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

image MR: Normal pancreatic parenchyma is isointense to renal cortex on T1WI and isointense to muscle on T2WI
image US: Normal pancreas transplant homogeneous and hypoechoic to adjacent mesenteric fat
• Imaging of major complications

image Allograft pancreatitis: Edema, enlargement and heterogeneous pancreas with peripancreatic fluid
image Acute rejection: Enlargement and edema of graft with increased T2WI signal on MR
image Chronic rejection: Small and atrophic graft with decreased T1 and T2WI signal on MR
image 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
image 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

image 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)
image
(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.

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(Right) Coronal MRA of a kidney-pancreas transplant reveals that the renal image and the pancreatic allografts image show normal perfusion and parenchymal enhancement.
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(Left) Coronal NECT demonstrates the right lower quadrant transplant pancreas image to be enlarged and hypodense with adjacent fat stranding and induration. Based on the CT findings, this could represent either graft ischemia or pancreatitis.

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

IMAGING

General Features

• Location

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

– Pancreatic graft survival is increased with simultaneous transplantation
image 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
image 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

image 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
image 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
image Venous drainage

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

image 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

image Pancreas graft gradually becomes well defined and similar in density (on both NECT and CECT) to normal pancreas, with no surrounding fluid
image MR: Normal pancreas parenchyma is isointense to renal cortex on T1WI and isointense to muscle on T2WI
• Imaging of major complications

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

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

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

image More typically a troubleshooting tool when ultrasound findings are equivocal
image 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

image Impossible to distinguish infarction from infected pancreatic necrosis after pancreatitis, although treatment is same (surgical resection)
image Ischemia or necrosis can affect graft focally or diffusely
image Postoperative hemorrhage: May be visualized on routine postoperative US, but full extent (and presence of active extravasation) best seen with CECT
image 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
image Post-transplant lymphoproliferative disorder (PTLD): New lymphadenopathy or solid masses in abdomen after transplant should raise suspicion

Radiographic Findings

• Radiography

image 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

image 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

image Delayed time between peak iliac artery to peak graft activity with diminished graft perfusion and radiotracer uptake suggests ischemia (possible with vascular thrombosis)
image Change in relative intensity, size, or homogeneity of graft suggests rejection
image 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

image Normal pancreas transplant should be homogeneous and hypoechoic to adjacent mesenteric fat
image “Y” arterial graft and graft vein should be visualized using color or power Doppler
• Unable to distinguish among different causes of parenchymal abnormalities

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

– Pancreatitis more likely to result in perigraft free fluid
image Chronic rejection results in shrunken, atrophic gland with increased echogenicity
image Elevated resistive indices nonspecific and may be seen with rejection, ischemia, or pancreatitis
• Color Doppler, power Doppler and spectral Doppler

image Arterial thrombosis: No color or power Doppler flow within artery and graft parenchyma
image Venous thrombosis: Echogenic intraluminal thrombus, absent flow in vessel and possibly in graft parenchyma, and high-resistance arterial waveforms with possible reversed diastolic flow
image Infarction: Little or no flow within enlarged, heterogeneous allograft on color or power Doppler

Imaging Recommendations

• Best imaging tool

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

– Best modality for guiding biopsy and drainage procedures
image 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

image 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

image 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
image 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

image Obliterative vasculopathy
image Pancreatic parenchymal fibrosis

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

image Pancreatitis

– Right lower quadrant pain; ↑ amylase, lipase
– Can result in pseudocyst formation (usually weeks after bout of pancreatitis)
image 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
image 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
image Rejection

– Affects up to 40% of pancreatic grafts
– May be hyperacute, acute, or chronic, and typically presents with diminished graft function
image 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
image Infection

– Fever, sepsis
image Urologic complications (with bladder drainage)

– Transient hematuria in almost all patients
– Cystitis, urethritis, and stricture are common

Demographics

• Epidemiology

image > 37,000 transplants since 1st transplant in 1966
image > 1,300 pancreas transplantations in USA in 2008
image 75% are combined kidney-pancreas transplants

Natural History & Prognosis

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

image With simultaneous pancreas-kidney transplantation, 1-year graft survival is 80-85% and 5-year graft survival is 65%
image With pancreas transplant alone, 1-year and 10-year graft survival is only 78% and 27%, respectively
image 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

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

– Hyperamylasemia is common in 1st week post transplantation
image More common with bladder drainage transplant technique
• Chronic rejection is leading cause of late allograft loss

image Allograft rejection is usually confirmed by biopsy
• Vascular thrombosis is 2nd leading cause of graft dysfunction

image Accounts for > 50% of early graft failures (< 30 days) and < 10% of late graft failures (> 30 days)
image Incidence of thrombosis is 2-19% of all transplants
image 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
image
(Left) Axial CECT shows the pancreatic allograft image with mild swelling of the gland and peripancreatic stranding, indicating mild pancreatitis, a finding seen frequently in the immediate post-transplant period.

image
(Right) Axial CECT shows diffuse parenchymal enlargement and heterogeneity with scattered areas of decreased enhancement in the transplant pancreas image, consistent with post-transplant pancreatitis. Note the normally enhancing transplanted kidney in the left lower quadrant image.
image
(Left) Coronal CECT shows a rim-enhancing fluid collection image surrounding the pancreas transplant image. Note the communication between the fluid collection and the duodenum consistent with suture line dehiscence image. Emergent surgical drainage and repair was performed.

image
(Right) Axial CECT demonstrates a fluid collection image adjacent to the transplant pancreas image in a patient with a history of pancreatitis, compatible with a pseudocyst. A transplant kidney is noted in the left lower quadrant image.
image
(Left) Coronal MRA shows normal appearance and enhancement of the right lower quadrant renal allograft image, while the branching arterial supply to the pancreatic allograft image is totally occluded. The infarcted pancreatic allograft was then resected.

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

image
Ultrasound demonstrates an anechoic fluid collection image adjacent to the transplant pancreas image, representing a pseudocyst related to a prior bout of pancreatitis.
image
Color Doppler ultrasound demonstrates an absence of color flow vascularity within the transplant pancreas image, in keeping with global infarction.
image
Color Doppler ultrasound demonstrates a complete absence of color flow vascularity in the transplant pancreas, compatible with global infarction.
image
Transverse color Doppler ultrasound in a patient with an allograft infarction shows the allograft image as an enlarged, hypoechoic structure with virtually no evidence of blood flow within it.
image
Axial CECT in a different patient shows a normal pancreatic allograft image in the immediate postoperative period. There is mild diffuse swelling of the allograft and soft tissue infiltration of the adjacent fat planes image. These findings are seen frequently in the immediate post-transplant period and represent the normal post-transplant CECT appearance of the allograft.
image
Coronal CECT in a patient undergoing multivisceral transplant shows the anastomotic site between the donor and recipient aortas image with this vessel feeding the small bowel, liver, and pancreatic allografts. All of the allografts functioned well and the patient made an uneventful recovery.
image
Axial CECT in the same patient shows the aorto-aortic anastomosis image and the transplanted pancreas image, small bowel image, and liver, all of which enhance and function normally.
image
Axial CECT shows a pancreatic allograft image and renal allograft image in the iliac fossae. Both show normal parenchymal enhancement and no sign of infarction or rejection. There are several small and large pseudocysts image near the pancreatic allograft. These were aspirated and drained with US guidance.
image
Catheter angiography shows a pseudoaneurysm image at the site of the arterial anastomosis (iliac artery of donor to recipient internal iliac artery). This was treated with coil embolization.

SELECTED REFERENCES

1. Khaja, MS, et al. Vascular Complications of Transplantation: Part 2: Pancreatic Transplants. Cardiovasc Intervent Radiol. 2014. [ePub].

2. Vincent, M, et al. Multi detector computed tomography (MDCT) for the diagnosis of early complications after pancreas transplantation. Abdom Imaging. 2014. [ePub].

 

Low, G, et al. Imaging of vascular complications and their consequences following transplantation in the abdomen. Radiographics. 2013; 33(3):633–652.

Norton, PT, et al. Noninvasive vascular imaging in abdominal solid organ transplantation. AJR Am J Roentgenol. 2013; 201(4):W544–W553.

Yates, A, et al. Imaging pancreas transplants. Br J Radiol. 2013; 86(1030):20130428.

Gimenez, JM, et al. Evaluation of pancreatic allografts with sonography. J Ultrasound Med. 2012; 31(7):1041–1051.

Heller, MT, et al. Kidney-pancreas transplantation: assessment of key imaging findings in the acute setting. Emerg Radiol. 2012; 19(6):527–533.

Holalkere, NS, et al. Imaging of miscellaneous pancreatic pathology (trauma, transplant, infections, and deposition). Radiol Clin North Am. 2012; 50(3):515–528.

Vandermeer, FQ, et al. Imaging of whole-organ pancreas transplants. Radiographics. 2012; 32(2):411–435.

Tan, ZY, et al. Multi-detector CT/CT angiogram assessment of acute pancreatic graft dysfunction. J Med Imaging Radiat Oncol. 2011; 55(6):571–576.

Dillman, JR, et al. Imaging of pancreas transplants: postoperative findings with clinical correlation. J Comput Assist Tomogr. 2009; 33(4):609–617.

Fattahi, R, et al. Magnetic resonance imaging in pancreas transplantation. Top Magn Reson Imaging. 2009; 20(1):49–55.

Heilman, RL, et al. Outcomes of simultaneous kidney-pancreas transplantation with positive cross-match. Transplant Proc. 2009; 41(1):303–306.

Rangel, EB, et al. Impact of pancreatic allograft function on 1-year survival rates after simultaneous pancreatic-renal transplant. Exp Clin Transplant. 2008; 6(4):301–306.

Boraschi, P, et al. Pancreatic transplants: secretin-stimulated MR pancreatography. Abdom Imaging. 2007; 32(2):207–214.

Hagspiel, KD, et al. Evaluation of vascular complications of pancreas transplantation with high-spatial-resolution contrast-enhanced MR angiography. Radiology. 2007; 242(2):590–599.

Freund, MC, et al. Spectrum of imaging findings after pancreas transplantation with enteric exocrine drainage: Part 1, posttransplantation anatomy. AJR Am J Roentgenol. 2004; 182(4):911–917.

Dobos, N, et al. Contrast-enhanced MR angiography for evaluation of vascular complications of the pancreatic transplant. Radiographics. 2005; 25(3):687–695.

Heverhagen, JT, et al. Pancreatic transplants: noninvasive evaluation with secretin-augmented mr pancreatography and MR perfusion measurements—preliminary results. Radiology. 2004; 233(1):273–280.

Nikolaidis, P, et al. Role of sonography in pancreatic transplantation. Radiographics. 2003; 23(4):939–949.

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