Updated: Oct 21, 2020
The vessel size and degree of vascular stenosis varies from patient-to-patient, which complicates the sizing and placement of endovascular stents. From vascular imaging to intraoperative stent deployment, Dr. Brooke Spencer discusses ways to improve stent placement in difficult cases of chronic venous disease.
The BackTable Brief
Intravascular ultrasound (IVUS) identifies the cross-sectional area of a vessel and can be used to assess for segmental stenosis; therefore in the majority of cases, Dr. Spencer prepares the internal jugular vein access point so that IVUS can be easily deployed.
Not all vessels are the same size - Murray’s law uses the radius of the parent vessel to approximate the radii of the daughter vessels. This helps in predicting the size of the common iliac veins for more accurate stent placement.
Dr. Spencer suggests a jugular approach may improve wall apposition when deploying Wallstents compared to groin approaches.
Concern for stent migration arises in cases of incomplete wall apposition; a few centimeters of wall apposition on both sides of an obstruction along with stent patency permits vascular remodeling and will prevent stent movement.
Disclaimer: The opinions expressed by participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable.
Assessing the Venous Anatomy Prior to Stent Placement
To accurately assess vascular stenosis, intravascular ultrasound is used to identify the cross-sectional area of a vessel. The degree of stenosis can be used to predict clinical outcomes such as clinical improvement, quality of life, and wound healing. For these reasons, Dr. Brooke Spencer prepares the ankle and internal jugular (IJ) access points, so that IVUS can be deployed through the IJ. Although she doesn’t use IVUS in every patient, Dr. Spencer states the majority (90+ percent) of her patients are readied for IVUS use.
[Isabel Newton] … Can you describe the access points that you prep so that you have many different options? I thought that was pretty interesting.
[Brooke Spencer] Well, I would say that 90-plus percent of my patients with chronic venous occlusions, I prep their IJs and their ankles. I use the jugular vein so that I can use intravascular ultrasound in the pelvis. If I have someone with a chronic fem-pop DVT that's been really symptomatic or has a wound and we're going to go in and re-cannulize that, I check every single one with intravascular ultrasound.
The more CTs and MRs that I do, the more inaccurate I'm realizing those studies are, in terms of determining whether there's significant flow. What I mean by that is that they're only very small studies, right? The VIDIO trial, which was industry sponsored, was 100 patients looking at multiplanar venography versus intravascular ultrasound for a diagnosis of a greater than 50% lesion, and all those patients were CEAP four through six, so these were advanced patients. These aren't just your non-thrombotic May-Thurners, right?
What they found is that the cross-sectional area narrowing is the most accurate in predicting clinical improvement, quality of life, and ulcer and wound healing. So you want to be able to measure the area of the vessel distal to the obstruction and then the area of the vessel in the obstruction and see what percent stenosis you have.
Now, if it's a 50% stenosis in an non-thrombotic 19-year-old who just has a chronic fem-pop DVT, you're probably not going to put a stent in that patient, right? But if you have a 90% stenosis in that patient, and you have filling through collaterals in the spine, para-lumbars, epidurals and parametrium, and they have pelvic pain, heavy periods, and back pain, you're not doing them any favors by not stenting that. The vessel's 90% occluded, and I really believe that those patients benefit from that. We still have a lot of data that needs to be gleaned from all of this.
Using Murray’s Law to Approximate Vessel Sizes
Vessel size variation is common; there is no “one size fits all” standard size for specific veins. Murray’s uses parent vessel measurements to predict the expected diameter of daughter vessels. For example, by correctly identifying the size of the IVC, you can predict the size of the common iliac veins.
[Brooke Spencer] … The other thing is that if you don't know how to place a May-Thurner stent correctly, it seems like a simple thing to do, but I will tell you, I think placing a stent in a non-thrombotic iliac vein is one of the hardest things I do in interventional radiology.
[Isabel Newton] So tell us about that. How do you size it, and what is your positioning?
[Brooke Spencer] Well, I'll tell you, every day I struggle with this. Just this week alone I had three patients I struggled with this because I think you get a pre-stenotic dilation, and so I'll geek a little bit. I'm the vein geek, so we'll talk about Murray's Law. If you don't know about Murray's Law, you need to know about Murray's Law in order to do venous stenting.
The radius of the parent vessel to the third power should equal the sum of the cubed radii of the daughter vessels, right? If your inferior vena cava is 17.8 mm, then your iliac veins should be 14 mm. So a lot of women have a cross-sectional area of an average diameter of 18 mm in the IVC, so their iliacs should be 14 mm. There are some six-foot-six guys whose inferior vena cava is truly 24 mm, in which case, their iliacs maybe 20 or 22 mm in diameter.
So you need to throw out this concept that every common iliac vein is 16 mm in diameter. It's complete nonsense. And people say, "Well, do you look at the contralateral side?" Maybe. You can, as additional information can help you, right? But you have a pre-stenotic dilation, so the question is, if you look at the size of the IVC, that should tell you kind of on average what size your iliacs should be.
How do I maximize stent wall apposition when treating venous obstructions?
Using a jugular approach is favorable over a groin approach when deploying a Wallstent within a large vein. Dr. Spencer prefers this approach as it maximizes the wall apposition of the stent throughout its deployment. Complications such as incomplete wall apposition may occur, which can be concerning for future stent migration. Migration is unlikely to occur as long as there’s stent patency and wall apposition both proximal and distal to the segmental stenosis, says Dr. Spencer. If the stent is being held onto by the obstruction vascular remodeling will occur.
[Brooke Spencer] Now what do you do with a person who has an 18 millimeter common iliac and a 90% obstruction, but their external iliac is 10 or 12 millimeters, and that looks like their normal size? These are challenging, challenging cases to fix. What I would say is that a lot of people are doing all these May-Thurners from the groin, and I've done that, but if you have a large vein, and you need to deploy a Wallstent, I will tell you that you're going to do a better job if you have a jugular approach.
And the reason is that if you have to put an 18 millimeter Wallstent in, and you know it is not going to open to 18 millimeters at the level of the obstruction, but maybe in order to get just a wall apposition, you have to do that. You want to deploy the Wallstent from above so that you can force the Wallstent out to have wall apposition before you've deployed the portion of the stent in the stenosis. If you deploy the portion of the stent in the stenosis first, the distal part of the stent will often not open, and then you'll have what looks to you like a floating stent. It can be really scary because now you don't know what to do, and now you've got this huge stent, it's floating in the vein. Do you overlap a second huge stent that now goes into a very small area of the vein, and the patients having an enormous amount of pain?
It can be really challenging, but if you do a larger stent like that from above, and you leave the point of no return exactly where you think that stent needs to land, it's very rare that you extend all the way into the inferior vena cava across the wall of the vein after dilating. It's also very rare that it pulls all the way back out of the stenosis. So if it does pull all the way back out of the stenosis, you have to put another stent in. And so that's the other thing I would say is that, if you're young, and you're doing this early on, you're going to misplace the stent several times in the process of doing these. Just put another one in. Use how short your current one is, put the same size stent in, and put it another centimeter or two centimeters or whatever it is. If you put in an eight, don't put a four in to overlap at the top because you don't have a great way of measuring exactly where that's going to land. Just put another eight in, and if it was two centimeters too short, leave it two centimeters further in and overlap it.
These are just some of the tricks that I've learned over time, but I do think that non-thrombotic May-Thurner stents can be some of the most challenging cases. The last thing that I'll say is that if you have incomplete wall apposition, as long as you have a couple centimeters of wall apposition proximally or distally in the common iliac vein before the obstruction, and as long as the stent is open but being held by the obstruction, I've seen all of those patients remodel around the stent. I haven't seen any migration from those stents, and I know migration is a big concern for people.
Podcast Participants: Dr. Brooke Spencer is a practicing interventional radiologist at Minimally Invasive Procedure Specialists group in Denver, CO. Dr. Isabel Newton is a practicing interventional radiologist at UC San Diego Health in San Diego, CA. Cite this podcast: BackTable, LLC (Producer). (2018, October 9). Ep 33 – Building a Comprehensive Vein Practice [Audio podcast]. Retrieved from https://www.backtable.com/podcasts Medical Disclaimer: The Materials available on the BackTable Blog are for informational and educational purposes only and are not a substitute for the professional judgment of a healthcare professional in diagnosing and treating patients. The opinions expressed by participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable. Disclosures: None.