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Surgical Management of Intraventricular Tumors: Anatomical and Operative Pearls

James K. Liu

March 22, 2021


- Hello, ladies and gentlemen, and thank you for joining us for another session of the virtual operating room from Neurosurgical Atlas. Our guest today is Dr. James Liu from Rutgers Neurosurgery. He's a professor and director of sculpting surgery there. He's dear friend, Jim and I have been colleagues together for many years. I have an immense respect for his technical excellence and commitment to skull base and complex intracranial surgery. Jim, I hear that you're gonna talk to us today about intraventricular surgery. A very interesting topic. We have asked you previously to be our speaker multiple times, and obviously it's a reflection of your international reputation. So with that, I'm looking forward to learning from you. Let's go ahead and listen to you talk.

- Okay, thank you, Aaron. It's certainly an honor to be here and to be part of the virtual OR series. Today, I'm gonna talk about interventricular tumors and let me just pick my telestration so I can telestrate the videos as we go along. So the ventricular system is probably one of the most beautiful parts of the brain that one will see. And when we have tumors or lesions that arise in this area, it requires a technical challenge to get to these deep areas of the brain and to remove these tumors while preserving the normal critical structures. And the structures that are mostly at risk in these areas are the fornices which control memory. And of course, the deep cerebral veins, which can cause venous infarct, if one is not careful and injures these structures. So what you're looking at here is a top view of the lateral ventricular system of Professor Rhoton's beautiful dissections. And later in the lecture, I'm gonna show you how to open the deep black box that we call the third ventricle. And this is a fascinating area. This is literally the center of the brain if you will. And of course, there's many routes to the ventricular system that you can see here. There's the anterior transcortical or anterior interhemispheric transcallosal approaches, subfrontal translamina terminalis approach. You can come in laterally into the atrium and temporal horn. Of course, there's posterior interhemispheric transcallosal approaches as well. So let's start with this example. This is a lesion here you can see in the right atrium, enhancing lesion. This turned out to be an atrial meningioma. She was having a trapped temporal horn. So we went ahead and did a simple transcortical route. We take the shortest route to the lesion and you can get there into the ependyma. You can visualize the ependyma that's here in the ventricular system, and basically you come around it extra capsulary. And these tumors will be fed by the arteries from the choroid plexus. So you can see this was adherent to both ends of the choroid plexus. And once you devascularize it and detach it, you can detach and deliver this tumor through a small opening. Now, I generally prefer to use a single blade retractor, and there's not much retractive forces here. It really is just brain holding. It's keeping the corridor open, and I know how some people have advocated fixed tubular retractors I generally don't like fixed tubes because you're working in a narrow corridor and you can't use the dynamic mobility of the brain corridor to get to deep areas of the target. So having this flexibility, I think makes you more mobile and more versatile. Next slide please. So this was the positioning. It was a lateral position. You could see the entry point was through the superior parietal lobule to get to the deep part of the tumor. And here's the postop scan. You could see the track that was going to the atrium. So this is your standard transcortical approach. Here's another lesion. This was a gentleman who had seizures from this hippocampal lesion that you could see is a cavernoma of the hippocampus. And there's many ways to access this. You can come in transsylvian, you can come and transcortical, or you can come in even supra cerebellar transtentorial as another route of access. In this case, I took the shortest distance to the lesion, which is a lateral transcortical approach. And we did it through this middle fossa craniotomy. And you can see here's the opening. We'll use image guidance to locate our entry point and we'll make a small core discectomy. And the idea here is to enter the temporal horn. And when you enter the temporal horn, you look for the pes hippocampus, which you see here. There's the choroid plexus. So this gives you orientation of where the cavernoma will be. So we'll use image guidance, and then take the shortest distance, make a small core discectomy into the hippocampus. And we can start to see the yellow gliotic tissue. And here you can see here's the cavernoma, the mulberry appearance. And then we'll start to come around it circumferentially using the bipolar suction and bipolar dissection techniques. We'll start to peel the lesion away from the gliotic tissue. And then on the anterior surface, we'll see some small vessels that are coagulated and divided sharply. And this will help detach the cavernoma from the resection bed. And I like to use this suction sweeping technique by just gently retracting the lesion. You can use your suction to gently suction dissect, and then now fully detach the cavernoma for delivery. And so here's the resection bed. This is the arachnoid over the ambient cistern, and then here's the choroid plexus. And here's the rest of the hippocampus that we kept intact. Let's go to the next slide. And here's the postop scan. You can see the trajectory, shortest distance to the target, and he had a complete removal and was neurologically intact. So what about larger lesions? This is a recurrent atrial meningioma that was previously resected by another surgeon, 10 years prior, and had radiosurgery to the residual. And you can see it's now presented as a giant tumor with worsening mental status causing multiple falls and gait ataxia. You could see the tumors occupied a huge part of the atrium, but also embedding into the parenchyma more superiorly. And again, you could see the sagittal view showing the large enhancing meningioma tumor. So this patient already had a previous craniotomy that you see depicted here. And so I used the same incision that the previous surgeon used in the previous craniotomy, and this is the shortest distance to the lesion. So I went ahead and just did a transcortical approach. There's the image guidance confirming the location of the tumor. And so in these large tumors, you wanna make the tumor smaller. So the idea here is to debulk the tumor and then come around at extra capsulary. And when you're working in the ventricular system, the ependyma is your friend. So when you start to see the white shiny walls of the ependyma, this helps you orient the surgeon to where you are. Now, the patient had a previous shunt catheter. You could see the shunt is embedded in the tumor, catheter is not working. So we're just dissecting the tumor away from the catheter to free it up. Again, the ependyma is your friend. And when you see the ependyma you wanna look for landmarks, that'll help guide you in terms of where you are. And one of the structures is the choroid plexus. So once you see the choroid plexus, this gives you an idea of where the thalamus is, where the medial septum would be, where the fornix would be. So these are very important. Now in these meningiomas, the deep feeders again, come from choroidal vessels. So here we are, we're seeing the ependyma, the ventricle, and here are the deep feeders coming from the choroid plexus. This is a redo, so there is a lot of scar tissue in the resection bed. You could see it's more fibrous, so you should use a good pair of scissors and sharply dissect and cut these adhesive bands to help release the tumor. And here's the tumor finally detached and will now carefully deliver it from the resection cavity. And here you can see the temporal horn. Here's the hippocampus. We're looking upside down. This is the hippocampus and this is the temporal horn. And this is the final view of the resection. Seeing the nice ventricular surface of the lateral ventricle. Here's the choroid plexus. And then here's the end of the resection. Next slide. Here's the postoperative scan. You could see a complete removal, no hydrocephalus. We'd replaced the patient's shunt at the same time of the surgery with a new catheter at the time of closure. Now, this is a different meningioma and a different patient. This patient was a 41 year old male who presented with progressive headaches, a new seizure onset. And in a tumor like this, it's very important to get preoperative visual fields. And he did have a left homonymous hemianopsia preoperatively. So in terms of surgical approach, what would be the best approach here? It's such a large tumor. Some can advocate an interhemispheric approach to the atrium, but it would be very hard to get lateral. Look how lateral it goes, it all goes almost to the surface of the temporal surface. So should we go laterally through the transcortical temporal route? I think those are all potential options. What I eventually decided on was using the longest axis of the tumor and using the long axis of the tumor to guide the resection. So if you come in through this occipital route, you can get to both medial part of the tumor, where it encroaches into the pineal cistern, and then the most lateral portion where it comes towards the lateral temporal surface. So this is done through a lateral position. So what we'll do is we'll put the patient in the lateral position and we'll pick an entry point along the long axis of the tumor. In which case the craniotomy will be this preoccipital keyhole craniotomy. Let's go to the video. So here the door's been opened. You can see the entry point that we're making with the linear core discectomy and we'll go ahead and dissect and come right down on the tumor capsule. And this tumor was a rather hypervascular. There was a lot of feeders coming from the surrounding white matter tissue. So we're gonna start to work around the tumor cauterizing and suction dissecting around the tumor. And then eventually we're gonna enter the ventricles. So here, we're starting to see the ependyma of the atrium, and we'll put a gel foam there to protect any blood from getting into the ventricle as we dissect. We'll continue to come around the tumor very patiently and slowly devascularize the tumor before we start any debulking. And oftentimes it's nice to put these patties in. It gives you a little bulk on the white matter, so you can gently retract the white matter and then peel the tumor away from the white matter as you cauterize. And then we're gonna come around the top part, the top part here, actually, this is the lateral temporal surface. And I often will just put a single blade retractor just to hold the brain up, so it doesn't fall into your view. If you don't use this, the white matter by gravity is gonna fall down and it's hard to dissect there. It'll obstruct your view. So we'll go ahead and debulk the tumor now. And again, come around the white matter. And then now we'll begin to debulk it with an ultrasonic aspirator, and then this will help allow us to further collapse the tumor as we come around it. So luckily this tumor was very soft, you could see it's very fryable, tends to fall apart on you. So you wanna make sure you contain it. You don't leave any small pieces behind Here was one attachment, you saw that big feeder. We just cauterized. And then here's removal of a big bulk of the tumor. And then deeper in the cavity was the another component that we had to dissect away before finally delivering it. So here's the final view. You could see here's the lateral ventricle, here's the choroid plexus, the ependyma and then here's the temporal horn, looking into the lateral ventricle. So I often will put an endoscope in here as well to look around and then on a big core discectomy, I'd like to just plug the opening with a piece of gel foam, just to prevent any fluid causing any subdural hygroma. Let's go to the next slide. Here's the postop scan. You can see a nice complete removal. Interestingly, this tumor was a grade two atypical meningioma. So I tend to send these patients for radiation therapy, even when I have a gross total removal. I just think these tumors are very aggressive and have a very high chance of recurrence. And then here's the three month postop scan. You could see the cavity is nicely healed, and we were able to preserve this lateral temporal surface by using the trajectory through the occipital route. So he did have a preexisting field cuts, so that remained unchanged. So let's move on to the lateral ventricular system. We've been talking about transcortical approaches, and I'd like to change directions and talk about the transcallosal approach. And I'm a strong proponent of the transcallosal approach because it's a natural corridor to the lateral ventricular system. You don't have to transgress the cortex. There's a lower risk of postoperative seizures. And when you have a big tumor like this central neurocytoma that occupies both lateral ventricles, almost from the frontal horn to frontal horn, you don't wanna take a transcortical route because the transcortical route is rather oblique and you'll favor the ipsilateral side, but you'll have a difficult time looking cross court to the other side. Whereas on the transcallosal approach, it's an equal opportunity approach. So you have access to both lateral ventricles. Now, when I started using this approach, I was doing this in the supine position and the supine position is favorable in the sense that it really keeps you oriented to midline. The major disadvantage that I've found using the supine position is that you often have to retract more to get to the interhemispheric fissure, especially when the brain is full, like this one. So I've since converted the supine into the lateral position. And the lateral position is great because the gravity allows the frontal lobe to fall away from the falx so that you can open up the inner hemispheric fissure arachnoids and find the pericallosal arteries relatively quickly without using any fixed retraction. The disadvantage of the lateral approach is that it is more difficult to see the ipsilateral lateral ventricle, because you're trying to look downwards, but it's easier to see the contralateral lateral ventricle. And I'll often use a self retaining retractor to hold the falx and the mesial contralateral frontal lobe upwards to increase that width of the corridor. So if I have a tumor like this, which side should we position up and which side should we position down? So, like I said, I find it easier to see more of the contralateral ventricle looking cross court. So in this situation, more of the tumor is on the left side. So for those reasons, I'm gonna have the left side up when I positioned this patient. So the right side is down here. This is the left side. This is the right side. So now you can see by gravity, it's really easy to open the interhemispheric fissure. Look how the arachnoids open up nicely by traction with gravity assistance. I did put a ventricular drain in upfront intraoperatively, and that really releases the CSF pressure to allow you to enter this corridor. We find the corpus callosum and you typically will do a callosotomy anywhere between two to 2.5 sonometers. In this case, I measured the postop scan. It was actually three sonometers and it's actually well tolerated in patients. So there's the lining of the ependyma of the left lateral ventricle. And then we're now dissecting the ipsilateral fornix away from the tumor capsule. And you can see it's very adherent. Most of this tumor was pre-forniceal. It was preseptal. And so you have to be very careful where the fornix are and the tumor was pushing the foramen of Monro on the left side all the way down into the third ventricle. So here's the final view you could see. There's the choroid plexus on the left side. There's the choroid plexus on right side. There's the right foramen of Monro and you can see the fornix is intact here. And then there's the third ventricle. This is the third ventricle, and everything's nice and pristine. Both fornices are preserved. And I like to use an endoscope at the end to look around the corner to make sure there's no hematoma that's left behind and make sure there's no tumor that's hidden around any corner. So you could see this as a nice view of the ventricular system. Next slide. And this is a complete removal. This is a case we just did three days ago, actually. And the patient's memory is intact. He's recalling three out of three and he's gonna be discharged today, actually. So this was a very, very gratifying case, very risky though, in terms of injuring the fornices. So you really have to be very careful when you get to the bottom of the tumor, so you don't injure them. So it's very important to use that those fine bipolar forceps and dissect the lesion away from the fornices.

- Hello Jim very well said. I really liked your pearls of technique on that case. Number one, that cross court approach is just critical that to able to come from the left to right when the bulk of the tumor is in fact on the right side. It's the same principle as transsphenoidal surgery. People don't talk about that enough. The second thing is the most commonly residual tumors just underneath the corpus callosum. It's that operative blind spot that you wanna be very careful about. So when the pearls of the technique, just like you very well mentioned is that cross court approach. And then really investigating just the underneath of the corpus callosum each see laterally more effectively to make sure there is no tumor left. And obviously, have to be very careful dealing with the ependyma. There is some forgiving this with the ependyma. So you don't wanna leave a lot of sheet of the tumor. Obviously, you have to leave some on the fornices if it's very adherent, but I think being able to do a gross total resection of tumor safely is very often possible. Don't you think?

- Yeah, I think so. And oftentimes if the tumor is adherent to the ependyma I'll use the technique where I call it the touch and go, where I just sorta touch the bipolar just to weaken the tissue, so you can vacuum it gently and just take off that superficial surface off of the ependyma layer. Kind of like when you're doing an ependymoma that's adherent to the floor of the fourth ventricle where you just micro sectioning that layer of tumor cells off of the floor.

- Yeah, it's like the bipolar morselizes the tumor. And I put a bipolar in a higher sort of voltage to be able to be more aggressive with a tumor. And that the difference between what the tumor responds to the bipolar and morselization is very much clear for a tumor versus anything in the pretumoral area. So really their reaction of the tumor to the bipolar is such a good like navigation technique for you to be able to additionally remove the tumor, especially in the ventricles. And it's such a soft way and non traumatic or a traumatic way to remove the tumor. Use the bipolar, morselize the tumor between your tips and then use this suction to evacuate it and just repeat that continuously. And it really works well on tumors that are somewhat a little bit firm and somewhat gelatinous.

- Okay, great points. Great points, Aaron.

- Thank you.

- So this is exciting. I love the ventricular surgery. It's just beautiful anatomy. It's really the soul. It's the center of the universe, I like to call it, especially this next topic. We're gonna change directions and talk about the third ventricle. And the third ventricle is located deep in the brain and it's surgically difficult to access. There's a lot of critical structures and there's really no consensus on the best approach. As you could see, this diagram shows all the different routes to the third ventricle. And when you first talk about the routes of the third ventricle, there's two schools of thoughts, microscopic surgery or endoscopic surgery. And the endoscopic techniques traditionally have lower rates of post-operative morbidity. But I would argue that it has higher rates of tumor recurrence and largely because of the technique, because it's mostly a one-handed surgery technique and you're just debulking, and you're not using two handed microsurgery where you're carefully peeling and dissecting these critical vessels and neural structures off of the lesion. This is a meta analysis we published some years ago, looking at the endoscopic versus microsurgical resection of colloid cysts. And what we found is that microsurgery had a lower recurrence rate, why? Because you had a higher gross total resection rate than the endoscopic series. And although the microsurgical series did have a higher morbidity rate than the endoscopic group. And if you looked at the microsurgical group, the transcallosal group had a lower morbidity than the transcortical group. And I think mostly because you're not violating the cortex. So when you do a transcallosal approach, it's a nice natural corridor between the two hemispheres with a lower incidence of seizures. And so when you get into the lateral ventricle, now you have three options of getting into the third ventricle. So after you do the transcallosal or transcortical rather, you now have three options, you can go transforaminal, which is right through the foramen of Monro, you can go subchoroidal or alternatively super choroidal which people have grouped together as transchoroidal, going through the tela choroidea, or you can go interforniceal, which is between the two fornices. So here's an example of this large colloid cyst. You can see, you can come in transcallosal in the supine position, and once you drop into the ventricle, how do you know which ventricle you're in? Well, again, I said, look at the choroid plexus. I think of the choroid plexus as the yellow brick road, like in the "Wizard of Oz". So I tell the residents follow the yellow brick road, but what I mean is follow the choroid plexus. So you follow the choroid plexus. It will take you to the foramen of Monro, and you could start to see the venous structures. So once you see the septal vein and the thalamostriate vein, then in the fornix, you will know you're in the right lateral ventricle. And if you see the mirror image of this, then you know you're in the left lateral ventricle. So that's how you get oriented. So again, if you're doing a transchoroidal route, you would go through the choroidal fissure to get into the third ventricle. And this is how you can widen the corridor. Now, I don't use this approach. And the reason why is I don't like it because it's not quite a pure midline approach, it's a slightly oblique. It helps you look contralaterally to the other side. And you tend to have a blind spot here in the ipsilateral third ventricular wall. So you could leave some things behind there. And alternatively, this is the interforniceal route depicted in this diagram. And this is the approach that I tend to favor, and I call it the road less traveled, because this is an approach that's largely been abandoned because of the risk to both fornices, which is a real risk. You can injure the patient and they could have memory and cognitive issues and can impair their quality of life. However, the major advantage I believe is that it's a pure midline approach. So you have equal access to both sides of the third ventricle, and if it's done properly and it's done carefully, you can gain so many advantages from this. And I'll show you a series of cases in the next line of videos here. In this picture, though, you see there's retractors being used on the fornix. And this is probably why patients got injuries after this kind of approach. If you look at the diagrams that are in the atlases, there's a lot of retractions that is used. Even in the original article, by Busch in 1944, you see a big retractor here, retracting on this fornix to get into this interforniceal choroidal. So how can we avoid injury to the fornices? How can we make this surgery safer and more effective? Or should we just abandoned the interforniceal approach altogether? And I've been working on this approach for the last 15 years or so, and I've come to really, really like this approach. And I think, again, the major advantage is that you have a pure midline access, and I do this in the lateral position now, and the lateral position again, gives you that gravity assisted opening of the choroidal, and it can sometimes open up this interforniceal corridor as well. And so when you position the patient in the lateral position, one technical pearl is I often will position the patient's head. So it's not pure lateral, but you have to think of the falx, the falx angle to the horizontal floor. You wanna make sure that the falx is roughly 20 degrees, 20 to 25 degrees from horizontal, so that when you're sitting down in the surgeons position, your line of sight is looking down the barrel of the interhemispheric fissure. And that'll be very helpful for surgeons comfort and surgical ergonomics. So here's that angle of the falx, roughly about 25 degrees from horizontal. When you do the bone flap, you should take the bone flap across the midline. And I often will just drill a pair of burr holes directly over to the sagittal sinus, strip the dural laterally to it, so the sinus is not injured. And then you can turn the bone flab. And by uncovering the superior sagittal sinus, this allows you better access to the interhemispheric fissure. So when you open the dura in a C-shape fashion, and you reflected towards the midline, you can mobilize that sinus. And just those few millimeters of space makes a huge difference in terms of your ability to work in these tight spaces. So we have to try to preserve the bridging veins. Sometimes you try to predict them on the image guidance, but when you see veins like this, you have to protect them. If you sacrifice them, there can be a risk of venous infarct. And I've seen several of these, unfortunately. So you have to be careful. If they start to leak by stretch or if they start to bleed, just build a gel foam dam around the leaking part of the vein. You can basically just put pieces of gel foam. So it just wraps around the vein. Sometimes you can the dura in such a way that it comes around the vein so that you get better access to the corridor. In rare instances I've had to extend the bone flab more anteriorly, so I can work anterior to these veins. But try to preserve these bridging veins as much as possible. Then you identify the pericallosal arteries. Don't be fooled by the colossal marginal arteries because they can be, you look for the cingulate gyrus, which is yellow. How do you know you're at the pericallosals? Look for the shiny white of the corpus callosum. Then you confirm that these are the pericallosals, work between the paired vessels, widen this corridor to see the corpus callosum. And then you can go ahead and make your callosotomy. And I generally will use image guidance and I'll plan the craniotomy. So I have the correct trajectory to the target, and you can make a callosotomy two to 2.5 centimeters. And again, the choroid plexus will help determine the latter reality of which ventricle you've entered. And if you need to, you can open up the septum pellucidum and perform wide fenestration. So you have equal access to both ventricles in both foramen of Monro. So you get this type of view. And then how do you define the interforniceal plane? This is probably the most difficult part of the surgery. If you look at this diagram, notice how the fornices get farther apart, more posteriorly. So more posteriorly, there's a potential space that you can land. If you go between the two leaflets of the septum with or without a cavum septum pellucidum, you can generally find this plane that's right here, and then start to separate those leaflets of the septum pellucidum, which will eventually take you to the fornix. And then you'll see a clear grayish membrane. And you keep inline with that membrane and you'll start to open it. And then you'll eventually enter the layers of the tela choroidea which formed the layers of the velum interpositum. What is the velum interpositum? It's this potential space that houses the internal cerebral veins. And it's formed by two membranes the superior membrane of the tela choroidea and the inferior membrane of the tela choroidea. And once you bust through the inferior membrane, you will start to see the choroid plexus. And then you will be in the true third ventricle. And then you expose your tumor and then you can remove the tumor. So let's look at some videos here. Now that we've gone through the chalk talk, here's the final inspection. You could see two choroid plexuses. I always look for both fornices, both choroid plexuses and both foramen of Monro at the end of the surgery. And this patient had this large colored cyst that was nicely removed and his memory was intact and he went back to work. So this is a larger one. This is a 49-year-old female. She was shunted for hydrocephalus. She presented with hydrocephalus with a colloid cyst at the center she was treated at they wanted to shunt instead of treat this, but it started to grow. So shunting is only a temporary measure. The thing about shunting is you lose your opportunity of your choroidal. So once you shunt the patient, you've collapsed your choroidal and you make the surgery a lot more difficult. So now you're working with small collapsed ventricles with this growing tumor, growing colloid cyst. We'll go ahead and take her and do in the lateral position, take the craniotomy across the midline. Let's play the video. So now we're working in the interhemispheric fissure. You can see the gentle traction on the mesial frontal lobe. You can see the arachnoid bands using scissors to spread and then cut sharply and we'll identify the pericallosal arteries. I'll then take a to spread carefully the arachnoid to spread the two pericallosal vessels, and then find the midline. We'll do our callosotomy. And then we'll eventually enter the lateral ventricle here. Here's the shunt catheter in the lateral ventricle. And now we're gonna identify where that interseptal plane is. So what you're looking at is the cyst pooching through the foramen of Monro. Now you can go through the foramen of Monro, but this thing is huge. And I didn't think it was gonna be big enough or big enough to deliver through the foramen of Monro. So what I'm doing now is I've developed the interforniceal plane. There was a nice cleft between the two fornices, and I was able to separate it using these fine bipolar forceps. And now I've entered the tela choroidea. You saw the inferior membrane there. Now this colloid cyst interestingly was in the velum interpositum. It was not in the third ventricle. It was sitting in the velum interpositum, which I think they often do. And so you can see it was invested between the two arachnoid membranes or the tela choroidea. So we try to keep the turgor of the cyst intact as much as possible, but at some point you have to pull the trigger and you have to puncture the cyst to decompress it. So once you do that, as you dissect around it, the cyst will slowly leak as you're dissecting around it. And you need to do that, otherwise you'll cause injury to the surrounding critical structures, and you must ensure that it is fully detached from all the choroid plexus attachments. So you don't averse any structures. And then you can nicely deliver this large colloid cyst from this interforniceal corridor. And now we'll inspect. Here's the left foramen of Monro. There's the basilar artery. This was a third ventriculostomy. The lesion had made a third ventriculostomy. There's the floor of the third ventricle. And then there's the other foramen of Monro. You could see both fornices are intact. And next slide. And you can see here's a complete removal of the colloid cyst and the patient was neurologically intact. And she was able to go back to work with intact memory. No deficits.

- Very nice technique. One thing that I have come to realize that helps me again, that everyone can use it at their own discretion is that I coagulate the septal vein and disconnected from the thalamostriate vein, and then expand the foramen of Monro posteriorly. We call it the transcallosal transforaminal transvenous approach. And this way you're really believing the thalamostriate vein intact, sacrificing step away in which we have never had any issue and using the foramen as part of your interforniceal dissection. So essentially you do a transforaminal slightly transchoroidal and through transchoroidal approach. It works beautifully and maybe the dissection is slightly less, but that's just the variation of technique that has worked for me, Jim.

- Yeah, I know, that's a very, very good option as well. Like I mentioned before, there's so many options you can take. And I think ultimately you take the best option. I think that the lesion gives you, but of course, you take the option that you're most comfortable and more experienced with. And I think that's a very good, good option as well. So here's another patient. This is the patient with acute hydrocephalus presented with Takotsubo cardiomyopathy. So hydrocephalus and ICP can cause some heart failure issues. So you have to be careful. You got to put an EVD in these people right away or otherwise they can go sour rather quickly. And again, this was done through the interforniceal approach. We ended up shunting her first, so we can have her heart recover. And once she recovered, we took her back to surgery to take the cyst out. Here's another one. This was a cyst that was aspirated stereotactically by another surgeon. And I show this to show you that cyst aspiration is not a definitive treatment. The cyst continued to grow, and he's been recurrence free for almost 10 years now, since we've definitively removed this colloid cyst. So here's a central neurocytoma of the third ventricle, a little unusual pattern of growth, but sometimes they can occur in the third ventricle. And here, you'll see, we've come in. This is the right foramen of Monro. This was done when I was still doing supine positions. There's the left foramen of Monro. You could see it's rather distorted, but you could see the left choroid plexus on this side. And then we were able to take out the tumor and here's the basilar artery. This is the natural third ventriculostomy that's formed after you take out the tumor. And then here we are looking at both fornices. Here's the right fornix on the right. This is the right choroid plexus right here. This is the right choroid plexus. And then here's the left foramen of Monro. Here's the right foramen of Monro. And then here's the final view of the interhemispheric fissure. Here's the pericallosal artery, and here's the postop scan. This is an interesting case. This is a dual lesion. I don't know if you could see this. There's a lesion here and then a colloid cyst here. Very unusual. I wasn't sure what this was, but he was symptomatic from this unilateral obstruction. Let's play the video. So this was done through interhemispheric approach. Here we're again, opening the inter pericallosal choroidal. Here's the callosotomy dropping into the left lateral ventricle. So this is the tumor in the left lateral ventricle. You can see it's rather avascular. It doesn't enhance on post gadolinium. So my suspicion was that this was probably a sub ependymoma, which it was confirmed on pathology, but we're using sharp dissection here. You could see very gentle looking for those adhesive fibers from the tumor to the septum pellucid. I mean, you can just gently peel it off the septum pellucidum without taking down the septum pellucidum and losing that counter traction of the plane. Then we'll come around it here. You could see it was slowly just peeling it away. Using the tips of the micro scissors. Using what I call a snip and peel technique, very gentle. And then here's the foramen of Monro on the left side. And then you could see it's not involving the fornix, which is good, a lot less riskier. And then you could see where the point of attachment is, the point of attachment is actually on the floor of the lateral ventricle. And here's that snip and peel technique, just using the tip of the blades of the scissors. And you could see it peels off nicely, and then we can deliver this subependymoma as one piece. And now we're gonna go after the colloid cyst. Here you can see there's the cyst. The cyst was not really presenting itself to the foramen of Monro. Sometimes you'll have these colloid cysts that are residing rather superiorly, and it's actually in the blind spot. It's actually behind that fornix. So in those situations, I find the interforniceal approach, rather versatile because if the cyst resides in the roof of the third ventricle between the tela choroidea membranes, then the interforniceal approach is the better approach. You can see here's the foramen of Monro. You see the cyst pooching out here, but we're able to open up the interforniceal corridor here and deliver the tumor from the top, or at least dissect the tumor from the top. This is the tela choroidea here. Some choroidal vessels here, and we're able to peel this tumor away from the contralateral fornix and we'll work in two corridors. We can work in this interforniceal corridor and work in this foramen of Monro corridor. So we have two corridors to work with. So I've delivered it and I pushed it down into the foramen of Monro. I put a little gel foam here to help keep the cyst down. And this is how I was able to bring the cyst down through the foramen of Monro, as opposed to trying to pull it from below through a single transforaminal corridor. So this is a combined interforniceal transforaminal approach. And again, these cysts, this is what you can't do with an endoscope. You can't do this very fine dissection, careful dissection to preserve the internal cerebral veins, detaching it from the choroid plexus. So this is the technique that you get from doing microsurgery. So here's the interforniceal corridor. Here is the foramen of Monro corridor. Let's go to the next slide. And here's the postop scan. You could see complete removal, no shunt, and the patient was neurologically intact. So let's change directions. We talked about anterior third ventricle lesion, but what about these posterior third ventricular lesions often are intertwined with pineal region lesions. There's different approaches to get there. And of course, the traditional supracerebellar infratentorial approach. Alternatively, the interhemispheric occipital transtentorial. And again, you could do a posterior transcallosal approach. And my favorite approach is this interhemispheric approach. I just find that it's just a natural line of sight. And I do this many times with colloid cyst that are sitting right here, but if you just change the angle of the microscope, you can use the same craniotomy and look backwards right at this post to your third ventricular lesion rather easily. So here is the beautiful Rhoton picture. And what's important to see here is this is the third ventricle. This is the posterior commissure. And then behind here, you see this calcification here. This is the pineal gland, and this is what you're gonna look for at surgery. Again, you can see in these diagrams, the use of fixed retractions for these fornices to get to the posterior third ventricle, using these retractors. We can do this now using the retractor list technique, and I'll show you some tips on how you can do that. Again, the lateral position which we talked about, this is the corridor. I use image guidance to form my hypothetical cone of corridor, working in these directions with different lines of sight, to get to the posterior third ventricle. We can go interforniceal. You can see there's the tela choroidea, preserve these internal cerebral veins. And then we can take out the tumor and you can see at the end, these are the leaflets of the septum pellucidum. And then at the base of these leaflets is the body of the fornix. So you can see, you can preserve these fornices, but by working posteriorly, the hippocampal fissure gives you that extra space to safely split these two fornices. And so let's take the example of this tumor. This was a papillary tumor in the pineal region presenting with hydrocephalus. Let's play the video. So we're gonna go ahead and again, open up the interhemispheric fissure using bipolar spreading, spreading the arachnoid. Now you have to do a wide splitting of the fissure, just like you do for an aneurysm of wide sylvian splitting. You should do a wide interhemispheric splitting because everything falls away from the falx and you get this beautiful space. We'll, then drop into this plane. We luckily dropped right into the two leaflets of the septum here. Sometimes you get lucky and you drop right into that space. You can see how it has that clear gray membrane. And you could see the tela choroidea there with the little choroidal vessel running through it. And there's the two leaflets of the septum pellucidum. So we're gonna open up the tela choroidea, get into the vellum interpositum and eventually get down to the tumor. So now we're gonna divide the tela choroidea. The internal cerebral veins have been displaced laterally here. So when you're working in this interforniceal corridor, you're working between the internal cerebral veins and by gently spreading them, it'll naturally fall away and you get this beautiful view of the tumor. Now we're gonna work on the tumor. And again, you can see we're not retracting these fornices like in those diagrams, in the textbooks. This is all working with just dynamic, gentle in and out entry. You have to be careful as you're introducing instruments in and out of this narrow corridor. I gently, I try to be very careful with the use of the bipolar, that the tips only touch the tumor and not the fornix. And towards the back, you're gonna get feeders that come off of those medial posterior choroidal feeders, and you'll devascularize those, and then detach it sharply to peel it away from the cavity. Again, here's the retractorless interforniceal corridor. There's another corridor feeder, going to this tumor. And then I like to use the fine bended forceps they are a lot thinner and finer to fit into this smaller corridor. And I generally, like to use those more than I use the bipolar forceps. So there's the view of the third ventricle, the body of the fornix. And then there's the cerebral aqueduct and the posterior commissure. You could see more posteriorly here is the pineal recess. And then inspection. You could see there's the left choroid. There's the right choroid. Here's the fornix, the other fornix was there. You could see the fornix here and the fornix there. So it's both intact. And here you can see, I leave a catheter in. I've actually stopped leaving EVD catheters in because I noticed that I usually just take them out at 24 hours anyhow, and I've hadn't had an issue. So I've stopped leaving catheters as long as the cavity is dry at the end of the surgery. Next slide please. So here's the postop scan complete removal. Patient was neurologically intact. Let's look at this lesion. This was a patient who presented with acute hydrocephalus. This is a non enhancing, but flare, a bright lesion. This ended up to be a pineal cyst. Now most pineal cyst I've observed, but rarely have I operated. And this is one that I did operate on. Let's go to the video. This one actually presented with acute hydrocephalus. And since it was in the posterior part of the third ventricle, I decided to come in anterior transcallosal interforniceal. Again, the same dissection that you see. Spreading the two hemispheres. Spreading the two pericallosal arteries to see the shiny white corpus callosum. We'll then do our callosotomy. Now we're gonna drop into the ventricle here, which ended up to be the contralateral ventricle. So we need to find the septum. You need control of the septum because you need to have equal access to both ventricles. And it's good to debulk the septum a little bit down to the base. And as you get closer, you go between the two leaflets of the septum. This is the intercept splitting technique using these fine bipolar forceps. Look for this gray tissue here. You see this gray tissue, that's the potential space that membrane between the two leaflets of the septum, which take you down to the two fornices. And now we'll start to see the CSF coming from the third ventricle. We've entered the tela choroidea, There's one internal cerebral vein there. And I've been lately using these, what I call these Biocol dams. This is a collagen substance. This is not gel foam. And I advise against using gel foam 'cause gel foam sticks to the tissue. And so at the end of the case, when you're taking the gel foams out, they tend to rough up the surfaces of the neural tissue. Whereas this Biocol material, when you remove it, it does not adhere and it creates a nice spacer if you will. It holds up the space as you're working. So they're kind of like placeholders for this interforniceal corridor. So we've gotten control there. You saw we've got control of the posterior margin. We've got control of the anterior margin. So now we can begin to dissect around the tumor. Again, I keep the cyst turgor intact as much as possible to give me that counter traction to dissect, but eventually you pop the cyst and then once the cyst is popped, it does become a little more challenging because now you're working with a flimsy empty bag of tissue. And so we'll have to dissect around it. And now it tends to be adherent here to the walls of the third ventricle. So you could see there's some neural tissue right next to the cyst wall. So you use micro scissors to sharply dissect, and then here's the posterior commissure, there's a little band of neural tissue that has to be dissected away from the cyst wall. So there's the tech mentum of the midbrain posterior commissure. You can see we're carefully peeling that cyst wall from the neural tissue there with these fine bipolar forceps. We've detached it now from the floor of the third ventricle. And the remainder now is attached to these arachnoid and vessels in the pineal recess. And it's attached to the pineal gland itself. You could see here's the calcification from that pineal gland. And so this is a pineal cyst. This is where it originates. So we'll coagulate it and then divide it sharply to then remove this component of the pineal cyst. And there it is coming out through that interforniceal corridor, And then I'll inspect at the end, get a nice view of the cerebral aqueduct posterior commissure Here's one fornix. Here's the other fornix. And then we'll take one more look with these gentle spreading of the forceps to look at the floor of the third. And then there's the foramen of Monro. That's the right side. Here's the left foramen of Monro, and there's the ventricular catheter that was existing there before. And then we recharge the CSF with some saline. And I always like to put a little gel foam dam. I don't know if this works, but it makes me feel better. I use it so, to prevent any hygroma from coming around the convexity. So I put it right over the callosotomy. You have to size the gel foam big enough, so it doesn't fall through the callosotomy defect. Let's go to the next slide. So here's the a three-month postop scan. You could see a nice, complete removal without requiring a shunt. Here's another example. This is a third ventricular ependymoma, complete removal. And this was an interesting case. Look at this lesion. This lesion was originating in the cerebral aqueduct itself. You could see it's going through the cerebral aqueduct. This was biopsied by another colleague with an ETV and the tumor continued to grow. You can see it's a lot bigger. Now you could see it's now protruding from the third ventricle into the fourth ventricle. So it's going through the aqueduct. So we're gonna do what's called a trans aqueductal approach through this anterior transcallosal corridor, my favorite corridor. And you could see we debulked the tumor. I left a small remnant of tumor stuck to the aqueduct, but we were able to get a nice removal. This ended up to be a Rosette-forming glioneuronal tumor. And he's been in recurrence free for about six years now, doing quite well. So let's take a turn for our last category. The fourth ventricle, and the approach I like to use is this telovelar approach, shown in this nice Rhoton Atlas going through these cerebral modularity, tonsillar uvula fissures, and it opens up this corridor widely so that you can look all the way up into the cerebral aqueduct. So here's an example of this fourth ventricular ependymoma entering both going into both CPE angles. And here's a still image showing the tumor within the cisterna magna. We opened up the membranes of the arachnoid. Here's the tumor underneath the tonsils. This is the console here. This is the tonsil here, and there's the tumor being peeled off the floor to the fourth ventricle. Here's PICA being preserved. And then here's the view of the cerebral aqueduct. Look at this view, looking straight up. This is without opening, without splitting the vermis. And the beauty of this approach is that you don't injure the vermis and you don't get the risk of cerebellar mutism. And then here's the floor of the fourth ventricle. You can see the tumor was a little bit adherent. This is an ependymoma, and I use the bipolar morselization technique that Aaron had alluded to earlier. And you could see here's the nice view of the fourth ventricle, just like the Rhoton Atlas picture. Here's the complete removal postoperative scan, and I'll have two more cases to show. This is one of a subependymoma arising from the rhomboid fossa. This was growing on serial scans. So we went ahead and did this through a traditional midline suboccipital approach. You take off the atlantal occipital ligament, take off C1, and then you get the cisterna magna. Let's play the video, please. So we'll go ahead and open up the arachnoid. We work cross table with your assistant, with the microscope. And I like to stand on the left side of the patient as a right-handed surgeon. That's just more comfort for me. There's PICA, there's the tumor coming out through that subtonsillar space. And so we'll go ahead and open up this cerebella modular fissure. You can see there's some arachnoid. All you have to do is follow the PICA. There's a little arachnoid membrane, overlying it, open up this tela choroidea here and the velum, and that will open up this space. If you need to, you can open up the tonsillar uvula fissure that will give you wider access. So now we'll begin to develop the plane around the tumor, and it's very important to try to preserve all these small vessels on the brainstem, as much as possible. Try not to coagulate. These don't look like tumor feeders, they just look like a feeders on top of the brainstem. And so we'll go ahead and debulk the tumor. It's always important to remember where the floor of the fourth ventricle is. And it's important to remember that on the bottom part, the floor of the fourth ventricle will dive anteriorly and that's an important nuance to remember. So we're gonna carefully dissect the plane here and then come around it laterally using these fine micro bipolar forceps. And then further debulk the tumor to make the tumor smaller, to make it more collapsible. Now, at some point, we're gonna go around the top of the tumor and here we are, we're going over the top of the tumor, dissecting these arachnoid bands, getting it off of the uvula. And then as we find the floor of the fourth ventricle, we'll put some Cottonoid patties to protect the floor. You can see the interface here looks rather adherent to the fourth ventricle. So we'll come back to that a little bit later, once we get rid of the bulk. There's the choroid plexus. This is a good landmark to have. it means we're right at the top of this tumor here. And as we come around it, we'll start to see the ependymoma. So there's the floor of the fourth ventricle now. So that's a good landmark to have. It actually creates more space for us, and you could see there separation of the tumor capsule from the floor. So now I can put a Cottonoid patty in there and then be a little bit more aggressive to debulk it. 'Cause now I know where the floor is. I know the depth of where this is, where I won't injure the floor and I'm gonna lift up the tumor and advance the Cottonoid patty so that I have a buffer of protection so I can keep debulking. So you wanna debulk what's easy to hard, right? Debulk what's easy and then save the most difficult part for last. The most difficult part in this situation is the point of adherence of the tumor. What's interesting is the point of adherence of this tumor was right on the rhomboid fossa on the inferior part, right over the hypoglossal trigone. So it's important to have neuro monitoring. I had the 12th nerve monitor, the vagus nerve monitor. and you can see this is the last point attachment here, and look how you can still separate it. You can still find a plane and I'm listening for the nerve monitor. I'm listening for the 12th nerve. And it would go on and off kind of like your facial nerve when you're doing an acoustic, but you just give it a little break. And I know I'm not injuring it. I can see the plane here and I can use this nice delicate patty, which is a nice delicate patty to slide right in here and help me separate this last bit of tissue. That's right on the rhomboid fossa. And I can remove this last piece of tumor. And so here's the final view you can see, this was the point of adhesion. You could see this is where it was adhesed. And then this is the final view, a gross total removal in a dura patch. Next slide please. So here's the final view. You could see a gross total removal. Patient was neurologically intact. And I think this is my last case here. This is a cervical modular tumor, brainstem tumor that not quite in the fourth ventricle, but it's important to use a fourth ventricular approach to get to this. You can see the brainstem is severely compressed by the tumor and here's the rim of the brainstem and spinal cord. You can see it's pushed anteriorly. So we'll go ahead and do this nice telovelar approach. Let's play the video. So we'll open up the arachnoid over the cisterna magna and expose the tumor. I thought this was going to be a JPA. This cervical medullary tumor. It ended up to be a ganglioglioma. So you can see cervical medullar ganglia gliomas, probably less common than JPA's. There's the frozen section. And as I started to inspect this tumor, there's the 11th nerve. There's the 12th nerve rootlets on the right side. I noticed that this tumor didn't have a great plane apart from the spinal cord. And so this became a bit dicey. What you see here is this is the rhomboid fossa here. This is the middle cleft. This is the rhomboid fossa, and here's the tumor along this side of it. And so once I determined that there was not a good plane here, I had to be a little bit more conservative. And so what I did was I developed a pseudo plane. So there's no clear plane between the tumor and the spinal cord. So you create a plane, you create a pseudo plane, and then you leave a little bit of microscopic margin of tumor on the normal cord. And then you take out the bulk of it. So you debulk the tumor. So I'm making core discectomy here along the lateral part of the tumor, close to where that, where I suspect that cord tumor interface will be. And then I can see the normal spinal cord tissue here. And there's no clear plane, not like ependymoma surgery, where you can see a nice plane between the tumor and the cord. Here it's just adherence. And so I'm just using sharp dissection, using scissors to create this plane being very careful. And every snip is like a decision you have to make, you have to decide, I'm I cutting into a safe zone? And you have to use your visual inspection and use your neural monitoring as your guide, and then use your tactile feeling of the tissue. Whether it feels fibrous like the tumor or softer like the white matter of the cord. And you can see there's a little subtle interface there that I don't know if you can appreciate on the video, but certainly at surgery, you can appreciate it. And so once you develop this pseudo plan, you can start to debulk the exophytic part that you've dissected away from the cord. So that here's the final view. You can see there's some normal white matter here. And then probably some microscopic tissue here is my guess. Here's the obex and the fourth metrical and the neuro monitoring. The motory-evokes remain stable throughout. Here's the vertebral artery and the 11th nerve. And then here's the final view. You could see surgical cavity, little lining it up with surgicel. And let's go to the next slide. So here's the postop scan. This is the immediate postop scan. You could see on the, I get the fiesta sequence. You can see there's a little bit of white thing. There could be residual tissue is my guest, but you don't really see it here, but in any event she did quite well. She had a little sensory proprioception issues, which recovered by three months, but other than that, her motor strength was intact. She's a health care worker and was able to go back to work in the clinic and she's done quite well from this. So that concludes my talk on the ventricular system. I thank you for your attention.

- Beautiful cases. It was really a masterclass in interventricular surgery. Jim, I really enjoyed it, learned a few things. In fact, I think the last case was really one of the toughest ones because the tumor was so much intertwined with the posterior upper part of the spinal cord and the lower part of the obex. So I wanna congratulate you. I really like the handling of the fornices. I think there's such a big taboo about the interforniceal approach, which I wholeheartedly respect. And that's partly related to user retraction, aggressive manipulation, but these days with more of that fine dissection that you showed and the ability to be able to do more within smaller spaces. I always emphasize, as you mature and become more of an experienced surgeon, it's less about operative space and more about operative angle. If you have flexible operative angles, you can do so much more within very small operative corridors that are disruptive to the normal anatomy. And I think that's what you beautifully showed. I bet 10 years ago, 15 years ago, you probably would have needed more exposure to do what you are doing now. And that's because as we gain experience in neurosurgery, we find the limits on this smallest space within our talent to remove tumors. And so I always say the more I sort of gain experience, the more I can do with less operative corridors. I think neurosurgeons traditionally are so careful about having all of their options available in surgery that tend to use a lot more dissection and operative space requirements as part of their strategy rather than operative angles. And that's, I think it's critical to know as we all evolve. I think I really liked the fourth ventricular approach you showed. One comment that I like to make, which is very consistent with what you mentioned is that most fourth ventricular , in fact, all the ones I have done, which is quite a few, don't attach to the proper fourth ventricular floor. They attached to the lateral part of the fourth ventricle not the, and really those almost inferior cerebellar peduncle or the lateral part of the obex. They're never attached directly to the fourth ventricular floor proper. Therefore if you create an middle dissection plane or like an apple, divide the tumor into to just parallel to the route of the fourth ventricle, you can really get most of the tumor out. And then as you showed, even shave off the tumor using the ultrasonic aspirator off of the lateral aspect of the obex and even inferior cerebellar peduncle. So I think those are the things we should remember. I often hear that well, the tumor was adhering to the floor of the fourth ventricle, and I just have not seen that. And just in my experience. What do you think of that? Have you seen an ependymoma that is really adhering to the fourth ventricular floor?

- I mean, I think it's how you define adherence and probably your comfort level of how much next step you want to take. So for example, when we were in training, we were taught to use the CUSA to suck out that last bit that's right on the floor. And I personally, I don't feel comfortable with that. I feel like the CUSA is like a punch biopsy instrument. I really like using scissors. So I like using a fine pair of scissors and just gently spreading and lifting and seeing if there's any like points of adhesions that you can just separate and just loosen the tissue and using the vacuum strength of the suction using the gentle, controlled strength of the suction to lift up, to see if you can create a plane.

- That is correct. So obviously at the end of the day, it's all about judgment. It's all about how you see the tumor adhering to what. But it's important to define where's the exact origin of the tumor rather than assume something preoperatively inspection is so important. With that in mind, Jim, I wanna sincerely thank you for being such a gracious and helpful contributor to the virtual operating room series. And just like before we hope to have you in the future for another one of our sessions. Thank you again.

- Great, thank you very much, Aaron. It was a pleasure to be here today.

- Thank you Jim.

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