Spinal Dural Arteriovenous Fistulas: Endovascular and Surgical Management

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- Colleagues and friends, thank you for joining us for another session of the Virtual Operating Room. My name is Aaron Cohen. Our guest today is Dr. William or Bill Mack from Keck, USC Neurosurgery. Bill is a dear friend, really one of the fastest and most affecting rising stars in neurosurgery without a question. I have followed his career from the time he finished his residency and he's currently at his very, you know, early career as the Vice Chairman of Academic Affairs at USC. He is on the Editorial Board of Journal Neurosurgery. He's on the Editorial Board of Journal of Neuro Traditional Surgery. He's the past President of the Society of Neuro Interventional Surgery and he's the upcoming Chair of the CV Section. You know, Bill, really, you have been an example for many, many young neurosurgeons in many levels. Not only you're an incredible surgeon, just an incredible academician. You're just someone who is truly a pleasure to work with and just get opinion and bounce things off of. We have had, you know, a number of times where we have had dinners together, and I can tell you that your intellectual curiosity and your ideas are just way advanced and ahead of time. And I'm really honored to have you here tonight and learn from you. Before we start, I'd like to ask a question that comes to mind to many of us, and for neurosurgeons who are finishing their fellowship and they wanna start a practice in open vascular neurosurgery that you do as well as neuro intervention, what are the pearls that you want to let them know that would, hopefully, work for them to get their career +somewhat as successful as yours has been? I think this is something that's so important for our viewers. What are those sort of nuances or secret sauce, ingredients of finishing as a comprehensive open endovascular neurosurgeon and start your practice? So, very interested and very honored to have you.

- Well, thank you, thank you, Aaron, for the kind introduction and I'm really honored to be here. And your question is a great one. There's so many facets to it and I think there's a lot of, it's not one-size-fits-all, it's different for every person, but there's some themes that I think are important. I think the training is absolutely critical. So, these are both fields with complex diseases that are evolving quickly, so a good foundation and training, which all our neurosurgeons seem to be coming out with today is absolutely critical. I found having mentors early in one's career, both on the endovascular side and the open vascular side is just invaluable. To be at a place where I am with someone like Dr. Giannotta, who is such a valuable mentor for the open surgery is, I think critical as those case numbers go down. And I think having colleagues, my team that I work with here is just supportive and pushes each other, and really helps in that way, and I think being curious. In this day and age, especially, the endovascular side evolves so quickly that reading the literature, going to the conferences, interacting with the industry partners, the devices we use today are exceedingly different than the devices that we used five years ago. So, on that side of things, being plugged in, being active involved, being curious, and balancing, I mean, we're taking care of a disease, not doing a procedure or a specific technique. The endovascular and the open vascular treatments are very different, and to be able to look at the patient and make decisions based on, you know, what would suit their disease and taking care of them is I think the most important thing. And it pulls you in a lot of different directions and there's been many people who have shown us all how to balance that very well. But I think falling back on mentorship, collaborations, partners, there's only so much time. So, pursuing an academic interest or research focus that's very much in line with what you do in the clinical arena, whether that's an endovascular or open vascular, or any other field in neurosurgery, to have those aspects of your daily life and your career aligned, I think with your operating room as your laboratory and being able to ask questions back and forth between the operating room and the laboratory is what I think has made the efficiency possible for me and many of my colleagues to achieve some type of success in this field.

- Very well said, and I think you have been, your curiosity and intellectual sort of prowess has been such an incredible key to your success to be, sort of, ahead of others. And I think this is sort of a very, you know, famous quotes that says, "There are a different group of people, and I think there are a different group of surgeons. There're those who watch things happen. There are things, there are people who make things happen, and there are a group of surgeons who wonder what the heck happened." And I think you are definitely in the category of people who may, surgeons and internationals that make things happen. And I think that's really the secret of what you're referring to, that you just don't wanna be a bystander, you just don't wanna watch others. You wanna be curious, you wanna be innovative. You wanna push the limits, and to do that, you need a supportive chair. You need the supportive colleagues that are so critical to your success, and I always tell my fellows, the most important factor you should look for in your first job is not the location, it's not the finances, it's your colleague and your mentors in your new job that are gonna make the biggest difference in your career. So, I think your comments are so well said and truly are the most important factors in the success of a neurosurgeon, and specifically someone interested in open endovascular neurosurgery. So, I know today, you're gonna talk about an extremely exciting topic, "The Endovascular and Open Surgical Treatment of Spinal AV Fistulas", one of the most satisfying operations we do in neurosurgery. So, we haven't had someone tackle that in depth. And so, I'm very excited to learn your philosophy. And with that, let's go ahead and jump in your slides, please.

- Thank you. So, yeah, I would like to take the opportunity today, to talk about spinal dural arteriovenous fistulas, and actually, spinal arteriovenous malformations in general, and focus on both the endovascular and surgical management of these lesions. And I, again, thank you for having me on the program. This is a wonderful opportunity. These are disclosures that do not relate to the topic matter in this presentation. So, I wanted to start by just classifying the vascular malformations of the spine that I'm gonna talk about. This was a picture taken from a beautiful article written in 2006 by one of my colleagues, Louis Kim. And although there's different ways to character classify these, I find this one very helpful, breaking into four types of vascular malformations, and we'll touch on each of these four in the talk today. The first is the classic dural arteriovenous malformation that Aaron referred to, which is a connection between the nerve root sleeve and the venous plexus of the spine. A one-to-one connection often. The second is what we call a glomus arteriovenous malformation or a true arteriovenous malformation like we're used to seeing in the brain parenchyma, but in the spinal cord. This is a tangle of blood vessels with arterial input and venous output, but has that true malformation. The third is what's often referred to as a metameric malformation. This involves not just potentially the spinal cord, but the dura and perhaps the bone, and the skin around it, often, a entire myotome and can occur in syndrome such as Cobb syndrome or others. And the fourth is per perimedulla arteriovenous fistula, which is similar to the Type 1, but typically, occurs in association with the anterior spinal artery and is classically, although not always, but classically ventral to the cord. So, those are, that's the framework in which I wanna conduct this talk and when I refer to those types of malformations or fistulas that's what I'm referring to. So, as we mentioned, the most common type is the Type 1, or spinal dural arteriovenous fistula, and it does have a male predilection and seems to occur most frequently in older patients greater than about 60 years old. We see these in both the thoracic and the lumbar spinal regions. But as I'll mention in the talk, these can occur anywhere. And when you do your imaging and your angiography, you really do have to look everywhere. And now, as you can see in the picture over on the right, this is classically located here at the nerve root sleeve where you can see the blood vessels coming in and connecting to the coronal venous plexus. So, this typically happens right at that level. There's arterialization of the corona venous plexus, and this causes venous hypertension, cord ischemia and potentially, myelopathy. And this is why this is often an insidious pathology that occurs over weeks to months to even years. And I'll tell you from doing angiography and understanding, and seeing these patients through our spinal surgery colleagues, I'd say the average amount of time that these patients take to get to our office is six months to one year. So, this is something that could clearly be improved upon. In terms of presentation, I mentioned it's often a protracted course with progressive neurological decline. Often, it's ascending. Back pain is possible radiculopathy, but more likely, it's myelopathy gait and sensory disturbances and even bowel and bladder dysfunction. Prior to the diagnosis, as I mentioned, most patients are inflicted with pretty severe motor and sensory deficits, so that's important to remember and understand when we see these patients. So, what are the goals of the treatment? When you're dealing with these fistulas, either surgically or endovascularly, it's to disconnect the fistula, eliminate the flow through the abnormal fistula's connection. There's no need to treat the veins, you just have to stop the flow from occurring into the draining vein that connects to all of the other veins, and thereby, reestablishing normal spinal cord perfusion. And you can do this, as I mentioned, both through microsurgery or endovascular surgery. So, moving along. The beginning of any workup, either probably microsurgical or endovascular spinal angiogram, and when you perform these spinal angiograms as we'll talk about, it's critical to understand a couple of key features, both when you're performing the angiograms and when you're reading the angiograms, if one is referred to you. Most important, perhaps, is the location of the anterior spinal artery. It's possible that a fistula could come off at that location, and that's critical to know in the operating room or the angiography suite. When you're doing endovascular treatment, you must have super-selective microcatheter angiography of the arterial supply. You need to know exactly where the supply is coming from and what will lead you to the fistulas connection to eliminate that connection. It's not necessary to eliminate every artery that comes into it, but you need to get into that fistulas pouch or fistulas connection. In rare cases, we do provocative testing with Amatol or lidocaine. More often lidocaine in the spinal cord, we do both. The lidocaine is more specific for the white matter tracts, and this allows you to put your catheter into a blood vessel or into a feeder to the fistula and see if perhaps, that's feeding something important besides just the fistula and whether it's a connection that can or cannot be taken. So, when we use our embolic agents, by far, the two most common embolic agents are Onyx, which is Ethylene Vinyl Alcohol and nBCA. Rarely coils are used. I use them often, to occlude past where I'm treating so that the liquid embolic goes in the correct direction, but it's typically difficult to occlude a spinal arteriovenous fistula with coils alone. Now, when would we choose each of these? Well, Onyx facilitates prolonged controlled injection that can infiltrate into the fistula. And although, this is more commonly used for cerebral arteriovenous fistulas, if you read the literature, I think there's a large number of operators using this for spinal fistulas at the present time, and that's only becoming more common with the technical advances we've had in balloon catheters and such. nBCA or glue, as we call it, can penetrate usually more into the small dural vessels, especially, when the catheter's wedged or takes up the entire diameter of the vessel, and you do not have space around the catheter for reflux. Glue is highly thrombotic and if you look back through the literature is actually the most common technique for spinal dural arteriovenous fistula. So, I wanted to share several cases and talk about how we do this and how we like to perform these procedures. This first case, you could see, is a 71-year-old gentleman with midthoracic pain, difficulty ambulating for six months. As I mentioned, this is the kind of time it usually takes for these patients to get there, and has urinary incontinence. As you can see, there's cord edema, which I'm trying to point to, but I'm having difficulty with the pointer. There's cord edema at the level of the midthoracic cord and dilatation of the conus medullaris region. So, on the angiography, what we see here is a Left L2 segmental artery that supplies a Type 1 dural artery arteriovenous fistula. And you could see the connection at the level of the root sleeve where the intercostal artery, which is the large artery, goes into the smaller radicular feeders and up the squiggly spinal coronal venous plexus, which I have the red arrows on in the middle picture. Now, off to the right, you see the Right L2 injection. That's a different injection on the other side, which supplies the anterior spinal artery or the artery of the damp cords. So, it's important to know that you can't have any reflux from one side to the other, or you may put the spinal artery and the patient's motor function in jeopardy. Next slide, please. So, this is what we did to treat this fistula. And what you could see here is at the bottom of the screen on the left, we first placed coils in the distal segmental arteries such that none of the Onyx went to the larger part of that artery that did not supply the fistula. Now, that artery can be blocked, so we did so, and then, we blew up a balloon at the red arrows more proximally to prevent reflux and injected our Onyx material into the fistula. So, the coils present prevented the Onyx from going forward and the balloon prevented the Onyx from going backwards. And as you see by the white arrows in the picture on the right, the Onyx cast went up the spinal cord through the connection into the fistula and even somewhat into the vein. So, that, you can see the coils at the bottom, and you can see the balloon on the left side picture. So, that gave a very nice penetration and cured that fistula. This is a postoperative picture where you don't see the fistula filling any longer. The coils remain in the segmental artery and there's no filling through that nerve root sleeve of the radicular artery that connected to the fistula. So, that was completely cured. I typically bring these patients back depending on their age, if they're young at six months, to just check that the fistula has remained cured, and it almost always does if you get penetration into the venous system or into the vein that connects the artery to the venous system. Next slide, please. Here's another patient. This is a 63-year-old, again, you're seeing the age range often in the early '60s, late '60s, healthy male, six months of progressive gait ataxia and urinary urgency. And the spinal MRI here is suggestive of a vascular malformation. You can see the flow voids in the back of the spine here on the picture at the thoracic level, and that's suggestive of a spinal vascular malformation. What was found was, again, a Type 1 dural arteriovenous fistula, and you see the segmental artery next to the catheter, the long artery feeding a radicular artery that then feeds this coronal venous plexus, which you see on the right side going both up and down the canal. So, this will affect cervical cord, this will affect lumbar cord. And just because you see flow voids in those regions, does not mean that that is where the spinal arteriovenous fistula is located. It needs to be located at one point, and here it was T9, and then the venous congestion can go all the way up and down the cord. Here's a picture with the catheter in what we would call wedged position. It goes up and finds a distal point where the catheter is just as wide as the vessel and plugs the vessel. And you can see this here in this picture, both on the left and the right, this is an injection of contrast from that position whereby you only see the fistula filling and you see no reflux, which is the same thing you're gonna see when the glue is injected. Here's a picture after the glue injection, and in the middle of the screen here you can see the glue cast in the exact shape of the fistula that you saw before, indicating that the entire fistula was penetrated. Now, again, it doesn't go all the way up and down the cord like the veins do, but the entire fistulas region was penetrated with glue and disconnected from the arteries supplying it. There's a picture of where the microcatheter is, and here's an angiogram postoperatively that demonstrates absolutely no filling of the fistula that you had previously seen. This patient had a very rapid resolution of symptoms that completely resolved by one-month post-procedure. And as you can see on the follow-up MRI, there's a resolution of the T2 signal. We don't see any T2 signal in the cord anymore, and the six-month angiogram showed obliteration of the fistula. A point that I will make in the diagnosis of these is what I try and indicate to the patients is the longer they've had the symptoms, the longer it will take for the symptoms to recover. At some point, they may not recover. It's a question of whether there's congestion of the cord or any ischemia, but in my experience or +in my practice, I've tended to see those with symptoms that have lasted longer than six months, have a less of a chance of a full recovery or a longer recovery than those that have symptoms less than six months. Here's another patient, a unique one. This is a 72-year-old male with weakness and sensory loss in the bilateral lower extremities. And if we play the video here, we'll see the AP view, you see two different entities. You see the spinal artery and you see the fistula. Now, I'm gonna let it go back to both the AP and lateral so we can look at these. The AP, the straight segment going up and then down is the artery of a damp cords, whereas the tortuous segment is the fistula. And the reason I shoot a lateral here is you can see the artery of the damp cords on the front of the spine and the fistulas engorgement of the veins on the back of the spine, so this is a interesting case in which the fistula comes off from the right L2 lumbar artery, as does the artery of the damp cord. So, when I thought about this case, the idea of injecting glue or Onyx into the feeder of these two arteries was not appealing because any glue or Onyx that did not perfectly blocked the fistula and either refluxed or blocked, some vessel supplying the artery of a damp cord, so the anterior spinal artery would cause significant problems. Let's go to the next slide, please. So, here you have a picture of each, I've outlined, you see the anterior spinal artery comes early in the picture on the left-hand side, but then a later frame shows the fistula and you could see the anterior spinal artery still in the backdrop. And then, on the far right frame, you see the venous phase of the fistulas vessels filling upward, rostral and caudal actually, on the cord. And you can see how this is set up. Now, when we do angiograms it often is said to delay the washout or the run of the anterior spinal artery if there's a fistula. So, the anterior spinal artery fills and hangs around with contrast for more than six seconds or six frames when you have a fistula because the congestion is stopping it, yet, on this one, the anterior spinal artery is filling quicker than the fistula, which is not uncommon. So, go to the next slide here. What we did is we did this open, and what you can see on the left slide is this is the dorsal spinal cord at the level of the fistula and you can see the fistula entering from the side of the view and going up and down the cord. What you don't see here is the anterior spinal artery. So, what we did is we found that radicular artery, we rolled the cord just slightly to be able to see a vessel coming off eventually that we were pretty certain was the anterior spinal artery. And once we had figured out the angioarchitecture and differentiated the fistulas artery on the dorsal side of the cord from the spinal artery on the ventral side of the cord, we just made sure by putting a clip on the feeder to the fistula on the dorsal side of the cord and noted that the motor evoked and sensory evoked potentials did not go down, or did not go away. And we were comfortable that we had the dorsal fistula and not the spinal artery. And then, we coagulated and divided that fistula right where the fistula crossed or the vein crossed the subarachnoid space from the dura. It's important to note that these fistulas may go up or down the spinal cord in the dura for a specified sum amount of length. So, what you see on the angiogram in terms of where things turn or where things might be in a certain configuration may be a little different than what you see in the operating room because you have to account for where that radicular artery is going up or down within the dura. So, once I've disconnected these spinal arteries, I tend to buzz the dura where I think the fistulas input vessels were just to make sure there's not any small connection that remained. And on this case, in fact, you see on the right-hand panel, a anterior spinal artery just as was seen in the prior picture, but with no fistula, and this gentleman recovered much of his function and had no issues with the anterior spinal artery. So, here's a video, can we play this video? This is of a 59 year old gentleman who presented with leg pain and had a classic Type 1 fistula off of the intercostal artery on the left there. And you can see along the middle going both up and down the spine, we see the veins. We took this, this patient was taken to the OR. This is done in a minimally invasive fashion with one of my colleagues Dr. Patrick Shea. And you can see here, the dura is being opened and we're gonna expose the fistula after +tacking up the dura. And there you see the vessel coming in from the dura across the subarachnoid space as I had mentioned to the plexus of the veins in the spinal cord. Now, because this is done in a minimally invasive fashion, we don't have a significant view above and below, but we were pretty confident of where this was. Putting a clip on the vessel that we're gonna ligate and checking motor evoked potentials every five minutes for 15 minutes, so there was no decrement in motor evoked potentials. So, the clip was taken off and this crossing vein was taken, as was the arterial input at the level of the dura, and coagulated and made sure that any vessel feeding that or around that was coagulated. Now, importantly, you only need to take the vein that's crossing but just to be certain, there's no harm in taking the small vessels that are giving input, and then, ligate and divide. And it's a really quick, really easy, really gratifying as Aaron said, procedure often used as +icy green to determine that the transit time has changed, and now here, closing the dura in a watertight fashion at which the fistulas entering. And +B, I could see the coronal venous plexus to convince myself that it looks similar to the angiogram and that I can watch the changes. But there are many advantages to minimally invasive approaches like this. And I'd say, at the beginning, it's easier to do with a true laminectomy and some rostral-caudal extension. These are narrow, they don't need fusions and it's a beautiful view and elegant operation. Next slide, please. So, now a couple of the other types. I talked about a glomus Type 2. Arteriovenous malformation or vascular malformation. This was a 34-year-old male who presented with bilateral lower extremity weakness, minimal movement, and loss of bowel and bladder function following rupture of a spinal arteriovenous malformation. And the MRI, as you can see there, demonstrates at T12 what looks like a true AVM in the region of the cord and would qualify as what we talked about a glomus Type 2 arteriovenous malformation. So, this patient actually had been quote, unquote biopsied and previously ruptured, and we saw him at the time of his second rupture. So, we performed an angiogram and, unfortunately, we saw, can we roll this video? Yeah, we saw what looked like an anterior spinal artery or a vessel that looked similar to an anterior spinal artery feeding this arteriovenous malformation on the ventral side of the cord. Again, a lateral angiogram confirmed that this was in fact ventral and looked like the anterior spinal artery. This is a patient where we did do provocative testing, and indeed, when we injected the lidocaine in Amatol, he did lose potentials on the very small amount that he had prior to the procedure. Next slide, please. So, this was a case that I did earlier in my career and I did actually have the assistance of, Dr. Giannotta did this with me. And what we did is we did a T12 laminectomy. We came from behind despite the presence of anterior feeder. And the reason was that the malformation and the bleed did come to the surface on the posterior aspect of the cord. We were able to resect this, and as you can see in the right-handed picture, the anterior spinal artery remains patent and no arteriovenous malformation is left. It does look like it has a little less flow or smaller and that's probably because of the lack of draw from the arteriovenous malformation. So, he recovered his proximal, and much of his distal function and at about three years afterwards had made a significant recovery to the point where he could walk with orthotics and he has had follow-up angiograms that persistently demonstrate no residual arteriovenous malformation. Next slide, please. Here's an interesting case of a Type 3 metameric arteriovenous malformation. This patient presented with subarachnoid hemorrhage and it's rare that that's the presenting finding of a spinal arterial venous malformation, especially towards the lumbar region of the cord. But it is possible only upon imaging of the spine did we find blood settled down in the lumbar region and make the diagnosis of an arteriovenous malformation. So, this shows what had happened, and the reason it was a, can we show the left side the AP. The reason it was a subarachnoid hemorrhage is there's an aneurysm associated with this arteriovenous malformation. The problem is when we're talking about an entire metamer that is affected by an arteriovenous malformation, it's difficult to take the whole thing out. Also, in this patient, there was not a good presentation to the surface of the cord, and this was right on the anterior aspect of the cord, again, off of the anterior spinal artery, and with provocative testing, he lost function temporarily in his legs, so we knew that going in. Next slide, please. So, as it says here, this is T11. It's a glomus Type 2 spinal vascular malformation with an associated aneurysm. And the provocative testing suggested it was supplied by the anterior spinal artery. But if you look here to the right side, you can see that that aneurysmal segment that looks like it's coming off of the left portion of that AVM. So, what we did in this case, is we put our microcatheter, we placed our microcatheter through the anterior spinal artery because it was so significantly enlarged and we were able to safely, after the provocative testing, get our catheter through that enlarged artery into the aneurysm and place coils, as you could see in the middle field, and on the angiogram on the right to address the high-risk feature with a plan to get him through the subarachnoid hemorrhage, and then consider further management at a later date. So, we were successful with that and have actually imaged this in the ensuing time and there's been no recurrence of that aneurysm and we continue to manage him in that fashion. Next slide, please. So, here I wanted to bring up, we get a lot of consultations for flow voids that are clearly, you know, have to be arteriovenous fistulas. But I bring this slide in to show that sometimes flow voids are not arteriovenous fistulas. And in this case, this is a 38-year-old woman with Von Hippel-Lindau and had flow voids and a mass. So, there's two ways. There's several ways a mask can cause flow voids. One is just by creating congestion in the spinal canal and in the veins that cause the veins to dilate and I think still worth an angiogram to make sure, but that's something that we've seen not infrequently. But, in this case, what it actually was is, as everybody knows, a hemorrhage neuroblastoma is quite a vascular lesion and this has flow through the tumor that if you look at the middle video here, goes back up the dorsal aspect of the cord. So, this is a, and we shoot a lateral here on the right again, and if you look at this, you can see the anterior spinal artery coming down the front, feeding the tumor, and then in the late phase, you see all the venous flow on the dorsal aspect of the cord. So, again, this looked like a patient that had parasitized the anterior spinal artery to supply a tumor that then had flow through it or maybe some type of fistulized flow just 'cause it's a tumor and had a dilated coronal venous plexus up the dorsal aspect of the cord. So, this was treated operatively. The tumor was resected with careful attention to the ventral artery and the patient did well afterwards, and we're awaiting postoperative spinal MRI in a delayed fashion. But I would imagine that the flow voids will be gone. So, I think that illustrates that not every time that there's flow voids on a sagittal spinal MRI is a fistula. I would say, as a neurosurgeon and as a angiographer, whatever is one's reason for being involved in these, I would, anytime I saw flow voids, I would put spinal fistula right at the top of my differential diagnosis because I don't wanna be the one to miss a fistula like I talked about before, in those patients that wait six to 12 months to finally get a diagnosis. I'd rather be concerned about it in patients like this where it turns not to be the case, but nonetheless, the angiogram is very beneficial for the operative intervention. So, in summarizing all of this, when I thought about conclusions and pearls that I've taken with me that people have taught me about this type of lesion is, I think endovascular embolization or microsurgery can be considered a first line of treatment for patients with a Type 1 AV fistula. I think microsurgical treatment is very straightforward, it's very easy, it's very low risk, and if there's any question about the endovascular treatment, I would go towards the microsurgical treatment. However, if there's a very simple one-to-one connection where you are able to get your microcatheter out to it, I think endovascular treatment is a wonderful option as well. I emphasized before, it doesn't matter what the MRI shows. The fistula can come at any level from the eye shoot on my angiograms, if I haven't noticed or found a fistula right away, I shoot all the way from the subclavian trunks down through the thoracic spine, the lumbar spine, median sacral artery, lateral sacral arteries. I've seen fistulas off of each of those, sometimes, the only MRI presentation I've seen is conus edema. So, conus edema makes me think of a spinal arteriovenous fistula. I know there's other things on the differential diagnosis such as tumor and stuff like that, but that should be, that should raise a flag of a fistula even without flow voids. Critical to document both the feeding vessels on angiography and the anterior spinal artery in every case, the last thing you want is an anterior spinal artery either in the operating room or in the endovascular suite that's intimately involved with the fistula and not knowing it as you saw from a previous case. When you know that's the case, it's easy to tease them out and to be careful and do the proper monitoring and dissection, but when you don't, it could result in problems. As I mentioned before, the anterior spinal artery transit time is typically greater than six seconds with a fistula that's abnormal. So, if you see a slow-filling anterior spinal artery on a run, even if there's no fistula on that run, I think it behooves you to go look at the other levels and make sure there's no fistula. Because remember we talked about the congestion from any of those veins will slow up arterial flow in the anterior spinal artery. Endovascularly, these can be performed quite easily through a 5 French system, a small system getting into the lumbar intercostal arteries. I've found balloon use with Onyx is very effective. Now, as the balloons get smaller and smaller, they can fit out into these arteries with ease and prevent reflux that could either be problematic or could just be, make the procedure more difficult. I mentioned that the feeding artery may travel in the dura, that's important in the operating room. So, if you're trying to match up the morphology of if there's a turn in the radicular artery or a little divot that you don't see in the operating room, I think it's important to understand that that may be occurring in the dura. You have to, you must in either of these procedures, endovascular or open microsurgical, the fistula must be disconnected from the coronal venous plexus or the veins that are draining. And in the operating room, that's as simple as a coagulation cautery and dividing, and in the angiography suite that's as simple as having your embolic agent infiltrate into that fistulas connection. I've had patients that look for all the world to be a spinal arteriovenous fistula flow voids, the symptoms match and I have not, I've done a complete angiogram and have not found a fistula, I think, in that case, a repeat angiogram is warranted when the suspicion is high and looking at particular places where a fistula can come from, but they're not the classic radicular, intercostal or lumbar arteries. So, that's what I've gained from my practice in these types of patients and situations and, hopefully, that's helpful for everybody else.

- Very well said. I really like the last slide is gold. I think some of the things that you reflected on, which are critical that I want to just sort of emphasize further is that early diagnosis and treatment is of such importance. Unfortunately, AV fistulas are very rarely diagnosed on time and patients present with almost years of myelopathy and neurological decline, and then, that really compromises the recovery after our procedure. So, if you can really have a low suspicion, if you can, you know, train your colleagues and family doctors the best you can for this kind of problem to the best possible, although they're extremely rare, is really critical for recovery of these patients. The second thing that you really emphasize that is so true is in surgery, you can disconnect the vein that you still sometime have to really look for that fistula's connection at the dorsal lateral aspect and just coagulate those tiny arteries. I think that's a good technique. You very well mentioned that's obviously from a lot of experience because you could miss some of these tiny vessels that still walk around the vein and sometimes, you can miss, and then later, they can really augment and reform the fistula, although in a much less degree. If there is evidence of cord edema without any flow voids, you gotta make sure you exclude AV fistula. You just can't say, "Okay, on MRI, I don't see it, the suspicion is low," and you can't just quit early on. You have to look for it until you find it. And it really requires a lot of experience in angiography to find this. You have to go level-by-level, and all the comments you made about what is important in the angiography to find it cannot be overemphasized, Bill, I think those are critical. Something that I'm sure you're aware of that I wanna emphasize is hemorrhage posterior fossa, especially, subarachnoid hemorrhage, especially, in the fourth ventricle, obviously, you have to roll out a PICA aneurysm if the angiogram CTA is negative, as cerebral angiogram is negative, you gotta look for a cervical IV fistula. I have had this happen to me at least 10 times in the past 10 years, once a year where we do, there's blood in the ventricles, blood in the posterior fossa, you can see the around the cervical medullary juncture and then, you're like, oh, the cervical angiogram is negative. And then you do a more thorough angiogram and there's a big AV fistula, and there's blood in the cervical cord. So, you gotta be really careful about those cases because if they're missed, really, patients are hurt, and they come back with another big hemorrhage region, the recovery can be really compromised.

- Yeah, I was gonna say, that's really well said. We typically, do angiography of the thyroid cervical and costa cervical trunks and if it's negative in our angiogram, we will routinely perform a cervical MRI just to make sure there's nothing else that we're missing.

- Right, right.

- On patients.

- Yeah, especially the blood around the cervical majorly junction tracking up. Even without that, you know, we have had patients, Bill, present days after their ictus and there's no blood even around the cervical Meier junction. All's, you know, super temporal or a little bit in posterior fossa, all sort of diluted around the CSF cavities everywhere. And then angiogram, cervical angiogram, cath angiograms negative, and then we did a cervical angiogram and there was a very, very prominent AV fistula there. So, I think the hemorrhage from these is not as sort of thunderclap as it is for a brain aneurysm and therefore, patients may go on, they do okay, and then in fact present with only symptoms of cerebral vasospasm. And then, you look and then there's no aneurysm, and there's hemorrhage and there's vasospasm in you're, where did this blood come from? I have seen people sort of quit and say, okay, it's just blood, it came from somewhere and this is just a result of vasospasm. You've gotta be more studious about that. The other thing that I really like about your philosophy is that the first line of therapy still remains for Grade 1 AV fistula surgery. I think it really provides a low-risk treatment for it, especially if the patient can tolerate surgery. It's effective, and I think those are critical aspects of it, but I think so much of the talent about areas this treatment is in the hands of neuro-interventionalists where you really have to skeletonize, understand the angioarchitecture, and in surgery everything becomes a lot easier, and it's really a pleasant and a beautiful operation. So, any other thoughts on top of these in terms of rare events that in your surgical experience you have run into, Bill?

- No, I think you hit the high points as you said. I think when I said that both surgical and endovascular treatment kind of parallel each other as frontline, the reason I say that is in my practice, at least, I get just as many patients that are old and medically sick that are not fit for surgery, that have these lesions. So, I find myself treating those in an endovascular fashion. But, yeah, I think it's just such a, it's a nice surgery and when it's done and done right, which it typically is by folks who do these, it's gone and you never have to worry about it again.

- Right, right-

- These are really happy patients, and really happy referring doctors because these patients are vexing in terms of the diagnosis for everybody involved. And finally, when it comes to a treatment, I think it's really a burden off on the patient's side and the physician's side.

- Well said. I got to agree, endovascular therapy is really a super treatment modality, no question. I mean, really hard to argue with it if you don't have to have a laminectomy and recover from the surgery. And so, I think those are valuable. Have you ever run into no cord edema? You see a few squiggly things that increases your suspicion, maybe questionable sort of T2 signal change in a cord, and literally, minimal or no edema, questionable flow voids, and then there is AV fistula. Have you had that by the way, Bill?

- So, I have had that once, and it, it sticks out in my mind or maybe more than once, but one sticks out in my mind because it was also, a patient where we did the angiography and it was literally the last vessel we catheterized. So, I remember it for both of those reasons. And I think the point you make is a really good one and it's that if the clinical syndrome fits the diagnosis of dural arteriovenous fistula, it may not be the top of your differential and it doesn't need to be the top of your differential, but it needs to be on the differential, and I think as soon as dural arteriovenous fistula is on the differential and there's no other cause found, I think, I feel, that an angiogram is warranted. And in that case, really drove that home for me. We're getting very good, and the imaging is getting very good non-invasively to localize maybe where the fistula is. Sometimes, you can see a vessel on an MRA of the spine, which is wonderful, and when you do, it's usually correct. The problem is if you don't. I think the angiogram still needs to follow, and I have seen cases where the symptoms are there, maybe not glaring, but the imaging findings don't, you know, don't parallel the classical textbook ones that you mentioned.

- I agree, I remember a patient who just had a minor full foot drop, maybe a four out of five foot-drop on the left, but definitely hyperreflexia, lower extremities. MRI was really clean and the neurologist really pushed us against our, you know, resistance to after everything was done, all the work common-neurological was done, that this patient could have a AV fistula and the MRI was really negative, all of us were laughing. So, what are they thinking? I mean, how could this be AV fistula? This is just almost impossible. And, my God, there was a, you know, I remember, which I don't remember which level his spine, a lumbar spine, there was a, it was AV fistula and it's just made us believe that you just can't quit. If the syndrome is there if everything is done, you gotta give the patient the benefit of the doubt. The last question I have for you is use of MRA with contrast angiography in the spine for diagnosis of AV fistulas. I do believe it is worthwhile to start as a first modality because it really can hone you down on the segments that push the questionable on the MRA. Although they're not diagnostic, I think they help you hone down your angiogram, especially for patients who can tolerate a lot of contrast load. Could you tell me what your thoughts are about that?

- Yeah, I think you're absolutely right. If you're in a center or a situation where you have good MRA angiography like that, which we do, I think it's great to focus you in on a region, and it's actually, it can make a diagnosis, there's no doubt about it. And that was the point I was alluding to before. I think in the case of a positive diagnosis, I think it's probably usually correct in a negative diagnosis where I still worry that we still do an angiogram in any case, even if we're going to the operating room, just to understand, as I mentioned, the exact angioarchitecture of what things look like, it makes us more comfortable. So, MRA is a fantastic screening tool. It helps us localize. If we're nervous enough that we're doing an MRA with contrast to look for a fistula, we're gonna probably end up doing a spinal angiogram.

- Yeah, no, I agree with you. Those are great thoughts, really valuable. Really appreciate your input, Bill. So, very thoughtful and I'm sure many neurosurgeon will find this talk something that is extremely helpful in managing their patients. So, with that, I wanna thank you and look forward to really your rise within neurosurgery at much higher levels that I'm sure will happen very soon. And really, I'm so proud to see people of your caliber are the people who are really gonna take the neurosurgery to the new level and heights. And so, thank you again, and wish you all the best.

- Well, thank you for having me, Aaron. I really appreciate it. This was great.

- Thank you.

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