Pancreatic Transplantation

Published on 19/07/2015 by admin

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Last modified 22/04/2025

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CT: Homogeneous soft tissue mass in right abdomen with adjacent suture line at duodenal stump

MR: Normal pancreatic parenchyma is isointense to renal cortex on T1WI and isointense to muscle on T2WI

US: Normal pancreas transplant homogeneous and hypoechoic to adjacent mesenteric fat

• Imaging of major complications

Allograft pancreatitis: Edema, enlargement and heterogeneous pancreas with peripancreatic fluid

Acute rejection: Enlargement and edema of graft with increased T2WI signal on MR

Chronic rejection: Small and atrophic graft with decreased T1 and T2WI signal on MR

Vascular complications: Venous thrombosis is more common than arterial

– Arterial thrombosis on US: No Doppler flow within artery or graft parenchyma

– Venous thrombosis on US: Echogenic intraluminal thrombus, absent vascular flow, and high-resistance arterial waveforms with reversed diastolic flow

– Graft infarction on US: Enlarged avascular transplant

Intraabdominal fluid collections: May represent abscess, seroma, lymphocele, urinoma, or pseudocyst

PATHOLOGY

• Goal of pancreas transplantation is treatment of diabetes by restoring endogenous insulin secretion

CLINICAL ISSUES

• Graft survival is better with combined pancreas-kidney transplant than with pancreas alone

• Graft pancreatitis is common after transplantation

35% experience mild, self-limited pancreatitis; usually related to reperfusion injury after surgery

• Chronic rejection is leading cause of late allograft loss

• Vascular thrombosis is 2nd leading cause of graft dysfunction (usually in acute postoperative setting)

(Left) Graphic shows the usual surgical anatomy of a combined pancreas-kidney transplant with pancreatic-enteric drainage. The donor iliac artery is anastomosed to the donor superior mesenteric and splenic arteries to perfuse the pancreatic allograft (inset). The venous drainage can be to the iliac vein (as drawn) or the superior mesenteric vein.

(Right) Coronal MRA of a kidney-pancreas transplant reveals that the renal and the pancreatic allografts show normal perfusion and parenchymal enhancement.

(Left) Coronal NECT demonstrates the right lower quadrant transplant pancreas to be enlarged and hypodense with adjacent fat stranding and induration. Based on the CT findings, this could represent either graft ischemia or pancreatitis.

(Right) Sagittal power Doppler ultrasound in the same patient demonstrates the pancreatic transplant to be enlarged and diffusely hypoechoic, without appreciable internal vascularity, compatible with infarction.

IMAGING

General Features

• Location

80% are placed simultaneously with or following renal transplantation (Tx) for type 1 diabetes

– Pancreatic graft survival is increased with simultaneous transplantation

Pancreatic allograft usually placed on right side (renal allograft on left)

– Graft in bladder drainage transplants is usually in right iliac fossa, parallel to ascending colon

– Graft position in enteric drainage transplants is more variable, but usually vertical on right side

Multivisceral transplant

– Usually refers to transplantation of liver and small bowel

– If pancreas is also transplanted, it is often placed in upper abdomen, in transverse orientation

– Liver, bowel, and pancreas allografts all supplied by donor aortic graft

• Surgical technique

Bladder drainage

– Older technique that drains pancreatic secretions into bladder via duodenal interposition segment

– Associated with many complications, including accelerated insulin resistance, atherosclerosis, urinary tract infections, and graft pancreatitis

Enteric drainage

– Now considered preferred technique, with allograft head (which is obtained with segment of duodenum) placed in cephalic location with side-to-side pancreatic-duodenal to jejunal anastomosis

Venous drainage

– Donor portal vein anastomosed to systemic vein (common/external iliac or IVC) or mesenteric vein (more physiologic, but technically more difficult)

Arterial supply

– Donor iliac artery “Y” graft with one end anastomosed to recipient’s common, external, or internal iliac artery and “Y” limbs anastomosed to donor splenic and superior mesenteric arteries (end blindly after supplying allograft)

• Normal imaging appearance

CT: IV contrast often not used due to renal toxicity and concurrent chronic renal failure

– Oral contrast very useful (and usually necessary) to distinguish graft from adjacent bowel

– For bladder-drained allografts, can introduce contrast into bladder via catheter

– Homogeneous soft tissue mass closely associated with adjacent bowel (typically with adjacent suture line at duodenal stump)

– Graft may be normally enlarged and heterogeneous in early post-transplant period (< 4 weeks) with surrounding fluid and hematoma, and should not be confused with pancreatitis

Pancreas graft gradually becomes well defined and similar in density (on both NECT and CECT) to normal pancreas, with no surrounding fluid

MR: Normal pancreas parenchyma is isointense to renal cortex on T1WI and isointense to muscle on T2WI

• Imaging of major complications

Allograft pancreatitis: Edema, enlargement, and heterogeneous enhancement of pancreas on CT and MR, typically with peripancreatic fluid

– Peripancreatic fluid can evolve into loculated collections or pseudocysts

– May see bowel wall thickening of adjacent intestine

Acute rejection: Nonspecific CT findings, with enlargement and edema of graft

– MR: Increased parenchymal T2WI signal and heterogeneous enhancement due to edema

Chronic rejection: Nonspecific CT findings, with small and atrophic graft

– MR: Decreased signal intensity on T1 and T2 due to parenchymal fibrosis and reduced extracellular fluid

Secretin-augmented MR may demonstrate diminished exocrine function with ↓ secretion of pancreatic juice from dysfunctional allograft

Vascular complications: Venous thrombosis is more common than arterial

– MRA and CTA can map arterial and venous anatomy to identify sites of stenosis or thrombosis

More typically a troubleshooting tool when ultrasound findings are equivocal

Can be used to monitor anticoagulation therapy in patients with venous stump thrombosis

– Pseudoaneurysms and arteriovenous fistulae may be due to prior biopsy, pancreatitis, or surgical technique

– Graft infarction: Heterogeneous enhancement of pancreas on MR or CT ± liquefied/necrotic parenchyma ± gas bubbles

Impossible to distinguish infarction from infected pancreatic necrosis after pancreatitis, although treatment is same (surgical resection)

Ischemia or necrosis can affect graft focally or diffusely

Postoperative hemorrhage: May be visualized on routine postoperative US, but full extent (and presence of active extravasation) best seen with CECT

Intraabdominal fluid collections: May represent abscess, seroma, lymphocele, urinoma, or pseudocyst

– Presence of excessive extraluminal gas, fluid, or oral contrast should raise concern for leakage at enteric anastomosis

Post-transplant lymphoproliferative disorder (PTLD): New lymphadenopathy or solid masses in abdomen after transplant should raise suspicion

Radiographic Findings

• Radiography

Normal pancreatic transplant: Vague lower quadrant soft tissue density (usually in right lower quadrant) with 2 or 3 rows of staples

– Stapled ends of duodenum, plus side-to-side anastomosis to jejunum (or bladder)

• Urethrography/cystography: Useful for evaluation of bladder-drained transplant to assess urologic complications or anastomotic leaks

Cystitis/duodenitis: Lack of distensibility; thickened folds

Nuclear Medicine Findings

• Most commonly utilized radiotracers include Tc-99m DTPA or MAG3-99m

• Rejection vs. vascular complications

Delayed time between peak iliac artery to peak graft activity with diminished graft perfusion and radiotracer uptake suggests ischemia (possible with vascular thrombosis)

Change in relative intensity, size, or homogeneity of graft suggests rejection

Findings are nonspecific and require further investigation with another imaging modality or biopsy

• Pancreatitis: Normal or increased flow with patchy or poor uptake of tracer and prolonged washout of static images

CT Findings

•

MR Findings

•

Ultrasonographic Findings

• May not adequately visualize pancreas in ∼ 20% of cases

Normal pancreas transplant should be homogeneous and hypoechoic to adjacent mesenteric fat

“Y” arterial graft and graft vein should be visualized using color or power Doppler

• Unable to distinguish among different causes of parenchymal abnormalities

Acute processes (rejection vs. pancreatitis) result in enlarged, hypoechoic, or heterogeneous gland

– Pancreatitis more likely to result in perigraft free fluid

Chronic rejection results in shrunken, atrophic gland with increased echogenicity

Elevated resistive indices nonspecific and may be seen with rejection, ischemia, or pancreatitis

• Color Doppler, power Doppler and spectral Doppler

Arterial thrombosis: No color or power Doppler flow within artery and graft parenchyma

Venous thrombosis: Echogenic intraluminal thrombus, absent flow in vessel and possibly in graft parenchyma, and high-resistance arterial waveforms with possible reversed diastolic flow

Infarction: Little or no flow within enlarged, heterogeneous allograft on color or power Doppler

Imaging Recommendations

• Best imaging tool

Ultrasound is best initial screening tool, with Doppler allowing evaluation of vasculature and perfusion of graft

– Best modality for guiding biopsy and drainage procedures

CECT and MR are useful troubleshooting tools for evaluation of vasculature and complications

Nonvascular Interventions

• US-guided biopsy of allograft is safe and effective means to distinguish rejection from other causes of graft dysfunction

Technical success rate > 95%; complication rate < 3%

PATHOLOGY

General Features

• Primary goal for pancreas transplantation is treatment of diabetes by restoring endogenous insulin secretion and preventing progression of diabetes complications

• Transplants typically performed in 2 groups

Patients with end-stage renal disease who have or will have kidney transplant: Pancreas transplant improves odds of kidney survival by preventing hyperglycemia

– Most often combined kidney-pancreas transplant

Patients with severe metabolic complications from diabetes who have failed exogenous insulin therapy may undergo pancreas transplant even in absence of chronic kidney disease

– Usually only pancreas transplant without kidney

Microscopic Features

• Chronic rejection

Obliterative vasculopathy

Pancreatic parenchymal fibrosis

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

Pancreatitis

– Right lower quadrant pain; ↑ amylase, lipase

– Can result in pseudocyst formation (usually weeks after bout of pancreatitis)

Vascular thrombosis

– Sudden loss of graft function (e.g., hyperglycemia, increased insulin dependence) and focal tenderness over swollen graft

– Venous thrombosis is more common than arterial

– More likely in acute postoperative setting (< 30 days) than in chronic setting

– May be more likely in setting of pancreatitis or underlying pseudoaneurysm

Postoperative hemorrhage

– Complicates 1% of pancreatic transplantations

– Patients present with pain and falling hematocrit

– Hemorrhage in immediate postoperative period usually due to leak from vascular anastomosis, while later hemorrhage often due to anticoagulation

Rejection

– Affects up to 40% of pancreatic grafts

– May be hyperacute, acute, or chronic, and typically presents with diminished graft function

Anastomotic leak

– Occurs in 14% of cases in bladder-drained grafts and 2-10% of enteric-drainage cases

– Severe local pain but usually preserved graft function

– Presence of ectopic gas, fluid, or enteric contrast should raise suspicion for this diagnosis

– Early leaks due to surgical technique, while later leaks due to pancreatitis, rejection, or infection

Infection

– Fever, sepsis

Urologic complications (with bladder drainage)

– Transient hematuria in almost all patients

– Cystitis, urethritis, and stricture are common

Demographics

• Epidemiology

> 37,000 transplants since 1st transplant in 1966

> 1,300 pancreas transplantations in USA in 2008

75% are combined kidney-pancreas transplants

Natural History & Prognosis

• Graft survival is better with combined pancreas-kidney transplant than with pancreas alone

With simultaneous pancreas-kidney transplantation, 1-year graft survival is 80-85% and 5-year graft survival is 65%

With pancreas transplant alone, 1-year and 10-year graft survival is only 78% and 27%, respectively

May be related to relative ease of identifying rejection in patients with kidney transplant (as creatinine serves as marker for graft function)

• 1-year patient survival after transplant is 92-98%

• Graft pancreatitis is relatively common immediately after transplantation

35% of patients experience mild, self-limited pancreatitis; usually related to reperfusion injury after surgery

– Hyperamylasemia is common in 1st week post transplantation

More common with bladder drainage transplant technique

• Chronic rejection is leading cause of late allograft loss

Allograft rejection is usually confirmed by biopsy

• Vascular thrombosis is 2nd leading cause of graft dysfunction

Accounts for > 50% of early graft failures (< 30 days) and < 10% of late graft failures (> 30 days)

Incidence of thrombosis is 2-19% of all transplants

Can result in parenchymal infarction or necrosis and may require pancreatectomy

DIAGNOSTIC CHECKLIST

Consider

• Imaging of pancreas transplant should begin with US, with MR or CT used as troubleshooting tools in cases of suspected complications

Image Interpretation Pearls

• Imaging lacks specificity in differentiating nonvascular etiologies of graft dysfunction, and biopsy may be required

(Left) Axial CECT shows the pancreatic allograft with mild swelling of the gland and peripancreatic stranding, indicating mild pancreatitis, a finding seen frequently in the immediate post-transplant period.

(Right) Axial CECT shows diffuse parenchymal enlargement and heterogeneity with scattered areas of decreased enhancement in the transplant pancreas , consistent with post-transplant pancreatitis. Note the normally enhancing transplanted kidney in the left lower quadrant .

(Left) Coronal CECT shows a rim-enhancing fluid collection surrounding the pancreas transplant . Note the communication between the fluid collection and the duodenum consistent with suture line dehiscence . Emergent surgical drainage and repair was performed.

(Right) Axial CECT demonstrates a fluid collection adjacent to the transplant pancreas in a patient with a history of pancreatitis, compatible with a pseudocyst. A transplant kidney is noted in the left lower quadrant .

(Left) Coronal MRA shows normal appearance and enhancement of the right lower quadrant renal allograft , while the branching arterial supply to the pancreatic allograft is totally occluded. The infarcted pancreatic allograft was then resected.

(Right) Axial CECT shows gas and fluid replacing the pancreatic allograft in the right iliac fossa, with a fistulous tract to the skin. At resection, infected necrosis of the pancreatic allograft related to pancreatitis was noted.

Axial CECT shows perigraft fluid and heterogeneous enhancement of the transplant pancreas . These findings are consistent with the clinical diagnosis of acute post-transplant pancreatitis. Unfortunately the pancreatitis was accompanied by graft rejection and this ultimately resulted in graft failure.

Ultrasound demonstrates an anechoic fluid collection adjacent to the transplant pancreas , representing a pseudocyst related to a prior bout of pancreatitis.

Color Doppler ultrasound demonstrates an absence of color flow vascularity within the transplant pancreas , in keeping with global infarction.

Color Doppler ultrasound demonstrates a complete absence of color flow vascularity in the transplant pancreas, compatible with global infarction.

Transverse color Doppler ultrasound in a patient with an allograft infarction shows the allograft as an enlarged, hypoechoic structure with virtually no evidence of blood flow within it.

Axial CECT in a different patient shows a normal pancreatic allograft in the immediate postoperative period. There is mild diffuse swelling of the allograft and soft tissue infiltration of the adjacent fat planes . These findings are seen frequently in the immediate post-transplant period and represent the normal post-transplant CECT appearance of the allograft.

Coronal CECT in a patient undergoing multivisceral transplant shows the anastomotic site between the donor and recipient aortas with this vessel feeding the small bowel, liver, and pancreatic allografts. All of the allografts functioned well and the patient made an uneventful recovery.

Axial CECT in the same patient shows the aorto-aortic anastomosis and the transplanted pancreas , small bowel , and liver, all of which enhance and function normally.

Axial CECT shows a pancreatic allograft and renal allograft in the iliac fossae. Both show normal parenchymal enhancement and no sign of infarction or rejection. There are several small and large pseudocysts near the pancreatic allograft. These were aspirated and drained with US guidance.

Catheter angiography shows a pseudoaneurysm at the site of the arterial anastomosis (iliac artery of donor to recipient internal iliac artery). This was treated with coil embolization.

Diagnostic Imaging_ Gastrointes - Michael P Federle

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Pancreatic Transplantation

PATHOLOGY

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IMAGING

General Features

Radiographic Findings

Nuclear Medicine Findings

CT Findings

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Ultrasonographic Findings

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Nonvascular Interventions

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Categories

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Pancreatic Transplantation

PATHOLOGY

CLINICAL ISSUES

IMAGING

General Features

Radiographic Findings

Nuclear Medicine Findings

CT Findings

MR Findings

Ultrasonographic Findings

Imaging Recommendations

Nonvascular Interventions

PATHOLOGY

General Features

Microscopic Features

CLINICAL ISSUES

Presentation

Demographics

Natural History & Prognosis

DIAGNOSTIC CHECKLIST

Consider

Image Interpretation Pearls

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