Imaging pancreas transplants

Abstract

Pancreas transplants are performed in multiple centres across the UK with good graft survival rates. This places an increasing demand on radiology services, particularly as the complication rates are not insignificant. The imaging appearances of pancreas transplants and their complications can be difficult to interpret. This review provides an illustrative journey through the anatomical appearances of a graft and the imaging appearances of complications, as a reference tool for radiologists.

Pancreatic transplantation is performed with the aim of providing sufficient islet cell mass to restore normoglycaemia in diabetic patients. Recipients are predominantly Type 1 diabetics in end-stage renal failure with other complications including neuropathy and atherosclerosis. Patients' quality of life improvement afforded by pancreatic transplantation is well documented [1]. It remains the gold standard treatment because current patient outcomes for the developing alternative of allogeneic islet cell transplantation remain less than optimal [2].

Various types of pancreas transplants were performed first in 1966, including simultaneous pancreas and kidney transplantation (SPK) and pancreas transplant alone [3]. Long-term life expectancy post transplant remains to be proven, but early results are promising [4]. Eight UK centres now perform pancreas transplants, with graft survival rates as high as 85% at 1 year [5]. This increasing patient population places increasing demands on radiology departments, particularly in the perioperative period, when the complication rate is relatively high, but also in the diagnosis of late complications. Such imaging can be challenging to interpret. We illustrate how the donor graft is prepared and give examples of the imaging appearances of early and late complications.

GRAFT PREPARATION

To understand the different multimodality imaging appearances of pancreas transplants, it is essential to understand how the graft is prepared. The pancreas is procured with a loop of duodenum (Figure 1a). A “y” graft of the common, internal and external iliac arteries is anastomosed to the proximal ends of the donor splenic artery and superior mesenteric artery stumps to allow the graft to be transplanted, usually in the right iliac fossa (Figure 1b,c) [6]. The y graft is anastomosed onto the recipient common iliac artery (most commonly). The donor portal vein is anastomosed onto the common iliac vein (Figure 1d) or inferior vena cava. The exocrine component drains via the transplanted loop of duodenum, which is normally anastomosed onto the small bowel. The normal CT appearances of a pancreas transplant are demonstrated in Figure 2.

Figure 1.

(a) Donor pancreas preparation: splenic artery (SA), portal vein (PV), superior mesenteric artery (SMA), superior mesenteric vein (SMV) and splenic vein (SV), (b) “y” graft preparation, (c) graft bench preparation. The y graft is anastomosed to the proximal SA and SMA stumps. (d) Recipient graft appearance. The donor portal vein (DPV) is anastomosed to the common iliac vein (CIV) and y graft to the recipient common iliac artery (CIA), usually in the right iliac fossa.

Figure 2.

(a) Axial CT of the normal appearance of a pancreas transplant in the right iliac fossa (arrows) and (b) coronal CT of the normal appearance of a pancreas transplant in the right iliac fossa (arrow).

COMPLICATIONS POST-PANCREAS TRANSPLANTATION

Peripancreatic collections

Peripancreatic collections are a common early complication (Figure 3a). Pancreatic grafts are prone to thrombosis and therefore many centres routinely systemically heparinise transplant recipients in the perioperative period to reduce this risk. The surgery requires extensive tissue dissection, which combined with anticoagulation, explains the relatively high incidence of bleeding. Although ultrasound can identify collections, their size can be underestimated or they can be completely hidden by a gas-filled bowel. CT is therefore the imaging modality of choice in the assessment of peripancreatic collections. It can be difficult to distinguish between the different types of collections, including haematomas, lymphocoeles and abscesses. Increased density in a collection can indicate haematoma, and gas is concerning for infection (Figure 3b). Pseudocysts are not common post transplant, particularly where surgical revision has been required. They can cause problems as they mature, including fistulas and sinus tracts (Figure 4).

Figure 3.

(a) Coronal CT demonstrating a peripancreatic collection (arrow) and (b) CT of a haematoma (*) posterior to the transplant (arrow).

Figure 4.

CT showing a sinus tract to the skin (arrow) from a peripancreatic collection with an air–fluid level (*).

Vascular compromise

Vascular thrombosis is a well-recognised early complication; if identified early, compromised grafts can be salvaged (Figure 5). Doppler ultrasound is a valued tool in the assessment of renal transplant perfusion and it can give an indication of pancreatic graft perfusion, provided the gland is not obscured by bowel gas (Figure 6). For detailed evaluation of graft vessels, CT or MR angiography are employed. Arterial or venous thrombosis can also be a late complication, occasionally related to sepsis (Figure 7). Rarely, injury or compromise to the recipient's vessels can occur (Figure 8).

Figure 5.

(a) Patient 10 days post transplant with splenic vein thrombosis and partial arterial occlusion. Sagittal CT demonstrates a tongue of thrombus in the splenic vein (arrow) superior to the pancreatic graft (*). (b) Angiography demonstrated an occluded graft superior mesenteric artery from the origin (white arrow), but a patent splenic limb (black arrow). Endovascular thrombectomy improved flow. After prolonged anticoagulation, the graft recovered fully.

Figure 6.

(a) Doppler ultrasound of a normal transplant. Normal flow is demonstrated in an intrapancreatic parenchymal arterial branch. (b) Transplant ultrasound with elevated resistive indices in a parenchymal artery adjacent to the origin of the “y” graft, indicating graft dysfunction.

Figure 7.

(a) Axial CT of a patient who developed arterial and venous thrombosis following an episode of sepsis, with subsequent poor perfusion of the graft. The pancreatic head is not perfused (*) and thrombus occludes a length of the splenic vein (arrows). (b) Angiographic series in another patient confirming arterial occlusion of the “y” graft (arrow). The vessel was recanalised and stented, but flow was sluggish despite thrombolysis.

Figure 8.

(a) A patient developed groin pain 4 days post SPK transplant. Formal angiography confirmed occlusion of the external iliac artery just beyond the “y” graft anastomosis (white arrow). The vessel recannalises distally at the common femoral artery (black arrow). Surgical bypass with vein graft failed. (b) Coronal CT identified a pseudoaneurysm arising from the aorta (white arrow) and a periaortic abscess collection containing tiny foci of gas (black arrows). The aorta was tied off to prevent rupture and an axillobifemoral bypass graft was performed.

Biopsy

Identifying rejection of pancreas transplants is difficult without reliable serum markers to indicate graft dysfunction. Hyperglycaemia is a late sign, by which time rejection is usually irreversible (Figure 9). In our centre, persistently or significantly elevated serum amylase prompts a percutaneous core biopsy of the graft, shown to both be safe and provide useful information [7]. The procedure is performed under ultrasound guidance using an 18-gauge needle when a clear view of the pancreas can be seen (Figure 10). The procedure does carry risks, and haemorrhage and bowel perforation are recognised complications.

Figure 9.

Axial CT demonstrating free fluid and a small amount of free air (arrows) in a patient who developed ongoing abdominal pain during treatment for antibody-mediated rejection. The free air is indicative of perforation of a hollow viscus. Laparotomy findings were of a perforation in the donor duodenum, necessitating graftectomy.

Figure 10.

Ultrasound-guided pancreatic biopsy. The biopsy needle is visible in the graft (arrow).

COMPLICATIONS RELATED TO IMMUNOCOMPROMISE

Transplant recipients may develop complications secondary to immunocompromise caused by their antirejection drug regimes. Recent advances in immunosuppressant regimes, including atypical lung infections from pathogens, such as aspergillus and pneumocystis carinii, have resulted in fewer serious infective complications, but they can still occur.

CONCLUSION

Improved patient and graft survival following pancreas transplantation has led to an increasing number of transplantation survivors: approximately 24 000 worldwide in 2011 [8]. Morbidity in the perioperative period is common, and the requirement for radiological support increasing. The cases we have presented provide a useful reference tool when interpreting the imaging appearances of pancreas transplants.