We're going to talk a little bit about the practical aspects of designing a posterior fossil approach, and specifically spend some time on the details of the posterior trans-petrosal approach. So we've, over the last day and a half, learned that you can get to the posterior fossil in a whole bunch of ways. The trans-collateral approach, anterior-petrosal-middle-fossil approach we did this morning. We're going to talk about the posterior-petrosal-trans-temporal approach. The retro-sigmoid is a pretty well understood approach, so we're not going to spend a whole lot of time, except to realize that you can see a lot through a retro-sigmoid approach. The far-lateral trans-condylar, we'll go over that in the OR tomorrow. And then the standard midline approach is for, you know, fourth ventricular or midline lesions. So this is a tumor that, you know, initially you look at it, well, you could do a retro-sigmoid, you can do a trans-petrosal, but it's really pointing anteriorly. It has a trans-clival extension. The bone is abnormal. This black line is the dura. So it makes most sense to do this in a trans-clival route. So that's a great endoscopic approach. You know, we take down the front of the clivus. It's extra-dural, so we're dissecting the tumor off the dura, and that's the way to do that operation, the posterior fossa from the front. Carl and John talked about the middle fossa approach. This tumor is extending into the posterior fossa. Patient has hearing. The middle fossa approach is a nice way to do that. Here we're opening up the IAC. The facial nerve is anterior. Yeah, there we are. Tumor's out. That's the acoustic. This is a little bit bigger. It's flaring the IAC. Hearing is still good, but we felt a little bit uncomfortable with the middle fossa. So again, this was a retro-sigmoid approach, able to maintain hearing. Now, this one is something I think we probably have a differing opinion on. Pretty large lesion extending both supra- and infratentorially, even up to the interproductor cistern. And again, this is the diffusion-weighted imaging, so again, this is an epidermoid. You know, here we decided to use a pretty standard retro-sigmoid approach, and I won't belabor you with this video, but what it shows is if you go slowly and methodically and work between the cranial nerves, here we're working in the high posterior fossa. There's above the patrosal vein, and you know, that tumor can come out completely with a retro-sigmoid because of the nature of the pathology. Carl talked about it. You can compress the tumor internally, work on its capsule, the capsule will come down, and through a very simple retro-sigmoid approach, can reach down from the 12th nerve to the third nerve. A larger acoustic without hearing, trans-labyrinthine is an excellent approach. You've seen that already. This one is not one that you're likely to do one approach for. Both has anterior pathology, posterior pathology. We actually did two. We did a far lateral trans-condylar approach to remove the posterior pathology, fused the patient because she was unstable with a complete condylectomy on one side, and then did the anterior approach endoscopically. Here's a hypoplastic vertebral on the one side, the tumor out from a far lateral approach. Here's the durer over the cervical medullary junction tumor. Now this one is extensive, has tremendous tumor in the middle fossa, the carotid arteries in the middle of it, a lot of posterior fossa disease. The approach here is a total petrosectomy. In this case, for a malignancy, if it's involving the facial nerve, we will sacrifice the facial nerve. If not, we try to keep it in its anatomic location as much as possible. In this particular patient, the facial nerve was not salvageable. But that allows you this kind of approach where the entire neoplasm can be accessed in one anatomic space. But finally, we're going to talk about the petrose approach and the mechanics of the petrose approach. We're going to use that, highlight it with this tumor here, which is a chordoma. Has mostly posterior fossa extension, some extension into the clivus, but predominantly in the posterior fossa. A lot of clivus to go through to get to it. So my thought was to get this through a petrose approach. And why did we choose a petrose approach? Well, this is two different pathologies, obviously. Chordoma anterior to the trigeminal nerve, medial and anterior to the trigeminal nerve. And this is just a petrous meningioma, which, of course, is accessed right here through a retrosigmoid. But when you take a retrosigmoid approach, this is what you see. You're behind the sigmoid sinus, you come along the petrous bone and into the back corner. The petrose approach, you come right behind the labyrinth. It does give you that more anterior look, lets you look over to the side. But there is an area that you have to be cognizant of, which is the area in this corner right here, where you don't have a great view from the petrose approach alone. And how much this is depends on the depth of the clival depression. When you look at some patients, you'll see sometimes petrous bones that are here, clivus is straight across and then down. Very shallow petrous clival depression. But others have a very deep clival depression. The deeper the clival depression, the harder to see that area from a petrose approach. So this is just the way I've come to do it. There's no particularly right or wrong way, but I have reasons for doing it that way. We elevate the scalp superficial to the temporalis fascia and to the sternocleidomastoid muscle. We elevate it up to the external auditory canal. This comes down to the root of the zygoma. And then I use a little neck crease here. And I elevate this in one piece. This is the temporalis fascia, some periosteum, and then the sternocleidomastoid muscle. We elevate that off of the temporalis muscle, off of the bone, the occipital bone, and then rotate the sternocleidomastoid muscle off of the mastoid inferiorly. That leaves you with the temporalis muscle and the splenius attached to the posterior fascia to the edge of the mastoid process here. We rotate the temporalis muscle anteriorly here. The suboccipital musculature, you don't have to individually dissect each one. You just can subperiosteally move that entire muscle bulk posteromedially. Gives you the entire mastoid process and the external auditory canal, and this is the area we need to look at for bone removal. Looking a little more closely, the temporal line is just the posterior extension of the zygomatic arch. That's one important landmark. The spine of Henle, which is right here at the back, just immediately behind the external auditory canal, is the other important landmark where you're going to, when you drill deep here, you're going to find the antrum of the mastoid. It's very anterior. And then the other one you have to kind of close your eyes and think about is where the sigmoid sinus is. These are old pictures, and there's lots of ways of deciding where to put your burr holes. Most people use image guidance. I mean, I use image guidance for one reason, to tell me kind of where the sigmoid and transverse sinuses are. It's real easy, and I put my burr hole directly on top of the sinus and work from there. But if you put your burr hole at the esterion, you're usually just at the transverse sigmoid junction. Then you put one anterior to that, and you can put one on either side of the transverse sinus. That's one way of doing it, doing the bone flap first. Personally, we've come to do the mastoidectomy first, because once you've done the mastoidectomy, you have your sub-temporal dura exposed, you have your post-sigmoid dura exposed, and you can simply take a craniotome and do that in a much more expeditious manner. We're going to do today in the lab a mastoidectomy. This is a relatively simple mastoidectomy where we've left the entire labyrinth intact, facial nerve intact. Here's the sigmoid sinus. All you really need to do this approach is have enough pre-sigmoid dura to open. But the more bone you leave behind the posterior canal, or the more bone you leave above the superior canal, the less your view is. And a few millimeters here make a real difference. So I think the ideal way to do this is to, I work with my otology colleague, and he brings that bone removal right to the back end of the posterior canal and right at the top of the superior canal. And we open the dura pre-sigmoid, and I'll show that in a sec. But that's what we're going to do in the lab. And I think we can, I would start here, get a look at what you can see, and then take down your posterior canal, see what you can see. Take down your superior canal, see what you can see. Then take out all the canals, do a trans-labyrinthine, and then look at your anatomy then. This is the mastoidectomy completed. You see we have not completely, this is when I used to do them back myself, and I did not skeletonize the entire trans-lab, the labyrinth here. I just got enough pre-sigmoid dura. That's what it looks like with the bone flap. But essentially once you've had the bone flap off and the mastoidectomy done, these are the dural incisions. One is pre-sigmoid. One is along the floor, the middle fossa. And then I like to come over here a little bit just so I can see what's happening in the venous anatomy here. We all talk about a venal abey. It's not necessarily a vein. There are reciprocal relationships between the veins here. You might have a very small superficially draining vein here, but very large sub-temporal veins. So before you make any decisions regarding where you section your superior petrosal sinus, I think you need to look under the temporal lobe. You need to assess where those veins are. You've got to make sure that the major venous draining is not into a tentorial lake that you might want to cut across. So there's lots of reasons to look under there. That's another reason to take the bone right to the labyrinth. That gives you some options for where you section your superior petrosal sinus, where you can move forward or back depending on the venous drainage in that location. Here we have a retractor on the cerebellum, one under the temporal lobe. This is the cut in the tentorium beginning. There are clips across the superior petrosal sinus. The cut is carried medially and anterior. Ideally you want to be just behind the trochlear nerve as it enters the tentorium and you progressively go through there. It's only when you finally divide that last bit of tentorium that everything just opens. Until then you're saying, oh this is not great, I'm a little tight. When you open that tent, the posterior fossa falls back, you get the view you really want to get, and you get the view above the trigeminal nerve. Here's the petrosal vein, trigeminal, 7a complex, ica. The tumor you see is medial to the trigeminal nerve and facial complex. Took down the petrosal vein, and here again the whole thing is exposed. 5, 6 is pushed way laterally, 7, 8, the lower cranial nerves here. This is sort of the lower extent of what you can do pre-sigmoid, 9, 10, looking at them from above. You don't have a good look at them from directly lateral or from inferior in this approach, but you get a good look at them from superior. And with the tumor out, the reconstruction starts by closing the dura here, cannot close here typically, so we do a fascial graft, lay in fat. And once we've laid in the fat, if you remember how we opened, we bring the temporalis muscle back, bring the suboccipital musculature back, and that whole flap, the sternocleidomastoid temporalis fascia flap goes back on top and is sewn in a watertight fashion all the way around the edges. So I like that, and I think it really helps with our CSF leak rate. And this is post-op, showing that, you know, excellent resection, being able to actually go all the way across to the opposite trigeminal nerve from that approach. We did come back later and finished off the clival portion. So in the lab today, it's the same side as Carl used for the middle fossa approach. And I think that's reasonable to do. Most of you have used a preauricular incision, you can just swing that back around, elevate the scalp down, take the temporalis fascia, sternocleidomastoid flap down, temporalis muscle forward, suboccipital musculature subperiosteally dissected away. And then you can do your mastoidectomy, expose the labyrinth, facial nerve, do the craniotomy, look at the tentorium, see what you can see, take out the posterior canal, take out the superior canal, see what you can see, take out the entire labyrinth, open the eye, see, and try to find the facial nerve from the brain stem all the way out to the stylomastoid foramen.

posterior fossa surgery

posterior trans-petrosal approach

retro-sigmoid approach

far-lateral trans-condylar approach

midline approach