Transcript

- Welcome friends and colleagues for joining us for another session of the virtual operating room from the Neurosurgical Atlas. We have a special guest tonight, Dr. Michael Lawton from Barrow Neurological Institute. Michael doesn't require any introduction. He is truly a pioneer in cerebrovascular surgery, a truly gifted master surgeon who has revolutionized open cerebrovascular surgery. It is an honor for me to introduce him. Michael, you have been an amazing mentor for so many young neurosurgeons, and your international reputation is truly remarkable. Before we start and talk about arteriovenous malformation surgery, which is truly my love in neurosurgery, I wanna just take a moment and ask you, what does it take to become a master cerebrovascular surgeon?

- Well, Aaron first, thank you for your introduction. Thank you for inviting me. It's a pleasure to be here and congratulations on the success of not only your Atlas video textbook, but also these other forms that you've put together. It's truly remarkable. So I'm glad I can talk about AVMs tonight knowing that it's one of your favorite things. And about the mastery piece, what I would say to the listeners who are trying to find their way, I don't think it's a secret simple answer to what leads you to mastery. But I think for me, what it is is that I just enjoy doing this work so much. I've been at it for 23 years now in my post-training career, 30 years, if you count training, and I don't get tired of it. And I think if you love what you do and you show up to work every day, enjoying yourself, trying to challenge yourself, and looking for ways to make contributions, then I think mastery comes really on its own feet. It just finds you and you achieve it. And I think it's that combination of loving it every day, working hard every day, trying to increase your experience and challenging yourself. All of these things compound themselves and result in a mastery or a skill level that is beyond the standard. Even today, I did a case that I'd never done before. I thought of this idea probably two years ago when I first saw patient and I didn't end up doing it on this guy 'cause I was worried about taking chances and he was nervous. But another case finally came around that had the same unique anatomy and tried something that I'd never before, and it was a real kick. So even decades into this, I would say that if you're always thinking and challenging yourself and looking for ways to make this fresh and new, you will become a master, it happens, mastery will find you.

- Thank you. Let's go ahead and jump into the lecture and look forward to your amazing lecture.

- So I'm gonna talk about AVMs. It's Aaron's favorite surgery, it's one of my favorite surgeries. I wouldn't say that it's all fun and games because these can be really a difficult and painful operations when you get in over your head. But I liked them because they really test the surgeon unlike any others, both mentally and technically. It really becomes this incredible game of chess. And I think hopefully in this lecture, you'll get a taste of all of those different elements that go into this. So I've titled it "surgical Master Class," because I want all of you to become masters. There's a lot that goes into learning AVM surgery. And my hope is that there'll be enough of you out there who will dedicate themselves to make this your life's work like I have and like Aaron has, and really carry this forward. So just to put this in some kind of context for you, like I said earlier, I've been in practice for 23 years, I've done over 900 brain AVMs. I kind of look at AVMs as home runs in a career. You can get the hits, you know, aneurysms are like base hits if we use the baseball analogy, but AVMs are like home runs and these are much harder to get into the statistics book. I've had some good numbers. I just put this in context of my mentor, Dr. Spetzler, and also in the context of the surgical volume in ARUBA just so that you have a sense of where my comments are coming from. I tried to boil down some of my ideas about AVM surgery in this book. It was the second book that I wrote as a single author. And the idea was to try and make sense out of AVM surgery. It really was something that I didn't fully understand when I finished my training, because you don't often get the opportunities to do a lot of these as a resident, and so much is happening that you don't always understand it. And so I wanted to just like pause and try and break it down. I wanted a taxonomy for AVMs that allowed us to recognize and discuss these different types of AVMs. I wanted to conceptualize the steps, and I wanted us to ultimately be better because we were under the scrutiny of a lot of other clinicians after the ARUBA trial. And I wanted all of us to kind of push ourselves to that next level. The metaphor for the book was war. And the reason is basically AVM surgery, you know, you've got a battlefield, it's your anatomy that you're dealing with with each particular AVM. You've got an enemy, which is the AVM type and subtype, and I'll talk about what that means. You can really break down this vast spectrum into simple classifications. And then finally you need some sort of idea of your progression through the resection. And I think it's important to have that in mind, and that's your battle plan. So you've got a battlefield, an enemy, and a battle plan, and you can put these together to win the war. So this slide is meant to show that AVMs come in so many different sizes and shapes. There aren't any two AVMs that are the same. And if you look at every AVM as being unique, then it becomes difficult to digest all of this. But if you stand back and you try and develop this taxonomy, then you can think of AVMs like we do animals in the animal kingdom; we define them by their genus and their species. And I think with AVMs the same can be done. Instead of genus and species, I call it type and subtype. But the types relate to the location and these are the seven different types in the frontal lobe, temporal lobe, parietal, occipital lobe, the ventricular and paraventricular regions, the deep areas, brainstem, and then cerebellum. These are the seven different types and you see them here. And the subtypes have to do within each of these seven types. What surface is the AVM based on? And there are different surfaces that we can think of. And AVS in my view, tend to base themselves on a particular surface and then cone down towards the ventricle or get into the parenchyma in various ways. But that idea of first, the region, and then second, the surface will lead you to your typing in your subtyping. And then with that, you can take any AVM that you see and fit it into one of these pigeonholes. So for example, if you look at the frontal AVMs, what you have is AVMs that are based on the lateral surface, the medial surface, the basal surface, and the Sylvian surface. This paramedian is one that we see over and over again. It's a combination of both the medial lateral surface and the superior medial surfaces, right at this corner adjacent to the sagittal sinus. And so there are five different subtypes within that type of the frontal AVM. Yeah, I forgot I should be using my annotator, but these are the five different types. Now, if we look at the cerebellar types, we've got the suboccipital type here that you can see on the suboccipital surface, Roten nicely defined for us these three cerebellar surfaces, the tentorial surface up here, and the petrosal surface here, and those are the three main surfaces, but there's also this vermian AVM here that lives in the vermis, could be either superior and inferior. And then here, this tonsillar AVM as well. So these are just two examples of how we use this typing and subtyping to really define, classify, categorize AVMs. Now, the next thing I wanted to do is to really give people the sense. When you watch somebody who's a master at doing AVM, it just kind of flows. You just see this process happening. And sometimes you don't really recognize the different resection steps, but these eight steps are really what's happening. There's exposure, there's the subarachnoids dissection where you're working through the different planes and you're relating your angiographic anatomy to your real operative anatomy, identifying the draining vein, which you need to preserve as the outlet for the flow. Then looking specifically at your feeding arteries next. The actual resection steps don't even happen until we get to step number five. All of this initial stuff is dissection and exposure, and that's so critical is to really kind of play with the AVM a bit, feel it out, do your reconnaissance, see what's going on here, open up these planes. And then when everything makes perfect sense, then we go into our attack and we go first at the pial dissection, then parenchymal, then finally ependymal. And at the very end, the AVM has been de-arterialized. It should be just hanging on by its draining vein. and we can take it out at that point. So just as an example of those steps, here's the fourth step; the feeding arteries. And within each of these steps, there's obviously an incredible amount of detail, and this is just an example of how when you think of the feeding arteries, there are many different types. This one here, the terminal feeder, this comes into an AVM and it terminates, it dumps right in, it doesn't give any other supply. So these are vessels that you can take right as they enter the AVM. If you contrast that with the transit artery here, this has flow coming in this direction here. And it goes along ascending branches to the AVM as you see here along its way, but you have to preserve this distal outflow, because if you don't, you'll end up with an infarct in this territory distally. Now, here's a perforating feeding artery that comes through the white matter here. We've got choroidal vessels that come up through the ventricle down here, and we've also got what I call the bystander vessel. The bystander vessel is one that comes along here and has no supply to the AVM. So these look like they're feeding the AVM but they're not. So you really have to be careful in how you manage that. So why is this important? Well, this is an example. Here's that transit vessel. You've got to dissect from distal to proximal if you're gonna identify this distal portion of the artery and preserve it. And then the process of going from distal to proximal is the skeletonization, taking off the branches that feed the AVM, but preserving the trunk. And here you can see an interoperative view showing the same. Now, one of the things that we do next is put these together as a battle plan. And this is basically what a battle plan looks like. You've got this concept of the cube. I'll talk more about that in a minute, but you can layer all of this information, the arterial feeding anatomy here in red, the drainage here in blue, and where you are going to find these different feeders, drains, and eloquence for the different AVMs. These are really shorthand ways of summarizing the plan. So these are the master concepts I wanted to cover in tonight's lecture. And I'm gonna start with the AVM box because we just looked at that and I wanna elaborate. So the idea here is that an AVM is a very complicated shape. You know, it's got all kinds of different curves and forms and what have you. It's never like a cube, but the cube is a way to conceptualize these complex shapes. And so when you do that, you convert this abnormal shape, this unusual shape into a box. It allows you to identify and put on the box the draining veins in blue, feeding arteries in red here, and the eloquence. So these are the key things that you need to sort of relate to that queue. Like on what side of the box are you gonna find the eloquence and so forth. And that is a really nice, easy way to organize your attack. Now, the next thing is a box has six sides. So there's going to be, if we think about those resection steps that I told you about, there's gonna be a pial side that's on that surface where the AVM is right on the cortical surface, and that's this here. Then there's going to be the four parenchymal sides, which define the interface between the AVM and the parenchyma adjacent to it. So there are four sides here. And then finally, the ependymal side is this one here on the deep side, which you see here. Our symbol for that is this little cup, because it's often like scoop that you get to at the last portion. But this is a way to think about the different stages of that resection as you go through them. So let me just show you an example of how all this fits together. Here is a medial temporal AVM. This is an artist's conception of what the medial temporal AVM looks like. It's on that medial surface where the uncus and medial temporal lobe lie here. Here's a case example. You can see angiographically how it lies along that medial region. If you look at this angiogram, you can see that plane of the AVM running right along this medial border here. You can see the AVM here on the MRI, in the region of the uncus. And so when we construct in our mind that cube, here's the cube. We've got the feeders that come from PCOM, that come from the P2 PCA, that also come from anterior choroidal artery. They're all on that medial surface of the box, that inside edge. And what does that mean for us? That means that all of our actions there. And so we wanna get to that surface as quickly as possible. So the way that we do that is with an open zygomatic approach that gives us a beautiful transsylvian exposure of that medial surface of the AVM, so that we can really come down right on those feeders that are right in here, right where the action is. These numbers refer to the resection steps. So we defined here, the feeding arteries, number four, the draining vein here. Number three, are our basal veins of Rosenthal. You can see here these are some later steps, five, the pial attack, six, the parenchymal dissection, and so forth. So to take that to a video now, here is the view that we get looking transsylvian and the temporal lobe is over here, the frontal lobe is over here. You can see the third nerve right here. And this dissection is basically going right along the medial border of the temporal lobe. You can see this is the carotid artery. And this right here is an enormous anterior choroidal artery. That is one of the main feeders. You can see these branches coming off, the anterior choroidal artery that go to normal structures and those have to be preserved. Here I'm working along the inside dura here to get that medial temporal lobe freed up from its arachnoidal adhesions. These are some of those feeders. And then finally at the end of all of this, we get to the draining vein. This is the vein going back to the basal vein of Rosenthal, which I'm interrupting at this point. I've already done some resection, which I haven't shown you in the video to free up the lateral margins here. But you can see now the AVM comes out completely. And the whole secrets of this resection was to get to that medial surface of the cube to de-arterialized this early. Here's a nice preservation of the choroidal. All of these feeders here are nicely preserved going to their normal anatomy. Here's the third nerve, here's that oculomotor-tentorial triangle that we've excavated from AVM. And you see nice preservation of all of that arterial anatomy in the depths. So I wanted to show you that video, you can switch now, Luke to the slides, just to show you the application of the typing and the subtyping, the cube concept, the mapping out of the arteries and the veins, and then the dissection steps. So simple AVM, but just to show the points. Now, the next thing is one of the eight different steps is the hardest one. It's really step number seven, ependymal dissection. These earlier steps are really pretty easy, they're enjoyable. You do your exposure, you do the subarachnoids dissection, you identify your anatomy. This is all very quiet, very methodical. And then here's where we start to engage the AVM. But it's this last step that is really, I think the hardest. And this is that part that we symbolize here by the cone. And it's hard because I think about it as the dark side of the moon, which you can see here in the background. When you're looking this way, you see the lit side of the moon, but you don't see the unlit side of the moon over here. And so it's really hard to see you've got this AVM that's kind of covering where you need to see. That requires the use of these retractors here and here. It requires lining the bed with tophus to protect the adjacent brain tissue. Sometimes it means pulling the AVM with some retraction, and you've gotta make really smart decisions as you go around this plane here. If you misjudge the depth of that deep border, that seventh step, then what you see here is you've left little tuft of AVM. It's got ependymal venous drainage here, and you're gonna have a remnant here on your post-operative angiogram. Instead, you've got to really drive down into the ventricle, see the CSF, see the ependyma, get into that space and then work your way across so that you make those full turns across the deep side. So here's an example of just how this can be challenging. This is a paramedian frontal AVM. You can see it's in that corner between the lateral convexity and the medial convexity here. And you can see how this goes all the way down to the ventricle. So we've gotta get around that deep portion. You can see how deep it goes here. So here's the artist's conception. Obviously this is a smaller version of what I'm gonna show you, but here's our box. We've got our patient here on the upper corner suit. You can orient yourself, the forks is over here. This is our cue here. And we map out our feeders in red, our drainers coming immediately in blue. You can see the various resection steps here, and here's the video. So Luke, you can roll this. The orientation is the same. So our midline is to the right of your screen, the basal surface's here now on the top of the screen. And this is now going along that medial surface, finding these feeders from the anterior cerebral artery and just interrupting them one by one. So this is not step seven, this is basically step six, going in these parenchymal sites. So going around the different sides of the cube. And as we finish that portion of the resection, then we have to make that turn and get to the dark side of the moon. And this is where we're starting to make the turn. You can see that I'm trying to work my way underneath this massive nidus in this direction. So I have to pull the AVM this way and that way, and it requires a lot of dynamic retraction with your instrument. So you can see that there's a lot hidden on that deep side. There are additional feeders, there's cavities. Here's one of the venous varices going across the system, some entrance into the ventricle here, frontal horn. And you can see with an AVM this big, you really have to manipulate and maneuver the AVM to get underneath it. So coming across this side here is I think a real challenge. And that's where sometimes people get into trouble, but you can see here all the different tricks in the video. So Luke, we can go back to the slides. Here's the postoperative angiogram and this patient did well. Now, the third point on my list for tonight was gravity and trajectory. And this is some ideas about, you know, just how to position. I think if you were dealing with a medial AVM as shown here on that medial surface. If you were like me early in my career, I would put this on the downside. I would put that with this hemisphere dependent, the AVM would drop down, the fissure would open up and I would look kind of in this direction here. But if you think about where this AVM resection is the hardest, it's actually here where the star is located. It's in coming around this corner and trying to see into that dark side of the moon space. And when you come in this direction, it's actually really hard to see that. If you think then about the contralateral approach over here, we take everything and we fit. We put the AVM here on the upside rather than on the downside. And when we do that, what we see is that our point of view changes by about 90 degrees. We're looking this way and that hard part where the star is, is actually much easier to see now 'cause we can see over the top of this thing, and we can see down into that space really comfortably. Now, putting the AVM further away from you, it means doing something that's counterintuitive, but you can see the advantages when you have this at play. The ipsilateral approaches here on your left, the contralateral approaches on the right. If you look at the left side, what we're doing here, we're right on the same side. So everything's in front of us, but we're having to kind of come around this corner here. And it's not an easy, natural way to get around this thing. We're having to pull the AVM into the the surgical corridor here, and we're having to look in a corner that's very difficult to see. Whereas if we put the AVM here on the upside, the AVMS sort of falls with gravity into our view. We have a perspective that goes across to that really hard part of the case where we can see more easily around this corner. The AVM continues to fall the further we dissect and it makes the surgery a lot easier. So I'm gonna show you two examples of that. They're both medial, frontal or in this case, this is actually a ventricular AVM. It's in our category of periventricular or ventricular AVMs. So it would be this one here. And you can see it's in the corpus callosum. It's a small one that drains down into the septal vein and into the internal cerebral vein here. And it's a really simple one just to show you the idea. Here's our cube with all the different anatomy, arterial and venous mapped out. And you can see the different resection steps here through this interhemispheric approach. But what I'm gonna do is put the AVM on the upside. So go ahead and roll this loop. The AVM is up here. This is now dissecting along the pericallosal here. And we find the medial border of the AVM in the corpus callosum in the midline. So this is now that skeletonization technique that we've talked about earlier, just picking off feeders from the pericallosal. This is now defining this plane of dissection between the corpus callosum and that medial border. These ventricular AVMs are so nice because you have CSF as your plane. That was a draining vein right here coming across. So we have to save that. And this is now working our way around this posterior border into the ventricle. Here's the ventricle down here. You see the thalamostriate vein down in the distance there, and this is just working our way around the sides. And now you see that as I go into that lateral portion of the AVM up in this space, up in here, the AVM is actually falling this way and it's allowing me to see with my vision this way. So I'm allowing gravity to help me on many fronts here. And this AVM just nicely drops into views. But here now I'm going to cross the septum, the AVM. You can see it's sort of falling into our view. I've gone across that lateral border. The AVM is pretty well circumscribed. You'll see here in a minute, this septal vein here, this is the septal vein here coming down, it's now blue. So we the AVM's been circumscribed. So we've finished step seven. We can now do step eight here with cauterization of the draining vein and removal. And you can see a clean and easy that was. So here's a nice overview showing the tuft of choroid at the foramen of the Monro down here. Patient also had a pericallosal artery aneurysm, as you can see, nicely in the same surgical corridor, easily fixed at the same time. So that's an example, a very simple one of how this idea of putting the AVM on the contralateral side can really help us out. We can go to the next video, and this will show you a more challenging case. This is the post-op of that previous case. And now here's another. So this one's more challenging. You can see this is a bigger AVM. It reaches further laterally, it's a bigger nidus here. So more work, but here's the ipsilateral hemisphere that's on the dependent side. Our midline plane is here, and the AVM is up in this space here. So I've put the AVM further away from me, but I'm gonna reap the benefits of that later. This is just skeletonizing some of these feeders coming off of the anterior cerebral artery. You can see some of the embolic material here inside of the vessel. And now as we finish off that medial border, we can now start to get into that lateral border. So I'm going over the top of the AVM. The AVM is here, it's starting to fall with gravity into the field. And you can see that with that gravity retraction, I'm really able to get into that lateral plane really nicely. I've got a lighted bipolar here, which really helps to see, but as I go over the top here, I haven't really easy time seeing into that space. So here is the AVM coming out from the contralateral hemisphere, good sized AVM. And there was no need to go through any parenchyma to get to there. It's just using gravity, using the medial interhemispheric fissure and cleaning it out. And you can see that that trajectory gave us a clear shot into that lateral border. Here's the postoperative angiogram. Okay, Luke, we can go back to the slides. All right, now the next idea is what I call high eloquence AVMs. And with these, you know, the two ideas here, I wanna introduce you. One is this idea of occlusion in situ. There are some AVMs that are just risky to take out and sometimes trying to actually remove it can incur morbidity or complications that you don't want. So if you just de-arterialized and then do a venous occlusion in much the same way that our endovascular colleagues are embolizing than doing a transvenous occlusion, then this is a way to deal with some of these high eloquence AVMs. So let me go to the next video here, and we can start this. This is gonna be a frontal sylvian and insular AVM. It's literally a large AVM. It sits right in the Broca's area. And you can see how extensive this AVM is here. So very challenging AVM and highly eloquent. And this we'll just show you some of the techniques it's again, going through those eight steps here, just we're in that step number two, just maximizing the subarachnoid dissection, opening up that sylvian fissure, identifying the venous complex. The venous complex here is enormous. You have this enormous venous receptacle here in the sylvian complex. Here are some of the veins. Now we're going across the superior border of this thing. Again, just defining the margins between eloquent cortex and AVM nidus. And this takes a lot of time. Now that we've done all of that, we can start our attack. So this is now getting into this pial dissection, taking the major feeders that join the AVM right on the pial surface. And just by going into the Sylvian fissure and taking all that I see there, you can see we've drastically reduced this flow. One of the ideas here is that this venous complex is so extensive that I need to sort of pare it down to get to the remaining planes and the remaining feeders. So I've taken one of those venous tributaries. This gets me to this deep feeder. I wanted to show you some bleeding. These aren't always so clean, but if you use AVM micro clips and you use your suction and really focus on the bleeding at hand, you can control these stepwise as you go. Here after a little bit more work, you can see that the AVM is alive in this corner, but these other corners have quieted down very nicely. So that allows us to prune once again this venous complex and work back into this area over here, where that live AVM persists. And now we find more supply. And here at the end, you know, you can see stasis, or new stasis in the venous complex here. Very little flow left now getting through. And her Broca's area is over in this territory here. So we've preserved that nicely. And then at the end here, just going across those last embolized deep feeders, taking the vein, and you'll see this thing come out nicely here. So this was a Spetzler-Martin III. This was a supplementary grade III. So it was VI, it really at the limits of what I normally would resect. She did have an aneurysm here. I believe this is an ACOM. So I took care of that at the same time. You wanna make sure that any feeding artery or associated aneurysms are taken care of since we're here anyways. So here you can see the post-operative angiogram. Nice resection here and she did really quite well. So that's an example of high eloquence. Again, just applying the same principles as before. We can go to the next. This is a slide. I wanna show you this idea of occlusion in situ. So we published this idea for our "Brainstem" series. I'm gonna show you this case. It's a thalamic AVM. You can see here the AVM is on that superomedial corner of the thalamus here and here. It's a Spetzler-Martin grade III. It's Lawton-Young or supplementary grade III. So again, it's at the limits, but you can see after embolization, I believe she had radiosurgery as well. She still has this persistent AVM. So here's our cube. We can map out our feeders and draining vessels. We can see our surgical steps here. We can see our surgical corridor, which will be interhemispheric transcallosal into the lateral ventricle. This is gonna be our surgical view. So the patient's nose is looking this way. It'll again, be one of these interhemispheric approaches. And Luke, you can roll this. So here, I'm just opening up the interhemispheric fissure. Now, I'm down to the corpus callosum. You can see the pericallosals, you can see the callosal marginals. We do a callosotomy here, this is my fellow getting in. And now as we enter the ventricle, you can see the AVM that sits right on that superior medial border of the thalamus. Here's the choroid plexus here coming along. The atrium is back in here. The foramen of the Monro is here. And you can see all of these feeders that come through the thalamus this way to get to the AVM. So these are ones you have to be incredibly careful with. You can see these small vessels coming through the thalamus, and if you're not careful in controlling these, these can start to bleed back and draw you into thalamic tissue, which you don't want. Here's one of these choroidal vessels. This is a posterior choroidal coming up from posteriorly from the posterior circulation. These are nice to deal with. They're very easy, they're not in parenchyma and they have thick walls. They're easily dealt with. You can see a nice interruption there. And then we work our way along that thalamic border. You can see some of these you can cauterize. That one behaved very nicely. Here's our choroidal fissure being open between our fornix, which is running here and the thalamus, which is running here. As we get into the choroidal fissure, we enter the velum interpositum. We can see the nidus here sort of unfolding in front of us. And here now are those transthalamic perforators. These are the ones that I worry the most in these cases. If these get out of control, then you can easily find yourself chasing them into the thalamic region. So I have to really be careful with those. This is now a view into velum interpositum. We're starting to see our internal cerebral vein back there. Here's a big feeder coming through the thalamus more anteriorly. Again, use of those AVM micro clips. This ensures that these vessels don't get out of control. If you just cauterize and they pop, then that's when you start to have to chase. So here now we've got a nice view posteriorly. This is our draining vein. It's the internal cerebral vein going back to the galenic complex back in this space. You can see how it's basically purple now. There's still a little bit of life to it. There's a view into the third ventricle and here a nice view through the velum interpositum. These are some of these embolized posterior choroidal vessels here. And now what I'll do is I'll do an indocyanine green angiography because I wanna see just how much arterialization of that vein we have. So before I do that, this is just a peek into the contralateral ventricle. I'm making sure that there isn't feeding artery supply from that opposite side. And there really isn't. It's all really sitting under the fornix in velum interpositum and fed primarily from that upside. So there's another view of the internal cerebral vein in the back. And here's that icy green run. You can see what I'm looking for is the vein. Here's the vein here. And you can see just very faint, slow filling. So that tells me that I've de-arterialized this. I haven't completely eliminated the flow in that vein, it's not dead, but it's quiet enough that I can now do my venous occlusion. So here's the vein. You can see how slack it is. This is an aneurysm clip that's going to complete my venous occlusion. If I get into trouble, I can always release the clip, but you can see how that nicely occludes the vein. I now do another indocyanine green run. And the vein is dark, there's no shunting that I've missed. This is the region of that vein and back, and staying dark. So this tells me that I've completely eliminated the shunt. And here's just an overview. I don't need to resect the AVM now. I'm not gonna put the fornix at risks or the thalamus at risk. I'm going to leave the AVM in situ. I know that the vein here is blue, that there isn't any shunting and it's basically dead. So there it is, there's the nidus. We'll leave that in situ. It's been de-arterialized here along these borders and we've done our job. So we can go now to the slides. Here's the angiogram. You can see my micro AVM clips. You can see there's no residual AVM and we're done. So last case. This is not a brain AVM, it's a cervical spinal cord AVM. And I just wanted to show you again this idea of how we sometimes have to think about high eloquency AVMs a little differently. You can see this is right at C4. So this is a very tricky AVM. She ruptured from this. You can see some encephalomalacia, which will help us. But obviously if we have problems here, this could leave her quadriplegic, it could leave her ventilator dependent. So we really have to be incredibly careful. So Luke, go ahead and roll this. This is a video showing the dural opening here in the midline. This is now the view of the spinal cord. It looks pristine. So we have to do a midline myelotomy, which I'm not a huge fan of, but obviously to get into that AVM cavity, we have to find that midline plane, follow those vessels down the median sulcus, and really as sharply and precisely as we can, split that raphe and get down into the cavity of the AVM. So here I am just slowly enlarging that. I actually use my bypass instruments because I like the sharp, precise points on that. So I can really separate those tracks nicely, those dorsal column tracks. And now you can see that we get to the AVM. So here we begin our process of occluding the feeders, defining the plane. And what I wanted to show in this is that unlike AVMs in the brain where you tend to kind of stay in the separation plane and really leave the AVM almost untouched, here you'll see I'm actually manipulating the AVM. I'm treating it almost more like a cavernous malformation in working in that plane. And I think when you've got one of these high eloquence AVMs, like in the very substance of the cervical spinal cord, it's I think important to preserve every last neuron that's on the outside of this plane here. And that means, you know, pulling the AVM a little bit away, developing that plane of dissection here. You can see I've gotten all the way to the front. This is the anterior spinal cord. You can see that pial surface there, and I'm using my dynamic attraction to kind of move the AVM from side to side, kind of pull it away from the spinal cord parenchyma. And you can see how by using more traction than I normally would, I'm just teasing it away from the spinal cord. I wanted to show this little sequence here because it shows some bleeding. And obviously in these very small places where you can't see and blood fills quickly, you have to just stay on the lesion, be very patient, use your sucker to really dry the field, find the bleeder, and you can see how simply that was controlled. It's just a matter of being patient and staying right on that source of bleeding. Here we are going down the home stretch. Again, teasing the AVM away from those tracks, using a lot of traction to mobilize the AVM, moving it from left to right from top to bottom. And finally coming around that deep plane where the anterior spinal artery is feeding this. You can see this is all the way to that anterior pial surface in here. That flash of blue is just that anterior pial surface. And that's gonna be our last remaining artery and vein on the front side. And again, I'm only working through this small hole. So I have to move that AVM around from side to side to see what I need to see in there. It finally comes out. So they have it, small midline myelotomy, good preservation of the cord parenchyma on either side. And this was a young lady, did very well, really no problems whatsoever. Okay, Luke, you can go back to the slide. I think that's the last of the videos. Here's her post-operative MRI or postoperative angiogram. And again, a nice result. A couple of closing comments, we're getting to the end of the hour. So, you know, when I thought about this idea of bleeding for the book, I call it "The Hurt Locker." It's one of my favorite movies. It's about this guy who detonates bombs for the Persian Gulf campaign. And it's one of the worst situations possible. When an AVM is bleeding on you, you can't just walk away. It's not like a tumor resection that you get tired of doing, or that you feel like you've done enough. You get into these situations with AVMs where you can't leave, you're stuck in the hurt locker. And this is just a way of thinking about bleeding. There's bleeding that's arterial from these feeding arteries sorry, let me go to yellow. These feeding arteries, when they bleed, it's usually a single bleeder and you just have to keep working your way more proximal on feeding arteries to track down those bleeders and control them. This kind of bleeding here, nidal penetration is also not the end of the world because, you know, if you penetrated the nidus, it means you've just carried your dissection too close to the AVM and you've actually breached that plane. But it's usually just a single point. And this can be controlled with pressure, with new knit, or anything that tamper on that point of penetration. These two are actually pretty easy to deal with. When you've occluded a vein, the primary draining vein too early, that's when things get really bad, that's sort of this situation here where the AVM explodes, you've got bleeding from multiple points. And really the only way out of some of those situations is to get that AVM out as quickly as possible. And it's not fun, but I don't think you can call yourself an AVM surgeon until you get into a couple of those situations and find your way out. That's really what helps give you that confidence. Now, Aaron asked me at the very beginning, what I felt it needed or it took to become a master in AVM surgery. And these last slides are really about that point. I think operator ability is point number one. I had the privilege of training with this man, Dr. Spetzler, who I considered to be a rare surgical talent. And I think each one of us have our own unique set of talents. And we have to make this very complicated surgery look easy. We have to master this. It's about developing touch, it's about being perfectionistic, not making mistakes, holding yourself to the very highest standards, looking at your results and finding out how you can do better, what you're doing that's working, what you're doing that's not working. This is all the pieces that go into operator ability. So much of that is anatomy. You know, you have to respect the brain, you have to know your landmarks. Know all of these relationships, really spending time with this anatomical approach to AVM surgery, it's so critical. And that's point number one. Now, the next point is inoperability. And what I mean by that is knowing when to operate and knowing when not to operate. I think so much of being a a master surgeon in AVMs is judgment. And that's about selecting your patients carefully, going through the process of deciding whether or not this patient should have the surgery. Sometimes, you know, the better part of valor is to tell patients not to have surgery and to manage them conservatively. But if you really believe in your abilities and you think you can do a good job, you know, this is part of that decision-making process that goes into it. It's one of the reasons why I and Dr. Spetzler and others have invested so much of our efforts in developing these heuristics, these grading scales that help us make these decisions. Because really at the end of the day, if you make poor decisions, no matter how good you are technically, you won't get the result that you're expecting. And that's, I think born out in this graph. What this shows is all of the AVMs, what I call the great sevens. You know, if you use the Spetzler-Martin grading system, and you used the Lawton-Young supplementary grading system, and you put them together, my cutoff is six. Anything, seven or greater is really above the threshold. And these are the grade seven that I've operated on and Dr. Spetzler has operated on over our careers. And what I thought I would be able to show is that, you know, if you did have tremendous experience and really pushed your skills, that you could bump this curve up, that you could get better results over time, and you'd see this gradual rise in the outcomes. But what you see instead is that this curve is completely flat. And I think what that means is that no matter how good we get technically, you can't beat AVMs. You can't overcome their formidable ugliness that is inherent. These AVMs that are too big, and too eloquent, and too nasty really make you pay the price if you make bad decisions or the wrong decision. So with that in mind, you know, we've really tried to define this border zone between operability and inoperability. I said it before, it's really between VI and VII. So anything VI or less over here, I think is fair game. Anything VII or greater over here is really too difficult. There are what I call these gray zone cases. There are some sixes that are particularly challenging. What I call the large and the older AVMs that are grade VI, these can be tough. And you might wanna think twice about those sixes. On the flip side, these younger and smaller grade sevens actually do pretty well. So those are one exception to crossing the threshold. But these are the things to be looking for when you make these decisions. These are just a graphic showing those different six plus. We call them the six plus subtype that are ones to be careful with. And here are the seven minuses that are ones to also maybe be a little bit bolder with. And lastly, I think what goes into being a master is what I call surgical courage. Yes, you'll go talk about it, others have talked about it, but it really means taking on tough cases and taking yourself to the limit. You know, it would be nice to stay in the territory of grade ones, twos, threes, fours. But if you really wanna become the best or become a master AVM surgeon, I think you've gotta take it into those outer reaches. And that takes courage, it takes looking at your failures, finding ways to improve, being resilient, finding ways to redeem yourself. And I think this idea of redemption, when you have the failures, you owe it to yourself and the patients you've hurt to learn from those mistakes. Find your lessons, teach those lessons to others and to yourself, and to redeem yourself. So I've talked a lot about AVM boxes, this idea of the cube. I think that hopefully is clear to you now, but this box over here is what I call the black box. And the black box contains all of these surgical traits that are difficult to quantify one's judgment, one's selectivity, one's anatomical knowledge, how strategic, how skilled, how courageous. All of these different things go into that black box that make up the neurosurgeon and everybody's different. Nobody has the same composition. So, you know, I think what's interesting about my position now as a mentor, I get to see a lot of surgeons operate, I get to see these different qualities and different proportions. And I think each one of us has to sort of figure it out and figure out which one of these matter, which ones we can improve upon, how we can improve some of these different traits that make us better in the operating room. So I've always said, it's hands, it's head, its heart. You've gotta have good technical skills, that's the hands. You've gotta have a really thoughtful approach to surgery with your strategy, with your judgment, with your subjectivity. And finally, you know, the heart, these are incredibly painful cases when they go wrong. We've talked about the "Hurt Locker." We talked about morbidity. This is, you know, where I think it takes grit to do this kind of surgery. You make mistakes. These are what I call the ghosts, they haunt you for your life, they never leave, but they keep us striving for perfection. So I'm gonna stop there. These are some conclusions you can read them for yourself. We've talked about all of this and in the end, you know, I just encourage all of you who are at various points on your pathway to becoming AVM surgeons, to just, you know, keep at it, find a way to enjoy it and stay with it.

- Very nice, Michael, spectacular talk, very revealing, shows truly tremendous expertise and a huge legacy. May I please ask you, if you don't mind, to tell us how you feel about embolization preoperatively? I personally am not a fan of it unless in a very select cases. And how do you gauge which AVMs you embolize and what do you think a second part question is the future of transvenous embolizaation and it's role potentially significantly affecting AVM surgery?

- Yeah, I think it's a great question. I think early on in my career, I embolized most of my AVMs, probably about three quarters of them. As I've gotten more senior and gray-haired, I find myself embolizing less. We've looked at this question and published on this. There's definitely a trend towards less embolization as the years go by. I think we've got a paper that's coming out shortly that looks at embolization with grade threes. There's no question that the higher the grade, the more they benefit from embolization. I think it's safe to say that you can be conservative with embolization for grades I and II, and we have kind of drifted in that direction. But for the grade III, I think there is a benefit. This review that was done by of my residents, Josh Kadopano really made me see that there really is a benefit. There's a difference in outcomes with the grade threes that are embolized. So I do think there's a role and I think grade is a good rule of thumb to help you make that decision. Now, is transvenous embolization gonna change the nature of AVM surgery? I don't know. It violates a lot of principles of AVM surgery, but as you saw in this talk, I've seen it work on the endovascular side, I've seen it work on the open surgical side. So there definitely is something to this. The Europeans are doing it far more than we are, and they say they're having good results. They're also having some pretty significant complications. So I don't think it's totally benign, but I think we will see more and more of that as time goes by and it will change the nature of our practice. I think there will be some AVMs that will be cured transvenously that weren't previously.

- Okay. And may ask, well, do you find a way craniotomy to have a role in AVM surgery, and as a second part question, what kind of monitoring do you use doing AVM surgery?

- So I did about a dozen of these and published that years ago. I think it has some benefit when you're operating on AVMs that are in the speech area where you have to go through parenchyma to get there. So if you're going transcortically to get to an AVM, then I think it's helpful to map that out with an awake anesthesia and figure it out. And also it can guide the extensive resection. If you're removing an AVM near speech and the patient starts to have a change, then that may be an indication that you need to stop. So I have used it. I'm using it less and less. I think it's kind of like our conversation about embolization. I think the more experienced you get, the more you learn, which of these in the language areas to operate and which not to operate. And I find myself using it less with years of experience.

- Okay. Well, I really, again, thank you Michael, for your tremendous talk. It was very interesting, really shows immense technical skill. You have been truly an international leader in many cerebrovascular sub-specialties, including AVM surgery. We had over 300 people who stayed the entire time and actually 450 participants that uniquely were with us the entire time. So this is really a huge session and we really appreciate for you to being with us and look forward to having you in the near future.

- Thank you, Aaron, and again, congratulations on the success of the Atlas and these teaching sessions. They're really phenomenal. My hat's off.

- Thank you so much.

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