Grand Rounds-Microsurgical Clip Ligation of Middle Cerebral Artery Aneurysms

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- Hello, ladies and gentlemen, thank you for joining us and welcome. Today's program will be a discussion regarding microsurgical clip ligation of middle cerebral artery aneurysms. We're happy to have with us Dr. Michael Lawton from University of California, San Francisco. Michael, thank you for your time.

- You're welcome, thanks for having me.

- Go ahead, please, with your presentation, after which I'm going to show some of my own slides, and then we're going to review some of your surgical videos and mine. Please go ahead.

- So I'm going to discuss middle cerebral artery aneurysms, and a couple points, as by way of introduction, these are some data from my personal surgical series, and you can see that of all the aneurysms that I've treated of this group of 2,500, the most common is the middle cerebral artery aneurysm. And it accounted for 1/4 of all the aneurysms that I treated. So given that, I think this is a very important aneurysm for us to learn how to treat successfully. These are some of the advantages of surgery. It's got very favorable surgical anatomy from an endovascular point of view. There are limitations in what can be accomplished with these. The surgical exposure is excellent, as we'll demonstrate. There are multiple surgical options, which we will also demonstrate. The risks are low and the outcomes generally are quite good. Now the anatomy for middle cerebral artery aneurysms is really fairly well worked out. These slides just demonstrate the different segmental anatomy that most of us are familiar with. I think it's very useful to consider the segments, the M1 out to the M4, as you work your way through the anatomy, both normal and abnormal, in treating these aneurysms. The anatomy of the branching is demonstrated in this slide. The classic we learn, the bifurcation or trifurcation anatomy, but you can see that there's tremendous variation in the dominance of one trunk over another, or whether these are bifurcations, trifurcations, or quadrafurcations. There's also some variations in terms of duplications and accessory MCAs, as shown here. Now the approach I won't dwell on, but most of my middle cerebral aneurysms are dealt with just through a simple pterional craniotomy, nothing special, as these slides demonstrate just a routine standard approach with drilling the pterion on to widen that space between the frontal and temporal lobes. Now, I think one of the most important skills for a neurosurgeon treating aneurysms is the Sylvian fissure split. And it's absolutely essential with middle cerebral aneurysms. You simply cannot treat these aneurysms without splitting the fissure and doing it well. So this is some pointers as to how that's done. This is the view that you get down the Sylvian fissure when you first expose it. The venous complex generally runs from the Sylvian fissure inferiorly to the sphenoparietal sinus. And so in getting in to the Sylvian fissure and gaining access to the arteries, I like to mobilize the temporal veins to the temporal side. So that puts you on this frontal side of the veins. I like to make an incision along the arachnoid and first, just get that arachnoid opened up so that that Sylvian cistern is open. Now, as the dissection progresses, you'll change your angle of approach from a more horizontal to a more vertical direction. And that's depicted here in going more on the surface horizontally, and then turning at this corner here to a more vertical trajectory down towards the carotid cistern. The veins are the gatekeepers to the Sylvian fissure. And this slide just shows how there's tremendous variation in the venous anatomy. There are some Sylvian fissures that had absolutely no veins, as shown here. There's some that have a single vein that's easily mobilized temporally. Sometimes you get these parallel veins that have to be split or worked through, and there can even be these very complicated complexes of veins that really have to be navigated to get to the arteries. The other thing I like to point out is that you should look at your angiogram beforehand and decide whether the veins have a superior, anterior, or posterior drainage pattern. If you've got a superior drainage pattern or a posterior drainage pattern, then in general, these patterns allow you to occlude or coagulate, if necessary, one of the more anteriorly directed veins. But if you have this kind of a pattern, this anterior drainage, then it's very important to preserve this whole trunk and its connection to the dura sphenoparietal sinus. If you have a mixed drainage pattern like is shown here, then you do have some latitude in working through these veins. In general, I try and preserve all the veins that can be saved, but I also recognize that in order to get down to the Sylvian fissure, you often have to take a couple branches or maybe even a trunk to get yourself in. Now, this slide just shows how, in some cases, the Sylvian fissure is very widely open as in this atrophic brain, atrophic fissure. You can have this more classic appearance in the, in most normal brains, where the frontal and temporal lobes are really opposed to one another here. And finally, you can get these interdigitations that really can lock a fissure together and make it very difficult to open up. It's important to recognize which of these situations you're dealing with as you're trying to split things. Now, once you've gotten through the veins and through the arachnoid, then the key is to identify one of these cortical middle cerebral branches. So this is an M4 artery here. And following that into the operculum, into the opercular segments, that will take you down into the operculum, down towards the deeper portions of the Sylvian fissure. And what you're trying to do is to deepen the exposure down to this insular segment. So these are your M2 branches and you want to follow the anatomy from M4, down to M3, down to M2, and that will take you down to these insular segments of the middle cerebral artery and down to these, ultimately, to these trunks. What you're trying to get to is the superior trunk and the inferior trunk, which will then lead you right down to the aneurysm in the neck. This is a little nuance about working your way down. Once you've gotten down to the insular segments, what you'll find is that there are branches off of the insular segments that can lay onto the temporal lobe, as shown here, and then also go to the temporal lobe. But there can also be branches that lay against the frontal lobe as shown here, but are actually going towards the temporal lobe. So you really have to look at how the arteries are laying out and where they're ultimately getting to. Arteries will choose a direction one way or the other. They will either go to the temporal lobe or to the frontal lobe. So you have to trace the anatomy and separate these and untangle these one way or the other. This is an example of how a frontal branch goes to the frontal lobe. But in this case, you've got a frontal branch here that's stuck to the temporal lobe. And if you misinterpret that, you can find that this artery really crosses your field and doesn't allow things to separate. Aneurysm projection is really important in your final approach to the aneurysm. You really want to avoid the dome because, particularly with ruptured aneurysms, you don't want to find, bring your dissection right to the hotspot of the aneurysm. So it's important to look at the anatomy. Laterally projecting aneurysms typically have this straight M1 segment, whereas, if there's a little bit of arc in the M1 segment, that can cause inferior projection here, or it can, conversely can lead to superiorly projecting aneurysms as shown here. And the same is true in this AP direction. If you have an M1 segment that arcs from front to back, you can have some projection here posteriorly, or vice versa, anteriorly. And again, in planning your approach to the aneurysm and getting to the neck, you need to consider where that dome is and how to avoid it. These are the steps that I like to follow when dissecting the aneurysm. So at this stage of the dissection, we're in the operculum along the insula, and we've found our superior and inferior divisions. What I like to do is get out to the superior trunk here and follow this down the safe side of the artery is to follow this frontal side away from the aneurysm. This is a more dangerous surface of the artery to follow, this here on the lateral side is safer because the aneurysm is going to be on the opposite side. And as we follow it down, it will take us past the aneurysm to the M1 segment. This is where we're going to get our proximal control and it'll give us the confidence and the security to make our final dissection maneuvers. Once we have that, we can then return up to the distal portion of the aneurysm. We can then follow that more dangerous side of the artery down to the proximal neck here. Once we've defined that, then we can work our way across the back portion of the aneurysm. Sometimes, the aneurysm itself will hide this inferior division. And so the anatomy may not be as laid out or as clear as is shown here, but we need to get across to the opposite side. We need to find this inferior trunk. It often is easiest to find this inner surface here, follow that down to the distal side of the neck here. And then finally, we should, at this point, have a good plane behind the aneurysm neck for one of the clip blades, but we then need to go across to the opposite side and map things out for that other blade across the front. Here's the opening into the aneurysm, and this'll be where the neck is, and we're going to want to lay that clip on both sides. So it's very important to work from front to back and open things up on both sides. This next slide just shows you a little bit of a variation for a ruptured aneurysm. For a ruptured aneurysm, if there's concern about gaining proximal control, what I will often do is go straight down to the carotid cistern here first, get the carotid arachnoid open up here, expose the supraclinoid segment here so that I have control. I follow this up to the A1 segment, and it's really when you get to this M1 segment here that you finally achieve your proximal control. Once you have that, then you can go back to those steps that we discussed earlier, where you follow the superior division down to the proximal neck, you go behind the aneurysm to the contralateral side, find the opposite inferior division, and then finally working your way across the front side of the aneurysm. Those are the steps that I think are important in this dissection. And it's really like a dance choreography where you follow those steps routinely on every case. The clipping at this point is relatively straightforward. You want to apply the blades of the clip in a way that's parallel to the neck, if possible. Oftentimes though, the anatomy is such that the neck is broad and the portions of neck that are both behind the aneurysm and across the, or sorry, behind the bifurcation and across here. So sometimes what you need is a more complicated clip arrangement, where you can stack clips here to tailor this reconstruction with the tips of the clips. You may need intersecting clips, as shown here, that take care of this back portion of neck. And then finally, this front portion of the neck, these two intersecting clips here allow you to contour that reconstruction. This is another technique with multiple clips that uses a fenestrated clip around the first clip to get that posterior portion of the aneurysm neck. In general, I like to clip the aneurysm with as simple a clipping as possible, but those other clip configurations allow for some, some flexibility. So that's the end of my talk, and...

- Thank you, Michael. I appreciate those pointers. I just want to add a few things to your very eloquent discussion of the nuances. So these are the disclosures that does not interfere with the presentation. As you said, the MC aneurysms are very common. Contrary to what most people believe, these aneurysms are awfully superficial and anterior in the area of the pterion. They are only about two centimeter posterior to the insular portion of the Sylvian fissure and about 2 1/2 centimeters deep to the cortex. So one might say that these aneurysms are awfully approachable and can be easily taken care of. The dome often points to the middle temporal gyrus. And again, these are not relying right on the front lobe in the insula, most common, but more in the middle temporal gyrus. And when you split the fissure, you have to look down toward the temporal lobe, straight towards the insula and the lateral lenticulostriate perforators can really offer special challenges in dissecting the neck. Any of those can be extremely critical. If you have any comments on any of these, please go right ahead, Michael. So what are the routes to the aneurysm? You mentioned a subfrontal approach, where the advantage is you have early proximal control, however, it requires a frontal lobe retraction and it's somewhat awkward to dissect the fissure from medially to laterally. The transcortical approach has been advocated by very reputable surgeons. It is simple, you remove the superior temporal gyrus. However, there is a risk of seizure because of the violation of the cortex. And this is probably best suited when there is evidence of intercranial hemorrhage from the aneurysm into the temporal lobe. And we're going to review a case of that in the video, our preferred route, both for Michael and I, and many of the surgeons currently, is the transsylvian approach. Again, it's the preferred route. It requires minimal cortical invasion, and usually you expose distally to proximally and you follow the M2s to the aneurysm. There is a certain amount of cortical retraction involved, especially along the superior temporal gyrus. So what are the nuances for the transsylvian route? You require a very wide Sylvian fissure dissection. You can't cheat on that. You really need to display open the fissure and dissect it widely. You follow the M2 branches and, to M1, and eventually to the aneurysm, you stay usually on the frontal side and the frontal trunk, because most of these aneurysms, 95% of them, point temporally, therefore it's safest and least out of dome's way. So what the really the steps are that Michael, you very well mentioned, is follow the frontal M2 to the neck of aneurysm and to M1 and in retrograde fashion, move back to the aneurysm and then identify the temporal trunk. The temporal trunk, typically, is hidden underneath the neck of the aneurysm, it can be very tricky, especially if there's a trifurcation, as we'll see in one of my videos. The dissection will require a temporary occlusion, deflation of the aneurysm, and careful dissection of the aneurysm neck and the temporal trunk. One of the most important nuances about this aneurysm is that if you feel like your clip is very well placed and it's causing minimal stenosis of M1 branches, it usually means significant intraluminal narrowing. So if you suspect a little bit of, you know, narrowing of the M2 branches, probably the intraluminal narrowing is much more significant and therefore, please be generous with leaving the atrium where the M1 joins M2, to assure no risk of ischemia. We do use generously the temporary occlusion for these aneurysms and consider bipolar aneurysmoraphy, as you'll see in a second in one of the videos, to create a neck as these aneurysms can have a very wide base. So very briefly, we're going to go through positioning. I turned the head not much, as you can see, most surgeons turn it more. This really helps me to use gravity to drain the blood out of my field. However, it makes the dissection a little bit awkward in terms of the angle of the approach. We try to put the assistant against the surgeon, across the table, for an ease of transfer of instruments. This is the linear incision. As you can see, just behind the hairline, there is no need to expose, in a curvilinear fashion, any of the frontal lobe. This would allow the flap to be reflected anteriorly without a temporalis muscle getting on your way. And this is really the roadmap. You start and go deep into the fissure and you split the fissure from inside to outside to go to the neck of the aneurysm at M1. These are the basic techniques for exposing. What, here is the craniotomy. As you can see with place a burr hole right here, we go with one cut along the, just beneath the superior temporal line, and then another cut along the temporal lobe. And as you can see, when you've make the first cut, you can turn your drill and bring the heel out. And that's really how you can sort of connect the pterion. Here is your craniotomy, opening the fissure. You start by opening the distal part of the fissure with a round knife, and then go deep in the fissure and open the arachnoid with the spring action of the bipolars in order to, in deep portion of the fissure, find the M2 branches. After you do that, you can sort of open the superior part or the superficial part of the fissure using micro scissors or jeweler forceps, as you'll see in the video. Again, you start from inside to outside as there are several mentions, like peeling an orange from inside to outside. You open the arachnoid from inside of the fissure to outside because the planes of dissection are much easier close to the vessels in terms of the arachnoid. And then along the anterior part of the temporal lobe, you can often have a adherence between the temporal lobe and the frontal lobe, and that's when you may use the round knife again. And deep, medially using this thick piece of arachnoid over the M1 and the spring action of the bipolars can open that very easily. Ultimately, you'll be able to find M1 and secure proximal control, then move more distally, be able to expose the aneurysm. You may use a bipolar cautery to coagulate the meat body of the aneurysm and create a more favorable neck across the aneurysm before clip application. Especially in the case of the MC aneurysms, which have broad base. After the clip application, this is really the final product. And again, there is a variations of technique. As you can see, if the MCA aneurysm is not coming out of the typical location from the bifurcation, he may originate from one of the, in two trunks, and you will try to put the clip parallel to the M2 trunk, if possible. And again, this is another variation of the aneurysm coming off of the trunks. Let's go ahead and review a video of mine, again showing how the fissure is split. Hopefully that would help our viewers with some of the basic techniques as clipping the fissure can be, at times, challenging. Here is the left frontotemporal craniotomy. This is the left temporal lobe, left frontal lobe. We use the round knife to be able to open the arachnoid. As you can see there. We use the spring action of the bipolar in order to go deep into the fissure and find M2s. You may use the jeweler forceps to open the superficial thick arachnoid. This often is a very efficient way to remove, to open the superficial arachnoid, and it can handle the veins carefully without causing any injury to them. Ultimately, as the retractor placed as you can see, and the fissure is open again from inside to outside. Michael, as you mentioned in your book, in terms of keeping the arachnoid opening from inside to outside. Any nuances you have here, Michael?

- Well, I think what really helps me is to find a cortical artery that you can clearly visualize and then follow that on its course down into that opercular cleft. And if you find an artery and stay right on top of it, it will help define that plane of separation between the temporal lobe and the frontal lobe. It is a really easy, convenient way to identify the right working plane. And it takes you right where do you want to go, deep into that opercular cleft to where the insular segments begin.

- Thank you. And as you can see, the retractor is gently holding the temporal lobe, not necessarily retracting, and just moving along and again, splitting the fissure from inside to outside with the thick arachnoid membranes more easily distinguished more deeply. And again, you may use this Baltic dissector to create a plane when the vessels are attached to the cortex, if necessary. As you can see, that's the Baltic dissector sort of working across the blood vessels and trying to dissect the vessel off. As you can see the bipolar action of their, bipolars or the spring action works real well more deeply, close to M1. Again, microdissection is the best way to go as much as possible. And here is really trying to get close to a M1 branch. Here, we're trying to the M1 and again, the neck of the aneurysm, as you can see here, is left alone. And we move more medially to find M1, rather than jumping into the aneurysm dome without proximal control. And here is M1 sorta distally recognized as it joins the aneurysm neck and the bifurcation. And one point that I would like to emphasize here is when you put a temporary clip, especially on the portion of the M1 that can be quite atherosclerotic, as you can see in a moment here. It is important to assure that your clip, your temporary clip, is adequately secured before you proceed with further dissection of the aneurysm. As you will see, I'm going to go ahead and place a temporary clip here, but the temporary clip will eventually be displaced by the frontal lobe. And again, that's one you want to assure and double check that your temporary clip is carefully sitting where it needs to be. At cost, the M1 with that displacement after the frontal lobe is released. As you can see, this is the temporary clip is placed across the neck. And as I remove it in a second, you will see that the clip actually was no longer secured across the neck of the aneurysm. So let's go ahead and present our next case you'll see in a second. This is a very basic aneurysm that we can sorta go through before we go to the complex cases that will come on in a second. A 48 year old female with an unruptured seven millimeter left MCA aneurysm. And as you see, Michael, this is a relatively traditional MCA aneurysm with a broad base. What other features do you look for in your imaging preoperatively?

- I always spend a little time with the films preoperatively just to look over the brain and look over the aneurysm anatomy so that I'm not surprised by anything interoperatively. In this case, it looks like a fairly flat M1 trajectory. The aneurysm is projecting laterally. It has two trunks, a superior or a frontal division, and then a inferior or temporal division. So it's a classic bifurcation. And then it gets a bit broad, so it'll probably need a parallel clip right across that T of the bifurcation. And the brain itself looks fairly normal for her age. There's not a lot of atrophy. The fissure looks a little bit on the snug side, but there's a nice CSF sign that I can see there that'll take us right down to the aneurysm. Those are the key features to look for.

- Thank you. And here is the CT reconstruction, as you were well mentioned, the broad base of the aneurysm that you can see more often in these MCA aneurysms. Go ahead and go. I'm going to go ahead and briefly show the movie for this one just to stress, again, the basic techniques. Here is this aneurysm we were just talking about. As you can see, the fissure is split widely. The aneurysm is being mobilized from the temporal lobe where it was embedded to. A temporary clip was placed across the neck of the aneurysm. Again, more dissection is used to mobilize the aneurysm after the temporary clip is placed. Again, a decompression allows you to immobilize it. This is again a reapplication after short period of reprofusion. And again, this is that aneurysmorrhaphy using, or aneurysmoplasty, using the bipolar cautery to create a neck across the aneurysm and better identify the temporal branch. As you can see here, sort of the bipolar shrinks this aneurysm and gets the mid body of it out of your way. Obviously you need to have temporary clip and don't use the bipolar on a high setting. And here we first tried to put the clip across the neck more from the lateral parts, and it didn't allow us to identify the trunks very well. And then we'll kind of come up from the more superior part and place the clip for the final location, its final location. Any thoughts, Michael?

- Yeah, well, I have seen this coagulation technique many times. I personally don't use it much in my practice, but, you know, I think it, it can be helpful as shown here. And I think if you're going to do it, that temporary clip is real important. I generally like to save my temporary clipping for the very last final maneuvers, the ones where you're likely taking some risk in doing whatever it is that you're doing. I'm a big fan of temporary clipping, but I, I do like to really keep those minutes down to the absolute minimum and just use it at the bitter end for that last little bit.

- Okay, I appreciate that. You can see the atrium, which was generously left, where the M1 joins the M2s, and here is really the ICG showing the aneurysm is excluded and all the trunks are open and we just place another extra one just to bolster the first one. I think it always helps to have more than one clip on the MC aneurysms where risk of displacement of one clip could be higher than expected. And here's really that case that I want to talk. Let's go to your slides and discuss your cases, Michael. I appreciate you being patient with me to show these two cases. And this is a left sided one, is that correct, Michael?

- That's correct. So what we're seeing here is a view down the, down the Sylvian fissure. Let me see if I can get my pointer going. And a couple of things that you'll notice. I like to use my instruments as my retractors. I'm left-handed. So you'll see the scissors here in my left hand, you'll see the sucker here in my right hand. And I like to kind of lay the instruments into the lobes a little bit so that they open up that space for me, rather than a rigid retractor. And as I work, they're providing me this dynamic retraction that changes with every maneuver. Those first couple of steps were just to separate or to, sorry, incise the arachnoid that covers the Sylvian cistern. And that, I think, is an important first step just to get the lobes detached. And now we can get down into where the aneurysm is here. You can see this is all aneurysm here. And what we're trying to do is to identify this frontal branch here, that's coming out of the base of the aneurysm. This is a trifurcated aneurysm. So what we've got here is a, there are three trunks. This is now the temporal side of the aneurysm. This is, that narrow division right here, coming along the sidewall of the aneurysm. And you can see that it's really quite adherent. There's really just this tiny little cleavage spot right here between the proximal neck here and this middle trunk and the rest of this artery here is really densely adherent to the aneurysm. You can notice here, the yellowish coloration of the aneurysm, meaning that it's atherosclerotic. And so here, I've saved the temporary clipping to the bitter end here, just before I'm ready to put the permanent clip on. And my strategy is to use that little opening right here to slide the clip blade between this middle trunk here and the distal neck on the front, on the temporal side, and really just gather the bulk of the aneurysm in this blade of the clip. And I know that this is not going to be an aneurysm that could be clipped with just one simple clip. It's going to take multiple clips, but I wanted to get that clip on first, just to sort of gather things up. And you'll see that now, with this primary portion of the aneurysm sort of sealed off, what we can do is add some booster clips. I know from just palpating the aneurysm that there's still some life to it. There's some pulsation that I can feel with a blunt instrument. And so this is a fenestrated clip. It's a tandem clipping type construct that goes around this middle trunk, but uses the blade to close that distal portion of the aneurysm. And then this is a third clip now, this is a clip that I'm sliding underneath the middle division here and using it to, again, booster the closure of this aneurysm. And now what you'll see is that this middle trunk really is not very happy. It was crimped by the way that these clips are applied. You can see here that there's just too much tension on this artery as it's coming across. So I've decided to take the permanent clips off and do a little work on this artery. So now I think this is sometimes an important thing that you need to do is to take down these adhesions in order to ensure that this branch is well-protected. This is a number six dissector and a round knife. And I can basically just use sharp dissection to dissect this artery down off of this wall of the aneurysm. You can see how indented it is into the aneurysm. And in fact, sometimes these lobes of the aneurysm will mushroom or develop around these adherent arteries. But now you can see the artery is coming free. It's now completely detached from the aneurysm. And instead of just that little opening at the origin of that middle trunk, I now have a wide open shot at the neck. So the permanent clip is going to go back on, this blade over here is as it was before, but now this blade on the frontal side can easily slide into this little space that I've created. This middle division here is nicely separated away from the aneurysm, so it's safe. And now we've got a good closure of the, the main portion of the aneurysm. I'm again, using this fenestrated clip as a booster. It will allow the distal portion of that neck to be nicely closed. And now, once the main body of the aneurysm is taken care of, now I can deal with these additional lobules. This is very atherosclerotic, but it projects in a sort of anterior direction. So the plane of closure is really along the blades as shown here. Sometimes with these atherosclerotic aneurysms, you don't get complete closure of the blades, but it's fine because that internal compression of the inner walls is closed. And then I've just, I'm stacking additional clips on here, around or in between those other blades to close off that little remnant that lives between the two. And the important thing is that it doesn't really matter so much how many clips are used on the outside. What matters is how you've reconstructed the flow through these important branches. So it's taken a bunch of these stacked clips, but now when we do our IC green, we can see that that middle division that I stripped from the aneurysm has nice perfusion all along its course. This is that other division on the frontal side. And over here, we have the temporal division here. So all three of our main trunks coming from the aneurysm are nicely preserved and the aneurysm is completely closed. Now, if you notice there is a little bulge or a small aneurysm on the origin of the middle trunk, between the middle and frontal divisions, and that last curved mini clip just to occlude that little beginnings of an aneurysm there. So again, here's our middle trunk here coming up nicely and with good profusion. So I think that clip demonstrates just how many times these middle cerebral aneurysms have very complicated anatomy with multiple lobes or lobules with these adherent branches that need to be carefully dissected away so that you preserve patency. It looks like a small trunk here, but those trunks can be very vital and can result in critical infarcts, particularly in the dominant hemisphere like this one.

- Thank you, Michael. I think we do have the slides for your second case.

- There we go. So this is the middle cerebral aneurysm on the left side, and you can see that the M1 segment is coming up here. Here's our aneurysm anatomy. It's got sort of a broad fundus to adhere but a very nice neck, and you can see the trunks coming out at the base of the aneurysm here. Relatively straightforward aneurysm. This is not what makes this case difficult. What makes this case difficult is that if we look over here on the opposite side, there's a small aneurysm on the contralateral bifurcation. So this is the internal carotid coming up. Here's the M1 segment. And you can see that the M1 segment is sort of tortuous and projected downward. So this is a very favorable anatomy for reaching across to the contralateral side. So in other words, from left side to right side and treating this aneurysm at the same time. So what I'd like to show you is the treatment of that. These images at the bottom just showed the postoperative view of the aneurysm showing clipping of both. So again, this is a left sided aneurysm. So what you'll see here is the Sylvian vein steer. We've gone deep to the Sylvian veins, and we're in the deep portion of the Sylvian fissure. Here's our aneurysm. You can see one trunk coming out of the aneurysm, other trunk coming out of the aneurysm. And this is the clip application right across the neck. The video is a little bit off center, I apologize for that, but you can see this is a relatively straightforward clipping. And so that's just to take care of the ipsilateral aneurysm. And now, what we're going to do is really to go to the opposite side. And what you're looking at here is the inner edge of the contralateral optic nerve. And the first thing you want to do in crossing to the opposite side is to separate those adhesions between the frontal lobe on the opposite side and the optic nerve. And these are really just arachnoidal adhesions. You can take those down sharply. Again, you'll notice there's no retraction. This is my scissors in the left-hand, suction on the right hand. Again, I like to really minimize the amount of retraction, and this is really such a straight shot that you can get all the way to the opposite side of the optic nerve. And now what we're doing is we're splitting the Sylvian fissure on the right side from the left. So again, here's the optic nerve chiasm, ipsilateral optic nerve, we're working across that optic apparatus. And here's our arachnoid of the Sylvian cistern right here. This is the sphenoid wing right here that you're seeing. And we can really nicely split that Sylvian fissure because we have the view that's straight across and right into the plane of the vessels. Here's an artery that we follow. Again, using those arteries to separate the plane between the frontal and the temporal lobe. These are some of those arachnoidal adhesions. Now we can see better the arteries and the aneurysm coming into view. Again, this is the arachnoid of the Sylvian cistern. And here we are seeing the very beginnings of this aneurysm right here. This is the, this is the aneurysm, we're just opening the Sylvian fissure a little bit more to see across. So we have the temporal trunk here on this side, the frontal trunk here on this side, and this is the smaller aneurysm, right in view. Again, no retractors, this is all just using the suction in my right hand as my retractor for a dynamic moving retraction. And you can see that we have a really straight shot right across, and again, the microscope's a little bit off center here, but you can see the straight mini Yasargil clip that's going across the neck of the aneurysm and I've applied it so that the blades are right across the deep portion of that aneurysm. That leaves a little dogear remnant on the proximal portion, but using a stacked intersecting clip, we can close both components of that neck very nicely. And this is just the overview showing how you're working across the optic nerve on the ipsilateral side, optic nerve on the contralateral side across the chiasm, splitting the Sylvian fissure, following the M1 out, and getting right to the contralateral MCA aneurysm. And this is all subfrontal, no retraction. You can see it's a really straight shot. I think this is important because it's not easy, but, you know, as we enter this area, this era of minimally invasive surgery, we want to be able to get the biggest bang for our buck. And if a patient has multiple aneurysms on both right and left sides and we can treat those with one operation, then I think we can really do a nice job for these patients and minimize what we need to do in terms of procedures or invasion.

- Thank you, Michael. That's a technically superb job by the way. And I think you were talking about the post-operative angio. I'm sorry I interrupted you. Go ahead, please.

- Yeah, so this just shows the clipping of the left sided aneurysm, and this shows the clipping of the right side of the aneurysm. You can see the trajectory of the clip, it's from left to right. And again, that down curve of the M1 segment here is what helps that, it helps bring that aneurysm into that plane of view for the contralateral approach.

- Thank you, Michael. Go ahead with your next case, please.

- So this is another challenging case and what you'll notice here, this is a middle aged woman. She had some neurologic signs and in doing a brain MRI for those, this aneurysm in the distal Sylvian fissure was identified. That led to an angiogram. And you can see that this aneurysm is quite unusual. It's located on the M2 segment, the insular segment of the MCA. It has a, really a fusiform morphology here. And it's really quite far from where we typically see your classic MCA aneurysm, which should be right here at my pointer. So it's quite a bit further up the insula, not a very easy area to access surgically, and quite deep. This is where it is in relation to the insular cortex. So this is the view in coronal sections, just showing how there's some thrombus intraluminally. And what we're going to do with this one is a technique of trapping and bypass. Actually, it's not trapping, but it's approximal occlusion and bypass. So we can go to the video now. So from the beginning again?

- Yes, here it is, go ahead.

- Okay, so this is the view down the Sylvian fissure. And just to orient you, this is a right sided approach. This is the frontal lobe here. This is the temporal lobe here. And we're just opening that arachnoid on the lateral portion of the Sylvian cistern here to get things separated. What I have done here is again, mobilize the veins and found some arteries that are right underneath that arachnoid. Now, I'm just going to follow those arteries down into the depths of the Sylvian fissure, cutting sharply these bands of arachnoid as I encounter them to the greater depths. So here you can see the artery here. These are these arachnoidal bands that I need to free up. And again, you'll notice, no retractors, I don't like to use retractors for this part because I can use my instruments to show me where I need to see. Once we get down on these larger vessels here, the dissection becomes much easier. This is the bend in the middle cerebral at the M1 M2 junction. You can see the division into these other trunks. Again, there's a real nice Sylvian fissure here with really clearly visible trunks of the middle cerebral artery and real clear arachnoidal bands that can just be easily cut to separate the frontal lobe and the temporal lobe. Now, what we're going to do in this portion is we're going to move out the insular segments of the middle cerebral artery. So I've placed a retractor here on the temporal lobe, and these are these M2 or insular segments that we're going to follow out. I followed it now all the way to the aneurysm here and what we're seeing now, let me pause it right here. This is the artery that's going right into the aneurysm here, so this is our feeding artery. You'll just notice a little bit of the aneurysm right here. This is, again, a dolichoectatic aneurysm. So we're just seeing this sort of fusiform dilatation beginning right here, and this other artery next to it is an innocent bystander. This is an artery that does not feed the aneurysm, but simply is going around the backside, on its way. So I'm gonna restart the video here. And now this is just another view of these insular segments. And I'm preparing these because I'm going to do a little trick with the indocyanine green dye to figure out my strategy for our bypass. So I'm going to pause here, this video, and what I've done here is I placed clips on everything but the artery that feeds the aneurysm. So all of those insular segments that were innocent bystanders, I put temporary clips on. And so when we get the indocyanine green dye, what we see is vessels that are coming out of the aneurysm. And so this is, this is the artery that really, that I'm particularly interested in right here. This, I now know from the flash of florescence through it, is one of the main arteries that's coming out of the aneurysm and right beside it is another artery that will illuminate as I take the temporary clip off of the vessel. So I'm going to continue with the indocyanine green run here. And what you'll see, what I learned from that was that the artery next to that other one was the bystander. So with that information, what we're going to do now is bring two arteries together. We're going to bring the outflow artery from the aneurysm, which is this vessel here on the left, together with this other artery here, which was uninvolved at the aneurysm. And now this artery here can act as a donor to this outfall artery from the aneurysm. This is a side to side anastomosis. And so what I've shown here in this image here is two arteriotomies in the vessels and a running continuous suture that brings those together. So I'm going to restart the video here. And what we're showing here is the suturing of the inner lumen of the artery wall. So we've got the two walls of the vessels being brought together with this suture. Now we're bringing together the overlying suture line, the second suture line over the top. This is 10-0 running nylon suture. All the sutures now have been placed. This is the side to side anastomosis. Here's one artery here, here's the other artery here. And now we're just going through and tightening these sutures that I've placed. I'm using two jeweler forceps and just gradually going from one loop of suture to the other, taking out these loosely thrown sutures and tightening them up so that we can complete the anastomosis and tie things down. I like this running continuous suture because it's quick. It allows you to make multiple bites of tissue with just what amounts to two knots in the suture. Here's our final knot here that ties things down. Again, I apologize that we're a little off center here, but now you can see this anastomosis. I'm releasing the distal clip. We get a little bit of bleeding through the suture line, but with a little bit of fibroline unit over the top and a little bit of pressure, that bleeding will stop. It usually takes about two minutes for the platelets to do their thing. And once they've had a little bit of time, we can take off the other distal clip. Now we can take off these proximal clips here. And with this last one, we now can initiate flow in the bypass. So now what we have here is the outflow artery from the aneurysm being fed by another adjacent, another adjacent artery in this side to side anastomosis. Now we can return down to the aneurysm. Again, here's that artery as it's going into the aneurysm here, and you can see that it just dumps right into this aneurysm, you can see how difficult it is to see the actual aneurysm itself, it's buried in the depths of the, of the opercular cleft. And we're going to just put this permanent clip on the inflow to the aneurysm so that we can proximally occlude the aneurysm. These are the other arteries that are adjacent and innocent bystanders. These are what we've used as our donor vessels for the bypass as they come out of the Sylvian fissure. And now what you'll see is the aneurysm has been proximally occluded, we've distally bypassed here, and the flow to that angular branch has now been revascularized. This is our postoperative angiogram, and you can now see that this side to side anastomosis fills out both the outflow arteries to the aneurysm and it's inherent vascular territory here. So this is our completed anastomosis. Our clip is down here, deep in the insula, and we've completed the job.

- Thank you, Michael. If you don't mind, I wanted to show a couple of videos of mine as well, if you have a moment, and get your opinion as well. This is another MC aneurysm on the right side. As you can see, this is the temporal trunk. This temporary clip has been placed across the neck of the aneurysm, M1 because of the anatomy, and you can see the frontal branch that's coming out or the superior trunk. And again, micro scissors are used, M1 is dissected more, you know, along the medial portion and depth of the fissure. And again, a clip is placed, one across the frontal trunk to the neck, and another one is placed on the other side. Again, some creative ways to put a clip across the neck of these aneurysms. It's sorta interesting to put that temporary clip across the neck all the way. And it had to do with the fact that anytime we tried to put it more laterally, it would really obscure our field. And so it's sort of, you have to do what the anatomy gives you in terms of placing your clips. And I think this is the second clip, sort of finishing the job on the, this more lateral part of the neck of the aneurysm and bolstering the first clip. Adhering again, making sure that atrium that we talked about is patent, again, this is right temporal lobe, right frontal lobe, and a right-sided MCA aneurysm. Making sure we have a generous atrium and the ICG shows that again, this is M1 patent frontal trunk, temporal trunk, and everything working just fine. You may put a needle just to deflate the aneurysm. Do you usually put a needle into the aneurysm or not, Michael?

- Yeah, I like to deflate it just to make sure that everything's taken care of. The IC green is also real helpful. It'll tell you if there's a little bit of leak of dye into the aneurysm. So before you puncture, if you want some reassurance that it's completely closed, the IC green is a nice thing to use.

- This is another short video of, again, and right-sided aneurysm. I'm sorry, left sided aneurysm. Again, left temporal lobe, right, left frontal lobe, putting the clip across the aneurysm. It has a little bubble. This is sort of ICG before we put the clip on. I know we don't use the, usually do that regularly. And again, the clip going across, leaving a good atrium straight clip. I know some people prefer to put a curve clip just to keep that atrium as generous as possible, where the M1 irrigates into the frontal and temporal trunks. And here, again, looking more underneath the aneurysm, making sure the temporal trunk and the frontal trunk, trunks are not stenosed. This is, again, an ICG revealing the aneurysm. It's spilling a little bit, and that's because of the first dye. And as you can see, the fresh dye shows that the trunks are patent and the aneurysm is occluded. And here you can see the nuance you talked about, Michael, is if you have a lot of veins and the veins are important, you should keep your dissection on the frontal side and keep all these veins patent. It requires good amount of dissection, but it really does pay off in terms of helping a patient. This is a 55 year old female with an incidental 1.6 centimeter right MC aneurysm. And here is the preoperative 3D reconstruction of the angiogram. As you can see a very broad base, a large MCA aneurysm, this is M1, M2s, and you can see another view with a lot of branches passing by. And here is the video of this case. Again, this is a right frontotemporal craniotomy. This is the right temporal lobe, right frontal lobe, two retractors. We first, or I first tried to bolster the first, you know, fenestrated clip with a straight clip, as you can see here, and even put another clip on this aneurysm. And then ICG was actually very good and didn't show any flow. And here, you can see when I put a needle in it, there was flow. And that very rarely happens to me. And then we had to reposition the clips. And I usually, it's the fact that you did not get the distal part. Have you had an issue where the ICG is really non conclusive or it's not showing any flow, but when you puncture the aneurysm, you have flow?

- Yeah, sometimes if there's a little connection between the normal lumen and the aneurysm lumen, there may only be just a little wisp of dye that gets in, and it's that hole that you puncture that really creates a circuit or some flow. So you really have to follow the IC green out for a good minute or a couple of minutes, just to see if that little puff of dye is going to get in. And even, there are cases where it just doesn't, there's enough back pressure in the aneurysm that there's nothing getting in and you puncture it and you get some bleeding like this. But most of the time, I would say that if the ICG tells us that it's closed, it's going to be closed.

- I want to show maybe one or two more cases here. And this is the post-op angio, by the way, on this case. Again, showing how you can bolster your aneurysms, just like you mentioned. A fenestrated clip to close the distal neck of aneurysms and more straight clips to close their proximal neck, just because they're blading, the blade and the pressures are not enough for large, one large clip to close the aneurysm. This is an interesting case. And it's a variation on the theme. A 55 year old male with a spontaneous right temporal hematoma and a left sided weakness. A vascular study obviously was performed for this, for this hematoma that you can see here. And the CT angiogram revealed the very small aneurysm causing this large hematoma. And you can see on this surgical video. Actually, this is another video before we get to the one and you can see it. I don't have the angiogram for this one. You can see sometimes these patients have a very dense clots and these dense clot in the fissure can be very problematic. And it makes dissection so difficult because they're fibrinous and you sort of have to continue going through clot layer by layer. Do you have any nuances in these tough cases, Michael?

- They are very challenging, you're quite right. I think the key is to find an artery, like you're showing here, and use that as your tether and just follow that through the clot. The arteries will help orient you and keep you out of danger rather than going through the clot blindly.

- I cannot agree with you, that's sort of following the, I think, the temporal trunk more medially, trying to find the M1. It's interesting, by the way, we're both left-handed and we use very similar scissors without either one of us watching each other operating before. I don't know, it tells you something. Anyways, I think this is the M1 trunk. As you can see, this aneurysm is more distal. So after evacuating all that dense clot, we moved distally, Michael, and try to find the aneurysm with adequate proximal control. Here is the neck of the aneurysm. This is the frontal trunk. This is the temporal trunk. This is the M1, as you can see right there, here is the M1 temporal trunk, frontal trunk, the neck of the aneurysm. And we put a temporary clip, just like you mentioned, at the last stages where you really want to put the final clip across the neck. Obviously small aneurysms, it sometimes can be more difficult because you don't have much space to work through unless you go to the dome of the aneurysm. Do you have any pointers here, Michael?

- No, I think this is nicely handled. It looks real nice.

- And obviously, the ICG afterwards show. And obviously after we have clipped it, we try to dissect the dome off, make sure we haven't grabbed any of the perforators on the posterior wall of aneurysm. And the ICG showing the temporal trunk, the frontal trunk and everything is patent. And this is that case I showed you the angiogram and the CT with a large front temporal clot. As you can see, we use the superior temporal gyrus as a transcortical approach to evacuate the clot and then go from the resection cavity for the clot into the fissure, and then follow, again, more proximally until you find the M1. So this is a technique, I think, for large temporal clots, when you can find the temporal clot within the superior temporal fissure, evacuate it, obviously don't go deep to run into the aneurysm dome and just sort of follow your dissection from the fissure, rather than into from the clot resection cavity. This is again, the temporal trunk. This is the frontal trunk. This is most likely going to be the dome of the aneurysm. And again, before getting into the dome, we move more medially and find the M1 branch for proximal control. Any thoughts here, Michael, please?

- Yeah, I think that's very important too, you know, before you really tackle the aneurysm, make sure that not only can you see the M1, but you've dissected it enough so that you can easily apply a clip. Sometimes, you know, if you just are seeing an artery, but you haven't fully dissected it, you can lull yourself into a sense of security. And I also like this technique of working proximal to the aneurysm while avoiding the dome. It's actually, Aaron, you nicely go to the inside edge of that aneurysm and get that temporary clip on and minimize your dissection of the dome.

- You know, Michael, you mentioned the trifurcation. That's the trifurcation. You see, we didn't see that on the CTA, but you see, this is M1 with a temporary clip, frontal trunk, temporal trunk, and that trifurcation. And that's why you have to want to make sure you see everything, even though CT angiogram can be deceiving. So you may not see the trifurcation or the third trunk, unless you adequately dissect around and find the exiting branches, don't you think?

- Yeah, I think it's very important once you clip the aneurysm to continue to dissect, make sure you visualize everything. It's particularly important in cases of subarachnoid hemorrhage, where there's a clot that you've deliberately left in there. But once the aneurysm is clipped, you can be aggressive about removing that clot and really look around and be sure that the clip is exactly where it needs to be.

- This is again, ICG showing the third trunk, patent M1 frontal, temporal, and ultimately the third trunk, third branch. I have one last case and that's a complication. And I want to know your opinion on these difficult cases. This is the postoperative CT showing the evacuation of the clot and clipping of the aneurysm. So let's talk about complications of these MCA aneurysms. Obviously they're challenging. They're associated with risks. 68 year old female with an unruptured 1.2 centimeter right MCA aneurysm. It's a sizeable one, the lady's on the older side, but we thought it's reasonable to go ahead and treat this patient. As you can see, a sizable aneurysm with a broad base. It is impressive how superficial this aneurysm is to the cortex. And as you can see in the video in a second, this is a right sided frontal craniotomy. And you can see a little bit of the superior temporal gyrus was removed to expose the aneurysm. This is the temporal trunk. This is M1 and you will see the frontal trunk at the depth of our dissection. Actually, this is the frontal trunk right here. I put a fenestrated clip, try to, again, close the distal neck and bolster it with a straight clip more proximally. And you can see sort of moving around a little bit. It's interesting, these clip appliers are so long, usually that makes placing them across more superficially located aneurysms difficult. And here you can see, it may be minimally is in stenoses, stenosing the M2, here it is. And we thought the flow was decreased after we did a micro-Doppler ultrasound evaluation. And just, things didn't look right. And here you can see it's just a little bit too close. The clip was sliding as well because of the atherosclerosis. And we did an intraoperative angiogram that revealed the M1 was slightly stenosed. As you can see in a second, I'll be able to show you. Here it is, the stenosis across the M1. I'm sorry, the temporal trunk. We repositioned the clip, the patient woke up with confusion. As you can see, she has evidence of hypodensities in the right temporal lobe. She was confused for about two weeks and was non-vocal. And when we repeated the CT a month later, when her neurological status returned to baseline, that hypodensity was no longer there. On this CT, I thought this is for sure a permanent stroke, but in a repeated CT, repeat CT scan, it's gone. Do you, have you seen this before? Is this the penumbra effect where eventually it goes away?

- Yeah, that's probably what, what it was. And it just shows that there often is good collateral flow to that posterior temporal region that can compensate for a little reduction from your clip.

- Yeah, so, but obviously this could have been a permanent stroke, but as you said, the collaterals made up for it. Michael, I want to thank you for your time. I know this was a longer session than expected. We do really appreciate your expertise.

- It's my pleasure, Aaron.

- Thank you.

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