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Bypass Techniques for Anterior and Posterior Circulation Revascularization Free

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- Colleagues and friends, thank you for joining us for another session of "The Virtual Operating Room." My name is Aaron Cohen. I'm honored today to be joined by Dr. Bill Couldwell, Chairman and Professor at University of Utah. Doesn't need any introduction. Bill is a master surgeon in his own class. He's not only an incredible surgeon, really a dear friend, but he among the very few that not only has changed the current status of neurosurgery technically, but has mentored so many to change the future of neurosurgery. That's something that is very exceptional and unique to Bill that I have personally very much benefited and enjoyed from for many years that Bill and I worked together. Bill, it is truly an honor. It's really been one of the greatest honor of my career to work with you as a amazing surgeon, mentor and a dear friend. Today you're gonna talk about the technical nuances of revascularization surgery, something that's important but less and less being used. But keeping the art alive is so important for those rare cases. Excited to learn from you, and please go ahead.

- Thank you, Aaron, for that kind introduction. It's really an honor to be able to contribute to the Atlas. And I wanna thank you and Luke for making it such a great system and a great platform for all to be educated around the world. Well, I just wanted to talk about my personal philosophy about bypass surgery, revascularization surgery, and some of the technical nuances, and some of the things that I've learned and some of the mistakes that I've made over the years. And much of this has been published, but we are just getting a large bypass series together that will have... I don't have any significant disclosures. I have one patent and I get royalties. But I want you to consider these cases. So here's a case where a partner of mine removed a middle fossa meningioma in 2000. And the scan was clean postoperatively. Then patient presented with recurrence of tumor in the pterygopalatine fossa and in the temporal fossa here. And then you can see over time the tumor grew and now is involving the region of the base of the skull at the midline and it's threatening the carotid. And when these cases can recur, especially these meningiomas, they can grow down into the face. And it's important to be able to manage these surgically. And we use different approaches to obviously remove the tumor when it recurs down in the midline and down into the face. But you're gonna have to at some point deal with a carotid artery. So here's the case where now the carotid is being encased by the recurrent tumors in the sphenoid, in the pterygopalatine fossa, and we have to decide whether we're going to revascularize the patient or not. And in this case, we're had enough redundancy, we were able to just most of the carotid. But you'll have to decide if you need to replace the carotid or do an interpositional graft to replace the carotid. This is another case for you to consider. This is a a woman, very common problem, that has a tumor in the cavernous sinus. It's a meningioma. And it's a very common area for them to be left obviously in place to preserve cranial nerve function. And this patient had radiosurgery at a very renowned center, and I started following her several years after her radiosurgery. And you can see here that the carotid is narrow already. And remember that we use radiosurgery to treat AVMs; it cause neointimal hyperplasia and thrombosis of arteries. And this can occur even at low dosages used for treating meningiomas. And she presented with aphasia and this large intraparenchymal hemorrhage. And you can see that she's had a carotid occlusion and likely has bled into her infarction. So losing a carotid is not a benign thing. And I think we don't see a lot of the complications acutely with carotid sacrifice. And I'll talk about that. But let's talk about bypass first. Basically performed by Yasargil and Donaghy in Vermont in animals first, and initially performed for high grade stenosis or occlusion of ICA or the MCA. But now the surgical indications are broader, but the frequency we do bypass is less because of the advances in endovascular. The COSS study, which was a landmark study which looked at carotid occlusion, demonstrated that STA-MCA anastomosis did not provide an overall benefit, mainly because of a much better than expected stroke recurrence rate in the medical group. So the medical treatment had been improving all along. And also there was a significant postoperative stroke rate, which is very important because if you're going to do bypass, you need to make sure that your complication rates are low to be able to justify the use of a bypass. These are the events, complications related to the surgical side. So there was a lot of less enthusiasm about STA-MCA bypass after these studies, but we know that we need to replace the carotid in some instances with aneurysms or with tumors. And in my mind, a high flow bypass may be necessary in planned carotid artery occlusion or sacrifice. We use a selective approach to perform bypass in such patients. The risk of carotid sacrifice is important to review. It causes earlier late ischemia. Patients may not get ischemic until they're stressed, until become dehydrated, for instance, or hypotensive. Development of aneurysms in other vessels. This is something that we saw many years ago with the routine use of the Selverstone clamp for Hunterian ligation for giant aneurysms of the carotid. And we would go ahead and ligate the carotid in such cases. And then over time the contralateral carotid and the basilar circulation would develop more aneurysms. And I'll talk about that in a moment. And then obviously if there's tumor left in the carotid wall, there's oncological issues and risk of rupture. Risk of aneurysm formation, it's interesting, there's a mean time period of one day to 20 years, but a mean of 7.5 years. And you can see the literature on this, and it's not a benign problem. The other issue you have is that the balloon test occlusion is an imperfect tool, and a false negative balloon test may fail to identify those at risk of sacrifice complications. So 10% with decreased cerebral blood flow on a Xenon-CT despite passing the test. And 5% of patients will develop neurological deficit after carotid sacrifice even if you pass the balloon occlusion test. So therefore, in my mind, this is the magical number, because you need to be able to do a bypass in these patients with a lower risk than that. And if you can't achieve a lower risk than 5% of complications then you shouldn't do a carotid sacrifice or a carotid sacrifice and a replacement in those patients. And we use a BTO with diamox challenge and a CT perfusion imaging to select our patients. And also consider risk of carotid rupture if tumor is left in the wall. Up to 18% of some cases in the head and neck surgery literature, the risk of bypass is less. There's roughly 7% mortality and 17% morbidity with carotid artery sacrifice across the board. And so I use this as a simple factor. My risk is less than 5%. So in young people with a long life expectancy, I replace the carotid with benign disease. So here's my personal selection of patients in cases of tumor resection, if it's a malignant tumor with an oncological resection, if they fail BOT, I replace a carotid, but I do not do a bypass if they pass the BOT because they're shorter life expectancy. But if you have a benign tumor and a long survival, then I replaced the carotid. So this is a picture of Thor's Sundt, the famed chief from the Mayo Clinic, who was really a pioneer in these high flow bypasses in the early eighties. And if you think about a conduit for a bypass, it's important to understand what kind of flow you're trying to deliver. And initially this is what you're going to get. And the reason I say initially is because we all see these superficial temporal arteries, they can actually get quite large and robust over time when there's demand on them and deliver much more than this in a delayed fashion. But the superficial temporal artery is really a low flow bypass. The radial artery in my mind is a mid flow bypass, and the saphenous vein is a higher flow bypass. And if I'm replacing a carotid, I use a radial artery or a saphenous vein. I'll show you, I do not rely on a superficial temporal artery to replace a carotid. So the interesting work recently, the game has changed obviously for thrombectomy, for large vessel occlusion. And it was really 2015, there was five trials that came out that demonstrated the number needed to treat was remarkably small to prevent one functionally dependent outcome, was 5.4, which actually supersedes the number needed to treat for MI prevention with aspirin and statin, which we routinely use. So it's a very effective treatment, and this has been the most dramatic change in management of ischemic stroke in our careers. So what are the current indications for cerebral bypass? For flow preservation, so replacement for aneurysms tumors replacement, rare, indications are decreasing the endovascular era. And then for flow augmentation, and it's important to understand the two different mechanisms that we use these bypasses. In moyamoya disease, it reduces the re-bleeding risk from hemorrhagic moyamoya and it also improves the ischemic outcome for these patients as well in those numbers you can see there on the slide. And then the steno-occlusive cerebrovascular disease is a more controversial indication, but there is a group of patients that were not identified with a COSS trial, for instance, that really benefit from this. And we have a number of patients and we see a lot of them here where the patients have terrible steno-occlusive disease and they can't get their head off the bed or if their blood pressure drops they become symptomatic. So those are the ones that we usually use or choose to perform augmentation. So as I mentioned, for the replacement, I really concentrate on a radial artery or saphenous vein unless it's a distal vessel from an aneurysm, and I'll show you videos on that. But for augmentation of ischemic disease, an SDA is a great conduit because it's a fairly low risk bypass to perform. You interrupt a distal M4 vessel in most cases. And it's very well tolerated and it's a simple thing to do. So you need to decide if you're augmenting flow or replacing flow. But let's talk about steno-occlusive disease. So this is at a long history. There was a important study performed in "JAMA" also in the an EC-IC bypass trial in 1985 that showed that there was not much efficacy. But we know that this group of patients, they're symptomatic despite medical management, not amenable to endovascular intervention or hypoperfusion. This has been nicely reviewed in this paper, but they showed that these particular patients, the stroke rate was less with bypass. So there is, I think everybody appreciates that there is this group of patients that should be considered for bypass. What's the optimal revascularization approach for moyamoya disease and steno-occlusive disease? Well, we've just published this series, and I want you to think about some of the technical issues that I'll talk about here and what we've identified as important factors. So we all think about the direct bypass using the STA, usually the parietal branch, but also the frontal branch in some cases. The parietal branch is the go-to branch if you can use it because it puts you directly over a great recipient artery. It's a very straightforward and simple operation and it's very easily trainable for the young people, and it's on the surface of the brain, so it's easy to suture the vessels. The direct, and then you can do an indirect as well. And I'll show you how we do our indirect bypasses. But we don't dichotomize into a direct versus indirect. We use an approach where we do both together. The direct is most commonly performed for steno-occlusive disease, and which branch should you use, and should you do an indirect? And we address that in this paper. And what you find in some cases, what we saw in this series, and we looked at a series of just over a year of my bypasses and some of these bypasses became extremely robust, you can see here. And some of them maintained patency, but the indirect was dominant. And in fact the frontal branch here is dominant that we didn't use for the bypassed recipient or bypass donor. So what we looked at is just over a year of bypasses, for steno-occlusive disease, not amenable to endovascular intervention and with hypoperfusion on imaging, and that's again CT perfusion study. We also looked at some moyamoya patients and we looked at the baseline demographics, perioperative details, et cetera, and the outcomes. We looked at the Modified Rankin Score and the patency grade of the bypass. And we use the grading scale here, no patency grade one less than a third of the MCA territory grade two, one third to two third or grade three greater than two thirds. And we then looked at the outcomes. And I'm gonna show you the bypass technique that I use for these patients. And this is both for moyamoya disease and for steno-occlusive disease. And we'll choose the parietal branch if we can, if it's of decent caliber. And as you'll see in the videos, I like to have a recipient branch that's greater than one millimeter, but we'll go down to .9 if we have to. And we've had very patent bypasses at .9 millimeter. The real key is the recipient branches. So what we do is we aspirin peri-op, we start this preoperatively. Incision over the parietal branch is preferred. if you mark seven centimeters above the EAC in the sylvan fissure, you'll find a decent vessel and dissect the STA under the microscope, divide temporalis about a four by five craniotomy. And then we pie-crust the dura, and I'll show you that in a video, and then we prepare the STA. I give a shot of about 5,000 heparin just before we cross clamp the distal branch. We use an end-to-side anastomosis and then we do EDAMS as well. We do the indirect component of the bypass in a hinged cranioplasty. So let me show this on a video. And this has been recently published.

- [Narrator] This case demonstrates the technique that's used for a combined direct and indirect bypass. We have a 68-year-old man with a history of coronary artery disease and other vascular disease with a left ICA occlusion and recent left MCA watershed infarcts. He had right arm weakness and aphasia despite maximum medical management on dual anti-platelets. His exam demonstrated a right hemiparesis with dysarthric speech. He improved with trace right upper extremity weakness and he was otherwise neurologically intact. His angiogram here demonstrates a complete occlusion of the left ICA at its origin. And the MCA was filling from the Acomm, and the ICA is reconstituted at the petrous segment from external collaterals. His profusion imaging demonstrated increased transit time in the left middle cerebral artery with preserved blood volume, and his MRI had scattered additional infarcts but no large strokes. He was recommended to undergo a left MCA revascularization with combined direct and indirect STA-MCA bypass. He's placed on the table and the left STA parietal branch is traced out with a doppler. We then cut down directly over the STA and separate the STA from the temporalis fascia with the cuff surrounding it. We place dilute papaverine over the vessel to avoid vasospasm. And then we plan our craniotomy flap. We identify the temporalis muscle and incise the temporalis muscle along the center of the opening and used periosteal to expose the bone, replace a single burr hole inferiorly at the end of the incision and another burr hole superiorly and lift off approximately at three by four centimeter bone flap. We open up the dura in a petal arrangement to be later used for revascularization. Here you see the vessel was left intact. We identify a recipient vessel, preferably in the temporal area of suitable size to accept our bypass. We remove the arachnoid over the recipient vessel for a distance of approximately one centimeter. Small side branches are ligated after cauterization. Place a rubber dam and ensure the vessel is one millimeter in size to be able to accept the donor STA. We clean the distal end of the SCA, bevel it and spatulate the end. We place temporary clips over a centimeter distance and perform an arteriotomy using 11 blade. This is extended using micro scissors and we use a dilute solution of methylene blue to help aid visualization of the arteriotomy wall. So we try to aim the vessel proximally and put a toe and heel sutures in first using 10-0 nylon suture. These are placed in interrupted fashion. We prefer to use interrupted sutures to avoid cinching the anastomosis site. Series of interrupted sutures are placed very precisely. And after three to four sutures on each wall, we remove the temporary clips including the clip on the superficial temporal artery. Dilute of papaverine is in place again, and we ensure patency of the graft using an ICG. The pedals of the dura are then inverted to allow a dural synangiosis. At the completion of the dural inversion, we close the muscle directly over the exposed cortical surface. Sutures are placed closely to ensure hemostasis. The bone flap is then placed in a hinge fashion from a superior burr hole cover, and small dog bones are placed but not facet. The wound is closed with interrupted vertical mattress sutures. These are left in for two weeks. You can see the bone flap initially, and one month later after atrophy of the muscle, it is settled in. Here's an angiogram performed six months following the anastomosis demonstrating the importance of the direct bypass. The patient improved and has remained neurologically stable since the operation was performed two years ago. Thank you.

- A couple of important points about the technical aspects of that. So we used 10-0 suture, 10-0, nylon suture on the smallest needle. And I train a lot of people, and when people are learning how to do bypass, I prefer to do interrupted suture. And what we do is we, if you anchor the toe and the heel well and then split the distance at every suture point, so make sure that you put your suture midway between each of those sutures and then keep doing that, going midway between each suture, you'll never end up with a dog ear. So it's much quicker. And if I was doing it myself, I would just do a continuous running suture. But if you're training people, that's the simplest way to make sure that the bypass gets done excellent. And I think that this is an important role for us now because I think the senior people like myself with a lot of experience we're trying to train the next generation and we want them to be as safe as possible. And as well as I mentioned in the video, it does not cinch the bypass if you used interrupted sutures. The other point is, is that there is two indirect mechanisms with this bypass. There's obviously the dural inversion and the muscle that you can see that we closed right over the brain, and then the bone flap was outside the muscle. So we do that operation and we wanted to see what the results were and the indirect versus direct. And I'm gonna show you some interesting results. Since I think this is the first study demonstrating both techniques in these types of patients and what we found. And what we found in some cases, obviously in some patients there's co-equal anterior and posterior branches of the STA, in some the parietal is dominant and in some the frontal is dominant. So there is a difference. And so we need to choose which branch we're going to use as our primary donor vessel or use both branches of course. So when we looked at this, we used parietal branches for the direct and 88% frontal branch in three cases. And the parietal branch as I showed you in that video is directly under the incision that we make. So that's easy. If we use the frontal branch, it's too frontal to come directly on it, so we lift the flap coming up the parietal branch and go forward and then harvest the frontal from underneath the flap, that's more cosmetically acceptable, and then swing it back and use it and find a recipient vessel. We had no strokes and we had two transient aphasia and one with intraparenchymal hemorrhage that was removed and the patient did fine. This is the revascularization outcomes, 96% direct patency, and the MRI score reduced. We had three hemispheres with strokes, one non-patent direct bypass, and one, watershed stroke and 2/2 had dehydration. And I wanted to show you a couple of interesting case examples. If you look at the preservation of the non-donor STA branch. So the question has arisen is what do you do with a non-donor branch if you're not going to use it? Do you ligate it, or do you leave it intact? And we found that even excluding STA, the non-donor branch, we found that the non-donor branch persisted, and in some cases remained and became more dominant. And I think it competes a little bit with the donor branch. So I think that's important to recognize. So we like to use the larger branch if we're just gonna use one, or we'll use both branches. It did not independently affect bypass grade, but there was a trend towards increased indirect grade with preservation of the non-donor branch. So that what happens is, is if you leave the non-donor branch open thinking that it's gonna be good for the scalp to heal, it may compete with your direct bypass and your indirect will then become more important. And that's what we found was not quite statistically significant in this group of patients, but I suspect it would be with the higher numbers. And the interesting thing was that the more perfusion deficit you had, we found that there was a large perfusion deficit and with frontal perfusion sacrifice we had very robust bypasses. So if you really need flow, you do a direct bypass, it really actually works very well. And it helps if you don't leave the other branch to compete with your STA branch that you're using for your donor. And I know there's a lot in this, I appreciate it. But what we found basically is, here's a couple of case examples which demonstrates these things, is here's a 41-year-old woman with moyamoya disease. She did a direct bypass and an EDAMS, the parietal branch and we reserved the frontal branch. The six month angiogram developed grade one filling from the direct bypass and more direct filling from the EDAMS, okay? So she had a very dominant EDAMS over time. The key findings from this study is that we actually defined very good safety for this combined approach to all these patients. So we don't dichotomize which patients get a direct versus indirect. We try to do both in all patients. There's inverse relationship between the direct and the indirect flow rates so that if the direct becomes dominant then the indirect is less. And if the direct, even if it stays open but it's not very dominant, then the indirect becomes the more dominant. The influence of STA branch management. So we don't want to have the branches compete with each other to the scalp versus the brain. So it might be best to actually sacrifice the branch, and we're doing a study on that right now, on the non-donor branch, or potentially use both. But then that doubles the risk, if you use two bypasses. Potential to tailor the revascularization based on the perfusion deficits. So more to follow. But I think it's interesting some of the nuances in that. I think the brain is seeking a certain amount of blood flow and it's going to achieve it through a direct or indirect and if it really needs a lot, it'll really suck on the direct and the direct will become very dominant. But if it is doesn't have a huge perfusion deficit, then I think what happens is the indirect becomes more dominant over time. It's very interesting. So what about posterior circulation? So here's an interesting case. Here's an eight-year-old girl with a spontaneous ICH. I've never seen this before. This has been published this case a big cerebellar hematoma in a moyamoya disease case, which is very unusual. You can see the extent of moyamoya vessels around the brainstem. And what we found here is that she had developed moyamoya changes in her distal basilar, which is quite unusual. And she actually had occlusion and she was refilling the top of the basilar through the superior or the anterior circulation through moyamoya vessels. And so what we did in this case is we did a combined bypass-

- [Narrator] Presented with-

- With a standard STM-CA.

- [Narrator] Hemorrhage. And this hemorrhage was resected emergently with good neurological recovery. On preoperative imaging you can see the hemorrhage that occurred in the cerebellar hemisphere. The vascular imaging demonstrated engorgement of vessels around the midbrain and the base of the skull. Angiography revealed moyamoya changes both in the carotid and the basilar circulation with an occluded basilar artery just above the ICA takeoff. The top of the basilar territory was filled exclusively with moyamoya vessels. The patient was positioned supine with her head turned to the left. And we'll start off with an ST-MCA bypass with an indirect bypass using temporalis muscle and dura as well. Tissue. We spatulate the artery and-

- [Bill] So I'm gonna move on. You've just seen that.

- [Narrator] Having performed the direct bypass, we now perform the indirect bypass. So we start by cauterizing the dural edges and inverting the pie cuts of dura underneath the edges of the bone flap. We invert the dura and then replace our bone flap and a-

- [Bill] So that was the STM-CA. And now we're gonna give another boost to this young person.

- [Narrator] One month later we'll perform an indirect occipital bypass.

- Occipital bypass.

- [Narrator] This is the occipital artery traced out. And dissect up the occipital artery over the occipital lobe. We then perform a craniotomy beneath the occipital artery. After the craniotomy is lifted, we open up the dura and again invert the edges of dura and lay the artery directly on the brain. Bone flab is replaced. Six months later, postoperative imaging demonstrates the direct bypasses widely patent and the indirect bypasses are also contributing to flow to the hemisphere.

- So this is an important point. We did a direct bypass through the STMCA and we did an indirect bypass through the occipital artery. And the indirect bypass was very dramatic. So these young people, we didn't have a large enough vessel to anastomosis to do a direct using the occipital bypass, but we've really helped her flow to the posterior circulation indirectly through the moyamoya vessels coming from above because the basil was occluded, as I mentioned.

- The moyamoya changes are stable, the patient did very well, remains intact neurological condition represented.

- So I think there's a lot to be learned and I really want to call out Cepi Hamil and Johnny and Fadi Charbel for their work on this. And I think this is the sort of the new territory is the posterior circulation in defining which patients need to be revascularized. And you can use this in Enova software that they've developed on the MRI to determine in a quantitative fashion what the blood flow is. But some of these patients are really dramatic, and this is an example of how you can revascularize the posterior circulation. And I think people don't appreciate this is actually a really a low risk bypass, what I'm going to do here, is this patient has bilateral vertebral occlusions and she's getting flow through muscular branches in her neck that revascularize the vertebrals just below the V3 segment. And so what you can do then is you can augment the flow just like we're going to do with this like we do with an STMCA to the posterior circulation through the extra cranial vertebral arteries. And this is a fairly low risk operation if you think about it because she's getting muscular branches already and you're just augmenting the flow in the same fashion that we just showed with an STMCA. And what we'll do is an interposition graft and we'll have our vascular surgeons help us with this.

- This is 60-year-old woman who presented with dizziness, vertigo and syncopal attacks, which were triggered with turning her neck. Angiography demonstrated bilateral vertebral occlusions at the origin with the distal vertebral artery reconstituting with muscular branches bilaterally. You can see the V3 segment filling nicely. We'll perform a subclavian artery to vertebral V3 bypass, we'll harvest the saphenous vein along the part of the leg that matches the diameter of the vessel that we're trying to replace. And we'll do a far lateral approach to V3. The saphenous vein is harvested endoscopically, then we'll proceed with subclavian artery exposure. This is performed through a four centimeter long incision and a direct cut down on the subclavian artery. The thyrocervical trunk is used as the proximal anastomosis site, given the fact that it's a perfect size match for the saphenous vein bypassed inner position graft. We now perform a far lateral approach to expose V3. We remove the adventitia off the vessel and expose it within the J groove on C1. We prepare to pass our interposition graft. We use a chest tube to pass this, cut to size and perform our anastomosis. And then decide anastomosis it performed using interrupted sutures at V3. And now we've prepared the thyrocervical trunk. The size matches beautifully, and we'll perform our anastomosis using interrupted suture. After completion, we back bleed and then remove the temporary clips. Hemostasis is secured. We proceed with closure and a postoperative angiogram demonstrates a patent bypass, and her symptoms improved immediately.

- So that's an option, one option. You can swing the interposition graft also from the common as well. But I just wanna give a couple of examples of bypasses and aneurysm surgery and then wind this up. The limitations of aneurysm treatment are is that we've got stent-assisted coiling, we've got flow diversion and surgical clipping, but we need a more effective and less invasive obviously treatment, and we still need microsurgery. Case in point, look at this aneurysm. This aneurysm grew over a period of eight years between two MRIs. And when the angiogram was done, complex middle cerebral aneurysm, there's a branch coming right outta the dome. So what would you do with this? Well, there's no endovascular treatment that I know that could treat this adequately than even we have right now. So what we'll do is we'll explore this aneurysm, and my thought was that if the angiogram was really valid and it was telling us exactly the anatomy there, then we would revascularize to that branch coming outta the dome. And indeed the aneurysm looks exactly like the angiogram showed us there's the branch coming out of the dome itself. So we'll do an STA bypass to that one branch coming out. STA's beautiful option. Now, you could do a local transposition of another vessel, but I'm going to make a point here with this in another case, in that if I can, I like to do EC-IC bypasses to avoid the risk of putting another intracranial vessel at risk. And I'll show you another example of that in a moment. So we'll do a bypass, notice on branch this vessel branches into two right after it leaves the aneurysm, and I close only one branch to do the bypass so I don't disconnect it. So we reduce the flow only to the one branch during the anastomosis. Bypasses patent, we'll go ahead and cut that off since it's revascularized and then go ahead and clip the aneurysm. So this is an example of I think in a case where there won't be an intermediate endovascular option that will be really good for this over time, and we're going to need to maintain these types of skills to be able to do these operations to be able to treat all these patients. This is unusual, but this is one such example of that. We'll do an ICG here and demonstrate that everything's patent, and I'm using a another small clip to take care of that dog ear. And the ICG looks good. Interesting case, what would you do with this? Maybe there's an endovascular option for this. Here's a distal SCA aneurysm in a woman who had a subarachnoid hemorrhage a month ago. And they did take a look endovascularly in another institution and they didn't wanna treat it, so she's back. And what we'll do is we'll take a look and see what we need to do. And just an example of maintaining these techniques really gives you the option of treating these in different microsurgical ways. And what I'll show you here is that we'll do a resection of the aneurysm and a anastomosis of the vessel and I'll show you a little trick that I use to help get a little bit more room. And you can use this in different areas. We had a meningioma the other day where the anterior cerebral was invaded by the tumor and we resected that part of the artery and used the same technique. But so we're dissecting this previously ruptured aneurysm and then what we'll do is we'll go back to normal artery, cut the artery and then re-anastomose the vessels. Now, what we'll do is we'll dissect along the anterior cerebral in both directions. And what I'm doing is I'm pulling out the artery and giving myself more room so that I can make the ends meet. And then we'll go ahead and reanastomose it. This is 10-0 suture, 10-0 nylon, smallest needle. And we'll go ahead and reanastomose the anterior distal cerebral here. These are more difficult because they're deeper bypasses. So a lot of experience with the superficial temporal is, is great. It gives you the requisite experience and there's the anastomosis. Occasionally you'll have to bail out a endovascular misadventure. Here's one with a flow diverter of a giant aneurysm of the internal carotid. And what we'll do here, this is what happened is it lost its footing distally and it's like a garden hose now going off in the aneurysm. And so what we'll have to do is we'll do a high flow bypass around it and then fetch the pipeline stent from the artery. It's right by the ophthalmic takeoff. And I wanted to preserve the ophthalmic takeoff here. And so what we'll do is we'll go ahead and do a high flow bypass distally and you can see here the graft. And then we'll go ahead and once we have our high flow bypass, we'll open up the aneurysm and remove the pipeline stent. Now, it's interesting on these cases, because this was actually about four days after the pipeline was deployed and it was still loose in the aneurysm. And so when you pull it, it actually elongates and pulls itself off the wall of the artery, and so it comes out like butter. It was really simple. And there's the pipeline. So again, we'll just go ahead and then we can just take the aneurysm just below and just above the takeoff of the ophthalmic. So ultimately what you're left with is a situation where you've got a high flow bypass from the carotid going into the distal internal carotid there and doing that. So when you talk about flow replacement, you're gonna talk about radial artery grafts or saphenous vein. The radial artery is easier to use, it's technically easier, it's smooth, endothelium. You don't need to worry about the valves and you need to reverse the flow through the vein. The one problem that you have is this spasm that can occur postoperatively, and we use a pressure to distension technique to dilate the thing before we put it in. And now it's more popular for CABGs. The saphenous vein has one advantages that you can use the ultrasound on the leg defined at exactly the caliber of graft you want to use to replace the artery that you're replacing so that you can match the caliber of the artery based on the size of the vein in the leg and distally versus proximally. And it's interesting when you look at the patency rate of these grafts, either the arterial or the vein graft, they're actually better than they are in the heart, and I think it's because the heart's so dynamic. But the patency is excellent. The artery grafts, the radial artery is a little bit better than the vein, but they're both excellent over time. Remarkably good. So anesthesia is critically important in these cases because you're clamping off a larger vessel, whether it's an internal carotid or whether it's an M2 branch. So we use mild hypothermia. We start aspirin as I talked about before. We heparinized it cross clamp and we put the patients in burst suppression during the bypass. And we've published a review on the technique that we use on this. But TIVA is excellent for this propofol and remifentanil. And again, as I mentioned earlier, I don't use an STA for a carotid replacement. IMAX maybe sufficient if it's large enough. But I've also gone to using a recipient of M2 or M3 rather than a proximal carotid. And the reason for that is that we had a lot of experience early using the ICA to ICA bypasses. And this is the Fukushima bypass, and this is one of my patients that we did these ICA in the petrous carotid to the supraclinoid or carotid for these giant aneurysms. And a lot of these patients, if they didn't tolerate the cross clamping, they'll develop ischemia in the lenticular stride branches in this area. So if you think about bypassing into M2 from the external carotid, you don't need to ever occlude the flow to the lenticular strides. So the cervical-to-petrous bypass, I don't use this, I find it, I use a internal or external at the bifurcation to the M2 branch preferentially as my bypass. So when you think about it, it's actually a perfect vessel to use and you can use the ICA or the ECA. I've gone to almost using the ECA all the time now, again, to reduce the cross clamp time from the ICA anastomosis. And we'll bring up the graft, I published this about 20 years ago. We'll bring up the graft directly through the base of the skull because it shortens the graft. And the shorter the inner position graft is, the better the long-term patency rates are. So if you bring the graft out around the ear or in front of the ear, it lengthens the graft significantly. So we've gone to exclusively using this submandibular technique, which I'll show you in a few slides here. So we'll do the craniotomy for Sylvan fissure dissection and then a carotid opening here. Open up the neck, and then depending on what vessel you wanna use, you can pass and you put your finger underneath the jaw from under the neck and you pass up a chest tube underneath the jaw. And then you bring the graft through your saphenous vein or your radial artery right through this, just like a shunt passer, and you do the anastomosis. And I usually do the proximal anastomosis first and contradistinction to a lot of others in that it's easy because you've got a great view here to do it when the vessel's loose and then you pull the graft up into the neck and then it pulls your anastomosis up there with it. So it gives you the opportunity of doing this proximal anastomosis with ease. And then size the graft and then plug it in usually to M2. And so here's such a case, bifurcation aneurysm, not good in a endovascular treatment. So what we'll do in this case is we'll revascularize into ECA-M2 here and we'll do an A3-A3 bypass. And I won't show you the video on this just for time. But this giant aneurysms in the cavernous of sinus have really been superseded now by using the pipeline stent for treatment. And this was a common indication for doing a high flow bypass, you know, 10, 20 years ago. But now it's really been superseded by the, sorry that's my epic, by the pipeline stent. If you can look here, you get unbelievable remodeling of the artery, and you just can't compete with this surgically. So it's a beautiful treatment for these giant aneurysms. So I will show you a case. I think I'll bypass this part here, Aaron, we can edit this out. It's just too long. But I'm gonna show you just a couple of quick cases and then we'll wind it up. This case is important. This shows you the use of the submandibular bypass has how I use it for a giant petrous aneurysm that was not able to be treated endovascularly.

- [Narrator] Who was diagnosed with a giant petrous internal carotid artery aneurysm. This was attempted to be treated with endovascular means with a pipeline stent, but they were unable to cannulate the distal vessel. She failed her balloon occlusion test so we'll have to revascularize her and trap the aneurysm for treatment. She's placed in the supine position, the exposure to the cranium and the neck. And her radial artery graft site is shown here. We'll first harvest the radial artery conduit approximately 20 centimeters of artery is harvested. We clean the adventitia off the end for approximately one centimeter. The artery is irrigated with heparinized saline and we do perfusion distention of the artery to avoid vasospasm. The frontotemporal craniotomy is performed, and we'll do a middle fossa dissection and identify the area just lateral to frame navali to drill our hole for the bypass graft. A hole is just over one centimeter in size. The dura is opened and will prepare our M2 recipient vessel. The proximal carotid is identified and will perform an anterior clinectomy to allow ligation of the artery below the ophthalmic takeoff. The dura over the clinoid is resected and we perform an andeoclenodectomy. The distal dural ring is opened to enable ligation proximal to the ring. The neck is opened and the external carotid arteries identified. We perform the submandibular bypass by coming up under the mandible with a tonsil clamp and bringing a chest tube as a conduit. The external carotid is cut. We perform an end-to-end anastomosis with our radial artery graft. After testing the anastomosis, we pass the graft up through the chest tube through the base of the skull. The artery is now cut to length and distal anastomosis is performed. We clean off approximately one centimeter of the adventitia off the artery. We'll perform an andicide anastomosis under burr suppression and mild hypothermia. 5,000 units of heparin is given. Anchor stitches are placed and the interrupted stitches are placed sequentially. The back wall is nas the most. Back bleeding is performed and the temporary clips are removed. We'll now clip the proximal internal carotid artery just below the ophthalmic takeoff. ICG demonstrates patent bypass. The internal carotid artery is tied off in the neck and the aneurysm is now trapped. Dura is closed, taking care not to constrict the graft. Bone flap is replaced, and the scalp is closed. The neck is closed. Her post-op CTA demonstrates a thrombosed aneurysm with a patent radial artery graft coming up underneath the mandible. She remained neurologically intact.

- So I think it's important that the skull-based surgeons must be vascular surgeons. And some of these cases I started this talk with demonstrate the importance of maintaining these skills and using them in a skull-based practice as well, cavernous sinus resection bypass replacing the carotid. And I think that it's important for us to think about, you know, maintaining these skills and passing them on to the next generation. And I think also too, we're learning from our techniques and from our experience along the way, such as an example of giant aneurysm that was coiled and we all know the future of a giant aneurysm that's coiled, it's going to recur and we have to then use a open vascular rescue in such cases. Nowadays, they would probably just put a pipe in there, which I think would be a great option. But we're all learning. Here's another indication in a skull-based practice. Cavernous sinus meningioma, occluding the carotid artery, and over time I'd have a series of these patients. After radiation or even without radiation, it can occur as the tumor grows and includes the carotid artery. So a conclusion, all cases need to be individualized based on vascular needs, the caliber vessel, and the flow that you need to maintain or persist or help with. Direct submandibular technique for high-flow carotid bypass is a direct and shorter route and promotes graft patency. And I think flow diversion is becoming increasingly used for unruptured and now ruptured aneurysms. It has rendered much open revascularization surgery obsolete with a carotid, especially as I mentioned. But open surgical expertise will still be important. We've got endovascular rescue, as I showed you cases here, giant aneurysms and bypass for some aneurysms and vessel sacrifice. And then obviously there's some controversy with flow diversion. I think the story's not completely finished with that, but it's an amazing technology. It's the only treatment that gets better for aneurysms over time as far as occlusion rates. But the long-term success of flow diversion still remains to be defined. The pending dilemma in my mind is the aging of the experienced open vascular workforce. I think I represent the sort of the tail end of the open vascular surgeons that had a lot of experience when they were young with simple aneurysms and more complicated aneurysms, which then we carried on into our practiced and then we do these more difficult cases. So we need to maintain a caliber of a small group of people with this type of experience to be able to carry on the techniques that we need for this. There's a lack of experience in residency now. There's very few open vascular fellowships. And the endovascular specialists are training in multiple disciplines such as radiology and neurology, which are gonna have no help obviously with some of these more complicated cases. So the potential solutions, I think we can centralize open vascular training. Maybe we need to have more intense vascular skull-based training experience for a few individuals with experience in revascularization and perhaps rotation among different institutions. And I thank you very much for your attention. It's, again, an honor, Aaron, to be here as always.

- Many thanks, Bill. Enjoyed the talk. Great skills, no doubt, as expected. I think think there were some great perils there. One of them was, you know, the balloon occlusion test does not secure safety of taking the carotid. You probably will be okay most of the time if the temporary balloon occlusion is okay, but there will be only few times where the patient is gonna suffer significantly. So I think I used the ballon occlusion test more as a measure of how long I can use temporary occlusion during surgery rather than a decision to completely take the carotid without vascular augmentation.

- I agree.

- on that topic. I think the other comments you made is that I think the issue of indirect revascularization is a critical component of every direct vascularization procedure. I inverted dura every time, no matter what kind of revascularization procedure I do, because we just don't understand the vascular flow deficit in the brain effectively. And it's very time dependent. I have seen great direct bypasses sort of weather way and I have seen very small direct ones really flourish, and you really don't know which one is which, but you know that the indirect will with you and is gonna be able to adjust to the brain. And the brain has so much more control over the expansion of the indirect vascularity from the dura. So I think these are critical pearls than one has to keep in mind. Do you have any thoughts on these comments, Bill?

- I agree with everything you said. My feeling about it, Aaron, is I think it's antiquated thinking saying that certain disease needs a certain type of bypass, period. I think there's no disadvantage in my mind at doing an indirect in every case. And I've shown you examples in that series that we just published, whereas the direct just never took off or withered away, as you mentioned, and then the indirect was dominant. And so I do think it's helpful to try to do the direct initially on all these patients, 'cause it gives them an immediate boost, it gives them bridge. But the indirect can be very dominant over time and it shouldn't be discounted. It's an amazing opportunity and so I feel that you should give the every benefit to the patient and we should do a combined bypass every time.

- Right. I called the indirect bypass, the customizable bypass. If there are certain things on the menu, the direct bypass, it comes the way it is, you can't customize it. Its specifications are set. How are the indirect bypass? It's more of something you can take customized to your own needs and the time that you give to the brain allows you to exactly customize it to the vascular deficit necessary. And you don't wanna deprive the brain to that. So my strategy has been any sort of, if someone has definitely demonstrated significant perfusion deficit if they are having multiple sort of ischemic episodes, if there's evidence that there is eminent ischemic risks, I have definitely immediately done the direct and indirect. But if someone really hasn't had any evidence of volume loss or ischemia for a while and there is these sort of questionable minor ischemic symptoms that have not threatened for a while to cause permanent ischemia, I really used the indirect bypass and I saved that very fleshy tissue around the STA and just laid on there and really do a lot of slits on the arachnoid and let that large segment of the STA that's not been used for direct bypass to provide the most amount of opportunity for the brain to grow vascularity as needed. It's been my experience. I know yours is maybe different, you are more aggressive to do the direct in every case. But for me, if there is not an imminent risk of loss, I have traditionally preserved all that vascular tissue around the STA and done the duras and angiosis on top of the arterial angiosis.

- Yeah, no, I think that's a good point. I try to give everybody the benefit of both if I can because I think even the direct is a fairly low risk bypass because you're going to a distal vessel. The importance of the indirect is interesting. I have a case, in fact I should probably publish it, that Mike Scott did an indirect on 30 years ago in Boston, in a child, and now she's an adult and she's got aneurysms on the STA extracranial just to show the amount of flow that the indirect got. And it's amazing testament to the power of the indirect bypass over time.

- So the other comment, Bill, you have that we don't have a great solution to, which I don't either, is what's gonna happen to the future of bypass surgery. I don't think anybody can sit here and claim that they know the future. However, and I don't want to be sort of nihilistic at some level, but I do believe endovascular therapy would advance further and further and would minimize the role of aneurysm surgery significantly. But there's always going to be a very small group of cases that are gonna be either complicated endovascular therapy that require for intervention or they're not amenable to endovascular therapy. But the numbers is gonna be very small. And there's gonna be those very, very few people that are gonna have to preserve their skills. They're gonna have the inherent talent. I always say surgeons are born great, but they're not made great. The surgeons can be made good surgeons but they cannot be made great surgeons. There's certain skills that unfortunately in complex intercranial surgery you can't teach. But anybody can become a good surgeon. So I think there will be few great surgeons who have those technical skills in their hands without even a big series of experience will be able to save the arts. And I think the art of bypass, the art of microsurgery would always be around, but it will be a much, much more limited fashion. Do you have any thoughts there?

- Yeah, I would agree with that, Aaron. I do think we need to sort of proactively plan how we're going to do this because I worry that, like, it's like clipping basilar aneurysms, you know, I have fellows that come in that have never seen a basilar aneurysm clipped in their seven years of training, you know, at outside institutions because they've all been done endovascularly. But some still need to be clipped. And I do think that we do need to find a way to protect the art. And bypass in my mind is actually probably going to increase a little bit more with ischemic disease. And I don't know whether you agree with that or not because we're seeing this select group of patients that we find with steno-occlusive disease, and of course moyamoya has always been in the background, but the steno-occlusive disease patients are being better selected and we've got more objective waves of measuring them like they never had during COSS, as you know. And so I do think that that's a growing opportunity for us to train people. And doing the STA is a great bypass to train people on because it's on the surface of the brain. They're not trying to tie in a hole and they're using shorter instruments usually. So it's a great opportunity. The difficult ones... And I didn't show a case 'cause I of time. And there's one other point I wanted to make about a bypass for aneurysms is that I mentioned it, but I have a case and it's just actually being published right now, of large PICA aneurysm, large PICA aneurysm. And I prefer to use an occipital artery donor to the PICA distally. And I've done many PICA-to-PICA of bypasses and I had an A3 day three up there, I showed you. But I think in general, it's a good philosophy to try and use an external vessel to revascularize a branch instead of an internal to internal artery just so you don't put a good artery at risk to the brain. And I think that's an important message for people too. And there's a nice video showing us doing that with this aneurysm. But I do think that you need to practice on the STM-SCAs, you need to practice on the carotid artery as a great opportunity to train people, and then ultimately use that as a springboard to train people to do the more difficult bypasses, the deep ones, the narrow corridors for that type of thing.

- Well said, Bill. Many thanks. Really enjoyed it. Always, always, always a pleasure. God bless you and thank you.

- Thanks, Aaron. Always an honor. Thank you very much. Take care.

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