Imaging of Liver Transplants - HD

Introduction

Hello, my name is We Chong from the University of North Carolina at Chapel Hill, and I'm gonna be talking about sonography of liver transplants.

Indications for Liver Transplantation

A number of conditions can be effectively managed with liver transplantations.

Indications for liver transplantation include acute irreversible hepatic failure, chronic end stage liver disease from cirrhosis, from Hepatitis B, C, or other infections, non-alcoholic steatohepatitis. But chiri or other forms of venal occlusive disease, hepatocellular carcinoma can be treated with transplantation if it meets a number of conditions in, namely, if you have one lesion less than five centimeters or two to three lesions, none of which are greater than three centimeters in children.

The indications for liver transplantation include biliary atresia, congenital biliary cirrhosis, congenital hepatic fibrosis from a cadaveric donor.

Types of Liver Transplants

The entire liver or part of the liver can be transplanted in a split liver transplant.

The liver is divided into two and the two portions given to separate recipients.

In a living donor transplant, the right lobe of the liver is transplanted from one adult to another, and in a child, the lateral segment is transplanted from a donor adult in an adult to adult living.

Donor segments 5, 6, 7, and eight are transplanted in an adult to child living.

Donor segments two and three are transplanted.

Intraoperative Image of Living Donor Liver Transplant

This is an intraoperative image of a living donor liver transplant in progress.

Here, the donor has been opened and the liver has been divided into two.

The right lobe here will be removed and given to the recipient.

This is the left lobe, which will be left to the patient.

This is the FALs formm ligament here separating the lateral and medial segments of the left lobe.

And this is a coronal MR image of the same liver in the recipient on the left side, and the donor on the right side, so on the recipient has received the right lobe and the left lobe remains in the donor.

Imaging of Liver Transplants

Imaging of liver transplants is performed with ultrasound as the primary imaging technique.

CT and MR provide a global view for evaluating the whole of the liver parenchyma and is more effective than ultrasound for evaluating x-ray hepatic fluid collections.

MRCP is particularly useful for evaluating the biliary tree angiography is used to confirm abdominal vascular ultrasound findings.

The limitations of CT and MR and angiography are that immunosuppressive drugs are nephrotoxic, therefore limiting use of ated contrast and gadolinium in these patients also susceptibility artifacts from hardware can cause artifact, can cause problems with MRI and there may be an increased risk of nephrogenic systemic fibrosis in the post liver transplant state.

Ultrasound Technique for Liver Transplant Evaluation

The ultrasound technique for liver transplant evaluation first involves a gray scale recording of the liver and biliary tree.

Then you evaluate the anastomosis.

That's where the surgeon has made the, has joined the tube, so to speak.

And there are four systems that need to be evaluated.

The hepatic artery, the portal vein, the bile ducts, and the IVC.

And there may be one or two anastomosis in the IVC.

As I will describe.

Doppler examination is performed of the common left and right hepatic arteries, resistive indices and acceleration in disease obtained from these vessels.

Then velocities from the main portal, vein proximal two at and distal to the anastomosis are obtained.

Doppler spectra are obtained from the left and right portal, veins and doppler spectra from the right middle and left hepatic veins.

And IVC.

Finally, a survey of the peritoneal cavity for free fluid and hematoma is performed.

Outflow Anastomosis: Hepatic Vein and IVC

The outflow, that's to say the hepatic va vein and IVC can be anastomosis in two ways.

In one way, the intrahepatic donor IVC is transplanted, so there's resection of the recipient IVC and there are two end-to-end and anastomosis between the recipient and the donor.

IVC one superior to the liver and one inferior to the liver.

More commonly now the piggyback anastomosis is performed.

In this situation, the recipient IVC is left in place.

There is only one anastomosis, where the donor IVC is anastomosis, the stump of the recipient hepatic veins, while the inferior end of the donor IVC is simply tied off.

For a fuller description of the A ium guidelines for ultrasound examination of the liver, I refer you to this sourced www.ai.org/resources/guidelines/solid organ transplants p This is a comprehensive protocol for the, for scanning of all solid organ, abdominal transplants.

Piggyback Anastomosis: The Two IVC Sign

When you have a piggyback anastomosis, you can get this image, which we call the two IVC sign.

This happens when you image in an axial plane that cuts across the donor IVC stump and the recipient IVC.

So in that axial plane, as we can see on the CT image on the left, you see both the donor and the recipient IVC in a single plane.

And this is the corresponding ultrasound image.

And there are two IVCs visible, the donor and the recipient IVC.

And this is a telltale sign that the patient has had a piggyback anastomosis.

Complications of Liver Transplant

Complications of liver transplant can be classified as those arising from the liver parenchyma.

These include hematoma, fluid collections, rejection, infarction, and malignancy, specifically post-transplant lympho of proliferative disorder, disorders of the bile duct, including biliary obstruction and leaks, x-ray hepatic fluid collection and hematomas and vascular patency.

Again, the four tubular structures, artery portal vein, hepatic veins, and IVC that are anastomosis vascular patency can be complete or partial, and anastomotic stenosis or thrombosis can occur.

Vascular Complications: Hepatic Artery

The hepatic artery can be anastomosis in the form of an end-to-end anastomosis between the donor and recipient hepatic arteries or as a aor hepatic bypass graft.

This is a typical wave from the hepatic artery.

In a normal patient, you see a sharp rise in early systole and forward flow during the whole of the cardiac cycle with positive flow.

During diastole.

The resistive index here is 0.65, which is normal.

The hepatic artery is the sole blood supply to the biliary tree, and patency of the hepatic artery is vital to survival of the graft.

If the hepatic artery is obstructed, it leads to biliary epithelial necrosis and strictures.

Therefore, establishing patency of the hepatic artery is one of the key tasks when you are performing.

Liver doppler ultrasound in the transplanted liver.

On the top is a normal hepatic artery.

Hepatic artery runs slightly anterior to the portal vein and is visible here on this color Doppler image on the image below.

This is a color Doppler image showing no visible hepatic artery.

If you look closely, you can see a rounded hypoechoic structure, which represents a thrombose hepatic artery without flow.

This is another case of hepatic artery thrombus.

Here we see the hepatic artery in lung axis as it arises off the celiac axis here, but no flow is seen in the hepatic artery beyond this point.

There is a thrombus in the hepatic artery just proximal to where it enters the liver.

And the entire hepatic artery beyond this point is occluded.

On the right is the corresponding angiogram showing the completely occluded hepatic artery just beyond the takeoff of the gastroduodenal artery.

And this is the of hepatic artery occlusion.

The biliary tree epithelium will slough off and two thirds of patients will develop multiple non anastomotic strictures.

As you can see on this MRCP image, you have multiple areas of focal dilatation and stricturing within the biliary tree, and linear membranes running across the bile ducts, which are caused by sloughed biliary epithelium.

And these patients would usually need biliary stenting to achieve appropriate biliary drainage.

Hepatic artery occlusion is absence of flow within hepatic artery altogether, but hepatic artery stenosis is a rather more subtle diagnosis that, but it is something that should not be missed.

We detect hepatic artery stenosis by looking for the tardis parvis waveform, and the tardis parvis waveform refers to an abnormal early slope in early systole.

So this is the slope of early systole, and it should be very steep like a very steep cliff, for instance.

This on the right side is a patient with hepatic artery stenosis.

On the left side is his normal hepatic artery waveform with a sharp rise steep slope in early systole.

And on the right Three months later, hepatic artery has become s nose somewhere proximal to where we are interrogating the vessel.

And note that the slope of early SST systole is much more shallow in this patient and the peak systole is much lower and more rounded.

So the resistive index, which is the difference between sly and Daly divided by sly, is reduce its less than 0.5, while the acceleration time, the time it takes to get from the beginning of early sly to where it starts to round off over here is prolonged.

So the acceleration time is prolonged, and the resistive index is reduced, and this is known as the tardis parvis wave form.

And here is the corresponding angiogram.

Here we see a stenosis within the hepatic artery on this angiogram, and a stenosis in the hepatic artery proximally will create a tardis parvis waveform in the hepatic artery distally, which is where you are interrogating the vessel with doppler ultrasound.

Here's another example of hepatic artery stenosis.

This patient here has a thrombus within the proximal common hepatic artery visible on this Mr Angiogram, we are interrogating the hepatic artery distally inside the liver, and we see a tardis parvis waveform.

The slope of the hepatic artery waveform is shallow, and there is a prolongation of the time it takes for the velocity to reach its peak while the resistive index is simultaneously reduced.

So we've seen that a low resistive index may be a sign of hepatic artery stenosis.

What about a high resistive index?

That can mean one of two things.

It is more commonly a benign finding.

It is a transient finding that is often seen in the first few days after transplant and is associated with an older donor or prolonged graft cold ischemia.

That's to say the liver has been in a box for a substantial time after it's been harvested before, and before it's transplanted to the recipient.

And this norm usually normalizes after one week.

And here's an example of high resistive index with no diastolic flow in a patient.

And this, we are interrogating the right hepatic artery here, and this resolved after a few days, and it's usually a benign finding.

However, if it does not resolve, it could be a sign of splenic artery steel syndrome.

And this means that when you have long standing portal hypertension, the spleen gets big and so does the splenic artery and post-transplant.

There is shunting of arterial flow away from the hepatic artery to the splenic artery in patients with large spleens creating a high resistive index wave form.

Now, this is not a benign finding and this has to be managed by reducing the shunting by embolizing the splenic artery.

Vascular Complications: Portal Vein

In the post-transplant portal vein.

It is normal to see a difference in caliber between the donor and the recipient portal veins.

The recipient's portal vein is dilated from years of portal hypertension, so there may be a mismatch in the caliber of the recipient and the donor portal vein, so that is normal.

You may also see the anastomotic suture line, which protrudes into the portal vein at the side of anastomosis, and this may appear as a linear echogenic structure.

And this is also normal portal vein thrombus is visible sometimes as an echogenic filling defect occupying the portal vein.

In this case, doper is not necessary on this gray scale image.

The thrombus is clearly visible portal vein stenosis may appear as a focal narrowing within the portal vein.

That is shows up on doppler ultrasound as an area of elevated velocity in this patient here.

The peak velocity in the portal vein is 2.14 meters per second, and this is a high velocity and a sign of portal vein stenosis here is the corresponding MR image showing the stenosis within the portal vein.

Postoperative Changes in Doppler Waveforms

Now, in the immediate postoperative period, there are a number of changes that you will see in the Doppler wave forms that are a consequence of postoperative edema and should not be regarded as a cause for alarm.

And these include high velocities in the hepatic artery portal vein and hepatic vein turbulent flow.

And this is due to temporary edema due to post-op temporary narrowing due to post-op edema and should not cause a diagnosis of vascular stenosis to be made in the period.

So here is a patient on day one post-transplant, and we see that the portal vein velocity here is very high.

It's 206 centimeters per second, or two meters per second.

And the flow within the portal vein, it has got a lot of spectral broadening.

In other words, it's very turbulent, but the velocity fell over the next week or so and everything normalized.

So don't make diagnoses of vascular stenosis in the postoperative period on the basis of high velocities because these are normal.

You may also see new mobilia in the immediate postoperative period, which was introduced as a result of surgery.

And this should not be regarded as a cause for a alarm.

And all these findings resolve in one to two weeks after transplantation in the immediate postoperative period, you should focus on the presence or absence of flow hematoma or thrombus.

Doppler Velocity Criteria for Anastomotic Stenosis

Now, what are the doppler velocity criteria to for anastomotic stenosis?

Well, outside the immediate postoperative period, we know that a high velocity is suggestive of portal veins nurses, unfortunately there is some overlap between normal and abnormal.

And I'm going to give you here some numbers for basically a gradient of two.

Basically a doubling of velocity between the pre and the anast.

Anastomotic velocity has a sensitivity of se 71% and a specificity of 80% for portal vein stenosis.

Now, if you wanna set your threshold higher at four, then your specificity is a 100%, but your sensitivity drops to 57%.

So here is a patient with a pre Anas velocity of 0.31 meters per second and a an asmatic velocity of 1.53.

So here, this is a step up of greater than four, and this is 100% specific for a portal.

Vein stenosis, if you prefer a numeric value, 150 centimeters per second or 1.5 meters per second, such as the patient this patient has over here has a 71% sensitivity and 90% specificity for portal vein stenosis.

Slow velocities in the portal vein are also abnormal.

This patient here has what we call two and fro flow in which flow is almost stagnant.

You can see it's less than 0.1 meters per second, and you have slow forward flow and then a little bit of reverse flow and a little bit of forward flow.

So the flow is the portal vein is almost stagnant, and the blood is sort of sloshing back and forth, and with very little forward movement, this indicates high resistance to flow and may be caused by extrinsic compression by a hematoma.

In this case, there is a large perinephric hematoma here, press compressing the liver and causing increased resistance to portal flow.

The other cause of slow to and fro flow is distal portal vein thrombosis, and this is the color doppler finding in to and fro flow.

Here we see a large hypertrophy hepatic artery here, which is this multicolored structure.

While running just superficial to that, we see a portal vein, which is flipping from red to blue, and this is caused by slow flow to and fro flow with a very slow forward and reverse flow.

Vascular Complications: Hepatic Vein and IVC

The normal hepatic vein is phasing with two forward spikes of flow in one reverse flow.

These are known as the SD and A waves, and a normal hepatic vein has this phasic appearance with forward and reverse flow.

A monophasic hepatic venous wave form is abnormal and can be caused by obstruction to the hepatic vein distal to the point of interrogation.

You may also see elevated velocities and aliasing at the site of obstruction.

So this is a patient with stenosis at the hepatic vein, IVC anastomosis.

Note that the hepatic vein narrows, there's a kind of waist here as it empties into the IVC, and we are seeing a velocities of a 1.3 meters per second at the anastomotic site.

And this is high for the hepatic vein.

And on the image below, we see that there is reversal of flow into one of the hepatic veins.

So what is happening is that this hepatic vein here is becoming very stenosed as it enters into the IVC and some of the blood can't get through.

So it's backing up into this other hepatic vein branch.

So reversal of flow in the hepatic vein, high velocities at the anastomosis, and you will see monophasic wave forms if you were to put your Doppler cursor more approximately in this hepatic vein.

And here is the corresponding angiogram showing a severe stenosis at the hepatic vein, IVC anastomosis.

And this is being treated with balloon balloon angioplasty so you can do your patients a lot of good.

If you make this diagnosis on Doppler ultrasound, you, the interventional radiologist can successfully treat this problem.

This is a case of IVC compression.

Note that the IVC is reduced to this little narrow slit here, and this is caused by a perinephric parahepatic hematoma that is lying between the liver and the IVC.

And this is the corresponding ct.

And the hematoma appears as this hypodense area, and it's compressing the IVC.

And this is impeding hepatic venous drainage.

Arterial Portal Fistula

Now this is rather unusual, but very serious complication.

This is a color Doppler image of the liver hilum, and we see some rather unu abnormal color doppler appearances.

Here we see two large vessels, one in red and one in blue.

On the gray scale image, we see that the portal vein is markedly dilated.

This is a case of arterial portal fistula, and the red vessel is actually the hepatic artery while the blue vessel is the portal vein.

And what has happened is that the hepatic artery has fistulized into the portal vein, and there is a jet of arterial blood, which is running in a retrograde manner down the portal vein.

So hepatic arterial blood is blowing into the portal vein in a retrograde manner as shown by this Doppler waveform.

The Doppler curse is now over the portal vein, and you're seeing arterial waveforms in the portal vein, but in a reverse manner because the fistula has opened into the portal vein while pointing Proximally.

So the portal venous blood can't get into the liver.

It's running into this jet of arterial blood, which is pouring into the portal vein.

And this is the corresponding Mr image, which shows that there is earlier ification of a dilated portal vein on this arterial phase contrast to mr.

So the you will see that there is contrast in the aorta indicating this is the arterial phase, but the portal vein is already enhanced and is markedly dilated, and it is due to an arterial portal fistula.

This is a rare but potentially serious complication that can lead to loss of the graft.

Reported cases are seen in children and particularly right lobe transplants, and they can present with varis and bleeding.

Summary of Doppler Abnormalities in Liver Transplantation

This slide is a summary of the Doppler abnormalities in liver transplantation in the hepatic artery.

You should look for absence of flow and occluded hepatic artery is a serious complication that can lead to the loss of the graft or serious biliary complications such as strictures and dilatation due to sloughing of the biliary mucosa.

Elevated velocities at the hepatic artery anastomosis, low resistive indices of zero less than 0.5, and an acceleration time of greater than 0.08 seconds or 80 milliseconds can be a sign of hepatic artery stenosis in the hepatic veins.

And IVC, you want to look for slow or absent flow monophasic waveforms and elevated velocities at the anastomotic site.

These are signs of stenosis In the portal vein.

You look for absence of flow altogether, or which is a sign of thrombosis, but slow flow less than 10 centimeters per second may be a sign of extrinsic compression, while a velocity gradient of greater than three or four to one at the anastomosis or greater than 150 centimeters per second at an at the anastomosis can be a sign of portal vein stenosis.

Biliary Complications

I'm now going to move on and talk about biliary complications, and these include bile leaks and anastomotic strictures, which can be at the common bile duct if there was a duct touc anastomosis.

Some patients have a biliary enteric anastomosis, and this is particularly common in liver living, donor liver transplants where the bile duct is anastomosis to a loop of bowel that has been brought up to the resection margin.

So there's a direct anastomosis between the bile duct and a loop of small bowel biliary necrosis, as I mentioned, is sec can be secondary to hepatic artery obstruction and lead to mucosal sloughing and strictures in the biliary tree and biliary obstruction.

Then there is sludge or stone formation.

Patients with liver transplants have an increased predilection to forming sludge and stones.

And there is also an increased incidence of sphincter of odd dysfunction.

Bile Leaks

And this is an example of a b leak we see here.

There appears to be a fluid collection at the liver hilum.

Remember that patients with liver transplants do not have gallbladders.

So this is not a gallbladder and this angiogram, cholangiogram shows a leak of contrast from the bile duct at the anastomotic site.

This is usually treated by stenting or sometimes percutaneous drainage of the myeloma.

Anastomotic Strictures

This is a patient with an anastomotic stricture note, markedly dilated proximal common bile duct and intrahepatic bile ducts here as shown on this color Doppler image.

And this is the corresponding cholangiogram showing a stricture at the duct.

Touc anastomosis, isolated segmental biliary obstruction is seen with biliary enteric anastomosis, which are most commonly performed in living donor transplants.

So in living donor transplants with Biliary enteric anastomosis, the individual segmental bile ducts are separately anastomosis to a loop of a small bile that's been brought up to the hilum and these individual anastomosis can obstruct.

So here we have a patient where you see a isolated dilated loop of a dilated bile duct, and this is the corresponding CT image showing the dilated bile duct.

And this is the corresponding MRCP image.

So only one segment of the liver has is obstructed.

The rest of the liver has a separate drainage from a different biliary anti anastomosis, which is not obstructed.

Sludge and Stones

This is a patient with sludge inside the common bile duct and sludge can be difficult to see because it, in this case, it is almost iso coat to the liver.

I'm drawing my a cursor here around the sludge ball, which is sitting inside the common bile duct.

And the only clue that you've got a sludge ball here is that you can see some tatic biliary dilatation, more proximally.

And this is the portal vein running behind the sludge filled common bile duct.

Here's the corresponding cholangiogram showing lots of filling defects caused by the sludge inside the proximal common bile duct.

He this is a patient with stones inside the common bile duct.

Do we see echogenic shadowing structures and the corresponding cholangiogram showing a a stone that is obstructing the common bowel duct sitting just above the duct to duct anastomosis.

Other Complications: Fluid Collections and Hematomas

This is a patient with a large hematoma.

So as part of our liver transplant scanning protocol, we do a quick survey of the extra hepatic spaces to look for large fluid collections or hematomas, hematomas that are this size.

This is about 15 or 16 centimeters, may require the patient to return to the or for evacuation.

Small hematomas say under five centimeters that are not causing mass effect or compressing of vital structures are usually left to resolve.

Liver Abscesses

Liver abscesses are associated with hepatic artery obstruction and biliary obstruction.

They have a very high mortality, greater than 40%, higher than non-transplant patients.

Liver transplant patients are all immune suppressed.

They are often caused by unusual organisms like fungi, candida, non amal, non-albicans candida cytomegalovirus or crypto caucus, and they appear as cystic areas within the liver.

So when you see cystic areas within the liver, don't just dismiss them as, oh, these are just simple liver cysts.

If that you are dealing with a transplanted patient who is immune suppressed, think if this could be an abscess, particularly if ultrasound done a couple days earlier had not shown these cystic areas.

So a cystic area that suddenly appears in a trans, in a, in the post-transplant period could be a liver abscess and the patient can rapidly go downhill if this is not treated quickly.

And this is the equivalent CT of of a patient with this liver abscess.

Here you can see large fluid collections rapidly appearing in the liver that grow, and this is a corresponding MRI in someone with multiple liver abscesses.

Here we, on this MRCP image, we see High signal fluid collections that are budding off the biliary tree.

And this patient had hepatic artery stenosis and with resulting biliary necrosis and development of little abscesses that are communicating with the biliary tree.

False Aneurysm

Well, this is a patient with a cystic area inside the liver that is not an abscess.

This patient had a liver biopsy and by applying the color doppler to the cystic area, one can see the classic yin yang appearance of a false aneurysm caused by the liver biopsy.

The hepatic artery has been punctured at this site and there is a leak of blood into this cavity creating this swirling appearance of blood or the the the yin, the so-called yin yang sign, which is classic for a false aneurysm post-transplant.

Malignancy in Liver Transplants

Malignancy can be caused by post-transplant lymphoproliferative disorder.

This is a B-cell disorder caused by the Epstein bar virus and presents six to 18 months post-transplant in co due to the immune suppressed state of the patient.

It is a form of non-Hodgkin's lymphoma.

Hepatocellular carcinoma can re can also occur and it can recur in patients who have had a transplant because of HCC and cholangiocarcinoma can occur if the transplant was performed for primary sclero in cholangitis.

Patients with PSE have a greater predilection to developing cholangiocarcinoma and this predilection carries over even though the patient has had a transplant.

PTLD rarely involves the liver itself.

It appears in the form of lymphadenopathy or parahepatic masses.

In this patient. Here we see a hypoechoic solid structure between the IVC and aorta, which is a large aortocaval lymph node.

This is a case of recurrent HCC.

This patient had hepatocellular carcinoma in his liver and he had a transplant, but a little bit of tumor may unfortunately have seeded during the transplantation process and it appears as a mass which is visible adjacent to the liver in Morrison's pouch On this haste sequence, this is seen to enhance post contrast and the image on the bottom is following radiofrequency ablation performed by an interventionalist.

The little residue of HCC here has been successfully ablated.

Conclusion

In conclusion, major biliary and vascular complications of liver transplantation can be accurately evaluated with cross-sectional imaging.

Ultrasound is the first line imaging modality in the immediate post-transplant period.