A Study of Thrombosis After Microwave Ablation of Liver Tumors: An Interview With Alexander Sheu, MD, and Gloria Hwang, MD

Alexander Sheu, MD, and Gloria Hwang, MD, from Stanford University studied the effect of microwave ablation on portal vein and hepatic vein thrombosis in hepatocellular carcinoma and liver metastases. They spoke with Interventional Oncology 360 about their study at the 2016 Annual Scientific Meeting of the Society for Interventional Radiology in Vancouver, where they presented their results. 

IO360: Could you describe some details about the design of the study?

Sheu: Over the course of 4 years, we looked into the electronic health record and imaging of patients who had been treated with microwave ablation for either hepatocellular carcinoma or liver metastases. For these patients, we recorded the treatment parameters with the microwave ablation device, and we also looked at vessels that were within a centimeter of the tumor to be treated within the expected ablation zone. We evaluated how many of those vessels were thrombosed using CT or MRI. 

IO360: Can you give us a rundown of the most important results?

Sheu: The results of our study were actually quite surprising. In a comparable or similar ablation technique, radiofrequency ablation, the reported rate of hepatic vein or portal vein branch thrombosis is about 1%. In our study with microwave ablation, we found the rate to be well over 80%, which was actually quite surprising to us. It was interesting to note that while most of the small- and medium-sized vessels, the vessels under 6 mm, were the ones affected by the thrombosis, but we actually never saw a large portal vein or left or right main portal vein that displayed thrombosis. 

We looked at laboratory values to evaluate all of the patients’ data after surgery. In terms of their liver function, we found that there was actually no impairment in their function after microwave ablation, despite this high and actually quite surprising thrombosis rate. We also saw that these patients never displayed damage to their left, main, or right portal veins, so these large and very important vessels were actually spared by microwave ablation.

Hwang: We found these results to be really exciting. The reason that we’ve been using microwave is we’ve always suspected that we would have results like this. We’ve always suspected superior results if we could shut down blood vessels running near the tumors that might otherwise take away the heat of the thermal ablation and hence might even increase the likelihood of a recurrence. We knew that with radiofrequency ablation, these nearby blood vessels were a problem, and anecdotally, from looking at the imaging after the procedures, you would get a sense that you were shutting down a lot of these vessels, but we never really went back and combed through and looked at each blood vessel in the vicinity of the tumor to see if the vessels were there. So this gave us an opportunity to do that due diligence and see how well we were shutting down the blood flow around the tumors. 

IO360: What does this mean then for day-to-day practice for an interventional oncology clinician? 

Sheu: One of the interesting things was that as we were reviewing these studies, we would find patients who did not have thrombosis in the small vessels as expected given the ablation procedure. Several of these patients actually had recurrence of the tumor on follow-up. So we suspect that in patients who do not demonstrate thrombosis as expected, this may mean that the treatment itself was not completely efficient or effective, and these patients are at an increased risk of recurrence. This is one of the future studies that we hope to perform. We hope to study the relationship between decreased thrombosis rates and increased recurrence rates.

IO360: How does identifying thrombosis affect treatment?

Hwang: We wouldn’t do anything to treat the thrombosis. What was reassuring was that the laboratory values in these patients did not change significantly, even with thrombosis of some fairly large vessels. There were some cases in which our ablation field or the amount of tissue that was not perfused was substantially larger than we would have expected because the patients did undergo vessel thrombosis. On further downstream imaging, we saw that there was atrophy of a larger part of the liver than we would have expected from the expected ablation zone because of the vessel thrombosis. 

In a patient who, for example, is already missing two-thirds of his or her liver, I might be more careful about where I place the probes and how aggressive of an ablation zone I create if I am afraid that chipping away at those vessels will cause a huge field defect. 

IO360: What else is important for an interventional oncology clinician to know about the results?

Sheu: The biggest concern with any ablation procedure is damaging vessels that will cause a life-threatening injury to the patient, so while it is important to be wary and careful that you are not damaging the large branches in the portal vein, the results of our study are reassuring in that you can ablate close to the large branches of the portal vein and be fairly certain that you will not experience thrombosis in those vessels. 

The other thing that is important to note is that if you expect a vessel to thrombose but it doesn’t after the procedure, then you may want to take a more careful look at the imaging as you are surveying that patient to make sure that they don’t experience recurrence of the original tumor.

Suggested citation: Ford J. A study of thrombosis after microwave ablation of liver tumors: an interview with Alexander Sheu, MD, and Gloria Hwang, MD. Intervent Oncol 360. 2016;4(8):E133-E135.