Temporal Lobe Anatomy and Surgery

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- Hello, colleagues and friends. Thank you for joining us for another session of the virtual operating room from the Neurosurgical Atlas. Our guest this evening is Dr. Juan Carlos Fernandez-Miranda, a dear friend. He is actually the most frequently invited neurosurgeon to our session, and there is a good reason behind that because he's truly not only a master microanatomist, but truly an amazing surgeon who has refined the techniques of endonasal surgery. We just had a great meeting with him where he directed the Rhoton Society, an immense course. Juan Carlos, I'm so proud of you. We are really people of... We have advanced together at the same time, where sort of our careers have really crossed paths so many times, and I'm so proud of you, of an incredible surgeon you have become. So I think you have had such great contribution in microanatomy and neuroanatomy, but I think your incredible talent has been in complex skull base surgery. So this evening, he's going to talk to us about temporal lobe anatomy, something that's often taken for granted. In fact, temporal lobe anatomy is much more complicated if one wants to dive into it. And so I'm really honored to have him to talk about the anatomy and the surgical cases. Juan Carlos, please go ahead.

- Thanks, Aaron. Once again, it's such a pleasure to be here with you. I actually am very thankful to you because you have been a enormous influence in my career and your support is been very important to me. You give me chances in the past that are unforgettable. So I'm very thankful for that. So, as Aaron said, we had this Rhoton Society meeting the past two weekends, which has been great, I think very successful in terms of the reviews and all the feedback I got. So I'm very glad for that. And I told Aaron, I was a bit tired of, not tired, but I wanted to change topics a little bit and not talk about, again, endonasal surgery or open skull base surgery. But I wanted to talk about a topic that is very relevant for me. And something that I've studied very intensely over the last year, the last decade or more, which is brain anatomy, and in particular, medial temporal lobe anatomy. As Professor Rhoton would say, "The brain is the jewel of creation." And when I was a very young resident, I came up with, into this paper, that Dr. Ture had put together influenced by Professor Yasargil on the white mater dissection technique. This really changed the way I approach brain tumors and the understanding of brain anatomy and surgery. And I recommend everybody, in training especially, to go to the lab and do dissections. This is much easier than going to the lab to do a skull base approaches because you need a whole head. But to do brain anatomy, you just need a brain. And any anatomy department will have a brain available for you to study. You can go and start with the gyri and sulci, understand them all really well, and then start doing dissection and see the fiber tracts and which areas are they connected. And this is really normally very interesting, but it's actually even fun. At the same time, we studied the fiber tracts with fiber tracking. And for example, this is a very important relevant tract. One of the most important. This is the arcuate fasciculus. And over the years we studied this, we compare dissections on fiber tracking and we studied the variability of this fiber tract. We compare left and right side, for example. I was fascinated to find that the right tract, what you see there is much more... The left tract, sorry, arcuate tract, is much more robust than the right one, and the connectivity is also different. There are areas that are particularly connected on the left side, but not on the right side. For example, the ventral premotor cortex, which is the common area where you find what's called Broca's area, but is the speech and rest area, where you find more common in surgery is robustly connected with the left arcuate tract but not so much with the right, or actually not at all with the right. And that's a major difference in this anatomy. Let's go to the next, please. There is another very relevant tract, which is the superior longitudinal fasciculus. It's a frontal parietal tract. And we describe a ventral and a dorsal SLF. And these are relevant on the left side, perhaps for language too, but very important also on the right side. And in fact, when we studied this, we found that there was some predominancy on the right side for one of the tracts of the SLF, which was very interesting. Also wanted to bring the attention to the terminology on SLF-1, 2 and 3. This comes from monkey studies. But the human brain is quite different from the monkey brain, obviously. And, you know, studying this, and I know this is controversial in the literature, I believe that SLF-2 and 3, which we call dorsal and ventral SLF, are the important tracts. SLF-1 is actually part of the cingulate cistern, as you can see in this picture. So let me point this so we can understand it better, but you look at the location of the SLF-1 right here. This is paramedian and is adjacent to the cingulate. So I proposed that this SLF-1 actually is part of the cingulate fiber system. And there is another controversy, which is the superior fronto-occipital fasciculus. Interesting enough, Dr. Ture published many years ago a paper, his first paper on white mater dissection that this fiber tract does not exist. And we actually sort of confirmed this and we proved with fiber tracking that this tract was actually false continuation between superior thalamic peduncle fibers and posterior thalamic peduncle fibers. So there's three terminals, give the impression of a unique tract, but actually is a false continuation tract. So that brings a point of this very important tract, the inferior fronto-occipital fasciculus, or fascicle, should be actually called inferior or just the fronto-occipital because there is no superior fronto-occipital fasciculus, in my opinion, in the opinion of other experts. This tract, the IFOF, we studied also in detail. We used segmentation to define three different subtracts, but importantly also, along with the uncinate tract, which you see right here, it forms part of the ventral external capsule, this area here. And this is important for, for example, insular glioma surgery. Because we need to enter into this so-called temporal stem, which is not a great temp, but is that connection between frontal here and temporal pole and then temporal occipital regions in this area. So all of this important anatomy to understand before approaching brain tumor surgery. We also describe this middle longitudinal fasciculus that runs like this, and importantly runs underneath the arcuate tract, which goes on top. And in the past, we saw dissections and we saw fiber tracking reconstructions where the arcuate tract would do like this, but that curve anteriorly is not accurate. It's this false continuation between the two tracts. So that, what we found is that arcuate goes in this direction, middle longitudinal goes in this direction. And not only that, but we also describe how this middle internal fasciculus goes to the superior temporal, superior parietal lobule right here and not to the angular region, which is in this area. It goes on the superior temporal gyrus, but it doesn't curve like this. It goes in this direction. And again, I believe the misconception about this tract was related to not-so-accurate fiber tracking studies, where you could see the false continuation between the middle longitudinal and the arcuate fasciculus. And in brain anatomy, we learn that this right angle turns are not very common. Only when you reach to the cortex, but not in the middle of the brain white mater substance. So you need to always have a critic eye when you do fiber tracking reconstructions. We also study inferior longitudinal fasciculus right along the basal aspect of the temporal lobe. And this is important also for temporal lobe surgery. And there is a very relevant tract, which we publish solely a few years ago. Which it was, is this concept of the vertical occipital fasciculus, but more important, what I like to call the parietal aslant tract, which is this area right here. This tract is very relevant because again, it's dominant on the left side, and it is also closely related to language function. That's why doing surgery in the temporal parietal junction, it is an area of high risk for speech disturbances and an area where brain mapping can be very useful to delineate the exact location of these cortical areas and fiber tracts and connections. Of course, when we are gonna talk about temporal lobe anatomy and surgery, optic radiations are a very important fiber system. You all know how it does this, how the optic radiations create this so-called Meyer's Loop. Some of the radiations curve, these are what we call the anterior aspect of the optic radiations. They come from the lateral geniculate body, but then you also have what we call the medial aspect of the radiations, which go like this. And then we have also posterior optic radiations, which go more in this straight fashion posteriorly. So anytime we cross the temporal lobe from lateral to medial to get into the temporal horn, we are at risk of injuring these fiber tracts in this area. So the more anterior we go, the better, and the more basal we go, especially at this area, the better. The fibers are gonna be turning into the basal aspect as you go more posterior. So this is a beautiful picture. This dissection is looking at the inside. Imagine this is the temporal horn right here. And the lateral wall of the temporal horn is formed by this optic radiation fibers. The anterior wall of the temporal horn is formed by this gray mater structure, which is no other than the amygdala. And that's why doing transsylvian approaches through the amygdala to enter the temporal horn is the best way of preventing, damaging these optic radiations here. Because you enter through the amygdala into the temporal horn. This dissection has so much information on it. For example, as Professor Rhoton would say, "A cup of coffee for the participant that knows why is this white mater tract curving around the thalamus right here?" And this is the stria medullaris thalami that goes from the amygdala and anteriorly. Now, this is not that important in surgery, this particular fiber tract, but at least not really for me, but this one is of course, very relevant. You see this fiber tract right here, is of course the optic chiasm and then the optic tract. The optic tract at this level forms a key landmark when we're doing our amygdalohippocampectomies, because it forms the upper aspect of our dissection or resection. Also more anatomy here important to understand, lateral geniculate body right here. You see these fibers actually go to the lateral geniculate body. And then this is the thalamus, in particular, the pulvinar in this area. Okay, so a lot of a good anatomy that we've reviewed, and a lot of this we put together in this now classic paper where we studied years ago, the fiber tracts, and we correlated them with fiber tractography. We came a long way from that paper, and we put together and published many papers on individual tracts with better, especially with better fiber tractography, what we call hi-definition fiber tracking. Now, that was just an introduction on brain white mater anatomy, because it's so important as neurosurgeons that we understand the brain white mater and we respect it. And anytime we do an operation, we wanna respect as much white mater and gray mater of course, as possible. Now, for the medial temporal lobe, it's a very didactic, there is a very didactic way of classifying the medial temporal lobe in three segments. And this actually was proposed by Evandro Oliveira in the past. And then we put together this paper on different segments, and describing the different approaches for each segment. So we have an anterior part of the medial temporal lobe, this area, which is formed by the uncus of the temporal lobe and this area called the entorhinal cortex, entorhinal area. An integral part of the parahippocampal gyrus. Then we have our mid segment right here. And this mid segment, which is formed by the posterior parahippocampal gyrus. And as you will see, the hippocampal body is a difficult area to access because it's just in the middle. So it's interesting to discuss how to approach this medial aspect of the medial temporal lobe. And then we have our posterior aspect of the medial temporal lobe. This posterior aspect is interesting because it has this sulci running through, and this is no other than the calcarine sulcus. The calcarine sulcus continues posterior like this, and it forms a Y-shape intersection. So let me clean this so we see it better. So there is a Y-shape intersection right here. Calcarine sulcus continuing, this is the anterior calcarine sulcus, this is posterior. This will be parieto-occipital sulcus right here, and this, we call the calcarine point. So this is the posterior in the middle of the medial temporal lobe. Whatever is below this calcarine sulcus here, it still belong to the medial basal temporal lobe. Whatever is above, this becomes the isthmus of the cingulum, another area that we might have to do surgery on, as we'll see at the end of this talk. Okay, so the medial temporal lobe has extra ventricular anatomy to remember, which is this one, and it has intraventricular anatomy and correlation. And the same we have on the anterior segment of the medial temporal lobe, we have the amygdala right here. It forms the anterior aspect of the uncus. We have the posterior aspect of the uncus here, and this is the head of the hippocampus. So you can nicely see here. And there is, in-between there is an apex right here. So this uncus has like a triangular side. Anterior is amygdala, posterior is head of the hippocampus. And this is a very didactive way of understanding this anatomy. There is also another important reference here, which is this one. This is the collateral eminence, and this is continuous in this way. And this is the equivalent of the collateral sulcus. It's the prominence of the collateral sulcus. Why is this important? Because this forms the lateral limit of your hippocampal disconnection, when you do operations in this area. Always important to see this part of the floor of the temporal horn as a key landmark? There is another very important point, with this one right here. This is the anterior choroidal point, where the anterior choroidal artery enters into the choroid plexus. Choroid plexus is gonna be occupying this portion right here, attached to the fimbria, that you see right there and to the choroidal fissure, but you don't see choroid plexus in the temporal horn in the anterior aspect of it, where the head of hippocampus is. So those are key tips during surgery. For example, if I wanna do a removal of the head of hippocampus, I need to remove it all the way until I see that I start identifying choroid plexus. That is a very good landmark, as you will see in surgery. Now, middle segment of the hippocampus here is the hippocampal body right here. As we said, difficult area to approach on itself. And then on the posterior aspect here, in the posterior aspect of the medial temporal lobe, we have the tail of the hippocampus going up, and then we have here, this prominence is the prominence of a sulcus. It's the prominence of the calcarine sulcus. If you remember how we see this here, you see this calcarine sulcus right here, this calcarine sulcus correlates with this area, which we call the calcar avis. In the past, you might know that two centuries ago, this was called the hippocampus minor. And there is an interest anecdote because the anatomists at that time, some of the anatomists, identified that hippocampus minor is exclusive of humans when you compare with monkeys. And they were thinking that is the seed of the soul. That's what makes us humans. Of course, they were not correct about that, but that's an interesting feature.

- Hey, Juan Carlos.

- Yes.

- Do me a favor. I love the anatomy. When you are starting, would you orient them what slides you're using and where you are, where the cut is? And show the cut slides. That will really help to orient them pretty quickly. Thanks.

- This cut is a little bit difficult, is in two planes. Is a way to just basically open the the temporal horn. So imagine that the brain stem would be here and the lateral or the temporal pole would be right here. So there are two cuts here, so you can see the whole ventricle wide open. So what you see here . And in the entrance, we said, we have the calcar avis right here, correlation of the calcarine sulcus. And up here, what you see here are the fibers actually going in a different direction. They go like, this is the prominence of the splenium of the corpus callosum or the fibers coming from the splenium of the corpus callosum, which we call the forceps major. So this anatomy is actually very important also from intraventricular surgery to identify all these landmarks.

- Yeah, essentially this is a top view of the ventricle on the left temporal lobe. I think that's the best way to describe it. I know it's not a perfect superior view, but relatively. So if you just orient top view, left temporal lobe, I think that would get them going. Thank you.

- Yes, yes. Definitely left and from the top, exactly. So we'll go to this next view. This is a view from the... It's another left side, and we're looking for medial to lateral. What we're looking is directly at the uncus, and there is a lot of important anatomy here. Now, you don't see this anatomy in the operating room like this, from medial to lateral. You're coming from the front usually, or you're coming from lateral if you do that approach. But what we see here, this is what they call the sylvian vallecula. It's where the MCA turns. And some people call also this, the temporal stem, or actually like they call the name, limen insulae, is what connects frontal and temporal lobes. And just behind it, we have this key area, anterior perforated substance. You can see the holes here. This is what the lenticulostriate arteries use to enter into the basal ganglia. In fact, I like how Professor Rhoton described the anterior perforated substance as the floor of the basal ganglia. So the basal ganglia are on the other side. Now you see also the optic tract right here, and of course the cerebral peduncle and these are key landmarks. You see the optic tract in surgery, you'll see the peduncle in surgery also. Now, if we focus on the uncus, there is this very important sulcus. This is called the uncal sulcus. And as I will show you, there are arteries going to this uncal sulcus? And this is important to recognize also during the operation. As we said, the uncus has an apex, which is right here. It's like a triangle, and then a posterior segment and an anterior segment. This anterior segment has the amygdala right here, and this is the cortical aspect of the amygdala, or the cisternal aspect of the amygdala, because it faces the cistern. And then we have here, the extraventricular aspect of the head of the hippocampus. So this is the head of hippocampus, but now seen from the cortical surface or the cisternal surface. All right, now we are looking now from the uncus now back into the medial aspect of the medial temporal lobe, here and here. And we're looking again from medial to lateral, left side. And what you see here is the choroidal fissure. The choroidal fissure is such an important structure to understand. And a very easy way for me to understand it is, you have your fist, this is the thalamus, and you have your other hand, the thalamus is always surrounded by the fimbria or the fornix, depending on where you are located. So, if you are in this area on the temporal horn, the fimbria is inferior to the thalamus, and this is lateral geniculate, medial geniculate pulvinar, and the choroidal fissure runs in between. As you start turning into the atrium, then the fornix, or the crus of fornix, as it's called, is gonna be posterior to the thalamus. As you go into the frontal horn, which we don't see here, it would be above the thalamus because it's just curving around. Okay, so choroidal fissure is extremely important because it's what connects the ventricle with the cisterns. So anytime you come from the cistern and you're gonna go into the ventricle, you need to open the choroidal fissure, or the opposite. If you're in the ventricle, and you're going to the cistern, and disconnect, for example, the hippocampus, you need to open the choroidal fissure. So on the medial aspect of the medial temporal lobe, you can see the fimbria, and below you can see the dentate gyrus. And this is where the hippocampal arteries enter in this area. And this area here or the parahippocampal gyrus is called the subiculum, but let's call it just parahippocampal gyrus. The body of the parahippocampal gyrus. You can see the dentate gyrus getting thicker here. That's the tail of the hippocampus. And then here, you see the fimbria just underneath the splenium of the corpus callosum. I know this is a lot of complex anatomy. It's so important to understand. So I recommend everybody to go to the lab, find a temporal lobe and start exploring this anatomy. Doing cuts, identifying anatomy, intra and extraventricular. Not only this white mater and cortical anatomy is important, but also the vascular anatomy of the medial temporal lobe. And we studied this extensively in the past. So you look at the... This is the parahippocampal gyrus right here, all this. And you see, there is a main artery that runs along the parahippocampal gyrus which is the posterior cerebral artery, as you all know. Now, for me, and I studied this in the lab with Professor Rhoton extensively, and studying the mid temporal lobe was important because it gives you a good understanding of all the basal cisterns, or most of them, because the medial temporal lobe surrounds all these basal cisterns. So you can start here and you can see here, this is the end of the sylvian fissure cistern, or the beginning, depending how you see it, and the connection with the optical choroidal cistern in this direction. And then here you have this branch right here, PCOM, but you have another branch right here, which is the anterior choroidal artery. This, we could call this, the choroidal cistern in this area, and a cistern we need to open when we disconnect the uncus of the hippocampus. And then we have in this area, the ambient cistern right here, where we have the PCA, the basal vein of Rosenthal, and the cistern in between the medial temporal lobe and the brainstem, or the mid brain at this level. And then as we go more posterior, the tail of the hippocampus will connect or relate with this cistern, which is the pineal cistern or quadrigeminal cistern, where we have the end branches of the PCA going, let's say, the choroidal branches of the PCA going to the third ventricle. So in terms of the vascular supply of the uncus, the uncus has vascularization from three main arteries. We have, as you will see, the choroidal artery, is the best known by many of us. Choroidal artery, is this branch stem, which we call the uncal hippocampal artery, because it goes to the uncus and to the head of the hippocampus. To the uncus here, branches in the surface, and then goes inside the uncal sulcus. This is uncal sulcus right here. Then we have another artery, which is the, of course, posterior cerebral artery that these branches, as we will see. You see another branch going into the uncal sulcus and also doing branches to the hippocampus outside. We call this the anterior hippo parahippocampal artery, because it give branches on the hippocampus, and to the parahippocampal gyrus. But we cannot forget about other branches. This is the MCA, as you see here. And this MCA also gives branches that stay just in the anterior aspect of the uncus and they mostly vascularize the amygdala and the anterior aspect of the parahippocampal gyrus here. So those branches are also important. And especially it's important to differentiate these branches from these key branches right here. The perforating vessels, the lenticulostriate arteries. It is possible, as I will show you one of the cases that one of these lenticulostriate arteries could do something like this. And on its way to the anterior perforated substance might lay on the surface of the uncus. And you need to make sure before you coagulate any branches on top of the uncus that this branch is not a lenticulostriate artery going to the anterior perforated substance in this area. So MCA, PCA, anterior choroidal, giving vascular supply to the uncus. And here it shows nicely the territories. So this territory, anterior here, this is territory of the MCA. This other one above here in blue, this is territory of the anterior choroidal. And this other one down here is territory of the PCA. And of course, remember the uncal sulcus in the middle, because that is a very important landmark. In addition to the uncal arteries, we have studied in detail the hippocampal arteries and the anatomy of this arteries. This had not been studied... There are not many studies about these arteries. These are the new ones. And for example, Professor Yasargil studied this in detail, and there is this beautiful book by Duvernoy called "The Human Hippocampus." I recommend everybody interested. It's a beautiful book with beautiful views. And basically what we studied is the branches that go to the hippocampus. And as I said, the most important ones, because are the ones that we find more often in surgery are the ones going to the uncal sulcus. Because most often what we do, is we take the uncus and the head of hippocampus. So these branches, again, they are coming from the anterior choroidal artery and you see here, they go into the uncal sulcus, and they go into the depth of this sulcus. But here we have the PCA. And this PCA gives another important branch that you see here. It's giving these branches that go into the uncal sulcus. Usually, they go a bit more posterior, so first you find choroidal. More posterior in the uncal sulcus, you find this so-called anterior hippocampal parahippocampal artery. Basically giving branches to the head of hippocampus, to the parahippocampal gyrus outside, and to some of the, sometimes extends to the body of the hippocampus in this area. Now, we publish this paper and there are a lot of details here that we're not gonna go over because there are many variations, but basically remember, there is an anterior artery going to the uncal sulcus. This is from the PCA, and often there are two arteries going to the middle part of the hippocampus, but sometimes, you have one large artery that gives all these in a treelike distribution. All these beautiful branches going to the dentate gyrus. And when you're doing surgery, you wanna differentiate these branches and you have to coagulate and transect them into your operation. Another example of a posterior branch here that supplies the body and the tail of the hippocampus. So you are disconnecting the hippocampus, it's important to recognize these arteries and differentiate from others. So basically, in an ischemia, this is the most common pattern where the... This is the PCA. So what we did here is we cut the carotid. This is the carotid we cut right here. So you can see the choroidal artery. And it gives this branch that go to the anterior aspect of the uncal sulcus, uncal hippocampal artery. This is your PCA, and the PCA runs like this. And then it gives this large branch that goes to the posterior aspect of the uncal sulcus and all these other branches. And then somewhere in this P2P segment of the posterior cerebral artery, you have usually two, but you sometimes you saw one branch that bifurcates two branches. We call the middle hippocampal artery complex that go to the hippocampus. And then here, posteriorly, we see these arteries more rarely, usually from posterior approaches. We see this artery, which is the splenial artery. The splenial artery goes to the splenium of the corpus callosum obviously, but it also provides supply to the tail of the hippocampus. And that's important also when we're doing posterior approaches. So why knowing all this detail, vascular anatomy? Do we need all this? For me, it's important. When I'm doing surgery, I like to understand everything I'm doing, I'm seeing. I like to understand every vessel, if possible, every vein. It gives me safety and confidence when I'm doing my operation, understanding all these anatomical structures. So I'm gonna ask you now, a step-by-step done in the lab, anteromedial temporal lobectomy as described by Spencer. And you can see here, this is a right-sided temporal lobe. Patient is, the head is placed in this location. This is the location of the nose. This is anterior, this is posterior, the middle fossa is up here. Let me just draw the middle fossa for reference is right here. So inferior, middle, superior temporal gyrus, sylvian fissure. So we've done here the initial removal of the neocortex, the anterior three centimeters or so of the temporal lobe. And then we get into the temporal horn right here, and we see the head of hippocampus. Once you see the head of hippocampus, you wanna identify the choroid plexus posteriorly and find the choroidal fissure. Once you open the choroidal fissure, you can see the anterior choroidal artery running in there. Now, then you open the choroidal fissure, and this is a natural opening. You can do very nice opening, very clean, but then from here to here, this is the part that there is no fissure here. And what separates you from the choroidal fissure, from the choroidal cistern and the location of the anterior cerebral artery. So here, basically you have to disconnect the white and gray mater until you find the peduncle on the other side and the anterior choroidal artery, and basal vein, as you see right here. And you can continue your disconnection posteriorly. And then as you're doing this disconnection, you see those vessels going into the hippocampus. These are branches of the medial aspect, body of the hippocampus. Here branches going to the anterior aspect. As you see, also right here, those branches going to the uncal sulcus. Now, the branches to the uncal sulcus are tricky because they go underneath here, you don't see them. So you need to see them through the head of hippocampus. And then finally, as we disconnect completely, you can see some of the branches going here. And as you remove this specimen, just done for anatomical reason and purpose to understand, look all the vessels we had to disconnect. So we had this branch for the choroidal artery, this branch into the uncal sulcus on the PCA and all these branches from the PCA, going to the body of the hippocampus. And at the end of your resection, it's gonna looks like this. You're gonna be looking at the PCA, you're gonna look at the basal vein, you have the choroid plexus. You have the, sorry, the optic tract here running. And this is, what you see here is the lateral geniculate body in this area. Now in surgery, you wanna keep the arachnoid covering all these structures, because that arachnoid protects these vessels, but you see through the arachnoid. And that's why working in the laboratory is so important, because you can see the structures, dissect them in a way you cannot do in the OR, or you should not perhaps do in the OR. So you need to see through the anatomy. And this is a nice drawing, schematics that one of my fellows beautifully did. And I'm gonna suggest an example of these arteries and this hippocampectomy in a brain tumor case. These is a tumor that is temporal insula glioma, recurrent. And I'm gonna go on operation to remove. I'm just gonna show you the little bit on the removing the head of hippocampus so we can see that disconnection. So these are the vessels in the sylvian fissure right here that we escalate on ice. And we went up here and we did our insular part of the operation. Let's go ahead. Luke, keep playing, please. Did I do something to stop that? There you go. So you see here, if we're opening the choroidal fissure and I see a little vein that I didn't mention, but there is an inferior ventricular vein that drains into the vein of Rosenthal. That white structure you saw, that was the cerebral peduncle and the optic tract just above. Now, I'm doing a posterior disconnection of the head of the hippocampus, and I keep working my way into the choroidal fissure until I see the anterior choroidal artery passing through. And then I'm doing the posterior disconnection, and now this is the sulcus right here, and this is the artery going to the uncal sulcus. That is the artery from the anterior choroidal main tract. You see the optic tract, and then that is the fimbria that I'm finally disconnecting And then I'm seeing another branch, this is gonna be the branch from the PCA. That's going to the posterior aspect of the uncal sulcus. So I know I have to go there and coagulate these branches, and finally cut, and I can remove this specimen almost in block, and remove the hippocampus entirely. So it's a nice anatomical exercise. You could, of course and just aspirate the whole hippocampus, and there is nothing left. That's one way of doing it. I like to do it in a more anatomical way, where I identify the structures and I disconnect this selectively. Let's go to the next one, please. So, we mentioned the veins. I'm gonna spend a couple minutes on the anatomy of the veins because I believe this is very important to understand. You see here, this is the basal vein of Rosenthal right here. And understanding these variations is very important, and this is important for brain surgery, but also for, for skull base cases that we do often, it's very important to understand the patterns of variation. So the most common one, this is the one that is always continues. This is the classical panel of the basal vein. It gets tributaries. All the blood is collected from this main pipeline, which is the basal vein, But embryologically, the basal vein is formed by different anastomosis. And if those anastomosis fail, you have disconnection within the basal vein cistern. For example, in this case, this part is gone. And what this means is that there is gonna be an anterior venous drainage through, for example, this called the preuncal vein, and one of the sylvian veins are gonna drain here and then all this other part is gonna drain posteriorly. So there are two patterns of drainage, posterior and anterior. In this case, for example, this is very important for a skull base surgery, for example, because here you see the basal vein is being formed by tributaries here, and as they go posterior, they drain down and they go into the lateral mesencephalic vein, which can at the same time drain into the interior petrosal sinus or into a tentorial sinus. So for example, if you're gonna applying a combined transpetrosal, or a transtentorial approach of any sort, you need to understand this patterns of variation very well. Another one here would, similarly there is a... Drains to the lateral mesencephalic vein inferiorly and an anterior drainage pattern. This one also in this case is draining more laterally through the sylvian veins. So there are multiple different variations, and it's important to identify. I like to always study, not really angiograms because we don't do angiograms routinely, but CT angiograms and venograms are very useful to identify this part. You see one here, this is going down, and this is going to the superior petrosal sinus. This one, if you coagulate the superior petrosal sinus, you're gonna be taking the venous drainage of central cord structures, and you can have problems with that. Okay, so let's move on some cases. Let's clear this. I'm gonna show you these few cases, all of them in the area of the medial temporal lobe. So this first case is this young patient with history of radiation, and he has this enhancing mass in the uncus. And you can see the flow signal. You can identify very nicely the anterior segment, amygdala posterior segment, head of hippocampus, the apex here, and the extent of the tumor right here. So for this tumor, you can do this approach. It has also the lateral cortex and just go into the tumor. That's one option and that one way of doing it. That has been recommended by some. For example, they call this the trans equatorial approach. And I guess you can do mapping to make sure that you are not disturbing language, but there is no language. This is anterior temporal lobe usually. But if you look at the post-op here, you are disconnecting the temporal pole. And this in the left side can have consequences. I think it would have the consequences. And at the same time, there is even some tumor left here, in my opinion, because you don't get the same clean view of the structure. So I don't like to do it this way. I like to do this a more selective way, which Jessica described long ago, transslyvian, opening where the fissure, and then... Let's play the video. And then this will give you direct access into the medial temporal lobe. To me, this surgery is enjoyable and less invasive because you are not crossing any normal brain, any brain that in my opinion should be preserved, especially if you are talking about left temporal lobe in a dominant, in a right-handed person, sorry. You can see the MCA branches. And this is the same exercise that you would do for an MCA aneurysm, for example, or for an insular tumor if you do it transslyvian. And as you will see, we are combining a cisternal approach with a transventricular approach. We combine the inside out views. There is always a, or often, there is a temporal branch that you have to gently mobilize to get access to the uncus. And you can also find usually a vein along the inferior insular sulcus, so-called the deep sylvian vein that you can use as references. You have to carefully dissect all these branches. And I like this because I also see this. These are lenticulostriate arteries, and those are key references for me. Both in this operation and for insular glioma, I like to see those lenticulostriate arteries at the beginning of the case before doing the tumor resection. So I know what is my upper limit. I also like to go outside and find the third nerve and find the outer aspect of the uncus. And that way, I can attack the uncus from outside and from inside. Now, we can directly go into the uncus and along the anterior aspect of the limen insula and inferior insula sulcus. You don't wanna go too posterior because then you're gonna go into the optic radiations. But you stay on the anterior aspect, you will preserve those optic radiations with a very good chance. And you see at the same time, I'm going again, outside the uncus. And I see the third nerve, I go along the third nerve. I try to preserve that arachnoid on the third nerve on the PCA. And now what I'm doing, I'm inside the ventricle and I'm disconnected the hippocampus posteriorly, and now laterally on my collateral eminence right here. And then you see I'm leaving the pia, the pia arachnoid covering the PCA, and I find my fimbria right here. This is fimbria right here. And you can see that vein, another important landmark, just the vein that drains into basal vein of Rosenthal. And I have opened that choroidal fissure and remove selectively the uncus and head of the hippocampus posteriorly. Let's go to the next, please, Luke. And then the post-op looks beautiful because you have just resected the area of the tumor. As you will see, you have a more extensive high grade glioma. Of course, you want, and with floor changes into the temporal pole, you wanna remove that obviously. But this case is selective. Just in the middle temporal lobe, and the post-op looks like a very selective resection. A case where I think this is even more important. This patient is a young 30-year-old man with years of seizures confirmed by EEG. And you see this flare signal does not enhance and it suggests it's some sort of low grade lesion right here. And if you see the upper limit of this is this. That is the anterior perforated substance. So for me, going to the temporal lobe all the way to the anterior perforated substance is very difficult. I don't think I can identify that as well as if I go directly through the cistern and I see those lenticulostriate arteries and I establish my upper limit. So let's go with this case, please. In this case, transsylvian is more difficult. Sometimes opening the fissure is really simple. It opens quickly and simple, but in a case like this, it's more difficult. We have so many large veins in the surface. That usually means there are no veins deep, but you have to carefully disconnect or detach, dissect these veins on the surface, and then go inside out. I like to do in the surface first, so I can figure out where the veins go in frontal temporal, so I can identify how to mobilize them. And then as we go deep, we find our MCA branches. And as routinely, we just follow them. But even in a case like this, I would persist. I would not just say, "Okay, I'm gonna go transcortical because this case is difficult to open the fissure." I would say, "Let's keep going, and let's open the fissure nicely." Now, important to keep your veins intact, well-hydrated. And now we are finally approaching the area of the MCA bifurcation, which you see right there. You can see the M2, M1 to M2. And I open all the way anterior, so I can disconnect temporal pole from frontal pole. And the vein is in my way, but you see, you keep persisting and dissecting this vein nicely. I want to emphasize as Dr. Cohen very often mentions, and he actually influenced me in using the mouth switch. It is so important for operations like this, because it can keep you focused and it keeps you moving, flying along this operation in a very smooth way. So you can see there, the M1 and the lenticulostriate arteries and you can see the thick gross uncus. It looks more pale. And those are the branches that I mentioned at the beginning, that you need to make sure those branches attached to the uncus are not branches from the... That are perforated branches going to the anterior perforated substance. And after you have done this nice opening, you can directly access the uncus without crossing any normal brain in this left medial temporal lobe for this young patient. And looking at my upper limit here, and I'm gonna be looking for the anterior choroidal artery which you just saw there. I'm coagulating the branch of the choroidal going to the uncal sulcus that I mentioned first. And again, we have this early temporal branch that I need to mobilize. Sometimes these branches can spasm during surgery if you manipulate them too much. So you can use drugs to treat the vessel spasm. Nicardipine is one I've used lately that is very useful, and cheaper than Papaverine. And you see those branches are of the choroidal, and then from the PCA, and then you see the basal vein, and you see that this up here is the optic tract. And then you see finally, posteriorly, I can see the choroid plexus. Then I know that I've finished my resection of the head of the hippocampus and the tumor has been completely removed. So let's go to the next one, please. You see, this is a beautiful post-op MRI. This was a DNET. Aaron.

- Yeah, that's beautiful work, Juan Carlos. I love the way you handled the tissue. Very gentle. You used that fine jeweler forceps that your Yasargil has talked about, and I use often to open up the superficial sylvian fissure. And as you do that, it lets the brain divide rather than force your way into it, especially on the very superficial opercular, where really, the brain can be very adherent to each other. I think those are really good pearls that you discussed. What I think was extremely important is lack of a fixed retraction on the opercular. I think that can really injure things or macerate it. And I think by using that dynamic retraction, let the brain guide you with your suction shaft rather than you forcing your way into it. I think all of those are just critical pearls that takes years of experience to be able to use the mouth switch, use dynamic retraction, stay on high magnification, but not too high or too low. And really handling those superficial opercular with the jeweler forceps is really special and important. Great case. Go on, Carlos.

- My credit to you, Aaron, because I was not trained using the mouse switch. And as you know, as you mention very often, 95% of neurosurgeons do not use it. And I was not trained to use it, but after I started hanging out with you, I started using it in Pittsburgh, already now, probably past seven years or eight years ago, and I cannot do a case without it. It feels like something is missing. It really helps.

- You have to have the microscope essentially part of your face. It becomes part of you. And that really improves efficiency significantly.

- Absolutely. So, a couple of more cases to finish. So this is a different beast because this tumor, as you see is much larger. It's occupying the whole temporal lobe, the whole medial temporal lobe. So we go back to this tumor. You see the whole hippocampus is tumor, but this tumor does not enhance, meaning looks like a low grade glioma. And it's again on the left side. So what do we do with this case? And you see span hippocampal. So I see this patient, it's a large tumor. One option is this again. This transcortical approach, I do not like it myself because it is in the left side. Even the right side is not ideal, but on the left side, it's even worse. This cortex here is being compressed. It's not invaded by tumor. As Jasmine described so well, these are limbic or paralimbic gliomas. They stay within the paralimbic cistern most of the time. Only on the latest stages, they are spread everywhere. But you do transcortical, you're taking a lot of temporal lobe out in this left side. And even if your mapping tells you, you can take the brain because there is no speech there, there has to be other functions that we wanna preserve on the cognitive aspect of brain function, that we cannot really test accurately with brain mapping. And even in a case, you see the uncus is still there. So I think you do a less efficient resection, and you are taking a lot of normal brain that should not be gone. So let's see this case. And in this case, I did similarly a transsylvian approach, but you see there is tumor all the way to the tail of the hippocampus. Actually, it's so beautiful how these tumors stay within the hippocampus and are spread along the hippocampal and parahippocampal gyrus. And you use that to your advantage to treat these patients. When I sell these patient, I knew that I would not be able to remove all the tumor in one single stage or one single approach. And I plan him to a stage operation. First one, transsylvian. Second one, as you will see, from a posterior approach. You see how thick the hippocampus is, but this is pretty not taking contract where you see there are vessels, and large vessels, perhaps, but not enhancement. So we do fiber tracking, just to see that all the fiber tracts that are around. But since I'm gonna do a transsylvian approach, I really don't need to do mapping in this case because I'm not gonna be taking lateral temporal lobe. I'm just gonna go transsylvian. And you see all the fiber tracts that are relevant, we review before, that surround this tumor. And tracts you will injure if you do this approach through a transcortical route. So the sylvian fissure is being opened. It's an easy fissure to open. It has one vein, no big deal. We directly go into the uncus. And from the uncus, I like to find the amygdala. You see that grease thing at the depth, that is the amygdala tissue. When I find the amygdala, I know just behind, I'm gonna find the temporal horn. Once I find the temporal horn, I need to find the head of hippocampus, the choroid plexus and choroidal fissure medially, the collateral eminence laterally. So it's such an anatomical operation, and I'm always trying to find this anatomic landmarks when I'm doing it. And again, you go from inside and outside, find the third nerve, the outer of the uncus to complete your resection. Now here, we're disconnecting along the collateral sulcus and collateral eminence, until I see the tent, then I know that I'm done. And then I continue going immediately along the choroidal fissure to disconnect the hippocampus medially. And you see the third nerve, the PCA, I'm just dissecting the arachnoid a little bit so I can de-tether the temporal lobe attachment. And you see the brainstem on the medial aspect. And then, you see, try to keep as much as I can the arachnoid intact for those perforating vessels along the ambient cistern. And now, the upper limit. It's so important to really be accurate on your upper limit. This choroidal fissure and the optic tract on the other side. As I open the fissure more, you always see this, or very often you see this inferior ventricular vein going to the basal vein. And now you see that very nicely white structure that is, of course, our brainstem and the optic tract above. The brainstem, particularly the peduncle, they're now open to the peduncle. You can see the basal vein, you can see the choroidal artery that we preserve. You don't wanna coagulate the choroidal artery at all. You just wanna coagulate the branches that come from it into the uncal sulcus. The rest of the choroid plexus, you wanna leave. And now we're looking posteriorly. It's important to have a good head position, 45 degrees or so, so you can really look backwards and I can look all the way to the atrium. And that is my limit. And then you disconnect this at the level of the atrium as we're doing right here. And you see it's a large, this is facilitated by the fact that there is a large temporal horn. So you have nice working space to go all the way back. As I mentioned the choroidal artery, remember the choroidal artery is not just an artery for the choroid plexus. It can give supply to the thalamus, even distally to the choroid plexus and choroidal point. So it's very important to keep that artery intact. And we stop, as you see, at the uncus, and this is our resection and the post-op. So let's go to the next, please. I know perhaps we're running a bit out of time. You see the fiber tracts are nicely preserved in this case. You see how close we are from the arcuate, but the arcuate stays all in the neocortical aspect of the temporal lobe, not in the mesial temporal lobe. And you see all these fiber tracts and how they preserve. Luke, let's go to the next one, please. You see the fiber tracts being nicely preserved. So here you see, this is eight weeks later. And this is a tumor resection cavity. You see the temporal neocortex is we expanded in just a few weeks, meaning that is intact, but we have this little bit of tumor left posteriorly, which you're gonna see right now. This tumor is in the ambient cistern and poking into the quadrigeminal cistern. What to do with this. We thought about radiation only, but this is a low grade, and my preference and recommendation was to remove that portion of the tumor out. For this, of course, we do a posterior approach. And in this one, we did a paramedian, supracerebellar transtentorial approach. I know Aaron is a big fan of this approach. It's a beautiful approach. You can do in lateral position or in sitting position. Go to the next please, Luke. This one in particular, I did in sitting position. I haven't done a lot of cases in sitting position myself. I've done some and for this one, it worked really well, but you could do this in lateral position, I think equally well, and perhaps with more comfort for the surgeon. Maybe a little less space, perhaps, but a bit more comfort, I would say. So this is the anatomy for that approach. Going above the cerebellum into the quadrigeminal and ambient cisterns. Luke, can I crawl through the video? Is it possible for me? So this is petrotentorial stage. Aaron has shown us also this many times, how that increases your working distance some. Of what you need to escalate your transsylvian sinus in your craniotomy. And now we are opening the arachnoid. And right after, we are looking right into the tumor beautifully. You saw the fourth inferiorly. These are superior several artery branches, and then we just carefully dissect and separate these. And it's key to open the tentorium, because otherwise you can't access the aspect of the tumor that is more anterior. And as we open the tent, we are going to be able to see the other aspect of the tumor. Now, here, you need to be very careful with the PCA. And especially with the branches that go on the inferior aspect, posterior temporal branches of the PCA, because they can be on your way. And you start to see beautifully there, the basal vein of Rosenthal in the depth. Once I have the tumor well-defined, then you can start debulking it. And as you debulk it, this dissection around it becomes easier. And you see, those are bases on the surface of the brains in the collicular plate that you want to preserve. And then there are branches on the temporal side. If there is a cortical branch, the temporal lobe that goes to what a tumor is, you can take that one, but it has to be a small one because it could be going distally in a temporal lobe. You need to perceive that one. As we take tumor, we start exposing the ambient cistern. And therefore we see a very nice view of both the basal vein of Rosenthal and the PCA. And we are gonna be looking at the PCA bifurcation. It bifurcates into calcarine and pareto-occipital artery at this level. And you're seeing that bifurcation right there. And then as we keep taking the tumor, we are gonna encounter this calcarine artery that we need to carefully preserve. As we say, we can take some of the branches, but they're going locally, but not distally. And as we take tumor, we're gonna at the end join or cavity from the first stage of the operation, the cavity that takes us into the atrium. So, we're gonna be looking at the atrium from this approach, which is possible because we did a previous resection. And you see how that large calcarine artery is sort of very closely attached to the tumor, but you can carefully dissect it and selectively coagulate. If it's giving small, cortical branches, you can take those, but not distal branches. It really is this corridor. You see there is no brain retraction by gravity. The cerebellum has retracted beautifully. And that is the view into the atrium. And that finished a resection from anterior and from posterior. And this is a complete tumor resection, which for low-grade gliomas, really makes a difference in the patient's outcome. This, as Aaron has mentioned often, this is a very easy, quick approach. Paramedian straight incision. Let's go to the next, Luke. Just exposing the cyanosis, small craniotomy. That's that's all you need. And this is the post-op after the two tumor resections with a patient that is actually cognitively doing better after the operations than before. It's impressive how these patients get better with tumor resections, when I believe especially you preserve the neocortex. Let's go to the next, Luke. Let's skip this case. This is just a GBM, large GBM. This is not a good one for transsylvian. I don't think it's a good one for supracerebellar. It's too large. So this one I did transcortical. So sometimes you have to do transcortical like in this one. I went to the inferior temporal sulcus and gyrus. I took some of the gyrus to get some space. Go to the next one, please, Luke. Next one. Oh, that's me. Just skip this video because we are running out of time. And this is the post-op with a very nice resection of this tumor. So there is a role for transcortical of course, but it's selected. And it's not about taking a lot of brain, it's just creating a corridor to work into the tumor. Identify your landmarks, choroid plexus that you can follow all the way to uncus, back to the atrium, et cetera. Let's go to the next one, please. Just to finish, next. Oh, this is me. Just a quick, nice, easy lesion. But just to make the point. Something you have lesions in isthmus of the cingulum. So if the lesion is above the calcarine sulcus, the supracerebellar route is not ideal. In that case, you wanna do a posterior, interhemispheric approach like we did in this case. This patient had this lesion. Looks like a ganglio glioma, and this young patient had seizures and dizziness. The seizure was a large, and it's a small, easy tumor. but it's beautiful from the point of view of the anatomy. Look at the Y-shape of the sulci. This is calcarine, anterior calcarine, posterior calcarine, parieto-occipital. This is the calcarine point. So it's in front and above. So this the isthmus of the cingulum. I would not dare to put a port, for example, and cross the whole superior parietal lobule to get there, when you have a very nice, easy interhemispheric fissure approach, just remember the cingulate fiber system, and let's quickly run into this video to finish. And there is, patient is in lateral position. So position is so important. Lateral position allows the occipital lobe to gently fall. And you wanna make sure that you don't trap the cortex on your craniotomy, and you preserve your veins. The beauty of the occipital interhemispheric approach is that there are usually no bridging veins in the last five, six centimeters. You have a good, large working corridor. So first, you open the cistern to relax the brain. You're opening to the quadrigeminal cistern. You wanna identify your neurovascular structures, you identify the splenium of the corpus callosum major, key landmark, and then I'm looking at my sulci and gyri. And here, image guidance does not help you. The brain has shift. Image guidance is unreliable. In fact, it can be very confusing. And in fact, image guidance confuses me. I try not to use it because it tells you that you're in a different place that you really are. You can use ultrasound in real time, that's one option, but for a case like this, is actually just looking at the sulci, the anatomy of the gyri, you can really go into the tremor and that's your best image guidance. The knowledge of the anatomy as Professor Rhoton always said. And then you can really go into the tumor and do a very nice selective resection of this tumor. And just surround it and do a nice extracapsular dissection and then take some of the white mater around and do a beautiful, beautiful resection. Luke, I think you can skip the video and go to the post-op. And you see that's a nice selective resection of this tumor with preservation of all the cortex around. And I just wanna finish sharing with you a picture of Professor Evandro Oliveira. He actually is the person that instilled in me the love for medial temporal lobe surgery. He's a true expert of this area. He's done tremendous ABMs tumors, selective cases for epilepsy. And I got from him this love for this medial temporal lobe anatomy. So Aaron, thanks for the opportunity again. I did a lot of didactics this time, a lot of anatomy. I just enjoy very much the anatomy of the medial temporal lobe. It's a bit complicated, but hopefully will stimulate some people to study this further.

- Beautiful work, Juan Carlos, as always. I think some of the important factors that one may consider in temporal lobe anatomy, I spent a year with Dennis Spencer at Yale, is that the moment you find the ventricle of the temporal horn, the anatomy fits. Everything, you get oriented. So I think the number one most important factor in temporal lobe surgery is get to the ventricle, because then you really know where's the brainstem, where the vessels, everything else. The most common reason for people to get disoriented and ended up in no man's land, such as brainstem, basal ganglia or crazy places, which I hope none of us will ever end up, is when they don't find the ventricle early on. And that disorientation can be disastrous. I think I've seen some of the best surgeons end up injuring the anterior choroidal artery because they just coagulated the choroid plexus indiscriminately, and that's another factor that one has to consider. So the most common pitfalls of temporal lobe surgery is getting disoriented, and because you didn't find the ventricle on time, because you coagulated the choroid plexus or had to use too much coagulation around that area and injured anterior choroidal artery. I think those are the big ones. The moment you're in the ventricle, everything is really great. And also you can make sure that all the arachnoid membranes over the basal cisterns are protected. And the third nerve can be quite vulnerable, especially the fourth nerve, which is right on the edge of the tentorium. So you have to be careful tugging and pulling and coagulating. All of that has to be done very carefully, because these nerves are very critically vulnerable, and tugging even on them can make the patient have three months of third nerve palsy. Lastly, the procedure described by Ugur Ture, and something that we also started using at the same time is the supracerebellar transtentorial approach to the mesial temporal lobe. No question, the most elegant, but technically the most challenging. It really requires significant understanding of the temporal lobe before one uses it. And I do not recommend the use of that technique for anyone unless they have truly mastered anterior temporal lobe surgery, because any disorientation via that route can really lead to almost fatal mistakes within the diencephalic structures. And the working distance is tall, and really requires significant familiarity with micro neurosurgery and related techniques. Besides that, I think one main question that often comes up, Juan Carlos, is if somebody has a seizure and they have a tumor that comes close to the hippocampus, but doesn't invade the hippocampus, would you do a hippocampectomy? And depending on the dominant or non-dominant temporal lobe. I have some thoughts about that. What are your thoughts about it?

- Well, I am unfortunately, not an epilepsy surgeon myself. I'm more like a brain tumor surgeon, and I enjoy doing medial temporal lobe tumors. So I think perhaps you need to do some interpretive recordings before you take, or maybe a study, not before taking someone's hippocampus without the hippocampus being involved itself, I would say.

- Right. I think that's a reasonable answer for the dominant temporal lobe, and that is correct. I'm an epilepsy surgeon, on the side of being skull base surgeon. And I think that's a very nice answer, Juan Carlos. For the non-dominant side, if the patient has medical refractory epilepsy, I do believe removal of the lesion and the temporal lobe isn't very reasonable option. And so that's what's been our strategy, that if the patient's dominant hippocampus is intact, you have to do everything to protect it because memory is residing there. Any injury to intact dominant hippocampus can be really, really disabling. However, non-dominant side is much more forgiving and that can be verified via a water test, which is quite effective in demonstrating which hippocampus is carrying most function of memory. The other pitfalls that I have learned, I've done about 400 temporal lobe surgery, and I feel comfortable operating around it just like you do, is the mistakes that the fellows and the residents make, is that they, when they're all in the ventricle and they expose the hippocampus, it's very difficult for them to go transecting the hippocampus very medially. And just like you said, you have to stay lateral to the choroidal point, the anterior choroidal point and the choroidal fissure, and be able to dissect and remove the hippocampus, superiorly transect the hippocampus, parahippocampus, I'm sorry, lift up the hippocampus, roll it back and forth. You can transect it behind the pass, and then remove the tear of hippocampus at a second stage. But the critical part is not to injure cornice almunus, a very old term that refers to those perforating branches from the PCA that irrigate the posterior hippocampus. So an elegant anatomy, much more complicated than one thinks, but really fun to learn. Do you have any other closing statements, Juan Carlos?

- I do. So first, two things I wanna mention. One is I haven't done hundreds of temporal lobe operations. I wish I could, but when I had my first one, I was ready to do it. And that is the message I wanna send to the audience. When I had my first medial temporal lobe tumor, I was ready to do it because I've spent so much time studying the medial temporal lobe, that I could close my eyes and see all the anatomy around me. I felt very comfortable in surgery. And since then, you can only get better. So for the younger people, get ready for your first case. Of course you get better with cases, but you need to not fail in your first case, but be ready for it. Second, we live in a time in neurosurgery where there is so much about, on one side, it's all about mapping. Mapping to remove parts of the brain that are supposed to be not eloquent and give you access, which is definitely finding some cases, of course, when you're working around eloquent areas, but sometimes mapping is used to remove normal brain. And I think normal brain has to be respected as much as possible. And at the same time with mapping, we have this transtubular approaches. We also have the indications to the ventricles, sometimes in surgery, but tubular surgery is crossing the white mater. So it has its indications as mapping, but it's not all about a tube or mapping. It's so much more about anatomy and especially for the medial temporal lobe surgery.

- No doubt. I think if there's one place besides skull base and endonasal surgery that requires extremely familiarity with the anatomy, is the temporal lobe, no question. And I think that is very well stated. You gotta be in the lab, you gotta learn the temporal lobe like the palm of your hand, and then you can do your first surgery and you'll be very successful. I think the anatomy of the temporal lobe is a classic example of why anatomical dissection in the laboratory is so critical in micro neurosurgery. Something that often doesn't get as much respect. Pam and Sandra is asking, for dominant hippocampal cavernomas, do you use deep... Do you also keep deep structures or especially for the left temporal lobe? That's a good question. If the cavernoma is affecting the hippocampus, you have to do a memory study with water, and analyze what is support of memory contralaterally, before you remove the cavernoma ipsilaterally. Contralaterally, which will be the dominant temporal lobe. So in dominant cavernomas, affecting again, the dominant hippocampus, obviously, one really has to maximize medical therapy before you invade the dominant hippocampus. I just cannot emphasize how critical and important the dominant hippocampus is for human memory as an epilepsy surgeon. And anytime you touch that, unless, number one, you have confirmed adequate memory support contralaterally in the hippocampus, on the right hippocampus, or you have definitely demonstrated that that patient seizures are so significant that the risk of memory overwhelms the risk of injury from intractable epilepsy. So with that in mind, Juan Carlos, an honor to have you with us. We had over 330 people, quite an accomplishment for your work.

- Wonderful. And great comments I'm seeing. A lot of people liked it. I'm very glad about that because I love temporal lobe and I like to share that love with all these people, absolutely.

- Obviously your love shows very clearly. And so anatomy is fun, and over 320 people is obviously a big audience. And we look forward to having you in the near future, and again, for an anatomical dissection, skull base and different approaches. We sure welcome you, and thank you.

- You know, anytime, Aaron. This is like being home. Thank you so much. Have a great night.

- Thank you, Juan Carlos.

- And thanks to everybody watching.

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