drilled prior to the osteotomy. The osteotomy is then performed with a reciprocating saw and downfractured.

Following tumor resection, if there is a dural defect it is repaired with an abdominal fascial graft as well as fibrin glue, followed by abdominal fat and, for larger bony defects, the repair is reinforced with titanium mesh, which is secured with screws. The maxillary osteotomy is reapproximated with titanium plates and screws. A lumbar drain is placed for 3 to 5 days postoperatively to promote a watertight dural repair and prevent CSF fistula formation.

For greater exposure extending from the entire clivus to the craniocervical junction, a palatal split may be performed following the LeFort I maxillotomy osteotomy. A horizontal cut is again made similar to the preceding approach, followed by a midline osteotomy in the midline of the hard palate from between the central incisors anteriorly to the junction of the hard and soft palate posteriorly. The maxillary split is then outfractured and swung laterally. A self-retaining transpharyngeal retractor is placed to hold the palate and maxillotomy apart, exposing both the nasopharyngeal space and the longitudinal extent of the clivus. A midline incision in the pharyngeal mucosa along the clivus and between the prevertebral muscles is then performed, and the lesionectomy is performed. Meticulous preparation of the plating system prior to the osteotomies and perfect realignment during reconstruction prevents postoperative palatal dysfunction. Dural repair is performed in a similar manner as described earlier, including postoperative lumbar CSF drainage.

Complications of the maxillotomy and extended maxillotomy approaches include CSF fistula formation, injury to the dental rootlets, and problems related to poor palatal reconstruction such as oronasal fistula, dysphagia and dysphonia, and malocclusion. The majority of these complications are avoided by careful attention to the planning and reconstruction of both the dura and osteotomies intraoperatively, making these approaches long and intricate.

Transoral Approach

The transoral approach is ideally suited for smaller midline lesions of the lower clivus and upper cervical spine; however, more superior exposure is substantially limited by the palate, and more lateral exposure is also restricted compared to maxillectomy and extended subfrontal approaches. This approach is therefore mostly appropriate for degenerative, congenital, or rheumatic disorders of the ventral occipitocervical junction.

Preoperatively, the oral opening must be assessed to be sufficiently mobile and large enough to facilitate the approach. The patient is positioned supine with a variable amount of neck extension depending on the location and nature of the pathology. A self-retaining pharyngeal retractor is placed, and the soft palate is retracted superiorly using a nasally placed rubber cathether. A midline longitudinal incision is then performed along the posterior pharyngeal wall, and the longus colli and capitis muscles are retracted laterally together with the pharyngeal mucosa. For more exposure superiorly, a midline incision through the soft palate can be performed down to the uvula, and the palate divided in the midline. The anterior tubercle of C1 and the C2 vertebrae are thus exposed. Superiorly, the lower portion of the bony septum may be partially resected to expand the clival exposure. Any compressive osteofibrotic pannus or tumor is resected. Dural penetration is repaired in a similar manner as described in the transmaxillary approach, and the pharyngeal mucosa and muscles as well as the palate are all closed in separate layers. Postoperatively, the patient is kept intubated until oropharyngeal swelling has subsided, and nasogastric tube feeding is continued until the mucosal repair has sufficiently healed.

Frontotemporal Orbitozygomatic Approach

The frontotemporal approach with variations of the orbitozygomatic extension is among the most frequently implemented skull base approaches. Vascular and neoplastic lesions involving the anterior and middle fossae, orbit, orbital apex and cavernous sinus, paraclinoid and parasellar regions, and basilar apex are accessible with avoidance of brain retraction (Fig. 43.3).

FIGURE 43.3 Frontotemporal orbitozygomatic approach. A, Initial exposure and frontotemporal craniotomy. B, Cuts for an orbitozygomatic osteotomy. C, Final appearance after removal of osteotomy. D, Cavernous sinus tumor exposed after splitting the sylvian fissure and the lateral cavernous sinus dura opened. E, Following removal of tumor, the upper clivus and cavernous sinus are exposed.

The patient is positioned supine with the head turned 20 to 45 degrees depending on the lesion, with slight extension such that the malar eminence is the highest point. A pterional or modified bicoronal incision is performed behind the patient’s hairline, from the skin crease anterior to the tragus of the ear, to the midline or just behind the midline frontal region. The scalp flap is reflected anteriorly, preserving the superficial temporal artery as well as the pericranium and temporalis muscle and fascia. Where the superficial fat pad is encountered laterally, an interfascial or subfascial dissection is required to preserve the frontotemporal branch of the facial nerve. If a supraorbital foramen is encountered, it is outfractured to preserve its neurovascular bundle. Once the orbit and zygomatic root are reached, the dissection is continued in a subperiosteal manner, exposing the entire course of the zygoma. The temporalis muscle is then mobilized, taking care to preserve and avoid cautery injury to the deep temporal fascia, from which the muscle derives its neurovascular supply. Once the muscle is retracted laterally, a frontotemporal craniotomy is done separately from the osteotomy. The medial extent of the craniotomy is usually the supraorbital notch, and laterally it extends to the floor of the middle fossa toward the inferior orbital fissure.

At this point the periorbita and subfrontal dura are carefully dissected off the orbital roof and walls. The temporalis and masseter muscles are sharply freed from the zygomatic arch, and approximately 1 cm of zygoma is exposed to allow placement of a titanium plate. The inferior orbital fissure is palpated from both the intraorbital and cranial compartments. Malleable brain ribbons are used to then protect the globe and frontal lobe, and a reciprocating saw is used to perform the orbitozygomatic osteotomy. The medial cut is made just lateral to the supraorbital notch, angled from lateral to medial and incorporating at least two thirds of the anteroposterior extent of the orbital roof, within safe distance of the superior orbital fissure posteriorly. Too shallow osteotomies after the remaining lesser wing of the sphenoid is rongeured are associated with persistent postoperative pulsatile enophthalmos and should thus be avoided. Laterally, a second cut is made from the inferior orbital fissure to the level of the zygomaticofacial foramen. This is connected to another lateral cut from the anterior, inferior edge of the zygoma, also directed toward the inferior orbital fissure. The final cut is performed obliquely from posterior to anterior at the root of the zygoma and its transition point with the squamosal temporal bone. The osteotomy is completed with gentle fracturing using a small osteotomy and mallet, and removed as a single piece, freeing any remaining attached periorbita or muscle.

Following the osteotomy, the lateral segment of the superior orbital fissure is unroofed, preferably under the operating microscope. The optic canal is then decompressed with a high-speed drill, and a clinoidectomy is performed. The anterior clinoid can be removed extradurally, either en bloc or piecemeal if it is more elongated. After drilling the attachment of the anterior clinoid to the optic canal, optic strut, and superior orbital fissure, it is gently fractured and dissected from its surrounding dural fold, avoiding pressure on the optic nerve. Bleeding from the cavernous sinus is controlled with oxidized cellulose and fibrin glue. The orbitomeningeal dural fold marks the lateral extent of the superior orbital fissure, and may be coagulated and divided to further mobilize the frontal and temporal dura, in order to facilitate the clinoidectomy. For lesions invading the clinoid or in the case of vascular lesions, the anterior clinoid may be removed intradurally. Occasionally, air cells within the clinoid may communicate with the sphenoid sinus, and care should be taken to occlude them with bone wax and occasionally with fibrin glue. Laterally, the superior orbital fissure dura can be incised and an interdural dissection performed, mobilizing the temporal lobe dura from the true dural covering of the superior orbital fissure, maxillary and mandibular branches, as well as the lateral wall of the cavernous sinus and cavernous carotid artery. Finally, for pathology involving the orbital apex, the periorbita is incised beyond the more lateral segment of the superior orbital fissure, which is relatively more devoid of neurovascular structures. The anulus of Zinn, if opened, is sutured after lesion removal.

Subtemporal Transzygomatic Approach with Petrous Apex Resection

This approach is well suited for lesions involving the petrous apex, upper clivus, posterior cavernous sinus and Meckel’s cave, including limited extension of pathology into the upper posterior fossa. Typical lesions resected via this approach include trigeminal schwannomas; petrous apex lesions such as cholesterol granulomas, cholesteatomas, and chondrosarcomas; meningiomas involving the cavernous sinus and tentorium as well as smaller petroclival meningiomas; and vascular lesions in the region of the basilar apex (Fig. 43.4).

FIGURE 43.4 Subtemporal transzygomatic with petrous apex resection. A, Tumor lying in the cavernous sinus and extending to the level of the horizontal petrous internal carotid artery (ICA). B, Exposed anatomy after tumor resection with this approach. BA, basilar artery; GSPN, greater superficial petrosal nerve.

The patient is positioned supine with the head turned 70 degrees to the contralateral side with slight neck extension. Central venous pressures are checked to avoid excessive neck turn. A smaller reverse question mark incision is made in the frontotemporal region, with the inferior limb just anterior to the tragus of the ear. As with the orbitozygomatic approach, the pericranium is preserved for dural reconstruction, and an interfascial dissection of the superficial temporal fascia is performed. The temporalis muscle is mobilized together with its deep fascia to prevent muscle atrophy, and reflected laterally. The zygomatic arch is exposed. If the condylar fossa is included in the zygomatic osteotomy, the temporomandibular joint (TMJ) capsule is carefully dissected from the condylar fossa, and a heavy suture is used to retract the joint inferiorly. Care is taken not to transgress posteriorly into the external auditory canal, and a bony spine serves as a useful landmark between the condylar fossa and ear canal.

A predominantly temporal craniotomy is then performed, and additional temporal bone is craniectomized as necessary to remove obstructing bone from the floor of the middle fossa. The zygomatic osteotomy is then performed, from just lateral to the lateral wall of the orbit, preserving the zygomaticofacial nerve, to the root of the zygoma. If the condylar fossa is included in the osteotomy, the temporal dural vessels are first followed to the foramen spinosum, which is a medial safe landmark for the condylar cuts. An osteotomy that transgresses medial to the foramen spinosum puts the petrous internal artery at risk. Additional cuts are then made from the foramen spinosum medially to the posterior aspect of the condylar fossa and anterior zygomatic cut, laterally. Positioning titanium plates prior to the osteotomy ensures perfect realignment at the end of the surgery to prevent complications related to TMJ dysfunction.

Under microscope visualization, the middle meningeal artery at the foramen spinosum, greater superficial petrosal nerve (GSPN), mandibular portion of the trigeminal nerve and foramen ovale, and the arcuate eminence of the petrous bone are identified. The middle meningeal artery and vein are divided. The GSPN is occasionally divided depending on exposure requirements of the lesion. The dura overlying V2 and V3 is incised and mobilized until sufficient exposure of the petrous apex is achieved. Venous channels around the trigeminal branches are controlled with oxidized cellulose and fibrin glue. Coagulation is avoided to prevent facial numbness and deafferentation. The greater wing of the sphenoid is drilled to further expose the foramina rotundum and ovale, which permits greater mobilization of their respective trigeminal nerve branches. Care is taken not to accidentally expose the mucosa of the sphenoid sinus between V2 and V3.

The petrous segment of the internal carotid artery is situated directly underneath the GSPN and is first identified at the junction of the GSPN and V3 anteriorly. Immediately lateral is the eustachian tube. The carotid artery is then followed posteriorly as far as the posterior genu, and carefully unroofed using a combination of microdrills and small Kerrison rongeurs. At this point the internal carotid artery is gently dissected out of its canal and reflected inferolaterally. Care is taken when drilling posterior to the posterior genu of the ICA due to the vicinity of the cochlea and jugular bulb. Mobilization of the carotid artery facilitates greater exposure of the petrous apex as well as the clivus. An anterior petrosectomy is then performed using a high-speed drill or ultrasonic bone curet.

Once the petrosectomy is completed, the petroclival dura is opened. For lesions extending into the posterior cavernous sinus, it is necessary to split the fascicles of the trigeminal root from within Meckel’s cave, reaching the posteromedial border of the cavernous sinus beyond the distal petrous ICA and petrolingual ligament. Alternatively, the trigeminal root may be mobilized superiorly. This is facilitated by opening the temporal lobe dura above the tentorium, and dividing the tentorium and superior petrosal sinus.⁷

Preauricular Subtemporal-Infratemporal Approach

The subtemporal-infratemporal approach is an inferior extension of the subtemporal transzygomatic approach, and is better suited for lesions requiring lateral exposure of the mid and lower clivus, such as petroclival chondrosarcomas and cholesterol granulomas (Fig. 43.5). In addition to an anterior petrosectomy, Glasscock’s space is also drilled and the eustachian tube divided, allowing the petrous internal carotid artery to be completed mobilized anteriorly.

FIGURE 43.5 Preauricular subtemporal-infratemporal approach. A, Skin incision. B, Temporal craniotomy, area of craniectomy and zygomatic osteotomy. C, Temporal lobe dura has been elevated. The middle meningeal artery and greater superficial petrosal nerve (GSPN) have been divided, and the horizontal portion of the petrous internal carotid artery (ICA) has been partially exposed. D, The dura propria over the gasserian ganglion and between V2 and V3 has been incised, revealing tumor extending into Meckel’s cave and the sphenoid sinus, respectively. E, Mobilization of the petrous ICA from the carotid canal after division of the fibrocartilaginous ring.

As in the subtemporal transzygomatic approach, the middle fossa floor contents are exposed. A zygomatic osteotomy incorporating the condylar fossa is performed as described earlier. The petrous carotid artery is identified, and skeletonization of its vertical segment is achieved once the tensor tympani muscle and eustachian tube are divided. This is performed by packing the anterior end with oxidized cellulose, and the posterior end with a small amount of fat. Each end is then suture-ligated. Toward the entrance to the carotid canal, the thick fibrocartilaginous ligament that surrounds the internal carotid artery must be sharply divided. The remaining bone medial to V3, and lateral to the petrous ICA, is removed, and the petrous and distal cervical internal carotid artery are completely mobilized. Care is taken to avoid the middle ear and facial nerve, which lie superior and posterior to the vertical portion of the petrous ICA, whereas the jugular bulb and lower cranial nerves are posterior and inferior. Inadvertent entry into the jugular bulb is controlled with gentle packing with Gelfoam and occasionally fibrin glue.

The primary concern and potential complication of the subtemporal transzygomatic and preauricular subtemporal infratemporal approaches is injury to the carotid artery. Frequent mapping with the micro-Doppler, neuronavigation, and preparation for possible exposure of the carotid artery in the neck are precautionary measures. CSF rhinorrhea is prevented with definitive closure of the eustachian tube. TMJ complications are avoided by perfect replacement of the condylar fossa osteotomy, which is facilitated by drilling guide holes for screw and plate placement prior to performing the osteotomy. Postoperative TMJ exercises also help maintain pain-free mobility. Other complications include temporal lobe retraction injury or damage to the vein of Labbé, minimized by use of a lumbar drain. Occasionally the dura is opened to drain CSF from the subarachnoid space and relax the temporal lobe.

Transpetrosal Approaches: Retrolabyrinthine, Partial Labyrinthectomy/Petrous Apicectomy, Translabyrinthine, Transcochlear

These approaches provide a more ventral trajectory to the brainstem, particularly for posterior fossa tumors with significant extension above the tentorium, of which petroclival meningiomas are most typical (Fig. 43.6). Extensive chordomas or chondrosarcomas with brainstem compression from a significant intradural component may also require a transpetrosal approach, as it would allow tumor resection with direct visualization of critical intradural structures. Finally, vascular lesions of the mid and lower basilar arteries, including basilar apex aneurysms in the setting of a low bifurcation, and vertebrobasilar junction lesions may also be better suited with a trajectory from the presigmoid region.

FIGURE 43.6 Posterior transpetrosal approach (partial labyrinthectomy/petrous apicectomy). A, Temporal and suboccipital craniotomy with zygomatic osteotomy and posterior transpetrosal approach. B, After opening the temporal and presigmoid dura, followed by dividing the superior petrosal sinus and tentorium, the entire craniocaudal extent of tumor above and below the tentorium is exposed.

Selection of the type of posterior transpetrosal approach depends on a number of factors, including the preoperative hearing status of the patient, the size and dominance of the ipsilateral sigmoid sinus, and extent of disease. Hearing is preserved in the retrolabyrinthine and partial labyrinthectomy approaches. In the partial labyrinthectomy/petrous apicectomy (PLPA), the superior and posterior semicircular canals are waxed as they are opened, in order to prevent leakage of endolymph and hearing loss. Preoperative vascular imaging is carefully reviewed. In cases in which the sigmoid sinus is small, a retrolabyrinthine approach is usually sufficient to have an adequate opening of the presigmoid dura. Otherwise, a more extensive drilling of the labyrinth is performed.

The patient is positioned with the head 70 degrees to the contralateral side, either with the body supine or in a park-bench position, based on the patient’s neck mobility. A U-shaped incision is performed from the retromastoid region superiorly to just above the superior temporal line and down toward the zygomatic root. The temporalis muscle and fascia are reflected forward and inferiorly. The posterior third of the temporalis muscle can be rotated inferiorly during reconstruction to provide vascularized tissue to seal the mastoidectomy. The suboccipital muscles are reflected away from the mastoid. A temporal craniotomy is performed superior to the transverse sinus dura and at least 2 cm posterior to the transverse-sigmoid junction. For the mastoid, different methods of removal are available. A retrosigmoid craniotomy may be performed first, down to the posterior fossa dura, with or without incorporating the bone overlying the transverse sinus dura. Alternatively, a cosmetic osteotomy piece may be cut first, including the outer table of the mastoid and retromastoid bone, and forward to include the superficial bone of the zygomatic root, glenoid fossa, and ear canal. Care is taken not to injure the sigmoid sinus during either exposure.

Under the microscope, the entire mastoid is then decorticated with a larger bur on a microdrill, exposing the mastoid antrum air cells, and skeletonizing the sigmoid sinus dura and middle fossa floor, or tegmen tympani. The bone overlying the lateral semicircular canal is gradually appreciated proceeding through the mastoid air cells. Immediately anteroinferior to the lateral canal is the posterior genu of the facial nerve. The superior and posterior semicircular canals are then skeletonized. For a PLPA approach, the common crus is opened and filled with wax to prevent leakage of endolymph in an effort to preserve hearing, and the superior and posterior semicircular canals are then resected. This step increases the bony exposure of the petrous apex, which is then drilled. In certain cases, the retrosigmoid bone may be removed as well, allowing the sigmoid sinus to be retracted gently if necessary, and allowing portions of tumor to be resected through a retrosigmoid dural opening. In a translabyrinthine approach, the entire labyrinth is removed to the level of the vestibule, and the bone overlying the internal auditory canal is unroofed. Rarely is a total petrosectomy required for adequate brainstem exposure. In this approach, the entire labyrinth is removed, and the facial nerve is completely skeletonized from the cerebellopontine angle cistern to the fibrous ring at the stylomastoid foramen, allowing it to be mobilized anteriorly after division of the GSPN, albeit with an attendant, at least temporary, postoperative facial weakness. In a manner similar to the preauricular subtemporal-infratemporal approach described previously, the petrous ICA is unroofed and displaced anteriorly. The remaining temporal bone is drilled away, protecting the jugular bulb and lower cranial nerves anteriorly.

The temporal dura parallel to the middle fossa floor and the presigmoid dura parallel to the sigmoid sinus and above the jugular bulb are then opened separately. Care is taken when incising the temporal dura posteriorly to identify and preserve the vein of Labbé. The dura overlying the superior petrosal sinus is suture-ligated and incised, completing the dural opening and exposing the tentorium. The tentorium is divided, controlling any bleeding with bipolar coagulation or surgical clips. The medial edge of the tentorium is incised, avoiding both the trochlear nerve and superior cerebellar artery. The lateral brainstem is then exposed, from the midbrain to the upper medulla and cranial nerves III through IX, and tumor removal proceeds with minimal cerebellar and brainstem manipulation. If necessary, the dura overlying Meckel’s cave can be opened, controlling any venous bleeding with oxidized cellulose and fibrin glue in the usual manner.

For reconstruction, the dura is closed either primarily or with pericranium or synthetic substitute. Any open air cells are carefully waxed off, and the closure is covered with fibrin glue. A pedicled temporalis musculofascial flap (usually the posterior third of the muscle) is rotated down to cover the defect. The bone is replaced, and if required, a titanium mesh is used to reconstruct the mastoid contour.

Complications of the transpetrosal approach include hearing loss or facial nerve weakness, if either the fallopian canal is injured from drill heat or contusion, or if the semicircular canals are injured or not properly waxed. CSF rhinorrhea and otorrhea through either the middle ear passages including the eustachian tube is also a risk. Injury to the trochlear nerve is possible if it is not properly visualized during incision of the tentorium. Also, particularly for left-sided approaches, retraction of the temporal lobe or injury to the vein of Labbé can result in seizures or dysphasia.

Extreme Lateral Approach

This approach is ideally suited for lateral and ventral exposure of the caudal brainstem and upper cervical spinal cord at the level of the foramen magnum. Several variations of this approach have been described, including the retrocondylar approach, the partial transcondylar approach, the transtubercular approach, true transcondylar approach, transjugular approach, and transfacetal approach (Fig. 43.7).⁸ For the purpose of this chapter, only the partial and complete transcondylar approaches will be described. Generally, the partial transcondylar approach is sufficient for exposure of ventrally situated intradural lesions at the lower brainstem. A complete transcondylar approach is most frequently indicated for extradural lesions that involve the condyle and lower clivus, such as chordomas.

FIGURE 43.7 Extreme lateral partial/complete transcondylar approach. A, Patient positioning and incision for a complete transcondylar extreme lateral approach. For cases in which a transcondylar approach is combined with a transpetrosal approach, then the patient is positioned supine with the head turned 45 degrees. B, A retrosigmoid craniotomy, including the lateral aspect of the foramen magnum, and C1 laminectomy have been performed. The vertebral artery (VA) has been mobilized medially after unroofing the C1 foramen. The occipital condyle is now accessible and is resected as needed for adequate tumor exposure. C, Tumor exposed after drilling the occipital condyle. D, Muscular attachments on the transverse process of C1 have been mobilized, illustrating the relationship between the VA, C2 dorsal root, C1 lamina, and occipital condyle. E, Extreme lateral partial transcondylar approach for a hypoglossal schwannoma. Intradural exposure shows the relationship of the tumor to the lower cranial nerve and VA. IJV, internal jugular vein.

Preoperative CT or digital subtracted angiography and venography are important to assess the caliber of the ipsilateral and contralateral vertebral arteries, as well as the dominant side of venous drainage of the brain. The course of the vertebral artery is studied as well. In cases of extensive condylar invasion by tumor, a staged surgery must be anticipated and consists of tumor removal followed by an instrumented occipitocervical fusion. Neuronavigation is also useful for guiding resection of tumor within the base of the skull, such as in chordomas.

The patient is placed in a full lateral position with the contralateral arm hung over the edge of the operating table with a sling or arm rest. The head is secured with pin fixation and rotated slightly toward the surgeon, neck flexed and apex dropped slightly toward the floor. Different incisions have been described for this approach. We prefer a C-shaped incision beginning superiorly in the posterior temporal region above the ear down in a curvilinear fashion behind the mastoid and toward the posterior border of the sternocleidomastoid muscle. A skin flap is raised, above the muscle but incising the fascial attachment of the sternocleidomastoid such that it is mobilized forward together with this superficial layer, exposing the entire proximal attachment of the splenius capitis muscle. The remaining muscles are elevated in layers. The next muscle is the splenius capitis, which is incised off the mastoid process. At this point the occipital artery is identified in the underlying fascia, superficial to the semispinalis capsis and either below or running through the longissimus capitis. These two muscles are then elevated, exposing the muscles forming the suboccipital triangle, namely, the superior and inferior obliques and rectus capitis muscles.

At this point the key step is to safely identify the vertebral artery, typically the V3 segment first. The microscope is used at this point. Immediately, inferior to the mastoid tip is the transverse process of C1, which is easily palpated. The attachments of the superior and inferior oblique muscles as well as the levator scapula are identified. The micro-Doppler is used to identify the V3 vertebral artery above the C1 arch and within the suboccipital triangle. The oblique muscles are disconnected from the transverse process of C1 and reflected medially. Subperiosteal dissection on the superior border of the posterior arch of C1 usually exposes the vertebral artery outside its surrounding venous plexus. Venous bleeding is controlled with careful bipolar coagulation and injection with fibrin glue. A fairly consistent muscular branch of the vertebral artery is encountered emerging from the suboccipital triangle; it is coagulated or clipped and divided. The dissection proceeds medially until the vertebral artery curves toward its dural penetration. The fascial tissue medial to this is incised down to the foramen magnum dura. The C1 foramen transversarium is unroofed with a high-speed drill and small Kerrison rongeurs, and the lateral third of the C1 posterior arch is removed. The V3 vertebral artery is now rotated medially, away from the occipital condyle and occipitoatlantal joint.

A small retrosigmoid craniotomy is performed. The thick bone of the lateral foramen magnum is drilled down and the foramen magnum is exposed. A low mastoidectomy is performed posterior to the facial nerve to blue line the posteroinferior edge of the sigmoid sinus and gain further access to the occipital condyle. Bleeding from the condylar vein is controlled with oxidized cellulose and bone wax. Fibrin glue is avoided because of the vicinity to the jugular bulb and possible embolization. The condylar vein serves as a reference point for the hypoglossal canal, which lies immediately inferior to it.

A high-speed microdrill or ultrasonic curet is used to remove the posterior third of the occipital condyle and lateral mass of C1 including the jugular tubercle, unroofing the posterior border of the hypoglossal canal. The hypoglossal canal lies approximately 8 mm deep to the posterior border of the condyle and has a posteromedial to anterolateral trajectory. Adequate bony removal for intradural exposure of intradural tumors is achieved when there is an approximately 1-cm cuff of dura lateral to the entrance of the vertebral artery into the dura mater. The dura is then opened, encircling the vertebral artery. The dentate ligament and C1 rootlets are divided, and tumor removal proceeds with minimal brainstem and lower cranial nerve manipulation.

For reconstruction, pericranium is harvested from the upper incision and a duraplasty is performed. Watertight closure is occasionally difficult and fibrin glue is used to augment the repair. Autologous fat is used to eliminate deadspace, particularly for complete transcondylar approaches. In the setting of complete condyle removal, an occipitocervical fusion is planned, typically around 1 week following tumor resection.

The principal risk of this approach is injury to the vertebral artery. This is avoided by understanding the course of the vertebral artery on preoperative imaging, and by taking the suboccipital muscles down individually and under the microscope. Inadvertent entry into the jugular bulb during bony drilling is possible, and is controlled with oxidized cellulose or Gelfoam. Postoperative occipital pain is prevented by preserving the C2 root under the C1 lamina. Watertight dural closure is difficult, particularly at the cuff of the dura around the vertebral artery, making CSF leak a possible complication.