Grand Rounds-Resection of Thalamopeduncular Tumors: Technique

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- Hello ladies and gentlemen. And thank you for joining us. Today we have with us, Dr. Rick Boop. From Semmes Murphey Clinic. He's a master surgeon. Who's gonna be talking to us about technical nuances for resection of very challenging regions. And those are the thalamopeduncular tumors in pediatric patients. With us and please go ahead.

- Thank you, and I appreciate the invitation to talk about this group of unique tumors to younger children. We've had the occasion to have experience with about a dozen of these tumors over the last few years. And with our newer functional imaging technology we've learned some lessons in the management of these tumors. This is an interesting group of tumors. And they typically will present with a progressive hemiparesis as the tumors grow from the cerebral peduncle. And as you can see in our group of children here. They typically present in the first decade or decade and a half of life. I've not seen these tumors in older people. They seem to be unique to the younger children. They don't have pain. They typically don't develop hydrocephalus or present with headaches. But they present with progressive spastic hemiparesis. And depending on where the tumor arises in the peduncle. The face may be more involved than the arm. The arm may be more involved than the leg. In some children it's the gait that first brings it to attention. And then the arm gets to be more involved later. Typically these children may be treated non-surgically or just with a biopsy at first presentation. Because of the deep location of these tumors. But, if you look at the scans that I'll show you in a moment. You'll see that these are focal brainstem tumors. And most of the time they are benign histology, almost always pilocytic. We've had one child in this group whose tumor biopsy proved to be a diffusely infiltrative low grade astrocytoma. And we managed him with low grade chemotherapy and not with resection. Given that his histology was infiltrated into the brainstem and basal ganglia. The understanding of these tumors is important. The recognition of them as a distinct group is important because if you look back through the literature on these tumors they typically are lumped in with thalamic tumors. Sometimes they're described as tumors of the inferior thalamus. And as surgeons when people think about thalamic tumors. They tend to like to approach them from a transcallosal approach. With these tumors they arise from the peduncle underneath the thalamus. And the normal thalamus is pushed up by the tumor. So transcallosal approach to these would take you through normal thalamus. And would be the wrong approach for these tumors. As you can see in our series here. A number of these children were treated with biopsy or partial resection. And then often sent on to chemotherapy given their young age. And when they progressed on chemotherapy, which they all tend to do over time. Then that's when they typically get referred in to us. So here are some representative pictures of these tumors. Sometimes they enhance, sometimes they don't. If they're good size and they enhance in a heterogeneous fashion. They're often thought to be glioblastoma. And sometimes these children are treated with chemotherapy and radiation without a biopsy with this mistaken thought that they're malignant brain tumors. As you can see here, they're focal tumors. And typically the normal thalamus is pushed up. So as I mentioned earlier. A transcallosal approach to these tumors would take you through the normal thalamus to get to them. If it's a large tumor like this. That may be a route to get into the tumors. But generally the normal anatomy of the thalamus is so thinned out. There are no accurate planes. Typically neurosurgeons have described more inferior approaches to these tumors. In the paper by Tad Tomita. He described seven of these children that he treated. And typically they were approached from a subtemporal approach. In some children the tumors may arise higher up in the brainstem. And that would make a subtemporal approach not a good approach if one wanted to achieve a gross-total resection. In other cases the tumor may arise lower in the brainstem. And the subtemporal approach may be feasible. Sometimes if they're at the edge of the tentorium they may grow down into the posterior fossa as well as up into the middle fossa. But the point is that these are benign tumors. And they should be considered for surgical cure. One of the interesting aspects about these tumors is that although they start out in the peduncle. They'll grow where it's easiest for them to grow. So typically as they expand they'll fill the ambient cistern. And as they continue to grow, they'll grow into the middle fossa and displace the anterior coital artery. And actually tear the fimbriae of the hippocampus at the choroidal fissure. And then continue to grow into the temporal horn of the lateral ventricle. So as you see here, it's not uncommon for them to cross into the temporal horn. Which gives a surgeon a good access point for these tumors from a middle temporal gyrus approach. And as you can see in this example. The tumor extends up much too high for one approach from a subtemporal trajectory if you plan to get a gross-total resection. So, the middle temporal gyrus approach takes you into the center of the tumor. And as you work in the tumor. The part that stretched the normal thalamus up will typically deliver itself downwards making a resection possible. So let's go to the video on this first case. You see her films here. This is a child that came to us in her first decade of life with progressive hemiparesis. Did not have any visual abnormalities. Although one wonders where the optic tract may be displaced in this case. And I'll show you a good example of that in the next case. So let me pause the video here to orient you. What we've done is to place the patient in a temporal lobectomy sort of position with a malar eminence fixed towards the ceiling. Co-registered to our frameless stereotactic neuro-navigation system. And using that, this is the middle temporal gyrus. We've performed the corticotomy, well actually we've used the frameless stereotactic to guide this ventricular catheter through the middle temporal gyrus down to the tumor in the temporal horn of the lateral ventricle. In our practice we tend to use what we call a "quadroscope." Which is microscope with binocular vision. The surgeon standing across from one another on either side of the head. And this allows us to use a forehand technique where once each surgeon has two instruments. Typically you see here a bipolar and a sucker. So we start out with the catheter. We know we've gotten there when we see clear colorless CSF come out of the catheter. And then on the video here you'll see us just spread the tissue on either side of the catheter to widen out the tract down to the temporal horn of the lateral ventricle and down to the tumor. By having the surgeons stand one across from the other. You can see, we can each retract for one another as we work down to the tumor. So these patties are half by three patties. And so that gives you an idea of the size of the tract as we work down to the temporal horn. Once we get there you see the typical gray. And that allows us access to the tumor. The interest in these tumors and the surgical approach to them came from our experience with our first case. In which we recognize that the tumor had crossed into the temporal horn of the lateral ventricle. And we thought that an approach through the Sylvian fissure, opening the Sylvian fissure widely would be the best approach. And would avoid having to violate normal cortex. We did that. We got into the tumor in the temporal horn, got a nice clean resection. But the patient woke up with a worse hemiparesis than he had pre-operatively. And that caused us some wonder as to where the corticospinal tracts might be displaced in these children. So in this case, this is a child with a typical thalamopeduncular tumor, typical presentation of progressive hemiparesis. And in the blue here you see the normal corticospinal tracts on the uninvolved side. In this case the corticospinal tracts are pushed medially to the tumor and draped over the medial aspect of the tumor. That's why our trajectory from a middle temporal gyrus approach brought us into the center of the tumor. And yet what allowed us to spare the corticospinal tracts as part of resection. This is a coronal view. And again, you can see quite nicely here the normal corticospinal fibers coming down this way. But on this side, the corticospinal tracts are pushed, deviated medially by the tumor. And you can see from middle temporal gyrus approach here. You've got a nice trajectory to both the upper and the lower aspect of the tumor. So this is our postoperative scan. The child whose video you just saw. And you can see the resection cavity. You can see the choroid plexus in the temporal horn of the lateral ventricle here. And you can almost see the tract that we made down to get to the tumor here. And this is the actual image. These patients are always worse in terms of their motor function immediately after surgery. But then with a few weeks of outpatient physical therapy, they'll typically get their motor function back. And all of these patients have gone on to be independent ambulators following resection of their tumors. Here's another child, the same sort of picture, same presentation, progressive hemiparesis. In this case, her leg was more involved than the arm. And you can see right here quite nicely how the tumor has grown across the ambient cistern. And again, broaching the middle fossa, temporal horn visualized here. In this case the tractography demonstrates that her corticospinal tracts are pushed anterior laterally in relation to the tumor. And this is actually the most common pattern that we've seen amongst these children. I believe six out of the 10 had the tracts pushed anterior laterally. And you can see if this is where the corticospinal tracts are, that transsylvian approach that I used on my first case before we had tractography was actually the wrong approach. Because it took us right through the corticospinal tract to get the tumor out. So in a case like this, here is her coronal imaging. Here's the normal corticospinal tract on the uninvolved side. Here's the tumor. And here's the corticospinal tract draped over the anterior lateral aspect of the tumor at the Sylvian fissure. So in this case, a middle temporal gyrus approach using frameless stereotactic guidance to avoid the corticospinal tract but to come through the middle temporal gyrus just behind the motor tracts will get us right into the tumor in the temporal horn. And so, as in the last case we placed the catheter. We saw the spinal fluid. We widened out the tract down to the temporal horn. And one of the things we've learned over time, we've had one or two patients that awakened within homonymous hemianopsia. And recognized that the optic tract can be stretched out and quite thinned out over the tumor capsule. So that's another important structure to watch for in the approach to these tumor. So in this case, we started with our thin section MRI at the chiasm and followed the tract around. And you can see it here stretched around the lateral aspect of the tumor. And it starts out at the inferior aspect of the tumor and comes up to the superior aspect of the tumor laterally. And knowing that that's there. We can watch out for it at the time of surgery and try not to violate it. I should mention that in the tumors that arise more inferiorly in the peduncle. The same can be said for the third nerve. The third nerve may be stretched in fairly around the tumor capsule. And we've had one case in which it was so thinned out we couldn't distinguish the third nerve from the tumor capsule. And actually cut the third nerve inadvertently because we didn't make that recognition. So here's this child. We've taken the catheter out after we've gotten down to the temporal horn. You can see here choroid plexus. You see us developing the exposure of the alveus of the hippocampus. And you'll see how the tumor has grown through the choroidal fissure into the temporal horn there. So here we're using those half by half patties to keep the choroid plexus out of the way. This white structure that you see here is the alveus of the hippocampus. You see us opening up the fimbriae. And underneath it you'll see the tumor capsule. The grayish blue of the typical tumor capsule in these cases. So again, we'll advance these patties to try to protect the hippocampus. And it's interesting even though we've manipulated the hippocampus in these patients. We've not seen any problems with short-term memory. We've not seen any temporal lobe seizures in any of these children to date. What you're seeing in the picture here, coming into view through the ambient cistern is the basal vein of Rosenthal here and the optic tract here. And as the video advances a bit. You'll see that even better. So again, hippocampus here. Hippocampus here. Alveus will protect that. Optic tract here. Basal vein of Rosenthal here. This is the capsule of the tumor underneath the basal vein. So here we protected the optic tract with our patties. We've opened the tumor capsule on either side of the vein. And once we've exposed the tumor, then we can bring in the ultrasonic aspirator. I'll tell you that in the course of taking this tumor out, as we started to debulk, the vein became less turgid. And we actually took the vein. And the patient seemed to tolerate that just fine. Once the tumor is exposed. It's the typical gray fish flesh appearance of a piloycytic astrocytoma. And that's very visually and texturally distinct from the subjacent corticospinal tracts or brainstem white matter tracts. So when you get to the end of the tumor. The brainstem comes into view. Is easily distinguished from the tumor. Let's see if we can stop it there just to show you. Right here. So this is the typical white of the underlying brainstem. This is typical gray of the tumor. And usually they'll come right off of the brainstem at this level. So, it's easy to identify the brainstem tracts when you get to that point. And here you can see her postoperative scan. This is our tract coming in through the middle temporal gyrus down to the temporal horn. This is enhancement of the choroid plexus within the temporal horn as you see here. This is the resection cavity. And through that trajectory, the corticospinal tracts that were pushed anterior laterally were spared. And she's probably three years out from surgery. Now she's doing fine clinically. No evidence of recurrence. So this is a video her parents sent me by internet. Approximately three months after surgery.

- [Father] Okay, can you wiggle your fingers. Okay, can you smile a bit. Lift your eyebrows. Okay, can you turn around and walk.

- So as you can see the gait is not perfectly normal. And most of these children will retain some residual motor deficit even after the tumors were resected.

- [Father] Okay, say, "See you Dr.Boop."

- See you Dr.Boop. Bye.

- So I'll make the point, and some of these children the leg has some residuals spasticity. And some of the children the arm may be more of a problem. Typically the face recovers quite well. This is another case that was referred to us. This is a three-year old from Southern California who had again, presented with this tumor. Where a local neurosurgeon had performed a stereotactic biopsy. And demonstrated that this was polycystic histology. Again, you can see focal tumor. In this case the normal thalamus is very thinned out over the top and pushed posteriorly. It's interesting to note that even though this is a pilocytic tumor, it does not enhance on MRI. And that's true of some pilocytics. They don't all enhance. You can see enhancement along the biopsy tract. But the tumor itself is non-enhancing. On the other hand on the T2 and FLAIR, It's very focal, very well circumscribed. She had gotten to the point where she could barely walk anymore with her hemiparesis. And could not use her arm. In this case, on her tractography. The corticospinal tracts that you see here were draped over the entire lateral aspect of the tumor. Making any sort of lateral approach not as appealing as it was in the prior two cases. Again here you see normal corticospinal tract on this side. And in her case. The involved corticospinal tract is draped over the whole lateral aspect of the tumor. So there was not a lateral approach that would work in this case. So based on that knowledge. We decided to follow his biopsy tract in from a frontal approach and resect the tumor in her case as you see here. And interestingly at the bottom of the resection, we were actually able to see the optic tract down here at the end of the case. And this is her postoperative scan two years after surgery, showing no evidence of recurrence and no evidence of residual. That tract has gotten smaller over time. So here's a video her parents sent me six months following surgery. And you'll see quite nicely that in this case her leg is recovered almost completely. But she still has some residual spasticity in the arm. Still has a clumsy hand on that left side. Her face is completely recovered. So a functionally good child but not a complete recovery. And as I mentioned, most of these children will have some residual motor deficits. So I would like to mention that we've had one child referred, in which on preoperative imaging, we thought that we had a confluent tumor that was surgically curable. We took it out, the child did well. But six months later he had a multifocal recurrence with several different areas within the brainstem and now in the posterior fossa. Where the tumor was recurring. And in that case, he progressed on chemotherapy and went on to focal radiation. But in general, these thalamopeduncular tumors are focal brainstem tumors that generally have benign histology. Being polycystic tumors they tend to displace normal brain anatomy rather than infiltrate brain anatomy. Which gives us the opportunity as surgeons to cure these children. They all present with progressive hemiparesis. As I mentioned, they don't present with hydrocephalus. They don't present with seizures. They don't present with symptoms or raised intracranial pressure. They don't present with diplopia or extraocular motility problems. It's purely a corticospinal tract presentation. We've found that the use of diffusion tensor imaging and tractography has proven useful in recognizing preoperatively where these tracts have been displaced by the tumors and in designing the best surgical approach for the individual patient. I'll mention again, that the normal thalamus is typically pushed up or draped over the top of the tumor. Making a dorsal approach to these tumors not so appealing. The three critical structures that we worry about, and these are the corticospinal tracts, the optic tract, which is typically draped laterally around these tumors. And the third nerve, which is stretched inferiorly. And if you get there and find that the tumor is down below the tentorial edge. Look carefully for the third nerve. As I've mentioned, had one case in which it was so thinned out we couldn't tell the third nerve from the tumor capsule. And actually cut it inadvertently as part of our approach to the tumor. Thank you.

- Thanks very much, really a spectacular talk for managing a very, very difficult tumor. Probably one of the most difficult tumors in pediatrics. My first question for you is what have your indications, could you please elaborate? Is it partial progressive hemiparesis? How about if the patient does have hemiparesis but it's static? Could you elaborate on that?

- Yeah. We've not seen any of these children who have a static hemiparesis. They all come in with progressive worsening as the tumors get larger. And given that they're arising out of the brainstem, they don't have to get huge before the children become symptomatic. Which is why they tend to come to the attention of the physicians before they get to the point that they've developed hydrocephalus. So they don't have static hemiparesis. The majority of the kids in our series have had a biopsy demonstrating that it's a benign tumor. And then typically are referred for chemotherapy, usually low grade chemotherapy because of their young age. They've not typically been referred for radiation. We had one child in whom the imaging was interpreted as probable glioblastoma. And he was referred for radiation therapy. But he came to us before he received radiation therapy.

- Would you offer surgical treatment or would you watch them until they stop progressing symptomatic?

- I've not had any kids who had a static hemiparesis. I guess if they presented earlier that's a discussion that one could have with the family. But, as I mentioned all of these children, even though the tumor comes out fairly well. Have had some sort of residual neurologic deficit. And it makes you wonder if it's because they often come to us at the point where they can't use their arm and hand anymore. Or can't walk anymore before the surgeon is invited to be a part of the discussion. And I think if we were able to get to these children sooner, our chances of maintaining a better neurological function are better for us, yeah. At a year post-op, they're all gotten better. There are none that are completely normal. As you've seen in the videos, they tend to be back walking independently. Some have had to have a brace for a tight heel cord or something like that. But they've all been able to get back to an ambulatory status. We've had a couple of kids who had an homonymous hemianopsia. And that's important to know. We've had the one child in whom we inadvertently cut the third nerve and she went on to have surgery by the ophthalmologists so that she still had a functional eye. Her parents sent me a picture a year after surgery of her playing softball. So she was able to get back to playing sports despite that. We do have one child who has had some early evidence of recurrence in the resection cavity. And so far it's small and it's not progressed much. And we're just watching that by MRI. But we've told the family that should that progress over time. Our recommendation would be to go back and try to get the rest of it out.

- Last question I have for you. I see that you're using a , transventricular, transchoroidal approach for instance. What about considering a transsylvian, transventricular, transchoroidal? I know you mentioned that you don't wanna go through the insular. That makes good sense.

- Yes, I misspoke in the first case. We did not go through the insular to get to the tumor. We opened the Sylvian fissure, got into the temporal horn of the lateral ventricle just as you would, if you were doing an amygdalohippocampectomy, your style. And that's the child that woke up with a worse hemiparesis. So the corticospinal tract is so thinned out at that level by the tumor. I think it's hard to tell where it is. In cases where the tracts are pushed medially. I think that's probably a reasonable approach. There's no question we could get all the tumor out from that approach. I think it's important when you look at these tumors on a coronal image to see how high up they go or how low they are along the side of the brainstem and make sure that their trajectory you choose will allow you access to the whole tumor.

- I wanna have you with us again in the near future. And thanks again.

- Thank you, I appreciate it.

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