November 11, 2015
Let's review an interesting case of an optic foramen meningioma resected via a pterional craniotomy and extradural clinoidectomy. This is a 46 year-old female who presented with progressive left-sided visual deterioration and visual field dysfunction, and on MRI was noted to have a medial or clinoidal meningioma extending into the optic foramen. You can see on the higher resolution T1 coronal MRI with contrast, presence of the tumor within the optic foramen just medial to the nerve. Again, the nerve is at the tip of the arrow, and enhancing, this tumor is just medial to the nerve within the optic foramen. Endonasal endoscopic approaches may be used for removal of this tumor. However, the more lateral extent of the tumor may not be easily accessible via the transnasal route. I therefore elected on using a transcranial approach via extradural clinoidectomy. A lumbar drain was installed, a pterional craniotomy was completed, the roof of the orbit was drilled away, and the lateral aspect of the sphenoid wing was resected. The decompress dura was mobilized away from the clinoid process, the posterior tip of the clinoid required more exposure. Supraorbital fissure is apparent at the tip of the arrow. About five millimeter of the lateral aspect of the supraorbital fissure was transected. Next, the dura of the interior temporal lobe was gently mobilized away from the dura along the lateral wall of the cavernous sinus. This technique provided additional space for exposure of the poster tip of the clinoid process. The diamond drill was used to flatten the clinoid and allow additional space to access the bone over the optic foramen. The bone over the dura of the optic nerve was removed so that the nerve is decompressed early. This decompression of the nerve protects the nerve from traction injury during mobilization of the clinoid process, which we'll perform next. Ample amount of irrigation avoids thermal injury to the nerve. I continued to thin out the bone over the dura of the optic nerve. The last thin shell of bone is removed using micro curettes. Fixed retraction is avoided. Such retraction, in fact, can interfere with the flexible working angles at the deep aspect of the operative corridor. You can see the dura of the optic nerve is now exposed. There's still a shell of bone more posteriorly where the nerve enters the foramen. This last shell of bone is also thinned out so the nerve is completely decompressed from it's intracranial segment and as it enters the optic foramen. Now, the last thin shell of bone is also mobilized. The more medial part of the bone is removed, and the nerve appears nicely decompressed. My next maneuver would involve hollowing out the clinoid process. Generous coring out of the process is necessary so that decline of process can be disconnected from the optic strut and the lesser sphenoid wing. The optic strut is located where I'm drilling, between the clinoid process and the optic nerve. You can see that the process is quite still adherent, most likely to the optic strut, so further drilling is mandatory. The medial wall of the optic nerve is nicely exposed. The posterior clinoid ligaments can often tether the clinoid process as well. Now, the clinoid process is more manageable and can be manipulated. Pituitary rongeur was used to remove the remainder of the clinoid process. Here's the nerve widely decompressed. Some slight venous bleeding from the cavernous sinus can be easily controlled using thrombin-soaked Gelfoam agent of tamponade. A multi-magnified view demonstrates the optic nerve and the dura over it. I used an alternative incision configuration for approaching optic foramen meningeal mass, in this case, the initial dural incision is just anterior and parallel to the Sylvian fissure. This incision next connects to the dura over the optic nerve at the level of the foramen. Most of the dura over the subfrontal area is left intact to protect the brain. The arachnoid membranes and bands over the nerve are sharply dissected using an arachnoid band. Also the optical carotid cisterns are dissected. I use a Karlin knife to cut the dura over the nerve, preferably just on the medial edge of the nerve where the tumor is located. You can see the center of the attention is essentially at the more proximal segment of the optic nerve. The tumor is at the tip of the suction, just medial to the nerve, entering the optic foramen. The Karlin Knife continues to cut the dura toward the surgeon. Micro scissors further extend the dural incision just medial to the nerve. Expanded exposure of the tumor within the canal is necessary for its complete removal and adequate decompression of the nerve. Now I'm gonna focus my attention along the medial capsule of the tumor, where the arachnoid layers over the contralateral optic nerve are identified before the tumor is devascularized using electrocautery. Obviously I wanna avoid any injury from bipolar coagulation to any of the optic nerves. The tumor is devascularized along its base. Next, it's capsule is incised and pituitary rongeurs are used to debulk the tumor. These steps are repeated. As the tumor is devascularized, its internal contents are removed, its capsule is mobilized and further tumor debulking is accomplished. I avoid any direct retraction on the optic nerve. Here is the piece of the tumor just medial to the nerve is being incised. The tumor capsule is mobilized into the decompressed cavity. Rather than retracting on the nerve, I continue to retract primarily on the tumor capsule. Some bleeding is tolerated as aggressive use of coagulation is minimized to prevent thermal injury to the nerve. Now, the medial and posterior capsule of the tumor is displaced away from the contralateral optic nerve. The operative trajectory is subfrontal, just medial to the nerve where the center of attention is. The challenging part of the operation is tumor removal underneath the nerve. Let's review some of the techniques to facilitate safe tumor resection. Here again, is the posterior aspect of the contralateral optic nerve. That part of the tumor is being removed piecemeal. The oblique operative working angle toward underneath the nerve is apparent. The posterior capsule of the tumor is now exposed, and again, mobilized into our resection cavity. This tumor is quite fibrous. Angled instruments are quite important for dissecting the tumor underneath the nerve. Here's another large piece of the tumor from underneath the nerve that is being removed. The bleeding from the dura underneath the nerve is not readily controllable, and aggressive coagulation in this area blindly is avoided. Here's the piece of the tumor entering the anterior part of the foramen. This piece of tumor also is dissected using angle dissecting probes. Following disconnection of the tumor, Pituitary rongeurs remove this compressive portion of the tumor. This small piece of the tumor should definitely be removed, as it's postoperative swelling can lead to acute compression of the nerve and visual deterioration after surgery. Some of the dura just underneath the nerve is now coagulated. Next, I explore the lateral border of the nerve to assure myself no piece of a tumor in this area is being overlooked. You can see the right-angled dissecting probe. Gentle handling of the nerve is mandatory. There's only a very small piece of the tumor is left behind more medially. The attachment of this part of the tumor has been quite coagulated to minimize future risk of recurrence. Now, some of the dura along the lateral aspect of the nerve is dissected, so this portion of the nerve can also be carefully investigated. You can see this was the discolored area of the nerve, where the falciform ligament was compressing the nerve by the mass effect of the tumor. The medial part of the nerve is quite decompressed. However, the lateral port may still contain a small piece of tumor. The carotid artery is apparent. This residual small piece of tumor is also being delivered into our resection cavity. Now, most of the tumor appears gone. The nerve is quite widely decompressed. The contralateral optic nerve is also investigated and its foramen appears unaffected. You can see the all-around circumferential decompression of the optic nerve and its foramen, you can see the configuration of the dural opening limited essentially to the area of our work. Most of the brain is still unaffected, and the dura of which is intact. A piece of temporalis muscle is placed within the clinoidectomy area, ensuring that the nerve is not compressed by the piece of muscle. Watertight dural closure obviously is not possible. Postoperative MRI in this patient demonstrated complete removal of the mass. The CT scan also demonstrates a complete clinoidectomy. This patient's vision recovered after surgery, and she also recovered from her surgery without any sequelae. Thank you.
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