Revascularization for Aneurysm Surgery

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- Hello Folks. Thank you for joining us for another session of the virtual operating room from the Neurosurgical Atlas. Our guest today is Dr. Dan Barrow from Emory University. Dr. Barrow doesn't recall any introduction. He's a internationally renowned Neurosurgeon in Cerebrovascular and Skull Based Surgery and truly, a dear friend of mine. It's been pleasure for me to work with him on number of webinars along the years. Dan thank you for joining us.

- Thank you Aaron, good to be here.

- I'm going to go ahead and show a case, and then we'll open up to your session, which will be on bypass techniques and revascularization for aneurysms. This is a case that specially interesting Dan and we'll get your opinion. This is almost a five and a half centimeter. I see a Bifurcation Aneurysm on the left side, on a young woman who presented with progressive right-sided hemiparesis. As you'll see the images. It's quite amazing how big this aneurysm has gotten. You can see the size of the aneurysm. Obviously it's partially thrombotic and it's associated with some edema on the frontal lobe. You can see the thrombus, you can see the jet of the blood on MRI and significant mass effect with a little bit of edema with a little bit of hydrocephalus, I'm sorry. You can see the open lumen of the aneurysm, very broad base as expected. And this is the contralateral side that shows relatively small amount of cross filling. So obviously a difficult aneurysm Dan and I wanted to just get your opinion, how you approach such a case. I'm sure you're gonna review in the endovascular era. There are such aneurysms that are not good fits, especially in such a young patient, for endovascular therapy. So could you please tell us your thought process about this giant aneurysm please?

- Well, one of my mentors with whom I did my fellowship was the great Thor Sundt, who was a wonderful Cerebrovascular pioneer for the Mayo clinic and Dr. Sundt told me once that he thought that a giant carotid bifurcation aneurysm was the most challenging of all the aneurysms. And this is a guy who had operated on some of the worst of the worst. So going into something like this, you have to anticipate that with the thrombus and the mass effect, you really have two goals, one is to eliminate the aneurysm from the circulation, but the also is to eliminate the mass effect and doing all that without compromising normal tissue and normal perfusion. I think in this day and age, there was virtually no case that I don't run by my endovascular colleagues to ask them if there is a good option because the field is evolving so quickly and I don't do that. So I always get their opinion, but my, my take is that there probably would not be a good endovascular option to get rid of that mass effect and the aneurysm. And so I certainly think this is one of the reasons, cases like this, why microsurgical techniques and particularly the use of bypass still has to be part of our armamentarium to revascularize that distal perfusion before dealing with that aneurysm so that you're protecting the brain beyond it.

- And that's exactly what we did. I think we're going to go review the technique, try to move forward and get to your valuable talk and hear your expert pearls. So we went ahead and did the radial bypass to revascularize the MCA, the M2 and then essentially occluded the internal carotid artery distal to the intrachoroidal artery. That was our strategy that seemed to work. Is that what you would plan as well Dan? Or would you do it differently?

- Probably I would. I would make the decision after the bypass, where to occlude, depending upon what I saw at the time of surgery, but that would certainly be what I would anticipate to essentially create almost a blind sac, if you will.

- That's exactly what we did. So here's the positioning of the patient, pretty standard, obviously the arm being available for the revascularization and the radial artery, our vascular colleagues prepare that for us very well. And this is the exposure in the neck. You can use either external carotid, or you can use the for end-to-end, depending on the size of their caliber of their radial artery, or use a side-to-end to use the internal. So here we decided to use a side-to-end for the internal and use the punch, create a very nice opening. And then because the radial artery in this case was a little bit shorter than we wanted, we actually did the proximal side first, even though, as we know the standard is to do the distal because there was some questions, how far this can go. So we did the proximal first, and then at that, then we came to the brain side of things, exposed a carotid artery at the level of the skull base, as you can see here, here's the neck of the aneurysm there's no way you can put a clip across it because the M1 is really originating from the aneurysm itself. We went ahead and exposed the M2. As you can see, this one is a really healthy M2, sizeable one, and then proceeded with papaverine to just make the artery avoid any spasm. We use intraoperative direct cortical stimulation to make sure that we're protecting as much of the structures as possible use intraluminal distension for the radial artery and proceed with end-to-side bypass, pretty standard techniques. In this case, for some reason, it was really barely possible to reach where we want it to. And I think one of the key factors is any tension is very detrimental to the survivability and durability of the graft. And then the rest of the, really, anastomosis is a lot of fun. Because it's really not too small and it's not too big, it's just the right size to enjoy the anastomosis and suturing. We use a 9-O, and do the intraluminal part first. And as you can see, because this was done reverse, usually we do intercranial first and then the neck part second but in this case, because of the size we did it the other way around. So the anastomosis on one side had to be done intraluminally do you have any thoughts Dan, if anything, you would have done differently?

- No, I think this is one of the problems with the radial artery it's my go-to donor for sure that's one of the advantages of the saphenous vein is you can get a longer segment if you need it. And I generally, rather than doing a sewing from the inside, I put two stay stitches. Sew one side tie it, sew the other side tie it, but you know, either is perfectly appropriate.

- And that's exactly what we did here actually, we did a heel and a toe, and then we ran it again I love these radial bypasses because STA you know, sometimes with a 10-O can be arduous, but a 9-O and a radial artery and a MCA it's just, it's just so easy, effortless and works beautifully. And then at that point we removed the temporary clips. A little bit of bleeding at the anastomotic site is very expected and it's healthy actually. And we had a good flow, both in the M2's And at this time we went ahead and occluded the carotid artery distal, you can see the A1, you can see the bifurcation. Here is A1, here's two or three I think, intrachoroidal one of which could be a perforator, and we just placed it just distal to those, to protect the irrigation to those small arteries. And as you'll see in a moment, so here's the anatomy at the level of internal carotid artery. Here's the intrachoroidal right at the level of the dissector and I think there was little space distals I think, in this case I put a permanent clip proximally and here you can see a nice flow retrograde, both in ICG and a floor scene. And it's this turned out well, she did very well. The aneurysm actually doesn't go away for another couple of years as you know, but it will regress completely. And it was really, and you can see everything filling out. All the intrachoroidals are filling out. I think there was not enough space between the bifurcation and intrachoroidal to place the clip permanently so we went a little bit more proximal. but everything was filling out retrograde fine, the cortex appear to be well vascularized. And here was the intraoperative angio in this case, very little flow into the aneurysm that we wanted still to somehow fix as well. And as you will see, in a moment, we paste the clip across A1 to make sure we occlude any entry into the sac via a one. And that's really made the sac very relaxed and this will trap the sac. And as you said, it's just empty sac without any flow of. And this is the flow of through their bypass, which was adequate. And this patient did very well and her hemiparesis actually disappeared within a few months. So any other thoughts before we go to your talk Dan?

- Well done.

- Thank you.

- Can't do any better than that.

- Thank you, Dan. Let's go ahead and proceed Luke with Dr. Barrows main part of the talk.

- Well, thank you very much as you have illustrated, you know, in an endovascular era, the cases that come for microsurgical management really challenge the skills of the, of the vascular neurosurgeon more and more. And so I think bypass has to be one of those tools that's in our armamentarium. So the indications as I see them for bypass with aneurysms are number one, to replace an artery that has to be sacrificed in the management of an aneurysm, as you demonstrated in your case. Sometimes for brain protection during prolonged temporary occlusion, if we're even able to reconstruct an aneurysm, sometimes the time it takes, we need protection and then also to reverse flow for either dissecting aneurysms or fusiform aneurysm. Those are kind of what I regard as the indications. There are a lot of options. Nature provided us a wonderful option, and that is the superficial temporal artery, which most patients have. And, you know, it's a mainstay, it's a relatively straightforward way to revascularize the brain and much, much safer than doing a high flow bypasses. But certainly there are times when the temporal artery either isn't available or it isn't sufficient. And both the saphenous vein and the radial artery are great alternatives. The saphenous vein has some advantages. It provides the highest flow, it is technically more challenging. The tissue is not exactly as robust as the radial artery. It's a little more fragile, it has valves. So you have to remember to reverse it or you're gonna really be in trouble. And is certainly is more prone to thrombosis. One of the benefits and I think it's a example that, that your case illustrates is that we can do very long vein grafts. The vein is as long as we could possibly need it. And we can also use it for short grafts. This is a cavernous aneurysm in which we did a graft from the petrus to the supraclinoid carotid with a vein. So the vein provides lots and lots of different options and is quite flexible in that regard. And it's even useful in the posterior circulation. This is a case actually, I mentioned earlier, my mentor, Dr. Sundt this is a case I did with him during my fellowship giant fusiform aneurysm, in which we did a bypass to the posterior cerebral artery using a vein graft. One of the very few cases that I remember it was successful in treating this horrible disease, I've figured out every way possible to kill these patients. And this is one that actually did well. So the, the vein is quite a versatile in that regard. I'll give you some examples of veins, today I generally use a vein graft only if I need something really long, which is not very often, or if the patient is a child, because I'm worried about the radial artery, potentially not being large enough. This is actually the youngest patient, I've ever done a bypass on when this child was five months old, she had a subarachnoid hemorrhage and had this bizarre congenital aneurysm, I'm presuming. And I did a M2-M2, a side-to-side bypass and trapped this aneurysm. And within a matter of months, you can see the recurrence, you can see the clip is migrated, and there's now a fusiform enlargement of the middle cerebral artery. And the child was exactly one year of age. And I really wasn't sure what we could use, whether the radial artery, the saphenous vein was large enough. So I did a saphenous vein bypass graft and this is the intraoperative angiogram you can see the year is 1991. So you can see the reverse flow into this, I still see this girl she's graduated from college. This is a 20 year follow-up angiogram showing that vein graft, which has now become arterialized and it's grown with the child into an adult, demonstrating the durability of that operation. As I said, that's the youngest person I've ever done this on. But I think, I think it is a great option for youngsters. This is a patient more recently that has this cavernous aneurysm presented with ophthalmoplegia. You can see the aneurysm here. And I do have some concern about putting flow diverters or endovascular devices in very young children that have a growth ahead of them knowing that a vein graft will grow with them and mature. And so, this is, the solution we created was to create a saphenous vein bypass, and then trap the cavernous aneurysm again because of the age not because there aren't endovascular options, but I am, I just don't think we know what those endovascular options will do over 40, 50, 60, 70 years. Certainly the radial artery graft has become our mainstay for high flow. There's a good size match between the middle cerebral, the posterior cerebral and the radial artery. It has no valves, it's certainly more stout and easier to sew, it's more the same consistency, much easier to harvest. There are some length limitations, and although it's not as prone to thrombosis, it is prone to vasospasm and that could be a problem. It's certainly important to be sure the patient has good collateral flow doing an Allen's test to be sure the radial artery, I'm sorry, the ulnar artery supplies the hand it's rarely a problem, but there could be some serious complications if you don't check that out. I have done both open harvesting and endoscopic harvesting, and I have moved away from endoscopic harvesting for a period of time, I did that and had our surgical assistants from cardiac surgery who were very slick at doing it, but I think it's more traumatic, I think they're more prone to vasospasm and I have gone back to just harvesting it and I do it myself. I think it's one of the most important parts of the operation and so I now do an open harvesting and I do it myself. Vasospasm can really be a problem as you can see in this arteriogram showing the spasm of this radial artery graft. A couple of tricks, one is, is to use the shyly vein distender and to irrigate with some cold heparinized saline and actually work the artery and try to break up some of the muscular contractions. Another trick that Laligam Sekhar has published is to take a vasospasm balloon, an endovascular balloon, and actually do angioplasty on the radial artery before you implant it and I've not personally done that, but I think it's a very clever trick and Dr. Sekhar, who I have great respect for says that it works very well. And it certainly makes sense. So let's just kind of go through some cases and those indications. So, as I said, one of the first indications is to replace an artery that's sacrificed in the management of an aneurysm. This is a patient who has this fusiform aneurysm, which you can see right here, an aneurysm in continuity with a branch coming out of it. So our strategy in dealing with this was to trap the aneurysm here and then to reanastomose the two ends together, which leaves this branch here, coming out of the aneurysm to which we perform the temporal artery bypass. And so here's the reanastomose primary artery, and you can see there's a void right here where the branch was, but when we inject the superficial temporal artery, you see that fill. So that's just a primary reconstruction by sewing the vessel together after resecting the aneurysm and doing a bypass to a second branch. Here's another example. This is a patient with a fusiform aneurysm of a duplicate middle cerebral artery. And in this case, what we did is we trapped the aneurysm here and here and did a bypass to this branch, very straightforward and simple. Here's the trapped aneurysm and here's the bypass filling that branch. So using this temporal artery is a great option, very versatile and very capable of carrying blood to a single branch or even a large branch with the middle cerebral artery. This is a young boy from Africa, who was sent to us with a subarachnoid hemorrhage from this large fusiform middle cerebral aneurysm. You can see on the 3D angiogram this is the aneurysm, deep, deep in the Sylvian fissure. Our plan here again was to simply do a bypass to the exiting branch and trap the aneurysm here and here and open it and gut it. And here's the intraoperative angiogram. As you can see, the aneurysm is trapped and there is a vascular void, but when we inject the external carotid, you can see that branch filling well, again just illustrating the utility of the superficial temporal artery. Now, sometimes we have to be a little more creative. This is a patient that has a huge aneurysm of the vertebral artery, which you can see on the Cat scan or the CTA. here is the aneurysm on angiography, markedly compressing it, distorting the brainstem, and you can see that PICA is coming right out of the neck of the aneurysm. So there really wasn't an endovascular option that would spare PICA. So if you move to the video here, what we did at this operation is took advantage of the fact there you can see the huge aneurysm compressing the brainstem right here. There's the vertebral artery and PICA coming out of it right here is PICA coming out of the vertebral artery, right at the neck of the aneurysm. So we take advantage of the fact that the two PICA's are right next to each other. Have you lost me?

- No, it's perfect we can hear you great.

- You can still hear me, okay I'm sorry. I thought so. So we take advantage of the fact that two PICA's are next to each other, make an arteriotomy on, on each side, and we will do a PICA-PICA side-to-side bypass. This seems complicated, it really isn't. The most important stitch is this first anchor stitch, which pulls the two PICA's together. And once we pull these two together, then we will use a running stitch all the way around the entire anastomosis, leaving a tail that we can tie to. And so the once we have anchored that stitch, we will sew the inside layer, sewing inside the lumen all the way to the apex of the two PICA's. This technique is also extremely useful for the distal anterior cerebral artery, doing A2-A2 bypass, very same technique through the interhemispheric fissure. So all these sutures are intraluminal. And once we reach the apex, then we sew the outside layer with one continuous suture, leaving that tail to which we can then tie the continuous suture. And that's, that's the completion of it. Now, upon taking off the temporary clips, we put a permanent clip on the PICA that we're going to sacrifice, do an ICG, which shows the bypass filling beautifully. And now we can trap the vertebral artery, the aneurysm above and below its origin since PICA has been reconstructed there's the permanent clip on the vertebral above and below the neck of the aneurysm, aneurysm now is completely trapped. Number 11 knife blade, you know, being used and scissors, and you can see the market decompression to the brainstem when we open the aneurysm sac. Can we go back to the slides please? So here's the intraoperative angiogram showing that bypass filling both PICA's. This is another example of the use of a superficial temporal artery, this is an endovascular failure. This is a young female physician, who had this large, giant middle cerebral artery aneurysm coiled at another institution. And you can see the large mass of coils, but the fact that the aneurysm is obviously not gone. I was very concerned that one or both of these M2 branches would be sacrificed but I wasn't sure which one. So at the beginning of the operation, I dissected out the superficial temporal artery so that it was ready and I could quickly do a bypass if we needed to. We got an angiogram to be sure we had this branch actually, both branches dissected out in case we needed them. And at the time of the operation, if you'll start the video, you'll see the error that we made and how the bypass bailed us out. So here is the neck of that aneurysm to the Sylvian fissure, temporary clip is being put on, and I am stacking fenestrated clips to reconstruct the lumen of the superior division of the middle cerebral bifurcation. In retrospect, what happens is these clips crush the coil mass and put thrombus into the M2 branch. You can see the M2 branch right there and when I doppler it, there was no flow. So now we've got a problem I take the clips off and there still is no flow and I'm worried that I put that a thrombus has gone up into it. So I immediately and rapidly do a bypass using a running suture so that I can do it more rapidly. And this is the benefit of having already dissected the superficial temporal arteries is I don't have to waste time and doing it in a running fashion. You can do that pretty quickly and I was able to rapidly revascularize that branch. Now I go back and open the aneurysm, remove the coil mass. Now I'm protecting the brain with the, with the bypass, but watch now, when I pull this, this thrombus out, you'll actually see that when I clipped this aneurysm, the first time, indeed, I pushed thrombus into the M2 right there you can see the thrombus in the M2 that my clips crushed it into. Now, when I back bleed, there's excellent backflow. Now I can re-clip the aneurysm and the bypass protected me during that time. So now that M2 is filling both anterograde and also filling by the bypass. Now, the doppler as a really good insanation and the final picture, go back to the slides, please. Now you can see, this is the intraoperative angiogram done, with, there is slow flow through that M2, which would have resulted in ischemia, here you see the intraoperative angiogram, the bypass filling that branch that protected me and the final angiogram showing both branches filling. So another example of the utility of the superficial temporal artery. This is another strategy that doesn't involve so much a bypass, but bypass techniques. This is a patient with a thrombosed PICA aneurysm, and what we did in this case, you can see the aneurysm on the 3D angiogram right here you can see the aneurysm, PICA coming into it and coming out of it. And so what we do is that we're going to trap the PICA here and here, cut it here, and re-implant it into the vertebral more proximally. So we're essentially trapping the PICA and re-implanting it. And here you can see the re-implanted PICA that has now been cut from up here and re-implanted into the vertebral artery. Here's another example of the same thing. This is an aneurysm that was, of PICA, that was treated by endovascular coiling, it actually looks pretty good on the original angiogram, but follow up angiography shows that there's marked coil compaction and recurrence of the aneurysm and what we did in this case, is we, again, we trapped the vertebral, cut the PICA and re-implanted PICA back into the vertebral artery proximal to where we occluded it. And you can see the ICG filling PICA through the re-implanted location. And there's the intraoperative angiogram showing the occluded vertebral on the ipsilateral side, PICA reimplanted here in the contralateral side, filling down to the sacrificed vertebral artery. This is a patient that had a large recurrent right middle cerebral artery aneurysm that had been clipped in Detroit, Michigan, 26 years previously, patient had had a stroke with left hemiplegia at the time, but made an actually very good recovery and presented to us 26 years later with a seizure showing that there are recurrences after surgery, as well as after endovascular therapies as well. This is the CT angiogram showing that recurrent aneurysm and the aneurysm clips that have been applied, a quarter of a century earlier. Here's the angiogram showing this very complicated aneurysm and the 3D angiogram and this is a case where again, we felt, very much like the case that you showed Aaron where we did a radial artery bypass graft. And there was no superficial temporal artery it'd been taken during the original operation. And here you can see the intraoperative angiogram showing reversible flow into that and the radial artery filling that vessel that we had to sacrifice. Another indication is to reverse flow in either dissecting aneurysm, fusiform aneurysms those without any necks. This is a patient that presented to us actually with a seizure from mass effect from this aneurysm, this fusiform aneurysm of the middle cerebral artery. Here's the 3D angiogram and our plan was to do a radial artery bypass here and in this case we were going to occlude the artery proximally and reverse flow into this concern that if we clipped it here, we may lose lenticulostriates. And so here is the postoperative angiogram showing the radial artery bypass graft in the neck. And here it is filling the middle cerebral artery and you can see the clip where we've trapped the aneurysm. And here's the delayed one showing that the aneurysm is completely gone and the CT scan showing before and after that the aneurysm is actually thrombosed and now is shrinking. This is a more recent case to show a little different strategy than that one. This is a patient who presented with this angiogram six years prior to us seeing him. At the time he was 26 years old and had this carotid bifurcation M1 segment aneurysm that was treated in Tennessee by endovascular coiling. He was lost to follow-up and came to us with this massively enlarged aneurysm and a recurrent hemorrhage, much of the hemorrhage into the aneurysm itself. Here is his current angiogram. You can see the coil mass here and you can see the patient has good superficial temporal arteries. This is an angiogram showing the mass of the aneurysm outlined by these red dots and the lenticular strides stretched around the large thrombosed portion of the aneurysm. If you look on the 3D angiogram, you can see there's a very high grade stenosis where the small amount of the filling is. So our plan for this one unlike the last case was to do a radial artery bypass here to the M2, but to then occlude the middle cerebral artery, distal to the aneurysm to allow the lenticulostriates to fill, but to create a blind sac that would eventually, we predicted would thrombose. And so, please turn the video on if you would. so at the time of the surgery, the first thing we did after opening the Sylvian fissure widely was to inspect the aneurysm and you can see the massive aneurysm here and the middle cerebral artery coming out of it. This is the radial artery being a fish mouthed, the donor vessel having been selected. I like to put the first stitch in before I put the temporary clips on just to minimize the occlusion time as much as we possibly can in this case there was, it was right out of bifurcation. So we have three temporary clips arteriotomy made with an ophthalmic knife, and here's the first stitch being put in. And so, very similar to what Aaron showed I put an anchor stitch both proximal and distal and leave a tail and then sew one side tie it to the tail. And sew the other side and tie it to the tail. In this case I'm doing it extraluminally not intraluminally. I do the blind side of the difficult side first run that suture and then tie it as we're doing here and then switch over to the easy side, so I can see inside the lumen to be sure that I have a Peyton lumen. And then we'll sew, tie that to the other tail. There's the final stitches being put in. And tying to the tail now as we removed the temporary clips you'll see the back filling, a temporary clip has been placed on the radial artery and now we backfill all the way down to the neck. And when we go to the neck, the shyly vein distender is on there. As Aaron showed, I like to make an arteriotomy and then use the cardiac punch, the cardiac surgeons use to get a nice arteriotomy, this is in the common carotid artery now. Is what we're doing an end-to-side anastomosis, you can see the fish mouthed radial artery being sewn into place with interrupted sutures, down here is my preference. And before putting the final stitch in, we will back bleed, wash it out with some heparinized saline, to be sure there's no air or bubbles within it. Put the final stitch in and then when we release it, you know, we should see it robustly filling. Now we open the Sylvian fissure some more there's the middle cerebral artery coming out of the aneurysm and you see that large lenticulostriate. And I'm going to clip the aneurysm, distal to the aneurysm, but proximal to the lenticulostriates and on the ICG. Well, now you can see it backfill and you can see the lenticulostriate right there, filling beautifully retrograde through the bypass.

- Beautiful work Dan, beautiful work.

- So going back to the slides and what we've now done, is we've created a blind sac. Here is the postoperative angiogram showing the bypass here, filling the entire middle cerebral artery. here you can see the bypass filling all the way down, and you can see outlined in arrows, the lenticulostriates, which were draped around the giant thrombotic mass that is now filling retrograde. And you see that the blind sac now has completely thrombosed and this patient did extremely well, had no neurological deficits whatsoever. So it was a strategy that's a little different from the last case I showed, but one that, that worked well. Finally, one of the indications for bypass is for brain protection during prolonged temporary occlusion. This is a patient, that has this complex middle cerebral artery aneurysm. And I was very concerned that this M2 right here would be compromised during clipping of the aneurysm. So what we did in anticipation of that is at the time of surgery, here you can see the aneurysm exposed through the Sylvian fissure. And this is that branch coming through the Sylvian fissure here and see the aneurysm here. What we did, is I put a temporary clip on that branch and then did an ICG video angiogram. Here you can see one branch filling, but this branch only fills when I take the temporary clip off, so this is the branch that I want to revascularize. So it's a nice trick to show you which branch on the surface of the brain is the one that you need to revascularize. So we did a bypass to that branch, we ended up clipping the aneurysm and I was able to use a fenestrated clip to reconstruct that M2 branch. And the angiogram shows that they were both reconstructed, but during a period of prolonged temporary occlusion, that bypass was filling this branch while I was reconstructing it and would have provided a safety valve had I, had to sacrifice it. So anticipating the need for a bypass, sometimes as an insurance policy, that's worth buying. Even if you have to do a bypass that in retrospect may have seemed unnecessary. It protects the brain both during prolonged occlusion and if you end up having to sacrifice the artery. Here's another example. This is a giant weird carotid aneurysm. You can see on this angiogram, in the three dimensional angiogram, and this case, we did a radial artery bypass and you can see that on the original angiogram, the carotid is occluded. We were able to reconstruct those clips and get flow through it but the bypass protected us for that long period of time during which we were working on it. And this is another example. This is not too dissimilar from the case that Aaron showed, but this is a man with this massive thrombotic aneurysm, they're presented with progressive hemiparesis. You can see the mass effect on the brainstem. This was not a carotid bifurcation aneurysm, but a proximal carotid aneurysm, only a portion of which filled angiographically, but a huge mass depressing the brainstem. I really wasn't sure if I would be able to reconstruct this, but I knew that if I was, it would take a prolonged period of time. So here's the Sylvian fissure on the left side, here you can see the vessel we choose for our bypass. This is the arteriotomy being performed. The radial artery graft being prepared and sewn into place here. You can see this was an endoscopic artery. Here's the arteriotomy in the common carotid artery and the proximal radial artery anastomosis, after a fish mouthing and sewing it in proximally to reconstruct this. We then were able to actually clip the aneurysm, open it up and take all the thrombotic material out of it. But during that time, here's the bypass. There's the proximal this is the intraoperative angiogram showing the bypass filling proximally and filling the entire middle cerebral artery. And during the time that we were able to reconstruct this, which was well beyond what the brain would have tolerated so protection during prolonged temporary occlusion. Let me end by showing a couple of cases to demonstrate that microsurgery and endovascular therapies are not mutually exclusive, they actually can be complimentary. This is a young man, that has this fusiform middle cerebral artery aneurysm. He's in his twenties. And you can see there is a middle cerebral branch coming right out of the dome of the aneurysm. And so any endovascular option for this, we were afraid would occlude this vessel and I really didn't think we could clip this aneurysm very successfully. So what we did is went in surgically and identified these two branches of the middle cerebral artery for potential bypass options. This again is an ICG done with a temporary clip on that artery coming out of the aneurysm. You see this branch filling perfectly, and you see this big void. When we release the temporary clip, you see this fills. We know this is the branch that's coming out of the aneurysm and that's the branch to which we do our bypass. There's the branch being isolated. There's the bypass completed. Now, postoperatively you can see that I've clipped the branch coming out of the aneurysm. You can see the pipeline device being put in and within minutes, it's already starting to thrombose and the external carotid injection filling that branch that came out of the dome of the aneurysm. And finally, just one other example. This is an aneurysm, massive aneurism on the patient's right side, who had on the left side, a smaller intracavernous aneurysm. And we were concerned about what would happen to this if we didn't revascularize the patient. So we did a radial artery bypass graft on the patient. You can see the graft in place right here, the proximal anastomosis, and here is the aneurysm beforehand filling. It was so big I couldn't really get proximal enough to put a clip on it and so after the bypass was done, you can see the bypass fills the middle cerebral artery. We then brought the patient back and endovascularly sacrificed the carotid, right at the aneurysm, you can see the coils here and here's the final result, the bypass and the aneurysm completely eliminated by endovascular techniques. So just some thoughts about the different uses for bypass, both the superficial temporal artery, the more high flow bypasses and the indications for which I think those bypasses still deserve consideration.

- Incredible work Dan, truly amazing and mesmerizing. Very, very difficult series of cases requires many, many years of experience. I think that's something we should keep in mind that doing cases of such complexity requires decades and decades of hard work and belief in technical excellence. So thank you again, we really enjoyed it. I really enjoyed it personally. Let's go ahead and answer some questions. You can see them at the chat function as well. Somebody is asking what were the strategy, Marcio Fava, is asking, what would be the strategy if they're lenticulostriates, instead of wrapping around the areas are encompassed within the giant aneurysm?

- I'm sorry, I just don't see that question. Could you repeat that?

- It says what would be the strategy if they're lenticular straight arteries, instead of wrapping around the areas that are encompassed within the giant aneurysm?

- Yeah, yeah. In that case, I would have occluded the aneurysm proximally and allowed the aneurysm to fill retrograde. So I would have reversed flow in the aneurysm as opposed to creating a blind sac, like the case that I showed right before that. And having said that, that is still a risk as that aneurysm thrombosis, which it generally will, there is a risk that the lenticulostriates may thrombose, but I think by reversing flow, you have a better chance of keeping those lenticulostriates open.

- There is a question, another question from Allie Tabacky, what factors must considering choosing between low flow versus high flow bypass? That's a good question Dan.

- It's a very good question. And there are both objective and subjective means of doing that. The device that Fatisha Bell has created the, the MR, Aaron, you know the name of the device, I'm drawing a blank on it right now.

- Go ahead. I know it too.

- Fati has created this wonderful tool that actually allows you to measure that I have not used that I have no experience with it, but certainly looking at his experience. I think that is a great tool to help with that decision. The other ways to do it, kind of the poor man's way of doing it is either with balloon test occlusions, which I have mixed feelings about. And just intuitively trying to determine what the amount of flow might be that, that you need. I think you can accomplish a lot with one or two superficial temporal arteries. I think more than what we used to realize we could, but I would say that I error somewhat on the side of providing too much flow, rather than not enough. I dunno Aaron, do you have other thoughts about how you make that determination?

- You know, I think anything that involves flow, proximal to the bifurcation, we have a lower threshold to do a high flow bypass. It's just a lot of more cortex you have to support. I think it comes with a lot of judgment, as you said, and experience, but overall, the STA's can be very low flow even a double barrel can be a challenge. The radial artery is so easy to do and so fun to do, to be honest, that it's just very, it takes very little time if their radial artery is there and it's, you can almost do the whole thing in 40 minutes. And it provides so much protection and if there's extra flow, I think there's always accommodation the brain will make for it. So we have had a lower threshold to do a high flow bypass. May I ask Dan if a patient passes a balloon occlusion test, would you say that it's okay to occlude the internal carotid artery? Or would you still perform the bypass?

- If I'm going to perform a bypass anyway, I don't do a balloon test occlusion generally, because if it's not going to change what I'm going to do, it's just another test that has a small, but some risk. And so I always ask myself, how is this going to change what I'm going to do? So as an example, that nine-year-old boy that I showed that had the giant cavernous aneurysm. I'm not gonna do a balloon test occlusion on him because I'm gonna replace his carotid with a high flow bypass regardless because I don't want him to live the rest of his life with one carotid. So there's no reason to do it. If I had an elderly patient that had a proximal carotid aneurysm, for which there wasn't a good endovascular option, and I'm considering sacrificing the carotid it may be very important. That's a patient where a proximal occlusion of the carotid alone without a bypass may be a perfectly adequate option. I think a balloon test occlusion combined with SPECT, some objective means of measuring blood flow, is reasonably accurate in predicting whether a patient will tolerate carotid occlusion. It's not infallible by any means. And so I think the first step is asking yourself, what is this test going to provide in terms of information that's going to change what I'm going to do? And oftentimes it's not going to change anything. So I don't do a balloon test occlusion. Having said that, going back to the previous question, I have used that on occasion to determine whether I could get by with a superficial temporal artery, as opposed to a radial artery in a patient where again, depending on age and other factors, I may feel as a much safer option for them.

- Yeah. I agree completely with you, Dan, an acceptable temporary balloon occlusion does not exclude the need for a high flow bypass, especially in a young individual. I think that's the take away message because I think there is up to 10, 50% of people who, very nicely, even our perfusion scan have a symmetric perfusion at the level of the balloon occlusion test, but still have a stroke if you occlude their carotid artery. So that's something very valuable to remember. And I think we both agree on that. This is a good question. Do you support the cost study regarding bypass for ischemic stroke Dan?

- Well, I was part of the cost trial, I was involved in it. And when you say, do I support it? What the cost trial essentially demonstrated is that from the time that that trial began and using the data that that was collected at Washington University, based upon what the medical management of stroke was from the time this study was started, until it was finished, the medical management of stroke improved so much that the trial would never be able to demonstrate, would never be powered to demonstrate a benefit of bypass. It never, it didn't really demonstrate bypass wasn't beneficial. It just didn't demonstrate that it was, but it was powered based upon what the expected rate of stroke would be from several years earlier and our medical management improved. So my takeaway message from cos is the following, is that indeed I believe very fervently there are a group of patients, a relatively small group of patients with carotid occlusion that have low flow, that absolutely benefit from a bypass. Do we have any objective evidence that's true? We certainly don't have a randomized controlled trial that demonstrates that's true, but my institution, my stroke neurologist, every year refer a handful of patients that have failed medical therapy, are still symptomatic and they believe, as conservative as neurologist can be. They still believe that those patients benefit from a bypass and I can give you all kinds of anecdotal evidence of patients that just do great when they, they get that temporal artery supplying a little bit extra blood to their brain. So, you know, it depends upon how you interpret the results. It was a negative trial. I mean, it didn't demonstrate any benefit of surgery, but if you really understand the reasons why it also didn't demonstrate there wasn't a benefit. It just, it never, the trial never would've been able to randomize enough patients to actually prove what we wanted to prove. So it's unfortunate, but I do think there still is a role in ischemic stroke.

- I agree with you completely on that, it's very well said. I will go ahead and do one last question here. And it says, have you had any case where you did a cervical occlusion with this previous test that show they could tolerate and later on needed a bypass, even a low flow?

- Yes, I have. That is, unfortunately, most patients you find out, they need a bypass after you've occluded the carotid it's too late. You only find out when they have a massive stroke, but I have had, I can think off the top of my head of a handful of patients, no more than a few that after a carotid occlusion had symptoms of low flow estemia, TIA's, but didn't have a massive infarction where we rapidly change our strategy and took them back to the operating room for a bypass. So, you know, you you're much better off, I think, anticipating doing the bypass, maybe if it's not necessary, as opposed to trying to do it under less than ideal circumstances, but it is an option. If a patient has evidence of low flow ischemic symptoms after therapeutic carotid occlusion, you can still do a bypass later, hopefully before they've suffered irreversible ischemic injury.

- I agree. Well Dan I'm sure there's a lot more questions, but due to the sake of time. Number one, I want to thank you for your incredible lecture. Number two, huge legacy as one of the very few Master Neurosurgeons in North America, congratulate you. And number three, to let you know that we both trained at Mayo clinic, I know you did for your fellowship and I did my residency. So I, God bless Dr. Thor Sundt and his soul. Great man, great legacy, and we truly miss saints like him these days. So with that, I wanna, again, thank you for being such a great colleague and mentor for many, many young neurosurgeons, and look forward to working with you again in the future sessions of your tour. Thank you again.

- Thanks Aaron, thanks everybody.

- Thank you.

- Have a good day.

- You too.

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