Grand Rounds: Clip Ligation of Challenging Posterior Circulation Aneuryms

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- Hello, ladies and gentlemen, and welcome to another session of the Grand Rounds. This will be a two-part session with Dr. Nick Bambakidis, a skull-based and cerebrovascular surgeon from Case Western University Reserve. The first session, we'll talk about complex posterior fossa aneurysms. And the second session, we'll discuss management of skull-base tumors specifically in the same region. Thank you.

- Well, thank you. And I appreciate the opportunity to discuss some of the nuances in dealing with some challenging cases, which we face, particularly in the posterior cranial fossa and skull base. And so what we'd like to do is discuss some difficult aneurysm cases in the beginning of our presentation. In terms of the posterior circulation, as we all know, surgical clipping has been the standard treatment for many decades, prior to the development of endovascular techniques, and overall is quite successful at the obtaining a high occlusion rate of these lesions with very low recurrence rates. However, the difficulty is, I hope to illustrate to you is the challenging anatomy and diminished visualization in dealing with these lesions, which can result in a relatively high morbidity and mortality range, anywhere from 15 to 30%, much higher than that of a carotid circulation aneurysms. So this discussion will be a case-based discussion, hopefully giving you some examples and some learning and teaching points in dealing with these difficult lesions, because they still do come up on a not irregular basis, even in the modern endovascular era. As I mentioned, the exposure is more involved in the vertebral circulation during the anatomic dissection that perforator preservation is critical. And so in terms of the specific exposures necessary, we generally discuss them in these and organize them in this particular fashion, first discussing the far lateral approach in approaching the vertebral basilar junction, The orbitozygomatic craniotomy is a standard approach for anteriorly-based lesions, superiorly based lesions, and the transpetrosal approaches are still utilized for specific instances, particular in certain tumors of the skull-base anterolateral skull base. And we'll discuss that near the near the end of the presentation. The far lateral approach is really a workhorse approach for accessing vertebral basilar lesions, particularly PICA aneurysms. Here in this illustration, you can see how the patient typically is positioned. In fact, this illustration probably overestimates the amount of head rotation that is utilized. I in performing this craniotomy. And in terms of the exposure, the standard approach utilizes curvilinear incision, starting at the midline at the level of C2, curving around up above the nuchal line and ending just posterior to the ear. And then, the exposure really involves the foramen magnum, as seen here, and the C1 vertebral arch. And of course, the important landmark here is the vertebral artery, which lies just above the C1 vertebral arch, before entering the dura. I typically try and do a craniotomy, particularly in younger patients, based at the foramen magnum, and then can either do a hemilaminotomy or hemilaminectomy at C1, again, being aware of the vertebral artery. Once the bone is removed, the dura can then be open in a curvilinear fashion, based laterally. This caudal vein typically is an important landmark that can be utilized during drilling of the occipital condyle, which allows for increased exposure laterally. And again, this shows the view that one can obtain once the dura is open.

- One detail I wanted to add Nick, if that's okay with you, is some of the muscular branches from the vertebral artery, and on dissection can be very problematic and cause bleeding. And one may confuse them with a bleeding from vertebral artery, especially around the area where it turns over the arch of C1. So if there is small muscular branches, it's best to coagulate them and cut them carefully, rather than evulse them, and potentially place the vertebral artery-

- And another important point of course, is the vertebral plexus that one often has to deal with around the vertebral artery can be variable in its size. And really, a great degree of patience is sometimes necessary when dealing with that.

- Thank you.

- So here, just start by showing a case of a 32 year old gentleman who presented with a subarachnoid hemorrhage and a headache. And you can see here, the vertebral artery giving way to PICA where you see a fusiform aneurysm arising at the junction of the vertebral and PICA branches. So this is the classic case that you would deal with, a left sided, far lateral craniotomy to approach. So you can see here, the positioning of the patient and the large incision, beginning at the midline, curving around, as shown in the illustrations. In this particular case, we're prepared for revascularization of the PICA, given the fusiform nature of the aneurysm. One of the bypass options that you have in the posterior fossa is the occipital artery's donor vessel. And you can see here the occipital arteries dissected out, as it runs just underneath the pinna of the ear, the mastoid, up through the scalp can often be found at the top of the incision and then traced back, dissected through the muscle and subcutaneous tissue can be quite tedious, but can give you a robust vessel that you can see here to save just prior to opening the dura and exploring the aneurysm. So you can see here just a quick video, the occipital artery coming down the PICA distal to the aneurysm has been exposed. This is the left far lateral craniotomy from the previous illustration and with temporary clips on either side of the PICA, and suturing the occipital artery, and an end to side fashion. It's important to have a set of long bypass instruments for these deeper anastomoses. And then you can see here, the, the final result with the aneurysm here, approximal, you can see here in the occipital artery being sewn into the PICA, which has been trapped distally, and here the final result with the occipital and the side anastomosis with the aneurysm occluded approximately.

- [Aaron] One question always is how difficult is it to harvest the occipital artery, Nick? And do you have any technical nuances about the fact that how torturous the artery is, and it's very difficult to dissect it because of its unreliable route within the muscle?

- [Nick] It can be very difficult to do that. Typically I'll find the artery at the top of the incision. And really, it's a matter of patience. And in dissecting the muscle, the artery out of the muscle, it can be very torturous. If you run into side branches from the occipital artery, it's important to coagulate them or tie them well away from the blood vessel. And it's also important to reduce any tension on the occipital artery is it's coming out from under the ear, because it can be caught in the underlying muscle. So you often have to divide that muscle to loosen the artery enough to bring it into your field. In this second case, again, this is a young gentleman with the sudden onset of a headache in subarachnoid hemorrhage from this fusiform PICA aneurysm. The right vertebral artery ends in PICA in this case, as you can see here. So this is approached again, with a, this time, right-sided far lateral craniotomy. You can see here again, this is a right-sided far lateral craniotomy. The cerebellar tonsil here is reflected superiorly. Here's the right PICA, here's the contralateral PICA, and here's the fusiform aneurysm coming into view. Here's proximal PICA here. We placed a clip on one of the aneurysm domes from which the rupture point was located, but you can see the entire PICA is diseased. So in this particular instance, we need to revascularize the distill distribution of the vessel. And so here, you can see freeing up the distal PICA. And in this instance, the options that you have are either the occipital bypass, a side to side PICA a bypass, or in this case, I elected to do a transposition, simply cutting the distal PICA and reinserting it on the proximal normal vessel, essentially excluding the aneurysm. So here you can see that this is the distal PICA here, proximal PICA here, and an end-to-side anastomosis with distal occlusion of the aneurysm.

- Nick, is there any advantage of intermittent versus a running stitch? I assume you were using 10-0.

- Yeah. 10-0 suture. I tend to go ahead and run the anastomosis in most instances, simply because it's a little quicker, otherwise, really no advantage, in my opinion. Of course, as with all anastomosis like this, it's very important to have a very tension-free vessel so that you can move it easily from one side to the other. And so you can see here once the proximal temporary clip is removed, you can confirm flow in the distal PICA. In this case, you see both PICAs are quite far away from one another. So a PICA to PICA bypass would have been more difficult. Another limitation in doing what was done here is that you can have brainstem perforators and PICA. Here's the ICG showing the bypass filling a bit slower than the other side, simply because this vessel ends in PICA. And this is the exposure, again, bottom here, top of the head here, and the right side. So in this third case, I'll demonstrate the third option that one has in revascularization for PICA aneurysms. This is a 43 year old man with a sudden onset of headache and developed this rapidly enlarging dissecting aneurysm with a surrounding hemorrhage of the vertebral artery on the left side, incorporating the PICA origin. Here's the midline cerebellar tonsils, brainstem here, lower cranial nerves are here. Here's the vertebral artery here. Here's the dissecting aneurysm there, and PICA is coming out of the diseased segment. Now, in this instance, as opposed to the prior case, you can see that both PICA loops are lying very close to one another. So this is an excellent opportunity for performing a side to side anastomosis. Here we are with both vessels under temporary occlusion, and some of the important points in performing this anastomosis are placing the anchoring stitches first and being sure that you're not outside the vessel lumen. Once both anchoring stitches are placed, then you can proceed to suture the inner lumen first.

- [Aaron] I think you very well mentioned, Nick, that the first stitches have to be somehow at the edges, maybe a little bit more inferiorly, and the knot has to be on the outside and not within the lumen. That could potentially cause thrombosis of your anastomosis site.

- Correct. Correct. So then once the inner lumen has been sutured, and again, to make sure that you're knot is on the outside, you'll pass your needle from the inside of the lumen to the outside, and then tie your knot outside the vessel. So once that's done, then the outer lumen can be approximated as shown here, again, using a tonneau and running the suture. And of course in this case, you have to perform a running suture, definitely on the inside lumen. The outside could be either running or interrupted, And typically I'll leave the loops loose until the very end so that you can inspect your wall as you're performing your suturing. And then finally, when completed, you can remove all a temporary clips. If you have a little bit of bleeding from the suture line, that's typically easily controlled, as long as it's a small amount with small piece of gel foam, as shown here. Here's the proximal clip, just distal to the diseased segment of the PICA. Here's ICG showing filling of both PICA distributions now. And I think the microvascular doppler's still an important adjunct. Here and, and here we've occluded now the vertebral artery proximally, and the PICA adjusted the origin, and we're here making sure that the proximal PICA of brainstem perforators are still filling because that's very important in preventing a brainstem stroke. And you can see that here. And this is the post-operative angiogram. One of the variations to the far lateral is the linear skin incision. What is your preference?

- I think there's a mixture between the two, Nick, it's pretty good in terms of maybe having a linear that curves a little bit, so you get a nice view. I think what you have here is a linear incision. And if you have to turn a little bit, usually that little bit of turn helps a lot. You don't have to do that big, hockey stick incision. So you can always prep and maybe curve the incision a little bit, and if you need to curve it more, you can always do it if necessary.

- Right, and I think patients have less incisional pain and heal a little better. Your exposure is almost the same. And really the only thing you're losing is the occipital artery option of revascularization. Again, the anatomic considerations are important, the PICA loop, the location of the vertebral artery over the arch of C1. We mentioned the vertebral plexus, which can be sometimes troublesome in exposing the vertebral artery. There is a tremendous variation in the anatomy of the arch of C1, which has been studied extensively. The foramen transversarium can vary in its width by several millimeters, as can the distance between the midline and the medial border of the arch of C1, as well as the width of C1, as well, several millimeters in variation, which really have to keep in mind, I think, in a preoperative study and a thorough investigation of your imaging is critical. Here's a case of a 45 year old woman with this, what you would consider a fairly straightforward PICA aneurysm rupture. And so undergoing, again, far lateral craniotomy, left sided, through a linear incision. And so again, we can see here what one of the potential downfalls of the linear incision or any approach near critical anatomy. So we can see here resident exposure here of the far lateral craniotomy. And I think it's critically important to pay attention to your landmarks and feel for bony landmarks because here we've seen that the Bovie, without doing that, can easily enter what was first thought to be a muscular branch, but soon turns out to be, obviously, the vertebral artery itself. And so in this case, after summoning for additional assistance and keeping pressure on the vertebral, which is done to determine where the C1 arch is. And once you've identified the bony anatomy, then you know where the vertebral is gonna be, right above it. And so you can see here, the vertebral artery after being dissected free is temporarily occluded. And you can see here, the injury to the vessel, which once you get to this point can be reconstructed in a fairly simple manner with some interrupted 9-0 sutures. If this wasn't possible, then one could consider a end-to-end anastomosis or even a graft. So it's critically important to pay attention to your preoperative anatomy and the bony anatomy as well. And you can see your, the post-operative angiogram. It's also important to follow patients like this because they can develop dissections in a delayed fashion, Transcondylar variations have been discussed even to the point of advocating in some cases for complete mobilization of the vertebral artery. I think that's rarely necessary. I don't know, Aaron, what do you think in terms of conduit drilling and some of the variations discussed?

- Thank you. That's an excellent question, Nick. I rarely ever use that transcondylar vertebral artery mobilization. I think that has significant risks to it, no matter whose hands is involved. I think the application of it is really rare, even for tumors that are located along the anterior cranial cervical junction or the lower third part of the clivus. I think the very lateral approach, again, we have this idea of skull-based that becomes lateral, far lateral, extreme lateral, extreme, extreme lateral. And it really is very difficult to see what the people talking about in terms of why would you need to be so lateral? Most tumors that are along the lower third part of the clivus create enough space by displacing the nervous structures that I think you'll be able to remove them with just by a very lateral approach, removing as much of the lateral part of the foramen magnum bony structures as possible, and really gently untethering the brain stem from the arachnoids and moving around it and removing the tumor. What are your indications for these extreme far lateral approaches with vertebral mobilization, Nick?

- No, I agree with you. I think the most important point and one of the common questions that we get from residents and students is how much of the condyle do you need to drill, which is really the main thing that I think gives you your a degree of freedom. And I tell people, "Really drill until you really get to that condyle or vein is a great landmark, and you really want to stop there." If you get the CA cortical bone, of course, you're probably getting close to the hypoglossal canal, which you don't want to violate. So I think those are the important points. Here is a 56 year old woman with this very large wide necked vertebral aneurysm arising at the PICA junction with a very small daughter portion of this aneurysm. And so for this instance, I think be I would be more aggressive with the condylar drilling. So again, this is a right-sided, far lateral craniotomy. You can see here, the lower cranial nerves, cerebellum, here's PICA, lower cranial nerves here. And now here again, you can see the difficulty in dealing with some of these lesions and why we talk about drilling that condyle down to give you a flat approach. Here's the vertebral artery. Here's PICA coming out. Here's the small aneurysm. I pointed out the larger aneurysm is back here. And you're really working between these branches of the lower cranial nerves. This is the 12th cranial nerve here, draped around PICA, going into the condyle. And so you can see here, placing a long clip, trying to get this across the neck of the aneurysm. It slides down and occludes the vertebral artery. You can see that here because there's no way to soften this aneurysm very easily because it's getting flow from the other vertebral. So here, again, trying to get this permanent clip across the base of the aneurism, working through these cranial nerves. The distal vertebral is underneath my instrument here, trying to keep that patent. The first time, that clip slipped down. So the second time trying to reposition it, but again, there's really no easy way to soften these aneurysms with temporary clips because the contralateral vertebral artery is supplying blood flow. Here, it looks again like the clip may have slid down. And so I wasn't happy with that either. One of the things you can do is place a second tandem clip atop the first one, and then remove your lower clip. In this case, I was able just to slide that first clip up, and you can see the distal vertebral this time looks patent. And so this was acceptable, and then the second clip is placed across that small daughter aneurysm with a good flow in the vertebral and the PICA.

- [Aaron] I have a question, Nick. Obviously here, proximal control is very difficult because you have a dominant vertebral on the other side. And if you put a temporary clip on each lateral side, that may not give you much. Is there any indications for putting endovascularly a balloon on the contralateral vertebral and potentially occluding interoperatively to get you a very nice a decompression if the aneurysm is very large.

- [Nick] I think that would be a good idea. And I have not done that, but that certainly is an option. Have you done that, Aaron?

- I have not. I came close to do it once when a PICA was very large, the aneurysm was large, and it was very dominant overt on the other side. And it was very difficult, just like you're showing right now. These are extremely challenging vascular cases, if not the most challenging aneurysms to clip, because PICA is so small and usually the neck is so wide, and any issue with clipping occludes the PICA. That's why they're so difficult to intravascularly treat. And so you need to quick reconstruct the PICA as much as you can. And I guess it was just a thought came to my mind that, because you need to reconstruct, it would be able to see around the neck of the aneurysm when it's so broad. And so an indication for maybe a contralateral balloon placement in the vert would be a nice consideration, although I have never done it.

- You can see here, the postoperative result with the reconstruction of the vertebral artery. And she did have some swallowing difficulty for two months after the surgical procedure. And again, that's part of the morbidity of working around these lower cranial nerves. Another way of handling these lesions in terms of clip strategy and the use of fenestrated eclipse to maintain the patency of PICA, as you mentioned, Aaron, is a very important consideration. This is a 54 year old woman with headaches. And in this particular instance, the original surgery was undertaken to treat what was believed to be a meningioma, which in retrospect, is not the case. This lesion, which was noted on the preoperative MRI scan was, in fact, a PICA aneurysm. Aneurysm, again, this was really a midline approach, which limited our lateral exposure. You can see here, on the right side, PICA coming up, this large fusiform aneurysm, and then PICA it coming out of this aneurysm with a lot of calcium. So here, a temporary clip really doesn't allow you to get much softening of the aneurysm. And in this case, the clipping strategy was reconstructing the PICA with these fenestrated clips. You can see them placed here, to allow PICA to continue to fill, and then a straight clip at the very end here to occlude this rest of the aneurysm. And here, in inspecting the bottom part of our exposure, it's apparent that some of the aneurysm sack is still filling. And so again, here placing another proximal fenestrated clip here. So here's PICA channel right through here, and here's some more aneurysm dome here at the base. So we have to take care of that with yet a fourth fenestrated clip. So we have PICA going through three fenestrations and then the distal aneurysm included by our straight clip. So here's the final result. And of course, this is really the beauty of ICG. Here are the patient's prone. There's no thought of being able to get an angiogram, but you can see PICA filling nicely and a occlusion of the aneurysm. So another clip strategy and an example of that. What do you think, Aaron? Would you have handled that differently?

- [Aaron] No, I think this is really a nice work, Nick. Really technically great job you did. One idea that I have come up with sometimes is on these very big partially thrombosed atherosclerotic PICA aneurysms, really, if you try to be too perfect, that's really the enemy of good. And that if you put the clips on just the way you did, which I would have done exactly the same way, if you have a little bit of feeling of the aneurysm, I would be okay with it because it will later thrombose. It's one thing to say, "Well, I have very little contrast coming in." Maybe you do an angiogram. It's just very slow and you know it's gonna thrombose versus you want to get an absolutely perfect result and have no contrast coming in. You'll find out that could potentially thrombose the PICA in a delayed fashion and have a cerebellar stroke. So if you know the neck is very atherosclerotic in these PICA aneurysms where the PICA is so small, the enemy of good is really perfect. Don't you agree?

- I agree. And I think the same thing applies to MCA aneurysms, where you have MCA branches coming out the aneurysm itself. I think AICA aneurysms deserve a mention. They're very rare. They encompass less than 2% of all aneurysms. They typically occur approximately at the origin of AICA and the basal artery. There's really no great way to approach these. Retrosigmoid is often adequate, but sometimes you can add a pre-sigmoid approach, again, depending on the patient's hearing status and the side of the lesion. Here's a case of a 58 year old woman with chronic headaches and this very large rapidly-filling a aneurysm AICA here, A very small AICA branch here coming out of the neck of the aneurysm. So in this particular case, endovascular option really would involve sacrifice of the AICA itself. And so we thought it would be a worthwhile to try and save that vessel. She did have intact hearing. We did it like to add a pre sigmoid component to the operation so that we could look in the pre-sigmoid space and give us a little bit of a flatter approach to the aneurysm here. So we see here, the right side of the approach, the seventh and eighth cranial nerves are here. You can see the aneurysm itself here. This is the distal AICA coming out of the aneurysm itself. You can see how very, very small that vessel is compared to the size of the aneurysm. Basal artery is back here, off in the distance, so to speak. And you can see here first attempt to try and occlude this aneurysm while keeping this AICA open. You can see the very narrow corridor with which you have to work. And attempting to use this tandem clip technique to try and remove the lower clip and keep AICA open. This was unsuccessful as well. There really was no way to soften this vessel. Even in attempting to visualize the neck, you can see interoperative rupture of the aneurysm here. And so that's controlled with a small cottonoid. And at this point, your options really are really limited. Again, trying to put both clips, stack them and then remove the lower clips here. So at this point, here's the basal artery. Here's the AICA origin. It looks like there's some filling of the AICA here, but still no filling of the distal AICA. So at this point, I try to place a second clip and remove the first clip again, which seemed to work. Some filling of the distal AICA with clips stenosis proximally, but at this point, thought that this was really the best result we could attain and stopped the procedure there. Do you have any thoughts, Aaron, on how to handle that?

- It's a, it's a very challenging case. I don't think anybody knows what's the right answer in that situation. The postoperative angiogram for you, did it show a retrograde flow here? You have it. Can you tell us about that within the AICA?

- There is some filling of the AICA, the distal distribution through PICA collaterals. It was a very small vessel. She actually tolerated it very well. And I think the argument can be made well, the open result really didn't achieve much when compared to the endovascular options. But clearly, I think there was a chance to try and save that vessel, and we decided to go for it.

- One thing that I have learned, ICG can be very good as well, Nick, is assessing retrograde flow in those small vessels. You see how intraoperatively you had maybe very difficult to do an intraoperative angiogram on the table and get a good result about how the AICA is feeling. But as I saw on your ICG, you had a good retrograde flow and that gives you a very good feeling that you may get away with trapping the aneurysm and sacrificing the proximal part of AICA. It is gonna be awfully difficult to save the AICA with an aneurysm when the vessel is so small.

- Yeah, I agree. I think the other teaching point is handling a rupture in a deep location like that. And I think, really, managing that with the pressure and the cottonoid and continuing with the operation as best you can is really the key to that, if you can't get temporary clips in the location.

- Right. I think the best approach when you get some bleeding like that is just put a small piece of cotton at the side of the bleeding and just gentle pressure. Obviously you don't wanna push too hard on the brain stem. Do you do motor evoke potential monitoring and some accessory evoke potential monitoring for these cases, Nick?

- We do. We do, as a routine.

- Okay. Thank you.

- Do you?

- Yes, we do. Absolutely. And this was a great teaching case, especially managing the intraoperative hemorrhage, Nick. Being very patient, putting a piece of cottonoid on the hemorrhage and just giving it a little bit of time and thinking and catching your breath, it really saves a life.

- So we'll talk a little bit now, moving up the vertebral basilar tree to superior cerebellar artery aneurysms and the basilar apex. I think SCA aneurysms are really minimal to open surgical treatment. They're laterally positioned when compared to basilar apex aneurysms. There's a relative paucity of brainstem perforators at the junction of the SCA and basilar artery. And especially in small aneurysms, as in this case in a ten-year-old boy with sickle cell anemia, really are minimal to open surgical treatment. We can start the video here. Here, you can see the aneurysm on the left side. So this is a left sided orbitozygomatic craniotomy. So the key to this exposure is wide splitting of the Sylvian fissure. So here we see the internal carotid artery here. Third cranial nerve is here. We can see the posterior communicating artery here. So the dissection really follows the posterior communicating artery down to the posterior cerebral artery, carefully dissecting it away from the third cranial nerve here. You see the optic nerve is located here. It really is important to be patient in sharply dissecting through the arachnoid adhesions. And typically, these aneurysms are approached through the space between the third cranial nerve and the carotid artery. You can see that posterior communicating artery nicely here, really robust vessel, leading to the PCA here. So the next step in the exposure is to identify the cerebellar artery, which we can see arising here. And then the basilar trunk now is seen proximally here, and that gives you a proximal control as well. It's important to follow the third cranial nerve all the way down to the brainstem surface. And so you can see now the PCA and carotid are retracted laterally. Here's the SCA aneurysm and here's placement of a long, straight clip through this narrow corridor right here, occluding the aneurysm. Here's SCA. And this is repositioning the clip because of perforating branches that you can see here. Here are the perforators at the very bottom. Making sure those are absolutely free and then placing a small aneurysm clip to take care of a small remnant at the top of the aneurysm. So here's SCA, PCA basal artery and occlusion of the aneurysm here. And I think ICG again is critical, looking at those perforators, which you can just make out at the base of the video. And here's the extent of your craniotomy. You get a full orbitozygomatic craniotomy exposure.

- Great to work, Nick. One idea would be maybe do a clinoidectomy sometimes. That may increase the working zone of how you can mobilize the carotid artery more medially. The other technical nuance that I have learned from other surgeons is if the third nerve is very tethered down, you may wanna cut a piece of tentorium over it, and that can increase the mobility of the third nerve without tethering it along the edge of the tentorium and potentially putting it at increased risk. Obviously, if the SCA is down, you may have to drill part of the posterior clinoid, and often you run into brisk bleeding from the cavernous sinus, as you show yourself in the subsequent videos. A little bit of gel foam powder really works well. But obviously in these cases, the critical part of the operation is adequate exposure to really see the perforators, how nicely you saved those low perforators, that life runs through them along the brain stem and P1 segment, especially. So those perforators cannot be overemphasized.

- Yeah, I think those are excellent points. And the next case, I think will illustrate a couple of those as well. Again, summarizing the sockets cuts of the full OZ can be done in one, two, or even three pieces. How do you do your orbitozygomatic craniotomy typically, Aaron?

- I do it in one piece. I think it's the dealer's choice, how much you feel comfortable doing it in one piece versus two piece. I think two pieces easier to do. One thing people should keep in mind, if you do it one piece and you're relying on cracking the roof of the orbit, especially if you have a tumor that has caused hyperostosis of the roof of the orbit, like a meningioma, you make crack the roof of the orbit all the way to the optic canal and you will make the patient blind. So in the tumorous lesions that have affected roof of the orbit, I warn against using the one-piece approach. But again, for those patients who have a normal anatomy along their bony structures of skull base, I think one piece versus two piece is reasonable. The one piece also may cause more bone loss around the keyhole because you really need to expose the roof of the orbit to cut across. How you're comfortable. Obviously, we don't use the full OZ anymore along the inferior part of the roof, along the anterior edge of the zygoma. We really do the super orbital osteotomy and really cut the zygoma all the way along it's frontal process. And I think that gives you all you need. Any thoughts in terms of... Go ahead.

- So this is a little bit more difficult case. This is a 48 year old gentleman with severe headaches, and now this very, very large, broad-necked SCA aneurysm. And in this case, the plan is to approach this again through an orbitozygomatic craniotomy from the right side. You can see here, the aneurysm here, very broad-necked with the SCA bowing down well below the aneurism. You mentioned, Aaron, the posterior clinoid, which can get in the way here and necessitate removal, particularly to see the proximal basilar artery. You can start the video. So again, this is a right sided orbitozygomatic craniotomy. You can see here, the carotid artery here, optic nerve here, And again, here, following the PCA batch, you can see already the SCA aneurysm coming into view, and you can see here, here's the posterior clinoid, which is obstructing view of the basal artery and the contralateral vessels. So here, using a one millimeter diamond burr to take down the posterior clinoid. The carotid arteries retracted medially. Any bleeding from the cavernous sinus is usually controlled with some gel foam or fibrillar. Here's the carotid. You're drilling right underneath it and the dura reflected inferiorly. So now you can see the aneurysm here and trying to get a control of the proximal basal artery. You can see here, this is the SCA on the right side. Here's a basal artery here. And so this is the PCA now, and you can see the PCA's very stuck and adherent to the aneurysm. And so careful sharp dissection is really the only way to get this loose from the PCA. So here in doing that, we have some bleeding from one point of the aneurysm, which is again controlled with some cotton pressure. And here, the difficulty is that the aneurysm, is really, without softening it in some way, very difficult to close completely, even with the long bay netted blades used here. They keep sliding off of the aneurysm, resulting in continued filling of the aneurysm. So here's a temporary clip now placed across the basilar and the PCA on the contralateral side. You can see here, the aneurysm is still filling in and probably from the ipsilateral pcomm. So really, the only way to get this aneurysm down to a size where it can be clipped is to put up a temporary clip on all three vessels, a pcomm, PCA, and basilar, and then clip reconstruct the neck with multiple curved clips to get the aneurysm occluded. You can see here, the narrow window in which you have to work. And you can see here. So interoperative angiogram shows reconstruction of the basilar apex on the right and filling of the PCA and SCA on that side. And again, you mentioned the third nerve and some of the tension you can have there. The patient did have a temporary third nerve paresis, which resolved over about six weeks. The last aneurysm case we'll just discuss is a very recent one, in which case you see here, this wide-necked basilar apex aneurysm. These are very difficult cases. And I think in this endovascular era, we see less and less of them and probably for good reason, in many instances. In this case, we have a very young woman with subarachnoid hemorrhage and also a left-sided, posterior communicating artery aneurysm, which you can see here. And in this case you have an anterior projecting aneurysm with the fairly high basilar apex. So I think in this case, it's reasonable to proceed with an orbitozygomatic craniotomy. A subtemporal approach is also an alternative for lower lying basilar apex lesions. Orbitozygomatic craniotomy here. First goal, of course, would be to take care of the posterior communicating artery aneurysm. And again, a wide splitting of the Sylvian fissure is really important here. You see the carotid, and this turned out to be a very proximal posterior communicating artery aneurysm. In fact, here, the instrument and the clip blades are running right into the posterior clinoid here. It's limiting the depth to which the clip can be placed. You can see here, a remnant of the aneurysm after initial indication, after initial clip placement, then necessitating repositioning. And so once this was done, it was apparent this wasn't the source of the hemorrhage. And so approaching the posterior circulation here, you can see some of the blood located deep to the optic nerve in the subarachnoid space here, laterally, the posterior communicating artery, again, tracking it posteriorly with these perforators, and a third nerve here underneath the temporal lobe. And I think it's an important distinction when compared to the previous cases, the basilar apex, of course, is more medial. And so your view is much more limited. You can see how the carotid arteries retract immediately. Here's the basilar apex. Here's the ipsilateral PCA here. Here's the contralateral PCA here. And the proximal basilar artery is in this direction. So here, just trying to get the neck of aneurysm exposed in a rupture case is very, very difficult. Here's a proximal clip place on the basilar artery below the PCA, and below the pcomm to soften the aneurysm. So with all this stuff in the way, it's a challenge to see the neck of the aneurysm. And this ipsilateral PCA was very adherent, again, at the aneurysm, trying to get that space opened up here, dissecting down so you can get your clip blade into that space, and really need to use the longest straight clip that you can find to give you that exposure down to get this ipsilateral clip laid into the proper space. And I do use the mouthpiece for these cases. I think it's very helpful to change your depth of vision. And again, here after placement of the clip, here's the PCA now, ipsilateral, contralateral. Here's the aneurysm. Here's inspection of the base of the aneurysm. It's very difficult to see here in this cut, but here's some perforators here on the ICG. You can see them light up here, right under there, and the aneurysm's totally occluded. So it's very important to inspect your clip blades after placement in this location. It's critically important. Do you have any other thoughts, Aaron?

- No. I think it's a very well done case and a very challenging case. I guess one consideration I would have been thinking about is clipping the pcomm and then the basilar. I think the first clip would definitely be on your way. Again, this is a decision you know a lot better when you're in OR and seeing everything in 3D. But first of all, let me correct myself. The pcomm was on the left side. So you had to approach from the left, which made it easier because the high riding P1 was also ipsilateral to you. But when you clipped the pcomm, then the clip of the pcomm is gonna be on your way and it would make it more difficult to clip the basilar. If you were sure that the pcomm wasn't the one that hadn't bled, you may have said, "Well, I'm gonna leave this aneurysm for now. take a little bit of risk that it could rupture if I pulled too much on it, but at least it'll give me more space to clip the basilar." Also, I really like the way you tried to clip the basilar cap aneurysm perpendicular to, let's say, its neck without having to do it parallel to the P1, because this way it really saves you from looking behind it to see the perforators. Those are really the considerations I was thinking in that case. What are your thoughts about those comments?

- Yeah, no. We were thinking the same thing in terms of the first aneurysm. Because it was so proximal, it ended up not being in the way in terms of the clip application. And I think this would have been very, very difficult to clip along the PCAs, given the anatomy and the size of the aneurysm would have been very, very difficult to do. So in conclusion, I think just in showing some of these short examples, I think it's important to remember that all lesions are certainly accessible. Really, the approach needs to be tailored to the location of the aneurysm and careful study of the anatomy is critically important in mastering these skull-based approaches to keep our morbidity as low as possible in the endovascular era.

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