Surgery

Surgery: General Principles Technical advances in skull base surgery have established the cavernous sinus as an approachable space whose contents may be navigated successfully during meningioma surgery. Core principles of these approaches include maximal bone removal for exposure; the avoidance of brain retraction; and control of the carotid artery in its petrous, cavernous, and clinoid segments. During tumor resection, arachnoid planes facilitate tumor removal, but these planes become scarred and obliterated after prior resection or irradiation, emphasizing the importance of extensive resection during the initial operation. If necessary, when no arachnoidal plane is encountered, small remnants of adherent tumor are left on the carotid artery. The same philosophy is true regarding the cranial nerves. Attempts should be made to remove all affected dura, and any affected dura that cannot be resected should be electrocoagulated, if possible. All involved or hyperostotic underlying bone should be drilled away. Any submucosal tumor spread within the paranasal sinuses should be removed. Sphenoid sinus defects must be repaired with extreme care during the reconstruction.

Surgical Approaches Two primary surgical approaches to the cavernous sinus are used by the authors: the cranioorbitozygomatic (COZ) approach, and the zygomatic approach.15 The COZ approach affords wide exposure of the entire cavernous sinus, including the proximal and distal carotid artery, with minimal cerebral retraction. The zygomatic approach is used for tumors in the posterior cavernous sinus and petrous apex. This approach is more limited, does not offer readily obtainable distal carotid control, and does not expose the medial or superior cavernous sinus as easily as does the COZ approach.

Cranioorbitozygomatic Approach A lumbar drain is placed for cerebrospinal fluid (CSF) drainage, and the patient is positioned supine with the upper body slightly elevated and the head rotated 30 degrees to the contralateral side. Leads to monitor somatosensory evoked potentials, brain stem auditory evoked potentials, and cranial nerves V and VII are placed at this time, with those to monitor III, IV, and VI placed subsequently (to be discussed). The ipsilateral neck is prepared should more proximal carotid control be required, and the abdomen is prepared for fat graft harvest.

The skin incision for the COZ starts at the zygomatic root and is carried behind the hairline toward the contra-lateral superior temporal line ( Fig. 25.2 ). The superficial temporal artery is identified and carefully protected, and a large pericranial flap is raised by undermining the scalp posterior to the incision and dissecting sharply against the scalp flap anteriorly. A subfascial dissection of the temporalis fascia is performed to preserve the frontal branches of the facial nerve ( Fig. 25.3 ). The zygomatic arch and superior and lateral orbital margins are exposed by subperiosteal dissection, after which the zygoma is divided at either end and displaced inferiorly on its masseteric pedicle ( Fig. 25.4 ). The temporalis muscle is then elevated in subperiosteal fashion, beginning low on the temporal squama and proceeding superiorly to detach the muscle at the superior temporal line ( Fig. 25.4 ). The entire temporalis muscle is then reflected inferiorly with the freed zygoma.

The superior and lateral orbital rims are dissected free from the periorbita, with the supraorbital nerve and vessels preserved ( Fig. 25.5 ). A burr hole is placed in the keyhole to gain simultaneous entrance into the cranium and orbit. Burr holes are then placed anteriorly and posteriorly, adjacent to the temporal floor. A cut is made from the medial aspect of the lateral orbital wall to its lateral aspect and is continued to the keyhole. The keyhole is then connected to the posterior burr hole by cutting through the temporal fossa. A cut starting at this burr hole is then brought superiorly to the frontal bone, then anteriorly through the supraorbital rim, taking care to protect orbital contents during any cuts involving the bony orbit. Care must be taken to ensure that the posterior wall of the frontal sinus is cut, if the sinus has been entered. A cut is made from the first burr hole through the orbit, again taking care to protect the orbital contents. A notched osteotome is used to incise the orbital roof from the second burr hole toward the nasion, while protecting the orbital contents during this cut. The bone flap is now elevated. Remaining portions of the orbital roof, lateral orbital wall, and sphenoid wing can be removed with the craniotome for later reconstruction ( Fig. 25.6 ). With the orbit now exposed, electromyographic electrodes may be directly placed into the superior oblique, superior rectus, and lateral rectus muscles to monitor cranial nerves III, IV, and VI.

Proximal control of the carotid artery is the next objective ( Fig. 25.7 ). The middle fossa dura is elevated in a posterior-to-anterior direction. The greater superficial petrosal nerve (GSPN) emerges from the facial hiatus and should be dissected free of the dura. Traction of the GSPN is avoided to alleviate transmission to the geniculate ganglion, which can lead to facial palsy. The middle meningeal artery is identified, thoroughly electrocoagulated, and divided. Continued dural elevation reveals V3 and foramen ovale. The apices of the Glasscock triangle are now exposed: the facial hiatus, the anterior aspect of the foramen ovale, and the intersection of the GSPN and the lateral aspect of the V3. This triangle overlies the carotid artery, and drilling here with a diamond bit and constant irrigation exposes the carotid artery. This may be sufficient for proximal control of the artery or to allow drilling posterolaterally from the known location of the artery. Proximal control may be obtained by sufficient exposure for placement of a temporary clip on the petrous carotid artery, if necessary. Alternatively, a Fogarty catheter may be inserted into the carotid canal. Should vascular control be required, the catheter balloon can be inflated to occlude the carotid artery in the carotid canal.16

Medial exposure of the cavernous sinus and exposure of the paraclinoid carotid artery are obtained by drilling out the remainder of the orbital roof, the superior orbital fissure, the anterior clinoid process, and the optic strut ( Fig. 25.8 ). Drilling adjacent to the orbital apex and optic canal mandates a diamond burr and copious irrigation to dissipate the heat of drilling. The anterior clinoid process is cored out with the drill and then disarticulated by drilling out the optic strut. The clinoid is subperiosteally dissected and resected. The optic canal is opened first. The superior orbital fissure is opened by drilling along the lesser sphenoid wing. This procedure exposes the subclinoid portion of the carotid artery, which is both extradural and extracavernous, and provides distal control of the carotid artery.

Entrance into the cavernous sinus has been described in relationship to the intervals between the neurovascular structures of the cavernous sinus. These intervals have been annotated as 10 triangles distributed among the parasellar, middle fossa, and paraclival locations.17 The actual approach taken depends on the anatomy of the lesion in relationship to the cavernous sinus structures and must be individualized for each patient. In general, there are two approaches for entry into the cavernous sinus: a superior and a lateral approach. The superior approach is particularly suited to those lesions adjacent to the anterior loop of the carotid artery, and those that are superior and/or medial to the cavernous carotid artery. The lateral approach lends itself well to exposing those lesions lateral and/or inferior to the carotid artery and those that are posteriorly located within the cavernous sinus. Frequently, these approaches are combined for lesions widely involving the sinus.

Superior entry ( Fig. 25.9 ). After exposing the superior surface of the cavernous sinus, the dura overlying the optic nerve is divided over the length of the optic canal to free the optic nerve. The distal carotid ring is now divided. The dura is then incised toward the oculomotor nerve, providing initial entry into the cavernous sinus. Exposure can be increased by dissecting along the length of the carotid artery. Further exposure can be obtained by subperiosteal dissection of the posterior clinoid process and drilling off the process, the dorsum sellae, and the superior clivus. These maneuvers allow increased exposure of the posterior fossa.

For tumors with medial extension, the planum sphenoidale can be drilled away. This allows exposure of the sphenoid sinus. Dissection and incision of the diaphragma sellae allows visualization of the pituitary gland. Great care must be taken during closure to obliterate any communication between the cavernous sinus and sphenoid sinus to prevent CSF leakage.

Lateral entry. Lateral entry into the cavernous sinus can be intradural or extradural. Extradural entry begins by incising the dura propria overlying V3. The dura propria is peeled away from the trigeminal branches and ganglion with superiorly directed traction. This will initially expose the third division and lateral ganglion followed by the second division and the majority of the remainder of the ganglion. Anterior extension from the region of the Meckel cave can be addressed by drilling away bone around the foramina rotundum and ovale to allow exposure of the sphenoid sinus and infratemporal fossa. Drilling bone here will also free the trigeminal branches, which will, in turn, allow greater mobility of these branches and the ganglion. A mass beginning to enter the posterior fossa can be further exposed by drilling the petrous apex. This drilling also allows greater exposure around and under the trigeminal ganglion.

For lesions requiring intradural exposure, intradural entry into the cavernous sinus is achieved through the Parkinson triangle18 ( Fig. 25.10 ). Cranial nerves III and IV are identified over the tentorial edge. An incision beneath the anticipated position of the fourth nerve is fashioned and extended ~8 mm anteriorly and 8 mm inferiorly. The external dural layer is peeled away from the thin inner dural layer in which nerves III, IV, and V are found. The dural flap can be further dissected from the trigeminal ganglion to expose the Meckel cave. Exposure can be increased posteriorly and into the posterior fossa by drilling the petrous apex. The trigeminal nerve can be mobilized by drilling the foramina rotundum and ovale.

The inner dural layer between the fourth nerve and the ophthalmic division can be incised to expose the lateral space of the cavernous sinus, the posterior bend and the horizontal segment of the intracavernous carotid artery, and the lateral cavernous and meningohypophy-seal arteries. The abducens nerve is the only cranial nerve coursing inside the cavernous sinus proper, often appearing in fascicles of two to five nerves, and should be carefully located and protected.19,20 Frequently, meningiomas necessitate the combination of extra- and intradural cavernous sinus dissection with a combination of superior and lateral entry.

Reconstruction after the COZ approach begins by directing attention toward preventing CSF leaks by searching for and obliterating any feature of the dissection that may result in a CSF leak. Any entrance into the paranasal sinuses or the eustachian tube should be obliterated with fat and fascia. Any tenuous or incomplete dural closures should be reinforced with tissue—preferably autologous—such as fascia, muscle, or fat. Fibrin glue can be used for further reinforcement. The thick pericranial flap is now brought down under the frontal lobe, over the orbit, and over any sinus entries in the middle fossa or petrous apex. The orbital roof is reconstructed to prevent late enophthalmos. Dural tack-up sutures are placed circumferentially, including the subtemporal region, to obliterate dead space and prevent postoperative development of epidural hematomas. If the frontal sinus has been entered, the mucosa should be exenterated and the cavity packed with fat or tissue to prevent mucocele formation and CSF leakage. The cranioorbital flap is secured in place with titanium miniplates. Bony defects can be obliterated with titanium plates or mesh, or any of several cranioplastic materials, such as hydroxyapatite cement. The temporalis muscle is sutured to the superior temporal line. The zygoma is plated into position with titanium miniplates. The scalp is closed in layers and a craniotomy headwrap is applied to decrease postoperative fluid collection under the flap.

Zygomatic Approach Lumbar drain placement facilitates brain relaxation and temporal lobe elevation. Scalp incision, temporalis dissection, and zygomatic osteotomies are performed as previously described ( Figs. 25.3, 25.4, and 25.5 ). Four burr holes are placed ( Fig. 25.11 ): the first in the keyhole, the second low and anterior in the middle fossa, the third low and posterior in the middle fossa, and the last along the superior temporal line. These four burr holes are connected using a craniotome. Residual bone along the sphenoid wing or temporal squama can be removed with the craniotome as well. Dissection along the middle fossa floor (dural elevation, middle meningeal artery division, GSPN dissection, and acquisition of proximal carotid artery control) is performed as previously described ( Fig. 25.7 ). Further dural elevation exposes the confines of the petrous apex: the lateral aspect of V3, the GSPN, and the facial hiatus. If exposure of the petroclival area is required, then the petrous apex is drilled down. Lateral entrance is similar to the extradural lateral cavernous sinus entrance previously described. The dura propria overlying V3 is incised and peeled away from the trigeminal branches and ganglion. Further dissection of the dura propria reveals V1 and the fourth cranial nerve. Anterior extension from the Meckel cave is exposed by drilling bone around the foramina rotundum and ovale to allow exposure of the sphenoid sinus and infratemporal fossa. If intradural extension of the tumor is discovered, such as with invasion into the temporal lobe and cisterns anterior to the brain stem, then intradural exposure can be easily obtained using this approach ( Fig. 25.10 ). Lateral intradural entrance as already described can also be performed using this approach, although distal control of the carotid artery cannot be obtained.

Closure of the zygomatic approach requires meticulous attention to prevent CSF leaks, as described. A strip of posterior temporalis muscle is placed along the petrous apex to prevent leakage. The remainder of the closure is similar to that of the COZ closure.

Dissection within the Cavernous Sinus Dissection within the cavernous sinus is performed with microdissectors and microscissors. Sharp dissection is performed, whenever possible, to prevent traction of intracavernous cranial nerves and arteries. Coagulation, where necessary, should be bipolar. As mentioned, once the cavernous sinus is entered, the abducens nerve should be located and preserved. Venous bleeding can be controlled using head elevation and judicious packing with hemostatic agents. Any cranial nerve that is frankly severed should be directly repaired. If a tension-free direct repair is not possible, an interposition graft should be performed. Injury to the carotid artery can be addressed in several ways. Temporary clipping and direct repair of tears can be performed with 8–0 suture; more severe carotid injury can be treated by vein graft repair.