Outcomes following pancreas transplantation have continued to improve, with a decrease in mortality and increased graft survival rates. However, posttransplant complications and subsequent graft loss remain significant clinical challenge [2, 5]. These complications can be classified based on the structure involved, i.e., arterial, venous, perigraft, and graft parenchyma, as well as by timing, with early complications occurring within 3 months after transplantation and late complications thereafter [26]. Though these complications have been managed traditionally with surgical intervention, there has been a growing role for minimally invasive interventional radiology procedures in recent years. Therefore, appropriate imaging is essential for early diagnosis, preprocedural planning, and successful graft rescue.

Arterial stenosis is uncommon, with an incidence of approximately 2.5%, and is typically classified as an early post-transplant complication [27, 28]. It most often develops at the anastomotic site and can cause graft dysfunction, arterial thrombosis, ischemia, or necrosis. Contributing risk factors include surgical technique, graft kinking or twisting, acute rejection, ischemia at the anastomosis, and pre-existing atherosclerosis in the recipient’s iliac artery [23, 29, 30]. On Doppler US, clinically significant stenosis is suggested by turbulent flow and a peak systolic velocity exceeding 200–300 cm/s at the anastomosis (Fig. 7A). This elevated velocity persists on follow-up US as opposed to improvement in velocity seen over time with narrowing induced by postoperative edema. Additional findings in significant stenosis include a tardus parvus waveform, decreased resistive indices less than 0.5, and decreased peak systolic velocities in the graft arteries distal to the stenosis and within graft parenchyma [30, 31]. CEUS may show weak, non-uniform graft enhancement [18]. CTA or MRA and subsequent angiography can confirm the diagnosis and provide detailed anatomical information essential for planning endovascular intervention (Fig. 7B, C) [23, 24, 27, 31]. Percutaneous transarterial balloon angioplasty has demonstrated a 100% technical success rate and a graft survival rate of approximately 60% for hemodynamically significant stenosis (Fig. 7D) [32]. In cases involving Y-graft bifurcation stenosis, the double wire technique is useful for securing access to both true lumens [33]. In case of recipient iliac artery stenosis, stent placement may be required to restore adequate blood flow [34].

Arterial stenosis. A 51-year-old male status post simultaneous pancreas and kidney transplant for type 2 diabetes mellitus and diabetic nephropathy. Spectral Doppler ultrasound (A) performed at 3 months shows persistently elevated peak systolic velocity of 301 cm/s with turbulent flow at the anastomosis. Magnetic resonance angiography confirms the finding of stenosis at the anastomotic site (white arrow, B). Conventional angiography (C) also confirms the stenosis at the anastomosis (arrowheads). Post-balloon angioplasty angiography (D) shows improvement of the stenosis (black arrow)

Acute thrombotic complications of the graft vessel occur in 2–10% of pancreas transplant recipients, with arterial thrombosis accounting for approximately one-third to one-quarter of all thrombotic events. [4, 28, 35]. Arterial thrombosis is classified as an early posttransplant complication with risk factors including long back-table preparation and cold ischemia time, graft pancreatitis, and graft vessel injury. Thrombus formation often begins at the vessel stump due to stagnant blood flow, potentially progressing to involve parenchymal branches and leading to ischemic graft pancreatitis and dysfunction [16, 36, 37]. Complete arterial thrombosis can result in graft ischemia and necrosis; however, in limited cases of single vessel occlusion, either the SMA or SpA, some collateral flow through intrapancreatic networks can maintain the segmental arterial supply of the pancreas graft (Fig. 8) [38]. On grayscale US, arterial thrombosis appears as echogenic material within the transplant artery. Color Doppler US demonstrates either absent or diminished blood flow depending on the degree of arterial occlusion caused by the thrombus. The pancreas graft itself may show heterogeneous enlargement if ischemic pancreatitis or necrosis develops [3]. Although grayscale and Doppler US are valuable for detecting arterial thrombosis, image acquisition of the complete arterial Y-graft and branch arteries can be challenging due to bowel gas and the deep pelvic location of the graft.

Arterial thrombosis and arterial arcade of the pancreas graft. A 45-year-old male with a history of type 1 diabetes mellitus and diabetic nephropathy status post pancreas after kidney transplantation. Magnetic resonance angiography (MRA) on postoperative day 38 during the arterial phase (A) demonstrates occlusion of the splenic artery (dotted red line). MRA during the venous phase (B) demonstrates normal parenchymal enhancement of the pancreatic tail (arrowhead) due to the intrapancreatic arterial network which avoids complete graft infarction. Conventional angiography (C) and 3D angiography (D) shows opacification of the intrapancreatic arterial network via the dorsal pancreatic artery (c), anastomotic artery (d), and transverse pancreatic artery (e). Notably, in this case, the dorsal pancreatic artery (c) arises from the superior mesenteric artery (a). (b) represents the inferior pancreaticoduodenal artery

CEUS can directly evaluate graft parenchymal perfusion and is useful in differentiating very slow flow, where contrast is seen within the artery, and thrombosis, in which contrast is absent or minimal depending on the degree of occlusion [3, 18, 39]. Further evaluation using CTA or MRA provides a detailed assessment of thrombus extent, graft vascular anatomy, and parenchymal perfusion, facilitating targeted treatment planning [16, 23, 24]. Management of thrombosis with graft necrosis typically requires surgical intervention. In cases without parenchymal necrosis, anticoagulation therapy or minimally invasive endovascular approaches such as transarterial thrombolysis, mechanical thrombectomy, thrombus angioplasty, or catheter-directed thrombolysis with aspiration thrombectomy can be performed (Fig. 9) [32]. Due to the small caliber and tortuosity of transplant arteries, endovascular interventions have a relatively limited success rate [32].

Arterial Thrombosis. A 44-year-old female with a history of type 1 diabetes mellitus status post pancreas transplant alone with elevated pancreatic enzymes. Color Doppler ultrasound (A) at the level stump of the Y graft demonstrates no arterial flow. Contrast-enhanced ultrasound (B) confirms the finding of thrombosis (arrow) as no contrast flows through the stump and no graft parenchymal enhancement (arrowhead). Magnetic resonance angiography (C) shows a filling defect in the stump of the Y arterial graft (arrow). Post-contrast magnetic resonance image (D) fat-suppressed T1-weighted imaging demonstrates loss of graft parenchymal enhancement (white arrowhead). Angiography (E) confirms an arterial thrombus as a filling defect (arrow) without parenchymal enhancement. Following percutaneous thrombectomy (F), contrast is seen in the stump of the Y graft and improved perfusion of the pancreas graft parenchyma (black arrowhead)

Arterial pseudoaneurysm (PSA) and bleeding are among the most life-threatening complications of pancreas transplantation, with an incidence of approximately 2.4% [40]. These are usually caused by surgical trauma, pancreatitis, infection, or biopsy [27, 41]. PSA often occurs at the arterial anastomotic site and the biopsy site. Active hemorrhage may present as perigraft bleeding or intraluminal bleeding into the graft duodenum [4]. On grayscale ultrasound, a PSA is demonstrated as an anechoic cystic structure. Color Doppler US typically shows a turbulent “yin-yang” flow pattern, and spectral Doppler reveals a classic to-and-fro waveform at the PSA neck (Fig. 10A, B) [14, 16, 42]. CTA and MRA typically demonstrate a saccular outpouching with surrounding hematoma (Fig. 10C). These modalities are essential for precise localization of the PSA or bleeding site, which is helpful for transarterial embolization. As the PSA is at risk of impending rupture, immediate diagnosis and treatment are essential [3, 16, 30, 41, 42]. Endovascular treatment is often feasible in hemodynamically stable patients. Covered stent placement has been effective in excluding PSAs arising from the donor or graft iliac artery while preserving distal blood supply (Fig. 10D, E). Endovascular embolization with coils, plugs, or particles is an alternative treatment [28, 43]. Although technical success and hemostasis can often be achieved with endovascular treatment, complications and potential graft loss remain a concern [32, 43].

Arterial pseudoaneurysm (PSA). A 40-year-old male with a history of both type 1 and 2 diabetes mellitus and diabetic nephropathy underwent simultaneous pancreas-kidney transplantation, presenting with abdominal pain on postoperative day 40. Grayscale ultrasound (A) shows an anechoic cystic structure (arrow). Color Doppler ultrasound (B) reveals a characteristic Yin-Yang flow pattern (arrow) within the anechoic cystic structure, confirming the findings of PSA. CT angiography (C) demonstrates a saccular outpouching with enhancement (arrow). Angiography (F) confirms the outpouching filling with contrast due to the pseudoaneurysm (arrow) at the anastomotic site. Post-treatment angiography (E) demonstrates successful exclusion of the PSA following stent graft placement

Arteriovenous fistula (AVF) is a rare vascular complication following pancreas transplantation, with an estimated prevalence of approximately 1.4% [28]. AVF is defined as direct communication between an artery and a vein without an intervening capillary, resulting from simultaneous laceration of both arterial and venous walls and subsequent union of the lumens. This may occur during surgical procedures (e.g., blind ligation or stapling) or after a needle biopsy. AVFs are most commonly observed in the early post-transplant period but can develop at any time following transplantation or biopsy [30]. Clinically, they may lead to graft dysfunction or major bleeding. On spectral Doppler US, AVF demonstrates a high velocity, low resistance feeding artery, and arterialized biphasic pulsatile venous waveform. Persistent color Doppler aliasing at the maximum pulse repetition frequency setting is one of the most sensitive signs for detecting AVF [31]. Cross-sectional imaging with CTA or MRA shows early enhancement of the vein in continuity with the feeding artery on the arterial phase (Fig. 11A). A small AVF may resolve spontaneously, whereas a persistent or symptomatic AVF requires intervention. Successful transarterial embolization with or without transvenous procedure has been reported without major complications [32, 43]. Since some pancreatic branches can be identified proximal to the fistulous point, care must be taken to avoid embolizing these normal branches to preserve graft perfusion and minimize the risk of graft ischemia (Fig. 11B–D) [32].

Arteriovenous fistula (AVF). A 30-year-old male with a history of type 2 diabetes mellitus is status post pancreas after kidney transplantation with delayed graft function on postoperative day 2. Magnetic resonance angiography (A) shows a tortuous, dilated AVF nidus (arrow) medial to the pancreas graft. Conventional angiography from the Y-graft artery (B) shows AVF nidus (arrow) and early draining vein involving the superior mesenteric artery and vein. Post-embolization angiography (C-D) shows complete occlusion of the AVF and improved enhancement of the pancreas graft (arrowhead)

Venous thrombosis is the most common vascular complication and the second most common complication of graft dysfunction after rejection. It typically occurs within 4–6 weeks of transplantation and is considered an early postoperative complication [36]. Thrombosis is multifactorial in origin. Common causes include surgical challenges, venous stasis, anastomotic stricture, venous kinking, pancreatitis, and graft rejection [27, 30, 38]. While partial thrombosis may be asymptomatic, occlusive thrombosis may induce ischemic graft pancreatitis and infarction. Thrombus in the distal SpV or SMV can be incidentally detected, which can propagate towards the central venous system [16]. Grayscale US demonstrates a distended vein with echogenic thrombus. Decreased or absent blood flow is detected on color Doppler US, depending on the degree of occlusion. Reversal of the diastolic arterial waveform is observed in obstructive thrombosis on spectral Doppler US (Fig. 12A, B) [44]. The pancreas graft becomes enlarged and is heterogeneous due to congestion [45]. On CEUS, venous thrombosis presents as delayed washout of the contrast in the venous phase despite preserved arterial enhancement. Intraluminal non-enhancement of the graft vein further supports the diagnosis (Fig. 12C, D) [18]. CTA and MRA are helpful in assessing the extent of the thrombus. Thrombus is seen as an intraluminal filling defect, and often accompanied by edematous changes in the pancreas graft parenchyma (Fig. 12E) [23, 24, 27, 31, 37]. Partial thrombosis without parenchymal ischemia can be treated with anticoagulation [28, 36]. Whereas occlusive venous thrombosis without graft necrosis, endovascular interventions, such as mechanical thrombectomy and catheter-directed thrombolysis with aspiration, may be effective (Fig. 12F, G). Catheter-directed mechanical thrombectomy with or without chemical thrombolysis has shown a graft survival rate of up to 76% [46].

Venous thrombosis. A 44-year-old female with a history of type 1 diabetes mellitus underwent pancreas transplant alone with clinical presentation of increased blood in the urine on postoperative day 1. Color Doppler ultrasound (A) shows a heterogeneous appearing and enlarged pancreas graft (arrow) with no color flow within the graft vein due to thrombosis (arrowhead). Spectral Doppler ultrasound (B) of the intraparenchymal artery shows reversed diastolic arterial waveforms. Contrast-enhanced ultrasound demonstrates prompt parenchymal enhancement at 19 s after injection (arrow, C) and minimal washout at 100 s after injection (arrow, D). Magnetic resonance angiography (E) during venous phase confirms the presence of thrombus in the splenic vein (arrowhead). Pre-treatment venography (F) shows a filling defect corresponding to splenic vein thrombus (arrowhead). Post-treatment venography (G) shows resolution of the thrombus and restoration of venous blood flow

Peripancreatic fluid collection occurs in approximately 11–16% of pancreas transplant recipients and is associated with reduced graft survival. These collections are seen in the early postoperative period but can occasionally present beyond 3 months after transplantation [47, 48]. Postsurgical seroma and lymphocele result from disruption of the lymphatics in the surgical bed [49]. Exocrine anastomotic leak may result in fluid collection, abscesses, or, less commonly, urinomas. Pseudocysts can develop in graft pancreatitis, while peripancreatic bleeding can cause hematoma or hemorrhagic fluid collections. On grayscale US, these collections typically appear as an anechoic cystic collection without an internal Doppler signal (Fig. 13A), whereas infectious or hemorrhagic collections may contain internal echogenic debris. On CT, simple fluid collections appear hypodense, while hemorrhagic collections demonstrate increased density (Fig. 13B) [3]. The presence of air bubbles can be seen in the infectious fluid collection, abscess, or enteric leakage. MRI helps further characterize fluid collections. Simple seromas or lymphoceles demonstrate high T2 signal intensity. Abscesses typically show peripheral rim enhancement on post-contrast images and restricted diffusion with corresponding low signal on the apparent diffusion coefficient map. Hemorrhagic collections vary in signal intensity depending on the age of the blood products [3, 41]. Percutaneous US or CT-guided drainage is a feasible treatment for these fluid collections (Fig. 13C, D). Around 80% of the cases can be effectively managed with image-guided percutaneous drainage alone, although surgical intervention may be required in refractory or complicated cases [50, 51].

Peripancreatic fluid collection. A 31-year-old male with a history of type 1 diabetes mellitus and nephropathy underwent pancreas after kidney transplantation. Grayscale ultrasound (A) on postoperative day 14 demonstrates anechoic simple fluid collection (arrow) adjacent to the pancreas graft (arrowhead). Contrast-enhanced computed tomography (CT) (B-C) shows hypodense to isodense and non-enhancing fluid collection (arrow) adjacent to the pancreas graft (arrowhead). Pre-drainage CT (C) demonstrates the extent of the fluid collection, and post-drainage CT (D) shows a significant decrease in the size of the fluid collection following percutaneous drainage tube placement

Exocrine leak may occur at the duodenoenteric anastomosis, duodenovesical anastomosis or duodenal stump. The reported incidence is up to 20% of pancreas transplants [40, 52, 53] and is responsible for less than 1% of all causes of graft loss [2,