Grand Rounds-Infratentorial Arteriovenous Fistulas: Nuances of Technique for Microsurgical Ligation

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- Hello, ladies and gentlemen. Thank you for joining us for another session of the double-A NS Operative Grand Rounds. We're privileged to have with us Dr. Johnny Delashaw. Congratulating him on his new position as the Chairman of University of California at Irvine. The first part--

- Thank you, Doctor.

- Thank you. The first part reviewed the basic concepts regarding microsurgical ligation of supratentorial arteriovenous fistulas. This part two will review the basic concepts and some of the nuances of technique for posterior fossa arteriovenous fistulas. As the most common form of this fistulae would be superior petrosal sinus, we are going to focus on the topic. As always, this is the disclosure acknowledgement for Johnny and myself. Let's go ahead and dive in, Johnny, if you don't mind. Directly in the case and review some of the basic concepts to--

- Sure.

- get some excitement, thank you, about this case. A 52 year old female with a sudden onset of severe headache, sounds like a pretty apoplectic event. And as you can see, the CT scan shows a large intraparenchymal hemorrhage as well as evidence of subarachnoid hemorrhage. Obviously these days, we go straight to a CT angiogram, and a CT angiogram demonstrates this abnormal vessel along the posterior fossa and anterior pontine area, and really no evidence of an aneurysm or other vascular abnormality. Johnny, if I may ask you, these days with so many of us relying so heavily on CT angiogram, this is a lesion that could be very easily missed. Any other pearls you have in looking at a CT angiogram to make sure this lesion is not missed?

- So, if you have a CT angiogram with a intraparenchymal subarachnoid hemorrhage and you have some abnormality and you don't understand it, it's important to get a cerebral angiogram, not only they get the four vessels intracranially, but it's also important to do an external circulation, looking for a dural AV fistula. In this particular CTA, there's clearly some abnormality located along the CP angle on the right side, and that abnormality suggests there is some kind of vascular malformation, and it really does look like it's probably going to be a dural AV fistula. But I would recommend an angiogram to get a full delineation of the extent of the vascular malformation and where the venous outflow begins, because that's going to be the important part in deciding how to treat this. Remember with dural AV fistulas it's very important to occlude the venous outflow. If one does that, one can successively treat the dural AV fistula. Just taking care of the arterial portion, will not always successfully treat the dural AV fistulas. So I'd get an angiogram in this case.

- And that's exactly what we did, Johnny. And as you can see on this angiogram, you can get some of the tentorial feeders from the internal carotid artery injection or the usual Bernasconi-Cassinari arteries often defined for meningiomas at this region, but hypertrophied from inferolateral trunk of the supra hypophysial artery. And as you can see it is often intimidating looking at these veins and varices along the posterior fossa, but often there is a single connection between these arteries along the edge of the petrous-tentorial junction, right where the superior petrosal vein is located, defining them as a superior petrosal sinus AV fistulas, and again, a preview of the angiogram late arterial phase defines that a little bit better. Anything else you look for in the angiogram, Johnny?

- Yeah, so this here this lateral view here really explains it, you see this small variceal in the superior petrosal vein here, and you see all these anterior feeders, if one tries to embolize these feeders there'll be others that they may not be able to embolize, and these are all very small and be very difficult to get to. But if one occludes the outflow right here that will take care of the fistula, it will also take care of a lot of this venous drainage. The venous drainage will be a lot more slack, and really the treatment is to take care of it right here, where you showed. So the angiogram really tells you where you need to go to treat this dural AV fistula. In actuality for many of these, if you can find the single outflow of the dural fistula, you can treat this very simply.

- Thank you. Let's go ahead and start with a positioning video just to show how the positioning for a retromastoid craniotomy can be done. As you can see the two pins above the contralateral ear, one pin on the ipsilateral ear, and the patient is really positioned in the lateral position for a suboccipital craniotomy. This is really one way to do it. I know some people use a supine approach for the suboccipital craniotomy. This is a typical retromastoid approach for a trigeminal neuralgia decompression. Do you have any pearls about suboccipital positioning or other details preoperatively that are important to you?

- Well, if one's going to do a retromastoid approach, which is what we're really talking about in our suboccipital craniectomy, I think either approach is fine. What you're talking about, one is supine position, with the head turned quite horizontally so that one can get a look around the cerebellum onto the brainstem, and the other is a lateral, or almost three-quarters prone position, which you're showing here. This is a little bit of a surgeon's preference. I like the position you have the patient in now, which is a lateral three quarters prone position, because I feel very comfortable. The surgeon is very, very comfortable and I like operating with my hands and everything pointing down and be very comfortable and not looking around edges. So I typically position the patient exactly the way you're showing in this illustration.

- And do you use a lumbar drain just to decompress the posterior fossa? Or do you feel like you want to open the dura and get through the cisterna magna, Johnny, first?

- So the way you can do here is there several things. One you can use a lumbar drain. Remember if you use a lumbar drain, the patient could develop a postoperative positional headache, which would require a blood patch. So I typically use a lumbar drain for very large tumors or those kinds of things for dural fistula I do not. For dural fistula, I make a craniectomy over the area that I'm concerned about, and then I come along around the 9th, 10th, and 11th cranial nerve. I take a paddy around the cerebellar edge there and open up the cisterna there and just spend a few minutes draining cerebral spinal fluid, and the cerebellum and posterior fossa become extremely relaxed. So in this particular case, and someone here who's had a hemorrhage, the posterior fossa may be very adenomatous, and I wouldn't hesitate to put a lumbar drain in to give me a little bit more room, but in an elected dural AV fistula, I would not use a lumbar drain.

- That makes great sense. I don't think really a petrosal approach or a more extensive skull-based approach would be necessary in these AV fistulas, because the target is only the draining vein, which is right where the superior petrosal sinus is, or the variation of that location. What are your thoughts there?

- Yes, you know, for this, you know, where the dural fistula is, where you have to go, and it's right at the superior petrosal vein entrance into the superior petrosal sinus. That superior petrosal sinus is almost always occluded with these fistulas. So you gonna go right there. So doing a small craniectomy like for a trigeminal microvascular decompression is plenty of space. You need to have enough space to be able to get your bipolar and sucker in there, and you need to have enough space to be able to place an aneurysm clip. You don't need a large craniectomy.

- Thank you. Let's go ahead and review the next step in this case. Let's go ahead and see what happens after we do the exposure and enter the pustule fossa. Here is the video. Again, the right sided suboccipital craniotomy, as you can see, this is the sigmoid sinus transverse sinus. We did place a lumbar puncture drain about 40 CC before starting the case. You can see ample amount of space, and here's that fistulous connection, Johnny, you were talking about through the edge of the tentorial-petrous junction, and that's the edge we follow along. This can be very adherent to the brainstem or the trigeminal nerve, as you can see here. It surprises me why these people don't have trigeminal neuralgia. What's important is there's always a big varix there, and you can miss another fistulas connection behind it. Any other thoughts about managing these lesions at this juncture, Johnny?

- [Johnny] So it can be very scary at times the varix can look quite large, but if you can get an aneurysm clip right along the tentorium there and take that venous outflow, that's really the case. One needs to remember that as you are exposing this, as you're showing here and taking the clip, be sure not to clip the superior cerebellar artery. It can be very close to this fistula, and one needs to look around after you've got the clip on and make sure you don't have an arterial segment so that you don't get a cerebellar stroke. Well done.

- Thank you, and you can see the ICG, so helpful, shows that the fistulous connection is obliterated, small, pretty, vessels on the trigeminal nerve and really a little bit of stagnant blood. Otherwise, really the fistula has been obliterated and there is no fluid across the clip. Again, looking behind the fistula because often they have a variable, a smaller branch that goes along the anterior pontine vein can be missed if it's not looked for, and we're going to review actually a video that. Let's now that we discussed this case, Johnny, enter the subject of really these infratentorial fistulas that can be very tricky, can be missed. And the recurrent hemorrhage can be very aggressive and obviously unfortunate to the patient. So dural AV fistulas are, in general, abnormal connections between an arterial feeder and a dural venous sinus, or a leptomeningeal vein with the nidus located within the leaflets of the dura, and it's tentorium is really where the fistula is, where there's so many of them, we catch them where they all come together to form the draining vein. The patients may present with subarachnoid hemorrhage, intracerebral hemorrhage, as we saw in our case, the case of our patients, and they cause hydrocephalus, venous hypertension and associated neurological deficits and potentially pulsatile tinnitus. More important, it can even be asymptomatic, but if they have cortical venous drainage, I believe treatment is indicated to prevent future episodes of intracerebral hemorrhage. They can be divided into galenic, straight sinus, torcular, tentorial, superior petrosal sinus, or incisural, but do you agree that all those are rare? They're all rare, but they're a lot rarer than superior petrosal sinus in general, and that's probably the most common one. Do you agree with that, Johnny?

- I would say that the superior petrosal sinus dural AV fistula is one of the more common dural AV fistulas that we see, and clearly the most common in the posterior fossa. The other dural AV fistulas do occur, but they're rare.

- Thank you. Now we're going to focus on the superior petrosal variant today that can be very variceal, and often associated with large veins, very intimidating posterior fossa, but really it's the fistulous connection that needs to be connected. And again, it's the Dandy's vein, where that Dandy's vein is, is where your fistula is going to be. As you very well mentioned, Johnny, these are very difficult to treat endovascularly. There's extensive meningeal arteries from carotid artery and vertebral artery, both internal and external, and it is difficult to embolize as compared to the usual external carotid arteries. Simple interruption of the duranial vein is the key to go, retromastoid craniotomy does the job, and again, the more extensive skull-based approaches are not necessary. Since you have tremendous experience with skull-based, Johnny, I thought we'd briefly review some of the details of a posterior fossa craniotomy. We do like to position the patient just the way you mentioned it, and we do like to have the assistant to be across the table from the surgeon to transfer the instruments. The resident fellow sits across from the surgeon, and that's usually how the operating room setup works. We are feeling very generous about doing the lumbar drain to decompress the posterior fossa. Relaxed brain means a relaxed surgeon. Place a lumbar puncture and drain about 35 to 40 CC of CSF that does decompress the posterior fossa very well, and again, you can go around the cerebellum very well. The venous bleeding could be also decreased from the sinuses because of the decrease intracranial tension. This is the Mayfield skull clamp positioning that we have come to enjoy using. As you can see, really is out of the working zone of the surgeon, which is behind the ear and also keeps the pinions behind the hairline. There's many ways to do a suboccipital incision for a retromastoid craniotomy. We have used the linear incision, but recently have come to enjoy the curvilinear incision. As you can see, this is the mastoid groove. This is the line between the root of zygoma and inion where these two lines cross each other, Johnny, that's the summit of our curvilinear incision, and we reflect everything inferiorly and you can see the same findings in the operating room on a patient. Do you use a linear incision, Johnny?

- I actually use a curvilinear incision, a little bit different than yours, but all these incisions are fine. What one wants to do is get nice exposure around the asterion and the area just behind it, so that one could expose a transverse sigmoid sinus junction.

- I agree. That's really the dealer's choice. The only thing I can say about a linear incision is, as you make your linear incision and you retract the soft tissues, including scalp and muscle with the cervical retractor, they bunch up and they really get on your way of your retractor. But if you reflect the flap inferiorly or any other way, your working distance to the posterior fossa does decrease. So these are the corridors to use. Obviously the supracerebellar infratentorial approach to the trigeminal nerve is what we're talking about here. After the incision is completed, we place a Burr hole just along the anterior inferior portion of the asterion, the usual craniotomy, obviously, the only removal of the sinus is completed last, and you may use kerosene to get a more lateral trajectory over the sigmoid sinus. These are really basic techniques. We all share in the same way. You can open the dura along the transverse sigmoid junction and the sinuses, and really follow the tentorial-petrous junction to the area of the superior petrosal vein that usually at this point is very arterialized, and it's very obvious, and usually contacts at least with one of its branches on the trigeminal nerve, and really placing that clip right where that fistula exits the dura, but not too close in order not to avulse the vein when you close the clip. Any other nuances here, Johnny?

- I don't think so. I think that looks exactly like I would do it. The important thing is to find that arterialized vein and clip it right up against the dura around the petrous-tentorial junction.

- Thank you. Yeah, it could be variations. This is what I was referring to before is, you may clip this one and you miss this one that is along the anterior brainstem. So when you clip one, always look for another one behind it, which could be hiding, and this is really the typical finding that you find the really enlarge variceal fistula along the tentorial-petrous junction really dividing into additional fistulous connections or draining veins that are arterialized. Let's review this very interesting case, and I would like your opinion. A 41 year-old female with a history of a brainstem stroke. Unfortunately this lady became ventilator dependent, really, nobody looked at any point about etiology of her stroke. A very young woman, ventilator dependent, was in a nursing home for about a year until he saw a new neurologist and a new neurologist decided to look into was the reason for her brain stem stroke that you can see so clearly on a sagittal flair image. They did a CT angiogram. They saw this questionable venous abnormality, and as you can see, a very diffused what we now know is venous hypertension in the brainstem. This is why I think these lesions are so dangerous because they're easy to be missed, they're under-recognized, and patients could become ventilator dependent in the nursing home for many years, and nobody knows that these are treatable conditions. A 41 year old woman is too young to be in a nursing home as a vegetable. Have you had any experiences such as this, Johnny, or what are your thoughts there?

- You know, I have not had an experience such as this in the brain, but this actually is not an uncommon presentation for a spinal dural AV fistula, where they get tremendous edema within the cervical cord or thoracic cord and have a quadriparesis from that. So, but I'm not surprised that one would see one like this from a superior petrosal sinus dural fistula, but I have not personally seen that.

- Thank you. We went ahead and proceeded with an angiogram and as you can see, there is this draining vein that continues along the anterior brainstem, and this is really an external injection. This is the edge of the tentorium, and you can see this draining vein, not very large, but definitely is there. These are additional views. You can see these draining vein much earlier than you would like it to see at the late arterial phase along the injection of the external carotid artery. Here is even more prominent along the anterior brainstem. And this would be the configuration of this lady's pathoanatomy that we'll review using the operating video. She had a fistula here and another fistula moving anteriorly, very difficult to clip all the way anterior to the brainstem, and I would like to review some of the challenges that you were going to face in this case, which I found very interesting. So we're going to go ahead, and this is again a left sided retromastoid craniotomy, Johnny, this is the seven and eighth cranial nerve. This is the lower cranial nerves, just opening the arachnoid to have a panoramic view. And as you can see, this is the fifth nerve, a lot of arachnoid around, very difficult to know what's going on, and at the first glance, it looks like there's not much happening and there's no fistula, but as you take your time and open the arachnoid all around the fifth nerve, and practice some patience, you're gonna find a very large fistula, right at that juncture. You can see some, it's like arterialized vein right in front of the fifth nerve, as it enters the Meckel's cave. Here is more pronounced large arterialized vein, sort of going all the way along the anterior brainstem. You can see it has one of the arterialized vein here and the other one is right behind it, and they both join the junction of petrous bone and tentorium. I try to put a straight clip, Johnny, as you see, and it was so deep that the clip was not long enough. So still there was some of the fistulas still patent. So I go ahead and remove this clip sort of tricky to work so deep and try to remove that clip all the way, anterior to the brainstem, where we remove that clip, used the longer clip, and again, it's all the way anterior to pons, working between the fifth nerve and the tentorium and placing a clip across there. As you can see, the arterialized vein collapsed along the anterior pons, and we placed another clip across the more posterior branch of the fistula. So one along the anterior brainstem, one along the more posteriorly located branch of the fistula. Any thoughts in this situation, Johnny?

- [Johnny] Yes, the operation that you performed, I think is the ideal operation. Had you done something else, like a middle fossa approach, which would give you a little bit more anterior direction, the problem with that approach is that you're going to have to go through the dura that's incredibly vascularized by the fistula, and it would be a real problem. It's better to open the dura way away from the fistula and then attack the venous outflow. So I think a middle fossa approach, or petrosal craniotomy, would have been very difficult, just because you would be involving the dura, thus involving the fistula. I think doing a retromastoid craniectomy and coming around the CP angle and attacking the fistula is the appropriate operation. Nice job.

- Oh, thank you very much. As you can see at the end, we saw a view of the ICG really demonstrating the fact that there is no more sort of feeling of the fistula. There's some normal veins on the brainstem, and so the ICG really helps to give you a feedback right away. So let's jump to the next case. I think this case is relatively easily give us some idea about how management of these cases take place. And again, this is ultimately the view or the illustration by Jared, our principal illustrator, who is defining the fifth nerve, the posterior branch, the anterior branch, again sandwiching the trigeminal nerve between those two branches. I think this illustration, more than anything, clearly defines the complex anatomy of this lesion, and really postoperatively, as you can see the clip, and no further venous bleeding or a venous drainage at the end of the arterial phase or shunting on the angiogram. This is more of a typical presentation, Johnny, and you can see a 36 year-old male with a sudden onset of headache, dizziness, and nausea, and typical hemorrhage along the lateral part of the brainstem some T2 signal change, potentially venous hypertension, that is more longstanding, and some acute hemorrhage due to, again, venous hypertension. Relatively classic, arteriovenous fistula, coming from the arteries of tentorium forming this glomerulus form of veins. Any thoughts there? I would say that's pretty classic. Don't you agree?

- I do agree. I think the one thing that a neurosurgeon might get confused with is seeing that hemorrhage within the brainstem, they might think that that's a cavernoma, and this is why it's important for these lesions, particularly around the superior petrosal sinus to get an angiogram with an external circulation. So as not to be fooled, this is not a cavernoma. This is a AV dural fistula.

- Thank you. That was a very good point, and you can see on CT angiogram in this situation, we could see these abnormal class of veins, although usually on a 3D CT angiogram, that is rare to see. Let's go ahead and review the video of this one. It's a relatively interesting case. Again, a right-sided retromastoid craniotomy, sigmoid sinus, transverse sinus, petrous bone, tentorium, petrous-tentorial junction, seven and eighth cranial nerve to sort of orient our colleagues here. You can see again that variceal expansion of the vein as it joins the petrous-tentorial junction, and the fifth nerve, and really a beautiful, what we call, you know, pristine case, when there is not my subarachnoid hemorrhage, I didn't like the first clips. So we went ahead with a bayoneted clip, and after we placed the clip, you go around and make sure you don't miss anything else. You very well mentioned. You don't want to clip the superior cerebellar artery in this situation, and we're gonna show an ICG in a second. Any other thoughts in this case?

- [Johnny] No, that looks terrific. It's nice to see one that doesn't have a lot of blood by occluding that there, the fistulas should be taken care of.

- Yeah, as you can see, the arteries look pretty patent and the fistula is taken care of, even though that fistula looked pretty sort of voluminous after the clip was placed, but thanks God that there was no complications, and the fistulous connection is taken care of. Really ICG gives you a beautiful view relatively immediately in terms of feedback of how things are turning out. Let's go ahead and review our last case. This was a patient and one of my most thankful patients because after resolution, the venous hypertension, he was extremely happy to know, he doesn't have the nausea, vomiting, and dizziness, which he was suffering for a while and just dramatically gotten worse with the hemorrhage. This was one of the first AV fistulas that I did. A 32 year-old male with a sudden onset of severe headache and left facial numbness, and you can see again, this classic CP angle subarachnoid hemorrhage, and in this situation, and you can see at later phase, these veins in the posterior fossa, and again, from carotid artery, early arterial phase, you can see sort of start of the fistula, and very typical of AV fistula. The 3D angiogram I included this case because of the 3D angiogram. You can see the petrous ridge, porus acusticus, and you can really see the branches off of the carotid artery, that come across the tentorium, form this fistula that creates this intimidating tangle of veins and additional varices that can rupture. Any other thoughts on the imaging here, Johnny?

- No, that's terrific that you don't always see that on a CTA, that's very nice imaging.

- Okay, if I may say, I may have confused you. This is a 3D angiogram, I believe, exposed post, overlaid over the bone.

- Ah, okay.

- So that may be why it looks better, but it is just nice to see it in 3D to appreciate the anatomy in terms of the arteries and the fistulous connection and the posterior fossa.

- That looks perfect.

- Thank you, Johnny, and this is the last video here, video number four. Again, a left sided retromastoid approach, tentorium, petrous bone, trigeminal nerve, seven and eighth cranial nerves, and often one of the branches of the fistula, very much indents the trigeminal nerve, as you can see, and again, looking around just like you mentioned, don't clip the artery right behind the vein, because that will not have a good consequence. Any other details and pearls that you would like to share with us?

- [Johnny] No, I think just reiterating that what's important here is to occlude the venous outflow. So, by putting a clip right along the petrous ridge, where the superior petrosal veins are supposed to drain into the petrosal sinus, which is not occurring in this case, you've got retrograde flow. You put a clip there, it should take care of the dural fistula, and that's what you seem to be doing right now.

- Yes and at this juncture, we went ahead and coagulated and cut the fistula just to decompress the nerve. I think, as we all know, the results are very satisfying in the patient and the surgery is real fun. Some very few pearls and pitfalls here. Just what you reviewed before. The clips should be applied close to the tentorial-petrous dura, not too close as the blades close to cause avulsion of the vein. Draining veins distal to the clips should darken after the fistula is interrupted, and the venous varix may sometimes hide an additional draining vein coursing posteriorly, and towards the brainstem. The varix should be mobilized after the clip is placed and the surgeon should take sort of those steps rather than being sort of afraid of manipulating the fistula to make sure not another arm is over that branch of the fistula is disconnected. Johnny, as always, I appreciate your great pearls. Any last minute or closing thoughts?

- No, I think we've covered it. I think again, the whole thing to remember is to occlude the venous outflow just at the petrous ridge and the dural AV fistula should be taken care of. It should be a very simple and eloquent operation, but one needs to look around and make sure that you get all the venous outflow, as you said, looking around the trigeminal nerve, looking for that extra petrosal vein and making sure that you've completely occluded the venous outflow. If that's done the patient should do extremely well.

- Thank you again as always.

- Thank you.

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