Imaging of Hepatic and Pancreatic Transplants - HD

Hepatic and Pancreatic Transplant Imaging

Good morning.
I'm Dennis Foley. I'm a professor of radiology at the Medical College of Wisconsin in Milwaukee,
and I'm gonna speak to you today about hepatic and pancreatic transplant imaging.

Hepatic Transplantation Indications

To begin with, the major indications for hepatic transplantation are cirrhosis secondary usually to hepatitis or alcohol abuse, primary sclerosing cholangitis, or primary biliary cirrhosis.

Surgical Procedures for Hepatic Transplantation

This is an anatomic diagram that shows you the effects of diffuse liver disease on the top and then the types of surgical procedures used to implant a liver on the bottom.
So on the top we see the patients with ascites and splenomegaly and varices affecting the portal hypertension.
We can see the inadequate protein synthesis reflected in their patient's muscle loss and osteoporosis in terms of the implantation of a donor liver in a recipient.
So following hepatectomy, we have to do arterial and venous anastomosis.
So this is showing you a cavocaval dichotomy anastomosis.
On the image on the left, it's showing you a direct recipient hepatic artery to donor hepatic artery anastomosis, and it's showing you a portal venous anastomosis.
In terms of the injury of any caval or hepatic veins, it's somewhat out of date in the sense that there is a caval to caval anastomosis shown these days.
Usually only a very short segment of the cava is used in a piggyback technique to connect to the recipient's inferior vena cava.
On the bottom right, you see an example of a choledochojejunostomy, which is the preferred technique in patients who may have biliary tract disease such as primary sclerosing cholangitis, and in fact, a patient with primary sclerosing cholangitis, if satisfying the criteria for liver transplant, would be evaluated in the operating room with a standby patient as a second backup liver transplant in case the patient with sclerosing cholangitis has undocumented cholangiocarcinoma.

Preoperative Imaging for Hepatic Transplantation

Preoperative imaging, which we're not gonna go into any great detail about for the recipient, looks at liver tumor.
Now, hepatocellular carcinoma is not a contraindication to a liver transplant.
In fact, it accelerates the patient's position in a liver transplant queue provided that there are not too many liver tumors or there's not one large more than five centimeter liver tumor.
Portal vein thrombosis is also assessed because if there is a portal vein thrombosis, then some form of venous collateral circulation such as with a saphenous vein conduit is used to connect the superior mesenteric vein of the recipient to the portal vein of the donor.
Biliary disease also needs to be evaluated, particularly in patients who may have sclerosing cholangitis.

Postoperative Imaging Technique for Hepatic Transplantation

In terms of the technique, the study is done as an initially after transplant as a portable technique.
The probe position either intercostal or epigastric, usually because of the chevron type incision, which is used by the surgeons, there is sufficient space either in the epigastric or intercostal to evaluate the hepatoren for the vascular structures as well as evaluate the liver.
So subcostal dressings and tubes do not usually impede the ability to image these patients.
Here's an example of a patient who's got two inferior vena cava as demonstrated.
One is the donor, which is the more anterior, and the other is the recipient, the more posterior and the donor segment of inferior vena cava comes with the attached hepatic veins, and then one is able to get normal hepatic vein waveforms subsequent to the surgery.
Here's an example of a patient that we've imaged early after the surgical procedure in which you can see there's a hepatic artery waveform, which is relatively high resistance, not unusual in the early phase post-transplant, but there's a sharp systolic upstroke which would indicate to us that there's been no pulse pressure drop across any more proximal anastomosis.
We don't see the anastomosis of the arteries directly, usually because of overlaying bowel gas.
The portal vein relatively high velocity and relatively turbulent, which as usual cause these patients have an acute decompression of a portal venous system in which there is increased volume and pressure.
So that leads to these characteristically turbulent high velocity portal venous flow waveforms post-transplant.

Early Post-Transplant Dysfunction in Hepatic Transplantation

For early post-transplant dysfunction, major issues relate to ischemia, which can lead to biliary necrosis and to bile lakes and abscesses biliary obstruction or rejection.
Here's an example of a patient whose mesenteric artery shows an expected normal waveform, a sharp upstroke and good continuous diastolic flow, but this is probably the hepatic artery of the recipient, not the donor.
When we look inside the liver at that patient's hepatic artery, we have a tardus parvus waveform.
So that's indirect evidence that between the proximal and the distal waveform sites, there probably is a significant stenosis.
And in fact, this was a patient who in the past had had a transplant arterial anastomosis treated by an angiographic stent and there'd been an in-stent stenosis.
And this patient had over the years had developed a collateral circuit between the right hepatic artery and the left hepatic artery.
So if you look at the image on the bottom right where we got the elevated peak systolic flow velocity was from the side of the stent.
Where we got the tardus parvus waveform was from the right hepatic artery, which has a feed supply both directly via a small caliber vessel at the anastomotic point, and more importantly, via collateral circulation from the left hepatic artery.
Here's an example of a good normal waveform from a transplant hepatic artery, peak systolic velocities in the range of 50 to a hundred.
And when we look at the transplant liver, there is a different waveform.
This is now distal to the anastomosis.
We're seeing tardus parvus both in the right hepatic artery and the left hepatic artery.
There is tardus parvus and this patient had developed as a result of ischemia, a leakage of bile where you can see leaking of bile adjacent to the left and right hepatic ducts and more distally in hepatic parenchyma demarcated by the red arrows.
And here's the angiogram for this particular patient that shows you the hepatic artery of the recipient proximal to the anastomosis, where we got the normal waveform the side of the stenosis, which we did not directly image.
And then more distally the site where there is a tardus parvus waveform recorded.
So if we have the combination of a recipient's hepatic artery normal and a donor hepatic artery within the liver abnormal, we infer the presence of an anastomotic stenosis.
Here's an example of a tardus parvus waveform, both in the right and left hepatic artery.
The portal vein is open.
Unfortunately in the time between doing the doppler ultrasound and doing an angiogram, this patient went on to totally occlude the arterial anastomosis.
It's a good rule of thumb to have a patient with a suspected hepatic arterial stenosis post-transplant to have some other form of imaging to corroborate that finding before the patient leaves the radiology department and then to plan an appropriate intervention.
What can happen is we've seen in an earlier study is that the ischemic ducts may leak form collections of bile and be also associated with abscesses as well as infarct.
And here's an example of a patient who basically developed an abscess, and here ultrasound used to guide a needle placement as part of the treatment for that abscess.
So here again is a patient with a normal hepatic artery waveform and a normal portal vein waveform.
Here's a study from some years in the past where we're looking at the portal vein as being open and slightly phasic.
The hepatic artery, unfortunately was occluded, and as a result of that occlusion, the patient had developed a focal area of bile leak and abscess that had to be treated by percutaneous catheter.
These patients have put back onto the transplant list, but in the meantime, before they can be re-transplanted, they may develop complications such as this patient with a hepatic abscess.
Here's an example of the main hepatic artery showing a normal waveform.
The right hepatic artery looks normal, but the left hepatic artery is abnormal, so we can conjecture then in this particular patient, the arterial stenosis may be selected only to the left hepatic artery, which in fact was the case where you can see the red arrow pointing at a tight stenosis of a intrahepatic left hepatic arterial branch.
How this occurred we're uncertain.
There was no specific treatment, and I don't believe this patient did develop any further biliary necrosis.
This was the CT angiogram and he was a CT portal venogram.
This is a situation where the patient had the celiac artery of the recipient occluded at its origin with a profuse collateral circulation through the gastroduodenal artery circuit.
So what the surgeons did in this case was to take the donor splenic artery and anastomose that to the gastroduodenal artery and anastomose the donor celiac artery to the recipient's common hepatic artery.
And then we see the donor hepatic artery spanning into both the left and right intrahepatic branches.
So just an example of surgical ingenuity in a patient with a celiac artery occlusion and this patient's hepatic artery waveform in the early postoperative period looked normal.
Here's something which is a reminder to us about the importance of not assuming that anything looks to be a fluid containing cyst or abscess as such, and in fact, this patient on CT angiography has a pseudoaneurysm.
So don't put a needle into something you suspect could be an abscess or a hematoma, and if in fact it could represent a pseudoaneurysm.
Here was the patient, an older study of a patient who has an arterial stenosis with tardus parvus waveforms.
It was treated surgically by a venous bypass graft with an overlay patch successfully, but unfortunately in the postoperative period, the patient had a portal vein thrombosis.
You can also see in accompanying you in fact peripherally in that right hepatic lobe.
So this patient's portal vein thrombosis was now treated via a transhepatic transhepatic vein approach to catheterize the portal vein and treat it with thrombolytics that was successful and the success was monitored by ultrasound so that post lysis, we had an open system.
In this particular case, the extrahepatic portal vein had been bypassed by using a saphenous vein in a position graft.
The biliary cast is something that can be due to ischemia or may not be due to ischemia.
This is due to denuded biliary endothelium becoming the nidus for formation of calculus material in stones.
And you can see this is associated with a dilated biliary system.
It may not necessarily be due to ischemia, and in fact, this patient's hepatic waveform is normal.
Returning to the portal vein, here is a patient with elevated high flow velocity portal vein at the hilum and more distally to the hilum, something which we expect to be normal in the early postoperative period.
If we see it later several months after transplant, then we may suspect a portal vein stenosis, which in fact in this particular case was.

Diagnosis of Hepatic Transplant Artery Stenosis

So for transplant hepatic artery stenosis, some of the issues, remember the anastomotic site is usually overlaid by bowel gas.
Remember that a flow jet is dissipated within a centimeter and that we concentrate our attention on the hepatic parenchyma.
I'm looking for distal tardus parvus waveform.
We may also simultaneously image the main hepatic artery of the recipient directly off the abdominal aorta.

Hepatic Transplant Outcomes

In terms of hepatic transplant outcomes, you can see that the graft survivals are relatively good, and this hasn't changed very much over the past five to 10 years.
The graft survival and improvements, better selection of patients from transplant, better surgical technique, good postoperative care, which includes sonographic monitoring as we have been evaluating better immunosuppression treatment of opportunistic infections, but with the remembrance that these patients, because they're immunosuppressed unfortunately, may develop solid or hematological tumors in the recipients.
Sometimes these solid tumors can be hepatocellular carcinomas, which had been metastatic at the time of the transplant, but metastases not known.
And then subsequently after transplant, these metastases from the patient's original hepatocellular carcinoma nest in the transplant and become evident.
The other type of hematological tumor is the post-transplant lymphoproliferative disorder.

Pancreatic Transplants

We now turn our attention to pancreas transplants.
They may be either simultaneous pancreas kidney transplants, where a patient who's on dialysis is also a brittle diabetic and requires physiological control, both of renal and pancreatic function.
That's called the SPK as distinct from the PAK, which is a pancreas after kidney, meaning the patient's dialysis dependent, but at this earlier stage can have their diabetes relatively well controlled.
However, subsequently with the diabetes becomes difficult to control then these patients are given a subsequent pancreas transplant.
Pancreas transplant alone is very uncommon.
The simultaneous pancreas kidney transplant, they have better outcomes than the other types.
It's also better, it's easier biochemically to detect rejection by monitoring the creatinine level because that's an indicator of kidney rejection and simultaneous pancreas transplant rejection, it would be considered likely.
Analyzing the serum amylase and lipase is not sensitive or specific for pancreas transplant rejection.
For pancreas transplant, the duodenum is taken with the pancreatic head and that's anastomosed to the recipient's jejunum.
So the pancreas transplant requires not just a pancreas graft, but a pancreas graft with duodenal C loop.
Here's an example of an older type of pancreas graft where we have a pancreas head connected to the duodenum, which is connected to the D of the urinary bladder.
So that's the form of exocrine output.
Notice that the arterial blood supply comes as a Y graft from the common iliac artery, the Y graft being made up of the common iliac artery of the donor, external and internal iliac arteries, which are then connected to the splenic artery, which to the superior mesenteric artery.
And the superior mesenteric artery branch has a that's a pancreatic duodenal branch, which now supplies the pancreatic head.
You can't use the hepatic artery of the donor because that's taken with the liver so that this patient donates both a liver as well as the pancreas.
Here's the portal vein of the donor transplant is connected directly to the iliac vein.
So this is now called a systemic enteric connection, meaning that the venous drainage is systemic to the iliac system and the exocrine drainage into the bowel.
So systemic venous drainage is a head down approach.
Transplant portal vein to iliac vein or inferior vena cava portal venous drainage, which is the converse, is a heads up where the transplant portal vein is connected to the recipients superior mesenteric vein, meaning that the venous outflow from the pancreas transplant containing insulin goes directly to the liver.
Though this physiologically may sound appealing it, there is really no difference in survival between a systemic venous drainage and a portal venous drainage technique.
So here's an example of a systemic enteric connection where we have the pancreatic head duodenal C loop connected to the jejunum.
So that is the enteric component.
And then the systemic component is the Y arterial graft in conjunction with the portal vein of the pancreas transplant going to the iliac vein of the recipient here is the different type of venous drainage where the portal vein of the pancreas transplant goes to the superior mesenteric vein of the recipient, such that the insulin coming from that pancreas transplant goes directly to the liver transplant imaging ultrasound is the technique that's most commonly used.
Gray scale imaging for collections of fluid and duct dilatation, color and spectral doppler used for real time arterial and venous connections.
The advantage of ultrasound is it's portable.
The disadvantages that some segments of the pancreas transplant can be obscured by bowel gas.
It's important to know what type of pancreas transplant surgery was done and to carefully evaluate the transplant bed to try and demonstrate head, body and tail.
So here's an example of a pancreas transplant with a normal dimension pancreatic duct.
You can see the pancreatic head as well as the pancreatic tail.
And the pancreas transplant is lying conveniently between the abdominal wall and the psoas muscle.
He's looking at the Y graft where we see the typical waveform of the Y graft in the common iliac artery.
Intra pancreatic, we see a normal waveform sharp upstroke, continuous good diastolic flow.
And this particular case probably lateral within the pancreatic body, and this was postoperative day six, is a CT scan of a patient who's had a systemic enteric pancreas transplant.
Where you see the Y graft, you can see the Y graft connected to the superior mesenteric artery and to the splenic artery.
You can see the splenic vein connected to the superior mesenteric vein and the portal vein.
The portal vein itself being relatively narrow vessel.
In addition, you can see a kidney transplant with a renal vein.
Looking at it from the back, you see the splenic vein and superior mesenteric veins connected to this portal vein, which is systemically connected to the either iliac vein or inferior vena cava.
This is another CT study that shows somewhat this is the portal enteric connection where we have the portal vein of the pancreas transplant connected to the superior mesenteric vein of the recipient.
You can see that portal vein has filling from both the superior mesenteric vein as well as the splenic vein.

Complications in Pancreatic Transplants

Some of the complications.
Here's an example of a patient with a very high resistance waveform in the pancreatic arcade region.
But this patient had a partially occlusive thrombus probably involving the splenic vein.
These thrombo detected can be treated by thrombolytics, so that in fact these can be dissolved and the pancreas then become relatively hemodynamically normal.
Here's another example of a partial occlusive splenic vein thrombus.
In a patient with a pancreas transplant, this is a systemic enteric pancreas transplant.
So the vascular complications can be venous thrombosis as we've seen occasionally the graft may be lost.
Uterine arterial thrombosis, anastomotic arterial venous stenosis may occur occasionally.
Vascular malformations usually post-surgical in origin and pseudoaneurysms.
So again, on CT scanning, here's a patient with a partially occlusive splenic vein thrombus.
This patient has a portal enteric connection between the portal vein and the mesenteric enteric vein.
Here we're looking at again, a partially occlusive thrombus in the splenic vein.
Nicely demonstrated in a curved planar reformation from a CT study, a patient with a totally occlusive venous thrombosis can have this characteristic reverse flow complete throughout diastole.
As we see in this particular case, in a patient who's transplant imaging under V demonstrates the thrombosed portal vein of a pancreas transplant.
Here's not a thrombosis, but there's a stenosis between the portal vein and the iliac vein.
And when this is suspected, we do spectral doppler to demonstrate the increase in flow velocity of the venous stenosis at the point of the stenosis.
Here's a patient who had a right lower quadrant pancreas transplant, who's got a large mass lesion.
We can't necessarily assume this is a solid mass as is a non-contrast enhanced study.
And in fact, this was ultrasounded initially and turned out to be a pseudoaneurysm related to a prior renal transplant into the right iliac fossa which had subsequently been removed.
So the important point is don't necessarily assume that what appears to be a solid mass is not a solid mass without necessarily ultrasounding it to make sure there's not a vascular complication.
Here's an example of a patient on CT scan who's got an arteriovenous fistula of long standing in the pancreatic tail.
This is something that wasn't treated because it was not hemodynamically significant in the patient's pancreas transplant functioned.
One thing that ultrasound is used for is to do a guided pancreas transplant biopsy because biochemically we can't make a distinction between transplant pancreatitis and transplant rejection.

Summary

So in summary, for hepatic pancreatic transplants, understanding post-transplant anatomy is critical to be able to do a satisfactory imaging study, whether that's a liver transplant or a pancreas transplant.
We've looked at doppler sonography, again looking on the liver side at the common hepatic artery as well as the intrahepatic arteries.
And the if there is a discordance and a tardus parvus waveform in the intrahepatic branches, then going and looking for the suspected anastomotic stenosis.
If that is not done, then the patients may suffer the complications of biliary ischemia.
In terms of the pancreas transplant, we've looked at the Y graft, arterial anastomosis, we've looked at the portal vein of the pancreas transplant connected either to the iliac vein, a systemic enteric connection or to the portal vein, a portal enteric connection.
And we've looked at ultrasound being able to diagnose partial or total occlusion of the venous system, pseudoaneurysms, and we've seen CT demonstrations of arteriovenous fistulas.
So with that, that's a relatively brief summary of the role of ultrasound in the imaging of patients with hepatic and pancreatic transplants.
Thank you.