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Grand Rounds-Hemispherotomy Techniques: Pearls and Pitfalls

James T. Rutka

April 03, 2012


- Hello, ladies and gentlemen, and thank you for joining us. The following session is a discussion regarding pearls and pitfalls involved in performance of hemispherotomy procedures. Dr. Jim Rutka from University of Toronto, will be our guest speaker. Thank you.

- Good afternoon, Aaron and thank you for allowing me to participate in this edition of the AANS Operative Grand Rounds, and it's a great pleasure for me to work with you on this particular one on hemispherotomy, I've enjoyed working with you on numerous of these various videos in the past, getting these up and running for the AANS and we're truly appreciative to you for everything you have done. Thank you.

- Thank you, Jim. I just wanna say on a personal note, you are one of my most respected, if not the most respected mentor in my career, and I wanna say these sessions were never, would have never been possible without your support. So all of us are appreciative of what you have done for neurosurgery in general, and for the AANS and our educations, especially. So we'll start the session as always with the disclosures, that are none for both of us, hemispherotomy and seizure disorders that are involved for these patients are very difficult. The parents, the families, the children who are often very young, go through very difficult times and I think both you and me have been very privileged to be able to take care of these children, and make such an important difference in their lives. While we are on this image, I would like to ask you one of the most important questions that I come up with and that's, at what age would you say a hemispherotomy or hemispherectomy is possible for a child, after which it will be too late due to functional organization of the cortex?

- Well, Aaron, I think the proper answer to that question is that the sooner you make a diagnosis that there's a catastrophic form of epilepsy involving one hemisphere, the better it is to do the surgery and we do know that after age two, the chances of functional recovery, plasticity of the brain, after age two that becomes increasingly more difficult. I've certainly performed hemispherectomies in older children, and the oldest on whom I have operated is 13 years old, but the vast majority of children are age two or under, and the youngest child, was one day of age.

- One, very young. It's by far one of the most complex procedures we do in pediatric neurosurgery. Let's start the session with reviewing a case of a 16-year-old boy, actually this boy was from Bosnia, and had generalized seizures up to about 40 per day that were observed, probably many more than were not detected, associated with progressive left-sided hemiparesis. The MRI that was performed as you can see, reveals a very dysplastic right hemisphere associated with almost cortical dysplasia, mostly affecting the occipital parietal region. Well, this is most prominent, most specific probably of hemimegalencephaly because one of the hemisphere is larger than the other one. What else do you look for on imaging for these kids with catastrophic epilepsy affecting one entire hemisphere?

- Yes, for megalencephaly, just as you said, Aaron, it's the size of the hemisphere, you can see the right occipital pole in your case that you're showing us here, has basically got all the features of the hemisphere itself, being larger and it wrapping around almost, it looks like the straight sinus and the , and that's quite typical of hemimegalencephaly. You mentioned the size of the ventricle, it's sometimes a little larger on the side that's affected, but typically speaking, you would see the whole hemisphere involved while it looks here, for example, that it's primarily parietal occipital and partially temporal lobes, in fact, you can make a very good case that the frontal lobe is also affected in this case.

- Thank you. This is not a picture of the same child but a similar age, whose video we're gonna sort of review at the end of this presentation, we're using the same picture sort of to pinpoint the positioning of the patient. Do you use pins and would you take us through how you would do the positioning differently in this case, please?

- Yeah, thank you, Aaron. You want the head position to be exactly flat, in other words, head turned to the side, of course, that you're operating on, at exactly horizontal and you've got a great position here, I don't know how old this particular patient is that you're having pins, but we would probably use pins in children two years of age and older. I use pin fixation, especially if I'm going to bring in image guidance, because that allows us to link the patient's head of course, to the brain lab or scalp device that we have at surgery, it's not always necessary, we can talk about that in the discussion period, but your position is exactly what I would be doing here, a little, you see you have a bolster under the patient's shoulder is exactly what we would do, and you have your head basically flat because this is the area in which you'll be operating, and that's where you want to have access exactly horizontal.

- The procedure we'll review momentarily would be the peri-insular C-shaped hemispherotomy. This is the incision we have been using, may I ask how differently you use your incision, Jim?

- Aaron, I think you can appreciate that the insular area is right here, where I'm drawing it on the image of his child's scalp, and you can see... incision a little bit tighter around the area of the insula but it's not really the size of the scalp incision or bone clamp that matters as long as you have the exposure. But I would say, this is the area of exposure that you really need, and so you can basically make a smaller scalp incision and of course, we'll be talking later about Schramm's almost keyhole approach, minimal invasive surgery for hemispherotomy and he uses a very small incision.

- Before we go to the video, are there any consideration preoperatively or intraoperatively? You mentioned stealth, choosing the pins for two years and older, anything else that's important for us to know?

- Yeah, sometimes you have a brain shift at the time of surgery, and you're trying to find those pericallosals, we'll talk about this subsequently, but sometimes the ultrasound with Doppler mode turned on, will help you find at least as close as possible to the region of the pericallosals, especially if they're up in the interhemispheric fissure, which they are sometimes, away from the traditional right on top of the corpus callosum location. So ultrasound with Doppler mode turned on, can be a useful adjunct as well.

- Thank you. Let's go ahead to the surgical video, this video has been speeded up because we would like to just review some of the basic concepts related to the case, and we're gonna have a more regular speed format of this video of a different patient at the end of our discussion. So this is after a craniotomy has been completed and a right temporal lobectomy is being conducted, again, Schramm talks about only removing the superior temporal gyrus to get into the ventricle, we perform a complete temporal lobectomy with resection of medial temporal lobe structures. If you don't mind using the video of mine and telling us how you would do this better in a different way, thank you.

- So, Aaron, I think this approach you're using is fairly traditional in terms of standard temporal lobectomy, I see that at the beginning you were following the Sylvian fissure basically, and you were doing a subpial resection, which is very important, the whole key to temporal lobectomy of course, is finding yourself in the ventricle, which is where you are, and you'll recall from some of the earlier works that for functional hemispherotomy, you actually don't need to do a complete temporal resection, as long as you disconnect the temporal lobe outflow at the fimbria-fornix, that's sometimes sufficient but in my opinion, after you do this procedure, there's often significant cerebral swelling, so in fact, a temporal lobectomy gives you a lot of room, that tissue, especially in cases of hemimegalencephaly, Sturge-Weber, and other profoundly affected cases, is not important to that child, and so to remove the temporal lobe, actually safeguards against the postoperative complications and allows you to get the procedure well underway and know that you started the procedure well by taking care of the infra-insular window, so removing the temporal lobe, I think is a very good strategy, which I would support doing. basically, you're trying after you do the temporal lobectomy, you basically wanna make sure that you're following the choroidal fissure, and at that time you're making sure that you're not causing any risk of course, to the diencephalon.

- Thank you, Jim. And as you can see, we followed the contour of the ventricle doing a sort of resection of the cortex over the ventricle, and if you don't mind taking us through it now, and then you follow the pericallosal arteries or edge of the falx, as you can see in this case, and then come more along the ventricle of the temporal bone of the lateral ventricle and follow the edge of the tentorium, until you've reached the falcotentorial junction, by disconnecting the white matter of the corpus callosum at the level of the splenium, and precuneus, and the atrium, and the tail of the hippocampus. Go ahead, please.

- Thank you, and I can see in this particular segment of the video, you just need to connect basically, the dots. You are going along the falx, which you can see quite nicely there, heading towards the tentorium, you have your choice at the beginning to find the pericallosal vessels, I have a standard way of doing this anatomically, which has helped me in good stead, I usually look at the foramen of Monro, where the fornix comes in around towards the mammillary bodies, about a centimeter above that, and behind the foramen of Monro is a great place to try to find a pericallosal vessels, on top of the corpus callosum. And then as you proceed forward, that's a pretty straight shot along the pericallosals, but as you go posteriorly along the length of pericallosals, you frequently lose sight of them, you gain access to the falx, you follow that to the tentorium, and out towards the, as you mentioned, the body of the hippocampus in a very important structure, that is the occipital lobe connection through the calcar avis. And here you're seeing the falx nice view, you're following subpial, very important, especially as you go posteriorly, that you remember the vessels on pass on from posterior cerebral artery, so the occipital and posterior temporal arteries that bridge over top of the falx, and I would strongly recommend anyone who's doing these procedures to keep those intact, because if you take those, you'll often see a postoperative infarct that sometimes can swell and in two of my cases over many years, I've had to go back just for mass effect because of an infarct that was created. And not that that's a huge problem for a child because... but it did require another operation.

- Thank you, Jim. And as you can see it in the video, we did a frontal disconnection that we'll review in more detail later in this presentation and following the sphenoid wing and obviously, preserving the bridging arteries that I could have done a better job here honestly, would be important to prevent the complications you've very eloquently mentioned. So let's review some of the basic concepts before jumping into the details of this procedure, again, the hemispherotomy, which is the focus of our discussion. History of hemispherotomy started with hemispherectomy as many neurosurgeons these days, pediatric neurosurgeons still perform the hemispherectomy or the anatomic procedure, Dandy in 1920's, really used hemispherectomy for glioma surgery because of the chance of occurrence, then Oppenheimer in 1960's discussed the complications of hemispherectomy, including superficial siderosis and need for shunting. And in response to those complications, Rasmussen's, he find the functional hemispherectomy, which was preserving more of the cortex and by preserving more of the cortex and doing a deafferentation procedure, you leave more brain behind and therefore decrease the risk of superficial siderosis and the need for postoperative shunting. So as you mentioned, Jim, the indications are hemimegalencephaly, Sturge-Weber, hemispheric maturation disorders, which really is all the disease processes mentioned on this slide, and the gyration, unihemispheric neoplastic disorders and Rasmussen's encephalitis. All these disorders really affect most of the hemisphere, the kids are already affected by hemiparesis, and therefore deafferenting the hemisphere is not gonna leave them with a much more deficit. Any other important indications for hemispherotomy?

- No, I think these are the major ones, Aaron, I'll just make a comment on your previous slide that McKenzie, he, that was actually K.G. McKenzie from the University of Toronto, I mention that of course because of my location, and that was the first time hemispherectomy was performed in the context of seizures and that patient did incredibly well, and the entire specimen was kept by McKenzie for many years, and that woman on whom he had operated in 1938, was basically his trophy case and everyone referred back to that particular case that McKenzie had operated on for many, many years and obviously with a very important advance in the way to think about treating seizure conditions in patients who had requirement for hemispherectomy.

- Thank you. So let's talk about what are the overall outcomes for these patients, 70 to 88%, and the outcomes are somewhat better for anatomic hemispherectomy versus hemispherotomy because obviously if you remove the brain, there's no chance that part of the brain would seize. Therefore otomy procedures are more challenging and you have to be very careful you do a very good thorough job of disconnecting, otherwise the patient may have postoperative seizures, which would be very devastating for these young kids. So functional Rasmussen's hemispherectomy or otomy we're gonna review first using the slides, and we're gonna briefly discuss hemidecortication, which has been used in John Hopkins by Ben Carson, however, the blood loss, especially in hypervascular cases can be really difficult for these young kids with very small blood volume. Vertical parasagittal is one of the new ones and we'll briefly touch on that, however, I would say both you and I feel strongly about more of a Keyhole or Trans-sylvian approach because you leave a lot of brand behind, blood loss is less, the kids do well, and the procedure is really more elegant and microsurgical. Any comments there, Jim?

- Yes, I think so, Aaron. The hemidecortication procedure is a technique that we used years ago when Harold Hoffman was my mentor here at The Hospital for Sick Children, we did that routinely, but the blood loss issue is what you had mentioned and that was true, and furthermore, it wasn't a very elegant procedure and oftentimes it's failed because you still left ribbons of cortex that had opportunities to cross the corpus callosum. We actually did a comparison that Neurosurgery published about a year ago, where we looked at hemidecortication versus functional hemispherectomy, the peri-insular hemispherotomy version and our results were better actually with the peri-insular hemispherotomy in terms of seizure control than with hemidecortication, so we've moved almost exclusively in that . I am interested in Delalande's procedure, which is the vertical parasagittal, it does require a little practice and also a complete understanding of the anatomy as you march forward from posterior to anteriorly, with the cut along the ventricle lateral to the basal ganglia, because I think in it's anterior segment, that's where you have to be very careful that you don't run into trouble with that last bit of disconnection. And then finally, the ultrasound guided is something we talked about earlier, and that helps you find the pericallosals and where the falx and midline structures can be.

- Thank you. So this is really a spectrum, we started anatomic early on in neurosurgery, we moved to functional, and then now we're doing hemispherotomy. So from the most resective to least resective, from really removal of the bulk of the brain, to really doing deafferentation procedure and I think it does make a big difference. I think the more of the otomy procedures rather than ectomy, is associated with less risk of shunting, potential less risk of superficial siderosis although no study can confirm that, however, if the deafferentation procedure is not adequate, there is an increased risk of postoperative seizures and those have to be clearly considered. Any thoughts regarding this spectrum?

- Yeah, I think that that's absolutely right, Aaron. Anatomic, the largest of all the procedures can be done, but shunting is definitely a higher incident, and we showed that even in our study with hemidecortication versus hemispherotomy, so I think that's a consideration. The superficial cerebral hemosiderosis problem, is one that has been discussed a lot and seems in recent times, not to have been as important consideration as it was in the past. If you start off by doing a hemispherotomy and you don't get the seizure control that you would like, you haven't burned any bridges and you can actually go back and do an anatomic hemispherectomy subsequently, or if you can clearly delineate where you've got crossing fibers, you can just attack those and I've done that as well in some situations.

- Thank you. No matter what procedure used for a deafferentation otomy, or hemispherotomy procedure, these are the four principles that we have to obey. You have to disconnect internal capsule and corona radiata, you have to resect or disconnect medial temporal lobe structures, you have to do a transventricular corpus callosotomy, and you have to disconnect the frontal lobe through a tractotomy. And this is really what it boils down to, it doesn't matter how you get into the ventricle; through a C-shape or insula, through a functional hemispherectomy by using, or removal of the frontoparietal operculum, you're gonna get into the ventricle, and you're gonna disconnect the white matter of the corona radiata, you're gonna disconnect the corpus callosum, you're gonna remove the medial temporal lobe structures, and you're gonna disconnect the frontal lobe. Obviously, the surgeon has to make sure all these four principles are satisfied. Jim, any detail otherwise, that the surgeon has to be careful about?

- No, these are the main steps, Aaron, and this is a very elegant operation when done properly but also exactly because the anatomy, while it is usually routine and you can find landmarks that will guide you, for example, to find the pericallosals, cutting through the corpus callosum from inside out, if you will, sometimes there can be anatomical variations, especially with hemimegalencephaly, profound cortical dysplasia cases, and so the anatomy can be a little bit unusual, making these elegant steps that you've described here in this slide, a little bit more challenging. But the basic and the fundamental techniques of hemispherectomy are outlined on this slide.

- Thank you. And here is really an overlay of this deep structures that the surgeon has to be very cognizant of, again, the temporal lobe, corpus callosum, obviously, you don't wanna injure the hypothalamus and diencephalon by violating the choroid plexus, as you do that, and we're gonna do that briefly, although we have videos of a hemispherotomy procedures, I think it's reasonable to discuss the functional hemispherotomy or ectomy because it is a good start for the novice surgeon, who may not feel comfortable walking the small area of the ventricle, and it would really obey the same four principles we talked about. Instead of getting into the ventricle by doing a temporal lobectomy, there's a frontoparietal large opercular resection, and the superior longitudinal fasciculus, is already disconnected, internal capsule is also disconnected and the way to the ventricle, the ventricle is exposed as you can see here, extreme capsule is also transversed, and within the ventricle, you can see septum pellucidum and you really follow that sulcus between septum pellucidum and corpus callosum. You can see right here, and you can find the pericallosal arteries, and you move both this way and that way, following the genu over the arteries and the corpus callosum along the body and the splenium, and obviously, you stay ipsilateral, you do not wanna cross and injure anything on the good hemisphere, and it's important to stay along the foramen of Monro and do not go deeper because of injury to the diencephalon. And as you go posteriorly along the splenium, you have to be careful of vein of Galen, and the important deep venous structures. Any other nuance of technique at this step of the operation, Jim, please?

- Yeah, I think you could convert a case like this to a disaster if you inadvertently got into let's say, the vein of Galen. So we were discussing how important it is as you're going posteriorly, and following the pericallosals, eventually you lose those, but you find the falx and then as long as you see the free edge of the falx and that turns into of course, the free edge of the tentorium, you will avoid any kind of exposure or risk to the vein of Galen but the other thing is there's a nice arachnoid layer that protects the vein of Galen. So that's a technical point that I would like to stress, in addition to, once again, suggesting that you try to preserve as many of the vessels on pass on as possible, to make this less of a worry in the postoperative period, with ischemic insults to distinct regions of brain.

- Thank you, Jim, and as you well mentioned, you really don't need to be this anteriorly, you can stay on the falx and disconnect this way, and avoid the vein completely. That may be best described rather than... what was done on this cadaver, which could place the deep venous structures at risk. And any injury to these, obviously is devastating for a young child. This is a sort of awkward view, unfortunately, to orient our viewers, this is the sphenoid wing right side, and you can see you follow this sphenoid wing to the clinoid and do the frontal fibers, to do the frontal... clinoid due to the risk of injuring the hypothalamus. So you follow the sphenoid wing, disconnect the frontal lobe above the Sylvian fissure, and do not get deeper. This is sort of a white matter tracks for the surgeon to orient themselves in terms of their disconnection techniques. Any thoughts here, Jim?

- Yeah, so the tracks are basically all how to cross by virtue of the C-shaped hemispherotomy, where you have access into the ventricular system, I usually start in the temporal horn and work my way around the atrium of the lateral ventricle and then come towards the frontal horn going forward, and that will basically disconnect almost everything, including the final disconnection of the corticospinal tract and the internal capsule as you have listed there, and once you've done that, most of the central fiber pathways that you're showing here have been disconnected, the exception being the frontal lobe, which you've already discussed, where coming along the sphenoid wing, staying on the anterior cranial fossa floor, right up to the clinoid process is actually the best way to ensure an adequate frontal lobe disconnection.

- Thank you. And this is a slide regarding the temporal lobectomy, as you remove the lateral temporal neocortex, you get into the ventricle, you remove the sorta uncus, the hippocampus, but you always stay lateral, as you move more superiorly to the choroidal line or choroidal fissure. The choroid plexus has to be always respected. A violation of the plane more medially or anteriorly would place thalamus and the diencephalic structures at significant risk. So this is really a nice outline as you're in the ventricle to prevent injury to the deeper structures. Let's focus on what the next video would be, which is the pre-insular hemispherotomy, the C-shaped hemispherotomy, and that's really following the contours of the ventricle as it would be in a form of a C and hence the name. This is a left-sided one, as you can see, we'll review the video, but after the disconnection has been completed, you can see there is really a large operculum of the hemisphere left, you would like to leave the bridging arteries here, which is obviously not present, and the disconnection has been done deeply as well. So you're really leaving the cap of the hemisphere disconnected from diencephalon and then doing insular corticectomy. Any thoughts about the big picture in terms of the hemispherotomy here, Jim?

- Yeah, no, this is a beautiful anatomic illustration of exactly the procedure you've described, Aaron, the arrows there are pointing to access into the ventricular system that you can see. There are these penetrating vessels that come off the middle cerebral, sometimes they're vessels that are on the insular cortex that continue to rise upward or superiorly towards the vertex, and you should try to preserve those where possible, but you can't preserve all of them, you can imagine there are a multitude of them, but I would certainly advise all surgeons who are undertaking this procedure, to preserve at least the largest ones that you can visualize, and you can mobilize them one way or the other, you often have quite a lot of maneuverability with those vessels once you've skeletonized them so that they stay preserved because they're feeding the parasagittal cerebral cortex, which will also take a hit if you take the larger vessels...

- And again, another image of showing the vasculature included, this is a right-sided right hemisphere, this is sphenoid wing by the way, to orient our viewers, and again, shows the pericallosals, how they should be followed and really the contours, how the deafferentation procedure is conducted. This is again right-sided, this is the eyes here, how removing a cap of the hemisphere would allow the surgeon to identify the path of C disconnection, and also respecting the choroidal point or the choroidal line and fissure, and staying always superior to that. This is really a very nice view from the top, showing how very important structures are medially as you're conducting your disconnection superiorly. So you don't wanna obviously violate any of the important diencephalic structures. Any pointers, Jim, on this view?

- Yeah, that's an excellent anatomical dissection, isn't it? It's absolutely beautiful. It's bilateral, and obviously in surgery, we have no view looking like this, but certainly as you can imagine coming off to the side here, and recognizing how close the edge of the tentorium is to the brainstem and staying away from harm's way by respecting the choroidal fissure, that is extremely important. Wonderful anatomical depiction here of how the lateral ventricle looks in relationship to the temporal horn.

- And here is an operative view, again, these beautiful images are from Dr. Rhoton, who has been such a big contributor to neurosurgery and especially anatomic features of sort of surgery and neuroanatomy, and really a wide exposure, this is his way of positioning the patient as you well mentioned, we do turn the patient's head more, and this is how he starts by finishing a temporal lobectomy, following the edge of the tentorium, this is the arachnoid over the basal cisterns, and following the edge until the calcar avis is exposed and staying posteriorly to the choroid plexus, and again, preserving all the bridging arteries into the arachnoid at the base of the temporal lobe or the arachnoid from the temporal occipital region. This is a view again, from the frontal horn, trying to depict how important it is to sort of find a pericallosal artery, make sure the cut is properly done, would you describe to us how would you find the pericallosals? You mentioned the ultrasound, Jim, any other techniques?

- Sure, and I'm gonna take my pointer in here now, and I'm coming now to this bottom right-hand view where you can see where they're suggesting a cut be made in this location, and this is a frontal horn of the lateral ventricle, here you can see the septum pellucidum, you are in front here, of the foramen of Monro. So I typically go behind the foramen of Monro, and then we'll watch the fornix, the fornix is a very close acquisition as you go posteriorly to the corpus callosum, and just behind about a centimeter behind the foramen od Monro, where the fornix is probably closest to the corpus callosum, that's a great point to go in and find the pericallosal vessels and only in rare situations have I not been able to find it, just with those anatomical pearls themselves. Occasionally, where I struggle to find it, I'll bring in the image guidance or the ultrasound as mentioned to you.

- Thank you. And as you can see, I think in this illustration Dr. Rhoton, or this section Dr. Rhoton is trying to explain the septum pellucidum and how it turns to corpus callosum and that's really that turn you see on a 3D microscope, obviously not evident here, and you just wanna stay a little bit superior to that and right around here, you will be able to find the pericallosal arteries. And here is really following the edge of the tentorium, not getting more medial to injure the deep venous structures, including vein of Galen, and preserving the bridging arteries that come from the base of the temporal lobe to the occipital lobe, to continue irrigate the banks of the brain left as a cushion. And here is really in the corpus callosum following the arteries and they continue to disconnect and perform the corpus callosotomy. And these are really the regions of the corpus callosum in a sagittal plane, you'll probably find the pericallosals over here, but you continue the pericallosals along the genu, as you will see momentarily, but do not go deeper into foramen of Monro, or at least leave a few millimeters of the corpus callosum to the foramen to prevent any injury to the hypothalamus. Is that a reasonable, I would say, rule of thumb, Jim?

- Absolutely, Aaron. The one thing you want to avoid is injury to the deep diencephalic structures, especially the hypothalamus, but also in so doing as you're coming down pericallosals, you can follow the pericallosals down until they have the junction, as with internal caroid artery, anterior cerebral and middle cerebral artery, but you have those penetrating lenticulostriate arteries and you certainly want to preserve all of those because in my experience in one case, injury to those basal ganglia structures, although it's on the ipsilateral hemisphere on which you're operating, has potentially, a profound effect on how that patient will awaken, it will not affect seizure control but the recovery period is much longer in those cases.

- Thank you. And again, the ultrasound can be used to locate the ventricles and perform a anterior and posterior disconnection and then follow the corpus callosotomy as has been described by some of the colleagues. The hemidecortication procedure by just removing the cortex is a very bloody procedure, it has been used in association with lobectomy procedures, and again, the risk of blood loss is significant. Let's go ahead and review this video more in detail, and this is a 20-month-old boy, with a complicated pregnancy, full term, fourth month of life developed seizures, very frequently, and progressive left sided hemiparesis. The seizure semiology is obviously written and the frequency was up to 30 to 40 of these per day, was tried on multiple medications, and continued to suffer from developmental delay. Interictal findings showed slowing over the right hemisphere, and what is most characteristic of these unihemispheric epileptic disorders is really most of the activity is focused in the right posterior parietal and occipital regions. And this is the MRI, the finding may be subtle, but as you can see, there is some evidence of cortical maturation disorder involving the posterior temporal lobe and maybe inferior parietal lobe and you can see the cortex is definitely abnormally shaped, most consistent with what we call a multilobar cortical dysplasia. Other cuts on T2, again, reveal some T2 signal change, characteristic of cortical malformation. This was a, I believe a postictal SPECT study, interictal SPECT study, which again, shows the affected hemisphere is hypoactive, and again, this is the patient that really the video whom we're gonna see momentarily, and we discussed the positioning, it's really difficult to prevent placing the pin anywhere by the forehead because of the large space required to do the scalp flap. So Jim if you don't mind, I would appreciate your thoughts on this video, again, starting with the temporal lobectomy, again, a right sided approach, temporalis muscle, lateral neocortical resection, go ahead, please.

- Yeah, so it's a nice technique you're showing here with the temporal lobe at first being resected in stages, lateral neocortex, as you're showing here right down to the floor of the middle cranial fossa, this buys you the room that you need, of course the landmark is the ventricle. So once you find your way into the ventricle, most of the challenges of temporal lobectomy, formal temporal lobectomy, including mesial structures is worked out for you, because by getting into the temporal horn, you're able then to find the choroidal fissure, you find the PACE hippocampus, you can do your anterior disconnection, your lateral disconnection, your posterior disconnection procedure, to remove the mesial structures. That still leaves you with the identification of the amygdala, which we'll talk about, but here you're basically exposing the PACE hippocampus very nicely, you're going to be able to see the choroidal fissure, medial, you're doing your anterior disconnection there, you're setting up to do the mesial disconnection by gently retracting on the hippocampus so that you can see the choroidal fissure, you'll be following that posteriorly, you're staying on top of the choroidal, or the choroid plexus, I often put a patty on top of the choroid plexus so as not to get it bleeding because as you know, it's quite a vascular structure, but you're nicely outlining here, the length of the hippocampus as you're proceeding posteriorly, and what you're going to see soon is that the ventricle, the temporal horn is going to start curving upward as what you're showing us here, and that then sets the stage for the ventricular C-shaped opening, which we'll discuss in subsequent phase of this video. Now you're working on the mesial structures anteriorly, it looks like the temporal horn, and doing subpial resection, I love the subpial resection technique because it keeps you safe, epilepsy surgery use this technique almost all the time so it's a routine part of the procedure, and this keeps you away from injuring any structures. The amygdala as you know, it abuts into the temporal horn, at the very front end of the lateral of the temporal horn of the ventricle, and deciding how much of the amygdala to remove is always a bit of a challenge, but I tend not to travel in superior mode to resect the amygdala 'cause if you look at your cross-sectional anatomy, if you do that, you will definitely end up in the basal ganglia before too long. So I err on the side of a little bit of caution and other people have different techniques of deciding how much amygdala . Here you're mobilizing the hippocampus very nicely, you can see the hippocampal vessels that are coming in to play, you can use that subpial technique again, following the choroidal fissure, and that keeps you safe all the while, there's frequently a band or a fold of arachnoid that you're coming up against here that you will stay subpial on, but then there's the other side, you have to put the specimen around and basically you'll be able to cut this, these are the penetrating vessels from the posterior cerebral that go into the hippocampus that need to be sharply resected after they're coagulated to remove the entire specimen. So you've got a very nice section of the hippocampus coming out here. So that's the infrainsular window that's been nicely removed, and now you need to do the same thing in the suprainsular window and cortex. And that is very important, you're showing a nice preservation of the middle cerebral artery there, it looks like to me, and now you're finding your way into the central of the temporal horn into the lateral horn of the ventricle, and this is following the anatomical landmarks that are created by the ventricular anatomy.

- I think I'm just pointing out the third nerve here, I know it's a little bit misplaced by just showing the medial extent of resection. So we're getting back into the ventricle, go ahead, Jim, please.

- Yeah, so now you've got a self-retaining retractor in place there, that's important if you don't have an assistant, let's say, that you need to at least open that space in choroidal because the problem is you're working in a fairly deep hole at this stage. So it's really important that you have accessibility and visibility. Now you're really nicely opening up the ventricle here and the different cuts are being used now to continue the opening across the broad face of the ventricle. And soon I think you'll be making your incision towards the pericallosal vessels if I'm not mistaken.

- And so we're gonna go to the second part of this video, which we'll review exactly, the details you just mentioned.

- Once again, you have a retractor on the brain, so as to open up the space into the ventricular system, to keep that opening available for you, so you can bring in the microscope now and start your dissection looking for where you will make an opening for the pericallosal vessel. As mentioned, I sometimes will think about bringing in the ultrasound or sometimes image guidance if I have any difficulty finding those, but once you've found them, it's quite nice to be able to follow those as you're showing here very nicely, the pericallosal as you're walking along the pericallosal, it's a wonderful demonstration. The inside out technique of corpus callosotomy, most of the time as you know, coming from the craniotomy from above we go outside in, where the pericallosal vessels are separated and we go in between the two coming from outside and this is exactly the opposite, inside out, a very elegant method of doing a callosotomy from the ventricular system, and you continue to follow those pericallosal vessels until either they give way, and you need to find a structure to follow like the falx, or if you're coming anteriorly, you basically can follow it into your pericallosal down to your vessels carotid artery. So here you're continuing on the dissection, looking at the technique to stay exactly midline, one of the points you made, Aaron, with which I agree completely is, always make sure that you're on the ipsilateral side and that you haven't missed an opportunity to stay ipsilateral, it's easy if you don't find your pericallosals, you can imagine you can walk right across the corpus callosum, into the contralateral hemisphere and that would be unfortunate for someone who relies on that intact hemisphere to be well. So here's, as you're showing again, pericallosals, you're tracing out for us nicely, you continue on sucking and showing us the pericallosals going forward, you're using a suction technique and bipolar, but you can also bring in the Cavitron, which makes work of the corpus callosum, especially in a case like hemimegalencephaly, which this really isn't, but if you did, you could use the Cavitron to speed things along with a very thick, bulky corpus callosum, it makes very minimal work to use the Cavitron and it's very safe of course, as long as you stay into the lateral plane of the pericallosal vessels. So it looks like to me, you're continuing looking at regions of the falx, I think, Aaron, that are coming into view here, that's a beautiful landmark that you've used in addition to the pericallosal vessels that you're following along here, as you're continuing on with your disconnection procedure, very safe to stay along the falx, especially from the falx to the tentorium, it's an excellent way to do the disconnection, stay safe, stay away from the deep draining vessels, like the vein of Galen, which you really don't need to see in this procedure, and basically to ensure that you're ipsilateral, all those things are very important. I actually like to try to find the free edge of the tentorium or the falx because that means that you're really close to the midline structures, and you're basically where you want to be according to the description of Villemure and his techniques.

- And these are...

- They got these vessels on pass on, that's great.

- And I think that's the falx joining the tentorium right there, Jim, again, this is the medial part of our resection... thank you. And I think we're gonna go ahead and do the frontal tractotomy procedure, as you can see here sort of following the sphenoid wing right here, this is probably getting close to the clinoid and really staying above the sphenoid wing and not going too much more medial to prevent injury to the hypothalamus.

- Yeah, that's...

- And here again is...

- Sorry, Aaron, sometimes what I do is I place a cottonoid, a long skinny patty that goes along the anterior cranial fossa floor, exactly along the length of the basal frontal disconnection, I want to complete because that will take us right close to the midline and one of the issues with the frontobasal disconnection cut is the possibility of going to the other side. So you have to find that interhemispheric cleft in the basal frontal disconnection cut that keeps you safe, that allows you to do the disconnection and which doesn't take you too far posteriorly for fear of injuring the diencephalon and the hypothalamus, which we mentioned earlier on.

- And I think this is removing the insula, really doing the insular corticectomy through the white matter, to preserve some of the vessels, it may be best to just remove the cortex rather than sort of remove the entire cap of the insula, occasionally surgeons have described tying off the MCAs early on in this procedure, through a transinsular approach that does decrease blood loss, but also deafferents a good portion of the hemisphere. To remove the insula is very important because that by itself can be an epileptogenic seizure focus, so removing it is critical in these patients.

- So the insular cortex, Aaron as you know, doesn't have the same depth as does the cerebral cortex. So Villemure has described doing about a three-millimeter dissection of the insular cortex down in between the penetrating vessels, I have a video later, we'll see where we actually shaved off into the cortex and clapped it down, which we can discuss as another technique to do the insular corticectomy.

- Let's go ahead and bring your video, I think we can start with the pericallosal, finding the pericallosal artery, so if you could please take us through it.

- Sure. So what you see, Aaron, is we're heading into the area, this is a case of Sturge-Weber, you can see the port-wine type of stain, the leptomeningeal angiomatosis on the cortex itself and that is right, and then right at the level there, you're starting to see the pericallosal vessels. We are just about at the level of the fornix that you can see, I'll show you that in a second, and we're staying well above that, the fornix is there, and there's the foramen of Monro coming into view right there, and then we're coming forward on the pericallosal vessels anteriorly, but a nice way, you can see the septum pellucidum, you can see the pericallosal vessels and just following those is all you need to do to be successful in this technique.

- Thank you, I think you have been kind enough to... kind to us to provide also a video of the frontobasal disconnection.

- Yeah, so to orient you, the retractor is over the sphenoid wing, and we've gone into the ventricle where we're operating with the suction techniques, and now you can see a bridging artery and vein that crosses the segment there, we are now gaining more depth following the anterior cranial fossa floor with the suction technique, and following it all the way down to the interhemispheric fissure, where we'll then connect that point up with the ventricular cut that we've made, staying in front of the plane of the middle cerebral artery vessels, basically to complete that cut so that, this is a very important part. Everything in front of that, everything in front of the disconnection is now disconnected and because you've done a callosotomy, all of the frontal lobe should be disconnected, but this is a very important cut that on occasion, early on in my practice, I found that I had left a little bit of frontal connection where I had to go back and do the disconnection. That's less of a problem now that I've figured out the anatomy through ample opportunity to go back. And now this is the disconnection that I was talking about of the insular cortex in Sturge-Weber case, and we're just now clearing some blood away from the ventricular system that you can see but I'm lifting up now, the insular cortex, it's about three millimeters thick, it's not five millimeters thick like the cerebral cortex, and by lifting it off, you've basically disconnected it and you don't necessarily have to remove it all completely, but you certainly can, but this is a nice strategy that keeps you lateral to the basal ganglia, at the level of the extreme capsule, if you will, and then preserving the basal ganglia beneath it, it's a nice way to disconnect the insular cortex from the basal ganglia.

- Thank you, Jim. And to close the discussion, I thought we can review some of the basic findings in these patients and you can see this is the specimen doing the en block resection as you saw in the video, this is a three-month CT scan, as you can see a good portion of the frontal operculum was left, probably I could have done a better job by preserving more of the bridging arteries at the temporo-occipital junction and preserving more of the cortex. So obviously, a portion of the temporal lobe will be lost, but the more of the bridging arteries you save, the more of the brain you're gonna also save. So what are these, the advantage of anatomic versus functional hemispherectomy? The anatomicals has the lowest reop rate because of the decreased risk of seizure recurrence, it's associated with significant blood loss and longer hospital stay, and highest shunt requirement. The hemispherotomy procedures have the lowest shunt requirement because you leave brain behind and can absorb CSF, and does have a higher reop rate, and less blood loss due to mobilization in the neuro cortex. So it is really difficult to reliably compare these because there's no prospective trial and obviously such a trial would be almost impossible. However, there is a methodological comparison performed by Mathern and colleagues a while ago, and really this describes exactly what we've mentioned that the hemispherotomy procedure, it does have a good seizure freedom, and the functional hemispherectomy procedure also has a good one and they really didn't find a big difference in seizure outcome, across different areas. One method that I have found useful that we published a while ago, is using EEG and how do you confirm disconnection is complete? It's really, there is no clear method obviously, but one way we have tried to achieve the confirmation is by placing EEG lids on the normal hemisphere on the scalp. The interictal discharges that are often found in these patients, disappear as the hemisphere or the bad hemisphere is disconnected. So if you're doing the surgery and you find these interictal discharges persist after your disconnection is complete, you may wanna look for a place, and I would like to ask you, Jim, in my opinion, the place most commonly surgeons leave a connection behind, is all there around the occipital lobe, splenium, or around the frontal tractotomy track. Is that correct or your experience is different?

- Yeah, so far, and I would say in my experience, the frontal tractography that we've used, in addition to what you're showing here on EEG, which is very good, the use of diffusion tensor imaging, now, I would encourage you to look at, in addition to EEG mapping because sometimes, these hemispheres are quite disturbed, but with DTI now, we can actually see if there's a residual small frontal connection, you can line it up with the corpus callosum, and if that's the issue, it's very straightforward to go back and make that small, final disconnection as opposed to converting to a complete anatomic hemispherectomy. I would encourage those in those situations, to do the smaller procedure before doing the larger anatomic hemispherectomy. Occipitally, it's probably less of a challenge if you've come up completely along the tentorium into the falx, you've probably adequately disconnected everything, so it's mostly the frontal disconnection where there's a small window of error and as I've said, DTI in conjunction with your EEG technique, those look like promising new strategies to make sure that you have got the best outcome possible. I will agree with Johanna Schramm, in the different subcategories of diseases that equate with outcome, Sturge-Weber does very well with the functional hemispherectomy, as does the peri-middle cerebral artery infarction cases, those do extremely well of course, hemimegalencephaly also does extremely well, but where everything kinda falls down a bit is with the holohemisphere cortical dysplasia. So cortical dysplasia cases are typically the ones that have less good seizure outcome and I would agree with his outcome in his large series of cases.

- Jim, I would like to sincerely thank you for really very enlightening comments, I really enjoyed talking to you on this topic and we'd love to have you again with us on the future sessions...

- Aaron, thank you for as well, wonderful Operative Grand Rounds, thanks to you.

- Thank you.

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