So what are the focal therapies we could use?
Well surgery's been used for years, and there's certainly clinical evidence for this in a number of scenarios. Pts who have colorectal metastases to the liver. They undergo a partial liver resection and they live longer. They are long-term survivors from that.
Same thing with resection of lung metastases, even adrenal metastases. Radiation therapy is certainly used for this in certain areas, particularly of the spine. Embolization is certainly used as a local regional therapy
for metastatic disease, particularly into the liver, and currently it's being used in patients who have more than oligometastasis, several metastases. Focus ultrasound is being used, it's really in the experimental stage now for actually developing local control,
not just in the uterine fibroid here or benign tumor, but in bone metastases.
But I'm really gonna focus on percutaneous ablation because it's particularly well suited to this application, minimally invasive for these potentially frail and elderly patients,
as well as high kill rate with tumors of many different histologies. So when we're choosing, this is the technique, so how do we do it? If we were facing a metastasis in the scapula like this, we can treat it with heat,
radiofrequency, or microwave ablation, or we can treat it with cryoablation, extreme cold temperatures, extreme cold or extreme heat, they'll both kill the tumor. How do we decide? Well, if we compare cryoablation versus microwave ablation
or radiofrequency ablation, ease of use, the heat-based therapies are certainly easier to use. They're generally faster, so the procedure duration is quite a bit shorter, but the energy transmission into bone is better with cryoablation.
It'll go through the cortex, whereas heat is limited in that regard. The predictability of the ablation zone, the cryoablation. As you can see in that scapular picture, we can actually see the edge of the ablation with several different modalities, CTMR and ultrasound.
Our ability to monitor that ablation then and prevent it from escaping into adjacent collateral structures. And then the ablation zone size, we can usually treat a larger area with cryoablation, and patient tolerance, their pain scores are generally less
after a cryoablation than a heat-based therapy. So in general, most of us who are treating for local tumor control would use cryoablation. These factors are a little less true these days where there are newer bipolar radiofrequency devices that are designed specifically for bone
so have better ability to control tumors within these sites.
This is basically kind of your anatomy in hemodynamics.
Celiac axis gives supply to the spleen, gives supply to the hepatic artery, and there's increased flow to the spleen for some reason. Then flow goes back from the gut and spleen back to the hepatic graft by the portal vein. This is kind of your general circulatory
kind of hemodynamics. What the Japanese for years have been talking about was a small for size graft, a completely different syndrome, called small for size graft. In other words the liver is actually too small
for the amount of portal flow that's coming to it. It's an undersized graft. So for example, a transplant in a kid put in an adult. The liver is too small for the amount of portal flow that's actually coming at it.
And what they found out was that there was slow flow in the hepatic artery as well, and they didn't know how that went about. So for years, the Germans were talking about splenic steal, and the spleen is stealing blood flow, the Japanese were talking about
there's a small size graft and there's increased portal flow, but as a coincidence we're looking at hepatic or slow arterial flow. Then, kind of the Americans came along and actually put it all together for them. This is probably a constellation of syndromes and problems
that are occurring at the same time. One can predominate, one can be the only sole problem, or it could be a group of problems. What happens when you increase flow to the liver by the portal vein, there is actually something
called the HABR, the hepatic artery buffer response. This is a partly-reciprocal, poorly understood relationship between the portal vein and the hepatic artery. If you increase portal flow to your liver right now when you eat, if you take a big meal,
portal flow will increase to your liver and your hepatic artery's gonna slow down, because 20% of flow to the liver is from the artery, and 80% goes from the portal vein. If you eat a lot, your portal vein flow increases, your hepatic artery compensates by dropping down to
maintain that flow to the liver. That's kind of a partly-reciprocal relationship. So when you put a small graft in a patient, with relatively high flow, too much flow for the portal vein, the hepatic artery slows down. Okay?
So this is not just a steal phenomenon, this may also be a response or a reflex response to a high flow situation. The graft- and just to add a little bit more detail to this- the graft could be small, or the graft could be non-compliant and poor.
A poor graft, as well, can do the same thing. So it could be a big graft that's not functioning that well, and/or stiff, that would do the same thing as well. Okay? So increased portal flow, decreased hepatic arterial flow.