 Anatomy is very important. I always say the anatomy that you know from the microscope, from your brain surgery you're doing every day, it's not different from what we see with the endoscope, but the perspective is different. And you should learn the perspective through the endonasal transfenoidal route. You have to know the anatomy of the perinaseous sinuses, but of course you have to know the interdural structures, everything which is behind the skull base. We differentiate the endonasal transfenoidal route into three different compartments. The first is the nasal stage. And the nasal stage actually may be for the beginner the most difficult part of the surgery. Why is that? First of all, we are not familiar, usually as a neurosurgeon with the nasal stage. And the second is if you use an endoscope, you would see you have plenty of space once you're in this phenoid sinus because then you can work bimanually and binasally. But at the beginning, you have to bring in an endoscope and instruments through one nasal orifice. So it can be very narrow, especially in your population here, you have a lot of people with polyps, thickened mucosa, and it may be very cumbersome at the beginning to start with it. So just for the anatomy at the moment, I always insert the endoscope through one nostril, which I think is the larger nostril at the beginning. I always have a CT scan MRI before that. And then I study the perinaseous sinuses. Most of the patients have some septal deviation. And usually I start with the larger nasal cavity. And I always insert the endoscope at the floor of the nasal cavity in between the nasal septum and the inferior turbinate. Usually this gives you the most, you have the most space in between these two structures. And if you follow that route, you come down to what kind of anatomic structure? What will you see if you follow in between the septum and the inferior turbinate? What will you come to? To the corner. And these are anatomic structures that you cannot miss. And once you're at the corner, then you know where you are. And then you just follow midline in between the septum and the turbinates. And then you always are at the anterior wall of the sphenous sinus. So it's not that difficult. You can never miss. What you have to know is how to deal then with the mucosa, which I will show you with the next talk. And middle turbinate, for example, it's a midline approach. I insert the endoscope here and then go along this phenoethymide recess and follow it up to the superior turbinate. And meter to it, you find the ostium to this phenoid sinus. This is the koana with the eustachian tube and the nasal pharynx. And a very important structure is the superior apex of the koana. Because from here, you orientate further upward to the ostium to the sphenoid sinus. This is the ostium to the sphenoid sinus. This is medial to the superior turbinate. You have the inferior turbinate, the middle turbinate, the superior turbinate. And the ostium is medial to the superior turbinate. Here's the nasal septum. The anterior wall of the sphenoid sinus is about from here to there. That means that the natural ostium to the sphenoid sinus is in the upper third of the anterior wall of the sphenoid sinus. That means if you open the ostium here, you must be careful not to go too far superiorly. Because you are in the upper third, what will happen if you go too far superior? You will come where? Where will you go to? You may enter the ethmoid. You may go wrong and enter the ethmoid and then maybe get confused and follow different routes and then you get a CSF leak at some point because you got wrong. So from here, I always go backward, open the anterior wall of the sphenoid sinus backwards, laterally to the origin of the superior turbinate. And then, of course, you have to go more medially. And for doing that, what will you have to do? You have to walk on the septum because there's this nasal septum. So you have to do some kind of posterior septostomy, taking it off. Otherwise, you cannot enter this sphenoid sinus. And then you do the same story on the other side and then you combine the approach. I will show you how we have to do that. So the distance from the superior apex of the koana following the phenoethmoid recess, which is here, to the ostium is about 1 to 1.5 centimeter. The ostium of the sphenoid sinus is not always parent. It's not like here in this nice specimen. In most of the cases, you will still have some mucosa covering it. But if you look with the endoscope, you will see if you have the mucosa where there is bone behind it. It's a different color to where it is at the ostium where there is no bone behind it. It's more bluish. And always take a micro-sucker, palpate at the ostium side. And once I feel it's very thin plate or even nothing. I perforate. But there are patients where the ostium is completely blocked and you do not find any ostium. Never force with a sucker or whatever and perforate it with your hand. In these cases, I just push away the mucosa. And then I have to take a drill. And then I drill into the sphenoid sinus. Other people like the Italian group of capobianca, they are not going for the sphenoid ostium. They go directly midline. This is another possibility. That you orientate koana, ostium, then break the septum, do a posterior septostomy, and then go directly midline into the sphenoid sinus, which is OK. I personally like to go via the ostium. Because with the ostium, if it's parent, you can take kerosene, for example, and you are in the sphenoid sinus. And then you can orientate how thick, for example, is the vomer, the rostrum, and then you can take the drill. If you go midline, you always have to take the drill. Without a drill, you get lost. You cannot take it by punches or whatever. So the parasyptl approach that you may know from the microscopic area, if you take a speculum, do you know where you open the sphenoid sinus? What is your key structure? Your anatomic key structure is the keel of the vomer. Where is the vomer? Is the vomer here? Is the vomer here? Here. It's far more posterior. So that is where we go in microscopically. That is where we go in endoscopically, just by different anatomical structures you follow. But of course, you have to take off the vomer with an endoscopic approach as well. Why is that? Instruments, absolutely right. I will show you. The one truth is what you can see with an endoscope, but the other thing is how you can handle with the instruments. And these are two different things. So next, a very important vessel is the spheno-palatin artery. You know, with its branches, especially the posterior nasal artery for the septum and for the turbinates, you must know where they are. The spheno-palatin artery is behind the middle turbinate. Usually, you don't see the foramen. You just see the branches. This is not only important to know for your routine approach. It's especially important to know if you want, for example, to create a flap. I mean, this is now something very special, but you may know if you do extended skull-based surgery, duroplasty is a matter, a factor, a very important factor. Because if you go into duroly, you have to cover your defect. And one of the strategies that you have to use is creating vascularized flaps, pedicle flaps. And this is your vascularization for the main flap that you use, the nasal septal flap. So what you have to know is the vessels are in between the osteum of the sphenoid sinus and the superior apex of the koana. This is your pedicle. So if you want to keep it, then it is important if you do enter sphenodotomy just to push the mucosa with the vessels backward and then take off the bone right here so you can keep the vessels. So even in case if you want to do the flap later on, you can do it. But if you coagulate everything right here, you can do if you don't need a flap. I usually do it in pituitary adenomers. But then you must know that you have destroyed the vessels for a flap if you may use it. This is now just in a specimen. We use fresh frozen specimen in my department. We get it from the University of Mainz, transnasal approach. You see, first of all, starting in one nasal cavity. Bring it in the endoscope and the sucker. That is how you start. And just inspect first. As I said, identify the nasal septum. Identify the inferior turbinate, the middle turbinate. Going to between infraterbinate septum to the koana with the eustachian tube, the tubal elevation, the nasal pharynx, superior apex of the koana. Then turn the endoscope superiorly along the sphenoethmoid recess. Lateralize the middle turbinate. And then, as I said, 1 to 1.5 centimeter above that, just media to the superior turbinate is the ostium to the sphenoid sinus. Once you have identified this structure, you can bring in, for example, as I said, a charism. We call it the Elegant Charism, the one that we use, a very nice one. And then you widen the ostium of the sphenoid sinus. This was on the right nasal cavity. And now we are going into the left nasal cavity. There's some septal deviation, but not that much. You have to lateralize the turbinates, the inferior and the middle beforehand. We rarely take the middle turbinates for a pituitary adenoma, for example. Just to show you now, it's a midline approach. But if you go, you know how you can work on the middle turbinate, this is now, again, ostium on the other side, media to the superior turbinate. And just to show you, if you now move the turbinates to the midline, I think that's what we're doing now. Yes. Now we are in the middle miatus. And this structure here is, do you know what this is? This is the unsincerized process. And do you know what kind of sinus you will enter if you take? Maxillary sinus. That is where you go into the maxillary sinus. This is important if you do extended scale-based surgeon, if you work on the pterygoid. You have to take the unsincerized process. You have to open the maxillary sinus. Otherwise, you cannot go that far lateral as you need it. But for pituitary surgery, it's a midline approach. And mainly, in most of the cases, lateralization of the inferior and middle turbinate is sufficient to work properly. So this is the widening of the ostium. Now we are in the sphenid sinus. In the sphenid sinus, there are often a couple of partitions. That's what Dr. Roy has shown to you. In some patients, you just have one intrasphenoid septum. In several patients, you have many. Interesting is, if you study it before on a thin-slice CT scan, you will realize that often one of the partitions run directly to the carotid canal, to the carotid, I'm sorry, to the bone, to the protuberance of the carotid artery. So if you study this, even if you don't have a neuro-navigation system that we routinely use in my department, even if you don't have this kind of device, you often can orientate just by analyzing the CT scan MRI beforehand. And once you're in the sphenid sinus, then you can follow these partitions and then you know where the carotid artery is and you just follow that. And now you see, once you have now take open the anterior wall of the sphenid sinus, then you have now to combine the approaches. And then you have to do a posterior septostomy. We usually break the septum 1 to 2 centimeter above its attachment at the sphenoid, taking the mucosa right there. And then with the mucosa, we usually take the cutting blakeslice, taking the mucosa, or you can use shaver systems. I'm much more in favor now to take shaver systems that the ENTs, some ENTs use. And once the mucosa has been taken off the bone, then you need drills. And a couple of different drill devices, whatever. I'm now using for this kind of thing a special drill with a continuous irrigation device that makes it much more easier, that you have irrigation all the time. And then you take off, as I said, the vomer and parts of the rostrum of the sphenoid. And this is important because otherwise you cannot bring in the instruments at the surgical site. Otherwise you always get stuck at the vomer. You have to absolutely flatten that, taking off the vomer so that you can go in parallel to the sphenoid sinus and then come to the cellar floor, which is not that easy here to detect. And this is another thing you should carefully, as I say, analyze the anatomy beforehand, especially in micro-adenomas. You sometimes have a very flat cellar floor. And even for an expert, you may miss the cellar floor in these cases. If you have navigations easy, otherwise it may be difficult. OK, and then you are in the sphenoid sinus. It's very important to create one single hole in the sphenoid sinus. Take off all the partitions. Go laterally to the border of the superior turbinate, both sides, open the lateral recess, and then have a wide opening. And before you start doing whatever you want to do, then at the skull base, you must be sure that you can bring in the instruments properly, and then you don't have any interference with your instruments. And there is the question on how much should the septum, the bony septum, been taken off? And always say, this depends on how you can bring in the instruments. And if, for example, you have narrow cavities, and you bring in the scope, and on the other side, the instruments, let's say a sacchar or bipolar, whatever, and you realize, by bringing in the instrument, you push the septum to the side, and you get some blood clots in front of your lens that disturbs you. You can be sure that this is not sufficient. So then you have to take off more of the posterior septum until you can clearly bring in the instruments and do not interfere with the skull. So if it's too close, some people take then parts of the middle turbinate that you can do. The turbinates are pretty much important for moisterin, your nasal cavities. I'm no more in favor of just taking off the bula et moidalis. So what I'm doing is now then medialize the middle turbinate, take off the bula et moidalis, some posterior ethmoidectomy, and then usually you can move the middle turbinate very nicely. In extended skull-based surgery, if you have to go more laterally, then it is a must to take part of the middle turbinate. But for a routine transfenoidal, it's not necessary. This is the midline approach if you want to go transfenoidally to the cellar floor. That is sufficient. If you want to work in the cavernous sinus, you can visualize it by a pure transfenoidal route. But it's very difficult to bring in the instruments properly. Then we have to widen the approach more laterally. And that means that you have to combine the transfenoid with the transethmoid route. And if you want to work even to the middle cranial fossa, or let's say ganglion-gasary, these kinds of surgeries, you're going to have to go even more laterally. And then you have to combine the transfenoid with the transethmoid, as I said, the transterrigoid. And that means that you have to open the maxillary sinus as well. This is what I want to say, skull-based anatomy. Once you are at the skull base, you have to identify the bony structures. Cellar floor, tuberculum cellae, planems fenoidale. Then you see the bony protuberance of the optic nerve. You see the carotid artery. And you see the medial optical carotid recess and often much better the lateral optical carotid recess. You see the paraclival carotid right here. Paraclival or trigeminal segment, as you want to know it. And you see the clivus with the clival recess. This is something that you should see. And once you've taken off the bone, then you see these structures right here. You know, this is the same specimen taken off the bone. You see the pituitary gland. You see the carotid artery. And you see how close the carotid, especially in elderly patients, come to the surface. That is interesting with the endoscope. You sometimes have patients where there's almost no bone or just a little thin plate covering the carotid at this upper vertical segment right here. And this is where you can easily do some harm to the carotid artery if you don't see the carotid artery. Carotid artery with a siphon here, the paraclival. The clivus, once you open the dory, you see the basilar artery right here. This is the chiasm here, the medial OCR, the lateral OCR. And this is still here, the arachnoid covering the rectus gyrus. This is more superiorly with the rectus gyrus here. And then you see the olfactory nerves on both sides as well. You see the ophthalmic artery. Ophthalmic artery coming from the carotid, pituitary gland, pituitary stalk. This is important. This is a very nice image that gives you a clue why, for example, for me, all the pathologies that are supercellularly going into the third ventricle or infracasmatic can nicely be approached anonasally because you come directly to these structures. And the big advantage, especially in the craniopharyngeumus, is you see the gland and you see the stalk. So the key structure of the stalk is directly on your view. And everything which is infracasmatically pushes up the chiasm so you are directly at the pathology and the nervous structures and vascular structures are pushed aside and you don't have to deal with them. Anatomy of the third ventricle, that you get an impression you can do with the endoscope the same approaches as you know it from your microsurgical route transcranially. You can open the laminar terminalis. You see it here above the chiasm. This is laminar terminalis approach with the endoscope. You see the ACOM, both A1, both A2 segments, inter hemispheric fissure. You can open the laminar terminalis. If you come from this route, you will see more to the posterior part of the third ventricle. And if you go prememulory what you can do and open the third ventricle as you do it with a ventricle ostomy, prememulory can do the same endoscopically then you can look up to the ferramen of Monroe. Paracellar area with a transphenoid, transethmoid approach, you should know that the pituitary gland has arachnoid fibers in between the carotid artery and the pituitary gland. You know the KnoS classification of the pituitary adenomas. So this is an area you maybe often have to deal with. And as pituitary adenomas are soft, you can often follow the tumors, especially once they are in the medial compartment of the cavernous sinus. If they are in the lateral compartment, that means in between the carotid artery and the superior orbital fissure, it becomes more difficult. If the tumor is soft, you can work in here. But for example, for a meningeomer, I never do that because you will do some harm to the nerves. As you know, this is the ocular motor nerve. This is the trochlea in between. This here is the abducent nerve and then there is the trigeminal coming more down. And you know that they are all attached to the lateral wall of the carotid sinus. So if you manipulate a lot there, patients will do some harm and the patient may have a ophthalmoplegia. Last is then clivalent anatomy. Clivus is very important. The nerve next to the midline is the abducent nerve. Must be very careful. If you open the clivus, always being in the midline and then carefully work laterally. But with the clivus, you have to know that there are a lot of connections from the basilar plexus to the sigmoid sinus and to the coronasinus. It can bleed a lot if you go through a normal clivus. Then there are different compartments of the clivus. If you work on the upper part of the clivus, you get a nice approach to the interpeduncal system. That's what I want to show you. These are mammillary bodies, basilar apex P1 segments, ocular motor nerve in between P1 and superior cerebellar artery. That is Pons and basilar artery. And that is where we do our ventriculostomy from the other side. Now endoscopically you can do it from this side as well. This is now the middle part of the clivus. If you open that, then you come to the pre-pontine cistern with the basilar artery. And then you can see the trigeminal nerve. You can see the bundle of the vestibular cork layer. You can see the pica down there, ferraman jugulari. And if you take the last part, then you can even go down to the ferraman of magnum and see even the rootlets of C1. This is all possible endoscopically, but then you have to go really drill everything down to the corona. Yes, I have to take the whole rostrum of the spinoid. So I think I stopped with the anatomy right now.