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Grand Rounds-Patient Positioning for Intracranial Surgery: A Guide for Residents and Fellows

William Couldwell

October 12, 2015


- We're lucky to have with us Dr. Bill Couldwell from University of Utah. We're gonna talk about a very common and a very important issue in neurosurgery, and that's patient positioning for intercranial surgery. So, Bill, I really want to thank you for joining us.

- It's a pleasure to be here, an honor, thank you.

- Let's go ahead and cover our disclosures and there are really none to interfere with this presentation. So the principal that I know of, Bill, is balancing surgeon's comfort versus patient safety. And more importantly, in the reverse order. And patient positioning has to be really carefully thought about before surgery rather than just walking into the OR and thinking about it last minute. Can you tell me what are the perils you always look for in terms of positioning your patients?

- Well, I try to pick a trajectory that gives me optimal exposure to the intercranial target, and also affords safety for the patient, comfort for the surgeon and optimal trajectory to the target. So those are the main features that I think of.

- Thank you, so the principles we'll look for is really positioning the body before the head, because when you position the head, there's really minimal changes you can do. You can do reverse Trendelenburg, Trendelenburg and tilt left to right but you really can't bring back, up or down because that could place the neck of the patient at risk. And as you very well mentioned, the ideal position of the head is based on three principles; the trajectory from the top of the skull at the highest point to the lesion would be the shortest. I consider gravity retraction an important part of surgery to avoid fixed retractors. And I think any position that places the brain that I have to retract more towards the floor, I really like. And then obviously the exposed surface of the skull and the perimeter of the craniotomy as much as possible should be parallel to the floor for easy maneuverability of surgeon's hands. Any thoughts there, Bill?

- Yeah, the only other factor that I consider is, I try to have the neck with the least amount of torque as possible for the trajectory that I'm choosing. And I think it's really important, especially in older people because I worry about the vertebral arteries and traction on nerve roots.

- Thank you. So these are the basic approaches we're gonna talk about today, bifrontal, pterional, temporal, retro sigmoid and midline suboccipital. Let's review very briefly head fixation. Generally we use the horseshoe headrests or burr holes for large frontal tumors, potentially transsphenoidals and three-pin fixation for microsurgery when any movement of the patient can be very problematic. Can you tell me what your preferences are in terms horseshoe versus a three-pin fixation, Bill?

- I mostly do everything with a three-point pin fixation because a lot of the surgeries that we do are longer. I'm worried about necrosis of the scalp, pressure points, et cetera, as well as if you want to use a retractor, my retractor system hooks to the Mayfield three-point head holder and so you need to consider that. You can retract using a Leyla bar and some fishers, et cetera, when you use a horseshoe. But mostly all the surgery that I do is in a three-point pin head holder.

- For the supine position which is our most common approach, you have to turn the head often very much. And the key part important issue that you very well mentioned is really not turning the head too much, using a generous piece of gel roll behind the contralateral shoulder and maintain the 2-3 finger-breadth thyromental distance between the chin and the upper part of the chest. The skull clamps have their own risks, obviously, intraoperative displacement, especially if the pins are too close to the vertex of the head or if the single pin line does not cross the longitudinal axis of the head across the two pins. And we're going to briefly review that at the end of our discussion. Obviously, bleeding from the pins can be an issue, however, most importantly air embolism has been reported and even a scalp and eye lacerations. Do you have any perils in placing the skull clamp, Bill?

- Yeah, I think we have to be careful where we put it. I try to keep the pins out of the temporal fossa and I always remind the residents and fellows to do that because I've seen epidural hematomas from that. We try to keep it away from the air sinuses, so the frontal sinus, so we don't pierce that and then obviously issues for cosmesis in the forehead, if we can avoid it. The other thing is with respect to the neck is that we really want to be careful and not turn the neck too much with respect to the shoulders because it can impede venous outflow. And especially on the dependent side, you may occlude the jugular venous drainage, and I've seen venous hypertension from turning the neck too much in the pins.

- So, after our positioning, after really getting the lines, the intratracheal tube, we'll go ahead and position the body first. And the most common positioning techniques are supine, lateral, prone, concorde, sitting, and three quarter prone or a lateral oblique. My most favorite is supine, lateral and lateral oblique. That's essentially 99% of my procedures, I hardly ever use prone. And we'll review some of those details with you shortly. Arm abductions should be really limited to 90 degrees pressure points, especially on the radial nerve groove of the humerus and ulnar nerve as we all know, should be very well padded to prevent neuropathy. And especially at the peroneal nerve at the head of the fibula. And, very obviously the bodies should be very well secured, especially for larger patients in the lateral position. When we do long skull-based procedures, when we don't use paralytics, the patient can become light and start moving and that can become a source of a significant complication. For the supine position, we try to put the patient with the hips and the knee bent at 15 degrees. We try to avoid placing the patient completely supine or completely angled in a reverse Trendelenburg position. Number one, it avoids the patient from slipping over the table and also you can pad the pressure points very well. Do you agree with that principle, Bill?

- Yes, I use the reflex position on the table significantly. And again, that elevates the knee and it keeps the leg veins from pooling dependently. And then also the midsection of the body stays at the flex point. So the body doesn't migrate down the table when you elevate the head. And so it achieves two important points, it elevates the legs and it elevates the head and the body stays in position.

- Thank you, and just to reiterate that, you push the reflex button on the control to create this and then you put leg down to create this action.

- Correct.

- Let's start with our most common positioning technique, which is a supine position, there's many ways to do it. You can put a single pin behind the ear to leave a lot of working zone for the surgeon, as you can see here, and the other two pins along the superior temporal line. You do not want to put this front pin, that's one of the most common mistakes residents make is put the front pin into the temporalis muscle. That compromises fixation, and also putting it too high, close to the vertex facilitates slippage. Also, as you can see the single pin, if you create a line parallel to it crosses the double pin. And that's another principle for placement of the pin on the head. Any other thoughts for pin placement, Bill?

- Yeah, one of the common rookie mistakes that I see is that you really want to have the head fall into the pins. And what I mean by that is, whatever position the head is in, think of it as a globe and make sure the pin fixation is below the equator of the globe. And that way, the natural tendency is for the head to fall into the pins. If you put the pins too high on the head, no matter what position you are, the head can fall out of the pins instead of in the pins. Very important fundamental principle and I emphasize that, no matter what position the head's in, the pins need to be below the sort of horizontal equator of the head.

- Thank you. Would you let us know, this is a one of your patients positioning techniques?

- Sure, this just illustrates a couple of important things. You know, I use a Fujita retractor system which uses a C-clamp on the elbows of the Mayfield head holder. And so no matter what position that you put the head in, I find it useful actually, and this is a little unconventional, but I put the screw fastener on the underside of the head holder and then kick the head holder out. So it's a little more proud and easier to get the C-clamps on. And so I find that much easier to place the C-clamps and then to quickly open and close the clutch on my head holder and my brain retractor system. This is a pterional approach. If you choose to use the pins in this position and I'll use them in this position or in a biparietal position, if you choose this, I put the pin in the mid-pupillary line, above the frontal sinus and then put the other pins posterior enough so that they're not in your way. And this works very well. And this provides good equidistance for your head holder clamps or your brain retractor clamps to be located at the elbows of the clamp.

- The other factor the surgeon has to think about, Bill, is what kind of retractor system you're going to use with. BUDDE halo retractor systems, you don't have the flexibility of where you put your Mayfield skull clamp on versus Greenberg, where you have more flexibility. So I think with this way you have done it here, the BUDDE halo would work very well, but the way I do it, with a single pin behind and two pins on the contralateral superior temporal line, the BUDDE halo retractor system may not be very easily attachable. Also, very well you have shown the position of the body in almost like a very mild semi-sitting position, because you want to take advantage of not extending the knee and avoid neuropathy. And also avoiding the patients slippage, especially for larger patients on the table. And a very generous, obviously, contralateral shorter pack. This is an exaggeration of how much extension of neck of the patient I would like to see. This is, obviously, a young patient. His neck is very flexible. This is a selective amygdalohippocampectomy case. And also I extend the head more just to make the hippocampus parallel to the axis of the floor. But as you can see, if the patient can comfortably tolerate this amount of extension, you can almost do the surgery without any fixed retractors on the frontal lobe. Most patients can't tolerate this much extension and you don't want to push obviously the patient to have the patient in it position that they're not comfortable with. But again, this is really the principle of using the malar eminence as the highest point for a pterional or craniotomy, extending the head as much as you can, to use gravity retraction, to move the frontal lobe away from you. Go ahead, Bill.

- No, I think that's an excellent point. If you extend the head and we certainly do that for anterior communicating aneurysms, et cetera, and sub frontal tumors, craniopharyngiomas, this offers actually the natural ability for the frontal lobe to fall away with gravity from the base of the skull.

- I think this is a transcallosal approach positioning, would you take us through it, please?

- Sure, so this actually is a patient with a cavernous malformation in her third ventricle. And this just shows you a classic transcallosal approach that I prefer to use, I like this L-shaped incision. But the point here is that I have my surgical access and the direction that I'm going to be operating on is in a comfortable position for myself. It's like putting in an external ventricular drain. And then once you do the bone removal, you've got a straightforward, comfortable direction that you're coming down to access the third ventricle in this particular case. The head is elevated slightly so you're going to have to be careful with the venous sinus to make sure that you don't have any air emboli, but it helps with the venous bleeding and keeps the field dry and offers a superb trajectory for a third ventricular surgery. Again, the bed is reflex here, you can see, and the back is elevated and this Mayfield head holder is kicked out to allow my retractor system as well. This is a bifrontal approach and I think it very similar to the positioning of the head holder that you showed for your cases earlier, Aaron. And basically I usually use the single pin on the side that I'm operating on and you can see that it allows great exposure over the entire bi-frontal area here. This was a recurrent meningioma and we needed access to bilateral frontal area and the left orbit as well.

- If I may mention something, I think a great point here is the single pin should be just above the pin and posterior. You can't put it too far posteriorly because then it would cause slippage around the curvature of the occipital bone. Also the double pins, instead of putting them in the horizontal direction, you have them sort of in the semi vertical position to get a good purchase without moving them too far posteriorly. So instead of putting them horizontally and moving them very posteriorly, you have turn to vertically this way you get a good purchase without increasing the risk of slippage. For awake craniotomy, obviously, the priorities become even more strict because the patient has to be very comfortable. He or she has to be able to swallow well, and you need a very large flap because you need to do mapping. And as you can see in this awake case that I did a while ago, you have a generous pad on the ipsilateral shoulder in this case, and the single pin behind the ear, creating a very large space for the surgeon to work. I do increase the weight to 80 pounds on awake patients because if they're uncomfortable, they really can try to get out of the pins. I think 60 pounds for an adult awake patient can be a little bit less than ideal. And that nuance has saved me a couple of times as one of the awake patient of mine really tried to almost sit up and if I had him in 60 pound pressure in a Mayfield pinion, I could swear he would have been able to lacerate his scalp and get his head out of the pins. One point that I want to emphasize that you mentioned is the more that lesion is close to the midline, the less you turn the head. The more the lesion is away from the midline, the more you turn the head. So for an ophthalmic aneurysm, for ACom aneurysm, you turn the head very little, almost 20, 30 degrees. For an MCA aneurysm, you turn the head almost 40 degrees. And because when you get closer to the midline, you don't want the temporal lobe to fall on your way. And that's why you turn the head less. So I think that's regarding turning the head of how much you do. Regarding extension, the more extension, the better, because it's gonna allow you to use the gravity retraction. And, obviously, the more things are closer to the skull-based the less extension you need. Let's go ahead and review the bifrontal craniotomy. I think that's another approach that can be problematic for some individuals with pin placement. And I'll let you take over and discuss your perils for a bifrontal craniotomy again, Bill.

- Sure, this is a fairly simple. An absolute midline hair head placement. I use the same position for the pins as demonstrated here. The incision may or may not need to be taken down to the tragus of the ear bilaterally, but oftentimes just on the contralateral side, not down as far, depending on what you're trying to achieve. But if you're planning to get bifrontal exposure, I think the key issues are how much you want to flex and extend the head. Because if you're focusing on the anterior aspect of the intracranial fossa such as the frontal sinuses, the cribriform area, you really don't want too much extension except to help you allow the brain to fall away from the head. And, in fact, it's harder to look up into the frontal sinus if you extend the head up too much. So we'll, again, plan on the amount of extension depending on what type of pathology you're trying to address. Whereas if you're trying to look posteriorly and super cellar lesions, such as a craniopharyngioma, you might want more extension to allow the frontal lobes to drop and then look up. So those are the key issues I think in this approach.

- One of the problem that I have run into, Bill, is if the pins are too close to the incision, no matter how secure the pins are, there's some automatic slippage posteriorly, and you may have a difficulty closing incision because the scalp flap is retracted posteriorly. So I think you have to leave a good amount of space while draping between the pin and the incision. And if you have a problem bringing your incision edges together it could be that your pinion has slipped more posteriorly.

- I think we've all experienced that, that's a good point.

- Thank you, let's jump to the lateral position, my most favorite approach, lateral and then lateral oblique. And as for parietal and temporal lobes, it, obviously, has risks because the pressure points are different and they lead to brachial plexus injury, or other stretch injuries and it can really cause ventilation profusion mismatch in the lungs because of a lateral position, especially the dependent portion of the lungs. The axillary roll is actually under the upper chest area and not directly in the axilla area to prevent arm ischemia, brachial plexus injury and compartment syndrome. The Park Bench approach is a variation of that, but really that's not as often I use. The supine position works for reaching the temporal lobe, but as you can see, it really requires a lot of torsion in the neck and a young patient may tolerate it, but an older patient may not be comfortable.

- So, I think I just wanted to emphasize that point that you just made that with respect to using the supine position to do a lateral approach. And I think you can get away with that in young people, it depends on the flexibility of their neck, but again, venous return can be an issue because you can occlude the contralateral vein when you turn the head that much. And I've seen problems with brain swelling and venous hypertension in the head with doing this. I prefer to either bump the shoulder significantly if I'm doing this approach or have the patient in a pure lateral position. And in older patients, I really prefer the pure lateral position because I really don't want to torque their neck so much and risk injury to the pterional artery, et cetera. And we'll use the full lateral position and I use it as a real workhorse position for skull-based surgery and a lot of posterior fossa surgery as well. And I think it's a superb position. The advantage of this particular diagram that you're showing is that your shoulder's not in the way as much when you're doing a retro sigmoid, et cetera, but the disadvantage is the venous return and the neck torquing.

- Again my favorite position, which is their lateral oblique or three-quarter prone, or semi-prone, it's a very versatile approach. It almost obviates the need for a prone approach. It avoids some of the difficulties with ventilation especially in the larger patients who are prone and allows the patients to sit for microsurgical procedures in the posterior fossa. However, the recognition of the midline dissection can be difficult because the head is turned. What are your thoughts about this approach versus a prone approach for posterior fossa pathologies?

- Sure, and I've developed a strong affinity for this approach over the years. I must admit that I've gotten away from using the prone approach almost exclusively. And the reason for that simply is because with bigger people, it makes them harder to ventilate. The brain is more difficult to manage because there's often more venous hypertension and brain swelling and so I use the lateral position. I find it very well tolerated for longer procedures. The anesthesiologists like it because it's easier to ventilate although there is some ventilatory mismatch as you mentioned. But it affords a very useful trajectory to so many different tumors and lesions in the posterior fossa and the parietal occipital area. And it's very well tolerated by the patient. I think some of the features that you included here on this diagram are important that you can, as you said, you can variably rotate the head. It's a little misleading sometimes because you're not perfectly square if the head is rotated. But the nice thing is that you could pull the arm down. This is very well tolerated and open up this space. We use a lot of tape to hold the patient in, especially at the hip. And we rotate the patient back and forth, especially when you're operating in the posterior fossa, you need a lot of rotation and then put pillows between the legs, so nicely diagramed.

- Thank you, one point I want to stress is the importance of not putting the tape too close to the fibula head. Obviously, letting the shoulder go down and forward so it almost completely gets out of your way. You let it sort of fall forward and really very important to have the proper auxiliary or the gel axilla to be able to avoid any neuropathies. So with that in mind, the position of the head is obviously very dependent on what pathology you're approaching. This is for a parietal occipital area where the highest point is where you're going to be working. And the head is toward the floor. If you're doing a posterior fossa, obviously, the head may be turning less and again, the shoulder will be pushed out of your way. So this is really anywhere after the frontal bossing of the head, anything in the front can be easily managed with a supine position. Any of lesion behind the frontal bossing can be approached using the lateral oblique very easily, very well-tolerated, especially if you're doing large acoustics, large skull-based tumors where the patient is going to be in that position for a long time. Having the patient in a supine position with the neck turned can really cause long-term neck pain that I learned early in my career. And this is really, really important, to have the patient's body in a very physiological, comfortable position in long skull-based approaches. And that's why this position has really become the most favorite for many surgeons. Don't you agree, Bill.

- Yes, I think the pure lateral and then the three-quarter prone are very, very useful for all the reasons that we discussed.

- Lesions for a parietal occipital area as you can see, you can use linear, you can use horseshoe incision. And also if you turn the head a little bit less, gravity works to clear your field of blood which really helps. I do think if you're doing an interhemispheric approach, it's best to put the ipsilateral hemisphere down because retraction would tremendously help you. The central collar cyst in the frontal area to put the dependent or the ipsilateral hemisphere down that retraction can be absolutely a blessing and should not be forgotten as another advantage of this approach. Any other thoughts, Bill?

- Yeah, I think you've covered the main ones, Aaron. I think the issue in his approach and especially for people that are not familiar with it is that you got to understand what your anatomical landmarks and your trajectories area and if you're uncertain, certainly using image guidance is helpful because it can be a little disorienting depending on how much the head is turned in relationship to the body.

- Yeah, I think that's very important. This is very disorienting, especially if you want to go into the ventricle, to the atrium, and you have a large AVM or a tumored glioma, you really need stereotaxi otherwise the surgeon can be easily lost. This is the position that we use for retromastoid, for acoustic, for all different cranial compression, cranial nerve compression syndrome, such as trigeminal neuralgia. And again, the patient is in a very physiologic position with a curvilinear incision as you can see. This is again, a large acoustic on a young patient. I use it curvilinear incision. This patient obviously very thin can tolerate pulling the shoulder down and forward. This creates a very large working zone for the surgeon. We do turn the flap in fairly and that keeps the flap out of our way. Again, trying to keep the neck of the patient in the most physiological position for a long operation. And I'll let you take us through your acoustic positioning on this picture please.

- Yeah, I think this just shows some of the features. We'll pull the shoulder down and then it depends if the patient is pure lateral, we usually pull the arm down and use a elevator, a Crouse rest here. The incision that we use is retroauricular. On smaller lesions I'll use a small S-shaped incision, either for trigeminal neuralgia, et cetera, or down here for a small acoustic, we'll just use a small S-shaped incision. I think the features, again, the head holder is kicked out a little bit to help with the retractor system. We watch very carefully the dependent arm, and then we use intraoperative monitoring. And as I emphasize to the residents and the fellows, one of the major reasons that I use somatic sensory and motor-evoked potential monitoring for all my cranial cases is to also safeguard poor positioning. So if you develop a nerve palsy in an arm, interoperably you'll recognize it. And so I just want to just emphasize that to the trainees, because I think that really helps you for patient safety, because it really protects everything. So if an anesthesiologist is not watching that a leg falls off the table, you could pick it up with inter-operative monitoring. And so I think most of the other features we've discussed already with the other picture, Aaron.

- And other patient position lateral for a parietal occipital angioma that again, the highest point is where we're going to be operating, a very comfortable position. This is for a pica aneurysm I did recently. The patient again in the lateral position, and this is where the pinions are placed and the surgeon can sit down and do the microsurgical part of position rather than being standing while the patient in a prone position. Would you let us know about your preferences for a pure lateral approach, Bill?

- Sure, this is a petroclival meningeoma case. And I just want to emphasize that when we do these cases, we really have the patient well protected, well padded and also well secured in the table so that we can rotate the patient back and forth. So I like to put this tape diagonally down here, and what that does is you laterally flex the head and it opens up the angle here and allows you exposure to the region of the posterior fossa when you're operating. And then this is very well-tolerated. I put tape down here and then tape across to the arm holder as well. And then this gives you a more firm secure of the patient so that you can rotate the patient back and forth. And then, of course, flex the legs a little bit. Pillows between the knees, watch the Foley catheter, inter-operative monitoring, and then careful padding all around.

- One more point that I want to add that I have recently been using. I use lumbar drain very frequently. I just, again, I relaxed brain leads to a relaxed surgeon, special for posterior fossa pathology early on. And instead of putting a lumbar drain, I put a lumbar puncture needle in and attach IV tubing to it and use it as a lumbar drain. I no longer pass a catheter intrathecally and I'll obviously pad it or pad it very well, so nobody bumps it or pushes against it. So the padding is the same level as the hub of the needle. That's another advantage of a lateral position that you really don't need to pass the catheter that at times can be very challenging.

- Yeah, that's actually an old variation of a Charlie Drake trick that he used to place just the lumbar needle in and then would take the stylette out in the middle of the case and just let it drain and then just remove the needle at the end of the case. And we've done that routinely on our subtemporal approaches to basil aneurysms.

- This is an interhemispheric powerful angioma on the right side, you can see the right side is down. Again, in the choice of the flap this way versus this way. This is large enough with a large flap. So I don't think the way the arteries are coming up makes a big difference. But the important point is the fact that the dependent hemisphere is down. So when you open the dural and reflect it up, the dependent part starts to jet down for you without any retraction and the lumbar drain specially helps you because you don't have any sisterns to reach here. And if the tumor has calodema you're going to run into a lot of brain swelling while opening the dural. So it's best to take advantage of the lumbar puncture drain early on on the case. Any perils there, Bill?

- No, I think you've covered them nicely there. Just to emphasize the dependent position and allow gravity to help you with your retraction.

- Let's go ahead and briefly review maybe a retromastoid craniotomy just to give an idea how the patient positioning was here.

- I always palpate the asterion which is a perfect surrogate for a finding the relative location of the sigmoid transverse junction. So if you have a line between your zygoma, which you can palpate here and your inion, the asterion lies along that and then you'll be able to predict the course of the transverse and sigmoid sinus from that. And then the incision relates to that point, because if you're trying to approach lesions here in the superior posterior fossa, such as the trigeminal neuralgia or trigeminal schwannoma, then we'll plan our opening just in the petro tentorial area right here. And then if we're going after acoustic, we'll be more inferior or an ABM with more cerebellar exposure. So it depends on the pathology, what type of incision we'll use. I noticed you like to use this flap, which I think is great, it gives you perfect exposure laterally. We'll often use a lazy-S incision here for a trigeminal decompression. For an acoustic we'll use a traditional curvilinear incision or a lazy S in this direction right here, a little inferior to the trigeminal opening. And then if we're trying to do a pica aneurysm, et cetera, we'll use a more far lateral incision, I'll extend it down into the neck if necessary. Or a flap, as you demonstrated earlier on your case.

- One point, Bill, is that for patients who have a large amount of subcutaneous fat, the linear incision can really increase the working zone on the surgeon. So some people angle it sort of further away, more inferiorally, but I think this incision, which is the old Dandy incision, that's how he did most of his posterior fossa incisions. It really helps because he really moves that large flap out of your way. And more, it may protect some of the neurovascular structures that are there in the region. Regarding turning the head for the cranial nerve compression syndromes, we turned the head very little toward the floor. Jannetta describes having the head or the longitudinal axis of the head very much parallel to the floor, but I think turning the head a little bit which allows the surgeon to go round the cerebellum a little bit more easily and really you don't need much turn of the head in any other situation for this exposure. The pinion, we put one just along the hairline. The other two is along the parietal occipital region, and that's really keeps this single pin out of the working zone of the surgeon, which is here. If you put the pin here and you were using the linear incision, it can be problematic because the single pin can get in your way sometimes and make the surgeon almost moved their incision compared to the pin and then cause some disorientation after opening regarding where the burr hole should reside. So that's been really our perils in terms of positioning the patient for a retromastoid craniotomy. And he has really worked very well in this area.

- One point that I'd like to make, Aaron, is that when you are planning an approach to the posterior fossa either a microvascular decompression or an acoustic, for instance, I have the patient well-padded and also well-secured because I rotate the patient. So when I open the posterior fossa, you often have to elevate the table and look around the cerebellum, as you mentioned, and then rotate the patient to see, and then as you retract and aspirate CSF, then you rotate the patient back towards you, and then you can see the pathology at the base of the skull.

- Thank you. Prone position obviously used very often, very successfully for midline posterior lesions. Obviously, it has challenges in larger people especially the abdomen can be on a pressure and prevent venous return. All the pressure points have to be very carefully padded, especially genitals in this area. And concorde position is a variation as you can see of the of the prone position, especially for transtentorial approaches with good amount of flection of the neck. But, again, we are able to do any procedure that we need, the prone or the concorde position in a lateral position with a patient in a more comfortable position. So here's one of your patients, I believe in a prone position. If you can please take us through the parts.

- Sure, this is a posterior fossa tumor, but we would position a Chiari decompression in the same way and you know, I think the key here is be careful how much you flex the neck and make sure there's a good distance, you mentioned two finger breadths, between the chin and the chest, which I think is a good ballpark. You'll notice what we've done here is we've reflexed the table and we have the knees in this trough. And so the patient doesn't fall out of the table and slide down. And so this is important to elevate the foot rest, to provide counter traction against the knees so it really secures the patient nicely. And then again, be careful where you put the pins. We usually put them just above the pin of here and then the double pins, we'll be careful not putting them too much in the temporal fossa, into the temporalis muscle, as was mentioned by Aaron earlier. And again, we kick out the retractor system a little bit to allow us better exposure here and placement of our retractors away from the surgeon.

- Overenthusiastic flection of the neck, especially in large muscular patients, I have seen some of the residents grab the both sides of the arms and because they really want to increase the distance in the C1 and foramen magnum bone area they really flex the neck so hard that almost makes the pin slip and puts the patient in a very uncomfortable position. So if the neck is not flexing comfortably and the patient is already paralyzed and under anesthesia, really forcing your pins to put the patient's head in a position that's not comfortable would only compromise your fixation. And I want to warn people against that, especially some of the orthopedic surgeons who do neck procedures you'll have seen do that and have later found out that the head has fallen out of the pins and the eyes were resting on the arms of their Mayfield pinion with unfortunate consequences. This is one of my patients in a position for a parietal approach for an arch venous malformation early on in my career. As you can see, all the pressure points were padded. In this case, the lesion was more along the parietal bossing so not much flection was necessary, but again, avoiding over inflection as much as possible is critical. But as you can see, this patient is relatively large and the amount of obstruction of venous drainage can be significant in this position. Sitting position is oddly enough one of my favorite approaches. Part of it is because of my training, the other part is I love the pineal region. And I think if there is one great advantage and one very good indication for sitting position, Bill, is for reaching the pineal region and letting the cerebellum drop especially approaching the pineal masses in young adults and children. So for posterior fossa surgery for pineal region I think this is the best approach. Many people are uncomfortable with it because they don't know how to handle the consequences of complications of venous air embolism.

- Yes, I mean, I think definitely for the pineal region, it's the approach of choice for a super cerebellar approach. And I use it for that approach all the time. I think the liability that you run into, I think with this approach is that if you don't do it enough and the anesthesiologists are not familiar, then it causes a lot of anxiety. There's a lot of extra time in setting up the room. They need to understand and have experience in recognizing problems with air emboli. But the advantages are superb, I mean, there's no venous bleeding, the CSF drains from the field. It gives you a perfectly clear view of the posterior fossa for acoustic surgery or the pineal region. And it allows you to use gravity as your friend in retraction of the cerebellum.

- And this is the position for a pineal region mass I recently did, again, you can see that transesophogeal echo, a central line or a long arm CVP. And the more you flex the neck comfortably, the better your angle would be along the tantrum to look up and it becomes more comfortable for the surgeon. Again, really a versatile approach. You need to TE, you need long arm CVP line or a central line and you need an anesthesiologist who's comfortable. And you need as a surgeon to be comfortable that if you have an air embolism, it's not a big deal if you know how to handle.

- I think the real issue, if you're planning a infratentorial super cerebellar approach is the angle of the tentorium because in some patients, no matter how much you flex the head, you'll still won't be able to do that. We'll come transtentorially in those cases and from the occipital approach and reach them, but both use the same position for that as well. And I think a couple of other minor points. Ron Apfelbaum, my partner who is now retired, he developed a short ocular lens for your microscope and it's superb. It actually shortens the oculars about two or three inches and allows you a closer reach to the patient when the angle of the microscopes completely horizontal and you're looking through the superior cerebellar approach. And that is really helpful on longer case. And you have to think about arm fatigue and resting your arms. And some people it's a very long reach, especially for big people trying to reach from the posterior area here to the region of the third ventricle posteriorly. If you're going to use this for a superior cerebellar approach, you need to map out exactly using the same landmarks that I mentioned before, where the transverse sinus is going to be. You need to drill off the bone so it's not overhanging the sinus because you need to look and this bone can be in your way so you need to really remove the bone just at the region of the inion. Either you need to take off the bone above the sinus so to expose the transverse sinus or else if you don't expose the transverse sinus, you need to drill the bone so there's not going to be in your way when you look just underneath the transverse sinus with your dural opening.

- If you don't mind, I'm going to go ahead and show a video of this super cerebellar approach for pineal region astrocytoma. I think that's really posterior third ventricle region mass. As you can see, this is the sinuses, transverse sinuses. The bone has been removed completely. We've put this stitch actually underneath of the transverse sinus. And without any retraction, we're looking at the pineal region very comfortably. Again, you can see the stitch, the dural has been reflected, the stitch is pulling up the sinus in front of it. And you can comfortably doing the procedure with a clean field. Very briefly, Bill, as a last minute discussion how we place a patient for a transsphenoidal operation. Ed Laws has taught me this trick of having the head of the patient sort of perpendicular to the wall of the operating room and turning the body away from you so the shoulder gets away from you. I think that really helps tremendously. I can't tell you how much tax it can be on your knees and on your back when you're reaching over to operate transsphenoidally if you're doing endoscopically or not. So if you turn the body away, but still keep the head in a straight position not to disorient yourself. I think it's very helpful. Any thoughts there?

- Yeah, I think I agree with you. So what you've done is you've laterally flexed the head. So you've got a good trajectory here yet the body's out of your way a little bit. The other thing that we'll do is we'll also rotate the head a little bit. So the patient's looking at you face to face. So again, it makes it a little easier to look at the ipsilateral part of the transsphenoidal area, it gives you a more true straight-on view to the face from when you stand at the side. Now, of course, some surgeons stand at the head and in those situations you want the patient completely square, but I prefer to side at the side so I can elevate the head and reduce the venous bleeding.

- I want to finish with one picture of showing the pitfalls in placement of skull clamp. As you can see this as a patient, one of my residents placed the head in the pinion, you can see the single pin and both pins are one side of the head across the superior sagittal sinus. This has a high risk of the head slipping and just like you said, Bill, instead of falling onto the pins, it's going to fall onto the arm of the Mayfield skull clamp causing significant injury to the patient. The other error that occurred is that the pins are too close to the vertex of the head. Again, facilitating slippage. Bill, thanks being a great mentor for me as always. And thanks for your time.

- Appreciate it.

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