Surgical Management of Focal Brainstem Tumors in Children

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- Colleagues and friends, thank you for joining us for another session of the Virtual OR. My name is Aaron Cohen. Our guest today is Dr. Rick Boop from Semmes Murphey. He is chairman emeritus at Semmes Murphey Neurosurgery. He's the current president of the ISPN. He is one of the most talented pediatric brain tumor neurosurgeons I've ever worked with. Today he's going to talk to us about resection of pediatric brainstem tumors. Rick, I wanna sincerely congratulate you on your tremendous legacy, your contributions to American neurosurgery as a leader, and your contributions globally as a neurosurgeon are truly inspiring. Very much looking forward to learning from you today about resection of these complex tumors. Please go ahead. Thank you.

- Well, thank you, Aaron. My mother would be proud after your introduction. If we could move to the slides, Luke. I would like to just let you know that I'm currently working in the St. Jude Global Program and I'm gonna make some introductory comments to this lecture on surgical approaches to focal brainstem tumors in children, just to give you a frame of reference in terms of neurosurgery around the world. So I'll be showing some videos of children before and after surgery, and I would just let you know that I've spoken to the parents, and oftentimes these are videos that the family has sent me, and I have their permission to use them in this talk, so there should be no HIPAA issues here, but understand that in the surgery of the brain stem, if we can't see the face and can't see how the children function, then it's a moot point. So we'll start out by talking about brain tumors in high-income countries versus low-income countries, causes of childhood mortality around the world, and then we'll delve into the various approaches to brainstem tumors. So when we look at our world, I think it's important to frame this in terms of our current fast-paced, fast-moving world in which our textbooks are out of date by the time they come to print, and whereas in the past it took decades for any significant change in population growth, climate change, et cetera, things are changing by the year now and it's changing so quickly. It's hard even for us to produce neurosurgeons quickly enough to keep up with population growth in our world, which is now approaching 8 billion in population. So in our world, when we look at the number one cause of death in children, it's accidents and injuries, with road traffic accidents being number one. And whereas in the United States over the last two decades, we've been able to reduce road traffic accident deaths in children by 50%, unfortunately, what we've seen in our country is that they've been superseded by deaths related to firearms with a steep increase in the percentage of gunshot wounds to children in the COVID era. So when we look at our world, you can see in this street, you've got poor vehicles, poor drivers, poor roads, the perfect setup for high incidence of injury and mortality related to traffic accidents. Fortunately, there are collaborative groups from around the world working primarily with Pete Hutchinson at Cambridge to try to address the global challenge of traumatic brain injury. But remember, the number one cause of death in trauma is a head injury, which is neurosurgical disease. The number two cause of death is cancer, and historically the most common type of cancer is acute leukemia, but now, in the last decade, as the acute leukemias have become curable in 85 to 90% of cases, now the number one cause of cancer-related mortality worldwide is a brain tumor, neurosurgical disease, and so it's important for us to keep this in mind as we talk about the importance of these surgical approaches. So when we look at this chart of the epidemiology of cancer in children, there are about 400,000 children diagnosed worldwide with cancer per year. The cranberry are the bloodborne cancers and the purple are the CNS cancers, and cancers of the nervous system will account for about 20% of the total cancer deaths in our world. As such, in 2018, the World Health Organization launched the Global Initiative for Childhood Cancer, or GICC, with a goal of trying to half the childhood cancer-related mortality by 2030, which would result in over a million lives saved worldwide. The World Health Organization has targeted six index childhood cancers, which are both prevalent in most countries but also highly curable with modern therapies, and it is the low-grade glioma here that we'll be speaking about today, so a neurosurgical disease. And when you look at the pie chart of pediatric brain tumors, it's a disparate group, but supratentorial, low-grade tumors, posterior fossa, cerebellar astrocytomas, and brainstem gliomas will comprise 35 to 40% of the total tumor burden in the central nervous system, and the striking statistic is that the five-year survival of a child with a brain tumor is not determined by the biology of their tumor but by where they choose to receive their care. So when we look at this study, this is a study published with Jeff Wisoff as the primary author, and this was performed through the Children's Oncology Group with patients operated in the late '90s and then simply followed over the next decade. And this is one of the largest pediatric brain tumor trials ever run, with over 700 children enrolled, and with no chemotherapy, no radiation, just simple observation following resection of a variety of low-grade gliomas, what we found is that eight years out, 96% of those children were alive and well and that almost 80% of them had no evidence of progression. And that's particularly of interest here, because in children who had measurable residual disease but a near-total resection, at least half of them had no progression of that small amount of residual tumor over the next decade. So when we look worldwide, in many countries, children may be diagnosed, may go undiagnosed with their illness and die without ever having a cancer diagnosis made. And another striking statistic is the disparity in outcome between high-income countries, such as mine, versus many other low-income countries with a 10:1 difference in the overall survival of children with brain tumors, hence the discussion today. So when I started into training almost 30 years ago, over 30 years ago, operating for tumors in the brainstem was really a no-fly zone, and so it's only been with progress in neuroimaging and surgical technologies that we've been able to safely address many of these tumors. Brainstem tumors can be either focal or diffuse, and with diffusion tensor imaging, we can tell when tracts course through the tumor versus when they're displaced by tumor. Diffuse tumors are not surgically curable and are relegated to just biopsy for molecular profiling and histology, but focal tumors may be amenable to surgical cure. Typically, if we start at the top, they may be intrinsic, they may be thalamo-peduncular, tectal, tegmental, aqueductal, and the pontine tumors may be also intrinsic or oftentimes are laterally exophytic into the cerebella pontine angle. They can be dorsally exophytic, and then we have the cervico-medullary tumors. So we'll run through examples of each of these over the next hour and discuss the surgical approaches. I'll tell you that the intraoperative MRI has allowed us great progress with operating on these tumors and having a high-field-strength MRI, such as this 3-tesla magnet can be very useful in finding residual and re-resecting before we wake the children up. Also, improvements in neurophysiological monitoring. We can now monitor all of the cranial nerves and the long tract signs at the time of surgery, and I'll show episodes of how this has allowed us to do intraoperative mapping along with our resection. So thanks to Aaron for these artist renderings, but if we start at the top with tumors of the third ventricle, remember that the corpus callosum covers the lateral ventricle, and once inside, then we'll see our foramen of Monro, which is bounded anteriorly and superiorly by the fornix and limited somewhat by the confluence of the septal and thalamostriate veins where they form the internal cerebral vein, or ICV, as we'll we refer to it, at the foramen of Monro. And to approach these third ventricular tumors, typically we'll enter the corpus callosum, work through the foramen of Monro, but expand the foramen to gain wider access to these tumors. Typically, it's been advantageous to work with vertex to ceiling. Some people like a lateral position, but for me, having a vertex to ceiling, with typically a linear or curvilinear incision instead of a trap-door incision, has been useful. If we think of the confluence at the venous angle of the septal and thalamostriate veins, this is a lock on the door to the third ventricle, but we can sacrifice the septal vein with impunity. I've been doing it for 20 years without any complications related to this. And once we take the septal vein, we can open up the choroidal fissure and have expanded access posteriorly to the posterior aspect of the third ventricle. It also allows us to be able to manipulate the fornix a bit more gently and broadly without damaging the septum pellucidum. So this is a six-year-old who came to us from Bermuda, with this large third ventricular tumor, and you can see how it's encapsulated on the left side but feathering on the right side, which was the side of her third-nerve palsy. So we thought that it would be best to approach it down the left side. Here you see our exposure, and we are operating with two opposing oculars, which is why you see four instruments in the field. But once we open the corpus callosum, you can see here the septal vein. We're separating it from the underlying fornix here, and once we've got it separated, we can coagulate it and cut it, and that will allow us to unlock the door to the posterior third ventricle. So you'll notice that there's a velum or a thin arachnoidal membrane over the floor of the lateral ventricle, and we'll open that membrane, working either above or below the choroid plexus, whichever works best. But as we open it, the internal cerebral vein will come into view, as well as thalamoperforating vessels and choroidal vessels. And there's another velum or membrane like this in the roof of the third ventricle, which you see is opening here. So note that these vessels are in the velum interpositum, which is the sandwich between those two arachnoidal membranes. As we open, you'll see here the tumor bulging in the floor, massa intermedia here, and as we work back, you can see the aqueduct of Sylvius coming into view here, and all of those structures are equally visualized. So with frameless stereotaxy, we want to open in the midline, because if we get off-center, third nerve fibers may be affected. But here's the typical appearance of a low-grade glioma. You can see the gray, gelatinous appearance, clearly different than the subjacent white matter. Here we're opening the massa intermedia to get further back and trying to stay in the tumor as we debulk it, and then using standard resection techniques, debulk tumor until we get to the point where it starts to blend with the underlying brainstem there, and at that point we stop. Here's a video her mother sent me three months postoperatively. You see she still has a third-nerve palsy, but cognition is normal, memory is normal. She has no motor deficits. And we've just followed that residual remnant over the last number of years. And you can see here, nine years postoperatively, she still has a bit of enhancement there that you can see on the sagittal images, but she's had no progression of that disease with no adjuvant treatment, and is leading a normal life. This next case is a 13-year-old who was referred to us. She had initially presented with hydrocephalus and undergone an endoscopic third ventriculostomy and endoscopic biopsy, and based upon a two-millimeter piece of tissue given to the pathologist, the pathologist diagnosed a glioblastoma. She was treated with chemotherapy and radiation and had slow progression of her disease over the next two years to the point that she developed hemiballismus, failure of upgaze, failure to ambulate, and was referred to our center for evaluation. So you can see her tumor here. It's cystic and solid enhancing, and we thought with that clinical history that this probably was not a glioblastoma. It was avid on hyperperfusion scans, suggesting perhaps a higher grade neoplasm. It was also avid on Met-PET, again, supporting a more metabolically active tumor. But again, when we look at this tumor, with a cystic and solid and no edema around it, we thought this was probably a lower grade neoplasm. So here we are again, transcallosal approach down the right side. So this is forward and this is backwards. And as you can see, we're dissecting out the pericallosal vessels and then working between the pericallosals to expose the corpus callosum, then using frameless stereotactic navigation to determine the anterior and posterior extent of our callosotomy and to make sure we're in the right ventricle on the right side of the midline. You can skip forward a bit there, Luke, maybe five or 10 seconds. And here you can see we're opening the corpus callosum, and once we've taken down those adhesions, you can see the septum pellucidum on the inside here, and you can see the septal vein in the septum at that level. When we look further inside, here is our fornix, here's our choroid plexus, and as we open up the choroidal fissure, in this case, the septal vein enters the internal cerebral vein behind the foramen of Monro, so we dissect backwards until we see where it enters and section it at that point, keeping our bipolars perpendicular to the fornix so that we don't burn the fornix as we take it. And again, we've opened the velum over the floor of the lateral ventricle, but the velum in the roof of the third ventricle is still open, still intact, and so we're opening that next. And you see the internal cerebral vein here, and we'll be working between the two ICVs to broaden our exposure. But you can see how, as we open up the choroidal fissure, it allows us not only better visualization but it takes the tension off of the fornix so that we're less likely to damage it. You can see in the distance here, the tumor where it's breached the ependyma in the floor of the third ventricle, and once we've opened up back to the massa intermedia, you can see here the tumor coming through the ependyma wall, open up that thin remnant ependyma in the midline, and then once we've exposed the tumor, you can skip forward a bit there, Luke, we'll get biopsies for pathology, always try to get pathology plenty of tissue so there's no question both about the histology and the molecular genetics. And then just typical low-grade glioma debulking using microsurgical techniques and using the ultrasonic aspirator on low settings until we get to the interface between that gray fleshy tumor versus the white glistening tracts of the brainstem. You can skip forward there. Once we've got the tumor out, we'll meticulously dry up, make sure there's no bleeding, make sure there's no remnants left. And once it's nice and dry, we'll typically get an intraoperative MRI, and you can move forward to... There you go. Here's our intraoperative imaging showing our approach and the resection cavity, and this signal change in the basal ganglia is likely related to the radiation therapy she had. So she woke up-

- Hi, Dr. Boop!

- with a third nerve ptosis, which resolved. and her mother sent me these videos three months later. Her histology came back ganglio glioma, and she's not required any other treatment. So now on to our thalamo-peduncular tumors. This is an interesting group of tumors. If you look at the neurosurgical literature, historically these were called thalamic tumors, and often the literature talked about approaching them from a transcallosal approach like we had in the last two tumors. But if you look, they actually start at the junction of the cerebral peduncle underneath the thalamus, and they push a normal thalamus up, as you see here. So you can see if you came transcallosally, you would go right through a normal thalamus to get to these tumors. Not a good approach. Other authors, Tad Tomita from Chicago and the group from Paris, tried a subtemporal approach and that will give you access to biopsy these tumors, but as you can imagine, you can't get to this portion of the tumor from a subtemporal approach. So what we observed with this index case was that these tumors will typically grow across the ambient cistern until they reach the choroidal fissure of the temporal horn, and then they'll put pressure on it until they tear the choroidal fissure and then they'll grow into the temporal horn, obstruct CSF flow, and you'll get a dilated temporal horn here. So in this index case, back in 2000, we thought that this was approachable from a transsylvian trajectory. So we came transsylvian, got into the tumor, and, as is typical, these tumors will present in the first two decades of life and they're almost always pilocytic histology. So through a transsylvian approach, we got a nice resection on this tumor, gross total resection, but the boy woke up hemiplegic and with a hemianopsia, not a great outcome, although I can tell you that I recently saw him back in clinic, and he's 20 years out, going to college, driving, and doing quite well with that deficit. But we decided to study these tumors, and over time, recognized that they can be cystic or solid, they can be enhancing or non-enhancing. Oftentimes if they're large and variably enhancing, they're diagnosed just based on imaging as a high-grade glioma and treated with chemotherapy or radiation therapy. So once we were able to get tractography, we were able to demonstrate that in 80% of these children, the corticospinal tracts are pushed anterolateral, and that explains why a transsylvian approach would cause a hemiplegia in these children. So with that, we started looking at a transcortical middle temporal gyrus to these tumors coming just behind the corticospinal tract to get into that dilated temporal horn, and use that as an approach, opening the choroidal fissure. The other thing that we recognized is that the optic tract is stretched around the outside of the tumor capsule and is vulnerable to a transchoroidal approach in these children. So here's another case. So you can see choroid plexus here. We're in the temporal horn. We've exposed here and our cottonoid is on top of the alveus of the hippocampus, trying to protect it. And as we depress it, you'll see the blue color of the fimbria here, the choroidal fissure, and we're able to open up that choroidal fissure and expose tumor in the ambient cistern just beyond that point. We'll focus in here in a bit, but by elevating the choroid plexus, we hope to protect that optic tract and to expose the tumor capsule. So as we focus in here, you can see the optic tract here, you can see the basal vein of Rosenthal here, and the alveus of the hippocampus just underneath the cottonoid. We'll focus down a little bit more and you'll see the tumor capsule as it comes into view here. So here's optic tract, basal vein of Rosenthal, alveus of the hippocampus, which we'll wanna protect and be gentle with, and underneath that is the tumor capsule. We open up and you can see the typical fleshy gray appearance of a pilocytic astrocytoma, And once we get our pieces for histology, we'll debulk. As we debulk the tumor, this basal vein became much less congested, and before we got all the tumor out, we ended up taking that vein, which I don't recommend if you can help it. But you can see, with the ultrasonic aspirator on a low setting, the typical yellowish gray, discolored appearance of a pilocytic astrocytoma, and when we come to the end of the tumor, you'll see the glistening white of the brainstem, which is both visually and texturally different than the tumor, and tells us exactly where we'd stop when we get to these tumors. You see here the glistening white of the normal brainstem coming into view. Next slide, please. There we go. And this is her intraoperative post-op scan. You can see enhancement of the choroid plexus, but a clean resection cavity. And this is a video that her father sent me three months postoperatively. You'll notice that most of the time these children are worse immediately after surgery and will improve over the next six or eight weeks, oftentimes with therapy. But you'll notice that she has residual circumduction gait with her left foot there, and she does wear an AFO, but you can see she has good fine-motor coordination of her hands and no asymmetry of the face any longer, so a reasonable functional outcome. Next slide. So this next case is a more complicated thalamo-peduncular tumor. This is a child. This video was edited by Chenran Zhang, who is a fellow of ours from Shanghai, and appreciate his help with this. This was a child who presented with a fairly extensive thalamopeduncular tumor, as you can see here, that was both supra- and infratentorial, and our decision was to treat him. He had been biopsied through a retrosigmoid approach. We thought we would start with a transtemporal approach to get the superior portion of the tumor, and then close and reopen his retrosigmoid tumor to get the craniotomy, to get to the posterior aspect of it. So here we've passed this catheter with frameless stereotaxy. Notice the CSF coming out of it. We take the catheter out and follow that tract down to the temporal horn, and once we get into the temporal horn, here's again the alveus of the hippocampus. There's choroid plexus, lifting up on the choroid plexus. We can open the choroidal fissure and you can see the gray gelatinous tumor capsule here. We want to look for en passage brainstem vessels and protect those, but we can take these smaller capsular vessels, as you see here, and then once we open into the tumor capsule, just standard microsurgical resection of, again, your gray gelatinous pilocytic tumor. Get tissue for histology, tissue for molecular profiling, and then you can see the soft suckable tumor here, and it's easily differentiated from normal brainstem underneath. So we have good visual and textural cues as to where the tumor is in relation to the brainstem. There you go, and using the ultrasonic aspirator on a low setting, as you see here, and trying to protect the normal brain with cottonoid as best we can, mobilizing the capsule to get a little bit better exposure. So we wanna watch out for the optic tract. We wanna watch out for the third nerve if the tumor extends over the tentorial edge. And you can skip forward a bit here, Luke, maybe 10 or 15 seconds. Once we've gotten the superior portion out, we close, and then we're opening the retrosigmoid part here, and using a standard retrosigmoid approach, we come down on the inferior aspect of the tumor below the tentorium here, watching out for the fourth nerve. But the tumor was cystic at this point and the previous treating physicians had placed an Ommaya reservoir into a cyst and were tapping it about once a week, whenever he was symptomatic, prior to referral. But you see, as we get into tumor here, again, the typical difference between the white of the brainstem and the gray of the pilocytic astrocytoma. You can skip forward here, Luke. And then just staying within that gray, fleshy tumor until we meet our dissection from above. We had left Gelfoam there, so the Gelfoam tells us when we've reached our previous resection cavity from above, and then just gradually debulking layer at a time, taking our time until normal brainstem comes into view. You can skip forward more. And you can see, here we're starting to see where the tumor blends with the brainstem, and this is a point where we wanna be very cautious. And once we're done, you can skip forward, we'll dry up, we'll look around for any remnants of tumor, and here are his incisions. He made a good functional recovery, but I can tell you, this is four years out, this picture, and he just came back with a focal recurrence, and Paul Klimo, my partner, has just re-operated on him for that. So some of these children can be cured surgically, some may recur and require focal radiation or other molecular targeted therapies. Tectal gliomas are interesting tumors. They are reputed to be the smallest tumor in your body that can kill you. And you can see a subcentimeter tumor here producing hydrocephalus in a patient. This is just an article that Jim Rutka and I co-authored on two cases, one each of patients who presented with ventricular obstruction from tectal gliomas, and following an endoscopic third ventriculostomy, the tumor involuted and disappeared without any treatment for the tumor on its own. But most of the time these are indolent, and once we treat the hydrocephalus, we leave the tumor alone and just follow them. But there are times where these tumors don't follow the rules, and this is such a case. This is a four-year-old child that presented with headaches and was found to have this large tumor here. And on MRI, you can see a large heterogeneously enhancing tectal tumor causing hydrocephalus, causing brainstem compression. So we decided to approach this in the prone position from a supracerebellar infratentorial approach. So our craniotomy extends above the transverse sinuses. We pull the dura up and try to preserve as many of the tentorial veins as we can, but just taking our time with a microsurgical approach, up to the tentorial hiatus. You can advance there, Luke, five to 10 seconds. And here the tumor comes into view, here, and in this case, it was very firm and fibrotic. It's pushed the precentral cerebellar vein over to the right and here we're preserving it, but it was very easy to see the gray tumor versus the glistening white tectum pushed over to the right, and here it was very tough at this level, so we had to actually cut pieces out to send specimens to the pathologist. And then once we get into tumor, just using basic microsurgical techniques with the ultrasonic aspirator to dissolve the glioma. We had good visual cues of the glioma versus the white of the tectum. And you can skip forward there, Luke. Spent the better part of the day just gradually debulking this gray, gelatinous pilocytic astrocytoma and stopping when we saw the white of the brain stem. You can skip forward further, and then some more. And we thought we had a pretty good resection. Keep going, if you would, Luke. And we stopped and did a scan and noticed there was significant residual, so we kept on working. Skip forward more. You can skip forward further. So here's her intraoperative MRI, a little bit of blood there, but otherwise what appeared to be a gross total resection. And here she is at the end of the week before going home. Her mother's holding her up because she's still ataxic, but you can see the motility is normal and we have good preservation of facial motor function. It took about a week for her ataxia to resolve, but she recovered fairly quickly, and with a clean resection has been relegated to observational MRIs postoperatively

- [Parent] Yay!

- and no further therapy. Next. So this next case is of a true periaqueductal tumor, and these are fairly uncommon. Shlomi Constantini and the group in Tel Aviv gathered a group of these tumors, and if you'll pause there a second, Luke, you can see that this tumor is in the aqueduct. She presented purely with headaches, but they were debilitating headaches, such that the treating physicians placed an ICP monitor. Her ICP was normal. She had no hydrocephalus, but severe headaches from this tumor in the aqueduct. Okay, you can go back forward. And you can see the tumor here. We talked about trying an endoscopic approach from above, but because of the angle we thought we'd be better off coming in from below, opening up the cerebellomedullary fissure, and getting to the aqueduct in this direction. So here's the top of her head, feet down here, and you can see a telovelar approach, taking down the adhesions between the cerebellar tonsils so that we can mobilize them. I'll make the point that in all of these videos you won't see any fixed retractors. We think that fixed retractors are bad for children's brain and we haven't used fixed retraction in 20 years. But opening up the fissure between the uvula and the cerebellar hemisphere, you can get visualization all the way up to the aqueduct without having to resect any normal brain tissue, just using standard microsurgical technique like you would opening the Sylvian fissure. And once we're open and once we can see up to the aqueduct, we'll put in a cottonoid to protect the floor from my clumsy fingers. And as we look up to the aqueduct, you can see the tumor crowning at the level of the aqueduct at this point. So you can see the tumor here, and these aqueductal tumors are almost always low grade. They're not particularly vascular. They're usually soft and suckable, so we got several pieces for histology and for molecular profiling, and then began just removing it with suction on a low setting. And you'll see that the tumor itself is discolored, is soft and suckable, whereas normal brain underneath it is not so soft and is white and the typical color of normal brain. So as we remove tumor here, you'll see the aqueduct and the third ventricle come into view and you can see quite plainly the difference between tumor tissue and normal brain tissue, and just with some patience and Gelfoam with thrombin, this bleeding stops. We halted when we thought we had a gross total resection and found that there was a little bit of residual in the roof of the aqueduct, and we went back in and resected that small amount of residual. And this histology came back a glioneuronal tumor. Here you can see the residual that we went back and resected. Glioneuronal tumor with multilayered rosettes, which is a WHO grade 1 tumor, and so she was relegated to observation alone. About a year later, on followup imaging, she showed evidence of early regrowth, so she had focal proton beam to that area and has been fine since that time. So next slide, Luke. So here she is at the end of the week before going home, and you can see-

- [Doctor] All right, look at my finger.

- Cognition is normal. Extraocular motility is normal. She has no facial asymmetry. She was a little bit ataxic for a couple of weeks, but has subsequently been fine neurologically. All right, next slide. So it's been several years since Kobayashi's group wrote this paper on safe entry zones through the floor of the fourth ventricle to intrinsic pontine tumors. Next slide. They described the suprafacial and infrafacial triangles to approach these tumors, recommending that we stay off of the midline to avoid the MLF, which is a millimeter under the surface, but entering through this zone or this zone, and that's been very useful. A paper by Cavalheiro from the Rhoton lab showing similar dissections. And this is a case of a child who initially presented to us when she was three years old, you can start the video, with a peripheral facial palsy, and you can advance the slides, if you'd like. This tumor, which was laterally exophytic into the CP angle, at that time, we debulked tumor but were unable to get much of a resection. Histology was pilomyxoid, which we now think is probably a maturational variant of pilocytic astrocytoma. She had low-grade chemotherapy and was stable for about five years and then returned with a bilateral internuclear ophthalmoplegia and this cystic and solid recurrence. We didn't think that we could get a clean resection from a lateral approach, but it came right up to the floor of the fourth ventricle, and so we thought that that would be our best trajectory to try to get this tumor out. So again, top of her head here, spinal cord down here, telovelar approach bilaterally, and for these tumors in the pons, they always deface the landmarks on the normal floor of the fourth ventricle, so we have electrodes in all of the facial muscles and in the lateral rectus so that we can monitor those nerves. We're also monitoring long tract signs. But again, opening up that cerebellomedullary fissure, we can get all the way up to the aqueduct without having to resect any normal tissue. And once we've got good exposure, we can use our frameless stereotaxy to see where the tumor comes closest to the surface, and then with a stimulating electrode, we can stimulate the floor of the fourth ventricle. And what we found was that this was where her facial colliculus was, sixth nerve fired just underneath it here, and this is where the tumor capsule came closest to the surface, so we decided to use that for our corticotomy and our approach to the tumor. And you can see, as we open into the floor of the fourth here, the gray appearance of the tumor capsule comes into view. And once we get into that cystic portion of the tumor, we can open more widely, and once again, standard debulking of the tumor capsule and the gray appearance of a polycystic tumor, and then just meticulous resection until we see normal brainstem underneath. And once we feel that we've got all of the tumor out, we will dry up. We try not to leave any Gelfoam, any Surgicel, any foreign body material there because it'll start to enhance. But here we can stimulate again at the end of the resection to verify that we still have firing of the sixth and seventh nerves, that those pathways are still intact. We get all of that packing material out of the wound and follow up. If it creates a foreign body reaction that enhances a year down the road, it confuses whether or not we've got recurrent tumor versus a reaction to the foreign body material. But a clean cavity, and here's her intraoperative MRI, which we can invert to interpret more easily. Here she is at the end of the week. It took about six or eight weeks for her internuclear ophthalmoplegia to resolve, but it eventually went away, but you can see her facial muscles are working quite nicely and she's ambulatory by the time she goes home. So she did have a focal area of recurrence about a year and a half later and had focal radiation for that recurrence, but has otherwise done well. Let's go to this case then. This is a case of a dorsally exophytic tumor, which, again, is typical of a childhood brainstem tumor. In the '90s, Fred Epstein wrote that he postulated that these tumors began in the cervicomedullary junction and grew longitudinally up inside the spinal cord until they hit the lemniscal decussation, the crossing fibers of the lemniscal tracts, and at that point they would not be able to grow any further, so they would grow rostrally and become exophytic at the junction of the spinal cord and the brainstem, and that's exactly what you see here. So when I see these tumors, I think of a volcano. As a volcano pushes up out of the ground, it pushes normal earth up on either side of these, and these tumors do that with the brainstem. So if you shave these off, flesh with the normal brainstem, you devastate these patients because you're cutting through that normal brainstem that's pushed up. So you need to approach them like you're coming down the cone of a volcano and stay inside the tumor, and we'll use a stimulating electrode to be able to monitor these edges along the side. In this case, this four-year-old presented with just headaches, and we thought she was probably developing a ventricular outlet obstruction, even though she didn't have any changes in ventricular size to suggest hydrocephalus. But you can see here, thresholding on the spinal accessory nerve and then dissecting tumor away from the normal cerebellum here, interposing cottonoids as we move along with our dissection, staying right on that junction between the gray, gelatinous tumor and the normal-appearing brain tissue around it, and yet, in this case, looking out for that brainstem tissue that's pushed up along the sides of the tumor and trying to stay in the center of the tumor where it's obviously gelatinous pilocytic tumor here. And as we work around it, we were eventually able to open into the fourth ventricle, and once we saw the fourth ventricle ependyma of the floor, we were able to debulk further to widen our fourth ventricle outflow obstruction and alleviate the hydrocephalus. You can skip forward a bit here, Luke, if you'd like, but you can see how we're staying on that interface between brainstem and tumor. And as we stay in the tumor with our debulking here, we want to be gentle with our manipulation with the CUSA. We don't wanna beat up the brainstem. We want to gently let the ultrasound dissolve the tumor tissue as we work until it starts to blend with the normal brainstem, and when we can't tell obvious tumor tissue, then it's time to stop. You can see along the sides here, we've got areas where the brainstem tissue starts to blend with the tumor tissue, and we leave that alone, particularly if stimulation gives a response. You can see here the fourth ventricular outlet coming into view here. As we unblocked the fourth ventricle, we went ahead and removed this confluent tumor. You can skip forward a bit there, Luke, if you'd like. And you can see here quite nicely how it becomes indistinct from the normal brainstem, and that's where it's time to stop. So I think we can move forward here. On the immediate postoperative scan, she did have some enhancing residual here and our oncologist had suggested low-grade chemotherapy for that, but the family refused, and over time, with just observation and follow-up scans, next slide please, that enhancement resolved. Here she is dressed up like Elvis Presley, which she likes to do, but you can see that enhancement went away, and here's her scan four years postoperatively. She's neurologically normal and following a normal life. So dorsal exophytic tumors. Remember the volcano. Stay out of the sidewalls. And then this case is a two-year-old that came to us with drooping shoulder on that side and what the family called a helper hand. He would grab his left hand with his right hand and use it because he had paretic arm on that side. See how he holds his paretic arm with his good arm? Next slide, Luke. And so that led to this MRI showing a typical cervicomedullary tumor. They always have a glial cyst at the top. They always have a focal syrinx at the bottom, and for a surgeon, that will help us delineate the extent of the tumor, but you'll also notice that a normal pons is always pushed up because these are tumors of the cervical-medullary cord, and 80% of them are pilocytic, which means that these children can anticipate long-term success if we can take care of them properly. So this is just showing how thinned out the brainstem is. It was about two to three millimeters where the tumor was at maximum. And in these cases you can see that we were able to confirm with tractography Fred Epstein's theory that the lemniscal decussation is what prevents further growth of these tumors, and they begin to turn exophytic at that point. So floor of the fourth ventricle is up here, you can advance about 20 seconds there, and you can see the median dorsal vein here. We're gonna start there getting into the tumor. If you'll look carefully, you'll see these small vessels coming up out of the median raphe into the median dorsal vein, and that tells us where the midline is. So if we do our myelotomy at that point, where these vessels come out of the midline, then we can work between the dorsal columns instead of going through a dorsal column. And in this case, the tumor capsule is two to three millimeters underneath, you can advance, and you can see the typical appearance of a pilocytic astrocytoma there. Here's the wall of one dorsal column and here's the other one, and we wanna both protect those and work in between them. So early on, biopsies for molecular profiling and for the pathologist. You can move forward about 30 seconds there, Luke. We expand the myelotomy up to that lemniscal decussation, but wanna stay below the floor of the fourth ventricle, stay below the obex, stay out of the brainstem. And then working here, we'll use, you can advance forward, this is a Spetzler micro dissector, which is like a broad cut curette with sharp edges, and use that to dissect the tumor away from this thinned out brainstem and then debulking the tumor with the ultrasonic aspirator gradually until we open into that cyst. You can see how thinned out the brainstem here is, but it dissects away from the tumor quite nicely. You can advance. And once we get into that glial cyst, we stay below the floor of the fourth ventricle, keep that intact, just debulk. You can see here extending our myelotomy more inferiorly. And you can see these vessels coming out of the median raphe between the dorsal columns, and we can keep our dorsal columns intact if we stay in that midline plane and come down to the syrinx, and that tells us where the distal end of the tumor is. You can skip forward here. And I'll tell you that working up rostrally, this is fourth ventricle. We've left it intact. He does have some choroidal cysts there that are congenital, but debulking the tumor there. We ended up leaving a little bit of tumor superiorly, and we can go on to the next slide there, because he became bradycardic and hypertensive. So you can see the residual up here, but otherwise, a fairly good resection there. And followup scan, six weeks postoperatively, replacement laminoplasty here, but residual tumor here, and eventually that progressed and that required adjuvant therapy, at first, low grade chemotherapy. Here he is back in clinic. Six weeks later, you can see his shoulder's back up. He's using that hand and that arm again. He's got good fine motor coordination of his hand. Next video here, please. And you can see . And we'll move on from there, Luke. So we published our series about a decade ago of 32 cervicomedullary tumors. 80% of these children were alive at 10 years. They're mostly low grade. They present with neck pain or long tract signs. The children who presented with high-grade gliomas all progressed to death, and surgery was not really a role in their care. But you can see quite nicely that extent of resection predicted the best longevity, and with aggressive care, they can be able to enjoy a long livelihood. This is an 18-year-old who presented with this focal brainstem tumor and hoarseness related to unilateral vocal cord paralysis. We started trying to resect his tumor here and it was pilocytic, but he also developed hypertension bradycardia, which caused us to back out. We gave him focal radiation at the time and it shriveled up, and here's his scan and long-term follow-up. His vocal cord paralysis did not get better, but he is otherwise normal child. And then finally, here's a case that demonstrates that not all of these children enjoy a great success, as I've shown you here. This is a 16-year-old who presented, a high school football player, and he'd had two arthroscopic surgeries because of stiffness and weakness in his right leg, and then ended up getting hit in the middle of a football game and developed lethargy and hemiparesis, which led to this scan showing an extensive midbrain tumor growing all the way through the midbrain. But, and you can see evidence of hemorrhage in the tumor, and on this coronal image, you can see that it was exophytic into the CP angle. So we decided to approach it at the exophytic area, get into the tumor there, and then to debulk, which we did. And you can see his scan a year later showing a good resection of what proved to be a low-grade glioneuronal tumor with multilayered rosettes. So again, a WHO tumor. Probably cured this tumor. He's not had any evidence of recurrence, but mother called me 87 days postoperatively to say that he started doing this. And you can play this next slide, this next video too, Luke. Cognitively normal, keeps his eyes closed because he has diplopia, but had developed hemiballismus, and subsequently we referred him to Vanderbilt for their functional program to see if they could get this under control, but good treatment of his tumor, but not a good functional outcome, unfortunately. Next slide, please. So I'll stop there. In conclusion, improved pre-operative imaging has allowed us to use DTI and tractography to tell which tumors are confluent tumors versus infiltrative tumors. Intra-operative imaging has allowed us to push the imaging on resection of these tumors. Better neurophysiological monitoring has allowed us some margin of safety in being able to stimulate and record. Gaining access to tumor tissue has allowed us molecular profiling, and in many instances, targeted therapies for these tumors, particularly if they're recurrent. For us, if these are low-grade tumors not amenable to resection, focal radiation has been our best adjuvant therapy for cure, and long-term survival should be anticipated in the vast majority of these children. So I'll stop there, and thank you very much for the opportunity, Aaron.

- Great work, Rick. As always, enjoy watching your technical expertise at work. The videos are phenomenal. I really wanna emphasize a couple of things you very well mentioned. One of them was that volcano phenomena in these tumors that are exophytic, that, as you said, if this is the surface of the brainstem, the tumor expands up and takes a piece of the brainstem on the wall of the volcano with it. So if you just cut across it, you're gonna cut across some of the functional tissue. So you really have to work on top and leave, like, a midsection to below of the wall of the volcano, because that's functional tissue. That, as simple as it sounds, it's really very much under-recognized. And I want to emphasize that, that these tumors start, they expand the brainstem, and they eventually break through, but part of them is on the wall of the volcano. So thanks for emphasizing that and on our viewers to remember that. The other thing is, really, the way you handle the tissues, lack of aggressive retraction. I'm not someone who says you shouldn't use fixed retractors ever. I think there is a place for them, rarely, if they're holders of nervous tissue, protectors of nervous tissue, but not necessarily retractors, they're not aggressively causing ischemia, and avoiding that as much as possible, what you showed, using dynamic retraction, being able to handle the tissue effectively, really opens up a lot of corridors for you. In fact, in that aqueductal tumor, if you put the retractor, you will never get there because the retractor is so wide that it's gonna retract a lot of tissue together and there will be so much tension that you are not gonna have the advantage of the very much fine and limited advanced retraction you get with the shaft of the suction. So in fact, by avoiding retractor, you get more mobilization right at the point that you're working with minimizing ischemia, and the wide, you know, width of the fixed retractor can really fight the brain very strongly. Any other thoughts you have here?

- Well, I think those are important thoughts. You know, if the ischemic time for neurons is three to four minutes, then if you put in a fixed retractor and you is ischematize that cortex, you're gonna see T2/FLAIR changes on your postoperative scans that are gliosis from the injury, whereas with dynamic retraction, you're allowing profusion of that cortex, or you may be compromising profusion of it for a few seconds at a time. But in the long run, once you get used to it, as you saw, we were able to work down through the inner hemispheric fissure without any significant retraction injury. And I will say that when you're working interhemispheric, it's important to tow in down below and not lean on the surface of the brain, keep your retraction towed in down deep and not retract on the motor cortex up high, but, yeah. The other is the comment that you made about not being overly vigorous. We'll see people who are used to resecting with a sucker use their ultrasonic aspirator like a sucker, whereas the ultrasonic aspirator is made for the ultrasound to dissolve the tissue, and so if you move it slowly and gently, you don't cause the manipulation injury to the normal brain tissue underneath.

- Very well said. Really enjoyable to watch. As always, Rick, I cannot thank you enough for, again, allowing us to learn from your superb expertise, and look forward to having you with us in our next sessions.

- Thanks, Aaron. Thanks for letting me be a part of your Atlas.

- You're welcome and God bless you. Thank you.

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