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Grand Rounds-Technical Pearls for Resection of AVMs by Dr. Michael Morgan

Michael Morgan

August 14, 2016

Transcript

- Hello ladies and gentlemen, and thank you for joining us for another session of the Dublin this operative Grand Rounds. Today, our speaker is Dr. Michael Morgan from Macquarie University Hospital in Sydney. He does not require any introduction. He's one of the pioneers of AVM surgery and Michael, I'm very thankful of having you with us this afternoon.

- Well, it's my pleasure and honor to be here. Thank you very much Aaron.

- Thanks, Michael one of the biggest question we all have in our mind is what makes Cerebrovascular surgeon a great one? In other words, what are the ingredients to be a good AVM neuro-surgeon? What is the essence? What are those unspoken pearls? And if you can take a moment--

- Well, I ...

- Yes.

- Yeah, I had the privilege of being a fellow, at Mayo, I was, I know you were a resident at Mayo as well, and working at a time when Dr. Sundt was there, so. I believe that I saw a truly great Cerebrovascular Neurosurgeon in Dr. Sundt. And, he had a number of attributes that I think contributed to what made him great. And firstly, he was a very gifted surgeon he had great hand-eye coordination and he had all the things and the physical attributes and the mind that allowed him to perform surgery repeatedly with great performances. But he had some other things as well. He worked very hard. He was absolutely single minded about Cerebrovascular. And you know, he would come into the intensive care, I know at 10 O'clock at night to check on his post-op patients, he'd be there early in the morning. And he was always thinking about it. His writing was in part to, reinforce or figure out what he thought about Cerebralvascular, as much as trying to impart his knowledge to the rest of the world. And he was always reflecting on cases, particularly those that went badly trying to understand the reasons and he was exceedingly or extraordinarily honest in his self criticism and trying to understand what went wrong in a particular case during the surgery. So he had an extraordinary amount of flexibility. So he would go in there, not have a particularly closed mind, as to what he was going to do. But when he got to the target, he had lots of things that he could do, he could suture vessels up, clip the aneurysm and he basically had enough competence that he could ramp it up very, very quickly and change direction really, extraordinarily fast, when times demanded. He also was not distracted by other things. And I think finally, Lois, his wife, provided a very good home life for him. He had a very extraordinarily stable life at home and he was well supported. Now, I think all of those contribute to that, working in a great team, working in a great place, is very important as well.

- Much appreciated, those are very important points. So we would like to have you share with us some of the pearls of technique for AVM surgery. I know that you have a set of slides and some great videos. So if you don't mind, please take us through it and in the middle, I will just interject and ask some questions. So we're all looking forward to it, please go ahead.

- So basically I'll just go through really from superficial to deep in some sort of order of slides. And it's gotta be mentioned of course, that the patient needs to be set up well at good anesthesia. The head needs to be elevated above the heart. The use of retraction should be minimal with kinda curve, but should be minimal on the brain. You've got to remember the surrounding brain might have a, a lower perfusion pressure than normal and any excessive retraction might cause problems. It's not to say that you shouldn't retract but should do it cautiously and sparingly. Retraction on the brain AVM itself is very good providing that there is no venous compromise. And if that were to occur, it can converse. The, Craniotomy needs to be performed in a way to minimize retraction. A lot of what I'll say is, is really the way I do it. It's not necessarily the best way or the only way. Put you in context, I don't use a chair to operate. I like to, to stand, I like to, be able to slightly move around the patient, I don't like my arms or wrists constrained in any way, shape and form. And I believe that allows me to get into good position and to basically use all of my joints to move minimally, but to have maximum effect. I know some people like to hold their arms steady and sit in a chair and that's fine for them. But the way I was brought up I guess, was to, to stand freely, use my hands freely. So looking at the, principles, one of the things about an arteriovenous malformation is different to lots of other surgeries is that we are operating almost entirely on physiology, abnormalities physiology, not on pathology. So, we need to worry about the physiology more than in most other operations. And although it said that all arteries should be treated first, this is absolutely essential. It's not like, cutting down the blood supply from and reducing it somewhat. All arteries have to be absolutely abolished first. If we take the veins early, even with the smallest artery input, the pressure will rapidly rise in the AVM and rupture. Even with the most minute arterial input, might take some time to reach that. But nonetheless, it would become, tight good and will rupture very, very easily. And that's one of the most difficult problems in surgically managing AVMs. When you're looking at arteries, the craniotomy is best plan so that we can see the arteries transitioning from normal to abnormal. But also it's important to allow them to go from abnormal back to normal. We need to see all that at the time of the surgery. It's also important because the distal arteries or the onus on arteries going to normal brain, are often very small and go back to their normal size. It's usually easy to mistake a distal feeding artery from some of the normal feeders. So in order to not make that mistake, I like to actually often dissect from distal to proximal. Go from distal normal through the AVM area, and then back to proximal which is normal. And that way, I find that I make less mistakes in trying to identify the distal normal artery. So, going from the more superficial location to the deepest locations. I don't use embolization anymore, I haven't done so for the last five or six years of practice. And, this is a sort of terrifying sight. And when I see, vessels look like this, they're going into the tent into the falx, I find that potentially very, very challenging for the surgery. It is tempting to embolize that, but another way of dealing with this and ultimately one has to deal with it, is to cut the meningeal artery supply at some distance. And we'll talk about that a little bit. So if we look at the basic principles, if we're looking at a convexity arteriovenous malformation, it's useful to cut the dura at some distance from the AVM, and fold it over the AVM in order to not tear or stretch the connections. The transdural arterial recruitment is very unforgiving and is very short so that if we try and separate the dura from the AVM, we could lead to catastrophic bleeding. Now, this is particularly the case when we're looking at the falx or the tent. The temptation is to try and push the brain away from the tent to the falx in order to get to this supply. But in doing so, we may will tear a very precarious blood supply. And it has been a source of maybe losing patients from blood loss in doing that. So when we're looking at trying to secure the meningeal supply and the tent and the falx, it's important that we respect the same principles as we can do on the convexity dura. And that is opened at some distance in the case of the falx, that means often opening it from the contralateral side and opening the falx at some distance so that we can have all the feeders and easily control that transdural arterial supply. In the case of the tent, it's important to remember to come as anterior as you possibly can when you're dividing the tent. When it's coming up from below to supply the, simply located AVM. So always think about it as where can I secure, the arterial supply to sight distance? And with that, we don't need to necessarily, embolize the AVM. So if we're looking at a more complex superficial supply, and this is an AVM that had been previously treated elsewhere, sometimes we have this absolutely nightmare scenario where we have blood vessels coming through the bone, to feed the arteriovenous malformation. And in these cases, we need to think about, the blood supply a little differently. If you embolize these AVMs, you're embolizing the scalp primarily. And that means that weren't feeling the exception difficult and can be very, very problematic. So in these particular cases, it's very important that we have a strategy of turning the flap and not running into catastrophic bleeding as it comes through the bone. So for these sorts of cases, if we just look at the postoperative imaging here, this gives an example of how I've done that. We plan the flap in the usual way, but I usually do very short, little strip craniotomies to complete the flap. And in that way, I can secure the bleeding at every little opening of the, of the bone. And that is a good way I found to minimize the amount of bleeding coming from the blood bone and the dura. Again, this can be a catastrophic situation. If you try and turn the flap in usual way. When we're, by, now look at the approaches and, and, one of the, different ways of approaching an AVM, down the midline. And I know there's different ways of doing this, and this is obviously the arteriovenous malformation with the draining vein. And one of the ways that we sometimes do this, and we'll just look at video, one if we can, Aaron, here is the arteriovenous malformation. And although it's tempting to think that one could go from lateral to medial, all the feeding arteries from this AVM are located immediately. So it's important for us to have a strategy of coming from the, midline. And there's when we're doing interhemispheric approaches, I know that there's some people who like to suspend the AVM side down. I like to have the, head in aligning the superior sagittal sinus in a vertical plane so that we can go from left to right with minimal retraction on the brain. So I'll just start this video. And the, you can see that it's a, a difficult access problem. And the way we do this is supine and flapping the back. I've got a horseshoe type of incision, many, many bullet holes over the midline. I wanna make sure that the, superior sagittal sinus can be very, very safely stripped away. Although I know that there's other ways of doing this, so I find this very safe and haven't really deviated from this. So I'm making sure that the superior sagittal sinus is not, stripped away and then hitching up the dura, particularly superiorly so that we reduce the amount of venous drainage. Often with the more posterially located exposures in this area, for me the superior sagittal sinus continues to bleed. So I usually turn the dural flap bilaterally, and now I'm going on the right-hand side. And then I'll put a surgery cell pledget over the superior sagittal sinus, and do a running suture, not too tight, because you obviously don't wanna preclude the sinus. And I've made that mistake before, but it's important to do a running suture quickly, and this gets the superior sagittal sinus out of the way. And then on the side, contralateral to the AVM will be concentrating our, our exposure. So I'll put in a couple of stay sutures into the, into the falx superiorly and inferiorly, and this'll allow me to, gently retract the superior sagittal sinus. Again, you don't wanna overdo this because you do not wanna include the superior sagittal sinus during this. And then having done that, you can do a slightly lower stitch in the falx, and that will again, allow a little bit more tension so that I'm gonna get a favorable exposure to the contralateral side. Now, I open up the, I open up the, the falx, from superiorly and inferiorly, and I've placed a lot of pledgets over the brain. And that's because I'm going to be retracting that falx across to the left hand side, and I don't want the sutures cutting into the brain. So having made the retraction and using the falx as part of the, the, the material that will protect the left side of the brain, I then can access with a good eye angle to the, the right side. And we were just starting the core dichotomy here, and you can see that I have a retractor on the brain and that's used very early on just to maximize that angle later on during the case, we can take that out and, so we can see that the AVM and the readily access on the contralateral side with nice exposure now taken the retractor off the left side of the brain, but I'll need it to get to the most lateral aspect of the, AVM on the right side of the brain. So we're out at the lateral margins, as you can see in this particular video. And, this is mostly a white matter dissection. We'll discuss that a little bit later with these broad insulated bipolars. So the, the lateral margin is, is pretty much coming up here and we've finished now with the AVM. You can see it's blue and we are just getting the bang there. So going back to, to the slides, we'll have, we can see that in summary, the angle of the, the angle of the, AVM is, is very favorable, if we can come from contralateral side. And you can see that the, I've got a very large craniotomy that provides a very significant angle, also superiorly and inferiorly that allows me to move around the AVM. So, when we're trying to preserve the arteries to critical brain, I mentioned earlier that I like to go from distal to proximal, and this is an example of an AVM in the region of the angular gyrus. And you can see that it's a very, very obvious, large feeding artery, but it's actually very hard to see the distal artery. And one shouldn't be thinking that because you cannot see distal artery that the distal by brain is not supplied by an onus on artery. So we'll just move on to video two. And with video two, this shows that particular case, and what we will see is the AVM located here, and the feeding artery, you can't see much of the onus-on vessels. This is the more proximal artery up here that I've just placed a temporary clip on, and this is the distal artery down here. So on my opening up the sulci, always mindful of trying to find the distal artery, and we do a very good all as complete a sulci opening as possible. This is a very small eye knife. The advantage of it it's relatively cheap, and it's very sharp and it's very good down the sulci where the 11 blade is a little too big. Having seen the distal artery, I now go through and proceed to take all the feeding arteries, the AVM itself, as under this heading here. And we will go through and, locate all feeding arteries having exposed it from distal to proximal. So, this is a, slow process, and I know that there's many ways to secure these vessels and, good ways with bipolar, but with these microclips that Dr. Sundt invented, I've gotten used to use those because they're a lot quicker to apply and secure the vessels, maybe on the patient, but there's a distal artery. And so I've checked the that's okay. And as you can see, it's actually not much larger than some of these little vessels that are securing now. Having taken all the feeding vessels, and I can take off the temporary clip and get into the sulcus, which is I'm pressing now. And we will deal with the arteriovenous malformation through the sulcus, but it's having secured all the arterial feeders. It's then a fairly easy job, to finish the job off. And that's the draining vein, and we'll leave the AVM in there. So, the postoperative results good. And as you can see that you can now see the distal artery quite clearly, and one would expect that to be potentially an important that could just sign. So going back to the, slides, will, it's very, very different. As I mentioned, it's very, very different removing the physiology of an AVM from removing a tumor of an AVM and that we need to think of them very, very differently. As I mentioned, it's critical to get all the arteries before the veins, and we'll just go to the next video. In trying to remove all the arteries, it's critical to, as I say, secure all of physiology. So this is an AVM on the surface, on the convexity surface and because it's physiology, and the arteries and veins are just reacting to having a, a very, very small pathology. The pathology is, you know, seven, maybe 13 little fistula. That may be only a number of tens to maybe up to 300 microns size. So it's within the interstices of this, but almost everything would see is normal vessels that have responded to physiology. And just like normal vessels responding to physiology, we saw bone bleeding arteries under veins, and we find that some have that access to the sulci very deeply. And it's important to think of, although we talk about deep supply, the deep supply can actually be from the, superficial arteries that actually dive into a sulci deeply. So, we don't need to necessarily only think about collateral supply and ventricular stripes is deep. Some of the feeding arteries will dive in deeply, and it's important to expose all of those. So again, we do a dissection and this is again with an eye knife. And we meticulously go around underneath the veins is where we'll find the arteries. That's a rule about the body everywhere. And we come and deal with the, just the feeding vein. For the pragmatic reasons, I dissect that late because I, you know, fear that if I cut that, will change the operation completely, but we always are looking for the feeding arteries under the veins. And when we get into the white matter, we can use a broader bipolar on a higher setting. And, and start to pull the AVM back into the, the mass of the AVM. So we go around the AVM, gradually getting to the deep component, keeping the draining vein intact until we have the very last of the arteries. So we still haven't dealt with all the arterial input. Even if we think there's only one artery, there's usually many, many that we need to get very close to the AVM. So we can see the padding on the other side, so that's a good sign. I'm feeling very comfortable that we're nearly able to complete this. You can see there's a lack of turgor in the AVM and that's because we still have the draining vein. That's the last little arterial input there, which we will take out before cutting the AVM and checking with ICG. It's important not to have patties in the, in the bed of the AVM. You never should cover up the AVM bed because if there's any little bleeding, you need to deal with this. So in summary, dissect the arteries from distal normal to proximal normal, we need to put temporary clips for regional hypotension, and that's allowed. There is very good collaterals distally because of the low perfusion pressure. So that's a very safe technique. And the superficial control needs to happen. So we need to have the nose cone of the AVM isolated very, very early, no corkscrew circumferential dissection. Now this is the way I do it. I don't know that it's, it's a uniformly accepted way, but for me, it seems to make sense. So if I can just have the next video, I'll just illustrate that when we're looking at arteriovenous malformation. As I mentioned before, the, the arteries and veins, because they're a physiological response, obey pretty much the same principles of arteries and vein development everywhere else. So if you're looking at a, an AVM like this, you can picture or imagine that in the later filling phase, you can see that the veins start to fill out, laterally over the surface of the AVM. So most of what we see on the surface, are the veins draining the AVM. When we're thinking about that and the principles of how we normally expose it, a lesion in AVM. Normally speaking, when we do most tumors how we've been taught, is to go circumferentially around the, the AVM. And this is our normal circumferential approach. The problem is that we've often got this deep, feeding vessel in an AVM. It might come from there, or it might come superficially and go to the deep component. Whether it's come superficially or from the lenticular strides, there's always some artery coming in at the deepest component. And this means that when we're coming around circumferentially, and we've gradually picking off all the little arterialised vessel that are looping in and out of the AVM, these are usually veins arterialised veins that we're gradually cutting. And just like, if you're in Australia we've killed, killed too many trees. The way we do it is ring bark the trees. We chop the bark and that causes the tree to die. And that's because it stops the, the inflow from the ground. And that's the same thing that's happening when we're circumferentially doing an arteriovenous malformation, we can cut off the venous drainage and that can make the final deepest part very turgid, swell, very tense and easily rupture. And, and for most of my career, this was a disaster for me until this is a, an illustration from Hashimoto, demonstrating that the veins are on the surface until I've picked up on, on the idea that why don't we just make a B line for the deepest part of the AVM very, very early on before we start the circumferential dissection. So when we're doing that, it means that we really can always operate with a very slack AVM without embolization. So here on I'm making a B line, even though this is a relatively, large arteriovenous malformation. I'm making a B line for the nose cone, and I deal with the nose cone of the AVM before I've even, performed a circumferential dissection. So I've still got most of the circumference to get around. And this illustrates another, issue is when we're looking at arteriovenous malformation. And what we're looking at here is the physiology. When we're making arbitrary decisions as to where we're gonna cut the, the input vessels, because underneath this is normal white matter. And the vessels that run over it are normally reacting vessels. So we're always making a judgment as to what is the, the margins of an arteriovenous malformation. The margin is where we believe it's safe to take the blood vessels without them bursting at the end of the day. So we'll go back to the slides. And so just recapping, you do get some superficial control, but as soon as you have got easy superficial control, then you do the nose cone. So I go to the nose cone without corkscrew circumferential dissection, The veins, as I've mentioned, we always leave these until all the arteries control both the superficial and the deep arteries. So another important principle is because I've mentioned that the veins or the arterialised veins are on the surface of the arteriovenous malformation. That means that as we're going down and we're seeing those arterialised vessels go into the white matter, we're tempted to think of those as, as small feeding arteries, when often they're performing a loop coming back into the plane of the AVM at a distance. So when we're trying to deal with the sulcus of the AVM, it's important to try and strip those blood vessels back into the plane of the AVM. So when we're dithering, we're dithering, or not just to a glue those vessels, but we're pulling them back into the plane of the AVM. Sometimes you can pull them back into the plane of the AVM without dithering it in other times, it's better to dithering. And, and that also helps with getting through the, through the white matter. So if we're looking at chasing the AVMs, I'll just look at the next video. This video illustrates chasing those looping in vessels that come in and out of the plane. So this involves a, this is a, an interhemispheric approach to an AVM, and I use all techniques, microclips, dithering techniques, and this dithering technique, you , dirty diathermy, which is a nice way to put it. We like to think of in the sulci that we use precise diathermy with the, minus bipolar on a low setting, but when we're going through the white matter, we're using dirty diathermy taking more material as well as the vein that helps compose it. And we've got the, a broader bipolar on a higher setting. So the idea is to whenever you see little veins like this, and it's an arterialised vein, for sure. We like to strip them back into the arteriovenous malformation. So I like to go out a little bit and then pull it back into the plane of the AVM. So the AVM is on this side here, and my action is to strip the blood vessels back into the plane with the AVM. And this is, something that you need a lot of concentration for, because some of those blood vessels you'll need to secure with the clip and you want to not put any tension on any of them. So now we've flipped it around. And the AVM is over on this side now, and we're gonna be pushing these blood vessels up. So using more, diathermy to incorporate surrounding white matter on a higher setting, we gradually creep around looking at the, looking at the white matter, but stripping all the veins back into the plane of the AVM. If you got to create any tension on those vessels, it's better to put the tension in the white matter than on the connection between the blood vessel and the AVM itself. So, this is stripping underneath, and again, always gently stripping a little bit towards the AVM itself. I don't like the, to use the word, ''Notus'', although it's popular to use that. That's a, just a radiology word. That's based on 2D angiography to describe the nurses vessels, but when we're operating, we're actually have to make the decision on each and every one of these normal vessels that have been altered by the physiology and where to take those, and we can make a good judgment directly with the microscope. So we've talked about the different sorts of diathermy techniques. And in the sulci, with a very fine bipolar. I like to use a very, very low bipolar setting that takes a fair amount of time to affect diathermy over a long length of the vessel. A lot further than you would normally make, and then making sure when you divide it, dividing it slightly closer to the AVM than the normal vessels. So that's, that's the approach I take the diathermy to the superficial sulcal vessels. And when we're in deep in the white matter, we can use a, use a broader bipolar, an insulating bipolar. And now we're in the white matter, we're using a broad insulating bipolar that can incorporate the surrounding white matter on purpose so that we've got more material to diathermy. As I said, this is what you are earnest near me, nine goodie diathermy. And it's, it's very important that we can always also use the diathermy to pull AVM. Blood vessels back to the AVM itself. So the, ligation technique on the thin wall vessels, and these are very thin wall. We need a very precise, bipolar, and we need in the deeper white matter where we have the small veins, these are veins usually rather than arteries. We usually use the, the broader bipolar that allows us to incorporate collateral material that allows the more proteinaceous material to help with the thrombosis of the vessel. Of critical importance at the end of the procedure is to inspect the bed and control all arterial bleeding. When we're, when we're looking at the AVM, to hide bleeding, the patti is to kill a patient. It's absolutely imperative that we minimize the amount of patties and they've used for just selective processes to maybe press a bit of surgery cell down onto a microclips. And I, I do use patties, but I, I find that they will stick to microclips. So I put a little cage or what I call cage of surgery cell it's tiny over the microclips that holds it down. So it won't get stuck to the patties. And I think that to use cottonoids is to cover up or hold the bleeding back is, is delusional and dangerous. If bleeding is occurring, it's going up the sucker and it's not damaging the brain and we can carefully and, can be very frustrating, but we can secure all bleeding points slowly, either with microclips or with the, the dirty bipolar coagulation techniques, mostly with microclips I find is, is more useful. So, most of the principles, but it's important also when we're looking at the physiology where we're actually selecting to divide the, divide the vessel. So when we're looking at an AVM, how would I approach this? And again, it's really, it's, it's, it's a gift when you see an AVM that, you know, you do not have to cut the white matter. So when you're looking at this, AVM, we can get to this AVM, cutting white matter alone going through the Corpus callosum and dealing with through the ventricle. So this is the angiogram of that AVM fed by the anterior collateral artery, very small AVM with deep venous drainage. So this is something that can be approached through the ventricular system. But because it is, the lateral margin is more difficult to reach than the medial margin, I'll approach this from the contralateral side. So I get a better angle on this side of AVM. So if we go to the next video, Aaron. So this is the arteriovenous malformation that we will go through the ventricles. And, the best way, but for me to do this, again, is in the supine position and approaching it from the contralateral side. So we've got the craniotomy opened, dura opened, and we'll go down to the Corpus callosum in the usual way. With this is an 11 blade, rather than the eye knife that I had before and, having exposed the Corpus callosum, then I'll put a retractor in so that I can make sure that I can get open the Corpus callosum slightly to the contralateral side, so that I'm in the opposite ventricle. The, this is, this is going through the white matter and into the ventricle, and I'll use the retractor now on the brain itself. So I can get a, a good angle to cross to the midline to get to this arteriovenous malformation. So again, using the broader bipolar, straight into the white matter surrounding this arteriovenous malformation, I'm able to get to the lateral extent early, which is the equivalent of getting to the nose cone of the arteriovenous malformation. So we'll just go back to the slides. Now, Aaron, we've talked a lot about the physiology and one of the things to sort of have a mental picture about, and this is a cartoon that is not absolutely accurate, but the principles apply when we're looking at the, the normal, flow normal pressures as we go along the arterial to the venous system. And we're moving along on the x-axis here, we have proximal arteries going through to the veins. Normally we're aware that the blood pressure stays fairly high until we get to the resistance to small arteries. And then the pressure drops off very dramatically with an arteriovenous fistula, where you've got a straight, pipe, so to speak between the arteries and the veins, there is a tendency towards moving towards this line where we have pressure in the arteries lower and the pressure in the veins higher. And what that means is that we need to be mindful that when we've finished, ligating, the arteriovenous malformation, the pressure moves from this lower line lower than normal to higher than normal. And it's hard because the system is dilated. So it doesn't go back to normal, straight away. That's a process that takes a week or two. So when we're selecting the point at which where actually ligating the artery, when we're making a number of decisions. How, robust the wall is? What the pressure change will be when we remove the AVM? So if we're making a decision and we're going from pressure here to the pressure here, there's a potential for the pressure within the arteries to go up 40 millimeters of mercury. And this is, this is why we have rupture in a delayed fashion after surgery, and why sometimes we have rupture during surgery. We've made a decision in which we're probably wrong in that we've put the clips too far distal. In fact, I think a lot of the mistakes in what we think are retained Notus is just that we have moved the clips, a little bit too far distal in the arterial system. And the small, very thin wall vessels have dilated up in response to us taking the arteries at that point. And they rupture during the, the operative period. And it's not necessarily that we have an AVM, as such, but we have to think of a retained Notus. And again, I don't like that term because it's, it's an adoption of the 2D radiological image. What we have done is we just selected the wrong place to put our microclips or our location. We needed to come a little bit more proximity to that. So, if we look at, an example of this, we'll go to video 10. So this is an arteriovenous malformation that if we can imagine what the pressure is now that we have taken this artery at this point, it's pulsating. You can see that on the ICG and, and this is the, I've made the decision that that is safe there. But if we were further distal, that might be that vessel may not be able to have the wall or the tolerance to be able to cope with that. So when we're operating on an AVM, the summary is that all our decisions are based on the surface of the AVM, and where we make the microclips, where we, perform the diathermy through the white matter. These are all the surface decisions, and this is why the, the Spetzler-Martin grading system is so good. It does reflect the, the truth of surgery. And it was very, an inspired piece of thought to be able to grade AVMs this way. So the surface is, is the critical factor. We're making thousands and thousands of decisions on the surface of the AVM and why it causes troubles or complications as we've made an error in those decisions. So it's very, very important that we retain our focus and continue to concentrate, have the same level of vigilance during the whole procedure from even when we think we've got only seconds left. I remember, Charlie Drake once telling me that he feared the last 10 minutes of an AVM. And he believed that that was for him the most, the time that he often calls trouble. And I think that's true. We've got to stay vigilant through the whole case. I think that we do not need embolization. For me, it really is. There's no help or assistance. The important thing for me is to get to the nose cone and truly deal with all the arterial bleeders first. And, and that's the physiology of the feeders. We see that when we're operating, you don't get a sense of that when you're doing the angiograms, you can count one or two or three feeders at a distance, but it's when you're operating, that you really, can truly count the number of feeders. Thank you very much, Aaron.

- Thank you Michael--

- Rounds up what I can say.

- And this is really a spectacular talk. So I'm sure many, many decades of experience, and some of these pearls obviously can never be talked because you obviously that's the touch and feel and the finesse and the craft of it. I like to emphasize a few points that I really like that, although I've never trained with you, never seen each other work. It's incredible that we, I have arrived to the exact same points. Although people that I have trained under did not do it the same way. One of the things you mentioned is that very selective or no embolization, I do believe that doing embolization actually can make the AVM more difficult, because what happens is that the pedicles that are embolized are those that are very accessible and very solid walls. And when you embolize those, because the function of AVM is shunting, those deep white matter feeders that are not accessible by embolization hypertrophy, because you're depriving the AVM, from the larger feeders that are easily controllable during surgery. So you actually make those white matter feeders that are the essence of the challenge of AVM surgery, more hypertrophied, more dominant, and therefore the surgery becomes more difficult. Is that, has that been your experience as well?

- Yes, I think so. I mean, one of Dr Sundt's description of the deep feeders is he calls him diaphanous, which is very thin-wall, and he believed in his experience that they were never adequately embolized. And, and I, I even with the newest and the latest embolic material, they still remain a challenge for the endovascular team. And they're the ones that we struggle most with surgically. So I think that I agree with you, absolutely Aaron, in all of that. I think that by driving the, increasing the amount of flow through those small, deep diaphanous feeding arteries, that creates more trouble for the surgeon, I think there is a role for embolization, but for people that find it useful and it works very well when, you know, in many units and I've seen it work very well, but I think that if, if it's not necessary, then we can do away with, with something that for me, just increases the complexity of managing AVMs.

- I agree, you know, I use embolization for large cerebellar tentorial AVMS, where I can reach the superior cerebellar artery feeders early on, because there are numerous draining veins that go into the tentorium. And because I can reach the feeders from SCA early on, I'll embolize those very close to the surgery and then perform the surgery. Those are key, very selective cases, where the dominant feeding vessels are surgically challenging because there's a bridging vein in front of you and you can safely get to them. Has that been your experience or what is your exact indication for embolization Michael?

- So, I don't embolize anymore. I have, for me, I've eliminated embolization altogether from, from my last use of practice from my last five to six years. I didn't embolize an arteriovenous malformation. And, but I do see a role there's been cases in which I've had intra-operative hemorrhage that I wondered whether my decision, not to embolize was a mistake. I think that when you're doing a lobectomy sort of an operation on an occipital AVM, for instance, there's probably little will come from from embolizing and killing that exhibit alive by embolizing the posterior cerebral artery. But having said that, once you've gotten used to not embolizing, that just makes, it's actually, it doesn't make my life more difficult for making that decision overall and, and my results, didn't deteriorate with making a decision not to embolize. So I'm happy to stick with that. It's an expensive, it really is an expensive treatment as well. An embolization can cost as much as doing the surgery, so. If you can eliminate that, it's eliminating the cost of treatment or reducing the cost of treatment.

- Well, we really appreciate your time. I think this was a spectacular talk and thank you for so much. You have done neurosurgery, Michael, thanks again for your time today.

- You are most kind. Thank you very much for the opportunity. And as I say, these are not necessarily the right way to do things. It's a personal way of doing things. So thanks Aaron for the opportunity.

- You're welcome. Thank you.

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