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Grand Rounds-Supracerebellar Approach: Expanding the Operative Corridor

Aaron Cohen-Gadol

December 10, 2013


- Hello, ladies and gentlemen, and thank you for joining us for another session of the Taponas Operative Grand Rounds. I would like to take the opportunity today and discuss operative pearls for expanding the operative corridor through this supracerebellar infratentorial approach to expose lesions in the pineal region, posterolateral mesencephalon as well as the posterior aspect of the third ventricle. Here is my disclosure, which does not interfere with the discussion today. We're gonna start with a video of the third ventricular tumors and then focus our attention to pineal region masses. For a suboccipital supracerebellar craniotomy, as you can see here, the OR set-up is relatively simple. The patient can be in a lateral position or in a sitting position. I'm gonna review the pearls for a lateral position as this has been my preferred approach. However, we're gonna review some of the pearls for a sitting position during one of the upcoming videos as well. So as you can see, the patient is in a left lateral position and the surgeon is sitting across the table from the surgical assistant, and this allows a very easy transfer of instruments between the two. The assistant may sit at the head of the table and the operative microscope comes over the assistant. The anesthesiologists may be sitting to the side or maybe move to the foot of the table to make it easier for the surgeon to have additional space to work with. Having the patient in a lateral position avoids some of the complications regarding air embolism. However, may not provide as much of brain relaxation or cerebellar mobilization in inferiorly using gravity retraction. I'm gonna review some of the pearls in order to improve the working angle through the supracerebellar approach, by mobilizing the transverse sinus superiorly and hopefully that will make up for some of the lack of gravity retraction with the patient in the lateral position. The other major advantage of the lateral position is that the surgeon can sit and perform microsurgical techniques, and the arm of the surgeon can rest over the armrest of the chair, and that can be important and preferred to some of the surgeons who perform such procedures. Patient positioning for a lateral position is very well known to us. Obviously, all the pressure points are well padded. The axillary roll is placed and a patient's head typically is rotated about 45 degrees toward the floor. Turning the head of the patient more toward the floor often may bring the shoulder of the patient into the working zone of the patient and turning the head of the patient less may also worsen the working angle of the surgeon. Importantly the lateral position , also provides an opportunity for gravity to clear the surgical field of the blood, and the prone position does not provide same advantage. Let's go ahead and review the first animation we'll discuss patient positioning for a lateral suboccipital craniotomy. So as you can see in this picture, the patient is positioned in a lateral position and the pinions are placed on the head of the patient. Often, I place the two pins on the superior temporal line on the dependent part of the head of the patient and a single pin would be on the non-dependent side of the patient and we'll go ahead and review this animation to really better illustrate the positions of the pins that are relatively simple in this patient positioning. And here's the final position of the patient as you can see here. So, now the patient has been positioned on the operating table, let's go ahead and discuss the incision and the muscle dissection. We may use a midline incision if we're planning to perform a bilateral suboccipital craniotomy, obviously, retractors are placed in the muscle. A midline fascial incision is also used and have to be careful of the vertebral artery, which is over the lateral superior aspect of C1. Following performance of the craniotomy which we'll review more in detail during the video, a curvilinear dural incision may be performed and lifted superiorly. The central vein may be coagulated to allow mobilization of the cerebellum inferiorly. Obviously deeper veins have to be protected but the more superficial mid-line vein can be sacrificed without necessarily high risk of venous infarction. Again, these illustrations are performed with the patient in a sitting position just to orient all of us a little bit. Here you can see the exposure after two retention sutures or retraction sutures are placed over the posterior aspect of the tentorium. This is one of the nuances of technique for expanding the operative corridor through the supracerebellar infratentorial approach. You can see the edges of the dura retracted up, and two sutures are placed just anterior to the transverse sinus in the leaves of the tentorium and these sutures mobilize and rotate the transfer sinus superiorly, further allowing a more straight operative corridor and a view toward the structures in the posterior third ventricle in pineal region. One of the other pearls here is that as you expose this region, the angle of the microscope should be later changed toward the more inferior direction to be able to expose the pineal region. And here's the nuance that I just briefly discussed. As you expose the supracerebellar corridor, you can have a straight look at the vein of Galen and confluence of the sinuses, but to be able to look more inferiorly at the mass, you have to change the angle of the microscope dramatically. So, initially again, as you go over the cerebellum, this is the angle of view of the surgeon, and as you reach the confluence of the veins here you have to change the angle of view dramatically from superiorly to inferiorly, to be able to see the region of the interest. The arachnoid over the tumor may be exposed, cerebellar retractors often unnecessary with maneuvers that we talked about including CSF egress, opening up the arachnoid membranes, mobilization of the transverse sinuses superiorly. The tumor is then debulked and dissected from the surrounding superstructures, and the tectal region is carefully protected. The posterior open to the third ventricle is evident at the end of the resection and the fourth nerve, can be also evident at the bottom of the resection cavity. So we talked about the general aspects of the pineal region tumor, let's focus on the resection of a posterior third ventricular mass. These are tumors that could potentially be approached through a transcallosal approach, but the morbidity of a transcallosal approach is much higher than using a supracerebellar approach. And in this case, a midline supracerebellar approach is necessary. And again, this is not a pineal region mass that we are starting with, this is rather a tumor in the posterior aspect of the third ventricle that has created just even a small amount of operative corridor through the posterior aspect of the third ventricle for the surgeon to work through the supracerebellar corridor and expose the tumor. Here you can see an illustration exposing the tumor that could be just partly extruding through the opening of the third ventricle. You can use ring curettes, suction and various instruments to debulk the tumor and use the small amount of working zone that you have to be able to mobilize and decompress the tumor to fall into the center of the tumor. And at the end, you'll be able to appreciate the internal cerebral veins, the walls of the third ventricle that have to be carefully protected. And again, the pulvinar and the posthypothalamus is often very resilient to manipulations to make this approach possible for the surgeon to remove the tumor. I'm going to review one of my cases of a 30-year-old female who presented with progressive headaches. And as you can see in these MRIs, a axial and sagittal MRI sequences with contrast, the tumor is filling the poster aspect of the third ventricle. Here's in the sagittal view the tumor is again, not necessarily in the pineal region, but in the posterior aspect of the third ventricle. And although some authors have advocated removing the lesion through a transcallosal transventricular approach. I think the reach is often very far, and you have to go through a number of normal structures. I think the supracerebellar approach often provides a very narrow corridor, but minimizes transgression of the brain to expose such structure. Of course evaluation of the veins, which should be draped over the tumor is important, as you do not want to be transgressing these important of dicephalic veins, including veins of Rosenthal or internal cerebral veins, as well as the transverse sinus while approaching these tumors. Here's showing that patient also suffered slight amount of hydrocephalus. We'll go ahead and position the patient in this case in a sitting position using various prophylactic measures in order to detect air embolism. As you can see here, there is a transesophageal echo that is present. I briefly mentioned at initial stages of this discussion, that I prefer the patient to be in the lateral position. And for patients who may undergo resection of their posterior third ventricle tumors where the reach is often very far as sitting position may be however, more advantageous. We'll go ahead and see the incision here is the point where inion has been marked with a horizontal line, obviously mark a point where we can tap the ventricle, especially in a patient who's suffering from hydrocephalus. If such a maneuver is necessary to decompress the posterior fossa while dural opening is being performed. Here is again another view of central line to deal with that air embolism if it occurs. Here is also some flection of the neck to be able to have a more horizontal surface along the cerebellum to reach the pioneer region. So now the first video, here we'll review the midline supracerebellar approach for post third ventricle tumors in the patient that we just briefly discussed. So this patient again, the images were more momentarily reviewed a post third ventricular tumor that is causing hydrocephalus. Here is again, the position of the patient. A midline incision was completed. You can see the inion in this location. We'll go ahead and place two burr holes over the transverse sinus. The Burr holes may be placed just right on the sinus. The transverse sinus, is often covered by a much more durable wall as compared to a sigmoid sinus. I'm placing the burr hole right over the sinus has in my opinion, relatively small risk. Also exposing the sinus early on, makes the procedure very efficient in terms of completing the craniotomy as you would want to have your border of bony removal go as fresh, just a superior aspect of the transverse sinus in this situation. This is important for us to be able to mobilize the transverse sinus and expand the operative corridor through those retraction sutures that we're going to review momentarily. Obviously, number three penfield may be used to dissect the dural over the sinus and the torcula very generously away from the inner aspect of the skull bone. This is a critical part of the operation. Small amount of bleeding often is related to the intradeployed veins that connect to the dural sinuses in this region. And we perform first, the bony cutter osteotomy along the suboccipital bone. The cut over this dural sinuses has to be performed last since if there's any risk of bleeding during bony cut over the sinuses, we can remove the bone efficiently to deal with the bleeding. A [Inaudible] at the midline requires a B1 without a foot plate to thin the bone to allow mobilization of their craniotomy bone flap. Here is bony cut over the torcula If there's evidence of resistance, as in this situation I faced forcing the drill footplate should be avoided and a straight bit can be used to thin the bone over the trocula. And these are again, all the measures necessary to prevent any injury to these important dural sinuses. The bone flap is now being mobilized, we'll continue to remove bone over the trocula as a second stage just again, to protect these dural venous structures. Exposing the entire transfers sinuses on both sides, as well as trocula is important to be able to mobilize them superiorly. Cara syringes may be used again to expose the sinuses more generously. The foramen magnum may not be open in fairly early as it is not necessary. In the sitting position, often you reach significant amount of relaxation especially, if you're using ventriculostomy catheter by tapping the ventricles supratentorialy and in a lateral position, I do use the lumbar drain generously to be able to achieve maximum amount posterior fossa to decrease in tension. The occipital sinus can be coagulated. tied off and then cut. Here is those sutures that we discussed the retraction sutures over their posterior aspect of the tentorium, just anterior to the transverse sinus that would allow mobilization of the sinuses more superiorly You can see as the suture is being tacked up, that the sinus is mobilized superiorly. We'll proceed and perform exactly the same maneuver on the right side. An ultrasound micro Doppler probe may be used to assure good flow within the sinuses after the sutures have been completely placed and retracted. We talked about the central vein and most posterior veins can be coagulated Again, this approach is designed for reaching posterior third ventricular tumors, and I approached the large pineal region masses through a unilateral supracerebellar craniotomy that I'm gonna review momentarily through our next video. I do not believe you have to use a bilateral suboccipital craniotomy to reach a pineal region masses no matter how large, since as you can see here, you have to sacrifice some of the veins through a bilateral approach and also you place both transverse sinuses at risk during your exposure. So in this case, we went ahead and as you can see, if you don't change the angle of your view, you're going to end up on the posterior aspect of corpus callosum and the large veins in this region, the confluences of their veins. And again, I have intentionally included as part of video to emphasize the importance of changing the angle of view of the surgeon, not to be lost and expose the corpus callosum and be disoriented in terms of where the adhesion is. Here's after the angle of view has been changed from the superior to inferior direction. You can expose the tumor, which is relatively grazing this area and extruding through the orifice of the posterior third ventricle. The tumor can be de bulked and micro surgically mobilized from the surrounding structures and ultimately, dissected away from the surrounding structures. Obviously a biopsy of the tumor is first performed. In this case, the tumor was an intermediate grade pineal region mass. The tumor is further dissected. A ring currate may be used to remove portion of the tumor that may not be easily reachable through our opening. And at the end of the resection, you can appreciate the internal cerebral veins. And here's the view after the resection has been completed. And as you can see this procedure allowed complete resection of the tumor without much transgression of the normal brain structures, You're getting another view of the MRI with extent of resection. So now we talked about the removal of poster, third ventricular tumors. Let's talk about a more common approach that we would like to use, the supracerebellar infrastructure approach, and that's for reaching pineal region masses and how we can expand the operative corridor while minimizing the cerebellar retraction and protecting normal structures. For pineal region tumors, I like using the unilateral approach. I know most of us and during my training, a pineal region tumor was approached through a supracerebellar midline approach. As you can see in this photograph, the unilateral suboccipital approach, the supracerebellar route provides an exposure of the tumor through the wing of the cerebellum, which is often more inferiorly located than to Coleman, which is the middle midline of the cerebellum. This more inferior trajectory through the lateral supracerebellum approach over the wing of the cerebellum prevents retraction of the cerebellum, and allows more an inferior trajectory to the inferior portion of this large pineal region tumors. You might ask that well through your lateral approach, you may not have a good view of the contralateral portion of this tumor. And you'll be absolutely surprised as we'll see in this video momentarily, that cross-court approach provides a beautiful view of the contralateral extent and capsule of the tumor, no matter how large and again, why using a unilateral approach, you protect the midline large veins, and you also do not expose the contralateral transverse sinus and you avoid retracting on the bilateral cerebellar hemispheres. Here is my preferred approach, again a lateral position, the head of the patient is turned less in this case. An incision is placed along the mid portion of a line between the inion and the mastoid bone. This midline incision extended about one third above the transverse sinus and inion, and two third below the line then joins the inion to the root of zygoma. Here you can see how the lateral trajectory provides a nice view of the tumor After the patient is positioned the incision is completed. Again, this is a paramedian incision and requires an intramuscular dissection. The bony removal starts with a Burr hole over the transverse sinus and extending the craniotomy below the sinus and slightly over the sinus. And this allows us to mobilize the sinus more superiorly. As we discussed briefly, you can see the midline is not exposed at all. We actually placed the first Burr hole lateral about a centimeter to a lateral to the midline. Here is after the retraction sutures are placed, the transverse sinus was mobilized. And here you can see without any retraction, you have a view of the tentorium and the supracerebellar space. This illustration again emphasizes the point that we previously used to expose the bone, just to the level of the transverse sinus and torcula. I'll leave the bone over the sinus to avoid its injury, but as you can see with meticulous technique, you can remove the bone without any injury to the sinuses. However, when you don't remove the bone, as you can see here, it would really prevent you from having a nice view over the supracerebellar space and would require additional retraction over the cerebellum. As you remove the bone, you increase your angle a little bit, but again, you have the sinus somewhat on your way to expose the supracerebellar space, but in this inferior picture, as you can see with mobilization of the sinus, by moving more bone, you'll be able to maximally expand your operative corridor, to be able to reach the regions in the pineal area. Again, occasionally we have to take a vein, which is paramedian in this case, but very posteriorly and we have not had any issues with taking the vein and you will expose the arachnoid over the posteriolateral aspect of mesencephalon. And you'll be able to expose the fourth nerve. You can see this approach, beautifully exposes the posterolateral aspect of the mesencephalon and it gives you a lateral to medial cross-court corridor to the midline pineal tumors. Let's go ahead and review, now a case of a large pineal region tumor in a patient to illustrate some of the advantages of the unilateral suboccipital approach for a resection of large pineal region tumors. Again, this patient was a young patient. You can see a large tumor, which turned out to be a pineal blastoma in this case. In an adult, this is extremely rare. This tumor also extends into the posterior aspect of the third ventricle. You can see it is very inferiorally located. And if you try to come through the midline, which we traditionally have approached this tumor, you have to exert excessive amount of pressure on the coleman to be able to see the inferior aspect of the tumor and therefore a lateral supracerebellar approach has significant advantages in her case. Here's the paramedian incision that we just briefly talked about, the location of the transverse sigmoid sinus. And also we used a stealth neuronavigation in this case. And if necessary, we can place the ventriculostomy catheter using stealth neuronavigation along the upper edge of our incision about placing a burr hole over the occipital lobe. You can see the turn of the head that is relatively less than what we discussed for reaching the posterior third ventricular tumors. After the paramedian incision was completed, you can see the two retractor sutures were placed early exposing the tentorium without any retraction here, ventriculostomy catheter was also placed to provide some relaxation as this patient was young and had a very full cerebellum. We used these very thin cottonoid over the cerebellum to minimize any mass effect from the cottonoids themselves. You can see the fourth nerve as it's exiting the posterolateral aspect of the mesencephalon. You can see the midline that was generously exposed We'd go ahead and expose the tumor through a lateral to medial approach. This is the posterior capsule of the tumor that was cut. I debulked the tumor very generously. This de-bulking of tumor, allows us to mobilize the capsule more inferiorly, medially, superiorly and laterally. You can see that this is the medial aspect of the tumor, and this is again, the tectum contralaterally that's very generously exposed. So I went from the raft. This is the right tectum and posterior aspect of the brain stem that is exposed without any difficulty through a unilateral approach. You can see some of the images of this stealth that sort of allows us to orient ourselves to where we are. The tumor was noted to be very, very fibrous in this case and ultrasonic aspirin was used to assure removal and debulking of the tumor. And again, the tumor is very adherent and we try to carefully use a piece of cottonoid to wipe the brain away from the tumor in this case. And here is posterior aspect of the third ventricle. And you can see a nice view through the ventricle by removing the more posterolateral aspect of the tumor here is the more medial and superior aspect of the tumor that are being mobilized here. You can see the tumor is being coagulated as it was decompressed. However the tumor was very adherent to vein of Galen, and confluence of the sinuses and vein of the Rosenthal as you can see here, and therefore to protect these important dicephalic veins, we had to leave a very small sheet of tumor to be able to avoid any risk of postoperative venous infarction. Again, a small sheet of the tumor is left, as much of the tumor is carefully removed otherwise. And you can see I'm working through the midline region without any difficulty through the unilateral approach and adhering a small sheet of the tumor that is being left on the dicephalic veins in the vena and the vein of Galen. And ultimately we removed the inferior portion of the tumor and was able to complete a 95% plus removal the tumor Here is I tried to play and see if I can remove the tumor from the sinuses. And this was vein of Galen, but because of its adherence, I was convinced we have to leave a sheet of tumor ultimately some of the deeper veins are also being protected here. Vein of Rosenthal rotating and moving anteriorly obviously have to be carefully protected. This is the medial extension of the tumor being mobilized from the contralateral tectum. And you can see both tecta, are well exposed by a unilateral approach. Here is the adherence to the posterior aspect of the third ventricle that is being dissected Safe gross total resection of any tumor obviously is the ideal goal of the surgery. Here is mobilizing the last pieces of tumor. And again, the superior part that was very adherent to the veins along the midline, is left and coagulated to decrease the chance of future growth. Again, trying to be a little bit more aggressive with a piece of the tumor close to the veins to remove as much as possible. And here is the nice view through the posterior aspect of the third ventricle. Here's the postoperative MRI demonstrating a relatively good resection with a small sheet of the tumor left over the veins and the rest of the tumor was adequately removed. So what are the variations of technique to expand this operative corridor? We talked about, you know, supracerebellar approach using a retention sutures versus maneuvers in terms of positioning and CSF drainage Talked about third ventricular tumors and how it could be approached through that and how we can manage pineal region tumors through a unilateral approach. Let's talk about expanding the operative corridor and reach lesions that are necessarily supratentorial such as a medial tentorial meningioma. As you can see, this is a tumor a meningioma causing edema, and it's very medially located on the dominant hemisphere. And in this situation, if you want to approach this tumor through a sub temporal approach, you will require a significant amount of retraction and significant risk to the speech and using approach through a superior part of the labial, which require a long reach and significant amount of transgression of normal brain tissue. So how can we remove this tumor which has completely supratentorial and minimize retraction protect normal brain through a supracerebellar approach. It's a very novel concept, removing a completely supratentorial approach through a posterior fossa approach. And I think it's, a very good way to remove this tumor through supracerebellar approach because that is the portion and that's where the tumor comes most closest to a subarachnoid space where you have to transgress minimum amount of tumor So here you can see, we're going to use the supracerebellar approach, which we have been talking about. Maximize the operative quarter by mobilizing the transverse sinuses. Cut a piece of tentorium and decompressed the tumor and deliver the tumor downstairs. These illustrations further illustrate the maneuvers that I just briefly talked about. You obviously cut the tentorium from downstairs through the posterior fossa. One point that I would like to emphasize here is that as you cut it in tutorial, you have to protect the fourth nerve, especially if you're cutting a large window of the tentorium as it would be necessary in these cases. You have to make sure that the area where the fourth nerve enters the dural is not violated and is not cut. Here as you can see the exposure through a supracerebellar approach. So what are the advantages of going this way versus supratentorialy? Number one, through the supracerebellar approach, you can identify the most anterior edge of this tumor, this medial tentorial meningioma, which we reviewed its MRI a moment ago. And you can see that by going through the supracerebellar route, you can see the extent of the tumor that is affecting the brain stem very early on. And by that you can identify the important structures of posterolateral mesencephalon the fourth nerve, carefully dissect them, maybe put a cottonoid across them and worry less about them during the later stages of the operation. When you come through the supracerebellar supratentorial route or subtemporal route, you will probably see these most important structure latest, and you may have to worry about them during the entire procedure, especially when the surgical field is very bloody, as you're within the tumor it would make protection of these structures difficult. But early on through the supracerebellar route you can identify these two structures and protect them. Also, you can see that early on, you can coagulate the tentorium and devascularize the tumor. And this will allow you a higher level of efficiency to debulk the tumor dissect it later. Here's after coagulation of the tumor, we're performing those tentorial sectioning in order to go around the tumor, ultimately to work through the tentorium, to debulk the tumor, and be able to dissect the tumor from the suboccipital and posterior Templar region, and be able to deliver the tumor completely. And here is the funnel view the operative corridor, and you can see that you can deliver the tumor without significant retraction of the paradox occipital region or necessarily cerebellum. So you're maximizing the use of subarachnoids spaces or subdural spaces to be able to reach this tumor by advancing operative angles, not necessarily operative distances or operative spaces. And that's the concept of advancing operative angles to remove tumors through the subdural and subarachnoid spaces to minimize normal brain transgression. So let's go ahead and review the intraoperative details of the case that we just reviewed discuss the medial tentorial meningioma. And you can see in this case, the patient was placed again in a lateral position and a hockey stick incision was used to be able to get a more inferior to superior trajectory among patients who necessarily have a larger body habitus. This patient who was 33, was suffering from occasional dysphasia. You can see the tumor with that we reviewed, you can see most of the feeders are pealed to this tumor. Again, a medial tentorial meningioma patient's face position laterally a hockey-stick incision was used rather than a paramedian incision in this case Here, you can see the craniotomy was completed. This is the supracerebellar corridor. Again, the tumor was on the left side. We're going on the left side His retraction sutures are placed. This is Dr. Ron Young and I who did this procedure together. He is placing the sutures over the tentorium mobilizing again the transverse sinus using the maximum amount of space available through the supracerebellar corridor, by expanding the operative angle, placing a tough piece of Teflon with the cerebellum to protect it. Now you can see that you have literally transformed this medial central meningioma to a convexity meningioma. You can see coagulating this tentorium downwards cut, and debulk the tumor and delivering the tumor downstairs Here is placing he's piece of cotton between the mesencephalon and the tumor early on during the procedure to protect the important structures here. You can see again, early on the posterolateral aspect of the mesencephalon that is being carefully dissected away from the tumor. here he's debulking the tumor through the tentorium. And again, mobilizing the tumor into our resection cavity from the supratentorial space into the infratentorial space to remove this large piece of tumor And here you can see we're able to remove the tumor without any injuries surrounding normal structures. This patient did very well a gross total removal seemed so great. One, since we were able to remove the affected tentorium, the base of the tumor, as well as the entire tumor, such seemed so great. One tumor may not be always possible through supratentorial approaches as removal of our cutting the tentorium, which was affected by the base of the tumor is not possible. Well, ladies and gentlemen, I hope this session was helpful in giving you some operative pearls that has worked for me in terms of expanding this corridor by using the retraction sutures, by going around the cerebellum and using a lateral approach to reach the midline and ultimately cutting the tentorium to be able to remove tumors located in the supratentorial space. Thank you for joining us and have a good day.

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