Optic Foramen Meningioma: Intradural Clinoidectomy
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Optic foramen or medial sphenoid wing meningiomas are well-suited for resection via transcranial corridors and more specifically via intradural and extradural clinoidectomies. This is a 40-year-old male, who presented with visual deficits affecting primarily the right eye. MRI evaluation demonstrated a relatively homogeneous enhancing mass along the medial aspect of the clinoid process. The coronal images confirm the location of the mass relative to the carotid artery and intraclinoid process. Slightly more anterior coronal sequence demonstrated double density along the optic nerve within the optic foramen, confirming infiltration and in-growth of the tumor into the foramen. This double density is not evident on the left side. Due to progressive worsening of his vision, he underwent a right frontotemporal craniotomy. The dura was inadvertently cut during the exposure. A lumbar drain was used at the beginning of the procedure, as I was planning to use an extradural clinoidectomy technique to remove the bone and decompress the optic nerve very early on. However, as you can see, the dura was noted to be very adherent in the subfrontal area. In addition, I attempted to cut about five millimeters of the frontotemporal dura or orbital meningeal band to further expose the clinoid to accomplish an extradural clinoidectomy. However, this was not feasible, partly because the tumor had affected the superior orbital fissure. Here is a attempt to decompress the optic nerve. However, the working space was very narrow. The dura was very adherent. This could have been partly related to the tumor in that area. I opened the dura in a curvilinear fashion. The tumor is exposed. All the arachnoid membranes over the chiasm and underneath the frontal lobe are dissected. This maneuver allows gravity retraction of the frontal lobe away from the tumor. Here is the ipsilateral optic nerve, just medial to the tumor that is identified early. Next, I'm going to find the carotid artery at the level over the skull base. Here, you can see the contralateral optic nerve, the chiasm for this section, again, along the medial aspect of the mass. Here is further dissection, just posterior to the tumor, releasing the arachnoid bands. Here's the A1, just underneath the frontal lobe. Now, I'm finding the internal carotid artery as promised. Identification of the internal carotid artery, and optic nerve, and other neurovascular structures early on adds significant efficiency to the procedure. Since I know the location of these structures early on, they can be kept out of harm's way while proceeding with efficient resection of the mass. I like this maneuver of scooping the tumor away from the carotid artery and the ipsilateral optic nerve, creating more mass to mobilize the tumor and conduct further dissection with the ipsilateral optic nerve under direct vision. Here's the posterior aspect of the ipsilateral optic nerve that is quite evident. Now, the tumor is being devascularized from the dura over the clinoid process. Tumor is removed piecemeal using pituitary rongeurs. Here is the more proximal aspect of the carotid artery at the level of the skull base. The arachnoid bands between the artery and the tumor are respected as much as possible. Here's the carotid artery. Here's the ipsilateral optic nerve. Here is the tumor along the lateral aspect of the foramen. Most often the tumor seems to affect the medial aspect of the nerve as there is a potential space within the foramen medial to the nerve. But in this case, the tumor was based more laterally, and it's affecting the nerve along the lateral aspect of the foramen. However, I'm unable to dissect the tumor within the foramen because the clinoid process is preventing adequate visualization. An intradural clinoidectomy is necessary in this case. The dura is open over the clinoid. The falciform ligament is incised over the nerve or just lateral to it. The lateral dural incision over the clinoid process is connected to the falciform ligament incision. Here is the clinoid that has to be removed. Here is the bone over the roof of the orbit. Here you can see opening of the falciform ligament as much as possible. The flap of the dura is reflected posteriorly to cover the internal carotid artery and the optic nerve, and keep these structures protected during drilling. Next, I'm using an aero drill to remove tumor of the clinoid process, thinning the bone down to a thin shell that can be mobilized using angled ring curates. Here's the bone over the roof of the optic nerve, which will be removed next. Here's the angled ring curate moving the thin shells of bone. Ample monitor irrigation is used during drilling to prevent thermal injury to the optic nerve. Here is additional bony removal over the nerve. So, the entire roof is decompressed from the bony structures. Here's the flap of the dura. Here's the tumor along the lateral aspect of the optic foramen. Now, that the bone is removed, tumor is more apparent. This is a residual tumor. A carlin blade knife is used to cut the dura over the lateral aspect of the nerve, and not just immediately over the nerve, exposing the intraforaminal contents. You can see the fragment of the tumor within the frame, and that's being mobilized away from the nerve. This removal of the fragment is the last step of the operation before cutting the dura affected by the tumor more laterally. Here's the inside of the foramen that is very well decompressed. The ophthalmic artery will be in view momentarily. Here's some of the tumor feeding vessels that are being disconnected. Here's the lateral aspect of that tumor fragment over the dura of the clinoid process. Inspection of the foramen does not reveal any additional tumor under high magnification. Here's the origin of the ophthalmic artery, just underneath the optic nerve. Inspection of the contralateral aspect of the foramen does not reveal any evidence of tumor infiltration or compression. The nerve has to be investigated 360 degrees around it to assure complete and thorough decompression. Next, I'm going to look across to the contralateral optic nerve and assure myself that the tumor is not affecting the contralateral nerve, which isn't. This is the final result of the decompression. Next, the affected dura is cut, and unresectable piece of the dura is heavily coagulated to prevent the risk of future recurrence. The carotid artery, ipsilateral optic nerve, adequate resection. Post-operative MRI demonstrates complete resection of tumor. As you can see on these coronal images, without any evidence of complicating features, this patient's vision significantly improved after surgery. Thank you.
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