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Foramen Magnum Meningioma: Transcondylar Approach

February 13, 2016

Transcript

The Transcondylar approach provides a very wide trajectory and operative corridor toward the ventral cranial cervical junction. Let's go ahead and review this approach for a magnum meningioma. This is the case of a 32-year-old female who presented with progressive quadriparesis and gait difficulty, and MRI evaluation demonstrated a classic foramen magnum meningioma primarily located along the ventral as well as a ventral-lateral aspect of the foramen magnum on the right side. You can see the dural tail and obviously evidence of the compression on the brain stem and encasing of the right vertebral artery. The patient underwent a procedure in the lateral position. You can see the acoustic incision, which is my favorite. The location of the mastoid tip. Location of the inion. I like the hockey stick incision because it reflects the myocutaneous flap laterally and out of my working zone. It also may be potentially associated with less postoperative pain because the vertical incision is within the avascular plane along the midline. Linear or lazy S incisions have been previously used. However the working distance may be increased due to the fact that the muscle groups are accumulated underneath these soft retaining retractors. The head is turned just about 40 degrees toward the floor so that the mastoid bone is the highest point on the operative field. The shoulder is mobilized anteriorly and inferiorly. Here is the rotation of the head. MRT magnified view. Again demonstrates the position of the body. Somatosensory evoked potentials and motor evoked potentials were monitored. The avascular plane along the midline is found. Suboccipital muscles are reflected in one layer with the scalp. This ponticulus posticus of C1 is found. Monopolar electrocautery is not used around the lateral aspect of C1MI lamina so that the vertebral artery within the Sulcus arteriosus is not injured. I typically use blunt and sharp dissection techniques to isolate the Vertebral artery encased by its corresponding venous plexus. Soft tissues over the artery are dissected. Lateral mass of C1 is exposed. I find the exact entry point of the vertebral artery in the dura. And again, the soft tissues are removed for anatomical orientation. Here you can see the exact entry of the artery into the integral space. A small suboccipital craniectomy is all that is necessary up to the lateral edge of the foramen magnum. Next a C1 hemilaminectomy is performed. And a medial part of the lateral mass is removed. They extend upon removal on the lamina of the C1 should be up to the point where the vertebral artery turns superiorly to enter the dura. Here you can see the minimal resection on the medial component of the C1 lateral mass. Next a very minimal condylectomy or Condylar resection is quite adequate. The condylar vein is found and controlled with bone max or monopolar cautery. Again this may lead to contractions of the 11th nerve. Here's the portion of the operation wherein very minimal amount of condyle is removed. The extent of condylectomy is essentially up to the point where the lateral rim of the foramen magnum is found, or when furthermore of the bone is stopped because of the lateral rim of the foramen magnum. This extent of bone removal essentially corresponds to the points just lateral to the entry point of the vertebral artery. Vertebral artery mobilization or the extreme far-lateral approach is unnecessary. This amount of bone removal is quite adequate for removal of purely ventral foramen magnum tumors. Since the tumor does provide some working space for its removal by displacement of the neurovascular structures. If the vertebral arteries is not mobilized, additional bone removal is not of any importance or practical usefulness since the entry point of the vertebral artery in the dura would tether further mobilization of the incise dural flap laterally. Here's the final product. You can see the vertebral artery entering the dura. A very minimal condylectomy. The cranial cervical junction and its corresponding dura. I opened the dura along the lateral edges of bone work. The dura is reflected aggressively laterally and medially so that the lateral to medial operative working angles are maximized. The vertebral artery's also gently mobilized laterally. In this case, the 11th nerve is apparent. Obviously the tumor is readily approachable. The arachnoid bands are then dissected and the important neurovascular structures, including the cranial nerves 11 and the vertebral artery just entering the intradural space are found. The first step is devascularization of the tumor from the lateral aspect of the dura and debulking of the mass. These two maneuvers allow early mobilization of the tumor and identification of additional important structures located more cranially. Here's a large piece of the tumor that has being removed. Here is the lower cranial nerves. You can see the entry point of the vertebral artery into the intradural space. Here again is a more magnified view of the vertebral artery displaced superiorly by the cranial pole of the tumor. Again the tumor is further devascularized at the point of its attachment over the lateral dura. Here you can see the vertebral artery turning medially and superiorly. I first identify the location of the neurovascular structures and then continue to aggressively de-bulk the tumor and mobilize it into my previous resection cavity. Here's the superior pole of the tumor that is again being dissected. Here's the final result of the resection cavity. The dura along the ventral aspect of the foramen magnum is not resected. However coagulated to prevent risk of future tumor recurrence. As you can see, this exposure provides ample amount of expanded operative routes or trajectories toward the ventral foramen magnum and craniocervical junction without significant manipulation of the brain stem or upper cervical cord. Here's a good view again of how this operative cavity was created. The dura is closed in a watertight fashion. Postoperative CT scan reveals really very minimal condylar resection, and again to the lateral edge of the foramen magnum. This upper provided a nice unobstructed operative trajectory toward the ventral cranial cervical junction and upper and the lower clivus. Postoperative MRI in this patient also demonstrated complete resection of the tumor without any residual mass and this patient's preoperative symptoms dramatically improved after surgery. Thank you.

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