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The Limits of Endoscopic Endonasal Skull Base Surgery (Sagittal Plane)

Daniel Prevedello

October 04, 2021


- Colleagues and friends, thank you for joining us for another session of the "Virtual Operating Room." My name is Aaron Cohen. Our guest today is Dr. Danny Prevedello from Ohio State Neurosurgery. He's the Director of Skull Base there. A pioneer in complex endoscopic skull base surgery. Danny, I sincerely appreciate for you being with us today, very much looking forward to learning from you. I know you're gonna address an extremely important topic and that's the limits of skull base surgery, in this case, the sagittal plane and how much we can push the boundaries of endoscopic skull base surgery safely. So again, thank you for being with us and very much looking forward to your lecture. Please go ahead.

- Yeah, thanks so much, Aaron. It's really an honor and a pleasure to be here and participate in this a great addition to the, all the students, all the residents and people who are interested in not only neurosurgery, but specifically the field of skull base surgery. And what I'm gonna try with this talk to really show some of the learning aspects of my career. And when we face situations that we thought was the limit, and we were able to actually push the envelope and other situations that will really face the limit of what we can do with endoscopic skull base surgery. And we had the compliment with craniotomies and other approaches. So once again, thanks so much for this invitation and the opportunity for me to participate here. So I'd like to start with the most common tumor that we actually deal with in endonasal surgery. And those are the pituitary adenomas. And I really started with these here demonstrating what is the limit, right? So for the most part, what we do nowadays, we can take care of lesions, pituitary adenomas in the sellae, in the cavernous sinus and even suprasellar extensions. But there's definitely situations where it goes beyond what we can do. And this is a great example here. If you noticed in this specific case, you notice that there is a very narrow space in between the two carotid arteries to go endonasal and reach this balloon of tumor that goes beyond superiorly there and goes in the direction of the third ventricle and really comes forward. If you look here in this area, it goes very forward in the frontal region. More importantly, we use expanded approaches where we go through the planum sphenoidale to reach tumors that are located on the other side, intracranially above the planum. But in this specific case, there is brain in between the planum and the tumor here. As the tumor had an angle growing in that direction and basically allows presence of tumor, is still present in the skull base here. So in this situation, we cannot really address this tumor by coming directly through the planum sphenoidale. And here is a situation that we started endonasal and we'll get the here demonstration where the exposure of the sellae was, and you can see this large mass on the other side. And we are opening the dura of the sellae. We will dissect the components. And at this point, I wasn't still like not, understanding if we will be able to remove the tumor completely up there or not. And this is, I started endonasal in this case, and this is very important to have a very wide exposure. We went up using angle drills and angles sculpts, and we drilled this part of the planum sphenoidale in that location there. By opening as much as possible, I thought this will be to optimize the ability for me to go up. And we really follow this tumor, was suckable, was soft. And in one point of the dissection, we got really restricted by that position of those carotid arteries there. We follow that tumor superiorly. Part of the diaphragma was coming down. We even then use a 70 degree endoscope to follow that. But the opening, as you can see here was very tiny, very restricted. And even with 70 degree endoscope, we had the limitation of reaching superiorly there. As you can see here, that is a very narrow space. We're using angle suction tips as well to follow the tumor. But as you can see, the tumor angles in a more anterior perspective and limits our ability to continue the dissection. Here even with Q-tip really try to really optimize everything we can remove endonasal, but that narrow space really limit us. We got a lot of diaphragma coming down, but we know that there was like a major part of the tumor is still there. So this is a case where we combine here with the endoscopic endonasal with a craniotomy. And we were able then to move here and get a complete resection of the tumor after a craniotomy. So the craniotomy was performed later on here, as you can see, I had to dissect the Sylvian fissure I didn't find much tumor there. And I had to use a port through the brain coming from the front to get the dome of that tumor and resect all the way back there. So we got a complete resection of the tumor at the sellae level, and of the component going through the parenchyma. But we had to leave a little bit of disease around the anterior circulation with a tumor in that region there. So that shows the importance of complemented with craniotomy for pituitary adenomas. And now we're moving here to meningiomas. So this is a tuberculum sellae meningioma. For the most part, tuberculum sellae meningiomas we do approach them endonasal. For the most part, they are located in between the optic canals and the optic nerves and under the chiasm. And I believe the best approach to address the medial aspect of the optic canals is the endonasal 'cause we have access to both sides and we obtain this type of resection with the tuberculum sellae meningiomas preserving the stalk and the pituitary gland and doing the vascularized reconstructions. These are examples here of some of the tumors that we approach earlier in our career with the before and after. As you can see here with preservation of the pituitary gland. If you look at the post-operative contrast, we can see the pituitary stalk enhancing the pituitary gland enhancing and the presence of the nasal septal flap. So we always do an MRI on these cases to confirm the type of resection. Of course, some of the tuberculum sellae meningiomas have some very unseen, sometimes in key vessels, or they have more lateral extensions. And that is some of the difference that we have to consider every time. So one of the technologies that we've been using is use of ICG during surgery. And ICG has been helping us to define the position of the internal carotid arteries. It really, even under the bone, you can identify the position of the carotid arteries and also identify the blood supply of some of these meningiomas. So this is a small tuberculum sellae meningioma that we use ICG for identification of the carotid artery to optimize our opening for safety there. And then allowed us to resect the tumor. And here's the small tuberculum sellae meningiomata that was causing vision loss on the patient's left side. And you can see it that optic nerve there. Then also help us to identify any residual of the tumor and also confirm the preservation of the mini vasculature like that specifically superior hypophyseal artery preserved for this patient. The other technique that is very important is to open the optic canal. So this is an example of a tumor that was evading the optic canal and after resection of the subarachnoid component of the tumor, we use this Daisy scissors to open the medial wall of the optic canal, and then to decompress the optic nerve and opening like a filet, opening like a book, both sides, we can then remove the tumor meningioma that is kinda following and compressing the optic canal and optic nerve inside the optic canal. The other technique and instrument that we design is this feather blade. I have to disclose here that I have royalties with this, and basically has a blunt perspective insight, and it cuts in the posterior part. And you can open the optic canal like a can opener. And really allows for a great preservation of the optic nerve, as you can see here, and decompression of the optic canal and exposure of the more anterior segment of the optic canal for a resection of the meningioma that is invaded. And you can do this on both sides. When the tumor starts getting a little larger is when it's more controversial. This is the first case in my career that I consider a two stage approach. I actually approached the family. This is a lady, a 48 year old, that was losing vision. She was at 2,800 bilaterally, and I offered to go with an endonasal debulking first with the possible resection of the tumor to be more complete. And a second stage, I thought that if I did a craniotomy only, I will probably reduce her vision quality. And it was already basically almost blind, functionally blind. So the tumor was going around the middle cerebral artery as you can see in this area, it was very important for me to consider that and explain that to the patient as another point the tumor also comes in the planum anteriorly there. So in this patient, you can also see that the tumor was going all the way to the basilar posteriorly and really surrounding the MCA there. So in this case, we offer the patient endoscopic endonasal. We were planning to perform a resection more for debulking. But with a wide exposure, we were able to perform the debulking of the tumor and progressively, we identified some of the behavior of the tumor, just going around the middle cerebral artery and in the direction of the bifurcation of the internal carotid artery. We were able to roll that tumor away from the Sylvian fissure. We identified here the pituitary stalk, as you can see down here and mobilize the tumor away from the suprasellar space. Sharp dissection in the posterior aspect of the tumor. You can see how the anterior cerebral arteries were causing these attenuation and thinning of the optic apparatus. You could see the anterior cerebral arteries through transplants on the other side. And we preserved here the superior hypophyseal artery that was just passing by in that area. And we ended up with a complete resection of the tumor, preserving all the important elements and a great recession here. You can see that the pituitary stalk and the resection from carotid to carotid. This is the a post-operative MRI, patient did very well. He had some improvement of vision, but not very impressive. As you can see in the video, he was extremely affected and compromised, but she is able to read nowadays and no recurrence of this tumor after several years. This is the post-op of the sagittal here. You see the pituitary stalk preserved and the pituitary gland preserved as well with the enhancement of the flap for reconstruction there. So it's not because the tumor is small, that we will always perform endonasal. This is a tumor that when we analyze carefully, it was evading the optic canal from the top. As you can see and then mark there. And it looked like the optic nerve was actually pushed down below the tumor here, as these tumor came more from interior clinoid down, pushing the optic nerve down. So it was a situation where we made a decision to come with an eyebrow incision here. And we came with a sub frontal approach for resection of this tumor. And you can see here, the post-operative imaging with no lesion for the tumor, for the patient. And we were able to remove the tumor completely there as well and we've being following this patient. So this shows that this is a limit based on the position of the cranial nerve, right? In this case, the cranial nerve too was pushed down. This is another case that we did during the pandemic here, not too long ago. And this patient had very severe compromise of her vision. She was basically blind on the right side. You can see the position of the optic nerve here, curved completely in that area. And the left optic nerve is more robust in that local there. The other important aspect is surrounding the anterior circulation, so 360 there. And there's a little bit of a spill of tumor past the position of the optic nerve. But more importantly, in this case is this. So the optic nerve is located right here and you see all these implantation that is located lateral to the optic nerve there. And possible even in the clinoid the presence of some tumor invading that area. So this is a tuberculum sellae meningioma with a major variant here. There is a lateral extension on top of the optic canal. So in this case, we decided to do a craniotomy and obtain a complete resection for this tumor here. You can see after surgery, the reestablishment of the chiasm there, the pituitary stalk and we were able to resect this via craniotomy for the patient. This is another case that patient had only headaches had normal vision. And this is more like a planum sphenoidale meningioma. And here this patient had lots of headaches and some edema on the brain, and we debated what to do here. She had a normal smell and because of the normal smell, we consider a craniotomy for her. But this is early many years ago, patient came to us and we discussed the possibility of endonasal. We were very worried about taking her smell, but because the tumor not really sitting on the olfactory groove and she had all of these hyperostosis here, with felt that there was a possibility for us to go endonasal, drill the hyperostosis and take the tumor out from that area. So that's what we decided to do. And we proceeded with drilling of that area, the hyperostosis. We opened the cistern in the suprasellar area to get some of these CSF drainage. And we had then dissect the tumor around and we identified the left olfactory nerve. As you can see there was really compromised, but we tried to dissect around. There was some of these branches of the anterior cerebral artery that we had to dissect. So very important to do the same technique we do in microsurgery, use two hands, dissect these vessels, the same way we would do in a craniotomy. We were able then to go around the this tumor, dissect from the arachnoid, a little bit of PA evasion in the upper part that we had to go around and do some sub field dissection. I like to use some of cottonoids. As you can see here to establish those planes. And with a little bit of a contract traction, we were able to mobilize that tumor using the cottonoids there. And if you look at here, you'll see the presence of olfactory nerve on the right side. And that was a nerve that we preserved completely. And we did this entire surgery with the 45 degree endoscope preserving all the septum function and the smell sensation for the patient. You can see here at the end of the procedure, the presence of the olfactory nerve preserved. We perform the reconstruction with Collagen Matrix followed by fat in the sphenoid sinus and the nasal septal flap over the entire skull base. This is the post-op. You can see the presence of the fat in the sphenoid and the flap covering that component. And the cribriform is to preserve with the anatomy and the structures related to smell preserved underneath as well. She did very well. This surgery is interesting, has been I think about 10 years, is one of my first cases at Ohio State. And she is doing well, there's still no recurrence. And she took about six months, but she recovered her smell. We measured her function and the function is basically normal. With the 40 points for the upside tests she got about 35, if I remember right. She's doing very well. So other situations when the patient basically doesn't have smell anymore, like this patient and the tumor doesn't go beyond the limits of the orbit or on top of the anterior clinoids. That's when we indicate endonasal surgery to take care of this tumors more located centrally. But again, we test our smell in every patient because I think the smell was very important for quality of life. If this patient had normal smell and there is a tumor in the olfactory groove, then we would do a craniotomy. I just did a case yesterday in this situation, patient with normal smell, that we indicate a craniotomy to be able to take the tumor and preserve the olfactory nerve for the patient. In this case where the smell was gone, then we would just go endonasal and do the reconstruction with a flap. As you can see here for a complete resection for the patient. The main advantage that we see is really the fact that we don't see footprints in the brain. We publish a couple of articles showing that the flare changes located in the frontal lobes, basically absent or minimal after resection of anterior skull base meningiomas, when you come through the nose. I'm sure that can be reproduced with the open approach, but when you're dealing with the brain with a lot of edema through stalk it's not easy because a lot of the brain wants to get out of there. There's lack of space. So that's why for some of these large tumors with lack of smell, we opt for the endonasal approach. The problem is when there is a tumor beyond the limits of what we can do with endonasal. And this is the best example that I actually learned with this case. This is a case that early in my career, that I decided to address endonasal only with this. And this is a can see, had major involvement of the anterior circulation. Had a spill of tumor beyond the position of the anterior clinoids there. And had a lot of hyperostosis located at the skull base. So we did this in two stages endonasal, and here's some of the aspects during the surgery of the second stage when we had addressed this patient. So here we initially debulk the tumor. We went down to the chiasm area. We identify the position of the chiasm and the tumor was more lateral than what we could reach. And our initial idea was like to perform a full debulking. And this can be dangerous when you have the tumor invading the anterior circulation. 'Cause you know that their branches are even the anterior cerebral arteries are inside the back of the tumor there. So the first response of the surgeon is to go on top of it. Like it makes sense to try to roll from the top initially, and to do some of the subpial dissection there. But you cannot keep going that direction an you end up with not good visualization and low proximal control of the vessels. And I start seeing vessels in the back there. So our idea was to roll it from the sides first. And we were able to kind of amputate some of that insertions that were laterally, debulk of the tumor. And here with the bipolar, we were able to roll it from side to side. But the most important was to really have proximal control on top of the chiasm, finding the anterior cerebral arch. As you can see them here a twos getting together and forming the anterior communicating artery and very carefully work here on the stage to surgery as I'm demonstrating. We're able to resect the disease that was located around the anterior circulation as you can see there. We perform the reconstruction with a Collagen Matrix, fat, and then we reutilize that flap. And because it was a realization of flap, it didn't look that great. So we actually had to use in this case a little bit of fat around, and this actually worked for this patient. It didn't have a leak, next? And here you'll see the post-op. But here's the problem, he did great. He had psychiatric problems before surgery. He improved completely. And you can see here, this is the residual on top of the clinoids there. It looked like something not relevant for me when I saw that before a small residual on the falx. But the problem is over the years that grew and you can see here, the presence of this tumor growing on top of the clinoids. And I had now, I had to go back and do a craniotomy to compliment those resections that I did several years ago. And this to me was really a learning process. Like how I didn't solve the problem for this patient. Probably if I had done a second stage craniotomy or the whole surgery craniotomy, it would have been better in terms of resecting the tumor. So those are the learning aspects. This is a another patient, just to show some examples here who came to me with normal smell and a little bit of edema in the brain. And also there's implantation triangular that goes beyond the clinoid area, like beyond the optic canal. So in these situation, I didn't hesitate here and because of the normal smell and tumor invading the olfactory groove is not just purely planum. Then I perform an eyebrow incision with a sub frontal approach. And I performed resection of that tumor for this patient. And I think this is a great example, of us being able to preserve his smell in this case and how you really have to look case by case for the patients. This is a similar situation with the difference here is a little older patient. But if you look at the olfactory groove on the right side, there's no tumor there. So in these particular patient, he loved to drink wine and appreciate life. He loved his wine. And because the edema is on the left side here, I felt that this was the best way to preserve his smell would be to do a craniotomy. Coming from the left, which is the side of the edema, when there's edema on the same side of my approach, then I remove the rim of the orbit. So I dropped the orbit and I got a very low skull base approach here. And I came from the left with the intention to preserve all the olfactory groove anatomy on the right side here. And this is exactly what we did. This patient actually did very well. You see my approach there? I was able to preserve the olfactory groove and the olfactory nerve on the other side. And these patients coming from recovery, he actually asked to page me, and he was like a former professor of the university, engineer if I remember correctly. And actually he became a donor for our department and so excited that we were able to smell, preserve his smell. And he called me from recovery room because he was able to smell and he'd test himself and he was excited. So then you start thinking, well, I would just do craniotomy for everybody, right? So, 'cause there's some limits with the craniotomy as well. And that's what I tried to show with this case. This is a patient that presented at Ohio State University 10 years before me. The surgeon who did this surgery is not even in our department anymore, but he did a good job. You see, there was edema here. He did a bicoronal, bifrontal, and he got this tumor out. And this is the post-op that I still have in the archives here. And a little bit of more of a footprint here, but not so bad. There's no DWI, maybe just a little bit there, but it's a good resection. The problem here is this, the hyperostosis was left behind. And this patient was following up with a neuro oncology team and they felt well, this is not cancer, this is great. So the follow up became like every so many years and the patient came back to me going blind 10 years later with this lesion, with this recurrence. And here you see the presence of lesion on the planum and in the tuberculum sellae area. And you can see here that previous craniotomy that was there. So because of the previous craniotomy and now is much lower tumor, I did an endonasal with the team here at Ohio State, and we were able to get these tumor resected for this patient, as you can see here. And we are just, her vision improved completely. And this shows to me how there's a limit in craniotomy. And also the fact that the endonasal and the craniotomy they compliment themselves. So with that idea, I started doing for the last few years, this type of technique where I stage this tumor. So I do an intentional stage when there's a lot of hyperostosis unilateral inflammation of the tumor. So if you look at here, there is a major hyperostosis, very thick in this case and lateral implantation goes very like lateral, like in that region. Very vascularized tumor, as well as you can see and the patient has some edema on the right side. So in this case, I go and I do a drill out endonasal of that entire hyperostosis. After that, I take the anterior and posterior medial arteries bilaterally. This patients don't have smell for years, as you can imagine. So that's not a concern. And we make a nice hole in the center of the tumor without going around, without going into the interface in between the tumor and the brain. With that, we obtain this type of visualization with the post-op MRI. You see the tumor is more avascular at this point and collapses down. The edema gets better. And then what we can do, it's a smaller craniotomy. I don't need to do those bicoronal or bifront, I just come with a small frontal lateral approach. And I get a complete resection of the tumor and the flap was already installed in the reconstruction in the previous surgery. So with the combination of the two surgeries, I feel that we give a much better result for the patient without fighting the brain and with a more complete resection with a very accurate out of the hyperostosis coming endonasal in stage one and resection of all those extensions of the tumor in the anterior skull base that are present in several of this meningiomas. This is another example of the patient, a young lady in her 40s with bifrontal edema. And these sizes of old tumor here that we did exactly the same. We perform the resection of the tumor and we were able to get the tumor decompressed. So here's how it shows that this is the stage two during a craniotomy, just to give an example how we don't even need to use retractors. You can see the, the optic nerve located right there. We are debulking the tumor and progressively rolling that tumor away from the optics. The technique I used with the lateral frontal approach is to identify the anterior cerebral arteries behind the tumor. And then we roll the tumor forward, protecting the optic chiasm and the optic nerve. As you can see here, we're looking at the vessels in the back dissecting, creating a nice space. But really the goal of this video here is to show you the advantage of not using any retraction. In the stage two, it's not that difficult fight with the brain cause the edema has improved. As you can see here, I use a lot of the cottonoids around the tumor, but I try my best not to use retractions. And you can see here the resection of the last attachment near the falx, and then we're then taking the tumor out. This is at the end of stage two. And then we will explore and this is interesting cause you see here, the optic nerve on the right side, the optic nerve on the left side, then you see the interior skull base with a flap that was reconstructed before with a complete resection for the patient. So this is a post-op MRI and this is really the closest I would say that we can get to a seeing someone for these patients. Other tumors in the anterior skull base are esthesioneuroblastomas. And these are interesting cases. There's a little more discussion because you're dealing with a malignancy. So sometimes we use chemotherapy first and that depends on the case on the grade. And I'm not gonna go into the details here. But this is a case that was lower grade in a 72 year old gentlemen. And the decision was to do a complete resection endonasal. You can see here the reconstruction with a little bit of fat and flap and patient did very well. So just to show a little bit of that technique that we used. The dissection we performed around the cribriform and we coagulate and cut the anterior and posterior medial arteries. We remove the crista galli and very important to remove all the bone of the . As you can see here, and get the dura exposed. And then we cut the dura around the olfactory groove and around the cribriform plate. Here's we then rotate the entire interior skull base down cutting the falx. Once you cut the falx, then you have access to the olfactory bulb and tract and then we bipole and cut the tract. And then once we do that, we cut the dura posteriorly and your entire specimen comes out in block. So it's like a removal of the anterior skull base and here the reconstruction with a Collagen Matrix and the nasal septal flap. This case is interesting 'cause we also scan margins all the way around to make sure you get a complete resection of the tumor. This is another case of esthesioneuroblastoma. And here you see the similar technique where we remove the cribriform completely. Some of these tumors can be extra dural. So we resect that first and then we again, take the anterior and posterior medial arteries, remove the cribriform plate and crista galli. And then we opened the dura around the olfactory tracks and very important to do it a draft three anteriorly, where we then opened the dura anterior to the cribriform and we were able then to get the 360 around and preserving the brain and rotate that skull base down. Very key element here is really to be lateral to the olfactory bulbs and the olfactory tracts, not to leave anything behind. And to cut the falx as we come anterior to posterior rotating that anterior skull base down from anterior to posterior. As you can see here, we get there all the way to the falx on both sides. Usually there's some veins in this area there you've gotta be careful and use this strait cutter here to cut the falx. Very careful to make sure you don't go too deep. And always look there to make sure there's no artery near the last cut of the falx. And then we rotate and dissect from the brain, see the olfactory tracts come down. You can see them bilaterally here and here. And that is a key moment there where we dissect. And then we send margins, we send margins of the olfactory tracts and olfactory tracts bilaterally and the dura all the way around to confirm free margins next? This is post-op showing the reconstruction with the flaps in place and this patient didn't have any leakage. The other tumor that important for us to discuss are the craniopharyngiomas. And for the most part, craniopharyngiomas we will really indicate endonasal approaches with some very rare exceptions of those more, the large ones that go laterally, Sylvian fissure and sometimes I have a patient who had the Ambien cyst and actually, and I went actually retrosig for a recurrent craniopharyngioma. But for the most part, primary craniopharyngiomas, we will perform endonasal approaches. And these are example here of an approach that we performed, drilling of the skull base completely, getting the hyperostotic bone removed. And here you can see the removal of the sellae. Some of these are so hyper static or there's no pneumatization, sorry. And you basically have to recreate the pneumatization. And navigation can be helpful. For craniopharyngiomas, we always open the sellae, expose the gland and we go above the superior cavernous sinus and we ligate that superior cavernous sinus that runs in between there. With that, the first thoughts in my mind here when I'm opening the dura is where are the superior hypophyseal arteries? 'Cause superior hypophyseal arteries can be pushed against the dura when you're opening. Here, we're performing a little bit of a debulking of the tumor, and then next we will be looking for to stalk. So this is what we call craniopharyngioma type one, where the disease is anterior to the stalk. The stalk is positioned posterior, as you can see there. And anteriorly, we will have the chiasm running superiorly there. So the entire surgery happens between the pituitary stalk and the chiasm. So carefully debulking of the tumor, and then progressively dissection of these tumor around the walls of the hypothalamus there, will allow us to free up the component of the tumor that is going into the third ventricle. See, now you can see the optic nerve and chiasm superiorly and we will debulk an dissect. And this dissection, we did circumferentially. and in one point then the tumor was free from the walls of the hypothalamus. We combined a 45 degree endoscope with the zero degree endoscope and I'm able then to bring that tumor out of the third ventricle. So you can see here, the presence of the tumor and the component that was the third ventricle. Then we just brought it down after dissecting the walls there. And here, you can see the view superiorly of the third ventricle and the reconstruction using Collagen Matrix and the nasal septal flap. This is the post-op and you can see the preservation of the stalk posteriorly there and the gland and the position of the nasal septal flap for reconstruction. So these are several of the pre-operative images, just to show some of the flavors that craniopharyngiomas can appear. Some of them more diffuse and laterally located, but for the most part, all these endonasal approaches, and these are the post-op images, just to give examples of some of the indications and the different presentations of craniopharyngiomas. That same case is of the video, like a few years later, that patient came back with these recurrence. So craniopharyngiomas are not easy. They tend to recur. And then the question is what to do now. And you can see this as off centric to the right side at this point. It looked like to me, there was on top of the optic nerve and with a very intimate relationship with the anterior cerebral arteries there. So in this situation, I didn't think that going endonasal again was a good idea, particularly with all the scar and the risk of leakage. And so what we did was we came with an eyebrow and you can see here opening the cistern around the carotid artery and dissecting on top of the optic nerve. Here, we notice the tumor definitely confirm our thought that was going on top of the optic nerve. So we were able to now dissect directly under visualization with an eyebrow approach, next? We follow the medial aspect of the right optic nerve posteriorly, identified the chiasm and basically dissect this recurrent craniopharyngioma away, next? Medially, we identify the position of the anterior cerebral arteries. We're able to resect all that calcified recurrence following the chiasm, next? And this is when we identified the position here of the anterior cerebral arteries mediately located. So the tumor was really attached to there, next? Here we go. And that's the piece that was then dissected away from the vascular structures. We were able to get very good resection for this patient coming with this approach. And this shows a limit of the endonasal, where we had to come with a craniotomy because of the recurrence that was more laterally located. And then you see the final resection of the tumor with the preservation of the neurovascular structures, next? And here we're closing the dura via eyebrow primarily. So this approach works very well for this lesions located laterally. And this is the post-operative imaging. We use radiation for this small little enhancement that stayed there, but insignificant compared to what we had before. So another limit is when the lesion for craniopharyngiomas is located purely inside the third ventricle. They can be very large. I have a few of these cases and options here are basically anteriorly transliminality analysis approach. It's definitely an option. I prefer to come trans callosal for these patients. And this is what I did for this particular patient, with the experience of having a very small window here between the optic and the gland to really work into this very large mass. So with that we performance transcallosal. And this is what happened, during the dissection, I was able to remove, I would say, 90% of this tumor, and I left this space anteriorly because I wasn't able to, with a transcallosal really understand the position of the optic nerves. And I felt that I was massaging too much of the fornix and I decided to leave this piece. And during the post-op, I thought I saw this and I thought, well, you know what? This can be a perfect compliment for if I come endonasal now and get just a piece that I can actually get with an endonasal. And that's what we did. So this was not my intention. I was trying that transcallosal to get a complete resection, just didn't feel safe, anteriorly. And that I compliment with an endonasal resection and got a complete resection for this patient. He never needed radiation. He is doing great. He's been from presentation. So, and his memory improved tremendously with this surgery. He was off like, he was not able to get to work. And now he's back to the workforce and doing very well, actually the with strategy. So now I'm moving a little bit to a posterior fossa tumors. Where we'll see some examples in the... So this is a great example from my career in terms of limits of other techniques here. This is a dorsum sellae meningioma that starts really at the dorsum sellae in the center of this lesion. This is difficult because the chiasm is pushed anteriorly there. But walking a craniotomy approach, you can do but you will need to work between the carotid and the optic nerve. And it's really a lateral approach. You don't get to see this whole mass. This patient was not my patient originally. He was my partner patient, and he decided to go transsphenoidal with an extended approach here. And the important aspect of dorsum sellae meningiomas is that they push the stalk anteriorly there. And this is what we noticed here during surgery. So what happened here, the surgeon started the procedure with a speculum. As a can see this as a microscopic view exposing the sellae next? And you can see how once the dura is opened, there is a presence of the pituitary stalk right in front of you. And the tumor is all located behind that plane, next? So he's a great surgeon, very good, very skilled, and able to resect most of the tumor using the corridor, working on the sides of the stalk, debulking the tumor posteriorly, working on both sides, next? And you can see the view of the microscope, next? And in one point here, the surgeon felt the difficulties and the limitation really to go behind the sellae there because there was decompression on the optic apparatus, but can we do maybe a little better here? So my partner called me and said, "Hey, can you maybe take a little more using the endoscope?" And next? So this is a great example here. We brought the endoscope and we were very limited by the presence of the speculum. We had to remove this speculum. And then with the endoscope we're able to dissect, and I did a himatransposition of the pituitary gland on the left side, next? So I disconnect there. I work above and below the pituitary gland. You can see here from the previous surgeon, the dissection, the optic nerve is decompressed, but there's still a lot of tumor behind the dorsum. So in order to avoid a full transposition and preserve the venous outflow of the gland, I kept the gland attached to the right side here. And these, it's a little in the way, next? Because the pituitary gland sits kinda still there. You have to rotate up and down, open the door type of movement as well. We're able to remove the posterior clinoid and both sides actually with exposure of the carotid here to allow for that, next? And we worked the behind the pituitary gland, and we were able to get a complete resection. As you can see here, you can see that that's the component of the dorsum sellae that we removed. You see the basilar artery posteriorly there, and we're able to elevate that tumor away, next? And you can see the final result with this video here, or the pituitary gland is there preserved. You see the pituitary stalk preserve and the pituitary gland preserved completely with the complete resection of the tumor, next? And with that, you can see how we did the reconstruction. I put the collegen matrix around here and we brought the nasal septal flap to cover everything. So this patient ended up with a mild persistent GI, but all the other hormones of the anterior pituitary gland are normal, absolutely normal, no other replacement. Here's another example of a small meningioma that was growing. And this shows very well, the limit of transcaval approach. I love this video, very old, but shows the last piece of meningioma located medial to the sixth cranial nerve, as he was entering into dura space before duralis canal. And you can see here that we were able to get the tumor medial to that sixth nerve. But you can imagine if the disease laterally there, we're probably not able to remove. And this patient did have a leak, we had to go back, but did very well with no sixth nerve palsy and a very good outcome, next? So other tumors that are very common on this transclival approach are chordomas. And here you see an example of 28 year old that plays the trumpet. And with this large tumor kind of pushing his brain stem and located completely intracranial there. So this is not a tumor that I would expect to be extra dura. It really like invading these structures. So here's the video, demonstrating the technique. And so here we went straight to here demonstrate that some of these tumors can be suckable, but this is an example of a very firm chordoma invaded the arachnoid. And this is the type of sharp dissection that we have to do in this cases, very meticulously dissect from the basilar artery and from the perforators there. So here you see the other arachnoid I was kinda really asked reckon this case here to come very close to make sure that I was not cutting any vessel and just arachnoid. So that high definition camera, right on top of the basilar artery, like very helpful. You can see how the chordoma it's already like invading the arachnoid space, and I'm just relying on suction here to really get that less pieces of next to the basilar artery there, as you can see. And continue sharp dissection. So I use a little bit of blunt there if you let it go, but if I feel resistance, then there's no to have to come with a sharp dissection. So here you can see this not a suckable tumor. We had to kind of really taking pieces to debulk and progressively decrease the size of the tumor. This whole surgery, even with the narrow spacing between the carotid arteries, we were able to work and intracranially, basically the surgery was limited to the six cranial nerves bilaterally. So that's your limit laterally. So this shows that this can be done. This is the final dissection on the vertebral arteries inferiorly. And then we did the reconstruction with the Collagen Matrix here, followed by the nasal septal flap, next? These patients did leak. We actually eventually had to do a temporoparietal flap for reconstruction. And he eventually did very well follow with proton beam. And he's a couple of years, three years out doing very well with no recurrence. And this shows the application of the transclival approach. When you're dealing with meningiomas, petroclival meningiomas or petrous meningiomas. The main thought that I have is what is the main component of the tumor? If it is in the petrous region, like the implementation like this one, no question. We will do an access coming with a retrosig or any other approach, but not endonasal because, that would not make any sense. So this is we did with the retrosig just to show as an example. This is another case where that petroclival as well. But if you look the here, the implementation on the petrous area is very small. For the most part is in the petrous. There's minimal clival contact and major petrous contact. So for these petroclival ones, I still will come with a lateral approach, not endonasal. This is just to be very clear. This case, I use a retrosig actually, we worked very well for this patient with a complete resection as well. Now, going down the region of the foramen magnum. When you have foramen magnum meningiomas, they can be a 360 degree located around the foramen magnum. The ones that make sense to do endonasal are the ones that are located above a line here, above C1 and C2. I will never go through C1 and C2, remove odontoid process to get a tumor that will be located retro odontoid. Those tumors will come with a lateral approach, for lateral, or sometimes even a midline approach if is low enough. And then this case was perfect for being above the line and was also located medial to both vertebral arteries. So with that position, I know that the 12 cranial nerves run lateral to the vertebral arteries. So I know I will be able to get that out of there by preserving the anatomy, the cerebral vascular structures laterally there. So here, this quick video of this resection, you can see here, we dissect it. And this is the final view that we obtain after removing the tumor. You'll see the bilateral vertebral artery is preserved, the PICA here and the 12 cranial nerves lateral to those vertebral arteries. So very carefully, we explore inferiorly with a camera as well, and made sure that the tumor was completely resected, next? This is eight years later. So he's doing very well and no signs of any recurrence. He's doing great with no deficits whatsoever. He did have leak as well, I just gotta say, but we took him back only one once and repair that. We augment the reconstruction with fat, he did well. So other variants here. This is the tumor that had a first quick look at like, oh, maybe this can be done endonasal, but if you pay attention here, it is completely located behind the odontoid. And more than that, if you look at the axial, the spinal cord is actually located unto the lateral there. So because the tumor is low enough, these actually I did the same approach. I will do a Chiari a little more inferior, removing a little bit of the arch of C2 as well, but this was actually a straightforward case. And the entire time here of the resection was 18 minutes. Here's the dissection of resecting from the implantation. The tube was only implanted on that little, the side over there, and we obtained the complete resection of the tumor just by coming mid line. So this is really just to show that you gotta look case by case, look at the anatomy and understand. You see the vertebral artery running here and here I'm covering the spinal cord that was protective, next? This is the post-op on this patient. And you see here the preservation of the spinal cord and patient did very well, here as well. So with these I'd like to thank really the opportunity to talk here, and hopefully the pandemic will allow us to still have our course in 2022. But we are start thinking that we may need to postpone once again, but we hope for now is to schedule for May, 2022 for our hands-on course here at Ohio State University. Thanks so much Aaron and I really appreciate the opportunity and I'll be happy to answer any questions now. Thank you.

- Thank you so much, great lecture. Really, really enjoyed it. I think it had a lot of pearls of technique. And so I wanna really congratulate you. If I may comment Danny, about olfactory groove meningiomas, I have come to a conclusion that a transcranial approach is a much better approach. Not only it allows you to preserve the olfaction, but also it allows you to really achieve, it goes through a resection. If you need to, you can drill the bone from upstairs using a pterional approach, a lateral trajectory rather than a super orbital approach which can be limiting. Therefore, we have completely switched to that and have had great success. My, again, this is my personal opinion. It doesn't mean everyone's. Staging these operations and placing the patient through two operations when you can do it through one and get it done, I think is something that has led us to use the pterional route. I see what you're talking about, the footprints on the frontal lobe. However, I think dynamic retraction and a lateral trajectory and only manipulating one frontal lobe, has really minimized that footprint. Can you tell me what your thoughts are on that?

- Yeah, no, I agree for the most part, like I just did one yesterday as I mentioned a patient that had a lateral projection of the tumor and still had olfaction. So we definitely favored that route. And we got a whole tumor out. And I agree with you with dynamic retraction. I don't use retractors as you said, and we were able to preserve the olfactory nerve control laterally. So I have an algorithm like the line of thought for these cases, we will publish in the near future. We are writing it up series. So basically it's interesting because if the smell is still present, I would do a craniotomy as the primary treatment, only one surgery, for the small and medium sizes. If the smell is gone and the tumor is located in the right olfactory and is in the middle, I still prefer endonasal because I just there's. I would just go there, the smell is completely gone we test on everybody. And those are the ones that do endonasal. And they tend to be larger tumors, but not gigantic to take the smell away. And that's what we noticed in our series. And we only staged the real big ones with hyperostosis and lateral implantation with a lot of edema. 'Cause we feel that when there is edema, at least on my hands, I tend to do a much bigger approach to avoid bringing herniation and to be able to go around the brain to two fight less with the brain. And with the staging, I noticed that I can still do on the second stage of small craniotomy and do the same technique I do for the medium sizes olfactory groves and completely resect it out of there. What we notice in our series is that the ones I did primary craniotomy tend to be small or medium. The only endonasal, actually are quite large, but still restricted, they tend to be larger than the craniotomies and the ones we staged and did this technique are much larger. Are really gigantic, like I would say, like similar to this examples that I gave, but we had some even larger than that.

- I see your point, however, as you know, it's the smaller tumors that are having intact to olfaction which lead themselves better to address cranial approach. So it's an inverse relationship size versus extent of preservation of olfaction. Nonetheless, a very illuminating lecture. I've learned a lot, beautiful technique. Danny, very proud of what you have done for endonasal skull base surgery. I look forward to having you with us in the near future for this section two or part two of this series of your talk regarding the limitation of the endonasal scopic surgery along the coronal plane. So with that, thank you again, I look forward to seeing you soon.

- Right, thanks so much. I appreciate the opportunity around and congratulations and everything you've done for education in neurosurgery.

- Thank you, thank you Danny.

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