Endoscopic Endonasal Surgery for Anterior Cranial Base Meningiomas

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- Colleagues and, friends, thank you for joining us for another session of the virtual operating room. Our guest today is Dr. Paul Gardner from the UPMC. Paul requires no introduction. He has been the most innovative endoscopic skull base surgeon of our times. His contributions to the field is for sure immense. He is Peter Jannetta, chair of Neurosurgery at UPMC, as well as director of Skull Base Surgery. Paul, well, I've followed your career and I cannot be more proud of what you have done for skull base surgery and microsurgery, and endoscopic skull base surgery. I know today you'll be talking about resection of anterior cranial base meningiomas through the endoscopic route, and its advantages and disadvantages. Somewhat of a controversial topic but at the same time extremely useful to hear both sides, so I'm very much excited to learn from you. And please go ahead, thank you.

- Thank you very much, Aaron. Thank you for the kind words and thank you for having me again on the Atlas. It's a fantastic resource for all of us. As you mentioned, I'll be talking about endoscopic endonasal surgery for anterior cranial base meningiomas, and essentially talking about pros and cons, advantages and limitations. One of the critical aspects of endoscopic endonasal surgery is that it be done really by two surgeons working side by side and ideally an ENT and a neurosurgeon working side by side introducing our instruments just through the nostrils. Obviously this technique has become very widely popularized, but it's critical that when using endoscopic approaches that the same technique be used as you would use when you're doing an open surgery. It's no different, it's just a different visualization tool. You might require some extended instruments and understand how to use those in this setting, but we're still doing the same concepts of internal debulking, extracapsular dissection with sharp and blunt dissection and hopefully you'll see that throughout the videos that I display today. But this is really critical. If you're not able to apply those same microsurgical techniques endonasally, then certainly you will not have the same advantages and the same type of outcomes. Here's a very typical planum or suprasellar meningioma with the bitemporal hemianopsia. And here we see one of the important aspects is a very wide removal of all of the bone of the skull base that underlies the tumor. This does a couple of things. It ensures that we have a wide access to resect all of the tumor, but also ensures that any boney involvement is completely resected. So in other words, we're truly going for a Simpson Grade 1 resection, which is not something that you do when you approach these tumors from above. Here we can see the how thick the rind of dura is here. That was resected on either side. And that rind of dura obviously is involved with tumor. It's not uninvolved, and so removing that is necessary to get a complete resection, at least for a Simpson Grade 1 resection. And here you see the tumor's been internally debulked and then the extracapsular dissection is done both with sharp. Here you see scissors being used to debulk the tumor and dissect part of the arachnoid as well as blunt dissection with rhoton style extended instruments. Here we can see working with a blunt instrument now at the inferior aspect of the gland along the diaphragma. And also for these tumors, I think often it's important to resect the diaphragma. You can see the thickening of the dura and the diaphragma here off to the left side. And then once we've done that dissection, then we can dissect, find one optic nerve, dissect straight across and find the other. Obviously, if there's not a great arachnoid plain, we need to work more carefully on the anterior cerebrals. And here where that's being done with again, blunt dissection. Here we preserve the arachnoid plain, enable to dissect the tumor very carefully from the contralateral optic nerve. There are of course the same kind of tools and toys we would use with open surgery and the same concepts, internal debulking, extracapsular dissection. And then once this final nodule is left and completely dissected free, you can see again where these attach. These tumors attach on the medial dura going right along the optic nerve and right along the optic canal. And I would argue this is the only approach that allows us to completely resect that involved dura. Here's looking out with an angle scope towards that right optic canal to ensure a complete resection of any tumor and any involved dura. You can see the ophthalmic artery of course coming off of the carotid right there, so a great view of that to avoid injury. And it can come off immediately like that in at least a quarter of cases. Here you see the size of the defect, we can see all the microvasculature and of course, the main vasculature of the anterior cerebrals, which has all been preserved. We then do our reconstruction, which in this case is a multilayer reconstruction with an inlay collagen graft followed by the critical part, which is a nasoseptal flap. But you can really see the width and the extent of resection. This is not a a less invasive resection, in fact it's a quite radical resection. And there's the nasalseptal flap going up as the final step. Okay, we can go on to the next slide now. And here you can see the postoperative view of the complete resection. You see this patient also has a secondary cavernous meningioma which is left untreated, and then we can see improvement in the visual field postoperatively. This is looking at a very early series only up until 2011. We probably time to redo this. I think we've probably doubled it in size, but we wanted to look early on at what really were the outcomes of this. And these are, majority of these are tuberculum or planum and then most of them are primary tumors. And you can see here, again looking from above in this cadaveric specimen with a tuberculum meningioma, really how its displays the optic nerves. And this is very common to have extension into the optic canal, not laterally or over the top of the clinoid, but most commonly since this is a medial originating tumor into the medial aspect of the optic canal. Most common symptoms as you might expect would be vision loss. And importantly here, gross total tumor resection here is not just a removal of everything see on MRI, but a true Simpson Grade 1 resection was achieved in 79% of cases with the majority of the rest achieving a near total resection. Now what about lateral extension for example, into the optic canal? As I mentioned, the majority of these tumors since they originate medially, come into the medial aspect of the optic canal as you see right there, so they're not coming into the lateral optic canal, they're not coming over the top here, but rather they're coming medial into the optic canal. And so endonasally, we have very natural access to that. ENT surgeons are well aware of our ability to access the optic canal in the orbital apex for decompression related to trauma or other type of disease. Here's another typical example of the tumor extending right into that optic canal causing greater vision loss on one side than the other. And here we see after a wide sphenoidotomy, we can really see how we have great access into that canal. And again, important aspect is the wide removal of all bone as well as any involved dura. So, in this case we do very early optic canal decompression. Here, the bones coming off of the planum, but all of this bone on the optic canal here will need to be removed in order to make sure that we get the widest decompression as well as the widest access to the tumor as well as removal of any involved bone, any involved dura. So, here using irrigation and a high speed drill, very carefully thin and remove the bone overlying that optic canal. And using those extended rhoton style dissectors can dissect the tumor free. And with an even finer drill can really do almost a pretty much 180 degree decompression of the optic canal. So, we're all the way out to the optic strut right here. That's the optic strut. You wanna be careful doing that maneuver because obviously the ophthalmic artery is very close by there. And if we can just fast forward this a little bit about 30 seconds to a minute or so, and we'll see how we can really open right into the optic canal. So, here we can see first internal debulking of the tumor and then this optic canal you can see the tumor really bulging in the canal. Once the tumor's been internally debulk, then we can take this hook blade and really start to extend into the optic canal. Now towards the patient's right side, there's really no issue because there's no extension with the optic canal. We have a nice arachnoid plane here, we can internally debulk the tumor and it practically delivers itself. But it's critical to resect this involved dura and to open this optic canal, so here's that careful maneuver being done. And what we're trying to do here is visualize the optic nerve, which sure enough we get a glimpse of right there. And as soon as we see the optic nerve, I know then I can open above the nerve along the falciform ligament here. I don't wanna open inferiorly, because again, inferiorly I'll see the ophthalmic artery. So, here again we see our optic nerve coming into the canal and you can see how much of this dura is invaded. So using that hook blade here, I can open, carefully open this until I get to normal dura. And finally, all the way out the optic strut I can finally see normal dura. Here we're resecting some thickened dura superior to the optic nerve, an optic canal. So, really trying to get the most radical, a true Simpson Grade 1 resection. And again, through an open approach you really can't resect this dura of the optic canal unless you did a full, bifrontal subfrontal approach. Here we can see the ophthalmic artery right there, and resect tumor right up to it. I'll even resect this distal dural ring and diaphragma that's invaded, and that gives us the most radical resection possible. All right, we can go on to the next slide please. This is just looking around to ensure complete resection. And again, you can see the width of resection all the way out into the optic canal. So, optic canal extension was not a limitation for gross total resection. And in fact, the key aspect of this, and I think this has been borne out in other studies that I'll talk about in a moment, really is that Simpson Grade 1 dissection that we just aren't able to completely get from an open transcranial approach because of the inability to access the dura and the bone over the diaphragma, over the medial optic canal, even all the way out to the optic strut. You can go on to the next slide, please. So here you can see the different locations and extensions, but the real question becomes, what did limit our degree of resection? And you can see here larger tumors and then configuration, so when you get these multilobulated tumors, that can be a sign of a tumor that's more invasive or more adherent. And then vascular encasement, which is probably the most important one. That's true certainly for any series within vascular encasement, the risk of surgery goes up. But with endonasal surgery, this is a key part of the learning curve. So, if there's a cortical cuff such as this anterior planum meningioma, this is really very straightforward. But as soon as there's vascular contact or extension that's pushing up the anterior cerebral arteries, there's a risk there that that tumor could be stuck to the anterior cerebral arteries. And then of course cases where the tumor completely encases it, now we really have to have a different level of dissection to be able to resect that. So, this is a video again showing resection of this tumor. Again the same thing opening all the way into the optic canal, complete internal debulking of the tumor. And then if you can, and then we identify the, I was just showing the anterior cerebrals being identified proximally and then they can be followed up into the interhemispheric fissure, and then careful internal debulking and extracapsular dissection really becomes critical here. This is working with zero and 45 degree endoscopes, and very carefully dissecting the tumor free. You can see same blunt and sharp micro dissection that's done with an open approach can be done here endonasally. Here we can see the anterior, the Acom coming out of its encasement in the tumor here and just very meticulous dissection being done. We can fast forward to the end just to show the final result here. But obviously this is a whole other level of dissection that's required and microsurgical ability to be able to dissect out those anterior cerebrals, dissect out the artery of Heubner. In fact, I think this was a case that Dr. Fernandez-Miranda did when he was in Pittsburgh. So, this is not just something that only one surgeon can do, this is something anyone can do. They just have to really have the right technique and go through that learning curve over time. Here we can see that resection all the way up between the optic and the carotid. The tumor really has grown between the optic and the carotid, and you can see what a nice wide radical resection we can get, which is very impressive. Here you can see the Acom and the Heubner, and the A1 coming over top of the optic nerve. Next slide. And here's our postop. So, indeed vascular encasement can be managed but it is higher along the learning curve. And here's a case where I injured the anterior cerebral artery, actually the artery of Heubner by dissecting this tree, able to get a complete resection but at the cost of the dominant lobe coated infarct. So, this certainly ups the anti and is a significant concern once there's vascular encasement. And something that really can be a split point for people until they get farther along in their learning curve. Now, recurrence here was very unlikely and I'll talk a little bit about that in a moment. Here you can see also the learning curve with resection rates improving over time. Importantly, visual improvement was very common. The majority of patients, almost 86% had improvement and very unlikely to have visual deterioration. Of course it's very difficult to do true comparisons between groups and I'll talk about a study that really did show that. And here you can see even after nasalseptal flap, there still was difficulty with managing this. Although our current rates for these high-flow leaks are down around 8% but still going to be higher than a craniotomy where we're not doing the same radicality of resection. Here we see recurrence rates are really quite low, less than 5%. And again I really think this is an ideal approach for suprasellar meningiomas because we can't have improved visual outcomes, but CSF leak really is a disadvantage. But I also think there's a radicality of resection advantage. Now, this is a study that was completed when Mike McDermott was at UCSF. Very interesting study with 40 different sites including our own, looking at a very large number of patients recently published I believe in Neurosurgery, or it's at least in the process of doing so. And you can see here that visual worsening overall was relatively uncommon. And you can see this was not statistically significant but actually there was a little higher rate of visual worsening in transcranial cases, although, and yet there wasn't a statistical difference in the size of these tumors. Gross total resection rates also were similar. So, this isn't looking at Simpson Grade 1 resection, but just quote, gross total resection rate. And this is an important point. CSF leak is expectedly higher for the transsphenoidal endonasal approach. But interestingly enough that CSF leak, I think it comes as a result of radicality of resection because you see that the risk factors for recurrence is that after gross total resection, transsphenoidal or transnasal approach had odds ratio of 0.3, so a third lower risk of recurrence than a transcranial approach. And I think that's simply a reflection of the radicality in the Simpson grade of the resection, which is possible from an endonasal approach. These are the conclusions of that study, which I agree with completely. That you need to be well trained in both approaches and you need to be able to shift depending on what the patient's symptoms are and what the goals of surgery are. But if you can get a gross total resection through an endonasal approach, you will have a decreased recurrence and trade off for that CSF leak rate. Perhaps even, you know, that certainly shows and provides pretty wide acceptance of endonasal approach and starts to really confirm some of the advantages, and how to apply that in your own practice. But a little more controversial are olfactory groove meningiomas. And you might say, Well, what's the best possible approach for this tumor? We can see it sort of between the orbits. There's a fair amount of frontal lobe edema. Do we do a unilateral approach? Do we do a bilateral sub frontal approach? Well, we looked at our series to try to get again some idea of this. Again, this is our early series, relatively large tumors. And often we stage these very early on, which I'll talk about again in a moment. So, here's a video again showing the resection of the olfactory groove meningioma. This is an older man who had both visual loss as well as loss of olfactory function, which is actually quite common, and was found to have this growing tumor. Now again, we want to look and there's a little bit of where the ACA just is a little bit involved posteriorly, this is an A2 or a frontopolar, actually probably a frontopolar going more distally. And here we can see one of the beauties of this approach is we really are coming directly on the tumor. Here we're sacrificing the anterior ethmoidal arteries bilaterally, removing all of the involved bone, all of the involved dura. Not only does this ensure the most radical resection, but also allows us to devascularize the tumor. So, there's the anterior ethmoidal on the contralateral side. Posterior ethmoidal have also been coagulated and cut. And now all of the involved bone is being removed. Obviously depending on the age of the patient you can make an argument this is not necessary but we certainly we don't want to have recurrence if we can avoid it. And you can see here as the posterior cribriform is peeled down that the posterior cribriform dura and tumor are inseparable in this region. So, if you don't remove the bone of the posterior cribriform in the planum where this tumor originates, there is residual tumor left in the bone, there's residual tumor left in dura, and therefore that tumor either needs to be treated or observed or potentially radiated or even resected through a different approach in the future. So that radicality of resection's very well illustrated in this case where you can really see how the tumor invades that area. So now working more anteriorly, dissecting out the crista galli. Again the crista galli is the last piece of bone that sort of holds this in place. And also removing the crista galli gives you better access to the falx which has to be released to allow the tumor to descend. Just widening the approach on either side and then dissecting this is an important step to dissect epidurally circumferentially. And then start to internally debulk the tumor. That epidural dissection is important because it allows us to tuck in an epidural graft at the end of the surgery. So now nice wide opening in the dura, we connect across the falx, at least anteriorly. We don't want to come too anterior because the frontal lobes will start to descend into our field. But you can see an extensive amount of time spent internally debulking tumor. Again, once the tumor's internally debulked, then we start the extracapsular dissection. So very, very meticulous dissection and very meticulous technique that's used here. And you have to be disciplined to force yourself to work posteriorly first, find those anterior cerebrals and then and only then start to work anteriorly and allow the tumor to descend. Here we can see the right frontal lobe coming into view right here. And as we cut the dura anteriorly and transect the falx, we can see the olfactory fiber there on the right side, and then further internal debulking of the tumor. And you can see the meticulous technique. We're not just reaching in and pulling this tumor out, we know there's an anterior cerebral or a branch of it stuck on the deep side of it, so it really requires splitting the tumor into multiple portions and piecemeal resection just as we would do through an open approach. We see the optic chiasm is well dissected free and we can protect that with a neuro patty. There's a little more involvement of the right optic canal and I'll usually wait to do this decompression of the optic canal that we're doing here until later on in the surgery. Simply because when we're working anteriorly, I don't want my instruments to inadvertently run into this non decompressed optic canal or this decompressed optic canal, so I wait to decompress it. And here you can see this gives us access to the last bit of tumor coming over the top of the optic canal, dissecting that arachnoid plain, again using sharp microsurgical dissection. And here we can see what's probably Heubner coming across, coming out of the A2. That was Heubner coming right across there on the deep side of the tumor. We can doppler it here. There we're doppler, the frontopolar and the Heubner coming off to the side. And now going after the lateral margins of the tumor, we can see we'll come back and resect this dura here. But you can see this is not a nice pretty plain with the frontal lobe. We're not relying on that. We're relying on the same microsurgical techniques we would do if this were an open surgery. So as we slowly start to peel this down, we use neuro patties to protect the frontal lobes and to protect those anterior cerebral branches. And very much a piecemeal resection and piecemeal dissection allows us to preserve. You see that frontopolar branch coming down through that very thickened invaded arachnoid. And here's another branch coming off a very even thinner branch. So you really can do the same kind of meticulous dissection and preserve these branches, which I think gives the best chance for long-term improvement in neurocognitive outcome. And these patients have neuropsychological effects which we don't pick up on our standard testing. And I think that neurocognitive testing is a critical part of the preoperative workup for these patients as well. So here finally now getting the last dural attachments, removing those with this little micro through cut instrument. And here's our final view, again, ensuring that we have even a resection of any invaded falx. We see the anterior, the optic chiasm carefully protected. You can see this frontopolar coming through here. The other A2 coming that way. We manage to protect all of these. And then a multilayer reconstruction really is key. This inlay of collagen with a split around the falx and then I've been using lots and lots of fascia lata. I've been very impressed with how well it works. And that fascia lata gets tucked into the epidural space carefully over the top of the orbits. It gets tucked epidurally. And the nasalseptal flap, this vascularized flap just lies on top of it to ensure that a vascularize quickly. We can go on to the next slide now. And so, obviously this gives us the most radical resection. We were able to achieve that not just, again, not just complete tumor but Simpson Grade 1 resection in two thirds of patients. And the majority of which had near total, there were a handful who undergo this intentional subtotal such as this 85-year-old woman who presented essentially blind from papilledema, and a simple internal debulking of the tumor allow complete relief of her symptoms. Of course there are limitations and they are chiefly anatomic once you have the technical aspects managed. And we can't come up to the poster table of frontal sinus or beyond the midorbit, but I'll show a little more evidence as to what these margins really are. Staging can sometimes help if you internally debulk the tumor. Here we thought maybe we'd have to come back to a transcranial approach. But after initially staging, you can see how the tumor fell in and then actually able to get all of it, a complete resection through a second stage endonasally. The vascular involvement again is still important but tumor size, so very large tumors, the larger the tumor was, the lower rate of gross total resection. Tumor calcification was a bit of a problem as well because we need these tumors to fall in to be able to resect them. And then again, that absence of cortical cuff, that's the same as vascular encasement. I'll talk a little bit more about location but mental status improvement. And again, we've been looking very closely at the neuropsychological outcomes associated with these patients, especially with olfactory groove meningiomas and great outcomes for vision as well as headache in these patients. So, really symptom recovery is excellent. Again, the trade-off for this radicality of resection is CSF leak. And you see in this early series of ours, a postop CSF leak rate of about 30%. Now, that has dropped dramatically over the years as I mentioned, our overall rate for high-flow rate leaks like this is around 8%. And interestingly enough, if you look at open approaches, here's a series quoted down below out of the barrel with it, a radical transbasal approach, which again is the same type of resection of that entire anterior cranial base in a very radical fashion. They also had about a 30% leak rate, so it's difficult to close this defect when you have a large defect at the base of the skull. The really only advantage of a transcranial approach from that perspective is that you can avoid resecting that with the acknowledgement that you're leaving tumor behind. Gross total resection rates improved dramatically over time and CSF leak rates diminished. Now, the technique we have used over the last at least half dozen years is this multilayer reconstruction where we used a collagen or a dura matrix inlay graft, and then take a fascia or an allograft. I've been using fascia again extensively. And you can see it's tucked into the epidural space as well as on the bone outside it, so you have sort of a double tucked technique. It can be tucked over top of the orbits. This really helps hold that fascia in place to counteract any pulsations of the frontal lobe. You need to hold it in place because it could obviously fall in, you can have a very large defect and a dead space with an olfactory groove meningioma. And then finally the nasalseptal flap just lies on top of this providing that vascularity for rapid healing. And we've proven that lumbar drainage with level one evidence through a randomized controlled trial that lumbar drainage dramatically decreases CSF leak grades for these large anterior cranial based defects. Now, more updated series looking at 75 patients up until June of 2020. Again, two thirds of patients had Simpson Grade 1 resection. And when you look at this, we have to acknowledge and we have to be aware that olfaction is dramatically impacted. You will lose olfaction with an endonasal approach essentially 100% of the time unless you have a smaller unilateral tumor. With a transcranial approach, there are some data in the literature that shows that perhaps somewhere around 30% of patients can have preserved olfaction. I've not seen this well tested with seeing things such as an upset or other type of smell score, but rather subjective sense of smell. Interestingly enough, when we looked at olfactory status here, the majority of patients had absent or dramatically altered, but a quarter of patients did have relatively in tact olfaction, at least subjectively. And I think this has to be discussed with them as a downside of this approach is that you will lose olfaction. Here's another very typical tumor, and I think we'll skip this video in the interest of time, but the whole concept here is again just showing how we can really radically access the tumor from below. If you wanna show, if you can scroll through this video real quickly, this will just show it the pre and the postop of a really an ideally selected case 'cause it comes right out to the olfactory on either side. We see a little bit of scarring left behind, but a complete resection and it's the radicality of resection we're able to achieve. Next slide, please. So, we tried to look at this group of 75 to see over time, you know, were we having more or fewer, and we sort of split it into 25 patients each, so relatively steady pace of these cases. And we did notice though that there were some changes in the surgical technique. So you would expect this, we're learning ourselves and improving our surgical technique. And we actually got to the point where, and this is probably a reflection of being more efficient with surgery, we didn't have any staging in the contemporary group, and this was very significant. We had to stage quite frequently and I would encourage people who are first starting to do endonasal surgery to stage whenever they possibly need to, both for your sake and for the patient's sake. We learned to use the Draf III frontal sinusotomy on essentially almost every case. And perhaps the most important was this multilayer where we went to an onlay of fascia lata graft. Oftentimes the vascularized nasoseptal flap is not quite large enough or is barely large enough leaving more room for a leak than if you have a large fascia lata tucked in between. Interestingly enough, our resection rate did not change dramatically, so we still were getting the same rates of resection, but we had a dramatic decrease in the CSF leak rate over time reaching that 8% that I mentioned in the contemporary group. So over those last 25 patients, our leak rate is down to 25%. There was no patient with permanent visual compromise and I mentioned that case of frontopolar injury or perhaps I didn't, but there was an intra cerebral hemorrhage related to a frontopolar injury very early in the series and not in the contemporary group. Interestingly enough, something I did not expect that was found by our trainees when they looked through this is that actually the rate of postoperative encephalomalacia was actually lower over time as well as the time for resolution of postoperative brain edema in the contemporary group, so something about how we were doing the surgery and our ability to get a microsurgical resection and perhaps the completeness of resection, we were having better impact on the frontal lobes even than we did early on. And this might be a result of lower leak rates, et cetera, that we don't have things like meningitis interfering. But this certainly is a significant difference that was found that suggests that we're continuing to improve our technique and our ability to resect this. So I do think that endoscopic endonasal resection of olfactory groove meningiomas, it's a logical and effective approach. And most importantly we get a Simpson Grade 1 resection with very clear anatomic limitations. So if we stay with those anatomic limitations, we minimize frontal lobe impact, but olfactory loss is a very clear trade off. This has to be discussed with patients. I also have a discussion if someone, I tell them all surgery that we do is traumatic. If we come through the nose, you're going to lose your olfaction. If we come from an open approach, we do have to manipulate the frontal lobe. I don't know what the impact is of that, but that's something that's avoided endonasally. I think that that's a fair trade off and a fair way to discuss it. And many patients who have olfaction or where that's important to them will choose a craniotomy as a result of that with an attempt. It's also important to recognize each one of our teams and each one of us as surgeons has a learning curve. And endonasal surgery has significant learning curve, which is especially pronounced in these larger tumors like olfactory groove meningiomas. But the limitations beyond technical really are anatomic. And so, we tried to look at a series of a hundred patients to try to see even in our own series, where did we leave tumor behind? So where did we have residual, again, the same rates of resection about two-thirds of the time were able to get a gross total Simpson Grade 1 resection, the majority of the rest get near total. And this is a combination of olfactory planum and tuberculum meningiomas. So, here you can see where we had residual and here's a graphical representation of the residual. And this makes a lot of sense anatomically, it's sort of what we knew. But it's fascinating to me that when we look at the postoperative MRIs, it really makes it very, very clear. The lateral half of the orbital roof, we simply can't reach there. We can decompress the lamina papyracea here and that allows us to retract the orbital contents over along with their fat to be able to reach all the way out to the midorbit, but we really cannot get beyond that and that's a very clear limitation. Similarly, a tumor that's in the optic canal, we can't come through the optic canal, that sort of defeats the purpose. We don't want to come through and destroy the optic canal. And so, both the anterior clinoid and the super lateral compartment of the optic canal are very real and practical anatomic limitations of the approach. One other aspect perhaps we don't think about in addition to the clinoid is the anterior falx. And coming transnasally, we have a very clear limitation. We can't make a 45 degree turn. Our instruments only have some ability to do that, and so as a result there's a cutoff on the anterior falx where we can only reach so high and so anterior. So when you see a large tumor, if you have a frontal tumor for example, that's crawling up the posterior table, it doesn't make any sense to do an endonasal approach because the tumor itself has done the brain retraction for you. Rather in that case I would always choose the transcranial approach, especially if there's significant involvement of the falx. So understanding these anatomic limitations, understanding the technical limitations in the vascular dissection are as well as your own learning curve are all critical points and choosing proper approach for these and indeed in progressing ourselves over time. So you might say, Well, look, you know you have these anatomic limitations. I can't resect every tumor this way or at least not completely. A transcranial approach will if I choose a wide enough transcranial approach will always give me access to these olfactory tumors. I can dissect the vasculature, I'm more comfortable with that. I have some chance even if a relatively minority of patients of preserving olfaction with a craniotomy. so why do this endonasally at all? Well, I would argue if I showed you this tumor, everyone here would absolutely say that this tumor should be approached through the most direct approach. You can see the bony involvement here, you can see the dural involvement. It's very obvious that this is the approach to take on this. Well, this is the exact same tumor just flipped upside down. Yet everyone would say, Well, many surgeons say, well, clearly you want to come from this approach to access this. Well, that simply defies that same principle. You can see the bony and the dural involvement here. It's quite obvious that the most direct approach onto this through an air cavity without touching the frontal lobe, without touching the brain, without touching structures which are not involved is a sub frontal or an endonasal approach. So, we actually looked at this and looked at whether or not there's a difference in MRI on for olfactory groove meningiomas. And this is a matched group, so we carefully matched size and the amount of edema of the tumor between ourselves and the Toronto group. And again, these are experienced skull base surgeons doing both approaches at both centers, both endonasal and open approaches. And we compared the amount of frontal lobe impact both encephalomalacia as well as the amount of long-term T2 or FLAIR change. And here you can see the impact on the frontal lobes. And when you look at the combined approach, it was essentially statistically significant that there was a clear difference in the impact on the frontals, at least radiographically. And again, as I mentioned, we're looking at what the neurocognitive impact of this. So I think it's hard to deny that any type of surgery we do has the potential to impact whatever structure you're working through. Certainly endonasal surgery destroys olfaction for an olfactory groove meningioma, but I think we have to be honest with ourselves that there is potential impact on the frontal lobes with a transcranial approach where the working under or around the frontal lobe that's not directly involved with the tumor. So, certainly neurocognitive and neuropsychology is an important long-term outcome for all of us to be studying. Another interesting aspect of this, when we looked at seizures in our own institution, we looked at endonasal versus open surgery, and we found that the risk of seizure with endonasal surgery was only 1%. And these were essentially always in patient who had complications such as dramatic pneumocephalus or are infection and a much higher rate of seizures in patients with open surgery for the same kinds of tumors. And this is despite the use of prophylactic anti-convulsant. So there really is an impact of exposing the frontal lobe and dissecting the frontal lobe when it's not directly involved. In the end I think there are all of these type of considerations that have to be taken into account, but the primary rule really is not crossing the nerve. If you have tumors like this, which are clearly lateral, these anterior clinoidal tumors or here another anterior clinoidal, here's a tumor that clearly involves on the right side here, clearly involves both sides of the optic canal. We can see the carotid artery and the MCA running right through it. This is not a tumor I would do endonasally because we're both crossing the nerve as well as crossing an artery we cannot control. Similarly, for an endonasal approach, these are all tumors that are inside, so this is inside the optic and the carotid. Here's the optical carotid cistern, so the tumors is expanding that cistern. Even though the tumor seems to spill over here, if we widely decompress the optic canal, it's actually going pushing the optic canal up and out. And these are all tumors that anatomically make sense to approach endonasally. And there are some that simply don't fit well into either category. You could argue for this one on the left here, do an initial endonasal debulking, let the frontal lobe edema resolve and come back and do either a transcranial or endonasal approach. This is a patient with a meningiomatosis. You can see here the optic nerves going right through the middle of this tumor. I would argue here that perhaps this requires first an endonasal approach to see how the vision might improve and then you could try either bilateral or a sub frontal approach for that clinoidal disease. And then finally this one, I really can't tell where the optic nerve is. We end up doing the endonasally, and sure enough we're able to get a complete resection because the optic nerve is actually pushed up and out. Something that can be very difficult to discern on preoperative imaging. I think that endonasal surgery is really finding its way in where it might fit as a standard treatment. It still is not accepted as standard treatment certainly for olfactory groove meningiomas. But I think there's more and more data showing it for any anterior cranial base and understanding where it's place fits and what the pros and cons are. And the more we study our own results, and compare them to others. And again I applaud Dr. McDermott and Dr. Magill, for their large tuberculum study, which I think probably has the most robust results we'll ever see for endonasal versus transcranial approach. Certainly craniotomy remains the gold standard and we have to hold ourselves to that standard, if not try to improve it with good microsurgical technique regardless of how we're doing the surgery. Also, we're finally starting back up courses again, in-person courses in Pittsburgh. These are the dates of those courses next year, and hopefully there will be no hiccups with that. We have everything in place. This is a new textbook with many of my friends and colleagues involved with what I think are some of the most important aspects of skull base surgery, which is the vascular considerations that some of the worst complications come from vascular compromise. And then finally, as always I invite everyone to view the the Skull Base Congress, which is largely based on anatomy, et cetera, and certainly one of the great resources online in addition to this magnificent resource of Neurosurgical Atlas, which I think all of us need to be following, and I myself follow regularly. So, Aaron, thank you again for the invite to be here and I know a controversial topic but all the more reason to discuss it.

- Absolutely. Very well said. All the good reason to discuss it. Beautiful videos. Obviously your technical skills are at a different level, Paul, and not everybody has those skills, and that's the challenge when we discuss these. We believe everybody has the same technical skills and now let's talk about what's right for the patient. And that's the main point that we never talk about. When people ask me, how would you do this case? It's always this difficult discussion is that, well, maybe somebody I know who's very good will approach it that way and work well, but how am I gonna tell that person that this may not have the same result in their heads? You see that's a very tough topic to approach. Do you have any pearls there?

- No, I think some of that is each of us has our own surgical ego. There's no question. And one of the things I always try to show is that there's a very clear learning curve with this, and you have to very carefully select cases that you believe you can do while slowly pushing not only yourself but your team. I think a good, perhaps more dichotomous example is if you look at endovascular versus open treatment. I don't have an endovascular skills and there are certainly most aneurysms are treated better that way, so I have to trust my colleagues when they say, Look, this can be treated well in neovascular. That's the best even in my hands. If it's me personally doing it, the best approach would be an open craniotomy 'cause that's what I'm comfortable with. But the same goes true with this. You have to either have someone at your center who has that skill set or develop that skill set yourself. I think we're seeing more and more young surgeons coming through, developing both skill sets at the same time. I was fortunate to do that and that gave me a little bit less of a bias towards what I was most comfortable that had been trained with. But I think we, you know, the best thing you can do is be honest with yourself about your learning curve and give that patient in front of you the best surgery that you can offer. And if that is a, you know, if I were to go to a new center and I were operating the first time with a set of ENTs, I would never approach a giant olfactory groove with a lot of vascular encasement, with a group I hadn't worked with. That's simply not in our group's learning curve, so I think you have to be honest about yourself, where you are with your learning curve and indeed where your hospital and your center is. And it doesn't mean that you can't progress through that. Certainly we've done that. It's taken 20 years to get to this point. And I think that's the important point to recognize, it does not happen overnight. And that's true for all of us with all of skull base surgery. We're all perfecting and learning approaches and trying to give our patients the best surgery we can. And sort of my arguments here are to look at the innate advantages, but also respect the learning curve and the technical challenges.

- Yeah, I agree with you completely. The other point is that we just don't have enough data, we don't have psychological detail analysis of these patients three months postop to see if it's open or endonasal is more effective. The issue of the staging and operation, so a large meningioma, staging it just because you want to do it through the nose. I mean, that has downfalls obviously. And does that necessarily, how does that balance to the advantages through the nose? The other issue is that obviously saving olfaction. We say that mid-small to mid-level olfactory meningiomas, we can preserve olfaction through transcranial approach. I can tell you that that's very controversial because the nerves are very much involved with the tumors. So either way you approach it, you may not have a chance to preserve it. So, there is just so many variables that will make it very difficult to define which one is the better approach. And there is gonna be so many patients that you need that they have to be so carefully sort of matched together, that it'll make it extremely difficult, if not impossible to know for sure which one is better to the other. My personal preference, again, this is personal, and when you get to personal preference, it's very difficult to justify for everyone is that if the tumor requires a staging through the nose, may be more reasonable to do it through a craniotomy. That's number one. That means it's already so big that the staging operation will require a large resection of bone at the skull base. The risk of CSF could be more than usual, and therefore doing it through the cranium is a better approach. Number two, is that if the patient has preserve olfaction, maybe doing a supraorbital triola would be a good approach. But please do note that as I said, that even may not guarantee that you're gonna preserve olfaction because sometimes the nerves are very much involved, so it doesn't matter what approach you use. And ultimately I don't use bifrontal craniotomy for olfactory groove meningiomas. I haven't done it for 15 years because a pterional approach provides a beautiful lateral trajectory, early identification of the optic nerves and carotid artery and really aggressive resection of tumor with only placing one lobe at risk, and not opening the frontal sinus or ligating the superior sagittal sinus. So, there is just so many variables embedded in this whole decision making process that one has to be extremely honest with themselves and say, What are my skills? How big is a tumor? Am I versed in both strategies, so I'm not having a personal agenda that affects the patient care, and make the decision accordingly. Any thoughts you have about that, Paul?

- No, I mean, I think admittedly we each have an agenda based on our beliefs of approach. I'll be the first one to admit my, I think there's no question what my agenda is. The only other piece I would add is, is again a unilateral approach, a pterional approach does not get you the olfactory sulcus. You can't get good resection, you certainly can't resect the dura there. You can try to burn the dura and scrape some tumor. But we see recurrence there. And I think the question is, you know, just being honest, that fine, I'm going to resect that, I'm gonna try to preserve olfaction. I'm gonna use radiosurgery or radiation for that residual. I don't think that's an unreasonable way to treat that, especially if you're trying to preserve olfaction. But I think you have to be honest about the long, about the radicality of that resection. There are, especially for olfactory, there are a multitude of factors as you say. And I think the more we define what those risks are, what is the chance of me preserving olfaction through a craniotomy? That data to me doesn't exist well enough in the literature. What are the neurocognitive outcomes with craniotomy or endonasal? Is there a difference? There may not be. But I think we, these are the questions that we still have to define over the next decade to try to really answer this question. And hopefully maybe by then we'll have figured out how to treat all meningiomas medically and we won't need surgery at all. Maybe that's the ultimate goal here.

- Yeah.

- But this remains an area of active. I think as we see our trainees pick up these skill sets earlier on and in fellowship, I think they will help us find as a group exactly where's the right place for these to fall without bias that we have. And I think over the next 10 years or so, we'll really see where this all falls out.

- Very well said, very well said. I think the ultimately one, number one, has to be honest with our technical skills. Number two, has to consider what's best for the patient under the information we have, which is very limited. Data on surgical outcomes are so limited. Besides that data on individual surgeons' outcomes are very different, so it adds such an incredible uncertainty to what is the right thing to do for a patient that really makes it extremely difficult in any way to assess what's right. Right in the meaning of good data. It's impossible. And probably it's gonna remain impossible for the near future. And we hope for other medical therapies to come over. But either way, Paul, really impressed, good perspective. I always say the best way for a surgeon to function is to have every perspective considered. Obviously the patient perspective is the most interest, most important interest to be considered. But the surgeon perspective has to be wide, has to be unbiased, objective as much as possible, which is never for sure objective. And using those be able to make a good decision what's right for the patient. I wanna, again, thank you for an incredible contribution you've done for skull base surgery, Paul. Really, really a role model for so many of us, and I want to thank you again.

- Thank you, Aaron. Always a pleasure, and hope to see you soon.

- Thank you. Same here.

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