The deceased donor (cadaveric) pancreas allograft is harvested along with a portion of the donor duodenum. Prior to allograft placement in the recipient, an arterial “Y-graft” is constructed from the donor’s common iliac, internal iliac, and external iliac arteries. The external iliac portion of the Y-graft is anastomosed to the donor superior mesenteric artery, while the internal iliac portion of the Y-graft is anastomosed to the donor splenic artery (Fig. 24.1).

Deceased donor whole pancreas allografts are usually placed in the recipient’s peritoneal cavity using a pelvic midline approach [12, 13]. The common iliac artery portion of the Y-graft is anastomosed to the recipient’s common or external iliac artery in an end-to-side fashion [12]. The donor portal vein is most commonly anastomosed to a systemic vein (the common iliac vein, external iliac vein, or IVC). Less commonly, the donor portal vein is anastomosed to the recipient’s portal venous system, even though this technique has the advantage of avoiding undesired systemic circulation hyperinsulinemia and potential associated complications [12].

Pancreas allograft exocrine secretions can be drained in one of two manners, either into the small bowel (duodenoenterostomy) or urinary bladder (duodenocystostomy) (Figs. 24.2 and 24.3) [12].

Enteric drainage is accomplished by anastomosing the donor duodenum to a loop of recipient small intestine (usually 30–40 cm distal to the ligament of Treitz) in a side-to-side fashion [12, 13]. Pancreas exocrine secretions are less frequently drained into the urinary tract by anastomosing the donor duodenum to the urinary bladder dome [12].

While urinary bladder drainage was previously favored, most pancreas transplantation procedures are now performed employing enteric drainage [1]. Advantages of enteric drainage include physiologic management of pancreatic exocrine secretions, fewer metabolic complications (due to less bicarbonate loss), no associated pancreatitis due to reflux of urine into the allograft, and no urinary tract complications [12, 14–17]. The primary disadvantage of enteric drainage is that urine amylase concentration cannot be followed over time to assess graft function and rejection [12, 15]. Because of a variety of complications, a substantial number of pancreas allografts managed with urinary bladder drainage require eventual conversion to enteric drainage.

Imaging of pancreas transplants is usually performed in the setting of abnormal allograft function or suspected allograft-related complication. Ultrasound, CT, and MRI can be used to assess the transplant pancreas. As always, imaging findings should be interpreted with knowledge of both the patient’s clinical condition and available pertinent laboratory results (e.g., serum amylase/lipase, WBC count).

Ultrasound is the most commonly used imaging modality for pancreas transplant assessment [15]. Gray-scale ultrasound demonstrates the allograft as well as adjacent structures. Doppler imaging can be used to confirm the presence of blood flow within the allograft as well as confirm patency of allograft major arterial and venous structures [15]. Vascular thrombosis, stenosis, pseudoaneurysm, and arteriovenous fistula can all be detected with Doppler ultrasound. In the future, contrast-enhanced ultrasound may play an increasing role in assessing certain allograft-related vascular complications, such as arterial thrombosis [18]. Contrast-enhanced ultrasound has also been used preoperatively to evaluate the vascular integrity of harvested pancreas allografts ex vivo prior to placement in the recipient [19].

Ultrasound has several advantages over other imaging modalities, including its nonionizing nature, portability, lack of need for oral and intravenous contrast materials, and the fact it provides excellent spatial resolution when assessing superficial structures using a linear high-frequency transducer. Disadvantages of ultrasound include its operator dependence and the fact that the allograft may be poorly visualized due to overlying bowel gas or bandages [15]. In the early postoperative setting, up to 20 % of allografts may not be visible for a variety of reasons, such as overlying bandages and adjacent hematoma [15, 16].

Current generation multidetector CT scanners also excellently depict pancreas allografts and associated complications [13, 20]. Pancreas allografts are best assessed by reviewing very thin-section axial images as well as isotropic coronal and sagittal reformatted images. Both oral and intravenous contrast materials assist with distinguishing the transplanted pancreas from adjacent bowel loops [14]. CT imaging in the arterial and venous phases may be helpful in identifying a variety of vascular complications [15]. The large field of view afforded by CT compared to ultrasound also helps determine the true extent of peripancreatic fluid collections as well as identify more distant intra-abdominal fluid collections [14]. CT imaging following the instillation of contrast material into the urinary bladder (CT cystography) may be helpful in the setting of suspected anastomotic or duodenal leak following duodenocystostomy. Disadvantages of CT include its ionizing nature, lack of portability, and the fact that intravenous contrast material may be contraindicated in certain patients due to kidney transplant dysfunction.

Although less commonly utilized, MRI can be used to evaluate pancreas allograft parenchyma as well as assess for a variety of related complications [21]. Standard precontrast and postcontrast MRI pulse sequences can be used to evaluate allograft parenchyma and intra-abdominal fluid collections. High-resolution three-dimensional (3D) MR angiography (MRA) can be used to accurately depict major allograft arterial and venous complications, including complete or partial arterial graft occlusion, stenosis of the arterial Y-graft, complete venous thrombosis, arteriovenous fistula, and pseudoaneurysm formation [21, 22]. MR pancreatography with secretin stimulation can be used to evaluate for rejection-related changes in allograft exocrine function as well as ductal changes in the setting of pancreatitis [21, 23]. Advantages of MRI include its nonionizing nature, excellent contrast resolution, multiplanar capabilities, and ability to assess larger vascular structures without intravenous contrast. Disadvantages of MRI include its higher cost, longer length of study, lack of portability, and the fact intravenous contrast material is contraindicated in patients with acute renal failure or chronic kidney disease with an estimated glomerular filtration rate less than 30 ml/min/1.73 m² due to risk of nephrogenic systemic fibrosis material [14, 15, 22].

At ultrasound, the normal pancreas allograft demonstrates homogeneous echotexture and appears hypoechoic when compared to the normal pancreas as well as adjacent intra-abdominal omental and mesenteric fat (Fig. 24.4a) [14, 16]. The margins of the transplanted pancreas may appear somewhat ill defined, as the pancreas lacks a true capsule [14–16]. Occasionally, normal pancreas allografts may be difficult to be distinguished from adjacent bowel [14]. Doppler ultrasound demonstrates the presence of blood flow within the allograft and its major arterial and venous structures. In particular, power Doppler excellently depicts the donor Y-graft and other major vessels (Fig. 24.4b) [15].

In cases where the allograft is difficult to identify from adjacent structures, Doppler ultrasound may assist in allograft recognition [14]. The presence of peripancreatic fluid may also improve allograft conspicuity [15].

At CT, the normal pancreas allograft appears relatively well defined, demonstrating soft tissue attenuation on noncontrast imaging and homogeneously enhancing on postcontrast imaging (Fig. 24.5) [14]. Postcontrast images show intravascular contrast material opacifying the major arterial and venous structures flowing into and draining the allograft. The main pancreatic duct may not be visualized or may appear slightly prominent [16].

The normal pancreas allograft appears homogeneous and relatively well defined on both precontrast and postcontrast MRI pulse sequences (Fig. 24.6). Transplant pancreas parenchyma is usually isointense to normal renal cortex on unenhanced T1-weighted imaging and of intermediate signal on T2-weighted imaging [14]. Postcontrast images should reveal intravascular contrast material filling the major arterial and venous structures flowing into and draining the allograft [22].