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Microsurgery of AVMs - Tips, Tricks, and Pitfalls

Peter Vajkoczy

March 15, 2021


- Ladies and gentlemen, thank you for joining us for another session of the Virtual Operating Room from the Neurosurgical Atlas. Our guest today is Dr. Peter Vajkoczy from Charite Hospital in Berlin. He's the chairman of neurosurgery there. A superb neurosurgeon and a dear friend with immense research in microcirculation of the brain. Peter, it's been an honor to have you with us. I know your videos are spectacular. The technique of pearls that you are gonna talk about are immense, and I'm very much looking forward to listening to your nuances of techniques. So, thank you so much again, and please proceed.

- First of all, thank you very much for having me. It's certainly a big honor and I'm grateful to become a part of your successful journey through neurosurgery. I think that you have to be congratulated together with your group for this platform. And now, I'm very happy that I can contribute a little bit to that platform. And I hope to share some tips, tricks, and also pitfalls on AVM surgery. Just at the beginning, a small anecdote. When we discussed what I could contribute to your series, and you asked for AVM surgery, I was going like, what? Because I only have talks about indications, decision-making, but not really about the details of the surgical process that you're interested in. And the reason why, because I always felt that AVM surgery, for sure, it's not straightforward, it can be very difficult, but in the end, take the AVM out and I didn't really think so much about the details that I had accomplished over the last years. But I have to be grateful for you, as well, in this sense that you have really stimulated me to put together a talk together with my fellow, Shigeki, and with our illustrator, Lucius. And I started to think about the details that I think are maybe worthwhile sharing with the community. And I hope that I could add some helpful details for those that are starting to learn AVM surgery or that are already experienced in the field. So, these are my conflict of interest and there certainly nothing to share which is related to this talk. This is where I'm coming from. As you have nicely introduced, my person, I'm currently working at Charite University Hospital in Berlin, where I started as a chairman in 2007. And my research, as you said, is about endothelial cell biology. And this is the content. So, I will start, very briefly, a few minutes on why are we operating on patients with AVMs? And what's our philosophy about AVM surgery? Then I have harvested the nine surgical videos. They are between two and eight minutes, and they will introduce different AVM types. Maybe not the most spectacular ones but those where I'm able to give you an overview about the surgical strategy that I'm using. And each of this video will highlight the specific pearls that I will introduce this pearl before I'm showing the video. Some of these videos are nice and they are polished. Like the ones that you usually see on congresses or meetings. And some of them are not so nice because I think it's also important to show, to show that some of these AVMs can be very difficult or they can surprise you and there might be pitfalls that you have to be aware of. And I think it's also important to acknowledge former masters and mentors, because all these tips and tricks or most of these tips and tricks, they are really coined or many mentors have coined me and I have stolen their tips and tricks while I was visiting them personally in the OR. Today, you just have to watch the videos and the young generation maybe will not understand us, but in the earlier days, we had to visit these ORs and we to steal small tricks and tips from these famous neurosurgeons. So our philosophy of why we operate still on AVMs is based on this meta analysis which has shown that overall, all sizes, all locations, microsurgery is still doing quite well when compared to radiosurgery or embolization. It's the treatment modality that is characterized by the highest cure rate, more than 90%. And if the patients are picked wisely, then the risk profile is very acceptable. And you have an immediate cure and you don't have to wait for years to see the result as with radiosurgery. And one of my dear mentors, Johannes Schramm who was the chairman in the University Hospital in Bonn and he is one of the most famous German or European AVM surgeons. He really made me understand that if you would like to compare the three modalities, you have to concentrate or focus on the use case for all interventions. And that's the AVM that is smaller than three centimeters. Because all representatives of the three treatment modalities would claim that they are very good at the small AVMs. And if you then go to the literature and this is what Johannes has already cited. The surgical literature looks much better than the embo and the radiosurgery literature with these small ones. So we really believe that small ones are better off with a surgical approach if the risk of the surgery, the morbidity of the surgery is acceptable. And this is why we have continued to argue or to criticize the results of the ARUBA trial of the first publication of the most recent publication. We have discussed the complete eradication and the different aspects and you can read up our line of arguing now recently in the stroke and why we still feel that surgery has a room. In fact, ARUBA does not really reflect surgically reality. It's not a study that is really intended to test whether the surgery makes sense. And here is our algorithm. AVM smaller than three centimeters in our eyes are clearly surgical cases if they are located non eloquently. And if they are in eloquent areas, we still believe that the microsurgery is doing quite well. It's performing quite well. Young patients are not good candidates for radiosurgery and if curative embolization might work, we go for it. But most cases, even if they're eloquent or surgical cases or do nothing as ARUBA has suggested. And if they become better, if they become bigger, we would combine. But already now, I would like to tell you that I'm not such a big fan of embolization. I would argue along with Michael Morgan from Sydney, that embolization should be really reserved for the very difficult ones where you need a control of the deep perforators. It shouldn't be a standard approach to embolize them because by combining the two techniques, you're adding the risks of the two techniques. And sometimes, surgery becomes more difficult if the patient or the AVM has been embolized before because the perforators become more angry and there's more flow on the perforators. So even though the big ones, we are reluctant to combine, and if they are good surgical candidates, we go for surgery. And if they are not good candidates, then we either keep our hands off or we combine embo with radiosurgery. Or sometimes, we even stage them down with radiosurgery. So this brings me into how we are preparing the patients for AVM surgery. So MRI obviously is helpful, but the functional imaging is not so helpful because the limitations of functional MRI. So we rather than rely on transcranial magnetic stimulation. Here is an example of a centrally localized AVM. And we can map the cortical surface and the tracks using transcranial magnetic stimulation. And we are quite proud because we were one of the centers that have pioneered the technique, especially also for AVM surgery. And here, I should acknowledge Thomas and his group from our department. Image guidance is useful to keep the craniotomy as small as possible and not to injure the venous outflow maybe through the sinus. Electrophysiology does not play such a big role because if you get a negative result or a negative signal on electrophysiology, you're not able to stop the resection. You have to go on. ICG limited value in AVM surgery in my opinion, it's not useful to show you whether you have remnants. And here, we like to use interoperative angiography. We have our hybrid OR setting where we are trying to use that setting as much or as frequently as possible. But especially during the pandemic, for example, and I will show you a case where we are limited in our maneuverability, it's not always possible to perform an interoperative angiography. My dear friend, Michael Lawton likes to has a view on AVM surgery that he's able to, or he tries to plan everything perfectly like going to the battlefield. In my opinion, it's very difficult to plan AVM surgery. I rather see AVM surgery as a one-on-one fight with a big fish, like Ernest Hemingway's book. When you go out, you wait for the fish, you hope for a good fish. And sometimes, the fish turns out to be very aggressive. And then you have to fight the fish and bring the fish into the boat. And maybe the fish is pulling you out in the big sea, and you have to find ways to get back near to the coast. And for me at least, it seems to be very difficult, really to make up your strategic plan about all the details of the individual AVM. So I rather tend to go in, have some kind of idea and then really see how my plan works out. When we position the patient, we have very limited rules. We try to avoid the prone position in order not to increase the venous outflow pressure. The craniotomy should be big enough and we rather make a bigger flap not to not to have a part of the AVM or the venous outflow below the edge of the craniotomy. The dural opening, we like to open the dura under the microscope, not to injure some kind of fistulas vessels or injure the venous the main draining venous system. We like to use a non-sticking bipolar. So as coming back to that analogy with the fish and Hemingway, our instruments have very reduced. We have a sucker, we have a non-speaking bipolar, we have some clips on the tray, but we certainly don't have many bipolars and many trays open. It's really a one-on-one fight like a tennis match. Where you have you kind of strategy. You have your rackets and you have the ball and you will see and you have to win the match. And then we don't do much. We don't have neuroprotective measurements. We just avoid hypertension and we keep the patient on the ICU. Which brings me to the first case. So the first case I would like to discuss with you is a small cortical AVM, which is paramedian in the precentral area, in the superior frontal gyrus. The patient is asymptomatic. A rather young patient. And we have discussed this case. And since still, it might be eloquent, but it's a small one so we have to decide to operate on this. This is the angiogram with the feeders coming from the anterior circulation or the anterior cerebral artery. The AVM is drained into the superior sagittal sinus. And since it's a small one and it's cortical, it's a rather straightforward case to begin with. And we can discuss about the positioning for these patients. So for these patients that need an interhemispheric approach, where you have to skeletonize the superior sagittal sinus, we like to place the patients in the 90-degree position. And we use the gravity for the brain to fall down and to get a good access. But on the other hand, this might be sometimes difficult if you have the draining veins into the superior sagittal sinus. You get tension on these veins and it will take some time until you free up all these vessels. So this is something that I like to do, especially on the left side, since I'm a right-sided surgeon. And if the patient is positioned in zero degree, it's difficult for the right-handed surgeon. But in the case that I was introducing to you, we are using a zero-degree position. And the details that I would like to highlight in this first AVM is number one, I learned from Hunt Batjer where I have spent a few days. And Hunt has really introduced me into the intellectual bias of AVM surgery. If you go for a cortical AVM, which might look like this. When you open the dura and you might perform an ICG, this doesn't really help you to understand the angioarchitecture. What you have to do is you have to dissect the arachnoid, you have to open all the arachnoid adhesions. And this is the first step. You have to understand the angioarchitecture. And this is the nice part of the surgery before you really attack the AVM. You need sharp arachnoid dissection as the first step. And this, I have learned from Juha Hernesniemi. Former chairman in the University of Helsinki. He taught me to use the microneedle. You might use a scissor and there are fancy scissors out there. You might use a expensive diamond knife, but a small needle does the job very well. And the risk of really injuring and draining veins or other vessels, or the nidus is really low. So this is how we start. And this brings us to the first video. Please start the first video. As I mentioned, zero degree position. You can see the AVM is outlined here. We have the cortical surface here. And we have the cortical surface on the interhemispheric area. So here, I'm starting to dissect the arachnoid adhesions with the needle. And as soon as it's opened, I will use the knife to further advance. And then I go back to the needle and we usually start with the draining veins. Most of the surgeons are afraid of injuring the draining veins, but I think that the draining vein often leads you to the pathology. And it's good to really have an understanding of the draining system before you go for the arteries. Here is maybe an artery, here's the draining vein. And here, we are slowly progressing in understanding the angioarchitecture, the vascular architecture of the AVM. Here, we are then going deeper to identify the lateral aspect or the surface of the nidus. And then we are going into the interhemispheric fissure. Here, we are lucky because it's a minor draining vein and minor draining veins can be sacrificed at an early time point. They usually don't really contribute to the draining system. But you should respect the larger draining system. And obviously, as everybody knows, they should be left for the end of the resection. In order to approach the cortical surface on the interhemispheric fissure. And here, you can see that dura is retracted, we have skeletonized the superior sagittal sinus. And the dura is retracted with stack of sutures in order to optimize our view into the interhemispheric fissure. You can see here some hemosiderin as signs of minor bleedings in the past. Coming in here. And now we are really circulating around the AVM. And this is usually the nice part of the AVM dissection. And this is what everybody thinks that AVM surgery might be easy in a way, because we now start to understand the architecture. We are advancing. We have a 360 view of the nidus and our understanding of the nidus is increasing. But then as everybody knows, if it gets deeper down, if it gets further, sometimes, it might get very nasty. Here is a vein. And we don't really know whether this is a vein that is passing in the nidus or this is draining the nidus. We will see that it's passing the nidus. And this is one of the major draining veins here that we are respecting and that we are slowly freeing. And this is even a loop of the nidus which is not coagulated, but it's freed out of the surrounding tissue. And as you can also appreciate, it always has to be the aim to really stay close at the border between the nidus and the brain. And this is what really helps in eloquent areas to really find this cleavage plane between the nidus and the brain. Because the brain immediately next to the nidus is often scarred or it's lytic. So you can really work safely in this area. As long as you don't get too far into the brain tissue. And what you can also see is that you can really manipulate nicely on the nidus. The nidus, as long as you don't disrupt the venous outflow, is soft and can be manipulated easily. Here we are using a non-sticking bipolar, and you can see again, how we are advancing into the depth. Getting closer to the cone of the AVM. We are identifying here, an artery that we coagulate and another feeding or feeding vessel that we have occluded. And that is reducing the flow. Sometimes, it's difficult really to coagulate these vessels because there is such a high flow. That means that you need more energy. And it's a good strategy not to cut these vessels completely, but also by 50%. And then you see whether they are still perfused and the vessel is not retracting. If you cut them immediately completely, then they will retract and you have to follow them into the tissue. So only cut them by half. And here we are advancing. And this is a good example of a nice AVM because the deep feeders are not giving us such a hard time. There are not so many feeders. And slowly, now we are at the bottom. We at the cone of the AVM. And we are getting this turn to the cone. Step-wise controlling the deep feeders. We like to use a low setting for the bipolar. If you use high settings, you increase the stickiness of the bipolar. And this is the end of the resection. And you see the nice resection cavity, no swelling, no hyperperfusion. And you have to make sure that there are no residuals within the cavity. So let's go back to the slides. So this is the post-op angio showing a good resection. No residual. And this brings us to the second. This is again, a cortical AVM. Now it's a little bit bigger. It's more than three centimeters, which increases the Spetzler-Martin grading. It's at the parietal occipital area. And these are AVMs that I would regard as eloquent because they have a high proximity to the optic tract. And especially if you're operating on young patients or patients that are driving cars, you really have to educate them what it means to have an hemianopia, because that will not allow them to drive the car anymore. So this is really an eloquent AVM and patients undergo intense discussions. So this patient asked, was willing to undergo surgery and we felt it's feasible because it's rather cortical and it's not going into the depth, not traversing the optic tract. What I would like to highlight here is the AVM in the early arterial phase looks quite compact, the nidus and quite small maybe. But if you wait for the venous outflow, you see all these congested venous, vessels on the surface, which gives the impression, especially on the MR that this is a big AVM and a very dangerous AVM. So don't get misled by all these venous outflow vessels, because they don't play the relevance when it comes to surgery. The AVM nidus is relevant and not the venous outflow. So the details that I would like to discuss with you here is it's not always easy to distinguish the nidus and the superficial drainers, as I've mentioned. And don't get misled by all these big vessels on the surface. Here, we are following the classical concept of the circumferential devascularization as Gazi Yasargil, Professor Yasargil has shown us is his famous books and his famous lectures. We are circulating from the superficial part into the depths and slowly devascularizing the AVM. And this is a good case to show you that even with big AVMs, we avoid to use retractors. This is the video. Following opening of the dura. This is a good example of why we like to use the microscope for turning over the dura, because there might be some connections and it's good to control them under the microscope. Here comes in the needle. And again, we are starting with the extensive arachnoid dissection in order to understand the anatomy. We are again, or I again start with the draining venous, one of the venous drainers. And what you can appreciate, it's quite difficult, really, even in the microscopic view to identify the borders of the nidus. And what I also like to show here is that I'm using the sucker for retracting the nidus. So the sucker is turned on a bit just enough to get to the nidus to grab nidus with the suction. And this brings the arachnoid under tension. And then I can use the needle to dissect the arachnoid. Here, I'm using the ICG to understand whether this is a part of the nidus or whether this is just the venous system. Or whether this is the nidus. You will see that this is in fact, the nidus, but at the beginning of my perforation, I'm misled by these cortical veins. And I have the impression that this might be also part of the nidus. So I'm starting here with the perforation, which is not, it's not a real mistake. It's just to show you that even under the microscope, it's sometimes difficult to identify the borders of the nidus. Here are some arterial feeders that I coagulated. And what you will see is that while we are reflecting these cortical veins, I'm now realizing that I'm in the brain and not reaching the border of the nidus. So now I'm understanding here that this is part of the brain. I'm switching the direction of my perforation. And here, I'm looking for the lateral aspect of the nidus. And this brings me back to the orientation. This tongue of cortical tissue together with the draining system is retracted passively dynamically. And this is what I will use dynamic retraction over the whole resection process. Again, we are working very sharply next to the nidus dissecting the brain away from the nidus and identifying the small perforators and the small draining vessels that's performing a stepwise vascularization. As long as you keep open the large venous drainers, you don't have to worry about these small venous drainers if they are real small venous drainers and not parts of the nidus. And here we are slowly circulating. So we have started to perform the perforation here, and now we are going over to the more interior aspect of the perforation, or I should say that since the patient is here in the prone position, to the more posterior aspect. Again, identifying the border of the nidus. So this is an example where we are circulating around the AVM. Understanding the anatomy step wise. Here we are sacrificing, or I'm sacrificing a smaller vein in order to get some mobilization. Again, as long as the bigger veins open. Two or three bigger veins, you can go ahead and sacrifice the smaller ones if it helps you to get a better view and mobilize the nidus away from the brain in order to reach the base. And here we are reaching the base, the cone of the AVM, and we are continuing with the slow devascularization. So I think I've met my point here so we can go back to the slides. Complete resection of the AVM. We always perform the post-op angio, either in the OR as I've mentioned, or within 72 hours following the surgery. We rather perform it early in case we have left some residual to take it out immediately. So this is the case number three. This is an AVM, which is localized, not on the cortical surface, but within the sulcus and which will be hidden when the open the dura. Again, it's not a big one and it's localized in the superior temporal gyrus on the non-dominant hemisphere. And the closest to again, to the optic tract was the reason why we assume that it's eloquent, but you can discuss it. Maybe you say it's not eloquent because it's not reaching too far into the depth. It's not always easy to understand whether an AVM is on the cortical surface or whether it's in a surface. And this is obviously a detail that one should know before we start the surgery, because obviously, the strategy is completely different. In the cortical one, you will go around and you will understand the angioarchitecture. In the sulcal one, you have to go into the sulcus. And sometimes, you see those AVMs that don't have a deep training system, and that have a very clear cut medial border. And this tends to be the sulcus ones. But sometimes, it's not always possible. So again, for those, the first step is really to perform an extensive dissection and open the sulcus. And not only the sulcus where you assume that the AVM will be localized. You should open up all the fissures, all the sulci which are around the presumed AVM. And really to have a good opening and get a good overview. And if you're close to basal cisterns, they should be opened as well in order to control the vessels that are feeding the AVM. And this has to be nicely detailed by Professor Yasargil again. But a very important detail or a detail, which we feel is very important, has been published by a Professor Hashimoto in his neurosurgery paper. And he has taught us that if you go down the nidus, you will see vessels that traverse your line of dissection. And these vessels can be either vessels that are really traversing because they are feeding or whether they are draining. But some of these vessels are really loops. Parts of the nidus, which go out and then come back in. And they are part of the nidus. So if you really disrupt those loops, you might get into trouble because you will end up within the nidus, or at least you will disrupt the flow within the nidus. And this is the situation or the moment when this nidus might become stiffer, because you have interrupted the flow within the nidus. And therefore it's really mandatory to identify these Hashimoto loops while you are going down into the depths. And this is why I like to use a dissection technique where I peel the nidus and the brain from each other. I've seen surgeons, which are dissecting bluntly into the depths. I have seen surgeons that suck the brain away in order to identify these vessels, but but this strategy works best for me in order to identify and spare these Hashimoto loops. And this is a nice example. If we start the video to really highlight these technical details. So here we are opening the dura again, under the microscope in fast forward. We are retracting the dura. And in contrast to the AVMs that I've shown you before, you can hardly see the AVM here, because it's hidden within one of these sulci. And another trick for these salcal AVMs is they usually follow the draining vein. The draining vein as shown here, leads you to the nidus that is hidden within the sulcus. And if you free up all the neighboring salci and if you open up the fissures, you can then understand the angioarchitecture again. You can identify the draining vein, you can identify the cortical draining vessels, and you appreciate that the nidus is somewhere here in the depth. So we have opened up the sulci and the arachnoid, it has been dissected. And now, again, we are freeing up the adhesions and we are getting an idea about the anatomy of the nidus, which will be like this. This will be the nidus. And here we are starting to understand what's going on with this nidus. And here, you can see this peeling technique. The suction is holding the nidus and the bipolar with some current on it, is peeling the brain away. And this allows to identify these loops like here, which are looping out into the tissue. And this will be the mother of all these loops here. A huge Hashimoto loop. If you take that as a draining vein and you interrupt it, you will disturb the whole flow completely. So always remember to be on the spot and look out for these Hashimoto loops. Again, we are now dissecting along the draining vein here. And I will show you another example of Hashimoto loops on this side. So obviously each nidus is different. Some have many perforators, others have few perforators, and some have these Hashimoto loops like this one. And then the peeling technique is very helpful. Since I'm a right-handed surgeon again, now it's changed. Now, the sucker is moving the brain and I'm peeling the vessels into the nidus. So don't be afraid of these vessels. You can manipulate these vessels as long as you have not disrupted the flow within the nidus. You can pull these Hashimoto loops to you as a surgeon. And you will see whether they are real loops or whether they are feeding or draining perforators, and then you will coagulate them. And here we are entering the trigonum of the right temporal lobe. And now we are coming to the cone of the AVM of these subependymal feeders that we can now coagulate. So the peeling technique really brings us down to the cone and helps us to identify. Here, another interesting detail. This is a traversing or vessel en passant. The vessel en passant are arterial vessels, where you see many perforator vessels taking off, but the main vessel is not part of the AVM and has to be spared. And it's very important to identify those vessels. Again, you can see how we are keeping the draining vein open until the bitter end of the resection. And in order to mobilize the vessel more and more, we are freeing the vein, and don't be afraid of this vein. You can play with the vein, you can mobilize the vein. If you once enter the vein and it starts to bleed, don't coagulate. Put something onto the vein. Either a muscle tissue or maybe some gel foam and the paddy and the compression will result in termination of the bleeding in most cases and you don't have to disrupt the vein. Again, the peeling technique. I think this is a very good example to highlight this detail, which I feel, it helps me a lot in performing these dissections. Again, another loop here, a Hashimoto loop, which we are now bringing to the nidus. So I think you have learned that lesson and what will follow now is the control of the deep subependymal feeders. You can see that they can be nicely coagulated here, and we can nicely control. And let's go to the next slide. This was about peeling technique and Hashimoto. And this is a complete resection of the AVM. So this is one looks a little bit more spectacular, but in fact, it's not so spectacular. Don't get mistaken. Again, the small nidus. If somebody tells you, oh, this is a huge AVM, take a close look. Where is the nidus and which is the draining part. This is the training part. So a presumably big AVM turns out to be as not so big and therefore, resectable. So here, I would like to highlight another detail, which I have learned from Michael Morgan. In this video, again, you will see the dissection of the arachnoid using the needle as I've shown you before. But in contrast to our general strategy where we circulate around the cone, this is a good example for the direct cone attack. And Michael Morgan has taught me this, that in some cases where you are really experiencing that one entry zone, that provides a highway down to the cone. You should use this highway and go down to the cone and get an early control of the deep feeders. This is a unique opportunity, and you should not be so standardized and stick with the circumferential perforation. If you are lucky enough to find a highway that takes you down to the cone, take this highway and control the deep feeders. And this is especially helpful if you have AVMs that have been partially embolized because of AVMs that have been embolized, these perforators might become very aggressive. And if you have the chance to get down to the cone at an early stage of the perforation, take this chance, this is really like a unique opportunity for your surgery. So let's start the video. Again, we have an AVM that is localized to the cortical surface. You can see the arachnoid. Sometimes this arachnoid can be very thick, and it's very difficult really to identify the vessels or understand the angioarchitecture. This is why I'm again using the needle. And you can appreciate how I'm pulling away the nidus using the sucker. And I'm using this simple needle. It's 27 gauge needle that you can get from your anesthesiologist. I'm using the needle to open up the arachnoid and then I'm using the knife, the scissors, which again, is a regular scissor. It's not a super, super special scissor. Curved in one way curve to the other way. My mentor, Peter has taught me. You have to learn to get to be successful with the least number of instruments. And he always taught me if you're not successful with this small number of instruments that I'm giving you, you're not our man. And here, now, this is an example of the direct cone attack. So here, I realize that this is a one quarter of the circumference of the nidus, and there are no perforators on the superficial aspect. And it's very easy to pull the nidus over. And I continue with my peeling dissection. And there are no vessels. So I really I'm really happy about that because I seem to have a highway which brings me deeper and deeper and deeper. And this is as I mentioned, the unique opportunity to control the deep feeding system, which we know is the most difficult part in the AVMs. In the beginning, it always looks nice. And you feel like the biggest fisherman or the biggest neurosurgeon. And in the end, when it becomes really rough, you feel like the smallest neurosurgeon in the world that is not able of controlling the situation. But here we have a highway and that's the right moment to perform the direct cone attack. And you can see that's the other three quarters of the AVM have not been prepared. And now we have a good control of the deep feeders, the corticals feeders are easy anyway. So let's now continue. Good resection of the AVM. This brings me to the case number five. Again, it's not a super spectacular case. It's maybe an spectacular in a way that it's eloquent, very close to the visual cortex, but it's again, small. And this AVM looks very easy. It's on the cortical surface, no deep draining system. And at least I thought that this would be an easy case. Let's go for it. And this is why I also suggested the patient to perform the surgery. Although it wasn't a really eloquent area. And this example is to show you that AVMs can look different from the videos that you see in the meetings. Because these videos are often polished. And you should understand that bad AVM days exists like bad hair days. And Robert Spetzler, which I'm very grateful to say that he's one of my mentors in cerebrovascular surgery in general and AVM surgery, cranial and spinal, and specifically, he really made me understand that we have really, to stand the difficult situations and we really have to be open and honest that AVMs are not always straightforward situations. And more importantly, he made me understand how to deal with these cases where you have one vessel and many perforators, deep perforators, and these perforators might have a very high flow. And it's very difficult to coagulate these vessels because due to the high flow, the heat of the bipolar is absorbed, and it's not working really to control these perforators. And he has, it's really his credit, Robert Spetzler's credit to introduce non-sticking bipolars that are very efficient, that help us to control these vessels. Another strategy is to have an assistance that is irrigating, but that is irritating me. I really try to use irrigation as little as possible. Because I understand AVM surgery in specifically or neurosurgery in general as a one-man surgery, as Professor Yasargil always used to say. It's a one-on-one surgery. And I get irritated if somebody is irrigating too much. That's maybe a personal thing. And this is why I like to use paraffin oil. And this is a trick that I've learned from Yuahana Stemi, not only use the non-sticking bipolars, but ask the nurse, the assistant nurse to use paraffin oil and she's dipping the bipolar, always into the paraffin oil, which again is reducing the stickiness of the bipolar. As if you used some butter in order to prevent adherence of your egg that you are a boiling or cooking. Trick number two is to use temporary clips, either AVM clips or the, the classical aneurism clips. And by using the clips, you reduce the flow. And this allows us to coagulate. The trick number three is to coagulate these vessels over a long distance. Because if you cut them, they tend to retract. And if you use a longer distance, you are sure that they have been coagulated and they have been occluded. And if you cut them by 50% to see whether they are still perfuse so that you can continue to coagulate. And they are not retracting into the tissue. Because arterial feeders, with a lot of pressure that retract. These are really the sources of morbidity, specifically in eloquent areas. It's not the AVM that is localized within the eloquent area. It's the feeding vessel that is retracting and that you have to follow into the eloquent brain tissue. So let's start the video. Again, we are opening the dura on the microscope. First in sizing. I like to use the suture to pull up the dura, not to cut the underlying tissue with a knife. Then I use the scissors. It's an AVM that is again, within the sulcus. I'm using the knife or the needle again. And I followed the vein in the depth of the AVM. And it looks very similar to the salcal AVN that I've shown you before, which is a good example, showing you that you cannot really predict whether an AVM is easy or not. You should take them all serious. There is not such a thing like an easy AVM. Sometimes, you are lucky and it's straightforward, and sometimes, you have to be prepared. And it's like going to the dentist. If you go to the dentist, you should be prepared that you have pain in order not to be surprised that suddenly, it's painful when the dentist is working on your teeth. And it's the same with AVM surgery, be prepared for the worst. It might become very, very painful. And as I said in the beginning, everything looks very aesthetic, very nice. You feel great. All the observers in your OR think that you are a master. And when you then start to fight the difficult part, you feel very small and lonely. Here, it's a good example how you can use the knife to dissect even about these dilated congestive drainers. And again, how we are freeing up the arachnoid dissections. And then you don't have to be afraid. If you have mobilized things, you can move them around. As soon as you don't have an increased pressure within your nidus, they are soft. So we are now going into our circulating strategy around the AVM. Here, you can see the nidus, and here, we are using the peeling dissection, which I've shown you. We're on the left side. So the I'm pulling the vessels over with my right-hand side. And I'm counteracting with the sucker, or I'm changing that strategy depending on where I am. You can see the different vessels, sometimes the loops. Here, we are working on another draining vein, which I'm pulling over. In order to mobilize the whole nidus and to get an access to the nidus. This is feeding vessel. And I'm coagulating the small feeder. Here is the draining system. Everything looks nice. And suddenly, working on the wrong vessel at the wrong time, doing the wrong procedure. This is the venous. This is obviously a dominant venous vessel that I have coagulated. It didn't feel so good. And suddenly, it starts to bleed from the depth. This is not edited. I have just cut one of these venous traversing vessels, and here are the perforators. So I'm using the clip as shown on the illustration of Lucius. And now I'm coagulating. And you can see that at this situation, it's very hard to identify the source of bleeding. You do not know whether it's this one bleeding vessel or whether they are other bleeders here. And the only strategy is to take it one by one. Coagulating, placing the clip. Coagulating and you see how difficult it is. I'm coagulating once another time and this thing is still red. It's a red devil that is not reacting to my coagulation. Now, finally, it turns into block black and I'm cutting. I didn't do the 50% cuts, which I have recommended to you. I was super, super safe about cutting it completely. And then it's still bleeding. Again, this is another perforator, which is not responding to my bipolar. I'm happy enough or I'm lucky that it's not sticking here. I'm using the AVM clip. Coagulating over a long distance. I even asked the assistant to help me. Removing the clip. And then coagulating again to be sure that it's not reopening. And then we are continuing. And every perforator that I touch leads me into another level of frustration, into another level of fighting. And here, you can understand when I say that this fish is really pulling me or dragging me out on the sea. I'm using the non-sticking bipolar. And the only thing that you can do. Be prepared that it's might be painful, be patient. And don't get into a chaotic move, don't do chaotic movements. Just take one vessel after the other. And it just takes a while of fighting. But if you are really going on one perforator after the other, it might be five, it might be 10, it might be 20. But you have to have the self-confidence that in the end, you will go away as the winner. Never ever use a compression or don't tamponade or don't place gel foam. If you do this, the bleeding will continue into the tissue. You should only leave or advance to the next level of your perforation. if the bleeding is controlled. And once you understand that you have a situation, again, another one, cut. And you see that this is a typical bath AVM day. I'm even not respecting my own recommendations that I'm telling you. Learn from these mistakes. Understand that AVM surgery might be complex, might be difficult, even if the AVM looks easy. And now here we have finished. We have won the case and we can take out and disconnect from the major vein. And then of course, we have to go back to the resection cavity and take care off of the hemostasis. And these are cases where very easy, you can leave something behind as here. Part of the nidus left behind, and you have to be sure that there are no remnants. And these are classically the sources of early rehemorrhage. It's not hyperperfusion breakthrough. It's just a part of the nidus left behind. So let's go to the next video. So this case brings you to the next level. This is a sylvian AVM. So now we are leaving the cortical or a superficial ones. We are not going into a intrasylvian AVN. It's unruptured in a male patient. Patient's suffering from epilepsy. And Spetzler-Martin grade three sylvian fissure. So the sylvian fissure is another ballgame in terms of vascular supply, complexity and understanding the anatomy. This is the preoperative angiogram. And sometimes, the flow is so high that it's difficult, really to understand the anatomy and the arterial phase because the venous face comes in so early. So the details I would like to share with you in this case, especially the sylvian fissure AVMs, you have multiple en passant feeders. Obviously, these are the M2 and the M3 segments. And from there, you have multiple feeders that take off to the AVM. So what you will do is go along, understand the M1 anatomy, understand the M2 anatomy, and then follow the major vessels. And respect that these are en passant vessels, not injure these vessels. And slowly, devascularize the AVM from these major feeding veins. And another detail I would like to share with you that sometimes, you think that you have taken all the arterials feeders, but there's one last arterial feeders that is hidden behind the major vein. Behind the sylvian vein or the temporal vein or whatever. And you think that you have taken off everything, but you still have a major arterial contribution to this vessel that you have identified, Which is hidden behind the major vein. So let's start the video. This is operated through a classical pterional craniotomy. We like to turn the heat by 30 or 45 degrees. Patient is fixed in the clamp. The mandibular is the upper point to optimize venous outflow. Here we are opening the dura below the microscope. Again, you can understand why this makes sense, because we have some fistulas feeders from the dura. And we are slowly identifying the sylvian fissure. Here, we are using the needle to open the sylvian fissure. We have a very dominant sylvian vein here, or two veins. I have decided to go in between the two veins, which will help me to understand the venous anatomy. Here, we have the venous pouch. This is the that was, that was drilled down so we are in the proximal segment of the sylvian fissure. But obviously, the craniotomy is big enough to have a good overview over the whole sylvian fissure. It's very important to open up the whole sylvian fissure in order to understand the anatomy and have a good control over the whole nidus. And what we are doing now is really using mainly sharp dissection to open up the sylvian fissure to freeing up the arachnoid adhesions, and to understand and identify the M2 branches and the M3 branches. And you can see that the nidus is mostly within the sylvian fissure. And we can mobilize the nidus very nicely. And the critical areas are the small arterial feeders that take off from the en passant arterial feeders. And these are taken step-by-step. Again, a long distance calculation. Making sure that you have a completely occluded the vessel and then cutting it. Here's a spontaneous thrombosis. Also interesting to see this patient was not pre-embolized. Sometimes, the embolic material looks like this. Here, the embolization was done by mother nature. Following here. The step wise devascularization. This is another feeder. And you can see that you don't have to be too afraid of sylvian fissure nidus. The anatomy is beautiful. You're not within the brain. It's quite straightforward to get a good idea about the vascular anatomy if you are familiar and experienced with the sylvian fissure anatomy. You can dissect the draining veins and they give you enough space and maneuverability. Smaller veins can be taken. So this is the major draining vein again here. We will end up with one natural feeder from here, and one arterial feeder downside here. But still we are in the face of freeing up the nidus. And this is really why we are doing these kinds of surgeries because the anatomy is so beautiful. This is our major M2 branches. This is within the inferior insular sulcus, where we can see other major arteries and free arteries. This is the temporal operculum. And here we are, again, identifying the smallest feeders. This is a feeding complex, multiple feeders. And obviously, they are making a turn here. And now I'm performing an ICG to better understand the flow within these vessels. So this is where ICG really plays an important role. To understand the flow and the anatomy and the dynamics within the different arteries. So I have identified this one as one draining major artery, and I'm placing a classical clip in order to control the bleeding as in the sketch. This is the complex. So I've seen that the flow is going like this. And this is a stump that is feeding the nidus. So I'm clipping this stump close to the nidus in order to preserve the flow here through these M3 vessels. Continue. So now I think that I've completely freed and occluded all the arterial vessels, but still, there is a significant pressure on the nidus, which I felt that it's maybe, I didn't really respect it. So I started or I continued with sacrificing the artery. Coagulation with the clip on. This reduces the arterial pressure. Then cutting the vessel, 50%, see whether it's occluded. 100, transected, done. Now the other one. Turning the nidus around. So the idea here is really to keep the flow within this arterial complex and cutting close to the nidus. And I realized that there's a significant backflow from the nidus and suddenly, nidus is again, soft. So if you have backflow from the nidus and this nidus becomes soft, you obviously have additional arterial inputs. And now I realize that there is another dominant arterial feeder. Unfortunately, it's out of the focus, but here, I'm coagulating the venous outflow plus this vessel. Now, I'm transecting the stump. And now I'm realizing that there is no backflow. The nidus is completely devascularized. There is some arterial filling that I will take care of with the bipolar, but now the nidus is resected and can be taken out. And then I will check the surrounding anatomy. Yes, now please continue. So lessons learned about sylvian. So this is a case that looks similar, but it's quite different. It's not a sylvian AVM, it's AVM within the insular cortex. It's an insular AVM. Obviously this AVM in this young patient with the med student has bled, and there is an ICH. And it's on the left side, on the right-handed patient, on the dominant side. So here we have, not an intrasylvian AVM. We have an insular AVM, which will be approached with a transylvian approach. And we have ICH here and this AVM of a patient that has been transferred to us from an outside institution. This AVM has been partially embolized. And when it was realized that the patient that the AVM could not be occluded fully, patient was transferred for surgery to us. The preoperative angio showing the significant venous drainage and showing that the insular AVM is not really occluded by the preoperative embo. And here you can see the embo material, which has been deployed by the endovascular colleagues. Patient was awake and his hemiparesis had resolved completely. He still had some problems with talking, but he had recovered very well. And we are performing the surgery two weeks or no, 10 days after the hemorrhage. So we tend to perform surgery on ruptured AVMs early. We don't wait until they have been rehabilitated. As soon as the swelling has gone down, we will perform surgery within 48 hours or one week following the bleeding. The lessons learned here is the ACH is your friends. It does a good part of the dissection. So if you see an image like this, you can be assured that the feeders from the perforators, from the insular compartments that have been dissected by the hemorrhage. Insular AVMs afford a wide opening off the sylvian because you have to move your opercula over in order to control the sylvian fissures. And this will show you how you deal pre-embolized AVMs. Please start the video. Here, we have performed the classical pterional craniotomy. 50% frontal, 50% temporal. The sylvian fissure is in the center of our . Temporal lobe, frontal lobe. Here we are dissecting or opening the arachnoid of the sylvian fissure. As an interesting note, this is a left-handed surgeon. So this is my fellow that has started. And obviously, he's using another strategy, not using the sucker. So here I'm taking over now using the suction again, I'm retracting the vessels or the nidus with the sucker and using the needle for the arachnoid dissection. Now switching to the scissors. Here, the first M2 branches come into site, but it's also part of the draining system that we can see here. Arterial here, venous here, frontal lobe, temporal compartment or temporal operculum. And this is the major draining vein here. We are mobilizing the frontal operculum here. Getting into the superior insular fissure or sulcus. Here below is the insular cortex. And an insular AVM is nothing more than a cortical AVM in the frontal area. It's just on the insular cortex. So as soon as you reach the insular cortex, you are working on a cortical AVM that is fetched by major arteries coming from M2. So, as soon as you understand that insular AVMs are similar to cortical AVMs on the brain surface, you understand that they are frequently feasible. And you can already see part of the ICH that is drained through the openings. You can see the hemosiderin on the brain tissue indicating that this patient might have bled before. And potential warning leaks or warning bleedings have not been identified. Here are the M1 or the M2 branches, which are then feeding the AVM. And we have a proximal control here of these vessels to be sure that what we are coagulating now is part of the draining system, which is going into the depth into the insular cortex. Here, the cortical AVM or the nidus becomes more and more into sites. And what you can also appreciate that even with a transitive approach to an insular and AVM, we are not using retractors. Everything is done dynamically. And again, you can appreciate that we are only using a suction. A 10 suction or a number eight suction and a non-sticking bipolar, not the very fine one, the medium one. Because very fine ones tends to stick more. And with the bigger ones who can coagulate. So we don't really have a fancy setup for tackling these AVMs. And I already mentioned the philosophy that I was raised with by my mentor, Peter Vajkoczy in Manheim in those days. So here we are slowly dissecting. And what I would like to show you, and this is why I'm waiting for this video is that while we are getting down to the cone and working around the AVM, we are opening up the ICH. And I'm really waiting for the moment when the ICH is drained or is coming into our field or to our visual field, because then I know that I've reached the cone of the AVM. Again, we are very close at the border of the nidus and the tissue, but we can be a little bit generous because we know that below here is not the capsular antenna or the cortical spinal tract, below here is the hematoma. And you can also appreciate the dealing of the pre-embolized vessel like here is really not a problem. You can coagulate them, and you can see that we did not really have to work on the cone of the AVM because the hematoma has done the job. Another lesson that I've learned from Professor Yasargil who liked to work on ruptured ones with ICH. And this is the single one deep here that has bled, and that we have taken care of now. Next one, please. Post-op angio shows the risk section. And this is now a case, which is again around the sylvian fissure but it's completely different. It's a pediatric case. And as you can already appreciate here, the nidus is not solid, but it's more diffused. As you can frequently observe that with pediatric patients. It's accompanied by arachnoid cyst, which is in close proximity to the basal cisterns, typical temporal mesial arachnoid cysts pushing back the temporal lobe. And this patient is suffering from epilepsy. He's 13 years old patient, and the diffused nidus is confirmed on the angiogram. And in fact, I'm pointing your attention to that. We have different compartments. One in the medial temporal gyrus or superior temporal gyrus even. Or one on the temporal pole or inferior temporal gyrus. And this will bring us into trouble. Because this is another case where I have not performed as good as I should have performed. So this will show you the unique properties of pediatric AVMs, specifically of the diffuse nidus. And I will show you next, please start. So we have performed a pterional craniotomy, which is centered around the temporal pole the temporal lobe, as you would perform for an anterior temporal lobectomy or for a selected hippocampectomy. The sylvian fissure is here on, it's hardly in our view following the craniotomy. So we are working, this is the tentorium. This has been the cyst, which has been opened. This is the temporal base here. And we are basically resecting the AVM along the temporal pole. And as it's typical for the diffuse AVMs, we cannot really identify a clear nidus. As we see many vessels. It's a profuse diffused bleeding that we are tackling, and all the time, we will find these aggressive, deep perforators. And you can never be sure whether these are the perforators at the edge of the nidus or whether you are traversing the diffuse nidus. In fact, and I'm already telling you the anecdote of this case, I'm traversing the diffuse nidus. So this will be a case where I will incompletely resect the nidus. I feel quite confident in this case that everything is going well. I have the anatomical orientation with the tentorium. I had difficulties of identifying the nidus, but I feel pretty safe that I'm resecting the whole nidus. And here I'm working on the bases on the vasal feeding compartment slowly resecting this. Next slide, please, or go back to the slides. And the ports of angio, which we have not performed in the OR, which we have performed on day one after the surgery, shows that we have nicely resected the one compartment, but the other compartment is still there. So we have to take the patient back to surgery. And we had to accept that we have done an incomplete resection. The patient was fine and everybody was understandable. And this is the second surgery. So again, the temporal basal craniotomy or the temporal focus of the pterional craniotomy. Here is the sylvian fissure. Here is the middle temporal gyrus. And we had resected here, down here on the basal medial area. Now we are more towards the sylvian fissure, more cranial, new cortical aspects of the temporal lobe. And please, I don't know how you feel about surgery, the temporal lobe. I feel that the temporal lobe is the most difficult lobe to perform surgery. Whether you're talking about epilepsy surgery, whether you're talking about glioma surgery, limbic surgery, or AVM surgery, it's always the temporal lobe that is, with all its neurovascular structures and functions and neocortical and limbic areas that is really the most difficult lobe. And now here we are identifying additional nidus, but this time, again, it's a diffused nidus. So we are working our way around and we continue to resect as long as the bleeding stops. And I should have done that in the first setting, but I was so confident that we had resected everything. And here, I think again, I felt that I had resected again, everything. And again, some additional nidus comes into the site, which is resected. And which, and in the end, luckily enough, this led to a complete resection. This time, we had performed an intraop angio. And again, bleeding from the deeper aspects while we did the hemostasis, we again identified some arterial bleeders. And if you find a teal breeders while you are doing the hemostasis, this is not necessarily just a simple perforator that has been opened. This might be part of a nidus as remnant. And you have to take care of that and follow that, and be sure that you have removed everything. Again, bleeding from the depth. Okay. While I'm struggling, let's go to the next slide. I think you got the point and you learned that lesson. And now everything has been removed. So we have two more videos to go. I hope you have patience and you stay with me. And here, we are going deeper into the brain. This is a deep cerebellar brainstem AVM at the junction of the cerebellum and the brainstem somewhere around the fifth nerve. We are working here through a small corridor, through a small retrocecal craniotomy and a infratentorial supracerebellar approach. And despite the depth of the corridor, again, I'm not using a retractor here. And not to compress any draining veins and not to confuse the surrounding brain. So this patient has a ruptured AVM. Again, a little bit of a diffuse nidus. Now deep inside, below the tentorium on the cortical surface, the tentorium surface of the cerebellum. And within the fissure that will lead us to the lateral tectum. This is a good approach also to get to cover in the thalamus. We are taking the lateral supracerebellar infratentorial route to get to that. This will allow us to control the feeding from the superior cerebellar artery, as shown here. This will allow us to control the venous system for the petrosal vein. And this will hopefully allow us to resect this AVM safely. So this is the retrosig craniotomy. Here's the mastoid. We have to form a curve incision. I've learned that incision on this platform. This is the transverse sinus. This is this sigmoid sinus. And we are opening the dura in a way that we are cutting here into the angle of the sinus. And we are taking the super cerebella infratentorial route. Here we have opened the basal cisterns around the petrosal vein in order to drain CSF. This is the tentorium. This is the vein. Here we have opened the basal cisterns to drain CSF to relax the brain. This is the superior cerebellar artery. Accompanied by the fourth cranial nerve that will come into site. The midline would be here. So it's a infratentorial supracerebellar approach. Sharp dissection and sharp working on the fourth nerve on the trochlear nerve. Which would lead us to to the brainstem and to its brainstem origin. Here is the feeding, the main feeding vessel, which is now, we confirmed that by ICG. So now we have the draining system. We have the main feeding system. We place a clip for the temporary occlusion of the feeder. And we will coagulate. If we temporarily clip and we feel safe, then we coagulate immediately. We would not continue to resect and leave the clip inside and do not coagulate and do not transact the vessel. If you feel safe, we transect. As we are doing here. And you can see how we are working again through this small corridor with the same strategies that we have applied to the cortical. And in the end, this is again, a cortical. It's a cortical AVM. It's located on the tentorial cortical surface on the hemisphere. And a little bit on the brainstem here on the fissure to the brainstem. And again, we are performing the incision of the cortex. And often, you have these AVMs which are located on the surface. And then might go into the depth. And this is a technique where we use the pile disconnection. That means we often stay on the surface and disconnect the pile compartment with the arterial feeders from the below structures, especially in the brainstem. Here, we are going into the depth. We have a small nidus and with these small nidus that have just bled in the differ locations, they are often or sometimes quiet angry. So here we would go along the nidus, since it's a small one, it's not forbidden to coagulate parts of the nidus. And what you also learned is that the dissection is not always as nice as on the cortical surface. But again, I'm performing the peeling technique and I'm following the same concepts. Going around the nidus, slowly devascularizing and mobilizing the nidus out of the surrounding tissue. But again, not only the pediatrics, but also the posterior fossa. AVMs tends to have a diffused nidus, not so compact, not so solid. And that's what I'm experiencing here. Multiple feeders from the cerebellum and from the cortical tissue, or from the cerebellar tissue. And dynamic retraction with the sucker. And I'm working my way around the AVM. And then all these deeply localized AVMs are usually first go and attack AVMs, because you will go down to the AVM and then come up on the other side. It's usually not possible to really circulate around it. And here, I'm mobilizing, and since I've already got the control, I'm also coagulating the nidus and pulling it over. And disconnecting the peel nidus, and still the vein is open here, which I have now occluding and taking out the small, but a little bit angry nidus. Okay, let's move to the next slide. While we are taking out the AVM. This is the postoperative control. You see the complete excision and the patient who recovered well, both from the surgery and from his SAH. The last case I would like to highlight is focusing on spinal AVMs. And I'm showing that because spinal AVMs are a little bit underrepresented in AVM surgery talks. And I really have a love for spinal AVMs. And I fell into love with spinal AVMs when I was taught by Robert Spetzler how to treat them. Meanwhile, I really believe that spinal AVMs are a different species and not really comparable to brain AVMs. They have a peel part and a medullary part. And the flow is much lower than in brain AVMs. And for these cases, the technique that has been published by Robert's group, where we disconnect the peel compartment, and devascularize the outflow and inflow from the medullary compartment. This strategy has really changed, at least my thinking about spinal AVMs. And it's really an intended subtotal resection. But if you perform the post-op angio in the end, the AVM has gone in many cases. And if not one week after the surgery, then weeks or months later. So this is a 12 year old kid, semi-professional tennis player with this complex medullary AVM. She has bled and experienced headache in an SAH. Initially, she had a weakness on both legs. This is approximate. This is at the level of C3 to C6. You can see the accompanying aneurism here. And you can see the nice reconstruction of the structure. So let's start the last video, please. We have performed the laminoplasty. And we are now incising the dura. The dura is retracted. And we will replace or put back the lamina with some mini plates. But before that, we have to take care of the AVM. We know that the first question is where is the nidus located? Is it more on the dorsal aspect? Is it more in the lateral? Or is it more on the interior aspect? The more anterior it is, the more difficult it is because you are getting into conflict with the spinal artery. So for these cases, electrophysiology is absolutely mandatory. Not because you are afraid of directly injuring the spinal cord, but we will perform tests occlusions of vessels, where we think that they might be related to the spinal artery. Here, we are taking a lateral approach. It's important to cut the dentate ligaments. And if you cut the dentate ligament, you can turn the spinal cord around. We have removed the hemorrhage or the false aneurysm following the inflow. And here we've identified an interior artery. We are performing a test occlusion with a temporary clip, and now, we are really following the electrophysiology. And if the electrophysiology after five minutes is stable, we will cut this feeding vessel because we are sure that this is not related to the spinal artery. The only thing that I'm really afraid of here is to injure the spinal artery. Now we have taken care of the lateral or anterior supply, and we have taken out this aneurysm or this false aneurysm. And now, we can draw our attention to the nidus. We perform an ICG, which nicely shows the is and the draining system. But in the end, again, it's difficult really to say what is the nidus and what are the drainer, the draining veins. But in contrast to an AVM on the brain, we now directly attack the peel compartment. And we separate the peel nidus on the surface of the spinal cord from the spinal cord. Not going necessarily into the tissue. Only if we have a solid nidus that we can follow. Number two difference is that these feeders are much easier to coagulate and to transect. And if they bleed, the bleeding is not so dramatic as with a real arterial feeder as you often observe on the surface. Number two and number three, this is the reason why it's not so dramatic if you get into the nidus. If you get into the nidus, you can simply coagulate with your bipolar. And you will not observe a nidus that will start to explode or that will start to pump up. You really get away with mistakes when you prepare, when you operate around the nidus. I admit that sometimes it's difficult to understand the anatomy and to understand the vascular anatomy and its relationship to the spinal cord, but you can see how I'm peeling away the peel compartment. The superficial compartment of the AVM from the surface of the spinal cord. Sometimes, we have an intact surface. Sometimes, the vessels are going into the spinal cord, but we will not follow the necessarily into the spinal cord, but slowly, disconnect. And again, we leave the drainer here to the end. We accumulate the drainer and we continue. I think spinal AVMs, most of the work is done before the surgery in order to understand where it's located. Dorsally ventrally, laterally, which approach to take. Is it possible to remove the pathology without injuring the anterior spinal artery? And if you have done all these intellectual work and you feel confident to do the surgery, then it will work out. And as you can see here nicely, I'm coagulating the nidus on the surface. And I'm getting away with it. Because I have interrupted the major arterial drainers. And this is why I get away with a diffused coagulation of the nidus and disconnecting the nidus. Here, another anteriorly located vessel, smaller arterial feeders. Here, we can see the C7. This was the C7 nerve root. Because the only thing that was that she was left back was a fine motor deficit in her right hand. She was right-handed and she was playing tennis with her right hand and she had problems with a forehand. She was playing the backhand with two hands. So what was it? The logical conclusion. She started to play the forehand with two hands overcoming the fine motor deficit that she had on the right hand. So she returned to a competitive tennis player at a national level following this. And this really shows that not only spinal cord AVMs can be removed, but also that pediatric AVMs are very grateful because these kids, they can recover amazingly. And the same with brain AVMs in kids, they recover very nicely. On the other hand, we have to follow these patients carefully because AVMs might come back, grow back, and we have to perform control DSAs until they are 18. And now we are closing the door and we are done. So please stop the video and let's go to the conclusions of my talk. This is the post operative control. And the conclusion is the surgery, the microsurgery for AVM is fascinating. And I'm still convinced that even in the light of studies telling us that surgery is inferior to less invasive technologies, I feel that surgery provides the cure with the highest success rate. And if you pick the patient reasonably, and if you are confident and you are aware of your capabilities, the risk profile is very reasonable. And even if you have an early post-operative deficit, it's like with insular gliomas. We know that 30% of our patients will have an early deficit but they recover well. The surgical strategy is difficult to predict the plan, and this is why I feel it's very hard to plan each step of the surgery. And I hope that I've introduced to the one-on-one technique with the Hemingway technique of resecting the big fish and bringing the fish back to the land. I have shown you some tips, some tricks, but also pitfalls. Some cases where I was not so successful or straightforward. And I've given you an insight into the large armamentarium that you need to really be successful with AVM surgery. I thank you, Aaron for inviting me. It has been a pleasure, and I'm very grateful to having the opportunity to share my experiences with you and your crowd. And I will be very happy for staying here and answering your questions. Thank you very much. This is our hospital. These are the different campuses, which I'm responsible for. And thank you very much again for having me.

- Great lecture, great lecture. Beautiful. Really enjoyed it, Peter.

- It was too long. I have to apologize.

- You know what? Nothing about it was long. It was all good information. I have to tell you, I really enjoyed the technique. Very meticulous, superb. Some of the things that I really personally liked that you emphasize is that manipulating the vein is not as dangerous as people think. This is an arterialized things so the wall is much thicker. It's almost as thick as a regular artery at times. So you have to obviously handle it carefully. You don't wanna, of all said, you don't wanna injure it, but mobilizing, it really gives you a lot of good information. On top of that, I don't know what you think about this, but often, what happens is that you disconnect the entire nidus and the AVM still filling. And there's always an artery hiding next to the vein that you won't find until you dissect the vein and take it. And then the vein turns blue. And I think that's one of the advantages of being able to have a circumferential dissection of the vein well. What do you think of that?

- Yeah, so number one is I completely agree. And I think the draining vein is your friend, number one. It's not so dangerous as young surgeons are told. And it gives you some times really the highway and at least be directed to the nidus. And if you are capable of mobilizing it, it allows you to free the nidus as with all its connections and to open up the fissure. So I completely agree with that. The second point about the hidden artery, one of my videos, I think number, the one with the sylvian AVM has really detailed that. I couldn't agree more. Sometimes, you think that you have, devascularized the AVM completely, it's still filled and it's still tight. And if you test occlude the vein, it pumps up like this. And you wonder, how is that possible? Because there's one feeding artery that is hiding below the vein. And please watch the case with the sylvian AVM. There Lucius, our illustrator has really drawn exactly that scenario. That you have a big vein on the surface and a smaller artery below that. And I couldn't agree more on your comment. And I think this has to be emphasized not only once, but more frequently.

- Thank you. The other issue that you very well nicely emphasized was that these AVMs, especially pediatric ones, and that temporal AVM you showed, Peter can have a much more diffused nidus than we appreciated on the angiogram. Remember the angiogram resolution is not that high. So the nidus of the AVM in fact is much bigger than what you see on the angiogram. Obviously, MRI and CT have even much, much less resolution. So one should always be prepared that you're gonna into the nidus and deal with it. I think this is such a big taboo in neurosurgery that while you got into the nidus of AVM, that is so terrible. Well, in fact, if it's done in a controlled fashion, it's not a terrible thing, and the surgeon should be able to handle it. I mean there has been a few times I intentionally got into the nidus because I was removing the AVM within the very important functional Wernicke's area. And actually did an intranidal dissection. There's a video of that on the Atlas. And the reason is that you can never appreciate the true nidus of AVM unless you're in surgery. And you have to keep your composure if for getting bleeding. And what I really like to emphasize is that if you can get good hemostasis, don't just persevere and coagulate. There is a residual AVM that has to be removed. Otherwise, you will be back to nidus. So those are things that have to be really emphasized that especially for cerebellar AVMs, because cerebellum has a different angioarchitecture and microcirculation than the cerebrum, the AVMs can be much more aggressive and the nidus can be much less appreciated in true size. What are your thoughts about that?

- There's not much to add to your very careful experience and analytical remarks. So this is why I put the pediatric case and the cerebella case into the collection of the videos. Because as you say, they can be very diffused. You underestimate the level of complexity because they're not only diffused, but the vessels are smaller and the veins are not so impressive. So they appear to be smaller than they are in reality. And sometimes, they even appear to be easier than they might be in reality. So this is really, as like going to the dentist, you have to expect that you might have to spend a little more rigor and fighting on that AVM. I also agree that sometimes, you have to enter or it's a good strategy to enter the nidus, especially at the cone, because sometimes you have AVMs that are within the insular, or that are bigger on the cortical surface and it gets very close to the cortical spinal tract. And we can really map that with the transcranial magnetic stimulation and the tract analysis that they are very close. And for those admittedly rare cases, we might, or I might go through the conus, the bottom of the nidus. And then it can be controlled as you say. But then you have to watch carefully when you have resected the AVM really that this remnant is controlled. But also if you really remove the majority of the nidus and then revisit this remnant, you suddenly realize that the flow has changed because you have occluded the outflow of these perforators. And suddenly it becomes very easy to remove the remnant nidus. So it might even be a strategy to decompartmentalize the AVM, cut it in two pieces in a bigger and a smaller one. And it becomes easier to remove the smaller one in a critical area. So I agree with you in that respect as well. And yes, I think that's a very important message not to, number one, if you find bleeding during hemostasis, take into considerations, it might still be a remnant. Number two, if you have that bleeding, take control of it, take care of it and not just tamponade it, because then, you will have an ICH.

- Well said. And I think in the closing, I have to say that one should not be scared of blood. I think there is much bigger number of vascular neurosurgeons that are scared of blood or get uncomfortable, let's put it that way when they see bleeding. And AVM surgery is a time where you have to have a high tolerance for bleeding. My residents and fellows always tell me that we have never seen a surgeon like me, as unafraid of bleeding as anyone else. And I think that's the mentality you should have. Bleeding is just blood. If you're very tolerant of it, you can do AVM surgery efficiently. If you get nervous and concerned when there's fair amount of bleeding, that can make the surgery extremely difficult and lengthy. Because that's difference between controlled and uncontrolled bleeding, I think defines the best line of decision making in AVM surgery. Don't you agree?

- I fully agree. And this was my intention when I made the remark. Many of the videos that you can see or that are shown, they are the polished nice ones. And they create wrong expectations for young AVM surgeons that think that they have failed if they get into bleeding. But the bleeding is the reality. And if we go into AVM surgery or into a case, we should have, we should be prepared for bleeding. We should concentrate on the case and to book something else in parallel. Because you might end up sitting there and you have to stay patient. And this is the analogy to the fish. The fish drags you out, but you know you shouldn't be afraid because you are self-confident, you know your techniques, but you also have to say, and you have to admit that it takes some experience until, or unless you don't get afraid if you see blood. Your first AVMs, where you encounter the real bad AVM day, they make you afraid, or they at least make you, you get more respectful with this. But with growing experience, you expect bleeding and bleeding comes as part of the natural AVM business. Let's put it that way.

- Yes. And I've always said the AVM surgery defines the best of the microsurgeons. Because not only you have to be a highly skilled technical surgeon, or you have to be extremely efficient, agile and reactive. Anywhere in microsurgery you go, you will see most often the surgeon has to be a good technical surgeon, but it's only an AVM surgery that you're taking agility and your efficiency and responsiveness is tested to such a high degree. And this is truly what I love AVM surgery, Peter. It is truly the most enjoyable part of the microsurgery for me. And as once I heard somebody say, AVM surgery is also the only surgery where you see the most beautiful scene. All the surgical exposure at the beginning of the surgery. And often, you end up seeing the worst picture of the microsurgery at the end. So it's a contrast between the most beautiful and the most ugly. So with that, I wanna sincerely thank you, Peter, for a sensational lecture. Tremendous skills, superior leadership. And you have definitely demonstrated why microsurgery is so enjoyable and it's only for the best. Thank you again for being with me today. Thank you for being such a great friend and colleague, and I look forward to having with us in the near future.

- It was a pleasure. Thank you so much.

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