Surgical Steps

Removal of clinoidal meningioma is best achieved with a wide frontoorbital craniotomy. Other names used for this craniotomy are extended pterional approach or extended pretemporal approach. In addition the craniotomy should include a very low threshold to include the orbital roof in the craniotomy flap (cranioorbitozygomatic approach) to be able to access the suprasellar extension of these tumors without the need of excessive frontal lobe retraction. In the overall majority of our cases, we are able to avoid or minimize the use of self-retaining retractors.

Once the craniotomy is established, we proceed with the extradural work that leads to the removal of the anterior clinoid process. The steps include dissection of the pretemporal and subfrontal dura away from the sphenoid wing, which will be removed with the posterior roof of the orbit. Then the dural fold at the level of the meningioorbital artery is cut to allow disconnection of the dura propria of the temporal lobe from its attachment to the frontal dura across the sphenoid wing over anterior clinoid process. This will bring the anterior clinoid process to a more superficial point. This process of exposing the anterior clinoid process in and of itself leads to significant devascularization of the tumor, which gets its blood supply from anterior dural branches of the middle meningeal artery as well as the meningioorbital artery. It also gets blood supply from posterior ethmoidal branches, which normally provide blood supply to the clinoidal and frontal fossa dura. In addition to tumor devascularization, this extradural work will help expose the clinoidal internal carotid artery segment. The exposure of the clinoidal internal carotid artery and later exposure of the sylvian fissure arterial branches will provide the two normal ends of the vascular tree, which can then be dissected proximally and distally as the tumor is being resected. This provides a good road map for the course of the internal carotid artery as it merges with the middle cerebral artery and anterior cerebral artery at the level of the carotid bifurcation.

Once the extradural work is done, the intradural exposure is performed by opening the dura and visualizing the suprasellar and posterior borders of the tumor. The sylvian fissure is routinely opened from the level of the limen insulae toward its proximal point to help visualize the whole course of the middle cerebral artery. Once this is achieved, debulking of the tumor is started with intermittent dissection of the tumor away from the adjacent brain and blood vessels. Once adequate debulking is achieved and the course of the different arterial branches is visualized, final tumor removal is performed. The dura at the base of the skull and over the clinoid region is totally removed. The underlying bone, which has partially been removed during the extradural removal of the anterior clinoid process, is further drilled and resected with a high-speed diamond drill and copious irrigation aiming at as complete a resection as possible and at the same time achieving bone hemostasis.

As part of the process of removing the anterior clinoid, the optic canal is decompressed by removing the optic strut and the optic roof. The dural layer over the optic canal is opened along the optic nerve. This allows access to tumor extending into the optic canal. Even though this is more common in type III tumors, we perform this step in all tumor types. The tumor is followed along its extension into the orbit. Extra caution is taken while dissecting the optic nerve to preserve the very small blood vessels providing blood supply to the optic canal from the superior hypophyseal branches. It is also important to pay attention to the fact that occasionally direct arterial supply from the ophthalmic artery close to its origin may inadvertently be injured. This can best be avoided by careful dissection with magnification and with the anatomical knowledge of those vessels.

In tumors that extend further laterally, the dissection of the temporal dura away from the lateral wall of the cavernous sinus may be extended to a more posterior point to remove tumor extending into the region of the cavernous sinus. In tumors with extensions toward the suprasellar and subchiasmatic regions, it is important that the dural ring around the internal carotid artery be dissected to widen the space between the internal carotid artery and the optic nerve to gain access to the tumor segments extending into the subchiasmatic and possibly retrochiasmatic region. Occasionally these tumors extend more posteriorly along the tentorial edge and compress the third nerve inferiorly. The third nerve can be identified extradurally at the level of the superior orbital fissure and followed from its extradural to its intradural segments under full visualization to mobilize and avoid its injury during tumor resection.

Gross total resection should always be the goal of surgery ( Fig. 24.9 ). However, in type I tumors where there is no arachnoid layer to separate the tumor from the wall of the internal carotid and its branches, good judgment is exercised to decide the extent of tumor resection to avoid injury to adherent vessels and to avoid additional morbidity ( Fig. 24.10 ).

Once the appropriate degree of resection is achieved, the reconstruction of the skull base is carefully attended to. The dural defect is reconstructed with dural replacement materials. In our experience, the best tissue to be used is either fascia lata or pericranium. This is reinforced with subcutaneous fat harvested from an abdominal incision to be used for obliteration of the clinoidal space, especially if there is communication with the sphenoid sinus. The closure is reinforced with fibrin glue. We avoid the use of lumbar drains because adequate closure rarely leads to a spinal fluid leakage.