Lateral Suboccipital Exposure and PICA Aneurysms
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Let's talk about the Lateral Suboccipital Exposure and it's use for clip ligation of a posterior inferior cerebellar artery aneurysm. This is a patient of mine who presented with subarachnoid hemorrhage and a six millimeter right-sided PICA aneurysm. As you can see on the CT scans and the angiograms, the patient had evidence of subarachnoid hemorrhage along the posterior fossa and interventricular area, the angiogram demonstrated relatively anteriorly pointing PICA aneurysm. Interestingly, on the angiogram, you can see significant evidence of either a spasm or a stenosis, just proximal to the aneurysm, and also evidence of a small blister on the dome of the aneurysm. Based on this angiogram, I paid a special attention in surgery to make sure I have proximal control to the aneurysm by obtaining distal control, actually to the aneurysm. In other words, the retrograde flow, is going to be a significant in this case because most of the blood to the posterior fossa is coming from the contralateral vertebral artery. With that consideration in mind, let's go ahead and review the technical nuances of the exposure. The patient is placed in the lateral position. I like the lateral position because gravity retraction will clear the field of the blood and the fluid, and also allows me to sit during the surgery and performance of microsurgery. I like to turn the head about 45 degrees or so toward the floor. The mastoid area is the highest point on the operative field. A hockey stick incision is used, the inion is just about here. So the incision stays below the superior nuchal line. And this incision is just along the midline. There are variations of this incision, including a S incision or a paramedian linear incisions. Those are reasonable options and have been used by colleagues before. In my mind, the shortcomings are the fact that during the Paramedian or the S incision, much of the dissection occurs within the muscle rather than the avascular midline planes and therefore postoperative pain can be more significant. However, the more important reason why I like this incision is that the configuration of the skull flap allows the entire muscle to be mobilized out of my working area. However, the paramedian and the S incision cause the muscle groups to be bunched up underneath the retractor and therefore increase my working distance towards this surgical target. Neuro monitoring may be used if necessary, including Somatosensory evoked potentials, and monitoring of the lower cranial nerves. You can see their skull flap has been mobilized laterally using a couple of self retaining retractors upper hole was placed just lateral to the sigmoid sinus. I'm using this opportunity to orient you to the opera field. Again, this superior nuchal line and transfer sinuses somewhere here, the inion is there, this is C1 down here and this is the craniocervical junction. After the initial blurr hole was placed, Kerrison rongeurs were used to expand the Burr hole all the way to the edge of the sigmoid sinus, you can see the initial blurr hole was somewhat more medial than desired. I am outlining the location or the craniotomy at this time. Again, you can see the C1 craniocervical junction and number three Penfield dissector is being used to mobilize the dura from the inner aspect of the skull bone. This aneurysm was somewhat more inferior than a traditional pike aneurysm, and therefore a C1 laminectomy was the necessary tool to be able to achieve a more inferior to superior trajectory, to be able to handle the neck of the aneurysm. The craniotomy bone cuts are relatively traditional. You can see the initial blurr hole was placed below the transfer sinus. The foot plate can be stuck at the edge of the craniocervical junction or require some maneuvering of the tip of the drill to complete the bony cut right there at the foramen magnum. Obviously the vertebral artery is located somewhere here and has to be carefully protected during drilling. The last cut is placed closest to this sigmoid sinus. So bleeding can be controlled if there is some injury to the sinuses encountered. You can see because of the floor, the posterior fossa becomes more flat. It can be difficult to maneuver the drill, we left the lip of the bone over the potential space of the vertebral artery to avoid any injury to it. Now we'll go ahead and do the C1 laminectomy using the foot plate. C1 hemilaminectomy. After that piece of the bone is removed. We have more work to do in terms of removing more of the lateral suboccipital bone and potentially part of the lamina till we get a more lateral trajectory intradurally. A condylectomy is not necessary in this case. This is primarily a lateral suboccipital approach for a PICA aneurysm. This approach is not the best fit for Forumen Magnum Meningioma that are most likely ventral lateral anterior along the intradural space. We'll go ahead and extend the bony remove just lateral to the condyle here again is the suboccipital bone, some bleeding from the venous plexus along the vertebral artery is relatively common. The Dura is turning away from us, which means that we are reaching the appropriate location for our bony removal. The ligaments along the craniocervical junction are mobilized. This is the entry point of the vertebral artery. After the lateral mass of the C1 has been drilled away. Here's the final product of this exposure you can see the vertebral artery, the C1 and the craniocervical junction dura. Further bony removal laterally on the conduct can sometimes not be effective as much since the entrance point of the vertebral artery would tether and obstruct the operative view intradurally unless, the vertebral artery will be mobilized through its framing, which I believe is exceedingly rarely necessary. Vertebral artery pulsating. Ample irrigation is used to clear all the debris before intradural work has started. I think this approach is very appropriate for reaching many of the lesions that were traditionally requiring a far-lateral transcondylar approach. The dura is open just parallel to the edges of the bone and reflected laterally. Switchers are placed at the root of the dura to mobilize the dura as much as possible away from our working zone. You can see they're really mobilized laterally. Small amount of bone can be obstructive, but most often is not. Here is the exposure of the vertebral artery intradurally as it's moving anterior to there. Can use cervical junction. The urachal membranes are widely opened. Now that we found a vertebral artery, we will go ahead and find PICA and then look for the junction of PICA and the vertebral artery where the aneurysm is located. So here's the loop of the PICA. Here's the lower cranial nerves. You can see here, the loop of the PICA goes up and then comes down where the aneurysm is most likely going to be here. Therefore, the entire skeletonization of the PICA may not be always necessary just as you'll see in this case. I realized that the PICA is looping down by the section, through the clot, within the subarachnoid space. Here again, you can see the lower cranial nerves, C1, nerve roots, the loop of the PICA going up and down, the vertebral artery going here. So the aneurism should be located at this location. Again, vertebral artery going up, the loop of PICA going or coming down. And here's the location of the aneurysm. Most likely pointing ventrally, or immediately. Here, you can see a peek of the neck, just about here. Actually, that was the origin or distal vertebral artery is very dominant here. It is not the aneurysm, but this provides a proximal control in fact, because as we discussed during the beginning of the video, this is the dominant retrograde flow to the aneurysm. So the aneurysm is on this side and you can see the neck just about here. You can see the stenosis in the ipsilateral vertebral artery. The distal control here acts as proximal control in fact, because of the angiographic finding we discussed at the beginning of the case. So now that we have proximal control, we can dissect the aneurysm more aggressively with a high-risk maneuvers, that would allow us to appreciate thoroughly the neck of the aneurysm. I spent significant amount of time, completely dissecting the neck of the aneurysm and thoroughly understand the path or anatomy rather than placing a clip more blindly across the neck and asking the blades of the clip to perform the dissection. Here is the near aneurysm more inferiorly and thoroughly dissected. I want to look anterior to the neck and be able to find the anatomy there. Now I move more distally and find the distal neck and work around it. Again, the ventral plane is not dissected very well yet. Here is more dissection sharply around the neck. A period of reperfusion was allowed and a temporary clip was placed again, both proximally and distally to trap the aneurism. So now I can really mobilize the aneurysm ventrally and appreciate the depth where the clips should be sitting. Because if I don't appreciate how far the neck goes, I can place the clip blindly and actually tear the aneurysm anteriorly. As the blades are trying to find their space or the route anterior to the neck. This is really important for safety of clip application, to make sure that the route of the blades are clearly clear of any obstruction Here, you can see the angle of clip, a chimney, a very nice reconstruction of the neck without any residual aneurism. Looking around the blades. There is no complicating features or anything else besides the aneurysm neck, within the blades, all the perforators are protected most likely. Here again is a higher magnification of the view of the neck and it's obliteration by the blades. I'm very satisfied with this clip configuration. You can see the magnified view of our operative working space. And this is a postoperative angiogram, which demonstrates complete exclusion of the aneurysm without any complicating features. You again, can appreciate the dominant flow from the contralateral vertebral artery, which requires control during surgery for management of the neck, and be able to deflate the aneurysm enough to dissect anterior to the neck for a proper application of the clip plates. Thank you.
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