Personal Reflections in AVM Surgery

Aaron Cohen-Gadol

September 22, 2020


- Hello, ladies and gentlemen, and thank you for joining us for another session of the Neurovascular Surgery series from the Congress of Neurological Surgeons. My name is Aaron Cohen from the Neurosurgical Atlas. I'm honored to be joined by Dr. Dan Barrow from Emory University. Our session today, we'll discuss nuance of resection or diminished malformations. One of my very serious conflict of interest is that I love AVM surgery. It's one of my most, if not the most operation that I enjoy and also, I wanna say that another conflict of interest is that I'm relatively not as interested in embolization of these lesions preoperatively because I think often the surgeon can reach them very early on those pedicles that are also readily embolizable. So, with that in mind, we'll go ahead and start the talk. Dan, again, thank you for joining us. I'll be very interested in your expert comments as we go along. So, for the next slide, I'd like to mention the conflict of interest, none of which really significantly affect the contents of this presentation. AVMs are most likely the most challenging surgery that we do. Any minor error can significantly affect the outcome of the surgery and the patient, and therefore planning, carefully managing every stage of the operation and every portion of the AVM is extremely important. The surgeon has to be very quick in reacting and reacting effectively. So one cannot just have a knee jerk reaction to bleeding as any bad response can lead to another chain reaction of issues and lead to catastrophe and significant intracerebral hemorrhages and compromise of important en passage vessels. So as others have referred to AVM surgery, it's like a war. You need fair amount of intelligence, you need to be very organized and you need to plan effectively how to manage complications each operatively. Aneurysm surgery is more like choreographically well-planned ballet, AVM surgery is a war and it requires a completely different set of mentality. Surgery is really evolving as you go through and there is no single plan that survives through the entire operation. The agenda has to be very flexible, the surgeon has to evaluate every stage of the operation and react accordingly. So a pre-planned agenda and forcing the AVM to conform to this surgeon's agenda is a mistake and one has to be very flexible and not dogmatic in terms of handling the lesion and the interpretive events. There is no question, AVM surgery has made me a better surgeon. It is not only an extremely technically difficult surgery, but also tests the reaction time and how fast and efficient the surgeon is. So you can be technically great, but if you're not efficient, and if you're not able to maneuver through the lesion and manage catastrophe extremely quickly, and this is not one time, usually there are multiple catastrophic events in a large AVMs along the way, that these lesion test many aspects of a surgeon, rather than just their technical skills. It also requires a good temperament. The surgeon has to remain composed and remember that this is part of the AVM surgery and you have to react accordingly and you cannot lose your composure and have an emotional response because that only would affect your emotional intelligence or operative intelligence for these lesions. And I have learned something that there are certain number of cases AVMs you have to do to become a master of it. After that, really is not like the maximum number you do, you're gonna be really great. I think many surgeons focus, "Okay, this is how many I've done, so I'm better than any other people who have done less." I think I've seen many people who do this thousands of cases but they repeat the same mistake, and therefore it doesn't matter how many times they do AVM surgery. I think there is at least 150 AVMs, 100 AVMs that are minimum requirement to become a master surgeon in these lesions if the surgeon is technically gifted to do these lesions. After that, it's gonna be really fine tuning those to become more efficient. Dan, would you mind comment, please, on these ideas that are relatively personal reflections? I wanna know what you think about that.

- I largely agree with almost everything you said. I do think that AVMs as a body of pathology represent the most challenging cases we manage. Obviously, there are very straightforward AVMs, but as a pathological entity, I think they represent the most challenging things we do and I do believe that it requires a combination of patients, excellent clinical decision-making, and I think one of the points about AVM surgery, unlike many of the other things that we do, is that the most difficult part of the operation is at the end of the operation, when you oftentimes are exhausted mentally and emotionally, when you're dealing with the little diaphanous vessels that are feeding the malformation from deep in the white matter. At that point, you have to be at your very best and it's usually towards the end of the operation. Many other procedures we do, the difficult challenging part happens relatively soon after the procedure. So I think your comments are right on track. I also agree to some extent with your comment on the use of preoperative embolization. I do use preoperative embolization, I would say fairly liberally, but only in cases where I clearly believe it's going to make the surgical procedure less risky, easier, tame an AVM that otherwise might be difficult to embolize an AVM just as a preoperative routine, I think is an error because there are risks of immobilization and I think it's extremely important to have a discussion with your interventional neuroradiologist, whether he or she is a radiologist, neurologist, neurosurgeon to understand what the goals of the embolization are. To embolize vessels that are on the surface of the brain exposes a patient to a risk that is completely unnecessary. It's only those vessels that we might encounter late in the procedure that can be embolized and will actually make the operation safer.

- I completely agree. Other metaphors that I've previously mentioned is that AVMs are pathologies of arteries versus cavernous malformation or pathologies or veins, are completely different. In addition, AVM surgery is a marathon while tumor surgery or aneurysm surgery, for example, is a sprint. So therefore, you have to be like an athlete, plan your energy level, and you can't just expand it on the exposure, initial stages of the operation. The other thing that I often mentioned in my operating room is AVM surgery is like managing the plane. You have an ascending phase of the plane that can be a little bit bumpy, you reach a cruising altitude where things can be going well, then you get into significant turbulence and things look really bad, and then you have to land the plane. And landing the plane can be very difficult. What I say sometimes to the fellows is that there isn't a phenomena as too dry of a field when you're finishing the last stages of the operation. You can't really be so focused on the operative field being dry, you have to have tolerance for what we call controllable bleeding versus uncontrollable bleeding. And that is something extremely subtle and requires experience, that if you're so fixated on everything to be dry, the operation can be extremely long. So there is a period of time at the end of the surgery where you have to have some tolerance for controllable bleeding to get the AVM out and the only way to achieve hemostasis at that stage is by disconnecting the vein and taking the AVM out, obviously, at the right time. I think all of those are extremely important judgment calls that AVM surgery is so part of. So this is another interesting thing about AVM surgery, just to make some interesting metaphors, that intrigues people and that's the AVM surgery is the only operation that starts as the most beautiful lesion in nature and beautiful view of an operation with these beautiful vessels, colorful and often, surgery closes as being the ugliest scene in surgery because there's always bleeding, and the brain looks a little bit confused around the edges, and I think that's really the only one can do that, and the AVM is the oddity of nature, and they're so beautiful and at the same time deceiving, and as the engagement almost every second can reach an intracranial disaster at any time during the operation. And, again, just very intriguing lesion, we still don't know much about them. What is their pathogenesis? As we know, AVMs, they're generally congenital lesions, they can develop dynamically throughout the life of a patient. And in addition, pediatric AVMs are intriguing because you can remove the AVM and geographically, it looks perfect and then three days later, you have residual AVM. So it shows that AVMs are not only dynamic and evolve as the brain matures, and so AVMs are not really static in any way. And especially for pediatric AVMs, you have to be very careful that when you remove it, there's definitely areas that you did not see angiographically before the surgery, and these areas mature later. And that understanding of maturation of AVM is critical. And as you can see, just beautiful view of an AVM, it's enjoyable to watch. These are the number of cases I have done, and the spread of them. As you can see, again, it's not all about the numbers, as long as you've done about 100, 150 of them and have really used every operation and every video that you have recorded as a method to do better next time. I watch every one of my AVM surgery videos and go back and forth, sometimes watch every video five or six times and see, what were the areas that the surgery was relatively inefficient? And why the five centimeter AVM took five hours to take. I think initially in my career, the AVM resection four or five centimeter AVM took about eight hours, then we came to six hours, then we came to five hours, then we came down to four hours, and now we can do it in under 2 1/2, three hours. So I think just like anything else, it's watching yourself, because during surgery, the intense emotional response of being within surgery clouds your judgment in terms of improving your learning experience. So there are different grading systems, and some people like using them. I'm personally not very much in favor of them because what is too important for me is the diffusivity of the nidus, and vicinity of the nidus core to the eloquent cortex, and obviously the depth of the lesion. In fact, the deep venous drainage is very advantageous, because actually, the veins are way out of your way as you're dissecting AVM during the later stages of the operation. And I do believe that resecting AVMs early on right after hemorrhage is very effective, and I'm gonna go ahead and review that with you in a moment. Dan, would you comment so far about your thoughts, please?

- Yeah, I agree with your comment on the grading systems. I think experienced surgeons can look at an AVM and in their mind determine what the risk of that is. Grading systems are wonderful for communication among physicians, for communication in publications and I really tip my hat to those individuals that have given the thought to developing the grading systems we use. But you're absolutely right, there are many, many factors of the patient, of the AVM and even of the of the surgeon that actually determine what the risk of an individual AVM is. Just as an aside, Robert Spetzler is one of my dearest friends in the world and at a joint meeting of our two travel clubs many many years ago, as somewhat of a spoof, I gave a talk on my new grading system, which I call the Barrow-Eastwood Grading System that I developed with Clint Eastwood and divided AVMs into three types, the good, the bad and the ugly. And although it was a tongue in cheek presentation, there's a lot of truth to that. There really are three types of AVMS, there are the good ones that we can remove with very, very little risk. There are bad ones, and then there are the ugly ones that we just don't have good treatments for. So I agree with your comments.

- Thank you. And general consideration, obviously, choosing AVM we operate on is so critical, just like any other vascular lesion. In this profession, it's all about indications that can really determine the outcome of the patient. And we estimate that the risk of hemorrhage is two to 4%, obviously, there are certain characteristics of lesion like recent intracranial hemorrhage aneurysm, venous stasis or stenosis, but again, the risk of hemorrhage most likely is very dynamic and we don't really know that risk very well. I don't believe embolization as a form of palliative therapy or as the only form of therapy. I know there's fair amount of discussion, especially in Europe about transvenous embolization and cure of these lesions, but there are occasional cases where severe headaches or significant steal phenomenon can benefit from selective embolization as the only mode of therapy, but those cases are very rare. I do think radiosurgery is a reasonable option for downgrading AVMs that are inoperable and that's been recently more and more used, if it's used effectively and not just liberally in terms of an AVM that can be very close to the motor cortex and then you can do radio surgery to downgrade the AVM, make those vessels to become very thick and very responding to the bipolar forceps, the deep white matter feeders. And it's no doubt that multimodality treatment is the way to go, just like anything else these days. And also ARUBA, It's something that has created fair amount of controversy. I do not believe that was a study that gave us good information, instead, it created much controversy and confusion for neurologist and referring doctors. So I do believe that ARUBA is something should not be trusted In terms of managing grade one and grade two AVMs. We're not gonna go through a lot of details about ARUBA just because to keep the talk simple, but that's a completely separate talk in terms of the misleading selection bias and other treatment abnormalities that were present that are much better performed in the United States as compared to the people who underwent the ARUBA protocol. So let's talk about the approaches. Obviously, these lesions have to be very well exposed. There's nothing minimally invasive about exposing an AVM in surgery because you wanna be able to have good control of feeding arteries and at the same time be able to manage complications and catastrophes when needed. I've always said the mouthswitch is the surgeon's best friend, the microscope has to be become part of your face, your hands have to be free. And this is most important, it cannot be even important anywhere else than in AVM surgery because as deep white matter feeders pop, you have to quickly respond. If you wanna hand your instruments, refocus the microscope with the handles, get instruments back, you could be losing really precious time. And therefore one surgery absolutely mandates the use of a mouthswitch and it really improves significantly the agility and response time of the surgeon and that's the mouthswitch, and please master it. I know both Dr. Burrow and I are extremely fan of this. It's awkward to use, it requires a learning curve but when you use it, you'll see that you will never do surgery without it. So please consider that. I know there are less than 5% of neurosurgeons currently using the mouthswitch, which is a surprise. Bipolar forceps are important for this surgery and using the forceps that are very nonstick and irrigating are critical, especially being able to see around the the leg of the forceps or the tines of the forceps are critical. Just remember that the heat sink depends on the width of the tips. So the wider the tips, the better heat sink, and the less chance of sticking. And somebody obviously has to also irrigate for you in a gradual manner so it's not irrigating too much or too little, and also often what I do is that I have two by four forceps, wide-tipped, 1.5 to two millimeters, and then one of them is in ice water while I'm using the other one and then they switch it for me. So I alternate between the two and I always keep the tips extremely cool, and that really provides a significant heat sink to prevent sticking and avulsion of the white matter feeders. Timing of the operation. Often, it's a very big dogma in AVM surgery that you should do it in a delayed fashion. I think early intervention is very much favorable for the patient, in my experience. If the AVM has caused significant edema and the patient neurologically is not doing well, there is significant mass effect, you definitely don't wanna operate on a very angry brain. We all know that, but there's a very small portion of the AVM when they hemorrhage, they cause these disasters. Most AVMs when they hemorrhage are compressive, and even if there's minimal mass effect or midline shift, I do remove hemorrhagic AVMs within 24 hours for many reasons. First of all, the patient will undergo one surgery and doesn't have to go under removal of the hematoma and then recover and undergo another surgery to recover from the resection. So it's a one single hit rather than a double hit. Number two is these hematomas, often patients tolerate very well, the symptoms are so little than another hematoma from another lesion, and if you remove it, they recover better and they go to rehabilitation much faster. And the acute hemorrhage really provides such easy resection planes. The blood is very gelatinous, versus later where the chronic gliosis can be challenging. So I do say that this is against the standard treatment these days that I do operate on AVMs that are hemorrhagic in a very acute stage and the outcomes have been very, very excellent. Obviously, there is no randomized trial but everything I've seen in terms of improvement of the patients and neurological status have been effective. I think the dogma for resecting AVMs that hemorrhage in a delayed fashion most likely refers to the difficulty of these lesions and the surgeon's discomfort of handing a lesion during the hemorrhagic phase of their malformation, and not necessarily the benefit to the patient. Dan, would you please comment briefly about these statements?

- Yeah, I agree with you. I do think there has been this dogma that you don't operate on an AVM in the acute phase. And I certainly don't if the hemorrhage is not life-threatening or causing significant deficits. I do delay surgery a bit but if a patient needs to go to the operating room for evacuation of the hematoma, I make the decision about whether to remove the AVM at the same time based on the complexity of that AVM. And oftentimes, if these are small, straightforward AVMs, even if the operation is an emergency, I'll do an intraoperative angiogram during the hematoma evacuation, identify the angioarchitecture of the AVM and remove it at the same time and not expose the patient to the risk of re-hemorrhage while you're waiting, as well as the risk of a second operation. I think what happens in many institutions is that the cold pool includes people of different specialties and subspecialties and it is the case that somebody may be taking a patient to the operating room at two o'clock in the morning for an emergency life-saving operation and it's perfectly appropriate if you're not an AVM surgeon or if you haven't done many, to save the patient's life by removing the hematoma and not addressing the AVM. So like most things in our field, it's an individualized decision-making that includes a lot of factors, many of which I've just mentioned.

- I agree with you. I think I have lower threshold than you others about removing AVM nidus at the hemorrhage. I routinely do them within 24 hours and very much not infrequently I have removed AVMs just based on a CTA. I think these AVMs really read the book very well and based on their location and their classification that you can really have a pretty good idea where the feeding artery is coming from, where are the draining veins, and be able to deal with them very effectively. They're really beautiful lesions if handled well and when they throw a tantrum. This is a classic case, a 16-year-old kid came in with a hemorrhage, hemiplegic on the right side and facing very small AVM and we removed this AVM within three hours that he arrived to the emergency room and next day his strength was 4/5, speech has significantly improved and really, this is obviously a dramatic case of that, but I think removing the AVMs that are hemorrhaging in the acute phase has significant associated advantages. What are the steps in AVM resection? these are very basic three-dimensional understanding of the malformation is so critical. Just like anything else, there's surgical intuition and intelligence about being able to really envision the malformation in 3D. And every time you're moving around, you just have this very beautiful map, just like going to war or a battle, you have so much great intelligence and know where you are and where's your enemy and you can accommodate, change your agenda, move efficiently, those are critical parts of this surgery. You have to be prepared, you have to be well-rested, you have to be like an athlete who is very, very much in shape and in the zone, in flow, to manage these lesions. These are not lesions who you have to be distracted or necessarily take your time. I think time is of extreme essence for these lesions. So timing is everything. You have to be able to manage the feeding arteries, protect en passage vessels, you have to do strategic the circumdissection around the nidus. Be careful not to coagulate the vein that's wrapping around the nidus wall. That's one of the common mistakes that I've seen younger neurosurgeons make, is they coagulate some of the draining vein or contributories to the draining vein during this circumdissection. And again, you have to have some tolerance for bleeding. You just can't have a dry of an operative field. Too dry of an operative field usually demonstrates that the surgeon is uncomfortable and is trying to be too perfect, whereas the enemy of good is perfect, especially in AVM surgery. You have to protect the dominant vein. Obviously, that's very basic. And you have to be very efficient in these lesions to get good them out. You have to understand the malformation. there are many things that can help you there. Embolization material can be a stereotactic guidance point along the malformation, resection, obviously, location close to the ventricle. The MRI can provide information about where the AVM is in relationship to eloquent cortex, to the ventricles, so that's why we do an MRI in general for understanding these lesions. Obviously, angiogram is the roadmap for the feeding arteries and draining veins, especially en passage vessels. And then obviously, the imaging modalities we often use is the MRI, CT and angiogram. I use the CT angiogram into operatively via their StealthStation to be able to adjust sort of my workflow and the depth of the section. However, most often I just stay close to the nidus, and I think that's something as I learn more and more, I stay closer and closer to the nidus. I know or I've seen surgeons that do a lobectomy for a small AVM, which I think is unacceptable. I think these days you can really stay very close to the malformation on nidus. And something else that I've learned with experience and I want you to comment on is that the AVM nidus can be quite smaller than what you think on an angiogram or an MRI. And the only way to truly know what a nidus is intraoperatively by letting the malformation guide you around it. If you get a little bit bleeding, step away a little bit. If you're very dry, get close, and just dynamically change the distance to the malformation until you're completely around it. What are your thoughts there, Dan?

- I think the current imaging modalities give us a pretty good and accurate indication of what the nidus is but there's no question, there's nothing like looking at it under an operating microscope with things magnified and brightly illuminated. By far, the most common cause of intraoperative hemorrhage is dissecting into the nidus, in my opinion, and that is one of those intraoperative misadventures that experience helps you manage. Anybody who says they never had bleeding during AVM surgery is either lying or they're not doing AVM surgery. So staying on the edge of the nidus is a critical step in AVM surgery to do it efficiently, but it is very easy in that attempt to stay out of the brain to wander into the nidus and you gotta recognize it, you gotta stop the bleeding and there are a number of ways of doing that, which go beyond the scope of this discussion. But I agree with you, I think intraoperatively, you have the best view of what the border is between the nidus of the AVM and the generally apparent glottic playing around the malformation, which sometimes isn't as apparent as it is in other cases.

- I agree. And one of the things that's very important is that the AVM is not a sphere, we always think it's a cube or a sphere. There is actually what I have learned is network of white matter feeders around the periphery. And you can get into these networks and feel like you're in a nidus but actually, you're just facing deep white matter feeders on their own. So that's something that requires significant intraoperative judgment. What is a nidus? What's a small network of deep white matter feeders? But these are very intriguing lesions, we know so little about them and therefore their resection is so often enigmatic, but one cannot be too worried or nervous as often surgeons get and say, "Okay, we're in a nidus, let's go away and take another centimeter of the brain." I think you have to have tolerance for bleeding. I mean, I've had people come and watch me do AVM surgery and after the surgery-is-over day, you feel there's some sweat on their foreheads rather than mine and they feel like they saw some bleeding they've never seen before and I always tell them that listen, there's difference between controllable and uncontrollable bleeding. And AVM surgery is not about you being a surgeon scared of blood. Blood has to be, and bleeding has to be just part of your agenda, and without it, you're not doing surgery. But again, you have to be very careful about that. You don't wanna have a field that looks like a butcher shop, you have to have a field that shows there's bleeding coming and going, but you're moving so quickly that you have an idea if there's bleeding at this point, you can go to this spot, you can't have too many bleeding points at the same time, otherwise, you'll get into trouble, and I think those are all fine points that as you go along, you can hone on and refine your skills. And you can never become great in AVM surgery, that's the great thing about it. It's a dynamic art, and you can always improve. So what are the surface landmarks I use? Draining veins, embolic material, CT angiogram and the cortical borders obviously are very simple because the feeding arteries on the cortex have very solid walls, they respond to the bipolar coagulation very well. So that's part of the operation, you really have to push the gas pedal on your Ferrari. And I know you're of Italian origin, so you can relate to that, Dan. And so for the feeding arteries on the cortex, I just push the gas pedal on the Ferrari and coagulate, cut and go, go, go because they respond so well. It's the deep white matter feeders that are just difficult to control, and you really have to take your time. So just like racing a Ferrari on Italian highway, you have to know when to speed up and when you slow down. So if you're going around the curve, you really wanna be careful and control the car, and when you're on a straight path, you know that you can run as hard as you can to be able to win the race. So, step two is really generous exposure and preparing for the battle. As you can see, you wanna have a good exposure of the AVM. Remember that sometimes the veins embed themselves within the dura and the bone. So when you lift the bone flap, you have to be careful if you have signs on the preoperative imaging that the vein could be attached through the dura and the bone, although that's rare. Obviously, when you open the dura, you have to make sure the vein is protected and it's not sacrificed because that could be a major complication if the vein is sacrificed too early. Managing the feeding arteries, obviously, you will have to be very careful of en passage vessels. Here are some of the images. I open up the arachnoid very well. Can you see my red dot? And you can see the opening the arachnoid and understanding the angioarchitecture of the arteries are so important, because you don't wanna sacrifice the en passage vessels, especially for those lesions close to the eloquent cortex. You can use a temporary clip just to analyze where everything is going, you can use ICG if you prefer to understand more of the superficial and angioarchitecture of the malformation and at the end of the day, just getting these feeders of your back early on is so important as you go through the malformation. Step three, as I said, is the managing of the arteries. The deep white matter feeders, have you managed these? These are really the part that makes everybody nervous and takes most amount of energy out of the surgeon. Remember, you can't just place too much of your energy at one stage of the operation and just be so exhausted at a later stage, there, you're not reacting appropriately. One thing that I believe surgeons don't emphasize enough is their fatigue. Fatigue really can significantly affect your judgment. And I think surgeons feels too much at times to admit that. So it's very important in AVM surgery, just like in skull base to a large tumor surgery that is very lengthy to manage and parcel your energy very effectively. And just again, like a marathon, an athlete who really can carefully design how much energy every step would require. And for these lesions, if you get into bleeding, which very often do almost every AVM for these deep white matter feeders, I stay close to the nidus, I get one of these guys who is bleeding and then the closer the segment of the deep white matter feeder is to the nidus, the less wall it has, and the less likely you can control it with a bipolars. So what I do is that I remove a little bit of brain around the deep white matter feeder and then I move a little bit away from the nidus and then you'll find a wall that's coagulable. Remember, you cannot let these guys retract into the white matter and cause remote hemorrhages. That's where really, I think, the issue with normal pressure breakthrough is an issue, not necessarily it's a phenomenon, but more it's an effect of the deep white matter feeders. And so after you remove a little bit of brain away from them, you can get them more coagulable walls and then coagulated and it would stop. This is the critical part where the mouthswitch is so important. When one of these gut pops, the one last thing you wanna do is remove your instruments and let these things retract back into the white matter. So it is really, really important, and I want everybody to remember this idea of removing a little bit of white matter around them, moving a little bit away from the nidus, finding the wall that's more coagulable and more normal, because you're moving away from the malformation and the pathologic flow of blood from the malformation that makes these walls less thin, and therefore responsive to a coagulation and be able to use a clip, which I rarely do because they get on my way, or you coagulate them effectively. Dan, do you have any thoughts here?

- Yes, I think one of the, in fact your slide just says what I was gonna say. We talk a lot about circumferential dissection and people don't don't really often explain why that is and what the purpose of it is, but what you don't wanna do is dig yourself into a hole, because if you are in a hole and you have these diaphanous vessels that are coming through the white matter, you need to be able to see them well, and the benefit of circumferential dissection is you get rid of the easy, superficial feeding arteries and you also provide a better view of the deep white matter feeders so that you have the room to deal with them, because they are the challenge, there's no question about that. And I don't use a lot of clips either in AVM surgery, but I do believe those little spring clips that are made specifically for these thin-walled vessels can be quite useful. I also agree with your point that you get a little bit away from the nidus and there is more of a wall to coagulate. The danger is chasing them into the white matter, the normal tissue around the AVM and that's where we can really harm people.

- I agree. This is a nice image. Again, you don't wanna dig a deep hole and get lost because then it's really gonna be difficult to see things. You wanna have a very even and democratic level of dissection around the malformation. One thing that I like to mention is you can see this draining vein, or along the nidus wall that's joining the deep draining vein, you don't wanna sacrifice these guys early, you wanna be very careful around the malformation, that's why just indiscriminate coagulation of the nidus is so dangerous. You really have to handle the nidus with respect and not just with something that just can't be coagulated at any time. Obviously, you wanna protect the dominant vein. One technique that Dan has really proven useful for me is that I really devascularize the AVM very quickly, deep white matters and then temporarily pinch the draining vein with the bipolar. If the AVM is not swelling, I take it and we're good to go. I think that simple test of temporary pinching of the vein, either with a temporary clip or the bipolar forceps can be quite effective. Although I have never proof of this, this is my personal opinion, again, that's something I wanna mention ahead of saying that idea, is that I think after you disconnect most of the feeding arteries and the disconnection circumferentially, there is a point where the potentially the flow through the vein reverses and you get some bleeding all over the place, and the only way to control the bleeding at that point is to take the AVM out. So the later stages, the last 10% of the operation, you will see the brain is bleeding, the AVM is bleeding, everything looks like hell, it looks like we're gonna lose the battle, but that's the time when you really have to use your agility, and it's not about how technically good a surgeon is, it's about how fast, efficient, effective they are. And so I think you have to remember that stage, and that's when you are landing the plane. It's the turbulence, you're changing altitude pretty quickly and you gotta land the plane, you can't just stay in the cruising altitude, otherwise, you're gonna pass your destination, you've gotta land the plane and go through the storm to reach area of tranquility. As you can see, I love these poetic and philosophical metaphors, Dan. I think it's part of my Middle Eastern roots. I know Italians have something similar to that. But maybe- Good or bad. Step six, obviously, efficient excision of the AVM, and we talked about that just trying to get this out quickly to be able to get the hemostasis. Really, the most efficient hemostasis is taking the AVM out. I briefly discussed these, some of the pitfalls. Some surgeons dissect far from the AVM nidus to be in control. I think that's a poor technique and demonstrates lack of experience. The true extent of AVM can really be appreciated intraoperatively. Again, dynamically, it's like a dance with the nidus. Again, another poetic metaphor from me, and you dance with the nidus, you can see how far you have to go and far and close to be able to just stay close enough but not too close. And there are auditory connections at the periphery of the AVM that are not part of nidus and you wanna protect those. That's again, something that's important for the outcome of the surgery. Again and again, there is a concept for me of too clean of an operative field. You have to have tolerance for controllable bleeding and intolerance for incontrollable bleeding. Surgical intuition, I'm sorry, for the misspelling on the slide, it's critical. In AVM surgery, surgical intuition is important when time is of essence. You don't have time to sit there and really think about things and how you should handle things, and this is an operation of timing. You've gotta maintain your composure. I think everything is going great, you look like the best surgeon on Earth, and before you know it, a deep white matter feeder goes off and the whole fields, the brain starts getting tight, there's blood everywhere and while you're controlling it, one of the deep white matter feeders, three other ones explode because you're trying to know where the bleeding is coming from. So a beautiful operation can turn into a disaster, four or five deep white matter feeders bleeding at the same time. So you have to remember when you try to control that one single white matter, deep white matter feeder, you try to dissect to see better and just at that point, I think there are networks of the white matter feeders next to each other and all explode at the same time. And you've gotta exercise judgment and be able to react effectively. Let the nidus guide you. Don't let the nidus obey to what your agenda. I think those are some of the most disastrous complication I've seen when it happens when the surgeon wants to exert his or her agenda. And I do believe AVM surgery defines the best of us. I think it not only defines those who are technically great in microsurgery, but those who are efficient, fast, have great surgical intuition and are able to handle pressure under most difficult conditions with excellent temperaments. Very briefly about resection of AVMs, brainstem and spinal cord. I do believe that epipial disconnection of the malformation is so critical. We're not gonna have time to go over this. For brainstem AVMs and spinal cord AVMs, I disconnect deep white matter feeders epipially and remove only the epipial portion of the malformation and leave the portion within the parenchyma intact. And this technique works beautifully for brainstem and spinal cord AVMs. Obviously doesn't work for cerebral AVMs but it does work here and therefore those lesions have become operable. Just one other thing as a personal reflection is don't confuse the small networks of the deep white matter feeders with the nidus. I think there's a difference between those and how to handle them. What I have done at occasions is remove the deep white matter network to get control of the feeders and areas, even though the nidus is still very much intact. And again, that's something that it requires significant amount of judgment. Remember, it's very easy to get lost and go round the deep white matter feeder or too close within nidus, the malformation is not a cylinder, it's not a sphere, so you have to be very careful, that's why you have to preserve your energy, you have to have that sort of a second level of surgical judgment. One of the basic level is controlling the bleeding, managing the issues, you have to have a second level of automatic, almost, thought process and work ethic where you control your other movements. In other words, it's like a computer processor that you have some local functions and processes going on but then you have a higher level where you are watching yourself operate. You can't just get lost in controlling the bleeding and letting the bleeding control you. You wanna have that second level of thought process where you're also, as you're controlling the bleeding, a small process is going on of dissection. You also have an idea, "How am I doing overall in the surgical plan?" And again deliberate dissection and efficient dissection is the only type of dissection in AVM surgery. Appropriate bipolar forceps, mouthswitch, agile response, tolerance for some control of bleeding and no question to sixth sense in AVM surgery. You don't wanna tamponade the deep white matter feeders with a cottonnoids or pressure because they can cause a rehemorrhage and remote hemorrhages. We talked about removing small amount of white matter on deep white matter feeders and radiosurgery downgrading. There are subcortical networks of deep white matter feeders that require resection for getting control. And embolization, friend or foe, I think there is a phenomenon that as you embolize more, the deep white matter feeders get bigger because the AVM has to shunt that sort of function. So you have to be very selective. In fact, embolization has to occur as a combination of a discussion with the interventional radiologist and the surgeon ahead of time. I actually asked them not to embolize very superficial cortical feeding vessels because I want the AVM to shunt through them and because I know I can take them very early on in surgery. I think the role of embolization is very important for large AVMs where you wanna downgrade them to avoid that brain edema because you're really removing a big shunt system and surrounding vessels and circulation around the brain can be acutely affected. It can also be effective for example for superior cerebellar or tentorial surface AVMs where the draining veins can block the deep arterial feeders early on and therefore you wanna take those early. Outside of giant AVMs where downgrading them for the surrounding brain to adjust to the change of flow regionally and specific AVMs where draining veins block the large feeding vessels early on during surgery, I think the role of embolization has to be carefully considered. The pitfalls again, violation of a nidal surface. There is a phenomenon that your just penetrating the nidus in a small part of it. In that situation, I don't coagulate the AVM surface, the nidal surface, I actually use a piece of thrombin-soaked cotton, ENT cotton and just cover the hole and a little bit of pressure and you'll be amazed how quickly that controls the bleeding from the nidus wall. So if you have bleeding from the nidus and it clearly it's from the nidus and not a deep white matter feeder, don't go crazy with a bipolar forceps, because that would only rupture more of the nidus and before you know it, you're in the middle of an nidus and you have massive bleeding and you have to resort to what I call a commando operation. And the commando operation is when the nidus is very much badly damaged, you have torrential bleeding and you have to take the AVM extremely quickly. And we wanna avoid that commando operation at all costs if you're in a battle. We talked about the subcortical surface of the draining vein. If, God forbid, you are injured a vein very early on during exposure, you cannot just coagulate the vein and feel like you're good, especially if there's one dominant big vein. I actually let the vein bleed while I disconnect the arteries extremely quickly. So there is one extreme dangerous situation where the large dominant draining vein is injured, and very early on during dural opening and there's no other significant draining vein. If you coagulate the vein, the brain will swell and there will be subcortical bleeding and that will be more dangerous. I think there is a phenomenon to let the vein massively bleed while you're extremely quickly moving in a super-commando operation around the malformation. That has happened to me twice and that's something I learned on my own in a hard way. You gotta land the plane, as I've said before. Excision is the best form of hemostasis when are properly used. There is another phenomenon, Dan, that as I'm sure you know about is when you're removing a malformation, suddenly you get the brain to swell. You see no bleeding, the brain is tight, and this is for AVMs that are very close to the ventricle, and that's because there is bleeding into the ventricle from a choroidal feeding vessel, and that often happens when you're at the depth of resection. So if you have an AVM that has a good number of choroidal vessels that you may not even see preoperatively but the AVM gets obviously into the ventricle, surface of the ventricle, always watch for interventricular bleeding. These choroidal vessels are very easy to pop, easy to miss, and intraventricular bleeding can be disastrous to make the brain tight. So the other issue is that when your depth of the dissection of these big AVMs close to ventricle, you can disconnect part of the nidus close to the ventricle. So you have to go all the way to the ventricle. Doctors Thor Sundt, God bless his soul, I know you trained with him, used to say that special and pediatric AVMs or any AVM that gets very close to the ventricle, there's always some malformation right on this ventricle and you have to go all the way until you open the ventricle when you're done. And that's, again, part of the AVM that may not be angiographically evident or it's actually a cult especially in pediatric AVMs. There's also a phenomena where I always find large significant feeding arteries next to a draining vein. So the draining vein can hide these feeding vessels. So if your draining vein is still remaining purple despite a complete disconnection of the malformation, look around the vein. There could be feeding arteries that are hiding. I think that's a very important pearl, and I do use intraoperative angiography more liberally than other people, especially for big AVMs just because I really would like to avoid bringing the patient back, and as we know, the most common reason for post-operative bleeding and hematoma formation is residual AVM in AVM surgery. A lot to.... I covered quickly, do you have any thoughts there, Dan?

- Yeah, I agree with most of what you said. I suspect based upon your presentation, I may have a little less tolerance for intraoperative bleeding than you do. I do like a dry field with AVM surgery, I don't always achieve that but I do try to make that one of my goals. I think that some of the technology that you touched upon and some that we didn't touch upon that I think is important, I think functional MRI has, for very selected cases, been very important in helping determine not only whether or not a patient is an operative candidate, but also helping with the specific operative approach to an AVM, particularly if it's subcortical. So I do think that's been an adjunct tractography and fMRI that can help with clinical decision-making. I routinely use intraoperative angiography. I see no reason not to use it for AVM surgery. The goal of the operation with rare exceptions is complete resection of the lesion. And the quality of intraoperative angiography today is such that we can determine that with a high degree of certainty. And so I don't ever do an AVM operation without doing a final intraoperative angiogram to document that I've achieved my goals, that the AVM is completely gone and the normal blood vessels fill normally. ICG, I think is valuable at the beginning of an operation to kind of see and reinforce the mental image you have of the angioarchitecture on the surface. I do not think ICG is reliable in documenting complete obliteration of AVMs, it doesn't allow you to see the subtle residual early draining vein that you can see on intraoperative angiography.

- Well said, a functional MRI I have had some issues there because I think that both phenomenon is significantly affected by the flow of the AVM. So, my experience has been that functional MRI has not been very effective and I do not do any AVM awake, by the way. I do believe you can remove AVMs in functional cortices effectively if you stay close to the malformation. So this is a 43-year-old female with history of subarachnoid hemorrhage, was diagnosed with this malformation. I wanna review this, this is obviously a very large AVM feeding vessels, as expected, from MC and ECA and a large lateral position right parietal AVM, big flap, the AVM is exposed. This is ICG demonstrating the superficial angioarchitecture of the malformation. This is my partner actually dared me if I can do this under an hour, that intradural part of the operation. So I'll show you more of what the efficient technique that I've used. Obviously, nobody should try removing a five-centimeter AVM early in their career under an hour, but you can see the very effective way of coagulating the cortical vessels with a very wide bipolar forceps using your irrigation and just going through, staying right on the malformation, as you can see. Everything is done efficiently in terms of coagulating the superficial vessels. And remember, there is always on the periphery a little bit of cortex that could be hiding the edges of the malformation underneath. So you can just use that as a landmark because then you can get into the nidus of the malformation. Here's one of the draining veins. Obviously, if there are multiple draining veins, I only sacrifice the smaller ones as parts of the AVM are coagulated. Here, you can see that dynamic movement. I stay a little bit away then come closer, you see that? I'm continuously on the nidus. I get into a little bit of bleeding of the deep white matter feeders, and here you can see just when you were coagulating, the other one goes off, and then that's when you need to use judgment. But again, I'm staying relatively close to this malformation, obviously the bleeding is more and then I open around the malformation, but you can see the malformation mostly is under my view almost at all times, and I just disconnect the white matter using the spring action of the bipolars. Here you can see these networks, subcortical networks of the white matter feeders that can pop. You see, I have pretty good hemostasis and I'm disconnecting these guys and you never know which one really doesn't have a good wall, which one does. And you're actually doing very well and suddenly you see something pop, actually in the white matter away from the AVM. So these lesions are very complex, the white matter feeders have a network of their own and therefore there's much learning to be done. So you can see the superficial portion of the AVM can be effectively devascularized within a few minutes, and then I use more stealth navigation for the deep part, because that's the part can be more difficult to disconnect. And you can see there's always some bleeding going on, but at the same time, we continue and be able to work during the part of the operation that we need to disconnect the malformation. So here we have some bleeding, I'm moving away from the malformation a little bit because I got too close to it, and then getting hemostasis. But the mouthswitch, as you can see these subtle movements in the microscope keep everything within the operative field. Again, this is a more dramatic view of the deep white matter feeder that started bleeding away from the malformation when there was hemostasis there before. And then that's where you remove a little bit of white matter and then carefully recognize where it is and then disconnect it. Here's that network of the white matter I'm talking about. The malformation is actually here. We're talking about malformation surface right here, but we have bleeding way away from it and I think that's part of these deep subcortical white matter feeders that you have to be very careful. In this case, I have included a lot of sort of the back part of the operation because that's where we learn from, that bleeding. So I've efficiently after I coagulated the white matter feeder subcortical network that's obviously very small on the periphery of the malformation, and after that there's one large draining vein that's been protected, and that's along the area. This is an area when I tore one of the veins, and here as I'm trying to cut, unfortunately, one of the veins I did not see. And as I say again, you have to remain composed and be able to just use the big suction, identify where it is and coagulate it. Obviously, it's on the surface of the pia and using the mouthswitch is so critical in this situation to be able to keep you under control. And as you sort of grab things, again, you can see the bleeding is too profuse, but again, you gotta remain composed, imagine where it is coagulate it, and then that controls the bleeding very effectively. In AVM surgery, unfortunately, it's not always about seeing, the surgeon has to have certain intuition of where the bleeding could be from and how we can control it. This is protecting one of the draining veins superficially and then we went around AVM, here you can see the majority AVM has been disconnected, the brain is relatively relaxed, the AVM doesn't have a significant amount of turgor and then at that point, we can do that temporary occlusion of the vein here and then coagulate and cut it. And this is how the rest of the AVM was delivered. Again, interhemisphericly controlling. You can see there's fair amount of diffuse... Oozing and bleeding is going on and the only way to control that is via taking the malformation. And then you have to inspect the walls, something I forgot to mention. If you can't get immediate hemostasis by coagulating the walls, that means there is a residual AVM in that wall. And here, I removed additional wall to get hemostasis rather than just coagulate and coagulate. So now I'm getting much better hemostasis on that wall with bipolar alone and then intraoperative angiography, in this case demonstrated complete resection of this 5 1/2 centimeter malformation. And again, this is way later in my career, I think we did this two years ago, and the whole operation was less than an hour, 15 minutes into intradurally. But again, requires fair amount of tolerance for bleeding, and I think requires for every move to be extremely efficient. Let's go ahead and talk about the next video. This is a case that went bad. I often learn things about when the case goes bad than the case goes well. This is an AVM that's very diffuse, as we know, cerebellar AVMs are a different beast because of the angioarchitecture of the cerebellum, which is often different than cerebrum, the AVMs within cerebellum can be quite diffuse and the white matter feeders can be more aggressive. I started the case in a relatively good note, supracerebellar approach. The AVM draining vein is apparent here and here you can see some of the other draining veins and I started getting to the AVM but unfortunately then, in this case, no matter what I tried, I always was within the nidus. I could never get out of the nidus. So this turned into a commando operation where I just the whole time had a lot of bleeding, remained patient and just the only way I achieved hemostasis was by taking the AVM out. Here is a supracerebellar approach and a superior cerebellar artery feeding vessel, the corkscrew vessels going to the malformation. I went ahead and disconnected these early on and then I got into the white matter using stealth neuronavigation. Here is again, exposure, you wanna see where the brainstem is early on, because when you get into bleeding, it can be very difficult with how far you are from the brainstem. So just like in a battle, you wanna see who are your allies, who are your friends and who are your foes. And early on, you wanna be able to keep the allies out of the harm's way when the battle gets to its critical point and warfare is happening. So here is the fourth nerve, I believe, here is the arachnoid over the posterior aspect of the brainstem, and I wanna make sure I know the depth of this section, I know all the structures around me, I know the feeding vessels, here you can see the hypertrophied en passage, supracerebellar arteries that were evident. So after all that is exposed, I'll go ahead and inspect the surface of the cerebellum here. There was not too much sign of an AVM, but we went ahead, and again, inspected all the territories, where we wanna go, what is important, what is not important and also this will allow the AVM to, I'm sorry, allow the cerebellum to mobilize itself away from the supratentorial and provide additional space to work with when the bleeding occurs. Again, a very small space, this cerebellum is full, relatively young patient, and it is hard to see what's going on, and this is usually when bad things happen. There's a small working space and bleeding happening, you don't see what's going on and then the surgeon can become impatient when he or she's fatigued and indiscriminately injure the important structures. I'll let the video run as Dan you're commenting, but you'll see I get into a bleeding very quickly. Again, it's a deep AVM, I'm coming over the cerebellum, it's hard to see and just showing the tolerance for the bleeding and moving quickly to remove the nidus. What are your thoughts in this malformation, Dan, and the case before, please?

- Well, the case before, I thought was managed well. You nicely show the circumferential dissection, the point I was making about not digging yourself into a hole and the challenge of the deep white matter vessels that invariably feed these large AVMs and how they pop and bleed sometimes when you're not even close to them. So I thought that was a very nice illustration of it. This particular AVM you're showing now, obviously, I think that decision to provide surgical treatment, it seems to be appropriate. The approach is the right one. That's what I certainly would have used. You look like you've got a good quarter to it. It looks to me like you're in the nidus of the AVM. Again, as we talked earlier, that is far and away the most common cause of bleeding, particularly in relatively small AVMs like this. And it is sometimes difficult over the surface of the cerebellum to identify the edge of the AVM, that is a challenge when there aren't any superficial landmarks to give you that clue.

- No, I agree with you. I think this was one AVM where I think the boundaries of the avian was extremely difficult to appreciate. I always find myself going into an out of it, and as you know cerebellar AVMs are very challenging because these deep white matter feeders are so much more exuberant. And here you can see, this appears I'm outside, you see I was first inside, then now I'm in the whites matters so I feel a bit better, but there was just no way... You can put a retractor in here because then you're really gonna confuse the cerebellum. The suction, in fact, provides more exposure where exactly you're working, but rather than the retractor that provides a bigger space, but then less in the exact area that you wanna work because the cerebellum would find it. So this is just sort of not a video I'm necessarily proud of, but I just want to illustrate the difficult moment in surgery rather than showing a beautiful case that you know everybody can cheer, clap for you and be your cheerleader. I think this is more of the difficult times in surgery, that how you just have to work through the blood. This is not a time where you're gonna enjoy a beautiful operation at going at your pace. This is an operation that's gonna be ugly and it's gonna be at the AVM space. And so there's fair amount of bleeding going on and then we got the, I think, nidus is fairly disconnected by now and again, working a little bit more posteriorly, there's still residual AVM. I almost felt like I'm losing fair amount of blood, but I'm removing this AVM like a tumor, in other words, from inside out, rather than outside in. Obviously sounds pretty bad for an AVM but it's was the reality in this case. So I think we're coming to the bottom of the AVM, you can see some of the deep white matter feeders, But again, it appears that we are outside of the AVM, moving more posteriorly. As long as you let the bleeding come out and don't tamponade it indiscriminately, the brain would be your friend and will let you work around it, and then as I went more posteriorly, again, I had an idea where the brainstem is, because of all that bleeding, it's very hard to know, but again, I'll be able to dissect it so when disasters like this happen, you can quickly and efficiently remove the AVM. It's hard to see which one is the feeding artery, and that's why I stay close to the malformation and just circumferentially disconnected it and anything else that was very near to it was disconnected in order to be able to remove the malformation. And I think here is the last disconnection more posteriorly. Just when the AVM was removed, Dan, you can appreciate you have hemostasis, all that bleeding suddenly disappears, which is very intriguing and it shows that the best mode of hemostasis often is remove the AVM itself as long as obviously, the nidus is completely addressed. There is some bleeding on the deep part that was controlled and here we have the depth of the resection reaching hemostasis. And I'm sure all our viewers and you are happy that our video is over at this time because it's sometimes difficult to watch. And here's a draining vein that still appeared a little bit purple that we disconnected. Here you can see a large draining vein there that was sacrificed to make sure there is no residual AVM Brain's cerebellum was relatively relaxed, which is obviously a good sign. I always inspect the surrounding areas, make sure we haven't left any cortical vessels that could be connecting to draining veins. The cerebellum, again, very soft. And this mission did well, did have some gait ataxia for a few months, but ultimately, made an excellent recovery. I think these are some of the techniques that I've already talked to you about. I have tried one other technique which sort of is been a very unusual technique, which I don't personally recommend at all, is intranidal resection technique or valve of malformations, and that's for AVMs in extremely critical areas of the brain like Wernicke's and Broca's area, right in those areas. It's a technique that I've tried a few times, it is tough, there's a fair amount of bleeding, but you just remove AVM, and as you have some bleeding, you remove it until you reach hemostasis because you wanna stay out of the white matter, and there's minimal white matter dissection. I think that's a technique that's really extremely unusual that has to be really evaluated further before it's advised. The other technique that I've tried is intraoperative embolization of the vein using the technique that Europeans are using endovascularly. For larger AVMs, I disconnect the superficial arteries and then I put a catheter into the vein and then my colleagues would embolize the nidus intraoperatively. We have had some good success. Again these are some extremely sort of unusual and new ways that their outcome should be determined. So with that in mind, Dan, do you have any closing comments about this discussion?

- Very nice. As I said earlier, I agree with most of your points. There are subtle differences, perhaps in the way that we think and approach these, but that's why we have these discussions. This is one of the most challenging things we do, but it's also one of the most rewarding because this is a potentially curable problem. You mentioned ARUBA and the details of ARUBA and the reasons why it was such a poor study are beyond the scope of this discussion, but I will say that the one thing ARUBA did teach us is that in the patients that were randomized to no therapy, over a 33-month period, there was a 10% group of the patients that had hemorrhages, indicating that there is a need for a low-risk treatment option for AVMs. And I think we have that treatment option, it's called microsurgery. The problem is ARUBA just didn't compare microsurgery with medical therapy, it really was not designed in a way to test modern therapy against no therapy. But it did demonstrate the danger of these lesions and they are curable. Your admonition about making sure that we follow pediatric patients is very important. There is a risk of recurrence in the pediatric age group but despite not really knowing what the etiology of these are, in the adult population, if we get a post-operative or good intraoperative angiogram, it shows that the AVM is gone, there is virtually no risk of future hemorrhage in those patients. So it's a rewarding part of my practice and like you, I really enjoy dealing with these.

- Right, AVMs give us an opportunity to prove our surgical technique, and that's what I enjoy. They provide you with the road and a marathon and an opportunity to run the marathon, "Ironman". And we as surgeons, we appreciate, obviously, as long as the patient benefits. And with really master of AVM in my opinion comes with instant translation of 3D anatomy to intraoperative findings. A proper surgeon called judgment and surgical intuition are difficult to define. Manual dexterity, endurance, mental toughness, calm composure in dealing with disasters, something surgeons often don't appear to learn, no matter how many years down their practice, that in fact a pilot or a captain never really looks great when he or she brings the ship to land under quiet or calm waters. The pilots or the captain who maneuvers and navigates the ship under very turbulent conditions is the one who's worthy of a praise. And obviously, experiencing these lesions plays a dominant role and as I've said all along is AVM surgery is the only one that not only our tests and qualifies this, offers technical prowess, but also offers perseverance and efficiency and this phenomena truly distinguishes AVM surgeries from all other surgeries we perform in our beautiful profession of microneurosurgery. Dan, I wanna thank you for being with me in this session and I really enjoyed the discussion and I also want our viewers to join us for the last session which will be on the topic of "Managing Intraoperative Complications", something that both me and Dan have, unfortunately, a lot of experience on.

- Thanks, Aaron.

- Thank you.

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