Transcript

- Hello, ladies and gentlemen, and thank you for joining us for another session of the Grand Rounds. We're privileged to have with us, Doctor Bill Couldwell, who will be sharing some of his challenging vascular cases in the videos, and his pearls of technique. This is a very exciting session. I have, personally, very much enjoyed watching his videos, and I hope you'll do the same. Again, thank you. Now, I wanna thank you again for joining us, Merry Christmas, and we're very excited to listen to your comments. Please go ahead.

- Well, happy holidays. It's a pleasure this morning to discuss some vascular cases with you. With no further introduction, let's talk about a giant intracranial aneurysm of the carotid terminus and supraclinoid carotid. This woman presented with visual loss and she had a large left aneurysm at the base of the skull, that you can see here. On the angiogram, it looked like it was emanating from the supraclinoid carotid, just distal to the takeoff of the opthalmic artery. The neck appeared fairly broad, but we thought that we'd attempt clip ligation. So, we'll perform a left frontotemporal craniotomy, and we'll get immediate exposure to the aneurysm. I just wanted to mention that, in this particular case, that we did a CT scan and the clinoid was eroded. So, we chose to perform proximal control with a neck dissection, and we've dissected the neck and we have proximal control already, and now we're exploring the aneurysm, directly. We thought that we would like to go ahead and try to see if we could clip the aneurysm, reconstruct the supraclinoid carotid, if possible, and we would bypass as a secondary option if we couldn't adequately assess the neck and reconstruct the neck of the aneurysm. So, here's the distal neck of the aneurysm, and you can see that it's occupying the complete wall of the carotid, so we'll have to try and reconstruct the carotid with this giant aneurysm. The other complicating feature is you can see the optic nerve and what we'll do is we'll drill the clinoid. I prefer to drill the clinoid, in a case like this, intradurally, so I can see where the aneurysm is in relationship to the bone removal. I'll remove the dural flap so it doesn't catch in the drill. Alternatively, you could use the Sonopet, but we first focus on drilling out the optic canal, here, and I like to release the untethering and untether the optic nerve. We'll take out the anterior clinoid process and then completely open up the distal dural ring to untether the proximal carotid artery. And this is an important step because we're going to have to place clips and make sure that we have a completely patent artery and have it not tethered at the base of the skull when we clip it. So, we'll trap the aneurysm at this point, burst suppression, mild hypothermia, and attempt to go ahead and reconstruct the neck and the carotid artery, directly. You can see that the aneurism is large and we have to reconstruct the artery. We, now, with the aneurysm trapped, we can dissect the aneurysm off the optic nerve, and I've had to use a opposing set of fenestrated clips here to be able to get the aneurysm completely controlled. The other problem was that the p-comm artery was coming out of the side of the large aneurysm, and we had to devise a mechanism to keep the p-comm artery open. So, we're placing a series of fenestrated clips, here, across the neck of the aneurysm to get complete control of the aneurysm, construct a new neck and a new artery, and then preserve the p-comm artery coming out of the neck of the aneurysm. And what we'll do, here, is we left a, we purposely left a little dog ear on the aneurysm and I'm, there, cross clamping the dog ear with a small, additional clip to maintain patency of the p-comm artery. ICG angiography, and here we demonstrate that the p-comm is filling, as well, and the carotid is nicely reconstructed. So, we were happy with this reconstruction. We felt we did not need a bypass and you can see the artery is filling nicely. And she did very well, postoperatively, and her vision actually improved. This is a 50 year old woman with visual loss and headache. She had a CTA, which demonstrates a giant, partially thrombosed aneurysm of the very proximal carotid, in the opthalmic segment. And you can see here, in the lateral view, that the aneurysm is partially filling. And the 3D reconstruction demonstrates this proximal carotid artery aneurysm that is partially filled. So, given the fact that she's got visual loss, we'll perform an open surgical clip ligation of this aneurysm. We'll split the Sylvian fissure and identify the proximal carotid and aneurysm and the optic nerve. So, we carefully dissect the optic nerve from the proximal part of the aneurysm, and our goal here is to decompress the nerve, in the canal, early in the case. We're dissecting around the lateral aspect of the aneurysm. In these cases, I prefer to control the carotid in the neck. We placed a vessel loop around the internal carotid. We'll bring down the dural flap over the anterior clinoid process and proceed with clinoid drilling. I prefer to do this intradural, given the fact that I can identify the nerve and the aneurysm at the same time. So, we'll then drill the clinoid and open up the distal dural ring to clearly identify the proximal neck of the aneurysm. We'll proceed with trapping of the carotid at this point in the aneurysm, by cross-clamping the carotid in the neck, and then placing a temporary clip just distal to the aneurysm, in this fashion. Now we can go ahead and fully dissect the neck of the aneurysm. We're sharply dissecting the dural attachment along the lateral aspect of the aneurysm, and then we'll go ahead and place our initial clip. This is an angled, long Sugita clip. You can clearly see the proximal and distal neck. I'll open the aneurism now and remove the thrombus to allow us to decompress the mass and more carefully review the clip placement of the neck, on the neck. The aneurysm neck is very calcified so I'm using a small clamp to crush the neck and we'll place a tandem clip on top of the initial placed clip. So, we'll go ahead and release the flow, and the problem that we have with this aneurysm is it's calcified in the neck, and so it's not, the clips are not occluding the aneurysm neck completely. So, it's bleeding from the distal part of the neck and so you'll see we'll place a fenestrated clip across the distal part of the neck, we'll drill the calcified part, and clip the rest of the aneurysm, and that controls the aneurysm beautifully. So, we'll check the Doppler and the ICG angiogram to demonstrate that the carotid is flowing well, and then we'll close the area where we removed the anterior clinoid process, muscle and fibrin glue to avoid a CSF leak and proceed with general closure. She did well, and her vision was preserved. This is a 59 year old female with a giant left cavernous carotid aneurysm. She presented to an outside institution, at this point, with retro-orbital headache. She was treated with coiling of the aneurysm and you can see they've done a reasonable job and they packed the coils fairly tightly in most of the aneurysm, but the neck is fairly loosely packed, and then, over the next six months, she develops increasing headache, retro-orbital pain and a new sixth nerve palsy, and you can see that the aneurysm is regrowing from the neck, and we felt, at this point, we would like to get rid of the mass and try to decompress the cranial nerves in the hope of improving the sixth nerve palsy, and then we felt that we would bypass the carotid, in this case, because she failed her balloon occlusion test. Left frontotemporal approach. We've trapped the carotid and we're removing the coils from the aneurysm to decrease the mass. This is done under hypothermia, as I said, she failed her balloon occlusion test so we're going to go ahead and bypass the carotid and we'll do an extracranial carotid, external to saphenous vein, and then a saphenous M3 branch, here, and decide anastomosis under hypothermia or suppression on the EEG and anticoagulation. We verify, now, that the bypass is patent, we do an ICG study, and then, now, we can formally trap the region of the aneurysm and flow has been reconstituted. So, this is an interesting case. This is a fusiform aneurysm in a male who had a subarachnoid hemorrhage. You can see the subarachnoid hemorrhage epicenter is down in the posterior fossa, adjacent to the vertebrobasilar junction. Also, interesting on this case, you can see that there's an acoustic neuroma or a vestibular schwannoma that's present within the field of the subarachnoid hemorrhage. So, we went ahead and did a CTA study looking for the source of the subarachnoid hemorrhage and we identified a fusiform aneurysm at the takeoff of the PICA. We did a formal angiogram because of the nature of the aneurysm, and you can see it's just distal to the takeoff of the PICA, and you can see the aneurysm on this rotational 3D reconstruction, clearly fusiform, and along the proximal segment of the PICA. We felt this was likely a dissection. So, what we're planning here is to do an open exploration, and I'm going to identify and dissect out the occipital artery in anticipation of a bypass, if we need to. So, what we'll do is we'll explore the aneurysm and if we can reconstruct the artery, fine, if we can't, then we'll do an occipital to PICA bypass. Now, I prefer to do an occipital to PICA bypass rather than a PICA to PICA bypass, because it does not put the other PICA at risk. So, we'll always plan to harvest the occipital artery on the approach, in a case such as this. So, we'll identify the occipital artery in the occipital region and harvest the artery at the time of the approach. We identify the occipital artery in the fascia, and we cut it a trench on both sides, isolating the occipital artery. It's very torturous in this course, careful not to injure it, and then we'll go ahead and do a traditional far-lateral approach. Bring the flap down, here, and identify the condyle and perform a far-lateral approach to explore this aneurysm. This approach is ideal for approaching PICA aneurysms. You're removing the soft tissue at the occipitocervical junction. We'll identify the vertebral. We'll open up the dura just adjacent to the vertebral artery as it enters the dura, and you can see when you're opening the dura here, the extensive subarachnoid hemorrhage. This approach usually puts you perfectly at the vertebro-PICA junction. There's the caudal loop of PICA, on both sides, visualized here, and we'll then direct our attention more anteriorly, find the vertebral artery and find the takeoff of the PICA, itself. So, I'm putting proximal clip, here, on the vertebral, just proximal to the takeoff of the PICA, and we'll go ahead and trap the region of the PICA where the aneurysm is located. As I mentioned, I think the genesis of these aneurysms mostly likely dissection, so we'll place, we have room for a clip proximal to the aneurysm, here, so they'll go ahead and trap the aneurysm and place a clip on the caudal loop as well, and then explore the aneurysm directly. Now, the only way to reasonably repair this aneurysm is to either exclude it from the circulation or clip-wrap it, and what we'll do here is we'll explore it and see if it's appropriate for clip-wrapping. I prefer to clip-wrap, if possible, because it saves the perforators coming off that segment instead of trapping the aneurysm and what we'll do is we'll take some muslin here, pass it around the artery, and gently clip-wrap it. It's important that when you place the clip across this sling, that you do not constrict the artery over this region of repair. So, what we'll do is we'll take the temporary clips off and assess the flow through the PICA. We do it with a Doppler and an ICG. In this case, the flow is excellent, and this was a satisfactory repair. We did not need to perform the bypass. So, this is an unusual case. This is a 11 week old infant who was injured by a falling television set and suffered a traumatic subarachnoid hemorrhage. You can see the right Sylvian fissure and temporal blood. So, a formal angiogram was performed here, which demonstrates a likely traumatic aneurysm at the takeoff of the anterior choroidal artery. So, what we'll do is we'll explore this directly. We try to preserve the carotid, if we can. So, this is a hole in the wall of the artery and we'll trap the area directly. So, we're putting a clip, both proximately and distally to the region of the choroidal, trap the area and explore the injury. You can see the hole in the wall of the artery, here, that's starting to bleed, is right at the takeoff of the choroidal, and we'll go ahead and perform a direct repair of that tear in the artery. This is a 9.0 suture and we'll repair the hole directly. We'll take off the clips and the flow is satisfactory. I also took the additional precaution, here, to wrap some muslin around the area of injury, to scar the area more sufficiently. And here's the postop angiogram, which shows an excellent repair. So, this is a carotid-saving procedure. So, this is a simple ruptured MCA aneurysm, and I show this case as if this is a 43 year old woman presenting with an acute onset of a severe headache and no focal neurological deficit on exam. She had a subarachnoid hemorrhage, with a little bit of right-side preponderance, you can see, and a CT angiogram shows a middle cerebral artery trifurcation aneurysm. So, this is a straightforward case. Right frontotemporal approach. We'll open the Sylvian fissure and we'll identify the carotid at the base of the skull for proximal control. In this particular case, the brain was whole, so we'll perform a third ventriculostomy and then trace the middle cerebral up into the Sylvian fissure. Now, the reason I show this case is I think this demonstrates the reason why these cases should primarily be explored in clips, because you can see that it would be a relatively simple one, I think, to coil, given the configuration of the aneurysm, but it's a much more complex aneurysm in real life because it's mostly thrombosed. And so, what we'll do here is, now you can see the true nature of the aneurysm. It's multilobulated, only one of the lobules is filling, needs to be dissected off of the branches. We'll do this under proximal control, short periods of time, under burst suppression on the EEG, and then we'll place a very well-placed curve clip across the neck to preserve the branches. And you can see that I, that a coiling of this aneurysm would not achieve the same result. So, a carefully chosen clip, preserve all vessels, and take off the proximal clip, and perform an ICG angiogram, and this is a DSA, performed postoperatively, which demonstrates filling of all vessels. This is a interesting case, a 59 year old woman presented with a right temporal lobe seizures and numbness in her left hand, and a MRI showed a large right posterior communicating aneurysm, and I think this is an interesting case. This is a large aneurysm coming off the proximal right carotid. The unusual aspect of this case is that there was a significant amount of edema around the aneurysm. And I think in, and you'll see it at surgery, how this contributed, likely, to her seizure disorder. So, this aneurysm, now we'll perform a right frontotemporal craniotomy and explore the neck of the aneurysm. Here's the right proximal carotid artery. We'll split the Sylvian fissure, to provide more room to explore the aneurysm and, in this case, we'll identify the complete aneurysm, go ahead and put a proximal clip on, temporary clip, we'll trap the area and then explore the aneurysm completely. This is a very large aneurysm, much larger than the filling on the MRI would suggest. And you can see the evidence of hemosiderin around the aneurysm and the inflammation in the brain around this. These larger aneurysms appear to be inflammatory around the area and causing a lot of edema, so we'll go ahead and clip the aneurysm and her post-operative MRI shows complete resolution of the edema and her seizure disorder was much easier to control. Here's your postoperative scan. You can see the edema has settled down. And I think it's an interesting question on these large aneurysms, they're active in an inflammatory sense with the brain around 'em. We'll talk about anterior communicating artery aneurysms. So, there's a large variation of anatomy. We must choose the side of the craniotomy very carefully, based on the filling of the aneurysm, the site of the hemorrhage, et cetera, and be aware of the projection of the aneurysm and the approach, and then we'll use a possible gyrus rectus corticectomy if we need to enhance the exposure. Now, it's been known for a very long time, almost a century, the variations of the anatomy of the anterior communicating artery, and there's often these variations that are associated with aneurysms, we think, in contributing to the unequal flow and the genesis of the aneurysms in this location. Here's one example of a variety of aneurysm or of variations of the anterior communicating artery that you could see. So, our corridor is usually a frontotemporal corridor, although we use interhemispheric occasionally on a very large aneurysm and we have to, I think, in anterior communicating artery aneurysms, is use all of our techniques for exposure, often using fenestrated clips and varying clip patterns and modalities, to close the aneurysm properly. So, here's a 60 year old woman with a history of subarachnoid hemorrhage, with a clipped a-comm aneurysm in 1995. She now has progressive growth and filling of an a-comm aneurysm, and so, this is a recurrent case, and I'll show you the surgical video. Here's our setup. We'll use the previous craniotomy, support from the right side. Here's the right optic nerve, the chiasm. You can see the previous clips placed across the neck of the aneurysm, and the aneurysm has recurred adjacent to the previous clips. There's the new bleb. So, what we'll do in this case is we'll completely dissect out the communicating complex. We'll remove the previous clips and then reclip the entire complicated aneurysm, here. Proximal clips in place on both A1s, and we'll go ahead and reclip the aneurysm, including the new bleb. Now, in this particular case, we clipped off the a-comm because we felt that we couldn't clip the aneurysm satisfactory and leave the a-comm in, open. And so, we'll check flow, with an ICG, in both vessels and make sure they're open, at the end of the case. And here's a interesting case of a 53 year old male with a subarachnoid hemorrhage. This was attempted to be coiled by our endovascular team. You can see the extensive Fisher three hemorrhage. An a-comm, predominantly filling from the right side. So, this was taken to be coiled and they had a complication during coiling, where the coil dislodged and flowed distally, into the right A2, and you can see it on this projection. Now, the other complicating feature, on this patient, is he had no vertebral arteries, and so, he was filling his posterior circulation through the carotid circulation, through these fetal p-comms, and he ended up with infarction in his posterior circulation following the procedure. Right side approach. Gyrus rectus removal, explore the region of the aneurysm, and you can see the coil in the aneurysm extending up into the distal A2. So, under temporary occlusion, we'll remove the coil completely, and then simply clip the aneurysm. We'll check flow with Doppler plus an ICG, everything's filling, and the aneurysm has been successfully treated. Here's the postoperative angiogram. So, this is another complication of coiling. This is a 52 year old male, whose status post subarachnoid hemorrhage, secondary to basilar aneurysm. He went underwent coiling in an outside hospital, with incomplete treatment. There was an intra-procedural rupture and external ventricular drain was placed. He recovered from the hemorrhage well and was sent to our unit, subsequently. He made a remarkable recovery, neurologically was intact, with the exception of a partial left third nerve palsy from his coiling in his aneurysm and he had a slight imbalance on tandem gait. So, the aneurysm, now, is partially coiled. There is a residual aneurysm, followed by serial angios, now shows more coil compaction and the aneurysm is now enlarging. So, here's the angiogram and you can see distal basilar takeoff at the superior cerebellar, between the superior cerebellar and the posterior cerebral on the left side, partially filling. So, the treatment options are repack with more coils or stent-assisted coiling, or clip the aneurysm, and you wish just to proceed with clipping the aneurysm. So, I want to just demonstrate here, adenosine-induced arrest to help with an aneurysm in this location. It's often difficult with basilar apex and superior basilar aneurysms to get complete temporary occlusion with clip placement, so you'll see the use of adenosine arrest. The other thing I would like to add is we've gone to complete, total intravenous anesthesia in our unit for all of our vascular cases. It's been our experience that the brain is much more relaxed with the use of this technique, and I encourage you to read our review paper on it, but it's well established and has been superb, in my mind, one of the best advancements in anesthesia over the past decade. So, we'll go to the video. So, left sided approach, pterional approach, working adjacent to the basilar, here, looking directly at the neck of the aneurysm. Here's the coils within the aneurysm. We're dissecting the neck of the aneurysm free. Here's the basilar artery, here, the neck of the aneurysm that I'm dissecting now. And so, we'll use adenosine for cardiac arrest. This gives you several seconds, up to a minute, of cardiac arrest and allows you to dissect out the neck of the aneurysm and soften the aneurysm well, for these aneurysms in difficult locations. You'll see the aneurysm soften. Cardiac arrest. We can dissect out the remaining perforators on the back side of the aneurysm, and then go ahead and pick a clip and clip the aneurysm during the arrest cycle. It allows us to soften the aneurysm and better visualize the perforators on the back side of the aneurysm. So, I'd like to just show a couple of bypass cases now. And, as you know, the first bypass was really published by Yasargil and Pete Donaghy when they were in Vermont, and it was initially performed for a high grade stenosis or occlusion of the ICA or middle cerebral artery. Now, the major indications, especially since the COS trial, is related to tumors, aneurysms, or in some cases, infection. So, I think it's important, then, when we choose to bypass a patient, we have to decide exactly how much blood flow that we're trying to achieve. And so, we either are planning to restore adequate collateral flow in a patient with insufficient cerebrovascular reserve or preserve cerebrovascular reserve in a young patient with long life expectancy. And I also want to point out that a false negative balloon occlusion test may fail to identify those at risk for ischemic complications. So, it's a very selective approach, and in younger patients I tend to go to bypass quite frequently if I'm planning to sacrifice the carotid because the long-term risks of living without the carotid lessen the risks of performing a bypass in my own series. So, a normal cerebral blood flow is approximately 54 mls per hundred grams per minute of tissue. The balloon occlusion test, 10% of patients with decreased cerebral blood flow on Xenon-CT, despite passing the test, so, and 5% of these patients will develop neurological deficit after carotid sacrifice, even if they pass the balloon occlusion test. So, this is the reason I believe in performing a carotid bypass in younger patients with a long life expectancy, because you cannot always select the ones at risk. And so, we currently use a balloon occlusion test with acetazolamide challenge, with CT perfusion imaging, as our gold standard, but as I mentioned, it's imperfect at selecting them. So, the selection of patients, planned carotid sacrifice for giant aneurysms, tumors and infections. A malignant tumor, we would only perform a bypass if they failed their balloon occlusion test, given their shorter survival. And in younger patients with benign tumors, when we resect a carotid, we do an oncological resection and a long survival is anticipated. We would then proceed to go ahead and do a bypass in a patient such as that without the anticipation of a balloon occlusion test. Also, we should consider the risks of carotid rupture if the tumor is left in the wall. I think this is under appreciated by a lot of surgeons. Up to 18% of patients, in some cases, occur with tumor invading the wall and the risk of bypass is certainly less than the risk of a carotid rupture from tumor invasion. There's roughly 7% mortality and 17% morbidity with carotid artery sacrifice. If you basically sacrifice all carotids without selection, and this should be compared, then, to the bypass risk, which, in experienced hands, should be 5% or less. So, when we talk about ICA reconstruction with interpositional bypass grafts, I think, or Sundt is really the pioneer of this, he popularized this interpositional graft and performed many of these in the early 1980s. And when we choose a conduit, we have to determine exactly what we're trying to replace. So, I think it's important to remember that the superficial temporal artery will only give you fairly low flow, at least initially. It can certainly give you higher flow down the line, but, initially, it's fairly low flow at 15 to 25 mls per minute. This should be compared to a saphenous artery, or a saphenous vein graft, which will supply 70 to 140. And the radial artery is excellent, as well. It's often easier to use, but it has less volume than a saphenous vein graft that is well placed. So, should we choose a radial artery graft or a saphenous vein graft when we're performing high flow bypasses? What are the differences? Well, the radial artery grafts are technically easier. The wall is thicker, it's easier to manipulate. It's often more equivalent in size. It has smooth arterial endothelium. It has no valves. There is spasm, and this occurs only with the radial artery grafts, but this can be overcome with the pressure distension technique that can be performed pre-operatively to basically overcome the elasticity in the wall and reduce the risk of this occurring afterwards. It's now become the more popular conduit for CABGs and the five-year patency rate is greater than 90%. The saphenous vein graft, it's readily accessible, it's varying caliber, and what we'll do is we'll perform an ultrasound of the leg and we'll match the area of the graft donor site to the caliber that we want to use when we replace the graft in the head. The cranial experience is interesting. There's 86% patency at one year, and the long-term patency is very good, and in fact, it exceeds that of the CABG patency rates, which is about 50% occlusion at 10 years, and I don't know the real reason for this, but I would assume that it relates to movement and the fact that the heart is beating and it may cause more wear and tear on the graft compared to sewing it in the cranial space. So, I'd like to first demonstrate an STA-MCA bypass for Moyamoya disease in a young Asian woman. She has a bilateral Moyamoya disease, worse on the right side, and we'll plan to perform an STA-MCA bypass, in this case. This is a drawing of the superficial temporal artery. We'll use the anterior branch. We start with the harvest of the superficial temporal artery. We'll be very careful and identify the artery along its course with Doppler. After we've dissected it, we placed papaverine over it, and then perform our craniotomy and identify our recipient branch, often the angular branch of the middle cerebral. This is located approximately six to seven centimeters above the external auditory canal. We identify approximately one centimeter segment of the artery, place a dam, and then go ahead and heperinize and harvest the artery. We place patients, already, on aspirin prior to surgery, you can see the temporary clip on the proximal pedicle. We'll then clean the distal part of the pedicle free of the adventitia, very carefully, bevel the mouth of the artery, and then clamp the recipient artery and perform an arteriotomy. I use an 11 blade for this, and I match the size of the arteriotomy to the length of the beveled, fish-mouthed donor branch. In this case, we had some side branches coming in, required an extra clip. A small bit of methylene blue helps visualize the edge of the arteriotomy and we'll perform our anchor stitches. I prefer to use interrupted technique for this, just so it does not constrict the orifice and the anastomotic site. You use 9.0 suture to perform that. After we finished the anastomosis, we'll remove the temporary clips, document flow, and here we've got a small opening that we'll have to close with one, single stitch, and then remove the proximal clip from the pedicle. Some papaverine is placed, dilute papaverine is placed over the anastomosis. We check patency with the Doppler and an ICG. You can see the graft is nicely filling and the angular artery is nicely filling in both directions. Place a small piece of Surgicel around the anastomosis site and then close the dura loosely around the pedicle. Be careful not to constrict the artery. And, obviously, we've made our burr hole in this location so the artery nicely goes through the burr hole. As you can see on the postop CTA, bypass is widely patent. Thank you very much.

- Thank you, Bill. Great case.

- So, I just wanted to share some of the lessons that I've personally learned over the years, with bypass surgery, and that I now use high-flow bypass for acute carotid sacrifice, exclusively. This is for reasons that I've had complications with trying to use an STA-MCA bypass to completely replace a middle cerebral artery flow in those patients with carotid sacrifice. And when I use interpositional high flow bypasses, I, again, in a young patient, I prefer to bypass rather than risk the, and avoid the risks of carotid sacrifice because the bypass risk is less than the risk of sacrifice, even if they pass balloon occlusion tests. If we perform an oncological resection of a low grade tumor, we'll perform a bypass with a high grade tumor, we usually don't if they pass the balloon occlusion test, and then, now I've gone to exclusively the recipient vessel being the M2 or M3 branch rather than the proximal carotid, and the reason for this is quite simple, is that if you bypass into the proximal carotid, you have to occlude the lenticulostriate flow at some point, unless there's very good collateral flow. And if the collateral flow is poor, then it's better to bypass into the M2 or M3 branch, because then you don't have to temporarily occlude the lenticulostriate flow during the time of the anastomosis. And then we watch the blood pressure, peri-operatively, very carefully, and the reason for this is twofold, is that we really want to avoid hyper perfusion hemorrhage in these patients, and so we'll keep them on pressors or antihypertensive medications to try and control them in a very narrow range, because we don't want to drop the blood pressure in order to bleed post-op, either, because they'll thrombose off their graft. So, when we talk about high-flow bypass, there's basically three different mechanisms that we can do. We can do a cervical to petrous, a cervical to supraclinoid, a petrous to supraclinoid, and a cervical to M2, which is just a variation of what we'll talk about subsequently, here. So, the cervical to petrous bypass is described some years ago, but I personally find this a bypass that we don't use very frequently, and the reason is, is because we often have pathology within the cavernous sinus that we're trying to bypass. So, from the cervical region to the petrous, it's technically possible, and we can do this, but oftentimes you're bypassing pathology that is very rare in this location. This is the petrous to supraclinoid bypass that was developed by Taka Fukushima in the mid 1980s. And it's a beautiful bypass. It's from internal carotid to internal carotid, in this location. It was designed to bypass pathology exclusively within the cavernous sinus, either cavernous sinus tumor, or a giant aneurysm in this location. Some of the advantages of the bypass is that it's completely within the confines of the head, so there's no stress on the graft with head movement. So, here's an example of a Fukushima bypass, and, basically, you can see that we're using this saphenous vein graft to bypass merely around this giant aneurysm within the cavernous sinus. The difficulty with this is that it's quite a challenging bypass. As I said, the advantage is, is that it reestablishes a high flow in the, from the internal carotid to the internal carotid, and it's entirely intracranial, it avoids stress on the graft, and it's very short, which usually enhances the longevity of the graft, the shorter that you can make it. The disadvantages, it's the most technically challenging of all the bypasses. It's a small working space, requires temporal lobe retraction, and there's a deep, narrow corridor. And this is an illustration of the bypass from the petrous carotid, here, to the supraclinoid carotid. It's very crowded to try and perform this proximal anastomosis. You're operating in a deep hole, you've got a limited, roughly one centimeter of carotid artery that you can expose within the petrous bone, to perform an end to end, or an end to side anastomosis. So, here again, is an example of a bypass that I've done around a giant cavernous aneurysm. Now, what can we do to enhance the exposure for the proximal carotid, in this case, to enable easier access to the petrous carotid, to make it a more easier bypass to perform? And there's a way of doing this and we can actually perform an extended middle fossa approach and enhance the access to the proximal carotid for the recipient vessel. So, we perform this as a standard frontotemporal approach, but what we'll do is we'll add an extended middle fossa approach to this, and we'll bring the temporalis muscle down. So, here's our middle fossa anatomy in a cadaver, the greater superficial petrosal nerve, which marks where the internal carotid artery is, here, just behind V3, and we'll drill out the carotid canal, here, just below GSPN. Remember, we will cut GSPN instead of putting traction on it. This gives the patients a little bit of a dry eye, but it's well tolerated, and this gives us beautiful access, then, to the internal carotid artery. Again, this is the exposure of bone you can remove. This is the arcuate eminence, internal carotid artery, and GSPN, if you bisect the line, this is where the IAC is. We'll not worry about this today, we'll just expose the internal carotid artery in the base of the skull. And, if you dissect out the internal carotid artery more proximally, you can mobilize the artery and enhance your exposure for the bypass. So, this is shown within a cadaver specimen. We've drilled out the petrous apex in a Kawase approach, here, as well, but you can remove the bone laterally in the middle fossa to the horizontal segment of the petrous carotid, here, and then mobilize the carotid. We can remove the bone, we can replace the bone later, and this, then, enhances the exposure of the carotid for your bypass. Laterally to the artery, here, there's no important structures to worry about, and this can be mobilized easily. More medially, we have to worry about the cochlea, just where the GSPN enters the geniculate ganglion, here. And if you look at the exposure of the artery, using this enhanced bone removal, it's quite remarkable. You get much more room to maneuver and perform your anastomosis if you mobilize the artery such as this. This is shown diagrammatically, the temporalis muscle. The zygomatic process is removed and the temporalis muscle is reflected down and more inferiorly. So, with the extended approach, you get much more exposure of the ICA within the middle fossa, compared to the standard situation, where the temporalis muscle has not been mobilized more inferiorly by removing the zygomatic process, and also, the middle fossa bone has not been removed. So, this again, shows it in a diagram, cadaver diagram. And so, that's the way to enhance the Fukushima bypass. More recently, we've gotten away from doing the internal carotid to internal carotid bypass, and this is the bypass, this is the workhorse bypass that I use at present, which is the cervical to supraclinoid ICA bypass, and we bring this up directly through the base of the skull. So, traditionally the saphenous vein or radial artery would be brought out, either behind the ear or in front of the ear, subcutaneously, and instead, what we do is we perform a small little hole, a dime sized hole, in the middle fossa floor and bring the graft up directly into the cranial space. This achieves two goals. It gives you a more natural course for the carotid, coming up, and it shortens the interposition graft. and the advantage of shortening the graft, as I mentioned earlier, is that it increases patency rates. So, a zygomatic osteotomy is avoided. The temporalis muscle and masseter are left intact by performing this, and we bring it up underneath the jaw, and I'll show you this in a couple of cases, here. Here's a young man with a rare syndrome, called PHACE syndrome. It's characterized by angiodysplasia on the one side, usually associated with some cardiac abnormalities, as well. And these are the incisions that we use. He has a giant skull-based aneurysm that you'll see, an internal carotid artery that's extending and projecting into the sphenoid sinus. So, we'll go ahead and perform the cranial incision and the neck incision, and then pass a tonsil clamp from the cranial space, down into the neck, and then we'll use this to bring the bypass up, directly, or bring it up through a chest tube. And so, the bypass is brought up directly under the jaw, and this is very easy to do. We make a hole in the middle fossa floor. You feel under the jaw, under the angle of the jaw with our neck incision and then advance the tonsil clamp. It's a very simple maneuver. Here, you'll see us bring back a chest tube, and then we'll use this merely as a passer to pass the graft and bring it up directly through the base of the skull and anastomose, then, usually to the M2 or M3 vessel. This can be done with a radial artery graft or a saphenous vein. So, the advantages are that you avoid kinking the graft, and then you bring it up directly through the base of the skull. Here's another case, a 61 year old male, with this giant carotid terminus aneurysm. You'll notice on this particular aneurysm, this is at the bifurcation and the anterior cerebral is coming out of the aneurysm, and the middle cerebral is emanating from the aneurysm, directly. Here's the reconstructed 3D image. You can see clearly that the aneurysm is involved in the bifurcation and both the branches are coming directly out of the aneurysm. So, we felt that we couldn't adequately clip reconstruct this well. So, what we'll plan to do in this case is revascularize. The other complicating factor is that there was no a-comm demonstrable in this case, at all. So, we felt that if we sacrificed the aneurysm, we would also sacrifice the blood flow to the anterior communicator or the anterior cerebral on the ipsilateral side. We could not demonstrate by cross flow that the a-comm was open. So, the plan here is to trap the aneurysm and then reconstruct flow both to the middle cerebral and to the anterior cerebral artery. And so, what we'll plan on doing here, then, is going ahead and performing a high flow bypass into the middle cerebral, first. And so, this is the dime-size hole that we'll make in the middle fossa floor. This is placed just lateral to the foramen ovale. This is the infratemporal fossa that I'm exposing, here. This is a right side approach. We'll place the tonsil clamp down through the middle fossa floor to the neck incision, bring the chest tube back up, or we could bring the saphenous vein back up, either one, it's no problem, and then pass the graft through this area. So, we'll perform a exploration and preparation of our recipient vessel. This is the right side, there's the neck of the giant aneurysm. So, we'll perform, prepare our middle cerebral vessel, here. Go ahead and ligate the extracranial, the ECA, the external carotid, bring it down into the field and perform an end-to-end anastomosis with the saphenous vein graft, because I do not want any constriction of the anastomosis site. I also prefer to use the extracranial, or the external carotid, initially, as our donor circulation, because we don't have to cross-clamp the internal carotid during this time. We'll bring the graft up through the base of the skull and prepare the distal recipient vessel. We'll size the artery to length, and then suture in the graft using 9.0 suture. It's important, here, we'll do this under burst suppression. I prefer to give heparin during the time of the anastomosis, distally. And again, I use interrupted sutures to avoid the risk of constricting the anastomosis site. We'll back-bleed, and then open up our vessels. We'll then determine if our bypass is open, and then proceed with trapping for the aneurysm. So, here's the vessel in place, coming through the base of the skull. We're just publishing our longterm results with this particular bypass, and it's very well tolerated, and we've got excellent long-term patency rates. So, in this particular case, because the circulations were completely isolated, we have to, then, go ahead and do an A3 to A3 bypass, and that was performed subsequently, and the patient did very well. So, here's the postoperative results. We've done an A3 to A3 bypass to revascular intracerebral circulation, which is feeding from the contralateral side, now. We do an angiogram, and what we'll do now is just merely occlude the native carotid, here, which is feeding only the aneurysm in the region of the carotid, and we'll now cross clamp and trap the aneurysm completely. So, we've revascularized the middle cerebral, we've revascularized the anterior cerebral, and now we'll go ahead and occlude the internal carotid. This is showing that the A3 bypass is feeding off the contralateral side now, and here's the CTA, which shows the appearance and the location of the submandibular graft coming up under the mandible, here, intracranially, through a small opening. And here's the second case that I'd like to show you. This is this 13 year old boy with PHACE syndrome. This is his large aneurysm presenting into the sphenoid. We felt that we couldn't do anything with this, but bypass around it, given the size and location of the aneurysm, there was no endovascular option. So, we went ahead and performed a submandibular saphenous vein bypass around this diseased artery at this location. So, we performed an extracranial saphenous vein to M2 bypass, in this case. And then we were concerned about the takeoff of the opthalmic artery, in this case, given the fact that the opthalmic was involved, and so, we performed a bypass and then proximal occlusion of the ICA without complete trapping of the aneurysm. And then, we felt that we would revascularize the ophthalmic, if possible. So, here's pictures of our bypass in place. And we went ahead, then, and performed a proximal ligation of the internal carotid artery, and he did well, and his vision remained intact. This is what it looked like, post-operatively. You can see retrograde flow into the top of the aneurysm and he ultimately thrombosed off the entire aneurysm.

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