Seven Sylvian Splits: Opening the Gateway to the Subarachnoid Space

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- Colleagues and friends, thank you for joining us for another session of the virtual OR. Our guest today, Dr. Michael Lawton, from the Barrow Neurological Institute. Obviously, Mike doesn't require any introduction. He is one of the most talented neurosurgeon I've seen at work. He has pushed the boundaries of microsurgery, innovation, and really an incredible author. So I'm very honored tonight to have you with us, Mike. You've been with us many times and very rightfully so. He's going to talk to us about what I considered the most important dissection in skull base and vascular neurosurgery, something that opens the world of arachnoid cisterns for us and makes microsurgery so much less traumatic. At the same time, this basic technique often can be quite difficult, and therefore it really attracts a lot of attention. And that's a traumatic split of the Sylvian fissure. Mike, again, thank you for being such an incredible colleague and dear friend, and I'm very much looking forward to learning from you. Please go ahead.

- Aaron, always great to see you, and it's an honor to be back for I think the third or fourth time on your show. So well, yeah. It's my honor to talk to you about a favorite talk topic of mine, the Sylvian fissure dissection. This was a talk that somebody asked me to do recently at one of these webinars. So you'll have to pardon my trademark sudden usage here, but I did categorize this into the seven Sylvian splits. And hopefully you'll indulge me with that. Sorry. Okay. So by way of introduction, as Aaron said, the Sylvian fissure really is the gateway to the circle of Willis, which is where all the action happens when you're in vascular neurosurgery. So I view it as one of the most important microsurgical corridors that we have. And if the fissure splitting is something that you can do well, it just opens that gateway so that you had incredible options for exploration and for accomplishing your mission. It's interesting, if you think about the Sylvian fissure split, it's the first thing you do really when you sit down and go under the microscope. And being at the front of a large, long sequence of surgical maneuvers, how that goes for you I think greatly impacts the tone and outcome of the case. If splitting with the fissure is a real struggle and it puts you in a bad mood or hurts the brain or upsets the rhythm that you're trying to establish, it really can throw you off a step. And so it really is important not just for the obvious access thing, but it's important for the whole surgeon mentality thing as well. So I call it perhaps the most valuable skill in microsurgery because I'm constantly using it. Just today, I used it to do a clip occlusion of the carotid artery in anticipation of a big skull base tumor resection that we we'll be doing later in the week. And we did a bypass, and I needed the fissure for that. So that was a tumor case where the fissure dissection was critical. And I did a basilar apex aneurysm. And you simply cannot do a basilar apex aneurysm clipping well without a good transsylvian dissection in the Sylvian fissure split. So I've divided this talk into the seven splits, and I'm gonna start with the first one, what I call the Intern Fissure. And this is the one that, you know, you almost want to just pick up your phone and call the intern into the operating room when you see this because it's just such a treat and it's such a confidence boost. It's illustrated here. The frontal lobe and the temporal lobe are slightly atrophic. They don't even touch one another. You can practically look through the arachnoid and see the MCA through these arachnoid layers. And, you know, it's embarrassingly easy, but this is sort of the beginner's fissure. And, you know, these are the attributes listed here. And you really are able to very cleanly and sharply get that Sylvian fissure split and get right down onto the MCA, which then leads you on your way into all those other arterial finds beyond the MCA. Okay, so this first video is an example of that intern's fissure. You can see there really are no veins. Very often, we'll talk about this more later, but very often you'll have veins that I call the gatekeeper to the fissure. But here, there are no veins. You can see that it's just a layer of clear arachnoid, You can see that it's just a layer of clear arachnoid, and you see right down to the middle cerebral vessels. These are the M3 segments coming into view. You can see the insulin below it. You can see these bands of arachnoid that bridge from temporal to frontal. And a couple of pointers. You see how my suction in my right hand, I'm left-handed like Aaron, but my right hand is pulling the tissues and putting traction on those bands of arachnoid, which is a very important thing. This is that whole dynamic retraction thing where you use your instruments to put tension on the tissues, which helps you cut and dissect and really facilitate the split. So here, almost effortless. We're already down on the dome of the aneurysm. And I like to make sure that I don't just see the aneurysm and get sucked right down to that action, but I like to make sure that I've completed the split. So I've moved a little bit forward to the sphenoidal portion of the fissure, right along the sphenoid ridge, and I'm doing those final snips here to disentangle or separate the edges of the frontal and temporal lobes. And think, you know, what I'm doing is creating a wide arena or a wide funnel and not letting myself get sucked down into a cone. And now once that's done, you have your view here to the aneurysm. And now we can really get to the attested hemorrhage. In this case, it's this middle cerebral aneurysm. So on many of these, you see the dome projecting right at you. It's a laterally projecting aneurysm. So it's important to jump around the aneurysm proximally to get that proximal control. Here I'm working the neck. You can see how the superior division is easy to see. It's on your side of the dissection. The inferior division on the temporal side is harder to see. It's buried underneath the aneurysm. And so that one takes work, almost always, to find it. So you've gotta get behind the aneurysm, find that temporal division. And here's a nice view. You can often see it in the deeper portions underneath the aneurysm, more distally. And if that's the case, you then just follow it more proximally into the neck. And so now we see the two trunks. We can see the neck. There's a sort of that extra lobe that's adherent to the temporal side. But now we're ready to clip this thing. I'm gonna use a stack of straight clips. So our first clip is just going across the neck with the tips focusing on the distal reconstruction. So that tip is going right over the shoulder of the inferior division on the temporal side. And I'm slowly advancing the tips so that the tips are right in that spot, past the shoulder, and in the hook of that contralateral, or that deep M2 right there. So you can see that that clip leaves aneurysm on the near side, which is fine. I'm gonna clip this in steps. But that distal reconstruction now on the distal side of the neck looks great. So now with that closed, we can just do a little bit more dissection here on the back just to see this hidden branch that needs to be inspected to make sure that it's not occluded. And you can see that that's freeing that trunk, and that just gives me a better chance of inspecting the clip placement. So I'm happy with that. Now I turn my attention to the near neck. I always clip from deep to superficial. So, you know, it's nice to take care of the hard stuff first, and then the easy stuff last. So here I'm gonna apply this intersecting, understacked curved clip with the assistance of a little temporary clip to soften things. And here there's a little remnant. So I put a second intersecting clip. And you can see this configuration nicely closes that near portion of the neck. And so this is an example of a stack of clips. There's actually four in total now. You can see that little mohawk or that little stack underneath the primary clip. And this does a good job. Here's yellow 560 as a way of confirming flow in the trunks and also the little perforators adjacent to it. And here just incising the dome, confirming that we have complete occlusion. So this is an example of the intern fissure, and you can see how relatively simple and straightforward it is. There's some atrophy, there's no blood, nice and wide open. The veins were very friendly to us, and it made this case a real joy. Number two is harder. It's what I called the Apposed Fissure. And unlike the Intern's Fissure, you can see from the illustration that there is no atrophy. The Pial is apposed against one another, and the Sylvian cistern is closed. When you look down the fissure, you don't see the MCA vessels underneath. The arteries are concealed. And so you have to go from cortical M4 segments down through the opercular portions along the M3 segments, and then find your way into the Sylvian cistern where the M2 segments are located. And that is the distal-to-proximal dissection order that's so important. Once you get down to the M2, then you can work from inside back out again. So you dive down, you find your M2, and then you work your way back out. And that's the inside-out dissection technique or the Yasargil, peeling the orange from the inside, which means digging your thumbs into the center part and then peeling it from pressure inside. It's the same concept. And this is really the best way to split a fissure. So a couple of illustrations to make some points. The Sylvian veins, when they are not so friendly, as that first video showed you, you have to mobilize them temporally, which means coming across a tributary or two on the frontal side. And that frees up the trunk, the Sylvian main vein, so that it mobilizes temporally. And the veins are descending over to the sphenoparietal sinus. So you want to get on the frontal side. If you get on the temporal side and the vein is descending into your dissection path, you're gonna have to cross it, so it doesn't help you. So it's really important to try and stay on the frontal side. The illustration to the right shows that distal-to-proximal order of the dissection from the cortical M4s down to the opercular M3s, and then down to your trunks. The key is to find an artery on the cortical surface and follow it. Because the arteries live in the subarachnoid space, they'll show you the way. And so you just have to find it and follow it. And if it keeps diving deeper and deeper through apposed tissues, you just have to keep following it and forcing your way down. So this next video, we'll show you one of those fissures. Here we are. I've gone past the veins here. And you can see the veins, again, are doing their gatekeeper function, kind of bridging and crossing. But you can see when we get to this portion of the fissure, you've got apposition of pial to pial. And the preservation of those pial surfaces, those pial layers is so critical because it protects the brain and allows you to do your dynamic retraction, allows you to put the tissues outstretched, and really guides your way down. So it's really important. Here, you know, once again, you go superficial like I'm showing here, where there's a nice layer of arachnoid, but then you get back into the de-proportions where you've got apposition. If you look down to the lower left corner, you can start to see the bigger vessels coming into view. And that's that inside-out technique. You want to get down to those deeper vessels. And once you spot them, then you advance a little, and then work your way back out again. So this is a carotid terminus aneurysm. You can see it coming into view here. The supraclinoid segment is in your upper left corner. The M2, M1, sorry, is in your lower left corner. The A1 is right in the center. I'm working my way across this aneurysm. There's a little recurrent artery of Heubner that's adherent to the dome. But you can see I can sweep that off of the dome, get everything freed here. And, you know, the name of the game with these terminus aneurysms is taking good care of Heubner, taking good care of the terminal perforators. And then once you've got that, then this clip parallels the M1-A1 plane, goes right across the terminus. And then the key is to get behind these things and make sure that you haven't compromised the perforators. And there we had a nice view of that perforator in the back. So in this case here, there was also a distal middle cerebral aneurysm, which you can see here. So that's also on our dance card here. And so here the aneurysm is in view. And once again, I'm gonna use an initial pilot clip to close the anterior portion. Then I'm gonna go underneath with a slightly curved mini 2.8. And I'll take out that other portion with the understacked clip. And here I'm creating this sort of mohawk of clips that take care of each and every little piece of that proximal neck. So that's just a nice demonstration of the Apposed Fissure, just showing how you gotta work your way through that zone of Apposition to get down to the trunks, and then you'll find your way through the rest of the fissure. So we can skip forward here. A slight variation of the Apposed Fissure is this Interlocked Fissure. And whereas the other one was straight layers of the temporal and frontal lobes that kind of are parallel to one another, these are interlocked. You've got frontal lobe herniating into temporal lobe or vice versa. And those interdigitated fissures are even harder because you can't just go straight down. You have to follow the contour of the lobes in order to free them. So that's the point there. And I love this image because it makes the point that the arteries in the Sylvian fissure go one side or the other. And that's such a beautiful anatomical truism because you've gotta part the waves. You've gotta like, find your way through this jungle of arteries. And knowing that the arteries go either temporally or frontally, but never both means that they're gonna be able to be swept to the side and allow you to get right down to the center of the fissure. You can be fooled. You know, in the examples that are lettered A, you can see how a branch is going temporally and it's obvious, or vice versa. A branch is going frontally and it's obvious. But the Bs are the tricks. You know, you can have an artery that's ultimately going to the frontal lobe, but sweeps over to the temporal side, and it looks for all the world like it's a temporal artery. But you've gotta be smart enough to recognize that, and you've gotta free it from its frontal, or its temporal adhesion to get it over to its native frontal side and vice versa. So those are the tricks to worry about and identify. So here's an example of one of these interdigitated fissures. So here, actually, my resident is dissecting here, and interestingly, he's not even going down the right plane because it's so confusing. He actually went into a sulcus adjacent to the fissure. And here I've come into the case, and you can see I've jumped over to my right, and the fissure is actually to the right of where he was dissecting. And that's really where these interdigitated fissures can be so deceiving. But once you figure that out and you find your trail markers, which are the arteries, of course, you follow them down and those areas of apposition starts a part. So here you can see a little artery that's going to the frontal side. And here is a zone of apposition, which we work our way through. And at the bottom of that, you see a trunk. And then we work our way inside out, peeling the orange from the inside to finish the fissure split. So now we're down in the carotid cistern, following the anterior choroidal artery back. And you can see as this gateway opens up, we really can get our way all the way back to the basilar apex. So this is a basilar apex aneurysm, a small one. And this is the clip going on. It's a small, sort of a blister-style aneurysm. And you can see a little side curve to the clip. The bigger of the aneurysms here is this superior cerebellar artery aneurysm. I forgot I can draw. The superior cerebellar artery aneurysm is over here, shown there in kind of that yellowish color. That second clip went onto that neck. But it was a twofer. We were doing both that basilar blister and the larger SCA. But once again, you can see how the gateway of the Sylvian fissure is what unlocks that space And gets you to where you need to go. All right, so number three is the Bloody Fissure. Same principles as we've talked about before, but there really isn't any easy visualization. You have blood that takes it away from you. And so it's almost like the analogy of flying an airplane in fog. You have to rely on your intuition. You have to rely on your other clues. You can't just look and see where to go. So there's that problem. There's also the problem of ruptured aneurysms causing the brain to swell. So you can have tissue edema. The natural spaces that normally you work in are obliterated by the brain edema. So those two factors alone make this a more complicated and more difficult task. And then you've got the re-rupture risk on top of it all. So you've got some tension on top of all of these preconditions that make it harder. I like to think of the Bloody Fissure as archeology. You have to excavate. You have to find your way through the dirt or the mud or whatever it is that you're digging through in that metaphor. And in this case, we have to excavate our way through the blood to find the arteries and find the pathology. So this is the Bloody Fissure. The key thing with the Bloody Fissure is to think about your dome projection. 'Cause the last thing you want is that re-rupture, which is typically done by inadvertently coming upon the dome. So you gotta think about how the dome is pointing, move your dissection away from that direction of the dome projection. And so as in this illustration, you wanna do your early steps down here. Let me draw here. Down here where it's one, two, three, four. Finding your proximal control, finding your A1 and M1. This gives you control of the aneurysm so that any subsequent dissection is safer. The steps that we've been talking about for MCA is that finding of the superior trunk first, working your way across the neck to the inferior trunk on the temporal lobe side. Same as before. But this illustration to the right here shows you these dome projections. These are Rotins rules. You know, the aneurysms project in the direction the blood would've flowed if it continued onwards. So the aneurysms often project laterally, they point towards you, and you've gotta just be careful not to inadvertently run into it. You can also have little arcs or curves that will project the aneurysm temporally or frontally and cause these points of adhesion. Those are also important to think about because, you know, where the aneurysm dome is adhesed, that's where you can sometimes tug or pull or over extend. And that's also important to be aware of. So here's our video example of that. This is a Bloody Fissure. You can see the Sylvian fissure is just filled with organizing clot. The arteries here are essentially buried in this thick, tenacious clot. So we had to cut through clot. We've got to pull and pick our way through that clot. But as we do, the aneurysm comes into view here. And again, this is that archeology in action. I actually kinda like this. It's sort of fun to have a lot of blood around an aneurysm. It actually creates some easy dissection because oftentimes the fissure is filled, and it's just a matter of finding those landmarks, like this artery here. And once you find one, you just follow it back to the neck. And the clot around the aneurysm and around these branches comes off pretty easily as long as, again, you remember where the dome is, where the rupture site is. And here you see we're getting to that inferior division. That's that difficult spot to find. But we can work our way in there. And again, some clot behind the aneurysm now, which we're loosening up and freeing. And now you can see nicely the pathology. There's this multi-lobulated dome. This is the M1 that we'll approximately occlude to soften things. We can now be a little bit more aggressive with the dome. Here I'm mobilizing it out of that insular space. And once again, our pilot clip goes across the distal portion. Take care of that first. Again, notice how those tips are lined up nicely over the shoulder. And then the second clip right across the back taking care not to grab that branch coming off. And then with the distal part taken care of, we can now focus on the near part of the neck. So there's that little remnant underneath the, the pilot clip. And we again go on with these understacked minis and this allows us to tailor that tissue so that it feeds the branch that's coming from it. But would've been difficult if we tried to do that with just a single clip. So again, the archeology or the Bloody Fissure, you can see how brain is a little swollen, but we've done a nice dig there, found the aneurysm safe, safely and successfully. And now once it's clipped you can do a little bit more excavation, make sure that you've taken care of all of your branch vessels, haven't missed anything in the back. And this is just our post clipping inspection. Very important to make sure that you've taken care of all of the branch vessels nicely. I see green. Very critical to check your work. You can see our little branch there is nicely illuminated. The main trunks are filling well and we don't see any flow into that aneurysm. So this was a trifurcation, two big trunks and a small middle trunk. And then just a little fine tuning here. Again, just sort of tailoring everything that could possibly be perceived or recur later as a new aneurysm down the road. And that should be our final overview. Alright, you can skip now to number four. So the talk about Sylvian fissure splits, the ones that we've been talking about have been pretty much aneurysm style, Sylvian splits, but there are portions of the fissure that can be valuable. And this one here is an example of the Anterior Fissure split. This is a just splitting the part, the part of the fissure that's gonna take you to the Limen insula or the short gyri of this, of the insula. So it's the vertical or sphenoidal of the fissure. You've gotta open that up. You also have to open up the, the horizontal part, which is overlying this. You gotta get down to the level of the MCA bifurcation. And then just deep to that, you get to your Limen insula and short gyri. And this is, this anterior fissure split is really nice for, for ABMS and cavernous malformations in this location. So these are those two segments. The the purple is that horizontal part of the split. And then you can see that you make this sort of right angle turn to the vertical portion, the sphenoidal portion. And it's usually a a two separate step, at least in terms of the arachnoid opening for the anterior splits. You dissect in this distal to proximal direction. And here's an example. So this is a Friendly Fissure. You don't see much in the way of veins that are in your way. There's just one vein right there that is in the neighborhood but not really a real obstacle. You can easily free that up and move it to the sides. But you can see we're working our way. This is that horizontal portion of the split. You gotta get through all that arachnoid, work your way past the veins, follow the opercle segments down. And at the end of that you get down to these M2 segments, the insular branches. So here those insular branches come into view. Sometimes it's not enough, you gotta keep going. So here I'm doing some dissection, a little bit more distally in the fissure. So again, you have to just go back to what I call another node, which means find another artery, follow it down into the insular region there, and you'll join with the prior dissection. And then you just connect your nodes and you can see how this really starts to open up the Lehman insula and the insular short gyri. Those are the stem arteries of the M2 segment. There are three of them there. And as we come upon them, you can see that they nicely lay out and define the insular gyri underneath them. I believe this is a cavernous malformation. Or not, this might be an AVM. Yeah, this is an AVM. So what you're seeing here is going through a little piece of the insula to get to the hemorrhage cavity that's adjacent to the AVM. You can see I made a second opening around the, that insular artery. This is now the M1 segment that I'm inspecting. I'm just getting a sense of how those feeding arteries come off of the M1 and feed the nidus. And now I'm tracing those to the borders of the AVM. So you're seeing here, these are those feeding arteries to the AVM They're right on the adjacent part of the hemorrhage cavity. This was a ruptured AVM and probably a few weeks out. So you see some encephalomalacia and some resolution of the clot. But here now I'm working my way around the small nidus and you can see how I've mobilized the nidus, there it comes out. And you can see that I'm not in the usual part of the fissure that we were talking about for MCA aneurysm. It's in further posterior, I'm in the insular portion. So this is that anterior part that gets you to that portion of your anatomy for these kinds of lesions. Number five, Posterior Fissure. So if what we've talked about just now got us to the short gyri, sometimes we need to go a little further to the long gyri. Again, it's primarily that horizontal or cortical part. You don't need as much of that vertical part that descends down to the carotid cistern. Again, you've got the veins as your gatekeeper, as you go back, particularly on the dominant side. You've got language areas and loader areas right next to you, you've got we keys area on the temporal side. So you, you are surrounded by eloquence, which raises the stakes. It makes it even more important to protect your pial and protect the tissue. But again, you're looking down into the opercular part of the cistern looking for the M2 stem arteries and trying to get down to the long gyri. Now the circular cell side are the parts of the, the distal cistern that go superiorly and inferiorly. So it's not just a matter of getting into that space, but also sometimes following them upwards or downwards, get into those little hiding zones for the lesion. But this is a good time to talk about the veins. So this is the kind of variation that you see with the Sylvian veins. That intern fissure that we started with had no veins. This I think the last fissure I showed you had a single vein, but you can also have two parallel veins or you can have a complex and you know, you've gotta find your way through the veins to even get started. When it comes to what you can sacrifice and what you can't sacrifice, you have to look at the drainage pattern, which means following the flow of the contrast on your angiogram, the superior and posterior drainage systems are favorable because if you've got that, then you can be a little liberal if necessary in dividing a temporal bridging vein. However, diagram B in your upper right as an example of the anterior drainage system. And if you have a a dominantly anteriorly draining system, you've got to preserve that connection to the spheno pial sinus, which may mean going extraordinarily and transposing the spheno pial sinus or working around that venous connection. But whatever, whatever your strategy, you've gotta preserve that. Otherwise you can compromise the venous outflow and end up with the venous infarction. All right, so here's our example of the posterior split. So here, I'm first just gonna work my way through the veins. You can see that the veins really are independent of the arteries. So you can mobilize them separately away from the arteries. Here I'm finding my, I'm finding my deep arteries here. So this is an example of one of those arteries leading down into the deeper spaces. So you get on top of that thing and you follow it down. Here is another one. So these are the nodes. So each one of these arteries provides you with a, a trail to blaze on down through this tight apposed tissue. And as you deepen your way down, you're gonna get to that cistern underneath where they'll all interconnect. So here we're getting deeper, we're getting to the areas of the trunks. Here's a trunk, there's a trunk. And as we get down to that level, this space starts to open up. So here I'm starting another spot more posteriorly, just to widen this up. This was a very distal, very distal MCA aneurysm. And we did a flash fluorescence study which identified the outflow from this distal aneurysm that identified the site of the bypass that we need to do. So this will be proximal aneurysm occlusion and a distal bypass using flash fluorescence to identify the outflow vessel. Our aneurysm is over here in this space here. This is our confirmation that the bypass has taken. So now, well actually this was a double bypass. We did a second bypass because the aneurysm had two outflow arteries. Here you can see one bypass there, another bypass here. And now with those two bypasses in place, we clip down the aneurysm and we've got a proximal occlusion and a distal bypass and a good outcome. All right, coming down the home stretch two more. The number six is the, what I call the "Whole enchilada." And what that means is that, you know, for some lesions you just need the whole fissure, you need the anterior portion, you need the posterior portion. And really the "Whole Enchilada" is really just putting those two together. You can dissect proximal to distal. You got the whole candelabra exposed from M1 out to M4 and it gives you the widest possible corridor. And this is great for the large lesion like this giant cavernous malformation. So the frontal lobe is to your right, the temporal lobe is to your left. Once again, this is that horizontal dissection. This is now in the vertical part of the fissure for the vertical dissection. Here's some arteries going down the veins roll away. And once they roll away and the gate opens, you can just follow the veins on down. Sorry, you can follow the arteries on down. There's your artery here, here's another artery there. And so once you get on top of those, you just keep deepening. And again, we're looking for the trunks and there's the trunk down in that space there. Once you find the trunk, it's that inside out technique you can, you can open things up down at the depths, but then you can start to go from inside out and you may need to expand, add additional range on your split, like I'm showing here, this is some additional stuff we need to keep working our way back in that direction. So we keep going. So this is now more towards the angular part of the fissure angular cortex or angular gyrus will be back here. And so you just keep adding nodes to the split and as you go down another node, you join it with your prior dissection and this whole thing just starts to join like connecting the dots. So you're joining your noble dissection like you do, you're connecting at the dots. And this fissure split just keeps on widening. So here there's a nice overview. So your angular gyrus is back here, your Sylvian fissure split is all the way this way. And you can see it just keeps going. So at at the end of all that you can see the entire length of the M2 segment from the Limen insula all the way to the very end of the long gyri. And you can see here that hemosiderin stain, that's our clue to the underlying cavernous malformation. Now I've cut through the capsule of the lesion, there's some nice liquefying blood inside of that. So we can evacuate the easy blood. Now we get to the malformation itself. And here I'd like to try and preserve the capsule because it helps to make sure that all of the lesion comes out a hundred percent. And you can see there this very large malformation comes out nicely and we have a good result all that done through the branches of the M2. Alright, the last one that I'd like to touch on is what I call a Contralateral Fissure. So everything obviously that we've been talking about has been ipsilateral, but it is possible to do a contralateral Sylvian fissure split as shown here. Why would you do such a thing? Well if you've got near MCA aneurysms or you have aneurysms on both sides and you wanna spare your patient two craniotomies, then the contralateral fissure split is the answer. So you've gotta work your way as this illustration shows on the right across the optic apparatus, you go from ipsilateral A1 to ACOM complex to contralateral A1 to contralateral terminus and then out the Sylvian fissure. And it's no question a long reach and has some risk but you have proximal control always, you have a good view. In many of these cases what I look for are a couple of things. This is a case example with this example we'll show you is the, there we go, good. So this example shows you the things that I look for in going across. You wanna have an aneurysm that's projecting either inferiorly or anteriorly. You want that contralateral Sylvian fissure to have a little bit of atrophy. You don't want subarachnoid hemorrhage because that makes the brain swollen and more difficult to visualize. And so you know, you just have to pick these wisely. So this is the view looking down the fissure and believe this is our, yeah, this is our Ipsalateral aneurysm. No sorry, that was our contralateral aneurysm. You see how hard it is to even know the difference. You know, once you're under the frontal lobes and you're looking across and seeing that contralateral Sylvian fissure, it's really no big deal. So now we're on the Ipsalateral side and you know we, we've got the optic apparatus here, the Ipsalateral carotid artery here. The temporal lobe is over there. There's a little PCom infundibulum here. With this blister type aneurysm on the back end of it. So we take care of that. These little sessile aneurysms, sometimes can ramp up the clips. So you can use that first clip as an anchor for the second clip as an understack. And it's a nice anchor for the true, for the better clip placement. So now this is the Ipsilateral aneurysm here you can see the pathology in better view. And now that we've got this aneurysm in view, we'll just clip it like many of the others, this first clip going across the base and we'll establish the pilot clip for the reconstruction. You can see how that blade slides across or underneath this adherent vessel. I used a temporary clip there because it just softens things up and makes it a little easier. And there's one other aneurysm here, a little bit more distally on the M2 and see it there. So using all the spaces in that Sylvian fissure, we find all of her aneurysms and take care of them through this gateway. So three aneurysms in one shot. You can see how that contralateral dissection took me all the way across to the other side. The aneurysm was very favorable anatomically for the Contralateral exposure. And you know, if you choose them carefully, you can do it. If you look carefully, there's a little flow in this aneurysm, you see that. So this one took a little bit of a booster clip to strengthen the closure of the blades. So you see that overs stacked clip there, our fluorescent green was very helpful in showing that small little leakage one. All right, we can skip, I believe I'm at my concluding slide. So there are the seven Sylvian splits from the Intern Fissure all the way down to the Contralateral Fissure. It's important to recognize that not only are they seven different types of technique, but it's also like a ladder of complexity where you just have to start at the lowest run and work your way up to the highest run. And you know that Contralateral Fissure, that "Whole Enchilada", those are some tough splits and you know, it really requires that you feel comfortable doing all the different techniques that we've discussed. So again, Sylvian Fissure is the gateway to the circle of Willis and beyond that makes it one of the most important microsurgical corridors that we have. Again, if you do a good split and you feel good about how the case starts, it just carries on through the rest of the case. So it's really important for both tone and outcome. And you know, I do think it's perhaps the most valuable skill in micro neurosurgery is just the ability and the confidence to really split whatever fissure is thrown at you and to do a good job with it. So Aaron, I'm at the end of my slides. Thank you.

- Mike. Great work. Really enjoyed your lecture. Great pearls in terms of this very important maneuver, I always think that people always underestimate the importance of Sylvian Fissure dissection. And in fact, as you very well said, it really sets the tone in surgery. If the fissure goes well, it really, it almost ruins the rest of the case and the brain looks banged up and it it just, you start wrong, it ends almost wrong. So it's best to be able to focus on that, keep that in mind. I really like the anatomical features you discussed about faithfulness of the arteries to the lobes and the fact that we really have to be able to dissect them and not try to take any arteries whatsoever. And importantly, the veins, they also get less attention unfortunately, but they're as important and something that I've learned is that if the Sylvian vein is very large and there is no vein of trolard, most of the hemisphere may depend on that vein for drainage and therefore you have to exercise caution in terms of taking it cavalierly. I think often if you do an angiogram, and I think there is study on that after doing Sylvian fissure dissection, even though the artery, the vein may look good, most of these throttles unfortunately, so in specific patients that have very large Sylvian variants and preoperative angiogram demonstrates that the vein of trolard is very atrophic and there's no other veins parasagittally. You have to be very cautious to really treat that vein a lot more respectfully. Do you agree with that comment?

- Totally, totally. There is a slide in there, sorry, I probably threw too many slides at our audience here, but there is one that broke it down into the posterior drainer, the superior drainer and the anterior drainer. The superior one trolard, as you mentioned, the posterior drainer is labade as you mentioned. If you've got either one, you can be a little bit more liberal with the temporal bridging veins, but if you don't have connections to those two, you've gotta save it. And you know when, when you're faced with that, the more I do it, the more I love it. This anterior or this sphenoparietal sinus transposition maneuver is really slick. You essentially keep those anterior connections. You go extradural, you mobilize the dural with the temporal lobe and you can still get pre temporal. It's just a combination of that intradural extradural. So that's one nice way to deal with it. The other way, you know, sometimes if you've got a big bridging vein and you just slide inferior to it, you can still look up, you know, for a baslow apex for example, to get that pre temporal view and you're just working underneath the bridging vein. Other times you can just maybe depress the vein and get enough of that pre temporal window to finish what you need. But you're right, if you're careless and you compromise or take a dominant anterior draining vein, you can get a venous infarction. That's what I worry about getting. It's actually pretty rare that you see that, but I think it's because we've learned our lessons in the avoidance.

- I agree. I also very much like the laton elite scissors, I think they have this samurai sort of curve to them and this upward curve to them really can nicely work both as a dissector and as a scissor. And I think that's really can add a lot in terms of using the micro scissors to do multiple tasks at the same time. So it looks maybe, well it's just like a scissor, but in fact there's several advantages that make Sylvian fissure dissection a lot easier with those. Don't you agree?

- Well, of course I agree because I'm biased, but my biases aside. I think those scissors have become, for me, like the mouthpiece, like once you learn how to use the mouthpiece, you can't operate without them. And the scissors, once you operate with sharp samurai style scissors, you really can't operate without them either. And the beauty of the the product that we developed was that they're what we call resposable meaning reusable and then disposable after some point. So the reposable scissor means that it's always sharp, you know, you use it for 10 times when it gets dropped or when it gets dull you throw it away. It's not like that $1,500 instrument that you have to keep using over and over again or sent for sharpening or, or that gets rusted because you've had it for so long. The beauty is, it's like, you know, when you're shaving, you know, you can always pull up that next razor and you know that it's gonna be nice and sharp and you'll get a clean shave and you won't cut yourself. Same with the scissors. I think it's got all of the ergonomic advantages of that design plus the reusability of it makes it sharp, which is really the other critical element.

- Right? Right. Because as you see, the sharp tip allows you to almost use it as a

- Yeah. as a knife, as a sharp knife and that, and you pull, you cut towards yourself, which is a lot safer and you can see everything. So when you close it, it becomes essentially like an 11 blade, but you are cutting toward yourself and the tip goes under an acaroid and scratches it toward you and cuts it. And I really think that technique is so valuable in Sylvian fissure dissection.

- Yeah, it's kinda like when you're riding a bike, you have to be able to turn the steering wheel left and right and it's the same with those scissors. I like to be able to turn left and right depending on the direction I'm moving. And by not having it be a banded instrument, but rather a straight instrument, it allows you to flip it very easily in your hand. It allows you to turn just as if you were, well I love to mountain bike and if you're on a single track trail and you're winding your way down the mountain, you've gotta be able to, switch from one turn to the other really quickly. And it's exactly the same way of dissecting. And your point about closed versus open dissection, when you close the, the tips, it's essentially, I like to think about it like a number six. There really is no nothing sharp other than the very point that's in the field. And you can use the, the body of the blade like a number six to sweep things left and right. If you open the tips, you can get tissue between the open blades and use it as an 11 blade and then third, you can cut. So it really gives you a six, a scissors and an 11 blade all really in one instrument. So it helps your efficiency even more.

- Yeah, I agree. And you know, ergonomic efficiency in the operating room is so important for a busy surgeon be able to get the case done quickly. I mean, just if you think about it, the mask switch is so critical to keep your hand free and then having scissors that are multifunctional even adds a new level of efficiency to your workflow. And that's so critical that really can save hours if you, if you add every little step to be able to do the case effectively efficiently and be able to deliver even a better outcome. So Mike, thank you for all your innovation. Thank you for all the great teaching mentorship. Really the seven series has been tremendous, such a incredible bible for so many neurosurgeons. And to be honest with you, the word as, as you enough talk, the number seven refers to the Old Testament and seven means complete. That's the seven days that God created the world and really testifies to really the completeness of this resource. So I really want to congratulate you for an incredible work.

- Well thank you Aaron. You know that I'm a huge fan of your atlas and I think this thing that I do and that you do so well is just really about transparency. You know, putting it out there, letting people see what we do for the purposes of learning and elevating the craft and my hat goes off to you equally for what you're doing with the Atlas. And as proud as I am of seven series, I still have a fraction of your following. So I'm on the hunt. Hopefully I'll catch you one day, but for now you're well ahead.

- Mike. I would say that those followers on social media, God knows how many of them are neurosurgeons, number one. Number two is everybody who reads that book knows the importance stuff in the advancement of the field. So anyways, I wanna sincerely thank you and look forward to having you again in the near future as we have had in the past. Thank you again.

- My pleasure. Thank you.

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