Grand Rounds: Endoscopic Endonasal Anterior Skull Base Surgery-Anatomy and Surgical Correlates

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- Hello ladies and gentlemen, and thank you for joining us for another session of the "Grand Rounds." Our guests today, a very special one is Dr. Juan Fernandez Miranda, he doesn't require any introduction, he's a truly a visionary neurosurgeon who has continued the great tradition of Dr. Rhoton and has really taken neurosurgical anatomy to a new level, with introduction of the endoscopic anatomy. Today, he's going to talk to us about the anterior skull-based surgery via endoscopic methods, and also review some of the surgical videos of his related to the topic. So, Juan go ahead and please review some of the anatomy first, and then we'll jump in to some of the cases. Thank you again.

- Thanks Aaron, it is my pleasure and honor to be here and thanks for all the great work you are doing with these webinars, I can assure you I've watched a lot of them, so I'm happy to be doing one right now myself and I hope they enjoy it too. So as Dr. Coyne said, I had the pleasure and honor of training with Dr. Rhoton for two years and remained working with him over the years, and then I joined the group at the University of Pittsburgh where we start applying some of these anatomy concepts into endoscopic endonasal skull based surgery, and today I want to introduce you to the topic of surgical anatomy for endoscopic access to the anterior skull-base, and review some of the importance anatomical nuances for surgery in this area. We need to understand the anatomy, both from endonasal perspective and from transcranial perspective, it is the same anatomy, we are not discovering anything new, but it is a new perspective, so we need to learn how the anatomy looks when we go from below and complete with the anatomy that we see when we go through a transcranial approach, so that's where we're gonna be doing, looking at the anatomy, both from transcranial and endonasal perspective in the next minutes. First, we're gonna start dividing the anterior skull base in different areas, and this is just for academic purposes to make sure that we can, accommodate lesions in one place or the other, so conventionally we describe this cribriform region anteriorly, and then there is this line, the posterior edge of the crista galli and falx and then we have this flat area, which we call the planum sphenoidale, and then there is this very important line right here, which is located at what we call the limbus of the sphenoid is the edge between the planum sphenoidale here and the pre cosmetic sulcus here behind, and this extension is very important from the surgical point of view, and we'll review why, then we have an additional division perhaps, which is laterally, we can adjust through a line from the optic canal anteriorly to the medial edge of the orbit, and then we define the area of the roof of the orbit and the area of the anterior clinoid that is located just a lateral to the optic nerve and the optic canal, and these are a way of dividing this cribri is also helps to decide what areas can be reached endonasaly and anything lateral to the red line, typically is not a good option for endonasal surgery because it's too lateral. Aaron you're gonna make any comments about this?

- No, I think it's really important, what you mentioned about the limits of the endoscopic surgery, I think we're gonna go through more detail about what tumors and what sizes are best, one of the critical factors is that mid orbital line under Kronos plane, that you have to be very careful, they really are, you can go beyond that, also the optic nerve itself, obviously the limits are significantly, so you really can go over the optic nerve and operate there, although there are occasionally tumor fragments that sneak over the optic nerve and you try to reach over the optic nerve, it's somewhat dangerous to do so, but again, realizing these limitations is so important for safe endoscopic surgery. Thank you Juan.

- Exactly, I will go back into those limitations, but if you look at how we classify the anterior skull base again, now we're looking through an endoscopic view, we are looking at the sphenoid sinus, we opened the sphenoid sinus bilaterally, we drill all the septations, but now if we look at this area, we see of course the optic nerve prominence on each side, they are easy to recognize in a well pneumatized, is sphenoid bone, and again, we see this line right here, and this line again is the limbus of this Fino, and I insist in this because it's a very important land mark anything that is anterior to this limbus belongs to the planum sphenoidale, anything that is posterior is the area that prechiasmatic sulcus and sphenoidale is difference is important now, if we do some drilling here that is behind the limbers, we are in the prechiasmatic sulcus area, so we're moving this piece of bone here, we can go anterior, and we are in the planum sphenoidale area, and if we look at both together, you see the doodle fall here is very easy to be identified, and these we can see in sphenoidale always look for this sulcus when operating in this area. I'm looking always for this dural fall, whatever it is anterior and always the plan on this fumi dally, whatever it is behind is the prechiasmatic sulcus, now, the difference is, if you open the dura in this area of the planum, you're gonna be looking at the suprachiasmatic space, if you look at this surgical view, you'll see what it look, this is where the limbo is, we're gonna be looking at these areas right here, the suprachiasmatic space contains the orbital surface of the frontal lobes, while if you are looking or working, behind or below the level of the limbos in this area, this is the prechiasmatic circles right here, and you're gonna be working into the infrachiasmatic space, which means into the sisterly space that is underneath the optic chasm, and this is the side for multiple lesions pathology like craniopharyngiomas and tuberculum sellae meningiomas while other tumor they just stay in the planum sphenoidale but may extend posteriorly. The main point here is, when you are dealing with lesions in this area, infrachiasmatic space, there is no need to extend often your exposure all the way anterior, unopened the dura here, because it can only get you in trouble by exposing unnecessarily brain in your approach. So the limits of this vineyard is a great landmark is very reliable, better than image guidance, using your anatomical landmarks to know where you are and where you want to be. We need to recognize the limits of the endonasal endoscopic approach to the anterior skull, base on, as you well said Aaron, we use our lines that go from the optic nerve to the mid point of the orbit, and I use here two lines, one yellow, one red, because the yellow is the caution line, you are up to the medial edge of the optic canal and a little bit to the medial aspect of the orbit, you can definitely reach this area and you can work beyond the yellow line, but this area requires some, more technical expertise is more difficult, it's more challenging, it might be more risky, you definitely can not work beyond the red line, and it's basically, you cannot work on detached to most are attached lateral to the red line, so tumor that is attached to them through a recliner, you will not be able to reach it, or tumors attached to this sphenoid wing or orbital roof is the same. Now, sometimes tumors, as you said also, well, is they are attached medially on the central portion, but they extend laterally without being attached, so you can, the ball those tumors or bring them down, that's still possible, but always remember these two lines, when you're a beginner perhaps, stay within the yellow lines, when you are more experienced, you can go all the way to the red line, but that's your limitation. And this is the same view of the limitations from anterior perspective, just to see, your limitations on the endonasal approach are based on the lateral extent, and you see roof of the orbit, area of the interior clined, also this chronal view you give us the opportunity to see the slope down of the area of the career form blade, would always make it a more challenging approach, when you come from a lateral approach to get all the way down, and across the mid line, than the area, the plan on that is flat, and he's at the same actual level as you can see here. So we're gonna now review some of the key aspects of the anatomy, we just reviewed the different segments within the anterior skull-based, now we're gonna review the anatomy of the bone, the bone anatomy is very important for anything in the skull base, so we start with a spinet bone from a transcranial view, and you will see this flat surface, the planum, as we all know is the lesser wing, so both of lesser wings are joined by the planum sphenoidale, and they continue posterior and medially to form the anterior clinate, the anterior clinate has the superior attachment that forms the roof of the optic canal, and then these inferior attachment which forms the optic start, on floor of the optic canal. But you can see again, the prechiasmatic sulcus, very well defined, prechiasmatic sulcus with a planum in front, with a prechiasmatic sulcus behind. We look at the frontal bone, the frontal bone from a transocular bone, we define different areas, most importantly here the ethmoidal notch, this is the notch for the ethmoids to articulate, this is the orbital plate, that forms the roof of the orbits, we see here the nasal spine and behind we have the foramen cecum right here, all these can be used as landmarks during surgery and the ethmoid point finally, with the crista galli in the center, the flat surface for the cribriform plate on each side, and then this slope is a little bit more vertical plate, this is called the lateral lamella, and is the lateral attachment of cribriform plate into the frontal bone that is gonna be up here, this is the roof, what we call the roof of the ethmoids, these are all the ethmoids cells, this is the roof, the frontal bone is gonna be just on top of this, and this lateral lamella is where we have frequently a spontaneous CSF leak, so it's an important area to understand. Now you can see actually even the groove for the ethmoidal arteries, the anterior and the posterior of the ethmoid arteries. Now this is the way both frontal bone and ethmoid bone sort of come together, and you see this is the orbital plate, form the roof of the ethmoids, and this is the lateral lamella where those leaks cannot cure with more frequency, and here we have the three bones together forming the skull base, the anterior of the skull base is formed by frontal, by sphenoid and by ethmoid bone all coming together. We have the same view from the top, now with the lining, with the dural and here I just wanna point out the importance of this line in right here, if you look at the lining in the area of the limbus of this sphenoid, these dural fall continuous laterally as the falciform ligament. So, if you recognize that the dural fall of the limbus, you follow it lateral, is gonna take it to the roof of the optic canal, and we'll see this in a different seminar hopefully, but you can transect this dura right here and detach your falciform ligament, when you work endonasally as a kind of equivalent to the same maneuver when you work transcranially. Now, what sits on top of these anterior skull base, we look at the frontal lobes, and here as we know, we have the gyrus rectus right here, we have the olfactory sulcus, with got factory track on it, and then we have the orbital GRI, medial, lateral, anterior, posterior, when we worked for an endonasal approach, we typically just see the gyrus rectus and part of the medial orbital gyrus right here, okay? This is the surface of the brain, we're going to explore through an endonasal approach, and the vasculature in this area is very important, to recognize the anterior cerebral arteries, they're branches and of course it is A1, the A arteries, the A2, very important to remember these artery, and these other one here, these are the frontal orbital arteries, these are the first cortical brands of the eight arteries, and these are the ones that are most frequently involved with tumors, meningiomas often encase these arteries and it's important to preserve them when it's possible during dural surgery, Aaron.

- I think those are good points, I think these frontal polars tend to be very engulfed by the meningiomas in this area and give you fair amount of trouble and make the surgery a lot longer, and so, we're gonna talk more about that, and if the tumor is very large and it's engulfing, the vasculature, maybe endoscopic approach is not the best way to go, you shouldn't necessarily just stage the surgery two or three times, two or three days of surgery, if it can be done through the transcranial route, through the transcranial approach, through one day, so that's something to consider. One other question that I like to have, you can discuss, is a relationship of limbus sphenoidale to tuberculum sellae, if you can discuss that a bit I would appreciate that Juan.

- Sure, sure, so let me just go back real quickly, actually maybe I can use even this one, so this here is the limbus right here, right? So the limbus means literally just edge, so this does this edge between the planum and the prechiasmatic sulcus, the prechiasmatic sulcus is these flat area that is between both optic canals, right? And then the tuberculum is just right here, the tuberculum is this bony prominence, this bone is also like an edge, it's a prominence or edge that is within the prechiasmatic sulcus and the sellae itself, so the tuberculum is, you had just a few millimeters of width, the same as the limbus which is just merely a millimeter, but the prechiasmatic sulcus is a larger, wider, flat area, and this, we call it tuberculum sellae meningiomas, but truly they are more typically arising from, this prechiasmatic, they are more sitting in this prechiasmatic sulcus, right? And the important here is that when you have a tumor in the prechiasmatic sulcus it spreads laterally and is gonna invade the optic canals in the medial especially, the middle that's of the optic canal, different than planum sphenoidale, they are gonna just sit on top of the optic nerves and displace the optic nerves back or down, as opposed to prechiasmatic sulcus tumor or tuberculin, and that pulls the optic apparatus superiorly in general. So, let me just continue with some more anatomy points here, we reviewed the vascular anatomy, we set the frontal orbitals, remember the first cortical branch, your fronto polar, there are typically within the interhemispheric fissure, they arise more distally from arteries, and they are important when the tumors are opening, the interhemispheric fissure, they can relay with their fronto polar too, and then this very important branch of course, that not that often is exposed by these tumors, because they need to open the cleft here, towards the anterior periphery substance here, but this is the hebner already, that's going to anterior for the substance, of course, giving the porphyrin assist. And another point of the anatomy, the thing is I believe is important is to understand the falx, the syllable falx, how it attaches. This is quite easy when we do, open approaches, we just like the signs and we transect the falx this way, nothing complicated, then when we go in the nasal, how do we call the falx to an endonasal approach? So first we need to understand where the falx attaches and it does attach mainly to the crista galli, so you look at the plan on this finny galli, that is not falx in the planum of finny galli, the falx is anterior, in the career from plate area. So what we do is transect the falx from anterior to posterior, towards the plan is finny galli, because when you come into nasal you get this trajectory, so it is easy to keep going up and up, and you can go up all the way, but that doesn't make any sense, so what we do is we go up and then we'll just turn back towards the planum, and then that's where the falx is detached, and then you can bring your whole dural specimen down, as we will see that in a surgical case. Now, let's look at the anatomy from the front, from an endonasal perspective, again, we start with the bony anatomy, the sphenoid sinus. Now the sphenoid bone, so here we have the body of the sphenoid, which contains the sphenoid sinus. Now the sphenoid rostrum, the sphenoid rostrum is the bottom of this sphenoid right here, this is the sphenoid rostrum, okay? And this is this sphenoid face or the front of the sphenoid sinus, where you can see actually the sphenoid rostrum right here, and then we have the lesser wing, the greater wing, the teddy rates, which are not important for anterior skull base, but we'll review in a different seminar, but the question I always ask, is which bone articulates with a sphenoid face in the front, which bone articulates with this sphenoid rostrum in the bottom, okay? So in the sphenoid rostrum we have the vomer, this is relevant, where we're doing approaches to the climbers, we need to detach the vomer, remove it from the floor of this sphenoid. For this sphenoid phase, we have the ethmoid bone attached in the front, and we look at the anatomy of the ethmoid which is a complicated bone, the anatomy is difficult for the ethmoid, that's why we work with our ENT colleagues doing these operations routinely, and we have here the crista galli in the center, and then down we have the perpendicular plate that forms part of the septum, then we have this prominence right here, this is the prominence, the skeleton for the middle turbinate right here, these are the anterior ethmoids, where we call the volatile with alleys and they form the laminae preparation here, or medial wall of the orbit. Now, these two bones come together as sphenoid and ethmoid, so anytime we need to go into this sphenoid sinus, we need to go through the ethmoid bone and we'll see how we do this, and now finally, the ethmoid articulates superiorly with the frontal bone and these here is what we call the roof of the ethmoids, we also call these the phobia ethmoidales, although it's not the right name, because there is not one phobia, there are multiple phobia, phobia means depression, so there are multiple depressions here, that they just allocate the ethmoid sinus that are located just in front of the low of it, and here we have the nasal spine, again, and the foramen second posterior, so these are ethmoids where the ethmoid bone is gonna just attach. So we see it from the front, frontal bone, we see the nasal spine, the ethmoidal notched, the sphenoid sinal, and now we have, all ethmoid bone coming together. and again, the three bones frontal, ethmoid, sphenoid, forming the anterior skull base and not only the anterior skulls but also frontal sinuses, and a lot of nasal cavity and part of the orbital cavity, as you can see in these dissection. Now let's look at this from an endonasal perspective, from a surgical point of view, how does it look, the anatomy? So this is looking at the left nostril, this is the septum, this inferior turbinate, the middle turbinate, so now when we go to this sphenoid sinus, we did take this avenue between the septum and the middle turbinate, we can also explore this lateral corridor between the middle turbinate and this so called uncinate process, this bone of the uncinate process forms, the medial wall of the maxillary sinus, and just behind it, we have this prominent this structure, which is the bulla, the bulla ethmoidalis So we mobilize the middle turbinate some, we can see the lateral, sorry, the base lamella going up, the basal lamella is what defines and separates anterior from posterior ethmoids, so everything anterior is bulaff Medallia's, posterior, we have the posterior ethmoids, and we're gonna do next, is we are gonna transect the middle turbinate, you see this is the superior attachment of the middle turbinate, you don't want to transect the middle turbinate up here because you are gonna be at risk of creating a CSF leak up here and fracture of the skull base, you just wanna di it just below the attachment, and when you do this middle turbinate detachment, you can see better this, as sphenoid ethmoid recess, where we have the ostium sphenoid, the sphenoid model recesses within the superior turbinate and the septum, and now we see the face of the sphenoid a right in here. So, I wanna review now this important anatomy, because we are exposing the face of this sphenoid and we're looking laterally here, and it's very important to understand the concept of the pterygopalatine fossa for endonasal surgery and for the racing, the harvesting of the septal flap, okay? So, the pterygopalatine fossa is formed by two bones, the Palatine bone in front, and the pterygoid bone in the back, the palatine bone has this vertical plate and this horizontal plate, the horizontal plate forms the hard palate, right? But this vertical plate forms part of the middle wall, the maxilla, and it has two processes here, this is the so called orbital process because he has this little piece here, forms the floor of the orbit, and then we have the finet process, which attaches this finet bone right here and in between this ideal opening, this opening is for the sphenopalatine already, is the sphenopalatine foramen. So, the anterior wall, sphenopalatine is this one right here, the posterior wall is a terrier guard and that's the vidian canal right here. So, the already gonna come out through this foramen, okay? This sphenopalatine foramen that is defined by these two process of the palatine bone, so now we see all the bones together with the ethmoid and still we can see here or opening for the sphenopalatine foramen, okay? Defined by the palatine bone, now, if we look at these in the dissections here, so this is the middle turbinate insertion right here, and this is the face of sphenoid and this is the septum, and in this we'll inject the specimen, you can see the arteries right here, these are the posterior septal arteries that we need to preserve for our flap, so our landmarks here are based on the corner, you see the corner right here, so one inferior cad in the mucosa goes at the level of the corner, you put it superior, you are risking this branch right here, and the upper cut, go just below the ostium, So at enough distance from the superior branch right here, you can see after doing dissection, you can see these two branches of the poster of sphenopalatine. Now we did some work in the lab years ago, and we described, because it was so debated, is there one artery, are there two arteries going to the posterior septum, and here what we did is we described, there is actually only one artery, it is a poster of septal artery, but it can bifurcate earlier or later. So if it bifurcates earlier, just at the exit of the tail, you are parting force, it looks like you have two arteries, but it's the same one, and this is a most common pattern which is better, 2\3 are like this, it is better because if you injure one branch, you still have the other, but if there is a distal bifurcation, then there is only one single branch crossing this mucosa right here, okay? That pattern is at higher risk for a complete devascularization of the septum if you don't do it the right way. So, how do we expose the ostium? We just take the inferior half of the superior turbinate by doing so we can see better, that's finished off right here, we can see better the mucosa that we need to preserve in the face of the sphenoid, in terms of raising the septal flap, and here, I did some resection, opening of the middle the maxillary sinus, we see the posterior wall of the maxillary sinus, which forms the anterior wall of interior part in fossa, and these tissue here is interior part in fossa, this is where the artery going to the septal flap is coming from, and understanding this is very important, so we can maximize this opening, we understand that this artery is coming through this foramen between the two processes of the path in bone as we said, and we can maximize the opening of this interior part in force to maximize the rotation, the axis of rotation of our pedicle, we don't want to have a trot pedicle for multiple reasons, but we wanna be able to mobilize our pedicle for which you need to understand how to open this study, apart in fossa. We have the flap now well-raced, we can move it down, putting the nasal of firing spring, the maxillary sinus and use it at the end of the operation. We're gonna go now through some dissection, a step-by-step from an endonasal approach going into the anterior skull base. So we have here removed the septum, so this perpendicular plate of the ethmoid, we have removed a lot of the septum, so we can see both nasal cavities, we have inferior turbinate, middle turbinate right here, and in this next sequence, we just resected the middle turbinate, we open part of the uncinect, so we are looking at the bulla right here. This is bulla ethmoidalis, this are anterior ethmoids. In the next step, we're going to remove the anterior ethmoids all the way back to the posterior ethmoids, and we see after removing the posterior ethmoids, we see the roof of the ethmoid itself, and this is the anterior skull base, and now from here to here, we're gonna open the sphenoid sinus right here, we're gonna open the maxillary sinus, we're gonna do what is called a medial maxillectomy right here, remove part of the inferior turbinate, open the maxillary sinus, and now we're also opening the frontal recess or the lateral recess, or the the frontal recess of the frontal sinus right here, and we're starting this structure right here, it's always just behind the frontal recess, this is the anterior onto your ethmoidal artery right here, we'll see this in more detail, But from here, you can see from the sphenoid sinus, all the way up to the frontal sinus, and this is the roof of ethmoids, roof of the anterior skull base. Now, we're looking at these unilaterally and we can see this is the lamina, we're looking at the right side, laminate preparation here, this is the anterior ethmoidal artery, this is the posterior ethmoidal artery, always remember these arteries do like this, they have a bifurcation where they diverse from each other as they go from the orbit towards the septum. You can also send them to see the little nerves, nasal ciliary nerves that innovate this whole saline nasal mucosa, okay? The post ethmoidal artery is typically at the edge between two different plate and planum. You see the front of this sphenoid, the planum is starting just behind. The anterior ethmoidal is just behind the frontal recess, so I know that right here, I'm going to find my frontal recess. I know we did bilateral resection, we've resected the septum, we transected the middle turbinate after the olfactory sulcus, so here, we have midline, the crista galli is gonna be just on the other side, olfactory circles on each side, and then we have, again, the anterior ethmoidal frontal recess, post ethmoidal, the front of the sphenoid sinus, so planum is gonna be just behind and the same as structures on the contralateral side, just looking at the roof of the ethmoid right here. Now, when we coagulate this ethmoidal arteries is very important that we leave a little stamp on the periorbital, don't allow the artery to shrink because he can bleed in the back of the globe, in the retropatellar space, you wanna coagulate the fabulous stamp and make sure you have now, preserve part of the stumble various, it doesn't back bleed, and this allows, quartering these arteries allows mobilization of the periorbita, this is a key step to mobilize the periorbita, and expose the roof of the orbit from an endonasal approach. And now we have bilateral exposure, we drill the roof of the ethmoid, so we expose the dura of the anterior skull base on both sides, go back to the planum, and go all the way anterior until we found the posterior table of the frontal sinus right here, so now this is like doing a craniotomy. We have each side is the rehold ethmoids, the anterior aspect is a poster table, the poster artery of the planum is finger dulla right here. In the center we have the crista galli, on each side we have the olfactory sulcus. Here, the mucosa of the nasal cavity, continuous with the dural, and that surrounds the olfactory fibrae to go and form the olfactory bone. So another important nuance here, is when you're trying to remove the crista galli, you want to first, dissect the dura around the crista galli, this dura that forms the middle artery of the olfactory sulcus needs to be nasty dissected all the way, before you detach the crista galli, because you detach the crista galli, is gonna be free floating there, it's gonna be more difficult to remove that dura around it, so we dissected the dura all the way around and now in the next step, we can now remove the crita galli. Another anatomical landmark that I sometimes use is the foramen cecum because it tells me, what is the limit of the anterior skull base? The foramen cecum is just at the junction between ethmoid and frontal bone, and when I'm taking the crista galli, I like to see this flat dural surface, that is just between the foramen cecum and the crista, because I'm gonna do my dural cut right in here. So you see the crista galli is been removed, and I have this flat surface right here, I can cut just behind the crista galli, and then you can see here, the two leaves of the olfactory sulcus, they're gonna come together and they're gonna form the serial falx as they go superiorly. So here in syda what we do is we cut the dural around it, and then we... On each side, then we get to the falx, we coagulate any potential venous channels right here, and then we cut the falx from anterior to posterior, remember, there is no need to keep going up, you don't need to keep going superior, we just cut anterior to posterior, at the planum sphenoidale there is no falx anymore, and then the last card is right here at the planum sphenoidal dural. And at the end you're gonna have the exposure of the intra dural space, will be not identified in the bag, the optic chasm, remember, we're in the supra chasmatic space, we have the olfactory tracts, for many of these lesions we have to identify and remove the olfactory bolts, the olfactory tracts, when we're doing santo nasal malignancies, for example, and always remember this already, these are the frontal orbital branches, they often attach to the... They share the same algorithm on the olfactory tracts, you need to dissect them from the tracts, and you want to preserve these orbits as much as possible, this is the olfactory sulcus, so this is gerald rectors, is the medial aspect of the orbital GRI. And at the same, the comparison from the lab, and how it looks in the OR with olfactory tracts been transected and all the dural cuts and the craniotomy. So, and you can see here, the remaining portion of the falx up here. So with this, we're gonna just move from the anatomy, silica anatomy, to the application into some cases, some case examples. Again, whether we select transcranial or endonasal approaches for many of these lesions, we try to base it on anatomical principles where deletion is located, but of course there are some other factors, there are patient factors, let's say a patient that is very obese, you may wanna avoid having a large skull this defect, because of risk of CSF leak, for instance, or age, a patient may be a factor in some cases, but of course CF preference, your experience, your training, where you feel more confident, and the way you wanna apply it, is what also waits in the decision of whether you use one approach or the other. So for sinonasal malignancies, regardless of the approach, the principles are the same, we wanna achieve negative margins, we've get a complete resection whenever it is possible, we review the key anatomy for these cases, and the last step is always reconstruction and we have different options, we use the septal flap when he's available, but often the septum is invaded by tumor, we cannot use a septal flap, so we use pretty coronial graft flaps, or some graft reconstruction in some instances. We reviewed the limitations already, for the particular case of sinonasal malignancies, remember, if it goes beyond the posterior wall of the frontal sinus towards the anterior wall, there is not point in doing endonasal, of course, if we go to the skin, some of these cancers do so, there is no point. Often, we combine these approaches, endonasal plus transcranial to achieve a complete resection because some of these tumors go beyond the lateral H, or lateral limit of our approach, and that's a way to solve and combine limitations combining approaches. Now, we're going to the first case, if you will Aaron, this is the first video is a of our esthesio neuroblastoma, with a dural invasion but no intradermal extension, so ideal for an endonasal approach where we could get a complete resection, there was a tumor right there, so, first the step we had the laminate preparation, this is coagulating the atomic, the ethmoidal branches, sorry, and this is during the dural opening. So, here we're using two hands, with a section we are holding the dural that was cuagnating with the artery falx, this is transcending the falx from anterior to posterior, we use patties to protect the brain and look at the front or riddle arteries on the surface of the brain, that need to be preserved, see how they serve their rocanate with the olfactory tract, these are posterior or dural cut right here, and these are dural specimen, that contains all the tumor, we'll get negative margins on every aspect of the dural and these the reconstruction, would use in a large septal flap. We typically use a multi-layer with a collagen inside, then a fascial allograph typically, and the septal flap and a lumbar drain for patients like this. Okay, so this a second case is an adenocarcinoma that has a true intradural extension, so we see how we can deal with this in this particular case. So let's go ahead and let's do video two, and again, this adenocarcinoma with a tumor going through the dural is not a contraindication for endonasal surgery, you see, we're transecting the falx right here, and now we are... This is tumor, we're finding these zoop arachnoid, that plane between brain surface and tumor, so we can separate one from the other. So these are the tumor invasion here, and we start seeing a frontal orbital artery right in there, and that artery needs to be preserved, and now we are carefully dissecting trying to find a plane in brain and tumor, and at the same time preserving the frontal orbital artery. So this is the same operation you could do with a transocular approach, just trying to find your plane, sometimes there is a PLM patient, and then you have to do CPL dissection in this case, it needs to be that is just racnoid that is invaded, so we can use the racnoid to separate the brain surface on the tumor, that was a vascular supply, a small vascular supply from the front of orbit to the tumor, there's the dural specimen right here with a tumor in the side, this is the contralateral olfactory bulb that we are transacting and coagulating, so this would allows us to completely remove and detach the dural with the tumor, and at the same time, we'll get dural margins in every corner to make sure they are negative, and that's transecting the last part of the dural right there, you can see the tumor, that is invaded through the dural, and this is your dural defect, and again, we used colagen, facet graft, nasal total flap, and in this case can be used and it covers very nicely the whole defect, and then we'll place a lumbar drain at the end of the operation. You can see here the nice reconstruction that has been done with a septal flap, covering the whole anterior skull base. So the next topic is more controversial because it's about anterior skull base meningiomas, in particular planum, an olfactory with meningiomas, whether we do them an endonasal, transcranial, or combining approaches in some cases, it's still a matter of debate and controversy. These are a few reasons of why endonasal makes sense to these tumors, first, endonasal is an external approach, so it follows the principle of skull, basically going to the source of the tumor, the attachment, the vascular is a tumor, manipulation of the neurovascular structure is minimized this way, and this might have an impact on frontal lobe function, you can have a small tumor, do it with little invasion, just one nasal cavity is being used, or you may be concerned about the amount of brain swelling around the tumor, so endonasal might avoid that problem. You might be worried about preserving this tongue of a frontal lobe that is just in front of the tumor, so these are reasons in favor of doing an endonasal, although the true impact on preserving the frontal lobe in these areas on the function, is still needs to be demonstrated. The cons of doing endonasal are mostly related with the complications rate of the reconstruction and the high CSF rate we still have in these areas. Aaron, you wanna make any comment in particular?

- Thanks for the opportunity. I agree with you all factor group meningiomas are somewhat controversial. I think the other issue is if somebody has a small or medium size olfactory group meningiomas with intact or faction, what to do, because as you know, endoscopic approach does not give you an opportunity for preservers shadow or factional, or faction is really important, I know as neurosurgeons, we may not pay as much attention to it, but it is really important to the quality of life of the patient. Therefore, I think if olfaction is intact and it's a medium or small size olfactory meningioma with significant minor demor that requires treatment, and eyebrow supraorbital craniotomy is an excellent option and also provides an opportunity to preserve oral faction. However, if you have a smaller medium size olfactory meningioma, and olfactory is already destroyed, I think it's reasonable to go trans nasally, but the giant or very large olfactory groove meningiomas, I think the best approach is still terional, going from the side, recognizing the neurovascular structures early on and protecting them, rather than using a large by funnel approach and going through this frontal sinus, transecting the superior sagittal sinus, et cetera. The reason is that if you really go through endonasal for large or a giant olfactory groove meningioma, the surgery is very long, you may have to stage it, and it's just not necessary. At some point, you have to realize that you're pushing the limits of endoscopy too much beyond what's necessarily indicated or could potentially be safe to the patient. So, although endoscopic surgery is extremely attractive and very effective, also it has its own limitations and just not every tumor can come out through the nose, and I think if you just know the limitations, endoscopy is an excellent tool and a skull based surgeon should know both, in other words, it's not to be an endoscopic surgeon and an open skull based surgeon, you have to be a holistic skull-based surgeon that can do both, so you can tailor your approach based on the need of the patient rather than your own expertise. What are your thoughts there, Juan?

- No, I completely agree with your thoughts, no question about it, I think first, the east west olfaction is very important and we should not underestimate the importance of olfaction for patients, so that's first thing to consider, and then I'll go into case examples also with giant tumors, but I agree, I think endonasal data for giant tumors, I've done it, I've done a number of them, but I'd rather do open approaches at this point, that's the way I do it at this point. I think it's safer, less risk for complications, just one operation. So, let me just move on, and for example, as we were discussing, this case is a medium size olfactory with OGM, the patient has no olfaction preop, have some swelling, middle age, this an ideal case for endonasal in my practice, because it has all the good features, it doesn't go to lateral, the patient doesn't have olfaction, so I don't need to worry about this, you see this a complete resection including dural including bone, so it minimize manipulation on the brain, so ideal for endonasal, and if you wanna pull the video three, this is just a short clip, showing this particular case for this olfactory, we are gonna give them a medium size. Now, these are not that common, but here, we are drilling the roof of the ethmoids, here, we're drilling the planum sphenoidale in the back, this is the crista galli in the center, olfactory sulcus on each side, and this is the hydrostatic plan on his sphenoidale, how this definitely is not normal bone right here, and then this sticking the roof of the admits on the other side, and now we are opening the dural and the beauty now is that, it's all gonna be tumor, and we can use the bulkhead and that's querying the falx and detaching the falx, cutting the falx and attaching the falx here, you see, because there, it is a medium-sized team or there is no basket in casement, these dissection becomes quite easy, and at the end of the resection, you have a nice frontal lobe that you haven't manipulated at all, this is curvature that is not too large, and it can be effectively constructed with a simple flap, is still a use a lumbar drain to decrease the risk of leakage, but this is I think an ideal case for endonasal surgery. So, this next case, that I did some years ago, this is a unilateral olfactory groove meningioma, and in this case, what I tried is to go through only one nostril, and you see the contrast or nostril is completely intact, this is post-op, secondary resection of the tumor here, and I did this because I wanted to present for olfaction in this particular case. Now, it happens that, is difficult to predict in this particular case, the olfaction was mostly not preserved, basically that significant decrease of olfaction post-op. So I have some other cases with better success in this, so we think that it's an dominant aspect in olfaction, one side is dominant on the other, maybe that explains why some patients are well-preserved, some others are not so well. So, difficult to tell, so just one word of caution about thinking you're gonna preserve olfaction because you have to go through one nostril, it's not always the case at all. So we can go to the video, I just wanna show another concept that is important for this case, especially the trial you can get in, so this is just looking anterior, this is the posterior ethmoidal, I remember we got to doing this all into one nostril, which makes it more difficult because it is lesser space, instruments need to go one on top of the other, as opposed to one on each side, and so this is the one side of the crista galli and this is the postural table, the frontal sinus, so these extend the approach all the way anterior, and this at the end of the reset, at the end of the exposure, you see the olfactory, sulcum from one side, back to the dural of the sphenopalatine, this is the prominence of the optic nerve, we don't need to go all the way there and all this is going to be tumor, So I congratulated dural, and now as I open the dural, see what's going to happen, I'm gonna open the dural, it's a nice soft tumor, and I opened the dural more, I was very careful open the dural, thanks God, because just underneath the dural, we find this artery right here, okay? This is a large frontal orbital artery, if you are not careful here, you can just cut through the artery and get into big trouble here, because this is a large area, you're gonna get a lot of arterial bleeding from this. So, this makes the case more challenging because these already is encased in the tumor, so we just continue the bulk of the tumor and working around it, in order to preserve the artery and remove all the tumor. So as we can continue with the resection of the tumor, we end up getting into the cavity that the tumor was created, which means the tumor resection easier, but you see the proximal aspect of the frontal orbital artery right here, and, this case, it was through the importance of the meticulous about even your dural opening, because you can even injure an artery by doing so. This is the distal part of the artery with some tumors, steel a stack on it, and we're gonna remove all the tumor that is around this artery. And again, this is all do all done through one nostril, we are using a 45 degree endoscope, that's why our section's looking that oblique position, and we're looking into any residual tumor, we don't find any, and this is the sort of the orbital surface of the brain, this is the dual attachment to this side of the falx in this area, that is just being coagulated, and now we'll proceed with the reconstruction as usual using the ELA collagen, you see this is the artery completely dissected, the frontal or with the artery, these are collagen layer here, and then we use a septal flap to cover nicely the defect, you see this the septal flap taking contrast post-op this is early post-op with a residual cavity. Again, this was, I think I need case because we do it all into one nostril, but, patients olfaction is still suffer from the separation, so I'll think twice next time when I counsel the patient appropriately about the risk of losing the sense of smell, even if you've go through one nostril. Now, some other cases we can do through this approach, this is a planum meningioma, and you can see this probably at the limit of you can do, or you can do effectively going endonasal, it is you remember those red lines, they are right here, this is the lateral aspect of the optic canal right here and here, this we can reach, but it's difficult, ideally, you wanna stop right here, but this goes more lateral but it can still be done, and you can see here the post-op with a complete tumor resection, although you can argue, whether there is some line in here that has tumor on it, it does look like that, but definitely the dural decline rates was not removed, but all graphs tumor has been removed extensively. So these are a good example of the limit of what we can do. I think this is a good indication, is a case that removes the tumor effectively, even from the top of the optic canal, but this is another case example where this is going beyond the limits, and this particular case has a lot of hyperkeratosis right here, is one of the reasons we decided to go endonasal, and these lateral attachment of the tumor is to be to lateral, and you see here post-op the receipt of residual tumor. So this is an example of... If you go beyond that red line, the tumor does, then you're gonna be leaving some tumor in here, where this is going to have any significant functional impact in the future or not, it remains to be seen, but definitely this is not a complete tumor resection. So let's look at the video clip of this particular case, it will tell you this variation that we call the superdomemedial or orbitech, where we mobilize the pretty Orbita, as you can see right here, and this gives me access to all these roof of the orbit that is all hypostatic. Look at the diameter of this bone, really thick and with this like real bone all the way lateral, this is going to both the orbit and I'm going to all from below by drilling this roof of the orbit, generally, attracting the periorbita to see a very wide exposure of the anterior skull based, now, all everything underneath this dural, is going to be two more on these, after the tumor resection, you can still see the frontal lobe, the the RA being nicely preserved, in this case, this patient had a lot of superior invasion, the tumor lead, and this is at the end of the resection, now this is also a large defect that can be reconsidered with a septal flap still, but there is a significant risk of CSF leak, or this person denoted one, is still the risk of leakage in a case like this is high. So, I would not recommend doing this allergy have advanced experience team doing these cases we use for these types of reconstruction. And this is just, the extreme of the application of endonasal of anterior skull base tumors, this is an olfactory equipment in humans we did in two in stages, and we actually needed a pericranial flap 'cause the defect was so large, that it cannot be covered with with a septal flap and with a two age stages, the central flap strength some, so it was not enough, so the pericranial flap had to be used, and all of these patients did actually well, he had no complications, you can perhaps identify a little bit of the CDL team or laterally, and I don't know if maybe hearing the falx here too. Now, this is the case though, this type of case that you wonder, is endonasal really worthy, and personally, after having done a number of these over the years, I prefer to do this open, because this require a two stage is too large, too much time consuming, and it's still the risk of leakage is high because the whole anterior skull base is gone. So if I have a case, this example of the peripheral flap, but if I have a case like this, this is added more recently the next six months or so, a case like this, I would not try in the nasal at this point, I would just do a transfemoral approach, I think you can do it all at once, in one single stage, reconstruction is much easier with a predictable flap, even actually you can maybe leave some of the bone, you drill some bone and leave a layer of bones, you don't have to go through them, through a scope, it's completely... So you actually can tailor the defect of the skull base, all the tumor is really destroying it, and a case like this has a lot of vascular encasement, and you might wanna have the opportunity to do this with a surgical microscope, with an endoscopic approach, so giant olfactory with meningiomas, I would rather do a transbasal approach, as has just described. I believe, Aaron, if you could pull the video six for this is the example of this particular case right here, and we can discuss approaches also. I know you like to do the material approach and it makes sense to find the neurovascular structures early, I'd like to do this modified, tooth frontal approach, because it gives me right down into the anterior skull base, and now once I open the dural, I can take the crista gallia, I can drill the skull base, I can devascularize the tumor, I can do this upfront, and I go to the base of the tumor at the very beginning. You see the dural is not even open to show the frontal lobe, so the frontal lobes are protected at all times, the dural is just open enough to find a tumor and I can go all the way down and find early on the optica Parado, is the up to chasm on the surface of the brain, and from here, I start finding the neurovascular structures. So it is the same council of the endonasal in the sense that we go, to the attachment of the tumor early on, we don't manipulate the brain at the beginning, but it's going to the groove frontal modified approach, and you can see there some of the vessels that are being dissected, these are eight two branches, you know, running towards the interhemispheric fissure, and even the small frontal orbital branches we can identify and dissect. And, Aaron, I see your point on using that terminal approach to find the A1 early and follow it. But I like this comes of going through the midline to get a tumor such as like this one. Just last piece, the top of the tumor here, and now we can find the vessels wrapping around and on the top of the tumor. The thing here is what is nice is as you see, we have not used a retractor, we have not manipulated the frontal lobe, the tumor has to be at all this space for us, and we can achieve a very effective resection of this tumor, you see that's the this delayed two branches, and that's in the last piece of tumor that are really stuck to these vessels, and this as you said, Aaron, this is what makes this operation very tedious sometimes, is to disect all these little branches and all this little vessels, and at the end this person doesn't have a skull base defect, I drew part of the skull but I still left some bone and mucus on the other side. So, I put a particular flat decode the frontal sinus on some of the skull but that's it, and I always like to look at the fallacy for legal mimics, where there is no tumor invading this optic canal, and that is not just quoting some of the dural of the planum of the sphenoidal there and that's the intercommunity fissure at the end of the resection.

- Just to comment for this case, I think this is very reasonable approach that you just described very effective, the reason I liked the terminal approach, Juan, is that, the terminal approach is very efficient to perform, you don't have to do a big bone flap, you don't have to enter the frontal sinus, you don't have to transect the superior sagittal sinus also inter durally, you can only manipulate one frontal lobe, also, you see the neurovascular structures from a lateral trajectory very early on, and therefore, you can be very efficient, you're removing the other part of the tumor because you're not always worried about running into the neurovascular structures and in all honesty takes much less time to do it. And for all those reasons, I think the term approach is ideal, although there's many ways to do this and the trans-basal approach as you demonstrated is quite effective. So, but I agree, removing a big tumor through the endonasal approach, staging it, making it more difficult, a very large defect, the increased risk of leak, that's just not, in my opinion a good use of a beautiful endoscopic approach.

- [Juan] No, I completely agree, and as you saw with this particular case, with this approach, the manipulation of the brain is zero, so that's the reason to the endonasal, so you can do the same normally position on the brain through a well-done skull-based approach from the top. So, just to wrap it up, just the cases as we saw the example of olfactory meningioma, ideal for endonasal, this one, this is not ideal for endonasal, it goes too lateral, this is one that I could do also through our modified frontal, I'm sure you will do throughout perianal, but either way it's a transvalvular approach, no question is a better alternative. And I'll just finish with this particular case, because this is just an example of how sometimes you can combine minimally invasive approaches, you can just do a conventional approach for these arteriorenal or a frontal or whatever approach you prefer for this, but this particular one is not good for endonasal not because of the size is not large, but you see, it goes too lateral, you see, it goes beyond that red line, this is not a good endonasal case. Now also, what worries me for any transcanal approach is, it is invading here the bone of the roof of the ethmoids, so this bone needs to be removed. This is a young patient, and you're gonna have a significant defect in the skull base here. So I thought that an eyebrow craniotomy won't be enough for me to give me access to this area and drill this area, and also I won't have an opportunity to repair this skull base. So, that's why in this particular case, which is located right in here, makes an opening right in this area into the sphenoid sinus here, I choose to do a combination of approaches going through one nostril, uninarial trying to pursue full faction, and then doing an eyebrow approach to go on, take the remainder of the tumor, that is two lateral for endonasal. You would please see the video is seven. So the concept for this is, I go first endonasal, I raised a septal flap, which I'm gonna use for reconstruction at the end of the operation and going endonasal like an early on, find all the bone that is involved, as you can see right here, this bone has tumor on it, I can drill it, I can remove it, I can quality with more the lotteries and devascularize the tumor early on, and it can get to the bottom of the tumor and I can enter the tumor and do some debulking, but I don't wanna do too much because I know I don't wanna compromise olfaction on the other side, because these tumor crosses a little bit towards the other side, so I don't wanna compromise that. So then, I go from above and we use an eyebrow approach that I think it would not be enough to take this tumor completely, if you don't combine it with an endonasal. So, this just doing a small pre-qual flap but this is just to cover the frontal sinus in case you open it, and then during the use of the usual craniotomy, supraorbital craniotomy, and during the floor of the anterior skull-base, so we can get better access, and now we've got intradural, inelegant and manipulation of the frontal lobe to get into the attachment of the tumor, this is working lateral to where we were before with the endonasal approach right here, and this is all done at the same time, this is the olfactory nerve right here, and then this is... The tumor is mostly detached, so you I can remove this tumor, or detach it from the endonasal, and then this is olfactory tracking this side that is completely invaded by the tumor, and no way I come preserve it, it was in cased, and it was already very thin out, these patients had normal faction pre-op and remain like that post-op, this is the trimming of the dural all the way to the optic canal and some of the vulnerable, but you see this is the hole of the endonasal approach. Is a hole that I can barely see with these eyebrow craniotomy, because he's very medial and inferior. And this was my worry, so how do I repair this hole, and this is your suture in a graft, but this is not watertight by any means, and it's sizable defect. So you can try with grafting techniques, but you're going to nasal and you use your septal flap, you guarantee that this patient is not going to live almost for sure, this is a very robust flop, it's a small defect, and then it will heal that nicely, and they will avoid the risk of a CSF leak while at the same time you achieve a complete resection of the tumor including all the bony invasion of this tumor. And for this patient now, we were able to remove all the tumor you see here, this is the post-op and pre-surgical faction, complete the preservation of olfaction because we didn't touch any of the control structures, not even the falx in this particular case. So, this is a case you can definitely do, with just one single craniotomy, but in this case, a combine of approaches is a possibility too. So just to wrap it up, Aaron, I would just conclude that is key when we do this for you to have some anatomical landmarks or nuances, really in consideration first, the bony and sinonasal anatomy is key to understand the bony anatomy and all the different landmarks within the bone, which gives you a lot of clues during surgery, ethmoidal arteries, the trajectory, how to deal with the periorbita, the foramen cecum landmark and the falx, how we can it from anterior to postrior, or the fronto-orbotal arteries, their importance to be preserved during surgery. Even when you're opening the dura, you can damage these arteries, so always consider these arteries at risk when you're operating here and how we do access to the medial aspect of the orbit, I'm going endonasal to extend our approach more lateral. And finally, indications for endonasal study, and anterior skull base have to be restricted, selected, sinonasal malignancies are ideal indications, but have to be those that are within the limits of a reach, and we can not compromise the goal of solidity, the oncological goal of negative margins. Ultimately, we have to combine more often approaches endonasal and transcranial, so we can achieve complete margins in these cases, then anterior skull base meningiomas, we discuss about it, we need to choose wisely, we've gone beyond the limits, and now, I'm personally going back and put it back the limits where they belong, giant olfactory meningiomas, I think transitional approach, whichever approach you choose is better, and finally, don't forget that endonasal surgery can be used as a corridor, as one approach that is combined with others to provide either vascular tissue for reconstruction or to get early revascularization or to get the tumor that is invading the anterior skull base. Thank you, Aaron. Thanks very much.

- You're welcome. Really, very, very excellent presentation, Juan. There is absolutely no doubt you're a pioneer in endonasal surgery on top of being a pioneer in clarifying the endonasal anatomy. So, we, on behalf of every neurosurgeon, I wanna thank you for your incredible contributions to neurosurgery which is very well-known, and at the end of the day, I think for someone who does infrequently endonasal surgery and wants to attempt to remove all these tumors through the nose, I think a great starting point, obviously, is removal of these sinus malignancies that already are in the sinus and create the operative corridor for you to remove them, as long as you have a capable ENT staff and rhinologist colleague who can do that, and as I guess the learning curve advances, you can talk about remove of meningimas, remain conservative, do not push the limits further than necessary, and remember the goal is safe surgery, the goal is not proving that you can do more through one approach than nobody else can. I think that's potentially can place the welfare of the patient at risk, with that in mind, again, Juan, thank you, thank you, and we look forward to having you with us for other set of lectures, discussing the middle and posterior skull base through the nose, thank you.

- That will be great. Thanks Aaron again.

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