Grand Rounds-Anteromedial Temporal Lobectomy and Selective Amygdalohippocampectomy: Technique

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- Hello, ladies and gentlemen, and again, thank you for joining us. This is part two of our discussion regarding evaluation and treatment of medial temporal lobe . The first session reviewed overall evaluation regarding temporal lobe epilepsy. This current session will review technical neogenesis** for anteromedial temporal lobectomy and selected amygdalohippocampectomy. Dr. Dennis Spencer, Harvey Cushing Professor and Chairman of Neurosurgery at Yale University who was a mentor of mine is a expert discussant. Dr. Spencer, thank you again, and please go ahead.

- Thank you, Aaron. Thanks for the opportunity to go over this in a technical way. So let's start by discussing the resection. As one knows, this evolution of more medial resections begun in the late '70s through the '80s. And in general, the resection is, as I perform in anyway, revolves around a three to three and a half centimeter neocortical resection of the pole, involving just the middle and inferior temporal gyrus as access to the temporal horn. And as access to the resection of the important structures that provide the triad of epileptogenesis in the medial temporal lobe, that is the intertidal cortex, the amygdala and the hippocampus. And when one uses this with the standard concordant evaluation of medial temporal sclerosis, this involves the same kind of technique. as if one taylors this based upon an intracranial study in a patient who has non-concordant evaluation and requires intracranial electrodes. There are, staring at this marker down here, the resection of the amygdala internal cortex in the hippocampus as all stated here, can be transcortical as we have described. It does allow preservation of the temporal neocortex in our hands. We will do the three to three and a half a centimeter pole resection, both on the left and the right side. We see no reason to alter this based upon which temporal lobe and it allows us of course, then to be able to compare outcomes reliably, if you're doing the same operation. About the same time that I was designing the resection of the pole and preserving neocortex, Yasargil was doing this transsylvian based upon the patients that, these are identifying with base of, medial temporal lobe epilepsy. Just, very briefly. This involves as illustrated here, the pole resection of the middle and inferior temporal gyrus with sparing of the spirit temporal gyrus in all documented language outcome studies. This is an area that is, that is predominantly free of language on the dominant side, whereas in the superior temporal gyrus language, can't be distributed throughout that region. One of these areas can be distributed throughout the spirit temporal gyrus, and then this illustrates the basal view with the total resection involving as much of the tail to the turn of the tail of the hippocampus, the topper behind the provenance of the thalamus, after you have resected the temporal pole. This is just a cadaver illustration of the, of the pole resection, try to change my, under the mouse and this is, so here's a sparing of the spirit temporal gyrus, the landmarks as illustrated in this cadaver or the section to the temporal horn. one sees the temporal horn here will be dissected down at three centimeters posterior to the pole, down to the fusiform gyrus arachnoid, followed that back as it then leads us to the temporal horn. One opens the temporal horn and the key issue of the appropriate resection of the amygdala. We will talk about it in a little bit, but it comes from all of your dissection being sub peel and identifying the Sylvian fissure sub PLA from that resection of the temporal pole until one binds the knee of the two middle cerebral artery. That is the key landmark demonstrating that you are just at the anterior perforated substance and the diagonal band, and that your basal ganglia lies superior to you. And if you then draw a line along this, to the which we're going to see to the choroid plexus choroid, a point, then you can resect all of the, of the without injuring any of the, of the basal ganglia. And this just points out that point of the line from the middle cerebral artery. This instance we see the hippocampus long here and the choroid plexus and the imaginary line illustrating the dissection as we in the cadaver, have retracted in the hippocampus again, as you can see, as it's turned this is the thalamus. And when we sex the poster tailor the hippocampus, as it turns inferior to the inferior thalamus and one carefully dissects the fornix, which lies along the lateral geniculate on the thalamus. This is in doing this cadaver study. We also did MRI's of the cadaver game, different of the dissection, but this is just a very good illustration of the relationship with the amygdala here onto the hippocampus, how it lies just anterior to the vertical hippocampus and that by identifying the chord portal point chord plexus here to the middle cerebral one gets a nice, complete diSsection of the amygdala. And then the finality is the term of the hippocampus tail behind the, behind the thalamus. And we're just retracting the passive, the hippocampus and identifying the cool idle choroid plexus and it's origin of where the from analysis and the vendor the fornix. Yeah, I just, I think probably, one of the key illustrations here, and then Aaron's going to go ahead and talk about this, but we discovered that one must extend the head in positioning 50 degrees, and you get obviously, after a period of time, you don't need to measure that angle, but, and you'll, you'll be able to visualize it, but that head extension is critical because it throws the hippocampus into a perfectly aligned view along your microscopic exposure. If you leave the head in the military position, then you're going to be moving the microscope too far anterior and tipping back, and you cannot see the tip of hippocampus tail. So this is an important illustration.

- I really appreciate that point here. Obviously his illustrations depict the entry temporal resection. As you very eloquently described them in the previous slides. The patient is supine , the hippies. Again, extended that extension. We'll talk about again, the incision is a curvilinear incision. We do want to expose a good portion of the temporal lobe. So the incision starts just at the level of design zygoma, zygoma or slightly below. As you can see here comes up, goes above the ear, trying to create a sizable base for the flap to avoid necrosis. And the next slide. Again it picks that extension of the head, So the head is extended backwards towards the ipsilateral shoulder in order to make the hippocampus very much parallel to the horizontal axis. And you can see the craniotomy. Go ahead. Did you want to add something please?

- Yes. I think an important, important point here too is how far posterior do you use starching most of your loop of the skin incision and I use the mastoid vertex line. So I'll measure the mastoid cortex line. And I know that, if my posterior skin incission comes up to that, and then of course, it's the anterior hairline that defines your anterior curve, but this gives you just the amount of tempora of exposure and wanting to do the appropriate retractions, where the medial exposure.

- Thank you. I think it's just the best standard craniotomy. Again this is the root of the zygoma. We want to make sure that we get as close to the middle , as we can seal William fissure. You do not need much exposure of the frontal lobe. Obviously this is a temporal of surgery, but you want to have a very wide exposure posteriorly. Again, this is some people may say, we can do this to a smaller craniotomy, but as you will see momentarily, this exposure is important for lateral mobilization of the temporal neocortex in order to visualize the posterior tail of the hippocampus. And therefore you want to be able to expose the temporal neocortex, to a be able to mobilize the temporal lobe as you do the white matter, dissection along the occipital temporal fasciculus. Would you like to add something here, please?

- The reason for the exposure to the parking of the base of the frontal lobe is we will have a retractor. Here there's gently retracting the superior temporal gyrus, and without a little bit of a frontal lobe involved, you run up against the bone and you cannot, you cannot appropriately retract as Aaron pointed out again. You're curving a retractor, that's going to gently elevate the lateral temporal neocortex. And so you to elevate that you need to have this posterior temporal regional exposed.

- Thank you. You mentioned that for dominant or non-dominant temporal lobe, you only removed about three and a half centimeters, or a protocol has been four centimeter on the non-dominant temporal lobe three and a half on the left temporal lobe. But again, not much is needed to remove. And by the technique of mobilizing the temporal lobe down, give you enough space to work. We use a number three Penfill obviously sliding on until you hit the bone over the temporal tip and measure the amount of the new cortex you need to remove preservation of the is important in this step. The first courticonomy is conducted along the superior temporal sulcus. We make the corticonomy more along the inferior part of the superior temporal gyrus. But again one has to be aware that there is functional cortex, especially in women on the superior temporal gyrus.

- Yeah, so obviously this measurement from the temporal pole can be somewhat arbitrary. And therefore, I think that you, I will always try to measure three centimeters, but it's, you know, it's going to vary between three to three and a half and sometimes over three and a half, depending upon the patient's anatomy. And they will always use the temporal sulcus. Do not violate the superior temporal gyrus at all. And again, try to make the uniform on both sides so that you can compare your outcomes.

- And the courticonomy along the sulcus, or in third part of the gyrus posterior aspect, it's very standard and then cutting across. Those are very basic techniques. This is something that has worked for us. And I've also learned it from you is that after you do the superior courticonomy posterior courticonomy. It's hard to know where you do your whites matter dissection, to remove lateral temporal neocortex. There is always this very constant across the middle And I guide my dissection toward this as the tip of the pyramid. So if this is the plane along the superior temporal sulcus, this is the plan along the posterior aspect of temporal resection. These two planes all meet together at this per two grits. Obviously you have to gently lift up the temporal lobe to be able to see this, but this will prevent the novice operator to get into the hippocampus early on, destroy the hippocampus and do this selective resection, because it's hard to know how far you're going and how deep you're going to go. And what the angle you're going to use, just to stay outside of the ventricle without getting into it. Neuro navigation may help. And I think this is a sort of a, a coronal view of showing how you can start your dissection from the superior temporal sulcus pointed there and just missed the ventricle and not necessarily get into the ventricle pyramid as should.

- As a corollary to what Aaron says, if you also use the form angyrus is a landmark along with the middle boss of . It will also keep you out of the, out of the ventricle and from getting too deep and, or the new epilepsy surgeon that is, it is critical because you can not only damage the hippocampus by moving to medial here, but you obviously need to stay out of the temporal stem, which has no landmarks and can lead you astray right into the actually the capsules.

- Thank you. You can use the, I think that fusiform gyrus just like you mentioned, and the sulcus. I have used a middle temporal gyrus, the central of the neural temporal gyrus as a, to go parallel and open the temporal horns invariably. The lateral wall of the temporal horn of the ventricle is just in line with the middle part of the temporal neural temporal gyrus. You may use neuro navigation, but obviously you want to open the ventricle just lateral to the hippocampus without injury.

- Yes. And it says, if you look at an MRI scans at the middle of the middle temporal gyrus is a line a straight line, but you're going through usually, you're going through the middle temporal gyrus. If you come to the, to the arachnoid and follow it, follow it up, you come into also into the temporal horn without injuring the hippocampus. The key here is to not go too medial into the temporal stem and not to go to inferior and medial into the hippocampus.

- Thank you. We have ghosted in the ventricle here just for our viewers to know that the ventricle is usually more posterior than we think and make the lives a very sizable structure. And one error often happens is that the operator opens the ventricle very anteriorly and often they miss it. So it's important to recognize that when you remove such a small portion of the lateral temporal lobe, the ventricle is almost located mostly behind you. And we're going to discuss how you can expand your exposure in this slide, you get a new from you that I have learned is that you open a very small part of the ventricle here. You only barely see the Pes hippocampus, but you are going to do a white matter dissection along the occipital temporal of the Sulcus. So in other words, you dissect the white matter along the curve of the hippocampus and mobilize the temporal lobe the laterally here, and this would allow you to see around the hippocampus.

- Yes. One point is that when you get down to the ependymoma are you getting down close to the ventricle or remember that there's all that there's the ependymoma vessels and you get this sort of diffuse munis reading. Like when you come to the ependymoma, that's another way of identifying the horn. And usually I'll take a Penfield four and insert along the anterior ventricle and directed towards the lesser and then use ultrasonic aspiration to open along that line just keeps you again, out of the as you're moving in, it makes it more efficient.

- I think identifying temporal horn, Dennis surgeon is relieved because you know everything now, you know how to protect the brainstem, the temporal stem, the thalamus, MCA. So exposing the temporal horn is a big step in the first part of the operation. Then you kind of situate your retractors. Again, we talked about mobilizing with this retract, a lateral temporal new cortex elevating sort of the roof of the temporal horn. And then identifying the core of the plexus, which you define as the coital point or the coital point. And this would expose nicely the hippocampus. And now we'll go ahead and focus our attention on the amygdalectomy. Go ahead please.

- Just note that this, so you've got one retractor that's under the superior temporal gyrus, and it's inserted to the to the depth of just above the amygdala. This retractor is curved. And that is important because you're not really retracting as much as you're putting this curb retractor into the integral horn into that occipital temporal dissection that you've done, and you're elevating the temporal neocortex.

- This is the pyramid you were talking about, or the plane, the knee of the M two in the Sylvian fissure is just very gently exposed interacting with what's left intact. And line from M two or actually you say the bifurcation of where the curve of M one is connected to the inferior coital point. He finds the border between amygdala and Paladin. This has to be carefully protected. Otherwise it will cause injury to the basal ganglia.

- Always, always, always stay, find that line early on, design it and then stay below us. And if you stay below that line, you're not going to injure any of the structures and you can safely remove, you know, all of the amygdala.

- Obviously amygdala can be used in a selective manner. This is a much more difficult than just removing it with suction. You can remove the superior part, just below the line we talked about, and also the portion over the anchors to expose the third nerve. Here is again removal of the portion of the amygdala and disproportionate as you moved until we find the third nerve. Often you may be able to cheat, go around, find a third nerve localize where it is through the arachnoid and then we move the anchors just to be very careful in removing the inferior part of the amygdala without violating the electrical.

- So I find in teaching this that the easiest landmarks to make you most comfortable about where you are, is to pretend is that you're going to be doing a circle of Wallace dissection and you go down and you're dissecting sub PLA the anchors of the para hippocampus. So you find, you know, actually you're going to find your carotid and find the third nerve, right? So those are landmarks that are critical to exposure of the circle. And then one comes up along the Sulvian fissure, but within the temporal lobe, in the using your ultrasonic aspiration, and you're clearing that you're clearing that arachnoid to the Sylvian fissure until you come to the knee of the middle cerebral. And that's the most safe way to find the near of the middle . And to begin to define the line that's going to as Aaron says, to find this pyramid with the amygdala below it.

- Thank you. Now that the amygdala has been removed, just like you very well mentioned, going around a arachnoid and third nerve through the arachnoid you may use a small piece of brain just to protect the arachnoid. You have to visualize the third note to make sure I make the right is complete. Then obviously we remove the hippocampus. We can use any one stage or two stage for selected resection and preservation for research. You have to first disconnect immediately, and then obviously stay lateral to the choroid plexus, and then undermine it along the arachnoid, and then cut it in across in two sections, one for Pes hippocampus, which we'll see momentarily. This is again undermining the hippocampus and part of hippo campo gyrus. And then ultimately using that line, we talked about to remove the hippocampus in two sections and really dividing it into two halves me personally to remove it in a very clean matter without injuring the specimen. Go ahead, please.

- You could go back to the slide that shows the Pes hippocampus being elevated and maybe it's going forward. And can you go forward? Yeah, this is really... No, yeah. This is really an important slide, because it illustrates it just under this scissors should be the fimbriae fornix. Now it's where these points, the middle cerebral and the inferior colloidal point, which is where the cord plexus originates is also at the same point where the fender the fornix and meet. And so that defined, and that defines the junction of the Pes hippocampus and the body of the hippocampus. So you can begin your cut along the body has junction here. And when you do that, you will come to the , which is where the perforators from the posterior cerebral are coming into the Pes. and going back to the hippocampal fissure to, to supply blood to the hippocampus. So what he's illustrating hear, is coagulation and division of those perforators, the posterior cerebral into the hippocampus and below us here is the incurrent limbic gyrus. gyrus is a portion of the posterior pear hippocampus, and that is your landmark starts just at the Umbria origin. And it lies directly over the of the midbrain. So underneath, as you dissect this intra limbic gyrus from posterior to anterior or anterior to posterior, you will be dissecting it off of the midbrain. Is a nice arachnoid plane there. And one can do this either with with ultrasonic aspiration or frequently in temporal sclerosis, just using a pancake. It will come off because the sclerotic hippocampus makes a nice disectable specimen.

- Thank you. And again, the hippocampus mainly removed in the same direction on involvement techniques, and here's the final product. I usually leave out small piece of brain over the basal sisters. I know PCA runs underneath just to protect these structures. Remember, the fourth nerve is along the edge of the tentorium. Please don't manipulate the edge of the tentorium too much. And the third nerve and you can see PCA peaking underneath.

- So important point here, Aaron that you bring up and that is as even more so than this all straights. I leave a large amount of arachnoid over the tentorium. You just never even want to see the tentorium. There's a frequency, I think is a temporary fourth nerve palsy. That is quite it's quite surgery variable. And it all depends upon whether you play around with this, the edge of the 10, 12. There's no need to do that. Just leave PO right along the floor of the middle faucet, don't even dissect the tentorial edge. You don't even really need to see that the nerve, you just need to follow the arachnoid and maintain your dissection sub PLA at all time.

- Thank you. And this is another illustration to emphasize that pyramid that defines the Neal, and the one or M one two and two to the inferior quarter point to delineate the amygdala. Again, this is another operative view of same thing. The MCA exposed connected in third point to define and is a image. Again me or from the bifurcation, going to the third point to define, they make a lot more accurately. Obviously a seeing is believing, let's go ahead and review a surgical video of mine. I've tried to do it as much as I've learned from you. When I was a fellow with some variations, this is a case of a 26 year old male with intractable seizures. You can see the the right medial temporal lobe is hyperintense on the images with a potential cortical dysplastic abnormality laterally. Misses in non-dominant simple lobe with a very much adherent and adjacent dysplastic lesion. So we plan to remove both the hippocampus and a lesion. This patient had concordance studies preoperatively in all phases of this study. We did not perform intracranial study for obvious reasons. Again, this is the extension of the head. It's very impressive. How much extension you need. You put the single pin behind the ear to give you plenty of space to do this surgery. And again, this can better illustrate the amount of extension you need to keep the hippocampus in a horizontal plane. Go ahead please.

- So this just.

- I think we can go ahead. I just want to make sure you don't have anything further to add. Here's the craniotomy. I think we reviewed these already, you know, illustration. Let's go ahead and go to the video and I appreciate your comments here. After the craniotomy...

- Obviously is that. Go ahead Allan.

- This is a poster part of corticonomy. This is superior temporal gyrus. Again, we did our dissection along the, along the sulcus of the superior temporal gyrus. This is removing the temporal neocortex pointing to that protuberance that we just talked about and then doing the coagulation underneath the temporal lobe. Middle temporal gyrus doing the whites matter dissection to be able to expose the roof of the ventricle. Let me know if you would like to add comments and I can stop the video. This is the temporal horn exposed. This is doing the white matter dissection of the occipital temporal . As you can see...

- I'm stuck with this Yeah, so I was just going to illustrate that you can use the appendima of the temporal horn and draw a straight line down to the middle basal floor. And that dissection of the separate account, for really is not necessarily within the fusiform occipital chemical , but it's medial in the for , having the collateral salters. You want to stay out of the posterior fusiform gyrus. It may be that some of the language problems that we see after a dominant temporal dissection is not necessarily retraction is not necessarily a dissection of a language points in the anterior pole but it may be bazell language issues. And so I always stress the importance of bone, the collateral sulcus around in that, dissection of this part of the occipital temporal suculus.

- Thank you. Here you can see every tractor has been placed the hippocampus has been exposed. You can see momentarily that the, anterior corridor fissure is being identified in the video. As you can see there. We may put a continuity there just to be able to identify that point clearly, after which we go ahead and find the covered by the arachnoid membrane underneath the cortex of the middle of temporal gyrus. That defines one point in the pyramid. And you can again draw the line between the points or the coital point and in to be able to remove the amygdala in a selective manner. After the amygdala is removed, you can peek underneath the arachnoid and be able to find a third nerve and assure that the complete. And he go further steps just to orient our viewers to the third nerve after which we'll go ahead and disconnect the choroid plexus from the hippocampus, and then undermine the hippocampus and para hippocampus from the arachnoid over the basal systems.

- So this is an incision between the Pes and the body of the hippocampus, is we looked at in the more static goings, and you're coming down to the ankle. Sulculus the sulculus curves inferior and anterior, and has the posterior booklet vessels coming along the incrilimbic gyrus, which is just below and over the brainstem. One important point, I think that is always, should be made as to always retract the flexes as you are coming, as you're inserting your retractor, that deeper you retract the choroid plexus toward the thalamus and another way.

- then you can see that you hippocampus moodiness selective manner. And here is really the tail of the posterior body and tail that you can poke hippocampus and identifying momentarily just sneaking in to see the medial edge of the tentorium. And you can see the PCA through the arachnoid membranes and it's perforators that have to be carefully protected. You can see that the reflection of their arachnoid and coroner and munis those perforators off of the PCA that inter the posterior hippocampus that have to be quite lated and carefully protected.

- I use the ultrasonic aspirator a lot in these cases. I think that it is a wonderful instrument. It protects, you know, the rachnoids is not violated by the instrument and it helps you to do a complete dissection. The other point to make is the, besides the choroid plexus, retracting it towards the thalamus and protecting the lateral geniculate, which is what the Cambria the cortex is attached to. One should never ever coagulate the choroid plexus because the intercoatal artery, which is often seen may have variations. It's a division and by coagulating the choroid plexus, even though it's tempting, because it may frustrate you, if you happen to suck on it against the bleed. If you coagulate it, you can get the anterior coronal artery and cause or hemiplegia. Thank you.

- Thank you. This is a post-op MRI. And as you can see, you really can get very far posterior along the edge of the plates using technique. The technique we discussed and doing a generous . This patient has been seizure free three years since his surgery. And really it's a very, very satisfying operation. And it's one of the most enjoyable parts of neurosurgery because we make such a big difference in the lives of our patients. Ultimately how you do this selected through the Fisher. Transcortical selective. There's really no study that has demonstrated a difference in seizure outcome. There is no randomized studies to demonstrate superiority of one technique over the other, and ultimately it's a surgeon's preference. What you feel like you're most capable to provide the safest procedure for that patient. Factors associated with improved outcomes. I think we talked about concordance or preoperative studies. Ipsilateral hippocampal selerosis interictal activity can coordinate with such an imaging finding and absence of preoperative generalized seizures, obviously very important. And the outcomes can be very variable, there is definitely some decline in the seizure freedom after the first year. There's one randomized trial showing that extent hippocanectomy is associated with improved outcome. And therefore we do advise removal of the hippocampus tail, as it turns to inter and the atrium of the ventricle. The only other point I would like to mention before we close this session is that patients who are seizure free at some shear have the highest chance of seizure freedom long-term. So the first year of seizure freedom can be a great predictor of long-term seizure freedom. The other issues that can be very important, preoperative neurophsychological texts, testing is a predictor of location and dominance, and can help define the neocortical/ medial epileptogenic substrate for dominant medial temporal lobe dissections. One has to be extremely careful with verbal memory risks, and there has to be very good reason to remove the dominant medial temporal lobe. If the patient is not already suffering from the two standard deviations below. I have reached verbal memory functionality. And with that, I would like to finish the talk today, Dr. Spencer, and thank you again, please go ahead.

- It's just a graph that illustrates the point that Aaron was making it. If you reset the normal functional dominance at the gyrus, that you will suffer a significant loss of learning global learning global short term memory, as opposed to the non-dominant temporal lobe. And I think with that, we've made, we made all the important points in the temporal lobe .

- Thank you, Dr. Spencer for your great expert opinions.

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