Microsurgical Resection of Thalamic Lesions

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- Colleagues and friends, thank you for joining us for another session of the Virtual Operating Room from The Neurosurgical Atlas. Our guest this evening is Dr. Uğur Türe from Yeditepe University from Ankara. He's truly a master of surgeon who has added so much innovative perspectives to complex intracranial surgery. He's a true protégé of Professor Gazi Yaşargil who has advanced microneurosurgery to a new level. He's going to talk to us tonight about most likely the most difficult deep operations we do within the cerebrum and that's resection of thalamic tumors. So, Uğur, I wanna thank you for being with us and very much looking forward to your session.

- Thank you very much, Dr. Cohen. Thank you for your kind invitation. It's great honor for me to be part of this webinar. Thank you. And I'll talk about the microneurosurgical removal of thalamic lesions, and I will share with you my experience with this difficult lesions as another surgeon. Thalamus is part of the diencephalon and consist of two interconnected ovoid nuclear masses and connected with the telencephalon cranially and with the mesencephalon, and rhomboencefalon and medulla spinalis caudally. The term of thalamus is Greek term. It describes the inner most chambers of old Greek house. This is thalamus. And it's commonly regarded as a gateway for all inputs directed to telencephalon, and it plays an important role for somatic, vegetative and cognitive functions. And it may be speculated that the little knowledge of the region and difficulty of surgical approaches are responsible for the conservative attitude, generally shown in the neurosurgical community toward thalamic lesions. Main syndromes in thalamic lesions are raised intracranial pressure, motor deficits, sensory syndrome, involuntary movements and seizures. Thalamic lesions is so-called deep-seated lesions. But the majority of these lesions are focal at diagnosis and amenable for surgical resection. But surgical treatment is still challenging. Vascular, arterial vascular, and venous vascular supply, and the location is difficult. And intraoperative ultrasound and MRI are valuable in the surgery. And of course, intraoperative neurophysiological monitoring is also, may be helpful. Maybe you can see my line here. And I can change the color. Maybe this is better. Yeah, so here is the left side axial section. We can see thalamus here, in the left thalamus. To reach this lesion, general altitude also coming from the lateral. But we have to keep in our mind that the lateral part of the thalamus is full of corona radiata and internal capsule. And we should not go through this way because there are other ways to go to thalamus. The half of the thalamus is covered by internal capsule and the corona radiata. But the rest of thalamus is, we can reach . And there are surgical thalamic soft surfaces that we can use it. As I told you, in the lateral side, we have many fibers, then we should avoid to damage them. This is axial picture, and this is also coronal picture. We can see this corona radiata and internal capsule. This is the lateral border of the thalamus. This is beautiful dissection of Dr. Sara that shows the anterior thalamic peduncle, superior thalamic peduncle, posterior thalamic peduncle and inferior thalamic peduncle. These are the part of the medial side of the corona radiata, and thalamus is really the structures in the middle. And we classify the surgical surfaces of the thalamus in four group. The lateral ventricular surface. In the lateral ventricle, between caudate nuclues and fornix or choroid plexus, we have lateral ventricle surface of the thalamus. And then in the velum interpositum, we have velar surface of the thalamus here. And then cisternal surface, pulvinar. Pulvinar is totally in the system. Pulvinar is in the surface. You can see here. And here also. And then the last part is the third ventricular surface of thalamus. This is the lateral wall of the third ventricle, third ventricular surface of thalamus. So, each surgical approach to thalamus, we have to think about to use these surfaces. This is the main critical issue for me to do thalamus surgery. We have to decide which surface we have to approach. And we published this classification recently. And in this picture, we try to summarize our surgical approaches to thalamus. First one is the anterior transcallosal approach. This one, anterior transcallosal approach. Second one, posterior interhemispheric transtentorial subsplenial approach. In this way, we can reach the pulvinar. It's not posterior transcallosal approach, it's posterior interhemispheric transtentorial subsplenial approach. The third one is the perimedian supracerebellar transtentorial approach. I use this approach in sensitive position. And then the fourth one, very rarely, I use perimedian contralateral supracerebellar suprapineal approach for third ventricular surface of thalamus. So, I will try to show some samples of these approaches to thalamus and discuss with you the indications of these approaches. This is the summary of my talk. And the anterior interhemispheric transcallosal approach, as you know, as I mentioned to you that this is the lateral ventricular surface of the thalamus and we can reach this part through the anterior transcallosal approach. And this is for the superior and anterior lesions, especially anterior thalamic tumors, we can reach with this approach. And when the tumor came out to the surface of the thalamus in the lateral ventricle, we can use this. And no cortical incision, but we have to do some small incision, the corpus callosum, anterior corpus callosum. And this is some virtual cadaveric picture of transcallosal approach. And we can see here, that right side foramen of monro left side in this right side. We have removed caudate nucleus. And we can see the anterior thalamic peduncle and superior thalamic peduncle, and here is the thalamostriate vein, and then choroid plexus, and here is the lateral ventricular surface of the thalamus. We can call it also lamina affixa of thalamus. This is the first case, simple case. This patient, just keeping your mind left is left always in MRIs. This is anatomically correct to me. So, this patient, a young patient, had a severe intraventricular hemorrhage two months ago, and they treat with the external ventricular drainage. And we can see there is some lesion in the anterior, right anterior thalamus. And in the angiography, we can see small AVM, right anterior thalamus AVM. It's supplied by the posterior choroidal arteries and anterior choroidal arteries and also thalamoperforator from P1. You can see that here is the, this is the posterior medial, posterior choroidal arteries. And this is thalamoperforator. And here is the small AVM. This is excellent example for anterior transcallosal approach, I go through the right lateral ventricle. This is right foramen of monro, the right fornix and this is blood clot. And I am trying to see thalamostriate vein and anterior septal vein. I use the anterior transcallosal approach in spine position and patient is in a mid spine position, lateral. So this is right lateral ventricle, and I'm turning around the cavity and here is the border of cavity here and I'm just turning around, there are small vessels. Again, the blood clot here, and this is choroid plexus, right? Choroid plexus there are some blood supply from choroid plexus. And then coagulating that part of choroid plexus . This is fornix, right fornix and choroid fissure here. And thalamostriate vein is here, this is choroid plexus. This is final connection of the AVM. Yeah, I'm checking with the endoscope. This is thalamostriate vein, this was the cavity of the AVM. This is thalamostriate vein here, thalamostriate and right foramen of monro here left foramen of monro here and left fornix, right fornix. And this is right foramen of monro. And here is the thalamostriate vein. This is right fornix, this is choroid plexus. And I am checking with the ICG, the venous system is working. Yeah, here is the thalamostriate vein, here. And right foramen of monro here. And internal cerebral vein. Anterior septal vein here. Okay. Next slide please. Yeah. And this is post-operative MRI here that the AVM was here right side anterior thalamic AVM and the angiography looks normal. And you see also from here the thalamoperforators are gone. And this is early post-operative picture of this patient. As a tumor case, this is one of the typical case. Again, this patient has an external ventricular drainage for acute hydrocephalus in another institution four days ago. And the hydrocephalus release and there is a big tumor in the left... It's not on the anterior thalamus but the tumor came to the surface, this is the main point. If it's in the tumor, in the surface, in the lateral ventricular surface and if the patient has a hydrocephalus, this is a very nice case for anterior transcallosal approach. This is left thalamus. I use always the right craniotomy. And then if it's left thalamus, or right thalamus, I use the right-sided craniotomy, as a right-handed surgeon. So this case I will use, this is tractography of the preoperative tractography we routinely perform. And the internal capsule is always in every case is intact. The thalamic tumors do not invade the internal capsule except of course the gliomatosis cerebri or something. But in normal case, the internal capsule is always lateral border of the tumor. And vascularity of the internal capsule and thalamus is totally different. Thalamus has arterial blood supply from thalamoperforator but the internal capsule, would you please next slide? Yeah. Yeah. And this is the case, this is left thalamus here. This left thalamic lateral ventricular surface of thalamus. My goal will be through the anterior transcallosal approach right side of craniotomy to go to the left thalamus. Left thalamus surgery is easier than right thalamus surgery. This is the surgical video right-sided anterior interhemispheric approach. The separation of the cingulate gyrus is important. And then we have to see the corpus callosum is a white color. And the main important point is the choosing the callosal incision side. I have to choose the correct point to do callosal incision. For this cottonoid is very helpful. cottonoid guided ultrasonography. This is surgical picture. You see cottonoid here, tumor is here So this angle is good angle. So and I go always between two pedicles callosal arteries and I just puncture to corpus callosum separate two fibers of the corpus callosum. And here is the left choroid plexus and this is left thalamus and this is left fornix. I coagulate that part of choroid plexus to have a space to work. And now I have the lateral ventricular surface of the left thalamus. This is left thalamostriate vein. And I just go through the thalamus and the tumor is on the surface, just underneath the appendix of the thalamus there is a tumor, I want to suction. Thalamic glioblastoma are very clear, it has a very clear border and the tissue is different. And if it's sackable with suction, I prefer to use suction because I can differentiate the normal tissue and tumor tissue with suction better. The advantage of transcallosal you see the eight millimeter incision is enough. The advantage of the transcallosal approach, this is now the septum pellucidum. I'm opening the septum pellucidum to have a CSF. This is right ventricle. And then next step to do, this is my incision to thalamus and this is foramen of monro. And I go to the third ventriculostomy. I routinely perform third ventriculostomy. This is you see the mammillary bodies. I do microscopic third ventriculostomy because when you release CSF, it's difficult to do it with endoscopes. So this is basilar artery nerve, here, basilar artery. So I routinely perform third ventriculostomy for then I perform a anterior transcallosal approach, because the main problem, especially in the high grade tumors in the thalamic surgery is postoperative CSF problems. So we have to prepare this third ventriculostomy for any CSF problems. And then we also have to open, this is the our thalamus. This is the rest of the choroid plexus. This is atrium here, and this is caudate and this is the tumor cavity here, tumor cavity. It looks clear. Yeah, next slide please. Yeah, this is post-operative picture. You see, I go through the right craniotomy and remove the left thalamic tumor through anterior transcallosal approach. You see my callosal incision and go through the here, I go through the lateral ventricular surface of the left thalamus and I routinely perform post-operative tractography to show that internal capsule is intact. Next please. Yeah, this was early post-operative picture. Another picture for the cordial transcallosal approach also in the large tumors, such as you see large tumor in the, again, left thalamus and extending down to the infratentorial area, but they are still, it has very nice border and internal capsule is always intact and the thalamic tumors do not go to midbrain. It just pushed down. And I go through the anterior transcallosal approach, I perform this 3D reconstruction to see... Preserving these veins is very critical issue. So we can see this before surgery, I can see that there is this bridging veins, so I can prepare my craniotomy with this information. Again, anterior transcallosal approach, anterior interhemispheric approach to find the corpus callosum. This is white color corpus callosum. So again, I will put my cottonoid to choose my surgical trajectory and I have to go more anterior. You see, this is all tumor. And then my cottonoid is here. So this angle is better for me to go more anterior. Then I can reach the inferior part of the tumor. Again, I go to left ventricle through the right craniotomy, and release CSF and checking with the endoscope to see the anatomy well, and you see the, you know, this is left thalamus, choroid plexus, left fornix, left caudate nucleus, and this is all tumor, left thalamic tumor. Again, this is now the left fornix. And I coagulate some choroid plexus to gain space to work. And you see tumor is directly, I reached the tumor. The same, just go inside of the tumor and suck it and also use CUSA. I don't coagulate when I remove the tumor, I just suck it with suction or CUSA. And when we remove the tumor, the generally the hemostasis is okay, you know, but I do not cognate during the removal of the tumor. And you see, there are still tumor. I go more posterior, more posterior. This is very big tumor. And the advantage of also the transcallosal approach, I see my lateral limit. My lateral limit is the caudate nucleus. So I do not go through that. And then this is curved suction to remove the posterior part of the tumor, but do you see, there is still tumor. This is atrium. This part is going to atrium. Then there is choroid plexus, but you see there are tumor underneath. So I coagulate more choroid plexus, and this is left fornix, so I separate it. I opened the velar surface of the thalamus nerve. After opening the choroid fissure, I can reach the velar surface of the thalamus. This is now the velar surface of the thalamus in the posterior part. And again, opening the septum pellucidum from the other side for the CSF circulation. And I go more anterior now. This is foramen of monro, and you see, this is the anterior border of the tumor, interesting. Thalamus tumor do not invade hypothalamus. They stay in the thalamus. There is a sharp border between thalamus and hypothalamus tumors. And I put a cottonoid to show my anterior border. Now I am going to do third ventriculostomy, microscopic third ventriculostomy. Here is the, I opened the, this is now the basilar artery here. So I perform third ventriculostomy. And you see, there is tumor in the anterior part. This is left fornix and there is tumor. I open also velar surface of the thalamus and I go more anterior and I will find my cottonoid, because I put cottonoid as a marker, you see, this was my cottonoid that I put through. And then this is my anterior boarder. This is choroid plexus again. And now I go again, the posterior and medial part of the tumor. And I am opening again, I am removing velar surface of the thalamus, left thalamus and checking with ultrasound. I love ultrasound. This is my, you see, this is the, here is the tumor cavity here. And the callosal incision and the, this bridging veins are intact. Right-sided craniotomy in spine position. And I always put a thin layer of gel foam to prevent the post-operative meningo-cerebral adhesions, I put in every case. And this is post-operative MRI through right-sided craniotomy. You see, I came through here and post-operative tractography also looks normal. It was anaplastic astrocytoma, which we perform. We gave a Ang-1 therapy. This is early post-operative picture. So the anterior transcallosal approach generally more preferable for me. Also now I have intraoperative MRI that I can perform intraoperative MRI. Next slide please. Yeah, now the posterior interhemispheric approach. This is for posterior thalamus and pulvinar lesions. In the underneath splenial, subsplenial area, we can explore this using this approach and the course of the cortical draining veins facilitates access. And of course the preservation of the optic radiation is another, would you show the video? Yeah, this is again left thalamus tumor, but it is more inferior. You see, and it is not in the surface. There is normal tissue in surface. So I do not prefer to use anterior transcallosal approach. I use posterior interhemispheric, you see, because under the splenial, you under splenial, you can see the pulvinar and that tumor is located in the pulvinar. And I prefer to use a posterior interhemispheric transtentorial approach for this posterior thalamic lesions. Majority of posterior thalamic lesions, I prefer this approach because I can use pronoblic position and I can have a intraoperative MRI. intraoperative MRI, is very valuable in the thalamic tumors in my opinion. In this case, I perform lateral position, lateral oblique position, but now I use pronoblic position because of the intraoperative MRI. Again, we perform this 3D reconstruction of the cortical surface to see those of venous anatomy, the parietal occipital vein. There is always vein here, but there are very rarely vein here. So this is the interhemispheric region that we can use. Next side is in the lower part. So I don't need retraction with the gravity. We can have access to go. The most important part is the op... After opening of the dura, I just released CSF from the, I opened the arachnoid here, and then I go direct to see splenial and release CSF. And then we have very relaxed brain. I go directly to splenial. And I see tentorium here, the galenic venous system here, and release CSF. And then you see the tumor is in the surface. So normally the pulvinar, normal anatomic pulvinar you can reach just underneath the splenium. But when there is a tumor in the pulvinar, it's come to the surface. Here I am waiting to release CSF. We don't need to be hurry in this part of surgery. We have to wait a little and to release CSF and to have a relaxed brain. And this is splenium here. This is internal occipital vein, splenium here, and under the splenium, tumor is protruding. Here is the tumor. I just go inside of the tumor and suck it and gain space. And then after that, I will turn around the tumor and the use CUSA also, but we have to prepare piece for CUSA otherwise I prefer suction more. But of course not every tumor is suckable with suction. Normally, I cut the tentorium from here and I have more space, but in this case, there is a lake here, so I didn't cut it. But normally in the approach, I cut the tentorium from here. And I do not coagulate any arterial vein directly. I have to see the anatomy well, and then I have to be sure that this artery or vein is belongs to the tumor or not. Otherwise I do not directly coagulate. And as you see, I debulk the tumor. Now I am trying to find the border of the tumor. You see, there is a tumor underneath the tentorium. So if I cut this tentorium, it could be easier for me to remove it, but I thought that it's okay instead of dealing with the tentorial stenosis. So now the more posterior and medial side of the tumors I am removing, and this looks like normal tissue to me, but there is still tumor underneath the galenic venous system. This is galenic vein, and we should not coagulate any part of this venous system. You see here underneath the galen, there is a tumor. And I'm checking, whether this is splenium, falx, and I'm checking with it. And this is the right thalamus, third ventricle. And you see there is tumor here in this part, in the upper part. There is residual tumor underneath galenic venous system. Again, I'm separating from the galen and now at the end of surgery. Okay, you see the right occipital parietal and not without retraction with the gravity, we have very nice space. And this is the reason I didn't cut the tentorium, but if I cut it could be easier surgery. Normally I cut it. And this is the tumor cavity here. Right thalamus, this is third ventricle, right thalamus and tumor cavity. And so the post-operative MRI, left posterior thalamic tumor And then there is I think, yeah, I think, yeah, this is late three months after surgery. Yeah, this is right pulvinar tumor remote using this posterior interhemispheric subsplenial approach. Next slide, please. This is normal, when we publish this technique. The similar case, again, left thalamus tumor, pulvinar tumor. I can go through here. And again, the cisternal surface of the pulvinar and this is advantage of intraoperative MRI. I perform intraoperative MRI, and this is my approach to go underneath the splenium to remove the posterior thalamic lesion. Intraoperative MRI is nice to have, but to be honest with you, for me, the most important one is intraoperative ultrasound because intraoperative ultrasound is also very good for navigation. I trust intraoperative ultrasound instead of navigation in the brain surgery. Navigation is very good for skull base and also to choose the cranium is cramped on the side, but intraoperative MRI is very valuable. And it's, you know, to compare intraoperative MRI and intraoperative ultrasound is not fair. They are different. One of them is like a car, one of them is like airplane. They both are important, but if you ask me which one is more, more important for you, car is more important for me, but of course it's better to have both. And this is three months after surgery. Again, posterior interhemispheric approach to come here, to come directly to cisternal surface of the thalamus without damaging anything. And you see, I didn't use anterior transcallosal approach because of this normal thalamus tissue to preserve, it was diffuse astrocytoma. The third approach is the perimedian supracerebellar transtentorial approach. I call it perimedian because I use midline incision, but then I do asymmetric craniotomy. For example, this is left pulvinar tumor. I do midline incision, but I do left asymmetric craniotomy here. I don't call it paramedian because paramedian incision is like this and I use paramedian incision for medial basal temporal region. It is more lateral, but for thalamus and pineal, and then take tomb tumors, I use perimedian craniotomy. midline incision, and then as asymetric . And this is also completely extra axial, and this is also for pulvinar tumors. But there are some difference between posterior interhemispheric and this approach. I use in semi sitting position, 25 degree is enough and very important to use transesophageal doppler, I found it's very suitable, in this semi-sitting position, but I am lucky to use original microscope from Zurich without auto-focus, without zoom, very short distance, and I can work easily many hours in this position. So I don't stretch my hand like this. So this microscope is very important I think in semi sitting position, in my opinion. This advantage of this approach is I cannot use a intraoperative MRI. May I see the video? This is 20-year-old female. Headache over the previous two months, and no neurological deficit. You see the tumor, but look at here, I cannot come through from here because it's totally under the corpus callosum. So I have to come from here. So this is the difference between posterior interhemispheric approach or parimedian supracerebellar transtentorial approach for pulvinar. They both are for the pulvinar lesions, but this is suitable for the pulvinar tumor if you go underneath the corpus callosum, I never go to callosal incision. I never done from posterior callosal approach, And in this case left sided, I opened the dura in the left side and I got just go through the transfers fisher. First, this is same semi sitting position. I release CSF from cisterna and the magna, and then with the help of gravity, I don't need to use any retraction. This is supracerebellar space in the left side, I preserve this tentorial veins and this is midline here. This is midline here, this is left supracerebellar space. Yeah, there are venous lake and there are bridging veins here that we have to preserve. And this is present trans cerebellar vein. I opened the arachnoid and to see the anatomy, and then I cut the tentorium. This is tentorial here perpendicular incision to the tentorium datus. And then I can see directly the pulvinar. Again, pulvinar is cisternal structure. Here is the pulvinar, here is the pulvinar. and this is basal vein of Rosenthal. And this is tumur here in the surface. And I just go inside of the tumor without sacrificing anything. This is the advantage of, another advantage of perimedian supracerebellar transtentorial approach for thalamus. Again, I say, I use this approach for pineal also for midbrain. Of course, for midbrain I don't need to cut the tentorium, but the philosophy of approach is same. And I just go inside of the tumor. This is low grade glioma, low grade glioma is a little more tricky, a little more difficult because the thalamus itself looks like low grade glioma. But we have to touch the tumor tissue and the socket, and then repair it. And I can tell that this is tumor. Of course, anatomic orientation is the very critical issue. Again, I love this in semi-sitting position, but again, this advantage is the not possible to use intraoperative MRI. And I prepare piece for the CUSA. You see, this is normal tissue. Now I can see. And the inferior border, again, the thalamic tumors doesn't invade the midbrain. This is fornix, bilateral fornix, in the upper corner of tumor. I am checking with the endoscope. This is tentorial incision, galenic venous system left cerebellum, and then this is pulvinar was here. Medullar basal temporal here. And these are fornix, bilateral fornix. Right thalamus, this is third ventricle. Residual tumor, you see. There residual tumor that I can see with the endoscope, then I can feel the normal thalamus and then this vein is intact. This space is enough for me to work. Again, no retraction and just with the gravity. And here is the midbrain, this is tectum, this is presentra cerebral vein, again, bilateral fornix and I close it. Again I put thin layer of gelatin punch always the ways to prevent post-operative meningo-cerebral adhesions. Yeah, this is postoperative MRI. You see I go this way. And the postoperative tractography also intact. Next, please. Yeah. Yeah. And the last approach is the exactly same incision, same approach, but the contralateral and not contralateral . Contralateral third ventricular surface of the thalamus. And I don't need to cut the tentorium this in this approach. This is perimedian contralateral supracerebellar suprapineal pineal approach for third ventricular surface of thalamus, completely extra axial approach. This is just for this kind of case. This is, I have five cases like this. third lenticular surface of thalamus. Third ventricular surface of thalamus. This is not pulvinar tumor, pulvinar is here. This is third ventricular surface of thalamus tumor and rave tumor. And it's fortunately low grade tumor. They're low grade. Pulvinar tumors, most of the high grade, but the third ventricular surface tumors are in all of my cases. Would you please work on? Yeah. They're all low grade. Of course, the it's far from the corona radiata. Next, please. Again, this is the third ventricular surface of thalamus, and I go through suprapineal recess, and then to reach the third ventricular surface of the thalamus for in the contralateral. And you see, this is the approach. Suprapineal tumor is here in this, in this case. Would you start media please? So there's really CSF from the cisterna magna, and I put some tube, and it's so continuously release CSF. And you see with the gravity, disintegrates with the bonds and the left sides. And again, I mobilize these veins and I preserve them. We should preserve them. We never know what may happen. And then go through the pineal glands, like a pineal tumor. I perform this approach exactly, this approach pineal tumors. For pineal tumors I can use right or left side. And then you see the pineal gland. And the fourth nerve is here. And I have to go up, here is the pineal gland. Here is the pineal gland. Just go superior then pineal gland. Yeah, this is third ventricular. Here is the third ventricle. This is arachnoid and third ventricle and the tumor. You see, I'm checking with endoscope. This is our bridging vein, and this is pineal gland here front nerve here. This is tectum and right sided, this is a choroid plexus roof of the temporal, roof of the third ventricle. And here is the tumor, anterior commissure foramen of monro. So this is the best way to reach the thalamic third ventricular surface of thalamus in my opinion. This is on the way to, without damaging anything. And you see there is nice border between tumors and normal thalamus. So I am now following that border. This is low grade tumor, all of cases thalamic, this third ventricular surface tumors are low grade in my series. All right, they're mostly tumor cases because tumors are 10 times more difficult than cavernomas. Cavernomas when you see the cavernomas surgery is finished almost, but the tumor surgery, when you see the tumor, surgery is just starting. So, especially in thalamus tumor is 10 times more difficult than cavernoma. I'm checking with endoscope. Again, bilateral fornix, anterior callosal, you see. There is residual tumor in the inferior part. This is left thalamus and there is residual tumor. So I use curved suction to remove that residual tumor that I was not able to see with the microscope. And I am checking again, this is tumor cavity. This is roof of the third ventricle and bilateral foramen of monro fornix bilateral and is here. Would you please change this slide? Yeah, this is postoperative MRI. You see, I go through here to remove this right-sided medial third ventricle surface of thalamus you see here and through the contralateral approach, I perform this approach for only these cases, these kinds of cases. And the advantage also the not effecting anything. And this is postoperative picture. We publish this approach. So most important is the extent of resection and histopathology and low grades tumors may be curative with this radical surgical excision. And then for high-grade tumors, we can have better prognosis. Of course, for small tumors and long response have good outcome. And especially if the patient has an acute CSF problem, this is the worst outcome. And it shows that also you may have headache with DCSF problem in the early postoperative period. I have now more than 100 patients, but this is in my publication, for this is from my publication, and mostly adult cases. And I use interhemispheric transcallosal approach in 35 cases and posterior intervention. These are my first choices because of intraoperative MRI, and also with anterior interhemispheric approach. I can perform third ventriculostomy. This is another advantage. And then I perform contract approach in four cases. But in this series, it was three, just only if the tumor is in the third ventricular of, third ventricular surface of the thalamus. And then in 19 cases, I performed supracerebellar suprapineal approach in semi sitting position. This is my approaches. I never go through the neocortex. I never go lateral. I have some case that I also operated four times. Most of the tumors, most of the cases are tumor cases. More than 80 cases is tumor cases. And in tumor cases, most of them, unfortunately, are high-grade tumors. This is typical in thalamus. In thalamic surgery, most of the cases are high-grade. In middle brain, just opposite, most of the cases are low grade. And no surgical mortality, but I have one major surgical morbidity that even the patient wake up very well after surgery, then like he started to have CSF problem. And I perform maybe four times VP shunt and three different VP shunt, and then the external drainage. And anyway, he passed away four months after surgery because of this continue CSF problems. It was below blastoma. Early post-operative problems of CSF circulation is acute in seven patients and they are high grade tumors. And eight patients are slightly worse, two months following surgery. The others are same or better than a preoperative period. And these cases, all GBM patients. safe removal of thalamic lesions with acceptable risk of morbidity and management has to tailor for individual patient. Neuroimaging is essential for evaluating the growth pattern and extent of lesion. And in our experience, all thalamic lesions can be accessed through one of these four, free thalamic surfaces or surgical surfaces. Lateral ventricle surface, velar surface, cisternal surface and third ventricular surface. You can reach these surfaces through transsternal, totally transsternal or transcallosal way. And without unnecessary manipulation of normal brain parenchyma, we can reach these surfaces. I performed this surgery high or low grade tumors, and radical resection is the goal. Prognsis is dependent mainly upon the extent of resection and tumor type. Adjuvant therapy should be utilized depending on histopathology. The CSF circulation problem is the very critical issue. This is the reason we have to open the cisterns and possible we have to perform third ventriculostomy. And this is the reason I prefer more to use anterior transcallosal approach. And the published this, it just came out today in Journal of Neurosurgery, you can find detailed information and results in this paper. And finally, I like to show this slide that we have many interoperative technology now in these days, I have all of them, but the success of surgery is not all kinds of these instruments. We have to put together all this information, and then we have to choose correct patient to operate and we should have aware about the surgical neuroanatomy and of course microsurgical technique. And we were planning to do future of microneurosurgery, in semi sitting position neurosurgery meeting last June because of Corona problem, we couldn't do it. But next year, I invite you to Istanbul in June to join us for this meeting. Thank you for your attention.

- Very nice, very nice. It was excellent. Truly, something extremely rare and not every neurosurgeon should be really operating in this area. It requires a set of skills that have to be very unique, tremendous experience. One of the great questions somebody mentioned, or it was that, how do you localize the tentorial venous lakes?

- You can see venous lakes, and also if there is a vein, if there is a tentorial lakes, if there were vein from below or superior, you can see that. And also you can see this venous lake. And then today, now it's easy I use also ICG to see that this venous lake. So, venous leaks are important, the sometimes to cutting tentorium can be troublesome. So these are because of the venous lakes. So we have to avoid if possible, to deal with the venous lakes.

- You also mentioned that it's easier to operate on the left thalamus. Can you explain why that is for you?

- Yeah. First I'm a surgeon, not like you. For you, maybe left thalamus is easy.

- That's right.

- Because it's contralateral lateral, to go the contralateral lateral thalamus as a right handed surgeon, it's easy for me. But for right thalamus, I don't use left craniotomy again, because of also the mostly dominant side is left and I am a right-handed surgeon, for me to go through left thalamus, left craniotomy to right thalamus can be more difficult. I use always right craniotomy for right thalamus. I go right lateral ventricle for left thalamus, I go left lateral ventricle.

- I've got you. One last question is, what's the advantage of the posterior and thalamus vein transtentorial approach over the parimedian supracerebella transtentorial approach for pulvinar lesions? That's the question. In other words, why? And let me finish, it says, you know, there was one I choosing a paramedian supracerebellar transtentorial approach for all pulvinar lesions. Could you comment please?

- Yeah. You know, if the pulvinar tumor goes inferior, I go through the posterior interhemispheric. But if the pulvinar tumor hidden under the corpus callosum, I go super cerebella. So this is main point, but there are some cases that we can use both approaches. That patient may be suitable for both approaches. If they are treatable for both approaches, I prefer to use posterior interhemispheric approach because of intraoperative MRI. Otherwise, if the tumor, . was callosal, I use supracerebellar approach.

- Okay. All right. With that in mind, Uğur I want to thank you for your spectacular lecture. Always extremely engaging. You woke up at 2:30 time in Ankara to give this lecture, which truly shows your dedication to know micro neurosurgery. You have been truly the and the only one who has continued the great legacy of Gazi Yaşargil. And well, you have, when you operate, I see the Professor, I spend a year with him. So I know, when I see somebody operate, I know where they come from and you have truly taken his, his expertise to a new level. We are, we appreciate all you have done for neurosurgery Uğur.

- Thank you very much Aaron. Thank you for kind invitation.

- All right. Thanks everyone for joining us wherever you are, morning, evening, middle of the night, or I'm a noontime again, thank you for being with us. I look forward to seeing you with us with Dr. Aquila next week, which he will talk to us from Japan about advanced bloodless microsurgical techniques. You definitely don't want to miss it. It's extremely engaging. And again, wish you all the best and see you in a week. Thank you.

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