Surgery for Complex AVMs

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- Colleagues and friends, thank you for joining us and happy new year. This is another session of the virtual operating room from the neurosurgical app class. Our guest today is Dr. Amir Dehdashti from North Shore University hospital. Amir is a very talented cerebrovascular and skull-based surgeon. He's the director of fellowship there. He's going to talk to us today about surgical management of complex arteriovenous malformations. Amir, thank you so much for joining us, and we're very much looking forward to listening your pearls of technique. Please go ahead.

- Thank you very much, Aaron. It's truly a pleasure to be here happy new year to everyone. And I, I am really honored to take part in the series of the neurosurgical apps class. This is a tremendous tool to not only trainees residents or fellows or even for attending neurosurgeons. And I think anyone will learn so much from, from your panel and from your previous presentation, there are so nicely orchestrated. And I really thank you for your contribution to our feed. And I'm very thankful that I am among one of the speakers and we'll be talking today on the management of more complex brain AVMs. And my goal today is to talk mainly about the AVMS debt or controversials. And specifically with the recent studies showing that the treatment for unruptured arteriovenous malformations are debatable or controversial. I think the most complex ones would be the grade three or some grade four unruptured brain AVMs that we really need to find out what is the best way of managing them. And I think the, a robust study did not address that in an appropriate fashion. So, we're going to focus only on those AVMs. You're not going to be talking about ruptured AVMs, which is a different entity, and we are not going to talk about a grade one or two AVMs that are or so to speak smaller and easier arteriovenous malformation to treat. I start with this illustrative case. This is a 27 year old woman who presents with headache, no seizure and normal neurological exam. And she has a platelets number of 1000 because she was just diagnosed with an ideopathic thrombocytopenic purpura. And you can see that she's diagnosed with this very large, almost six sonometers left frontal AVM that has the extension posterially almost to the region of broca here, and you can see this is the area of this AVM. And the posterior extension is really, could become critical in terms of the eloquent area here. However a vast majority of this AVM is in the frontal basal region. This AVM does not have a deep venous drainage, and it's because I consider that it's a non eloquent location. Although we have to be careful with the posterior extension of this AVM. So the question is, so what should we do? In 2020, this 27 year old patient comes with this unruptured, very large AVM and what is the best answer or treatment for her? Another one we can see here, a patient with, again, headache, no seizure, normal neurological exam, and these complex Corpus colossal AVM, which has some intranidal aneurysms and with significant venous varices, as you can see here, like these big venous varices here on the, the other one in this location. So, there's also some stenosis of the venous drainage, which could potentially be a risk of rupture, but this patient is intact. What is the best option for these patients? So we will get to that. If you look, and this is the patient with the AVM or characteristic of this AVM with various Venous varices and complex morphology of these arteriovenous malformation. So these grade three AVMS, as you know, they are different than all other AVMs because it's a very heterogeneous group of arteriovenous malformation. And depending on the eloquence or venous drainage or size, they could have different risks in terms of surgical excisions. And also there is a supplementary AVM grading that Dr. Lawson has popularized. And I think it's important mainly in terms of the aspect of tinnitus, whether nitris is compact or it's diffused, and also whether the AVM is ruptured or unruptured. This will add to the complexity. And obviously all the AVM I'm talking about today are unruptured. So that per se adds a risk factor for surgery because these patients are coming into us most of the time, completely intact, and we want them to leave the hospital intact. If we suggest the treatment. Now, ARUBA, it's a very nicely and carefully designed study, but unfortunately, as far as I'm concerned, poorly executed, and obviously we don't have time to go over ARUBA. I have one hour talk, criticizing the ARUBA, talking about its good part and also its weakness. But you can see that ARUBA at the end will not give us an answer for what to do with grade three AVMS. ARUBA shows that get a grade one AVM do better with interventions. And then when you put all together, we get to the conclusion that a intervention is not good for unruptured AVM, because there was 11 adverse events in the observation group versus 35 in the intervention group. But then there are so many, so many problem with this study, the methods use for treatment evaluation of the treatment, efficacy by each modality, the selection biases, followup lengths, and also no rigorous vision equitation. So I think we have learned two major thing from ARUBA and that are very important. And I think this is the credit that I give to the ARUBA. One is the natural history of the AVM and we know that their rate of rupture per year is not 4%. If you get all together without specificity of each AVM, the rate of rupture is about 2.2% per year but obviously for some AVM that might be higher if they have some risk factors. And the second most important thing that we have learned from ARUBA is that, eh, incomplete treatment of AVM is not efficacious and could potentially even be dangerous. So, that's why the ARUBA does not really address the issue of surgery for AVM because when there is surgical expertise, and even there is a complete obliteration rate after the surgery, I think the results would be dramatically different than what ARUBA is showing to us. And as you can see in the ARUBA, there is only 18% of patient who had open surgery for AVM, which is the most important treatment of AVM. AVM should be cured. AVM should be eradicated in order for us to achieve a complete results. And that is what ARUBA is not really addressing At the same time, I think all these randomized studies, including ARUBA improves our surgical results because there is always a little bit an apparent overestimation of surgical risk. But I think that improved the quality of care because they raised the bar high for us as surgeon to show to the neurosurgical community that we can achieve better resulted surgery. So all these randomized study at the end of the day, I think have improved our surgical outcome in centers of excellence. Now, grade three AVMS. If you look at the results published, this is from Mike and Morgan in Sydney, one of the largest experience in AVM surgery, you can see the vast majority of patients end up with very good results. Only 3% of patients in that series had MRS of two or above. And the recurrence after complete resection of brain arteriovenous malformation is very low It's about 3%. This is nowhere close to what ARUBA alluded to. And this is another study posts ARUBA from our friends in Toronto, showing that microsurgery in the cohort of patients that were similar to the patient in the ARUBA has produced less disability or neurological deficit compared to what was shown in ARUBA. So that clearly also shows that in center of excellence with appropriate patient selection, the results are better. Of course, these are not randomized study because these are retrospective from every specific center, but at the end of the day, that's what you're dealing with. That's what the centers that are treating the patients and these are the centers where seeing a lots of brain AVMS, and you can see that we can achieve better results in terms of surgery than what is portrayed in ARUBA say. Now, when you look at the specific AVM, these are the risk factors for hemorrhage, and then you can read by yourself. I'm not going to go through the list, but the most important is the presence of intranidal aneurysms. And I think that's one of the important features that should make us more aggressive in treatment of arteriovenous malformation. As you can see this is a study that was published in 2009 in stroke, shows that if there is an intranidal aneurysm, the risk of rupture of the AVM almost doubles to close to 7%. And depending on the study that we read the location of the AVM deep seated AVM. And also if there is a stenosis of the venous drainage in some studies can be a risk factor for hemorrhage. So these are all individual factors in every AVM that has to be considered. At the same time, we also have to be cognizant of natural history. So this is the study that was done fused ago by Christian staff, showing that there are effectively some AVMS and unfortunately the easiest one, the superficial AVMS with no venous, no deep venous drainage that can have an extremely benign natural history. And as you can see here, 0.9% risk of rupture for those AVMS, with a superficial and a small size superficial drainage, Basically great one, the best ones for surgery the best one to achieve cure and excellent results. Also per this study have the best natural history. So, this is also another issue of debate, whether we should treat those grade one AVM because the natural history seems to be so benign, but this talk is not about those smaller, simpler AVMs. So, but I think these shows also this graph also shows that the more complex the AVM will get potentially the risk of rupture goes up as well. The um, on the surgical side, we have had significant improvement. If you look at the, this list and I would like to emphasize the embolization before the surgery. I am very much in favor of preoperative embolization. And I think that in the right hand, in the right setting, it's extremely helpful specifically for grade three AVMs and some of the grade four. I think that the pre-op Onyx embolization is very helpful. Now we have to be careful with embolization because unfortunately most of the complication of the AVM management happens during the pre-operative embolizations. So we have to make sure that the sessions of the embolization are carefully assessed. We do not want to inject more than five to eight CCs per session. And this is mainly because the patient will develop a significant edema after. And we have had that in our series and we have learned from it. Too much embolization and can lead to changing the hemodynamic of the AVM and cause hemorrhage. And also the issue of the obliteration of more than 30% of the AVM with whatever modality in each session could potentially a problem in terms of changing the hemodynamic and rupture, not necessarily just the material used, but also the amount of embolization. So the Onyx embolization, if it's done carefully is extremely important and that's what we use and I use regularly in my practice. Now in, in the recent years awake craniotomy, we have used in AVM surgery and I'm gonna show a couple of cases in a specific cases, awake craniotomy could be very helpful in order to monitor the language. ICG video angiography be published about it a couple of years ago and that is something that is helpful during the surgery to identify denied the nidus of the AVM and doing the surgery in the hybrids, this suite that you can see here, it's our hybrid suite, where we have the ziegel angiogram plane that, and it creates an very high quality angiogram view into the surgery. And this will help us to identify any potential residual AVM at the end of the surgery. I think this compared to using a CR in a normal or setting has an advantage of identifying those tiny remnant of the AVM that might not be visible in a normal operating room setting. However, it will be visible in the ziegel room. And this is the setup that we have that we use before the surgery, put the sheets in, and we can have the patient in any position, including prone. Although I would try to avoid the prone position in this room but any supine or lateral position with head rotation is possible. And depending we can use the radial artery also as a access for angiogram, if the patient is in the lateral position, depending on the location of the AVM, and this is very helpful. And we have published also about the value of the interoperative uni plan or by plan or rotational angiography you in your vascular surgery. So, going back to this list, using a non-stick bipolar, is it paramount interest? I think it's just almost impossible to do it without full complex AVMs and navigation and augmented reality. These are new tools. And finally the post-operative care in the ICU in terms of managing the patient's blood pressure and also managing the patient post embolization with edema. That's very important. So these are all important advances that we have had over the past few years that will make finally the outcome of our surgeries better. So going back to these patients that I showed at the beginning, this patient obviously we did the plasmapheresis and improve the platelet numbers. This is a grade three AVMS in, in AVM that has a significant size, no deep venous drainage. And it's very close the posterior aspect, as I mentioned, very close to the zone of Broca, but not invading the zone of Broca. So we did an embolization on this and it's a partial embolization. As you can see, there is some Onyx in the nidus of the AVM in the middle of the nidus here. However, it's definitely, this is the area of the nidus, but at the problem during this embolization was that the high flow of the AVM was a contributing factor to one of the draining vein of the AVM being occluded very quickly after Onyx embolization. And that will make the rest of the surgery more difficult in terms of embolization, because the fear was that if you include the second vein, then the AVM will be with no outflow. So that was a relatively suboptimal embolization and we have to take this patient for surgery that we can start and look at here. So this is a left large perianal craniotomy. This patient also had a, an aneurysm that you can see here, AECOM aneurysm that was clipped at the same time. And we start with section of this AVM by identifying the ACA feeders that, or going directly to the bottom of the nidus at the front of Bazell location. And here we start the resection of the AVM by staying just outside the nidus. So all we see here, this is the nidus, this is the plane between the Nidus and normal brain parenchyma. So as you can see here, this potentially could go very wrong if we end up inside the nidus of the AVM, but here we can see by staying just outside the nidus and separating these tiny, tiny feeders, all of these deep perforating feeders that are going from the brain parenchyma. These are parenchymal white matter feeders, and you can see can easily bleed as you can see here, but we control that one by one. This is obviously tedious surgery in terms of the length of the hours, Do you saw the falx surgery just on this slide before and separating now the feeders from the ACA from the midline, and this is the Alasta draining vein, and this is that we can see the AVM can come out completely. And we'll look at the surgical beds to make sure that there is no remanence left and we can move on. Now with the post-op pictures, this is a post-op picture, complete resection of this AVM. The patient remains completely intact, and I truly believe in this 27 year old woman, she's much better off without, without this AVM for the rest of her life. than just carrying the risk of rupture or any potential complication with that, that AVM for the rest of her life. And she has been now several years, post followup angiogram at three years negative, and she's completely normal back to her life. The same for this lady, she's a, she, this lady was actually a family member of my own secretary who had this AVM, incidental AVM that we did the surgery. I'm not going to show the video on this. It was the basically interhemispheric approach for this AVM. This Corpus colossal AVM might look scary, but when we expose the anatomy and when we identify the ACA feeders, then one of the ACA feeders in this patient was directly going into the nidus without any on passage vessels. And then it just turns out to become much more clearer and we're getting around it, this AVM was totally resected. As you can see the post-op imaging, this patient had a little bit of a cognitive issue. I would say for a few months after surgery, not cognitive in the sense that she needed to go to rehab really, but she really did not. She was not herself. She was saying that for a few months, but then back to normal life after that, without any functional discomfort or, or decline in her daily activity. This is a 22 year old patient who was diagnosed with two AVMS. As you can see, there was one in the left Sylvian fissure, right, sitting below the region of Broca. And the other one that is at the base of the frontal lobe here. So there's two distinct AVM, one at the base of the frontal lobe here and the other one on the lateral aspect and the Sylvian fissure. When we look at the, this patient did not have a hereditary telangiectasia. We did the genetic testing for it, and you can see here, these two distinct AVM separate. And if the patient had a serious, significant left supraorbital headache and 22 year olds, so we decided for treatment and in this patient, also, if you look at the topography of the location of the AVM, you can see this AVM. Also the second AVM, the smaller AVM is fed interestingly by the artery of Heubner from the left side, but we can mainly see it when we do the right injection, because there is no force injection of the left side. So the right injection shows very well. The artery of Heubner that contributing to the front of Bazell a smaller AVM. If you look at the topography of this AVM, you can see here that the, this AVM is just around the region of the ascending Sylvian Rams here. And for this, we decided to do this awake. So these patients, as you can see here, this is where this AVM was very close to the speech location. And therefore, we decided to do this surgery awake. and this is opening up the Sylvian fissure. Now here, we want to make sure that we identify the Sylvian branch that goes directly to the nidus. Well, we want to make sure that the major Sylvian branches and also the emphasized vessels, which is dissolved, the emphasized vessels here, you can see are completely preserved. So here we can see, this is the branch that goes to the nidus and the rest they are all normal Caelian fissure. Once we identify the two feeders that are going to the AVM directly, the rest would be just a matter of getting around it and dissect and separate. And at the same time, I have a neuropsychologist talking to the patient. I talked to the patient, ask questions constantly. And these patients tolerate this wake surgery very well. It's no different than removing a tumor is obviously vascular lesions. It could be a little bit more challenging, but it's not that difficult, that more difficult than just resecting a tumor and getting around the nidus and resecting the tumor. Now, one might ask the question of what is the value of a awake, and this is, you can see this, the tumor is coming out here. And one might ask the question, and then again, looking into the cavity, make sure that there is no residual nidus here. And this AVM is resected. Now at this point, I put the patient into sleep, LMA, but not being aware, awake enough to collaborate because for the removal of the other AVM that is on the front of basal region at the region of the artery of Heubner, I don't need this patient to be awake. So and then we remove that AVM while the patient was sedated and we can switch to the next slide. And this is a, at the end of the surgery, this patient had followup also angiogram at one year, complete resection of both nidus and a completely intact with no neurological deficit. She still had some headaches, super orbital, which I really felt that it's going to go away after the AVM, but it didn't totally go away. But the patient at least has no risk of bleeding in the rest of her life. She's a psychology student right now, and very happy with the outcome. Now, the issue of what do we do when we do the awake, in terms of what is the help of the awake, craniotomy, or a resection for AVM resection? What is the objective? Because the goal is to remove the AVM totally. Anyways, that's correct. So I think the, there is a difference between this and for tumor surgery in a sense that first of all, we monitor the region that we will be resecting the AVM. If at the beginning of the surgery, you clearly have a speech arrest and you're a 100% sure that by going into the white matter, that separate the nidus from the normal brain parenchyma, we will create a permanent neurological deficit, we can abort the surgery. We can just not resect the AVM. So that will give a, at least one information at the very beginning of the surgery. And the other thing is that this has not happened in my series, but it's also the possibility of revascularizing the nidus and in case we see that a complete resection will cause a permanent neurological deficit, you one can do a complete devascularization of the nidus, or at least to some extent. And then if we see that this will lead to a complete neurological decline in terms of speech, then one can stop the surgery at that point. And then that AVM is partially, devascularized not ideal, but then that can be treated with stereotactic radio surgery. Again, this has not happened in my series. I have only five or six patients with awake craniotomy. You can see another one. This is this patient that we just show with the post-op imaging showing no complications. This is another patient with a posterial temporal AVM, a grade three in an eloquent location. There is no deep venous drainage. As you can see here, there are superficial venous drainage, but it's a clear in eloquent location. And we did the speech mapping and you can see this patient had very, very intimate relation between the nidus of the AVM and the area of the speech activation. So I thought this patient really benefit from the awake craniotomy again, this is a grade three Spetzler-Martin AVM. And we did this patient awake, and maybe we should skip the video on this patient, but what I'm just going to show you is that during the surgery we were able to monitor, and this is not only the cortical mapping is also sub-cortical mapping. When we are getting around the nidus of the AVM, we will monitor in a sub-cortical location, with a bipolar simulation or monopolar simulation this speech and see if that will create any speech arrests. And this was also the patient who had preoperative embolization. This is before the surgery, both Wayne remained open. And I just going to show you a glimpse of this video, if you can go in not going to show the whole thing. So here we can see the AVM despite embolization remaining very still alive. And what I would like to hear, we have already monitored the cortical surface, and we made sure that we can get into this area without damaging the speech. And then the sub-cortical simulation will happen when we are further in the depth of the surgical cavity. And that will give us an idea of where we can be more aggressive with the tissue resection, if we don't want to be too close to the AVM. However, as a rule, we always want to be very, very close to the nidus. We don't want to resect any brain specifically in a awkward location. And you can see here is the location that I would do the subcortical stimulation. Now for this patient, the speech was not an issue, but with the patient became sort of tired at the middle of the surgery, specifically at the deeper part of the surgery, where we got into some bleeding that you will see. And at that point, I felt that the speech evaluation would be limited by the patient discomfort. So this is also the limitation of the surgery. You can see these direct feeders, a very large feeder. I decided to clip as opposed to just coagulating , this is one technique of doing it because when we see that these veins are, these arteries are very, very torturous and big, instead of just coagulating and cutting, I would prefer to put a clip on then coagulate and cut, and then I take the clip off at that point. But for some of those, it's just enough using the bipolar non-stick bipolar and getting the control of those feeders. You can see these can bleed profusely, as you can see here, but that can be managed with a careful coagulation of each of those feeders. And you can see here again, another technique with same technique, we putting a clip on the vessel, coagulating that perforator from brain parenchyma, and then taking the clip off. So at this point here, the patient was getting very tired so we put her into LMA and continued the rest of the surgery for the deeper part. But the surgery at least helped me in terms of being awake in a sense that I was able to make sure that the cortical and subcortical area that we were going around the AVM is not causing any speech arrest or deficit to these patients. And then we're getting around the rest of the nidus here. I think for the sake of time, we can just pass on this video because it's going to be, you can see there are lots of feeders getting to the AVM, and this is the post-op showing complete resection of the AVM. This is actually an interrupt angiogram, but also be completed at one year and a three years already because this patient's young. For any patient younger than 40 year old, I will repeat an angiogram at three years. And this patient had a neurological deficit. This patient had the syndrome of digital into OSI with a left right sided pain. And that was, I have to say pretty, debilitating for the patient for about a year or so. And we did not have any reason for it. Even an MRI did not show any stroke in the thalamus area, which would be probably the cause, but this patient had the terrible pain syndrome on the right side of the body, but that disappeared after two years, she was completely pain-free. But for the first year, she was miserable with the pain syndrome and this, this bizarre sensation that she would describe, although the sensation to tack to tackle examination was completely normal, but she would say, I have a very bizarre sensation on the right side, but that's fortunately got better at very long-term followup. And we published our experience and awake craniotomy. This was only, I think on four or five patients. So on the very specific patients and situation, these cortical and subcortical mapping would be helpful. Obviously, these are very limited number of patients. Now we get to this kind of AVM that are very large, and this is also a young patient. I think 30 something year old male with this massive brain AVM who has been seen in other institution. And they considered that as they said, this is unruptured, just leave it alone, it's very risky for surgery. And obviously you can see, this is a very large AVM and you can see here we did the speech mapping was not very reliable because everywhere in the brain was lighting up, but it seemed that the area just around the nidus of the AVM remains free of speech activity. Specifically, if you can see here or on the base off the temporal lobe here, you can see there is no activity of the functional MRI and the angiogram shows that this is a very complex AVM fed by branches of the MCA, PCA. And also, very importantly you can see here this is the branch of the PCA going to the very high flow AVM, massive Venus. Ectasia some venous stenosis. I felt that this AVM has a very high risk of rupture has internatal aneurysm and also branches of the middle meningeal. This is the picture of squamous branch of the middle meningeal giving a significant supply to this AVM. And you can imagine if this patient is operated without embolization, that could be very hazardous, even just born and dural opening. So we did three sessions of embolization for these patients by going first through the MCA, second PCA and third to the middle meningeal. And we achieved a decent result. As you can see at the end, we still have a very significant AVM part that is Peyton, but this is the price to pay, to get an embolization as efficient as possible without causing a rupture of the AVM prior to surgery or without causing a major neurological deficit, including fatality that can happen, if the preoperative embolization is not done carefully. And this is at the end of the third session of the embolization. I would not say that this is an extremely aggressive embolization, but he's not very conservative as well because all the branches were addressed. But again, careful to leave these patients intact before the surgical intervention. And you can see in this video that the, if you can play the video, this is the AVM. This is a posterior temporal craniotomy. So the bottom of the picture here, this is the base of the temporal lobe. This is the tentorium here where the arrow shows and we were getting around and I just have the AVM. This is not done awake. It's not needed based on the functional MRI also is very posterior and inferior. And the vein of flabby here is reversed. That means that the vein of Labbe is not draining the normal brain is all, all it does it just drain the AVM in an abnormal fashion. So that's why they are able to sacrifice the vein of Labbe at the end of the procedure. So here we were getting around the nidus and this is also several hours of surgery, as you can imagine. And it has to be done very carefully, really one artery by one artery. We can't rush into this because if it gets into the bleeding and brain swelling, it will be very difficult to reverse the, the surgery. So as you can see, beginning around the nidus, has almost two compartment. This is the compartment in the front that you're working here. This is a compartment in the front and there is also a compartment here in the back, which I'm gonna show you in a little bit. Once you're getting around, the nidus here, this is the compartment in the, and you can see these feeders that are very tedious to control. And some of them really take one minute or two minutes, and you can see here, this is the posterior part of the AVM. This is a vein, varise vein that I just temporary clip to see if I can get around, but you can see there's such a high flow that, that by just touching it, we get this significant bleeding from the venous outflow. So that means that I cannot get this vein at this stage of the surgery yet. So I have to control this bleeding and get around the nidus. As you can see, this is a large nidus. This is going all the way from here, all the way I'm showing you. It is, this is all where the nidus is. And we're getting around the nidus again, carefully separating this feeders that are going directly to the nidus as we stay also very close to the brain parenchyma. We do not want to remove or resect any brain. At the same time you don't want to be inside the AVM. There is a sweet spot, which is just at the intersection of the brain. And the AVM nidus like here and separation of those feeders. And you can see here by identifying the margins of the AVM and we are not done with the AVM surgery until the last feeder has being taken care of, which would be most likely around the venous drainage. There is always the last feeders that are the most important one that are sitting by the last venous drainage. That and that was the ventricle that we just showed. And by getting around the rest of tinnitus, and you can see everywhere this AVM is extremely vascularized by deep feeders, despite three sessions of embolization. But finally, we are able to get this. And this is what we get at the end. The ventricle was exposed where the patties coming out and this patient, this is the tentorium. As you can see here, this is the base. This is the area of the tentorium. And if you can go to the next slide, showing interoperative angiogram, showing complete resection of this AVM, this patient did not turn at her completely neurologically intact. And I'm true. I truly believe this patient is better off for the rest of her life, his life with no AVM, as opposed to conservative management of that AVM. And this is his post-operative MRI. Now Sylvian fissure. AVMs are very important because the complexity of this AVM is really the emphasized vessels of the MCA, going to the AVM and continuing into the normal brain parenchyma. Young patient as you can see, second seizure, 4.2 centimeter, upper color AVM, mainly fed by branches of the MCA that are on passage You can see these branches of the MCA here, the opercular branch of the MCA right there, and also the posterior parietal branch. They are going through the nidus and coming out. And there were three different venous drainage here in terms of the anatomy. This is the vein that goes into the senior parietal sinus, and then turns anterior posteriorly and goes into the vein of Labbe. There is this vein that is going through the basil vein of Rosenthal is a deep venous drainage going to this system of vein of galen. And also there is a smaller venous drainage superiorly toward the superior sagittal sinus. So this AVM, is we decided for treatment because of symptoms and patient's young age, and his Sylvian exposure. And he's a craniotomy basically Again you can read the history of this patients. We talked about the anatomy already. Now, the Sylvian fissure, again have four different categories are all medial and they are pure Sylvian. And this one is on the frontal side. So he's considered sort of like a medial type Sylvian fissure AVM, and you can see how robust the blood supply in the Sylvian fissures vessels are involved. And again, it's a little bit in terms of analogy, similar to the, you can see there was MCs going into the tinnitus here, and you can see there was a very nice borders just around the insula on this AVM. It does not involve the basal ganglia, and it is the medial type because it's on the frontal side. And we did also a functional MRI that shows that the speech activity is not on the right side, which is a good thing for, for us. In terms of analogy, I consider this AVMs very similar to Corpus callosum Avion, because once you expose the AVM in the Sylvian fissure, you can identify the anatomy and understand what is the Sylvian vessel that goes into the AVM. What is the unvisage vessels and try to separate those. We also did one session of embolization for this AVM. We, we went through the venous drainage already. You can see the basal vein of Rosenthal and the vein to the skin of parietal sinus. The most important exposure for this is that before starting the resection of these AVM after a doodle opening is to fully open the Sylvian fissure and identify Blair or the main MCA branches. So this is after the embolization. And again, as you can see, the Onyx is not a complete embolization, but it's good enough to have reduced the flow into the nidus and allow us to get around the nidus. The one other advantage of the eminent Onyx embolization is that it gives you a nice plain for resection where you see the Onyx, the plane for the dissection is very nice. It might be a little bit heavy because there is Onyx inside the nidus, but it will make it very favorable as far as I'm concerned for sure. The um, we will show the exposure through the turino craniotomy and Sylvian fissure opening. This is a 3D video. So just to look at the screen on the left side, this big vein, which is arterialized vein on the, would you just side there? This is the main Sylvian vein that is arterialized here. So that's the vein that needs to be preserved. We get around the nidus of the AVM, separate the nidus. At this point, the Sylvian fissure has been widely opened. We are dissecting the AVM on the frontal side. So frontal side is the left side and this vein this red vein is on the temporal side. We are getting around the nidus, open the Sylvian fissure, and here you can see the direct feeders from the MCA that are going into the nidus and identifying the normal border of the insula. These are the normal border of the insula here and small feeders, insular feeders going to the nidus are being disconnected. And obviously we have monitoring of motor evoked potential and some of the sensory of potential. This is one of the brain draining vein. This is the one that was going superiorly that almost got turned blue here. We get that. However, the draining vein that is deep and the draining vein that is toward the spin of parietal sinus, which you see here, this green vein remains intact for now, until we get the feeders from the lower part of the Sylvian fissure. Now the turnaround, and I just have the AVM and we go on the temporal side and I still have not identified the Sylvian fissure main vessels because they were hidden by the nidus of the AVM. So this is my main concern at this point, after surgery, as you can see, I'm very careful here, because we lose one of those vessels, the patient will be hemiplegic and here we were getting around the vein. This is the last draining vein. I think at some point, the, you can see here, that's the main, Sylvian vessels here and we separate, and you can see here, that's the main MCA vessels here. That's the main MCA branch. And the one on top would be the emphasized. So this is the main MCA branch. This one is not contributing to the nidus, but this vessel here, just above that here, this one, this is the one that is going from that emphasized vessels to the nidus. So the identification of this detail can only happen when you have fully exposed the Sylvian fissure and identify what is the vessel? Is it going to the nidus? And what is the vessel that is separate? And finally we get around this nidus and resect, the nidus of the AVM completely. And this is finally, you can see, this is the main MCA vessels. This is another branch again on passage vessel is here, and this is a branch from the an passage going, this is the emphasized vessel. This vessel is the an passage vessel. We will keep it preserved, but the vessel that is going from that to the nidus has been resected, has been coagulated and cut. And finally the nidus is as being disconnected from the last vein. So at some point, the deep draining vein was also coagulated. And this is where the deep draining vein is, the one that was going to the basal of Rosenthal And again, you can see, there are small feeders attached to those draining vein that or discontinued coagulated and separation of the nidus from the rest of the nidus and final disconnection from the main draining vein. And once this AVM is out, obviously we look can be followed at Sylvian fissure vessels. Make sure that there is no remanence of tinnitus anywhere. And this is the last training minute we can see is completely turned blue. Now, as you can see, that thing was completely red at the beginning, and this is a resection of the AVM showing the final status here. You can go to the next slide. And I think we slow, actually, I think the interoperative video video was also showing the post-operative angiogram showing complete resection. This patient remain completely neurologically intact with complete resection of his AVM, her AVM. Now I want to talk a little bit about the contralateral approach for these complex AVMs. So this is one case for instance, of a, a colossal AVM that is on the left side. Is a patient who had a ruptured MC aneurysm. You can see the MCA aneurysm here is a lenticle or straight aneurysm that was coiled and incidentally, we identified this AVM on the contralateral side. I don't think that aneurysm was a floor related aneurysm because the AVM was the, on the other side, but it's a possibility still. This patient, let's just skip this video. We're going to go to the post-operative picture. This patient was treated through a contralateral approach and I'm going to emphasize on that on the next case. So these AVMs sometimes our best approaches is the paper we recently published or best approach from the contralateral. So I've been through deep in the deep colossal or frontal or parietal region. It's much better to come from the contralateral side, because first of all, there was no direct retraction on the ipsilateral brain. The retraction on the contralateral brain is relatively minimal and the gravity will help with that. Plus we are not pulling on the draining vein of these AVMs that are most of the time coming up directly against the angle of view. So if you come from a, and you can see the angle of view specifically for the dissection of the lateral aspect of the AVM, which is here. Much better by coming from a contralateral exposure, as opposed to, if you come from the ipsilateral exposure. If you look at this picture on the left, you can see that you need to do significant amount of retraction on the ipsilateral brain to get to the lateral part. Obviously, if these AVMS are small, this is not a problem, but the AVM of this size, three cell 2.5, sonometer three sonometer or larger, like the example I'm going to show you here. We can go on this video. And this is a contralateral transfalcine approach where a deep parietal AVM in the patient, to very young patient, 21 year old intact. She had possible subarachnoid hemorrhage, but we were not able to really confirm that. You can see this AVM that is in the posterior aspect of the parietal lobe and very deep. And for this one, obviously again, we can discuss the options of observation. I felt that if we can help this 21 year old patients with embolization followed by surgery and cure her from this AVM, if that can be done safely, that would be the best option for her. You can see there are feeders from ACA, from PCA, and it was deeply venous drainage directly going into the basal vein of Rosenthal. So it is a true grade three AVM on the dominant side, in a young patient who had virtually no neurological deficit. I can see all the features from the posterial Croyle arteries. So this patient underwent two sessions of embolization. We did the partial embolization of feeders from ACA NPCA, and you can see we achieved a good amount of embolization. However, the nidus remains patent after both sessions of embolization, A good part of the nidus has been embolized, but the most difficult one, unfortunately, which is the deep part, the deep feeders from the PCA remain patent. And that's also another reason to do this from a control lateral view. You can see these deep feeders from the posterior coital arteries that are still patent from both sides. This AVM was getting feeders from bilateral PCAs and you can see that a tortious vessels that are on the bottom of the AVM nidus. However, the bulk of tinnitus has been nicely embolized. So if you're going from contralateral side to right side of the brain is here, and this is the left side, the patient's head is rotated about 45 degree toward the right to allow the right frontal or parietal lobe to fall with the gravity. Here we're cutting the falx cerebri and we are getting exposure of the contralateral brain. So the falx cerebri cuts below the superficial sinus and then goes all the way down to the inferior sagittal sinus. And the inferior central sinus can be a sacrifice with impunity. And it has to be sacrificed in this deep parietal AVM, because that will allow a full exposure of the interhemispheric fissure and Verde PCA, feeders are coming. And here we can see the ambulation materials, but most importantly, we'll see this feeders from the PCA that could not be embolized like this one. And the we'll take care of those little feeders or like this one here. These are important feeders that or first address before even getting into separation of the nidus. So at this point, the most difficult part of the surgery that is getting the deep PCA feeders from both right and left PCA have been taken care of. And now would be the matter of just getting around the nidus of the AVM, and nidus of the AVM now is very nicely demarcated by the Onyx materials and we are getting around and we separate the nidus from the normal brain parenchyma, as you can see here, a nice identification of the brain AVM and Onyx interface right there. And it's just a matter of getting around this nidus. The most difficult part has been already taken care of. Obviously the venous drainage is still there and we do not want to interrupt that venous drainage. Again, you can see here and other major feeders to the nidus right in the center of the, the video. There is a, there might be some on an passage vessels here. I can't remember if I clearly saw it a passage vessel, but you can see there are still direct feeders until we are not around the circumferential aspect of this AVM. The AVM was not going to be dead because there will be this little parenchymal feeders. And, and you can see here, this is the part that has been Onyx symbolized, and we will get around the nidus. And this is the important part of the axis You can see now I'm getting to the lateral aspect of the AVM. Look at this unobstructed view that you have to the lateral aspect of this relatively sizeable AVM without almost any retraction on either of the brain, whether the ipsilateral or contralateral. So you see, you can have a direct view on the contralateral brain. If you come from the effci lateral side, you will have a significant retraction on that brain, which is not ideal. And this way we can get around the lateral aspect, which is the more difficult aspects to reach, because it's further away from us. And now I'm separating those feeders from the contralateral brain. And you can see in a little bit that the salvia can be rolled now from right to left and from anterior to posterior. And we will be able to take the salvia out completely. Monitoring of SSEP and MVP is done This patient did not have any change in the monitoring. However after the surgery, the patient some foots drop of which I believe footdrop on the left side, which is basically because of, I think the sagging of the right or contralateral brain that because we came from the right side, I think the sagging of the brain called the foot drop because the foot rub improved at the followup already at six weeks. And you can see here this nidus is being now removed. Although we, you can, you will see the ipsilateral brain or the right side of the brain at the end of the resection with all the drain, all of the old normal rain that remain a patent and intact, but I believe the length of the surgery and the fact that the patient's brain was in the dependent position against gravity that caused the drop foot or foot drop. And here this are the last feeders around the nidus. There's nothing that we can really rush with these AVMs. They are very complex. They have tons of feeders and you can see very robust feeders from the parenchyma. And, you know, it's really an exercise of caution and patience also, because if you try to rush these things can only get worse, but, you know, by just being ready when you start this kind of case, you have to be ready and relax and prepared for a relatively long hours of surgery and keep your composure during the whole case, because this case will get more complicated when you get at the end of the case, not necessarily at the beginning and until the last feeder is not taken care of this AVM is still can bleed in a dramatic fashion. So these are the lessons. You can see you're almost at the end of the surgery here. And you can see how those deep parenchymal feeders that are on the poster inferior aspect of this nidus are so robust that are not dead yet until we take care of them. And here we are getting to the hopefully the last part of the resection. So it's a matter of circumferential resection. I try to avoid to create a tunnel. So we try to get around the nidus in a homogeneous fashion. So advanced a couple of centimeter on each direction, and then just continue on the frontal side and then the posterior side and then go deep in a regular fashion, as opposed to creating a long tunnel and narrow tunnel and leading the rest of it still connected. And these are, I believe that this is the final venous drainage going into the venus vein of galen. And you can see there is some Onyx actually in the vein of galen connection, but nothing significant. And again, we cut the vein, but you can see here, there is still a feeders to the nidus right below that draining vein that has been taken care of. So the clip is under vain, but you can see here that there is a, still a draining vein above the, eh, there is still a feeder is just below the draining vein. And this is the final view resection of this nidus. And I cut the Onyx material around. You can see this is the ipsilateral brain completely preserved with a nice looking brain veins, preserve and angiography confirming complete resection. But this patient, as I said, had a footdrop which improved at six weeks. Let's move on to the next patients. I got to show one more video. If you can skip and go to the next patients, Let's skip, I'm going to skip this one. This is pretty similar. And, we will go with, I think there were two more videos that I will like to share with you. These are important. I'm going to go quickly through this. This is a hypocanpic AVM in also again, a 22 year old woman who presents with seizure and decided to treat this by embolization. You can see this is the actual coital artery directly going to the nidus. And also there is feeders from the PCA here. So we decided to embolize this with Onyx. The choroid can not be embolized because of it's important cisternal segments, but the PCA was embolized. And this is an exposure. Again, look at only in the left sided picture to the Sylvian fissure. So is a transsylvian trans-limen insula exposure of this nidus and mainly, the most important thing here is the identification of the anterior choroidal artery. And once the anterior choroidal is identified in the carotid optic cistern, we will follow that intercurose fissure until we get to the plexus segment. You can see here, this is the anterior choroidal artery until we get to the plexus segment of the anterior choroidal artery. And that is the location where we can interrupt this artery not before because otherwise they will be an injury to the internal capsule. This is here I'm resecting some part of the anchors to get access to the anterior part of this hypocanpic AVM. And once we have that, then we have the anterior full access to the nidus, which is deep and is hidden from us by the hypercapnic basically tissues. Now here, this is the limen insulae that I'm showing with the bipolar, but with the navigation that confirms that the limen insulae does not give us posterior enough to the nidus. So I added a transcortical trans T2 exposure to the choroidal fissure to get to the posterior exposure of the AVM. Here we are inside the choroidal fissure and we get to the posterior aspect of tinnitus. And so this way we have a control of the anterior part by having the anterior choroidal artery plexus segment and the posterior part into the choroidal fissure. And then it's a matter of just getting around the nidus and separating in from the choroidal fissure and the rest of the brain parenchyma. And here we can see, this is the distal part of the intra cranial artery. And I put the permanent clip on that. This stall partial basically Plex segment, the rest would be to get just around the nidus. We can skip the rest of the video, please. And if you can go to the, this is the video is published to, you can look for it and it's showing a complete resection of this nidus, the preservation of the anterior choroidal artery and you can see the clip and embolization material and the vein of one of the venous drainage that was the basil Rosenthal and all is completely thrombosed now because it was only draining the nidus of the AVM and now it's trombone, and this patients remained intact after the surgery. So occipital AVMs are also could be complicated because of the risk of hemianopia. These patients have as operated through a suboccipital interhemispheric approach. And this is probably what I published when I was in Toronto as a fellow and the largest series of occipital AVM. And there is a significant risk of hemianopia with surgery for occipital AVM. So the decision of treatment of unruptured occipital AVM has to be carefully weighed against the risk of hemianopia because there was 17% risk of hemianopia in that series. And as you can see this patient of mine that we operated, fortunately, she did not have any neurological deficit. She had actually quite an opia after surgery, but that was not functionally important, but the AVM is eradicated. And finally, this, this is the last patient I'm going to show. It's a AVM in the superior cerebellar peduncle unruptured in a patient who presented with the tinnitus. And this puts your first AVM has a higher risk of rupture, specifically, if they have deep venous drainage, diff this one has a deep, does not have a deep venous journey. This one drains on the surface of the cerebellum with this draining vein that you can see. And we just published this approach to the superior cerebellar peduncle. We have a few of these patients that we have approached to with extreme lateral super cerebellar, trans superior cerebellar peduncle. And you can, that will get you there just behind the fifth nerve here and to the superior cerebellar peduncle as this pictures shows to the AVM nidus. And you can see on this video that the patient is in the lateral position. You can see the superior, This is a transfer sinus here. And the sequent sinus here is a retro seek mine exposure, but he's extreme lateral in a sense that you are very high and coming from the very lateral aspect. Here, you can see the tentorium. This is the tentorium here, and we get to the top of the cerebellum and the posterior aspect of tinnitus with the navigation during the surgery to be confirmed. And here view they are where the nidus of the AVM is, this is the backbone of the tectum or a confluence of arteries and veins, there's lots of traffic with superior cerebellar artery branches that some of them are on passage So it's here is a matter of, and also use an ICG to identify which one is emphasized, which one is going to the nidus. This is the more difficult part of this procedure to identify the real culprit and leave the normal vessels alone. So here I identified this as to be the one going directly to the nidus while the other one is a normal. And once this feeder, which was the only feeder to the nidus is identified your insight distributes or developed with Danco here. And just getting around this nidus and you can see, is complete through attractor, less with the gravity, the cerebellum falls, and we get around this nidus and the resect the nidus. The posterial fossa AVMs, specifically the steep one could be torturous because if we get into a bleeding, the window is very narrow. As you can see here, in one of these cases, I had a significant inter operative bleeding that caused the interventricular hemorrhage after surgery. The patient needed to have a drain and a shunt, but ultimately she did okay with some residual tremor and had bobbing after surgery. That was a complication of the surgery, but not this particular patient. This particular patient's symptoms were tinnitus we cut around this nidus, as we removed the nidus, completely confirmed by a post-operative angiography. However, I was disappointed by the fact that the patient's tinnitus didn't improve. I really thought that the patient's tinnitus is related to this AVM, but she did not have a significant difference. Maybe tiny, little bit better, but not a significant difference. This is after the resection, you can see, I will look into the surgical cavity, make sure that there is no residual nidus, and this is the tentorium up at 12 o'clock. And this is the final view of the resection. Can it be advanced to slide please? And this is the postop angiogram preservation of the superficial surface superior cerebellar artery, and absence of any, or So I am, when I look at our experience over the past, this is a, this series is up to last to June, 2020, and a vast majority of these AVMs 137 AVM surgeries, almost half are ruptured half are unruptured. And you can see, we have had a significant number of grade three and grade four. Obviously, most of the grade four that you can see here are ruptured. And the grade five, the two that I operated on that was in its very desperate situation and they're both, they were both ruptured but vast majority of the grade three that you see here are unruptured AVM. This is really the topic of, of the talk today. And you can read by yourself the neurological deficit. So we have had obviously new neurological deficit, mainly in the ruptured group, but also the unruptured group. You can see, we have had three hemianopia, three quarter nopia, two hemisensory deficit, three hemiparesis, two out of the three hemiparesis that we have had was because of this swelling after the Onyx embolization. And that will settle after the some time, those patients can go completely back to normal. So all these new neurological deficit that you can see in the unruptured group, the vast majority of them completely improved. Some of them are still there. The quadranopia, the patient with the hemisensory deficit and delirium and who see that I mentioned, but overall, if you look at that, the only mortality we have had in this series is in the ruptured patient grade five AVM with multiple, I think, five or six hemorrhage that I had to operate on. And he ended up having a multiorgan failure. So, but overall, you can see the results specifically for unruptured AVM could be very good. And in terms of residual AVM, 4% residual AVM in this series. However it, since we are using the angio suite for AVM surgery with high quality in droplet angiogram, there are risk of missing a residual AVM has gone down to only 1%. And I think we will not leave the operating room until we have a 100% confidence that the AVM is completely obliterated. Obviously in a very dramatic situation, if you feel that that's it and they can't do anything more besides hurting the patient, we would stop. But usually, we would like to have a complete obliteration of the AVM confirmed with the final inter-operate in geography. So I think that we can not give a uniform paradigm to unruptured brain AVMs. Brain AVMs are, is a dynamic disease and is really individualized. And I think depending on what the patient's wishes are and the presentation and the anatomy and the characteristic of the AVM. Each AVM should be treated and considered for treatment in an individual fashion. And I think we should, grade three Avm should strongly be considered for treatment because based on what I showed, we can achieve excellent results Thank you very much for your attention.

- Excellent work, really appreciate feeling your pearls of technique, Amir. I wanted to ask you a question, "Do you believe that embolization can potentially increase difficulty of the operation by increasing the numbers or strength of the deep white matter feeders, as you know, those are not usually embolizable. You just, embolize the ones that are very accessible in surgery anyways, do you have any comments there?"

- I think the comment to your question is yes and no because yes, because embolization cannot address those feeders. So some of those feeders might actually become more robust after embolization of big arterial feeders because the AVM recruit very quickly. And this also depends with each individual's AVM, some AVM we could dramatically. That's correct. That's yes to your question. But the note to your question would be when the embolization actually is as good as it really fills the nidus and in a retrograde fashion, sometimes it fills into those parenchymal feeders. So I have seen that also happening. So both scenario can happen, and this is something that you can really not predict until you are in surgery. So I have seen both that in some of the AVM, I'm ready for a very big fight with that particular AVM and then I realize that some of those deep parenchymal feeders have been already taken care of by the nidus, by the Onyx in a retrograde fashion. So basically embolize through the MCA and the Onyx went through the nidus and backwards through those deep feeders. That can happen. But sometimes also I go in, and those parenchymal feeders, are so much more robust than what I would expect. This is just because the AVM has recruited. So I think this is in a situation that we can't predict until we are at surgery and we have to be ready for those robust white matter feeders, as you mentioned.

- What are your thoughts about great success to Europeans have had with transvenous cure

- We have not done that in our group. We always talk about it. I know that Jack Moree is really almost one of the pioneer and very in favor of doing that. The problem with that transcendence occlusion of the AVM is that you get one shot. Is really one shot, whether you succeed or the case is over. So I think it's, it can work. The idea of occluding an AVM to the vein is, and I think is a very interesting and elegant idea. And this has been going on now for many years. It's not just recently. I mean, Jack Moree has talked about it. I think I invited him to about eight, seven years ago, and he was already doing that for many years. The, the problem and that's also one of the reason that it has not become so popular is because it's not as easy. And it's also that if you do not succeed, then you are left with no options. You will be left with an AVM that has occlusion of the outflow with whether you have to somehow manage to occlude also the arterial feeders, you still will be left with an non occluded AVM with no outflow, which most likely will lead to hemorrhage, or you have to emergently do a surgery. It's just not an, I think it's an idea that is very interesting. I don't think it has become popular enough to be the main say where treatment at the AVM. Now, can it become in the near future? Yes. I think that's one of the venue that people are thinking about, but has not become as, as common in our practice. What about you? Have you done that in your institution?

- No, we have not. You know, some of the results are very impressive when you go to the lectures, but again, I don't know what are the ramifications when the case doesn't go well? So it's very difficult to know. It definitely provides an amazing potential in terms of curing these lesions. So I think I'm still waiting to hear more people reproducing this data rather than the ones that founded the idea.

- That's right. That's also the other thing is the reproducibility of the data technique. If only one person can do it or only two or three person and they claim to have good results, then that cannot be something that is generalizable to the neurosurgical community, or even just all centers of excellence. You know, one of the thing I always say about like a pipeline embolization of the aneurysm is it's such a reproducible technique that that's the reason for the success of their flow diverter because it's extremely reproducible It's an excellent and challenging technique. I'm not underestimating the complexity of it, but it's reproducible. Is something that anyone can do once they are well-trained, I'm not sure if transvenous embolization of AVM is as such.

- Yeah, now, that is well said. Well, you know, I think I really enjoyed the videos. You have showed your courage in removing these AVMs. Obviously removing in large AVMS requires more than just technical expertise and technical efficiency, it requires certain courage. Obviously you have to have some tolerance for the risk, no matter how good you are, and really have to be able to be agile in the operating room in the form of efficiency I just mentioned to go manage bleeding, being able to orient yourself and being able to be patient to work in, in the face of adversity. So I really want to thank you. I've really enjoyed it and enjoyed your friendship and the great work you're doing, Amir. I've been following your career very closely and look forward to hearing from you in the near future.

- Thank you very much, Aaron. And again, thank you very much for, for including me in your program. And this is a tremendous tool for, for trainings, for residents, for attending. In fact everyone should look at these sessions and learn from it because I think that's the way we can improve the field and it can improve the microsurgery and thank you again for doing it.

- Thank you for the kind words. And again, we wish everyone a happy new year, a much better year than 2020 full of health, happiness and peace. Thank you.

- Hopefully, thank you very much. Thanks for having me.

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