Pancreas Transplantation - HD

Introduction

Hello, my name's Mange.
I'm an associate professor from University of Washington in Seattle
and my lecture today will be an ultrasound of pancreas transplantation.

History and Statistics

Pancreas transplantation was started first at University of Minnesota in 1966.
Approximately 1200 pancreas transplantations are done every year.
If you look at the number of pancreas transplantations alone, it's a smaller number, 10%,
but a larger percentage, almost 75% are done simultaneously with the kidney and a smaller percentage, 15%
after a successful kidney transplantation.

Indications and Contraindications

The indications for pancreas transplantation are wide.
And as you can see in the list over here,
but most commonly the pancreas transplantation is done for insulin dependent diabetes
or for secondary diabetic complications like neuropathy, retinopathy, et cetera.

Some of the absolute contraindications for pancreas transplantation are listed over here.
These include HIV infection, untreated cancers, psychiatric disease, psychosocial problems, et cetera.
And then there's some relative contraindications as well,
like cardiovascular disease or treated malignancy and substance abuse.

Organ Retrieval and Preparation

Thinking about pancreas transplantation,
it's important to think about the organ retrieval or the back bench preparation as well.
The pancreas is retrieved in block with the liver and the pancreas with the liver
and the rest of the organs from the same donor.
As you can see over here,
the pancreas is also harvested with a short segment of the duodenum and the splenic artery
and the proximal SMA, this is so that a y graft can be created and the Y graft is
because the head of the pancreas is supplied by the inferior pancreatic cordin artery via the SMA
and the body and the tail by the splenic artery.
So those two are joined together with the graft,
which is shaped in the form of a Y,
which is usually the donor external iliac artery and the common iliac artery.
And then a common anastomosis is created,
which is then grafted on to the recipients common iliac artery.

Okay, so you can see that in this movie
where you can actually see from the angiogram a y graft
that is supplying the whole pancreas located in the right lower quadrant.

Surgical Techniques

There are two types of surgical techniques, bladder drainage and enteric drainage.
Bladder drainage is a side-to-side duodenovesical anastomosis to the bladder enteric drainage is side-to-side duodenojejunostomy anastomosis to the jejunum.

Vascular Anastomosis Variations

In primary anastomosis to the bladder, a Y graft is created anastomosis to the external iliac artery,
and the portal vein is anastomosis to the external iliac vein.

In primary anastomosis to the bowel with portal vascular drainage, the Y graft is anastomosis
as usual to the common iliac artery.
However, the portal vein is anastomosis to the right side of the superior mesenteric vein,
and in primary anastomosis to the bowel with systemic vascular drainage, the Y graft is anastomosis
to the right common iliac artery and the portal vein is anastomosis to the right iliac vein.

Advantages and Disadvantages of Drainage Types

Bladder Drainage

What are the advantages of bladder drainage?
It allows for direct measurement of graft exocrine function by just measuring the urine amylase levels
and the complications are treated less invasively as well.
But the disadvantages are that there's a higher incidence of pancreatitis, bladder leaks, urethritis
and infections in the urinary tract, as well as hematuria with almost 35% of those needing future enteric conversion.

Systemic Enteric Drainage

In terms of systemic enteric drainage, the advantages are that it's more physiologic,
there are fewer metabolic imbalances because all the pancreatic secretions are resorbed into the system.
The disadvantages, however, are that infections due to possible enteric contamination are more common.
It can lead to sepsis, which can be secondary to abscess or fistula formation.
There's higher incidence of vascular thrombosis and the complications need more invasive procedures to handle.

Portal Venous Enteric Exocrine Drainage

In terms of the portal venous enteric exocrine drainage, the advantages are that it's more physiologic glucose control
and may help with the lipid profile.
However, the disadvantage is that we are unable to monitor the urine amylase
and it's difficult to biopsy when there's a portal venous enteric exocrine drainage technique.

Imaging Modalities

For a pancreatic transplantation in terms of imaging, ultrasound is a primary modality.
We perform ultrasound with doppler imaging.
It's cheap, portable for the bladder drained pancreas.
It may, it's helpful to have a full bladder to use that as an acoustic window with enterically drained pancreas.
It is difficult to image the pancreas because of the overlying bowel.
And it's important to remember that resistive indices are not useful in the pancreas.
We use CT and MR only for complications and not as a routine.

Normal Ultrasound Findings

So these images here show the pancreatic head with the vascular vasculature coming in pancreatic body
and the tail in a normal pancreas.

In terms of doppler, it's important to assess vascular flow within the head.
You can see the arterial flow and the venous flow here in the body, arterial and venous flow and tail arterial and venous flow.

In addition, it is important to assess the Y graft as well.
So you can see this is the vein and the artery in the pancreas.
Transplant vein shows low velocity phasic or monophasic waveform,
and this is the Y graft which shows arterial flow within it.
And it's important to assess the y shaped appearance with patency of both the arms of the y in a pancreas transplantation.

Complications

In terms of complications, you can have vascular graft or enteric complications and will review these complications.

Vascular Graft Complications

In terms of vascular graft complications, thrombosis is seen in immediate postoperative period,
usually less than 72 hours.
And the reason for the vascular thrombosis is usually technical, could be because of micro thrombin formation trauma
during the surgery or post surgery.
And poor vessel mismatch size seen commonly with pediatric donors.
Venous thrombosis is more common than arterial thrombosis and it can result in necrosis of the graft.

In terms of clinical signs we watch for drop in urine amylase, especially if bladder drained
or there may be rapid rise in serum glucose, amylase and or lipase in these patients.
Treatment for these patients is immediate laparotomy with possible pancreatectomy if the graft cannot be salvaged.

Arterial thrombosis is a most serious complication.
And in terms of imaging, we see heterogeneous echogenicity in the pancreas with complete occlusion of the vessel
and non enhancement of perfusion of the pancreas with lack of flow to the pancreas
and absence of arterial flow in the graft and the artery as seen on these images on power doppler,
there's no flow seen within the pancreas.
And on spectral doppler, there's no perceptible flow seen within the pancreas.

This is another case of arterial thrombosis.
A similar case showing heterogeneous echogenicity in the pancreas with lack of any flow seen within the pancreas.
And this is the angiogram in the same patient shows complete occlusion of the Y graft at in the right lower quadrant
and with no perfusion of the pancreas at all.

A second case seen here with pancreas seen in the right lower quadrant,
there's some perceptible flow in the right lower quadrant.
However, a CT done in the same patient shows no evidence of perfusion in the pancreas,
suggesting that there's complete vascular thrombosis.

In some cases there is collateral formation, however, it's not seen in the acute phase seen in the chronic phases
when you may see some flow in the pancreas transplantation.
This patient had a color Doppler image showing small amount of flow in the pancreas,
which on spectral doppler showed an arterial waveform.
And the angiogram here shows that the y graft is patent,
but there are collaterals which are supplying the pancreas in this particular patient.

In terms of venous thrombosis, it's seen in 5% of transplant graft and the first few weeks of transplantation,
they may be complicated by graft pancreatitis, necrosis or infection.
On imaging, we see an enlarged heterogeneous graft.
There may be a small amount of peri graft fluid,
an absence of flow seen on spectral doppler.
The arterial flow may be present, but the venous flow is absent in this particular case.
An echogenic hypoechoic area is seen in the right lower quadrant, which correlated with the splenic vein.
Treatment for these patients is anticoagulation with surgical thrombectomy.

This another patient presented with abnormal lab values and shows presence of arterial flow in the head of the pancreas
shows presence of venous flow in the head of the pancreas as well.
However, it was absence of flow in the tail and the body of the transplant pancreas suggesting thrombosis in the head and the body of the pancreas
reversal of flow and diastole is a very typical sign seen with venous thrombosis.
In this particular case, you can see an enlarged heterogeneous pancreas
and on spectral doppler you can see that there's reversal of flow in this latest later part of the arterial cycle suggesting venous thrombosis.
A CT in the same patient confirmed a venous thrombus in this particular patient.

There can be extrinsic compression or kinking of arteries and vessels which can mimic arterial venous thrombosis.
And these are usually fluid collections which compress on the common iliac arteries.
So here's a patient who has pancreas transplantation in the right lower quadrant with a large fluid collection
compressing on the vasculature as seen in this particular image as well.
You can see that the vessels are patent.
However, there's a fluid collection in the right lower quadrant compressing on it.

Pseudo aneurysms can be seen at the anastomosis or biopsy site and result from focal loss of arterial integrity
can happen with pancreatitis or graft infections.
On ultrasound, they are usually seen as cystic fluid collections,
which on colored dopplers have the yin yang or the swirling sign appearance to them.
On spectral doppler the neck you would see a to and fro waveform within the pseudo aneurysm.

AV fistulas are rare complications and are usually seen post-surgical or post biopsy.
On ultrasound, you'll see an area of high flow or aliasing within the pancreas.
You're usually seen in the tail since biopsy is done within the tail and on doppler of the draining venous structures,
you'll have arterialized waveform seen within the veins.

Fluid Collections

Fluid collections can also be seen post transplantation.
The first one that we'll discussed is a pseudocyst and can be seen with prior graft pancreatitis
and occur within or adjacent to the graft as seen on this particular case.
The pancreas transplantation is located here and is a fluid collection seen right adjacent to it.
So they're seen as well circumscribed fluid collections with posterior acoustic through transmission.
They have a thin wall.
They have minimal adjacent inflammatory appearance as seen on both the CT and the ultrasound.
And if we aspirate this fluid collection, there'll be elevated amylase levels within it.

Hematomas on the other hand are seen in a typical postoperative setting.
They can be round or oval complex collections with heterogeneous echogenicity in them.
They're usually echogenic in the early phase and then may be septated or contain a hematocrit level.
When they're longstanding.
They will not have any perceptible color flow within them on doppler,
suggesting that they're hematomas.
CT confirms presence of complex fluid collections in this particular patient,
which are consistent with hematomas.

An abscess is uncommon but can result from an infected pseudocyst or in the setting of a duodenal leak.
They usually complex fluid collections.
They have a thick irregular wall to them and doppler would show hyperemia along the periphery of the wall.
You may sometimes see gas as echogenic foci within the fluid collections.
In addition, you'll have adjacent inflammatory fat stranding from the abscess as seen in this particular case on CT
with the thick wall fluid collection and surrounding inflammation.

Enteric Complications

In terms of enteric complications, leak or perforation is relatively common, about 14% of cases
and they happen in the first three months.
Clinical signs include pain, a rise in amylase and lipase,
and imaging is able to detect most of these leaks.
They occur more after either the enterostomy or the duodenocystostomy and arise from the anastomotic site.
Treatment would require re exploration and repair of the anastomotic leak graft.

Pancreatitis is seen early in about 10% of patient.
Subclinical pancreatitis can happen in the immediate postoperative setting as well.
And patients present with elevated serum amylase.
Early pancreatitis is usually secondary to preservation injury
and late pancreatitis is usually from reflux if it is bladder drained or from infection or trauma.

In terms of imaging, there's variable appearance.
The pancreas can appear normal, can have non-specific enlargement or heterogeneous appearance.
They can be peripancreatic fluid or fat stranding and loss of vascularity in severe pancreatitis suggesting ischemia or necrosis as seen.
In this particular case, we have a large heterogeneous appearing pancreas with peripancreatic fluid
and on ct there's presence of fat stranding in the lower quadrant suggesting pancreatitis

Rejection

Rejection is a clinical diagnosis.
It is often difficult to diagnose and we look for increase in serum amylase or lipase.
Patients also have an increase in serum creatinine, especially if they have simultaneous kidney and pancreas transplantation
because 90% of the pancreas and kidneys reject simultaneously since they come from the same donor,
there may be decrease in the urine amylase if it is bladder drained and patients present with pain over the pancreas graft,
they may also have malaise and fever and hyperglycemia is usually a late indicator of rejection.
Biopsy in these patients would be positive for lymphocytic infiltrates.

Pancreatic biopsy is done because serum biochemical markers lack the accuracy in diagnosis of rejection
in this particular paper by Atwell et al.
96% of the ultrasound guided pancreas biopsies specimens were adequate for histopathologic evaluation
and they had a low procedure related complication rate of 2.6%.

Biopsy Procedure

How do we biopsy the transplant?
Initially an ultrasound is performed to assess if it is possible to reach the pancreas safely if there's a window for biopsy.
And then if it is, we biopsy real time with ultrasound.
An 18 gauge needle is used and if there is an ultrasound window,
the patient is then shifted for biopsy under CT guidance.
The preferable site for biopsy is the tail since the pancreatic duct is very small on the tail
and the vasculature is similarly smaller in the tail without major vessels being in the region.

So this is a patient, you can see the needle in the pancreas on CT guided biopsy.

So in terms of transplant biopsy with ct, a grid is placed over the patient to mark for the adequate position of the pancreas transplant.
And under CT guidance, a needle is then inserted into the pancreas for biopsy.

Conclusion

So in conclusion, ultrasound is a mainstay of pancreatic transplantation imaging.
It is important to diagnose complications early,
and we reviewed some normal imaging appearance and imaging of complications as well.
Thank you very much.