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Encasing Foramen Magnum Meningioma: Transcondylar Approach

April 29, 2016


Let's review resection of a very fibrous and partially calcified foramen magnum meningioma encasing the surrounding neurovascular structures, including the vertebral artery and the lower cranial nerves. This is a 51 year old female who presented with hypoglossal nerve palsy and mild gait imbalance, and my evaluation revealed this foramen magnum meningioma extending from jugular foramen all the way to the ventral aspect of the brainstem. The vertebral artery was encased by the tumor. There was no evidence of edema within the brainstem. Obviously there is significant amount of mass effect on the brain stem from this tumor. CT scan, and more specifically, a CT angiogram demonstrated partial calcification of this tumor and significant encasement of the vertebral artery. Sagittal imaging again demonstrates the proper location of this mass. Further CT angiogram sequences are also included for analysis of their relationship of neurovascular structures to the tumor. Preoperative MRI examination revealed left-sided tongue atrophy as expected based on the effect of this tumor. You can see the positioning for this patient. "Hockey-stick" incision was utilized. Brainstem auditory evoked responses were monitored. Preoperative evaluation of the lower cranial nerves did not reveal any evidence of cranial nerve 10 palsy. Let's go ahead and first review the techniques for a minimal condylectomy or a minimal transcondylar approach. You can see the skull flap has been reflected laterally and inferiorly. I like the hockey stick incision because it moves their thick myocutaneous flap off the suboccipital region, out of my working zone. The suboccipital bone is exposed. Here's the C1 lamina, cranial cervical junction. I'll go ahead and start with small lateral suboccipital craniectomy. Rongeurs may be used to resect more bone. Floor of the posterior fossa is evident. Kerrison rongeurs may be used to further extend our bony removal. Posterior portion of the mastoid bone is also resected. The region of the sigmoid sinus is unroofed. The forum to magnum is then opened. Want to remove all proceeds laterally. Drilling of the more lateral lip of the foramen magnum continues, until the condyle is encountered. You can see at some point, the inner contour of the foramen magnum is evident as the bone curves anteriorly, marking the start of the condyle. Next I conduct a C1 hemilaminectomy. Troughs are created. Here you can see the vertebral artery entry point into the dura. C1 hemilamina is then resected. Here you can see the vertebral artery, one more time here. The condyle and I continue a minimal condylectomy. Unless the vertebral artery is mobilized out of its foramen only a minimal condylectomy is necessary for resection of the most ventral foramen magnum meningiomas. I do not believe extreme far lateral or immobilization of the vertebral artery is necessary for any ventral foramen magnum meningioma. Here is continuation of our condylectomy. You can see that the bone is moving away me now. Essentially I'm drilling the bone along its long axis. The condylar vein may be encountered, and it's bleeding from this structure can be readily controlled with bone wax or thrombin soaked gel foam. Here you can see the, again, the entry point of the vertebral artery. The thin shelf bone more medially is also subsequent resected. We're just about ready to open the dura. Here's the extent of the bony removal. Craniocervical junction, vertebral artery entry point into the dura. Coronal near dural incision is in order. CSF is drained from cisterna magna. You can see the dural incision starting first inferiorly and then superiorly, joining each other at the area of the foramen magnum. So here's the dural opening. The dura is mobilized laterally. Here's the tumor readily visible without any significant retraction of the brain or spinal cord. Since I expected the neurovascular structures to be engulfed in the tumor, my first role is to find the entry point of the vertebral artery into the intradural space and estimate it route within the tumor. So you can see some of the C1 nerve roots are incorporated in the tumor. Here's the accessory nerve, ascending superiorly into the jugular foramen. You can see the nerve is definitely engulfed by the tumor. Some of the lower cranial nerves appear engulfed by the tumor as well. This appears to be distal PICA. Let's go ahead and start with devascularizing the tumor. The 11th cranial nerve is mobilized. Now I want to find the route of the vertebral artery. Here you can see the artery within the tumor, micro doppler ultrasonography is used to confirm the artery. Next I continued to work around the artery to remove tumor. My goal is devascularize the tumor along it's base. On the lateral dura, again, working on both sides of the 11th cranial nerve. Here is further devascularization of the tumor from the lateral foramen magnum dura just beneath the jugular foramen. Again, the artery is apparent. One has to be careful not to enter or injure the wall of the arteries inadvertently. Sharp dissection is used as much as possible. I continue to familiarize myself with the morphology and the boundaries of the tumor. Now that the tumor is devascularized as much as possible I continue to use the ultrasonic aspirator to debulk the tumor. Further debulking would allow me to identify the more medial capsule of the tumor. More debulking is necessary, therefore I continue to disconnect the tumor from the lateral foramen magnum dura. You can see the artery, a tumor, some of the C1 nerve roots engulfed in the tumor mass. I suspect that the lower cranial nerves are also engulfed as this tumor invades the jugular foramen, therefore subtotal removal is mandatory for protection of neurological function. My goal is to decompress the brain stem and use radiosurgery as an adjunct to deal with the tumor. Tumor quite fibrous and partially calcified at this location, and the artery, curving now medially and anteriorly, the tumor mass, the brainstem gently mobilized by the suction device. Here's the vertebral artery traveling anteriorly and medially. The tumor fills in essentially this space within the contours of the vertebral artery. Here are the branches of the lower cranial nerves engulfed in the tumor. I continue to debulk the more superior pole of the mass. Now I'm working essentially inside the space where the vertebral artery turns around to reach the ventral brainstem. Here is, again, the more distal aspect of the vertebral artery. Tumor appears to be less adherent to the artery at that point. You can see the procedure is quite tedious. Tumor has to be removed in really very small layers or thin layers in order to protect any injury to the surrounding neurovascular structures. Here is the most distal part of the vertebral artery that is visible at this time. I'm able to create a plane between the distal part of the vertebral artery and the tumor capsule. Obviously it's quite anxiety provoking to use the ultrasonic aspirator in such a close proximity of the vertebral artery. Reasonable decompression is achieved. The portion of the tumor that is entering the jugular foramen is left behind to protect the lower cranial nerves. This is a more anterior part of the tumor being coagulated and resected away from the brain stem, to again, achieve my ultimate goal of relieving the pressure on the brain stem and the upper spinal cord. Working along the ventral aspect of the brain stem to remove additional pieces of tumor. And the vertebral artery's turning more laterally and posteriorly. Now the tumor is being dissected away from the distal vertebral artery just before where the artery joins the basilar artery. Arachnoid membranes are exploited to remove tumor. Here's part of the dura along the ventral brainstem or on the contralateral side that appears intact. In working around the curves of the vertebral artery to remove additional tumor. Now I'm rerouting my focus to removing the tumor below the vertebral artery. Space is quite limited. Here, again, working underneath the artery to disconnect the tumor and debulk the tumor using the same set of steps that were used to remove the tumor above the vertebral artery. And you can see how close the ultrasonic aspirator is to the vertebral artery. Proximal control of the artery has to be kept in mind at all times. Now, working deeper within this small triangle to remove the tumor and relieve the pressure on the upper spinal cord. Part of the tumor appeared softer. Now that part of the tumor in this area is decompressed, the tumor capsule is mobilized away from the spinal cord. You can see an angled curette is utilized to push the tumor into our resection cavity. Working just anterior to the age of the artery to remove this portion of the tumor embraced by the artery. Somewhat a high risk procedure. One has to obviously avoid any injury to the wall of the vessel. Now the ultrasonic aspirator works just anterior to the artery to remove the tumor. Tumor is quite fibrous at its space near the dura. Again, this angled curette is very useful to gently mobilize the calcified part of the tumor. This maneuver minimizes any retraction on the spinal cord. Again, unfortunately, it's impossible to achieve a gross total resection here. The goal is preservation of function and sub-total tumor removal with maximal decompression of the brain stem and the spinal cord. I'm reaching the dura on the ventral aspect of the brain stem. Sickled landmark to confirm that reasonable decompression of the upper spinal cord is accomplished. Here's the dura. Again, I continue to curette the part of the dura that is affected by the tumor. The involved and infiltrated dura is heavily coagulated. You can see the two operative working channels around the vertebral artery. Here's another piece of the tumor just underneath the portion of the artery that is curving around the brainstem. This part was very fibrous and highly calcified. Nonetheless, I persisted and worked around the vertebral artery to remove the tumor from the brain stem. Here's the route of the vertebral artery. See the portion of the tumor infiltrating jugular foramen. It's a better view with the lower cranial nerves incorporated in the tumor. Again, part of the tumor that is unresectable is heavily coagulated when safe. Another view of our operative cavity, essentially at the end of the operation. And the magnified view. Postoperative MRI revealed reasonable decompression of the brain stem. This patient did not have any new neurological deficits after surgery and subsequently underwent radio surgical treatment. Thank you.

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