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Ready, Aim, Ablate: Optimizing the Liver Ablation Zone

Author Taylor J. Robinson covers Ready, Aim, Ablate: Optimizing the Liver Ablation Zone on BackTable VI

Taylor J. Robinson • Dec 9, 2021 • 121 hits

The size of a liver ablation zone can vastly affect the outcome of a patient. If it is too small, malignant recurrence can occur. If it is too large, the patient can decompensate and lose remaining liver function. The current standard for the effective zone of ablation within interventional practices is ill-defined. So then, how does a practitioner determine the most effective ablation zone?

In this BackTable article, Dr. Raissi, an interventional radiologist from the University of Kentucky, discusses his experience with expanding the ablation zone margins past the normal standards. He and Dr. Beck discuss the benefits of this, compares this to the standard surgical approach, and the difficulty of navigating a disrupted tissue parenchyma in sequential ablations.

The BackTable Brief

• The data for current ablation zone margins comes from open surgical resection cases unrelated to percutaneous microwave ablation.

• Dr. Raissi has found expanding the ablation zone one to two centimeters has resulted in significant relapse reduction for hepatocellular carcinoma.

• An interventionalist’s first ablation distorts the native tissue and changes the target ablation zone.

Physician opening microwave liver ablation device to create ablation zones

Table of Contents

(1) How to Determine Liver Ablation Zone Margins

(2) Comparing Ablation Zones to Surgical Resection Margins

(3) Navigating the Ablation Zone after Parenchymal Desiccation

How to Determine Liver Ablation Zone Margins

The standard ablation zone for liver lesions, particularly for hepatocellular carcinoma, is half a centimeter to one centimeter, but where does this standard come from? Most authors cite the aforementioned zone, however there is currently no consensus on these safety measures for microwave ablation.

[Dr. Christopher Beck]
Yep. So let's talk a little bit about margins. So actually, there's two things I want to talk about. I want to talk about results in a fibrotic liver and a fatty liver, but first, I wanted to talk about margins. So will you kind of talk about maybe, for the younger interventionalists or some of the trainees out there, you're trying to ablate the tumor, but also, talk about how margins play a role in your ablation zone?

[Dr. Driss Raissi]
Yeah. I mean, if you just go by the data, what does the data tell us? The data tells us if you're dealing with HCC, you need to ensure that you get a .5 centimeter surgical [ablation zone] margin….And you can find data also that says, one centimeter for both, one centimeter for HCC and one centimeter colo-recs. But you know what?...Where does that data come from? That data comes from surgical resection, open surgical resection where you have the benefit of looking right directly at the tumor or using beautiful high-resolution images of intraop ultrasound.

And I don't feel like anybody has ever raised that question, where is that data coming from? And why did I start asking myself that question? Because my surgeon started becoming super happy with me when I started, "Oh yeah, I gave you a two centimeter [ablation zone] margin." And I thought they were going to be like, Hey Driss, take it easy, this guy doesn't have too much liver." No, no, they were cheering me up. There were like, "Oh, that looks great. That is awesome. That is beautiful."

With time, I mean, I've been doing this for a long time. They started seeing that this patient actually did rather okay. The extra centimeter didn't make them too sick. The extra centimeter ensured they didn't have very early recurrences or they never had any recurrences at all in that surgical bed, where some of my more junior colleagues may have had, let's just say and don't tell them, this is just between you and me, I'm hoping this is a secret... may have had a little bit more recurrences with a more conservative .5 surgical margin. So I started getting a little bit wilder and excited about ensuring, you know what? I'm going to give you a good surgical margin, I haven't written any paper about it, but that made me think, "We're going by this data that has absolutely nothing to do with percutaneous microwave ablation, maybe I'm up to something."

Listen to the Full Podcast

Microwave Ablation for Liver Lesions with Dr. Driss Raissi on the BackTable VI Podcast)
Ep 158 Microwave Ablation for Liver Lesions with Dr. Driss Raissi
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Comparing Ablation Zones to Surgical Resection Margins

With a five to 10 millimeter ablation zone being the current standard of practice, it can seem daunting to consider a three or four centimeter zone of ablation. Some practitioners fear that a cirrhotic or steatotic liver may be compensating and that a larger ablation zone could be the tipping point for hepatic function. However, when you expand the context to include the hepatic resection done by the surgical colleagues, that three centimeter ablation zone pales in comparison.

[Dr. Christopher Beck]
But that also raises the point. So whenever you're talking about margins, I think the other side of the coin is preservation of healthy liver, or maybe not healthy liver tissue, preservation of liver tissue, right? And so, it's a balancing act, but basically in your practice what you say or how you approach it is, if you're going to ablate it, you might as well come in and ablate it and give them nice clean margins. And if you're dealing with Child-Pugh A and Child-Pugh B, then that's just the cost of doing business?

[Dr. Driss Raiss]
Yeah, yeah. Correct. And often honestly, one centimeter, two centimeters, it's not what we think. My surgeon and colleagues, I go with them and do intraoperative microwave ablation once in a while, I may see when they do the resections, it has nothing to do with our 20, 30 cubicle centimeters of ablation, really that we do. I mean, when they chop the liver, they chop it.

[Dr. Christopher Beck]
Gotcha.

[Dr. Driss Raissi]
And obviously, that's why you're concerned because patients might be compensated. But our ablations, even if you take it maximum all, I have a four, five centimeter ablation zone. It's nothing compared with what they resect. So a lot of our practice really is based on data that really just doesn't apply to what we do.

Navigating the Ablation Zone after Parenchymal Desiccation

With any liver ablation technique whether it be cryoablation, radiofrequency ablation or as in this case, microwave ablation, the initial ablation affects the native tissues apearance. Once the first liver ablation has been done, the zone of ablation changes. The tissue ablation zone has been desiccated and Dr. Raissi discusses how he utilizes a multimodal approach to sequentially ablate the same liver lesion. Dr. Raissi first and foremost relies on an initial snapshot of where things are with an emphasis on landmarks. This in combination with his intuition and experience allows him to successfully complete subsequent ablations. Maintaining the appropriate zone of ablation is as much an art as it is a radiographic and physical science.

[Dr. Christopher Beck]
...when you're trying to mark your way along the lesion, I feel like once you've put in the probe and done an ablation zone, everything starts to look a little bit funny. And so, do you just kind of know that your needle placement is the one true thing and then everything's referenced off the original needle placement?

[Dr. Driss Raissi]
...So ablation desiccates the tissue. Your first ablation is going to shrivel the ablation zone, the capsule is going to look different, things just change. I think I take a first snapshot of where things are because of my heavy reliance on landmarks. I stick to my landmarks. I stick to my gut. I will repeat another CT, that combination of my initial gut of where the landmarks, where the second ablation was supposed to be and the repeat ablation is really what I do. So I think it's a complex, hard to explain cognitive effort of hitting it right on the nail.

And I think I'm doing well, just depending on the results, but I think it would be very hard if somebody asked me something like, "Can you write it up on a piece of paper?" I'm like, "I can't." It just seems to work whatever I do, just have a very good idea of what you're doing initially and where things are and when you're going to go and you already know what's going to happen to that ablation surgical field. So you kind of have an idea of where things are going to go. And I could say that that's one of the weaknesses of ultrasound, after you mess up that ablation zone the first time, things are kind of like, "I don't know, I'm not sure." There's a lot of artifacts that pop in with all that gas.

[Dr. Christopher Beck]
Yeah, I'll second that. Once the ablation zone is really or once the ablation has kind of gotten going ultrasound can sometimes go out of the window. I think it speaks to whether you've done a lot of these or a handful of these and just clearly, you have a good feel for it. But one of the things that I'll do pretty commonly is, you can expect things around your ablation zone to contract, not always, but different things around the liver that are outside of your ablation zone will kind of give you an indication whether things are contracting towards your ablation zone.

And then usually what I'll try and do is, I try and reference my next sequential ablation, if I'm going to move that needle relative to my needle. So I know the needle position was true if it was on the left side of a tumor then if I'm going to move, I mean clearly, I want to move relative to the initial needle placement. So I'll move it over a centimeter and a half relative to where the needles are following the ablation...

Podcast Contributors

Dr. Driss Raissi discusses Microwave Ablation for Liver Lesions on the BackTable 158 Podcast

Dr. Driss Raissi

Dr. Driss Raissi is the Chief of the Division of Vascular and Interventional Radiology with UK Healthcare in Kentucky.

Dr. Christopher Beck discusses Microwave Ablation for Liver Lesions on the BackTable 158 Podcast

Dr. Christopher Beck

Dr. Chris Beck is a practicing interventional radiologist with Regional Radiology Group in New Orleans.

Cite This Podcast

BackTable, LLC (Producer). (2021, October 3). Ep. 158 – Microwave Ablation for Liver Lesions [Audio podcast]. Retrieved from https://www.backtable.com

Disclaimer: The Materials available on BackTable.com 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.

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