Role of imaging in the evaluation of vascular complications after liver transplantation

Diagnostic value of ultrasonography for post-liver transplant hepatic vein complications

Liver transplantation (LT) is the most effective treatment for patients with end-stage liver disease, and maintaining vascular patency of the transplanted liver is one of the crucial prerequisites for surgical success. Despite hepatic vein complications following LT occurring at a relatively low frequency, ranging between 2% to 11%, delayed diagnosis and treatment may lead to graft dysfunction and even patient mortality. Clinical manifestations of hepatic vein complications are often subtle and nonspecific, posing challenges for early diagnosis. Signs may initially present as mild abnormalities in liver function, delayed recovery of liver function, unexplained ascites, lower limb edema, and perineal edema. Prolonged duration of these complications can lead to hepatic sinusoidal dilatation and eventual liver failure due to prolonged hepatic congestion. Ultrasonography has become the preferred imaging modality for post-liver transplant evaluation due to its convenience and non-invasiveness. Although hepatic vein complications may manifest as disappearance or flattening of the hepatic vein spectrum on routine ultrasound imaging, these findings lack specificity. Contrast-enhanced ultrasound that visualizes the filling of contrast agent in the hepatic veins and dynamically displays blood flow perfusion information in the drainage area can, however, significantly improve diagnostic confidence and provide additional information beyond routine ultrasound examination.

The Use of Intraoperative Transit Time Flow Meter for the Early Detection and Prevention of Vascular Complications Following Adult Deceased Donor Liver Transplantation

PURPOSE

This study aims to determine whether intraoperative analysis of arterial and portal venous flow using transit time flow measurement (TTFM) data is associated with a reduced incidence of vascular complications after orthotopic liver transplantation.

METHODS

This is a retrospective chart review of all adult orthotopic liver transplant recipients at Saint Louis University Hospital from 2015-2020 (n = 188). We reviewed intraoperative flow probe use, as well as documentation of abnormal flow patterns detected during surgery. Normal graft flow measurements were defined as hepatic artery flow >100 ml/min and portal vein flow >0.5 ml/min/gram-liver. Postoperative imaging and ultrasonographic data were then reviewed for reports of vascular complications requiring intervention between the time of transplant and December 31, 2020. The incidence of VCs was compared between those who received intraoperative TTFM and those who did not. We then compared the demographic composition of these 2 groups to ensure similarity and screen for potential confounding factors.

RESULTS

188 liver transplant operative reports met the criteria for inclusion and were reviewed. TTFM use was documented in 78 (41.5%) cases and abnormal flow was detected in 8 (10.3%) of these cases, prompting intraoperative correction. Subsequently, no patients who received intraoperative TTFM developed vascular complications during the postoperative course. Conversely, of the 110 (58.5%) cases with no reported intraoperative flow data, 6 (5.5%, P = .042) patients later developed vascular complications. Reported vascular complications included hepatic artery stenosis, hepatic artery thrombosis, portal vein thrombosis, hepatic vein thrombosis, and IVC thrombosis. There was no significant difference in patient population between patients who received intraoperative TTFM and those who did not, apart from the type of liver implantation. There was a significantly higher prevalence of bicaval liver implantations in the group of patients who did not receive TTFM than those who did (P = .002).

CONCLUSIONS

Transit time flow measurement may be a useful tool for the detection of vascular flow abnormalities intraoperatively, allowing for early correction and prevention of vascular complications during the postoperative course. This could potentially result in enhanced graft survival and reduced recipient mortality following orthotopic liver transplantation.

Grading portal vein stenosis following partial hepatectomy by high-frequency ultrasonography: an in vivo study of rats

PURPOSE

To evaluate the diagnostic value of ultrasound in grading portal vein stenosis (PVS) in a rat model of 70% partial hepatectomy (PH).

METHODS

A total of 96 Sprague-Dawley rats were randomly divided into a PH group and PVS groups with mild, moderate, and severe PVS following PH. Hemodynamic parameters were measured using high-frequency ultrasound (5-12 MHz high-frequency linear transducer), including pre-stenotic, stenotic, and post-stenotic portal vein diameters (PVDpre, PVDs, PVDpost); pre-stenotic and stenotic portal vein velocity (PVVpre, PVVs); hepatic artery peak systolic velocity (PSV); end-diastolic velocity; and resistive index. The portal vein diameter ratio (PVDR) and portal vein velocity ratio (PVVR) were calculated using the following formulas: PVDR=PVDpre/PVDs and PVVR=PVVs/PVVpre. The value of these parameters in grading PVS was assessed.

RESULTS

Portal vein hemodynamics showed gradient changes as PVS aggravated. For identifying >50% PVS, PVDs and PVDR were the best parameters, with areas under the curve (AUC) of 0.85 and 0.86, respectively. For identifying >65% PVS, PVDs, PVDR, and PVVR were relatively better, with AUCs of 0.94, 0.85, and 0.88, respectively. The AUC of hepatic artery PSV for identifying >65% PVS was 0.733.

CONCLUSION

High-frequency ultrasonography can be used to grade PVS in rats, with PVDs, PVDR, and PVVR being particularly useful. Hepatic artery PSV may help in predicting >65% PVS. These findings provide valuable information for PVS rat model research and offer an experimental basis for further studies on PVS evaluation in living-donor liver transplantation (LDLT).

CLINICAL SIGNIFICANCE

Ultrasonography serves as a first-line technology for diagnosing PVS following LDLT. However, the grading criteria for PVS severity remain unclear. Investigating the use of ultrasonic hemodynamics in the early diagnosis of PVS and grading stenosis severity is important for early postoperative intervention and improving recipient survival rates.

The application of computational fluid dynamics in hepatic portal vein haemodynamics research: a narrative review

Background and Objective

The diagnosis and treatment of many liver diseases are related to the assessment of the hepatic portal vein (PV). Noninvasive methods (medical imaging) and invasive methods (hepatic vein catheterization) are commonly used to analyse the haemodynamic information of the PV. In recent years, computational fluid dynamics (CFD) has emerged as a transformative tool in haemodynamics research, revolutionizing the understanding of blood flow behaviour, especially in various artery systems. The purpose of this review is the following: (I) introduce clinicians to CFD as a novel tool and describe its role in PV assessment; and (II) for clinicians and researchers who already use CFD, outline the progress in the application of CFD to the PV.

Methods

The English-language literature published from 1987 (when the first study supporting the study's aim appeared) to 2024 was selected for inclusion in a narrative review.

Key Content and Findings

This narrative review commences with an overview of principles of CFD and methods in PV studies, which involve model establishment, grid partitioning, boundary condition formulation, and error analysis. The focus then shifts to CFD's impact on the examination of the PV under different conditions such as portal hypertension in liver cirrhosis, PV thrombosis, post-transjugular intrahepatic portosystemic shunt (TIPS) procedure, and evaluation of the PV after liver transplantation. Finally, challenges and future directions about the CFD application in PV are outlined.

Conclusions

CFD has potential application value in PV haemodynamics, but of the few studies available, most involve only small samples. Therefore, more research is needed to clarify the feasibility and reliability of this new tool.

Use of Intraoperative Doppler Ultrasonography in Predicting Life-Threatening Vascular Complications After Adult Deceased Donor Liver Transplantation

Aim This study aims to determine if routine use of intraoperative Doppler ultrasonography is preventative of life-threatening vascular complications (VCs) after orthotopic liver transplantation. Methods This single-center, retrospective study reviewed all adult orthotopic liver transplants at Saint Louis University Hospital from 2015 to 2020 (N = 188). The sample population consists of men and women in the age range of 18 to 75. Operative reports were reviewed for the use of intraoperative ultrasound (IOUS) and the associated resistive indices, peak systolic velocities, and qualitative assessments of flow. Postoperative VCs were identified as complications requiring intervention between the time of transplant and December 31, 2020. Life-threatening VCs were defined by the presence of vascular thrombosis. The primary outcome was the incidence of postoperative life-threatening VCs between those in which intraoperative DUS was performed and those in which it was not. Results IOUS was documented in 35 (18.6%) cases. All cases using IOUS demonstrated good flow and no abnormalities, as reported by the operating surgeon. There was no difference in patient population between those who received IOUS and those who did not. Postoperative life-threatening VCs were identified in five cases. Of the cases in which no IOUS was performed, five (3.3%) had life-threatening VCs. Of the patients with documented IOUS, 0 (0%) had life-threatening VCs. Conclusions The IOUS group showed a lower incidence of life-threatening VCs (0%) compared to the no IOUS group, which had a 3.3% life-threatening complication rate. However, this was not statistically significant due to the small number of VCs, as VCs following liver transplants are inherently rare. With these results in combination with current literature, there is support for the use of IOUS in preventing and predicting VCs.

Utility of nifedipine use for Doppler ultrasound early after liver transplantation to predict short-term complications and long-term outcomes

PURPOSE

To evaluate the response to nifedipine administration measured by changes in hepatic arterial (HA) flow on post-operative Doppler ultrasound (US) to predict short-term complications and long-term outcomes in liver transplant (LT) patients.

METHODS

Patients who underwent LT with post-operative Doppler US within 3 days between 1 January 2005 and 31 December 2015 were included in this retrospective single center study. The patients who received and did not receive nifedipine during the Doppler US comprised the study and control groups, respectively. A positive response to nifedipine was defined as the detection of HA flow when none was present initially or a reduction in HA resistive index (RI) ≥ 0.1 after nifedipine administration. The rates of re-transplantation, re-operation, percutaneous intervention (PCI), and overall survival (OS) were recorded. Cox proportional hazards regression was used to evaluate the association of clinic-demographic variables and Doppler findings with the outcome measures.

RESULTS

444 LT patients (305 M/139F, mean age 51.7 ± 17.4 years, mean interval between LT-Doppler US 1.12 ± 0.9 days) are presented. 220 patients comprised the nifedipine study group [n = 157/220 (71.4%) responder, n = 63/220 (28.6%) nonresponder] and 224 patients comprised the control group. There was no difference in re-transplantation or PCI rates between the groups (all p-values ≥ 0.2 and ≥ 0.08, respectively). The responder group had a lower rate of re-operation vs. the control group (15.9% vs. 24.1%, p = 0.03) and nonresponder group (15.9% vs. 31.8%, p = 0.004). 1-year and 2-year OS were similar between the groups (all p-values > 0.37).

CONCLUSION

Short-term complication rates and long-term outcomes for patients with liver transplant who responded to nifedipine administration on Doppler US are similar to those who did not require nifedipine administration. A lack of response to nifedipine was associated with a higher re-operation rate.

Improving the radiological diagnosis of hepatic artery thrombosis after liver transplantation: Current approaches and future challenges

Hepatic artery thrombosis (HAT) is a devastating vascular complication following liver transplantation, requiring prompt diagnosis and rapid revascularization treatment to prevent graft loss. At present, imaging modalities such as ultrasound, computed tomography, and magnetic resonance play crucial roles in diagnosing HAT. Although imaging techniques have improved sensitivity and specificity for HAT diagnosis, they have limitations that hinder the timely diagnosis of this complication. In this sense, the emergence of artificial intelligence (AI) presents a transformative opportunity to address these diagnostic limitations. The develo pment of machine learning algorithms and deep neural networks has demon strated the potential to enhance the precision diagnosis of liver transplant com plications, enabling quicker and more accurate detection of HAT. This article examines the current landscape of imaging diagnostic techniques for HAT and explores the emerging role of AI in addressing future challenges in the diagnosis of HAT after liver transplant.

Imaging and Intervention in the Management of Vascular Complications Following Liver Transplantation

Liver transplantation is the treatment of choice in majority of the patients with end stage liver disease. Vascular complication following liver transplantation is seen in around 7-13% of the patients and is associated with graft dysfunction and high morbidity and mortality. Early diagnosis and prompt treatment are crucial in management of these patients. Advances in interventional radiology have significantly improved the management of vascular complications using minimally invasive percutaneous approach. Endovascular management is preferred in patients with late hepatic artery thrombosis, or stenosis, whereas retransplantation, surgical revision, or endovascular management can be considered in patients with early hepatic artery thrombosis or stenosis. Hepatic artery pseudoaneurysm, arterioportal fistula, and splenic artery steal syndrome are often treated by endovascular means. Endovascular management is also preferred in patients with symptomatic portal vein stenosis, early portal vein thrombosis, and symptomatic late portal vein thrombosis, whereas surgical revision or retransplantation is preferred in patients with perioperative portal vein thrombosis occurring within 3 days of transplantation. Venoplasty with or without stent placement can be considered in patients with hepatic venous outflow tract or inferior vena cava obstruction. Transjugular intrahepatic portosystemic shunt (TIPS) may be required in transplant recipients who develop cirrhosis, often, secondary to disease recurrence, or chronic rejection. Indications for TIPS remain same in the transplant patients; however, major difference is altered vascular anatomy, for which adjunct techniques may be required to create TIPS.

Vascular pathology in patients with alveolar echinococcosis: framework for assessment and clinical management - a retrospective case series

OBJECTIVE

Alveolar echinococcosis (AE) is a parasitic liver disease with infiltrative growth similar to solid organ malignancies. Major vascular damage is frequent and often remains untreated until catastrophic events precipitate. Detailed clinical and radiological assessment is required to guide individualised treatment decisions. Standardised radiological reporting templates of malignancies with profiles resembling AE are candidates for adaptation. Our objectives are to describe vascular pathology in AE and establish a framework for structured evaluation as the basis for treatment decisions and monitoring.

DESIGN

Retrospective case series.

RESULTS

69 patients (37.1%) had vascular involvement: portal vein (PV) 24.7%, hepatic vein (HV) 22.6% inferior vena cava (IVC) 13.4%. Significant stenosis/occlusion of vessels was present in 15.1% of PV, in 13.4% of HV and in 7.5% of IVC involvement. Vascular pathology needing specific treatment or monitoring was present in 8.6% of patients. The most frequent clinical presentation was high grade IVC stenosis or occlusion which was seen in 11 patients of the cohort.

CONCLUSION

Advanced AE requires early multidisciplinary assessment to prevent progressive impairment of liver function due to vascular damage. The focus at first presentation is on complete evaluation of vascular (and biliary) involvement. The focus in non-resectable AE is on prevention of vascular (and biliary) complications while suppressing growth of AE lesions by benzimidazole treatment to improve the quality of life of patients. We developed a framework for standardised vascular assessment and follow-up of patients with AE to recognise and treat complications early.

Low hepatic artery resistive index on Doppler ultrasound performed on the first post-liver transplant day is associated both with hepatic artery thrombosis and decreased graft survival

PURPOSE

Although liver transplantation (LT) outcomes have improved significantly over the last decades, early vascular complications are still associated with elevated risks of graft failure. Doppler ultrasound (DUS) enables detection of vascular complications, provides hepatic artery Resistive Index (RI). The aim of our study was to evaluate the association of the RI parameters of DUS performed in the first post-transplant week with post-transplant outcomes.

METHODS

All consecutive patients undergoing a first LT between 2001 and 2019 at a single center were included. Patients were divided into two groups: RI < 0.55 and RI ≥ 0.55. Patients were also divided according to the presence or absence of hepatic artery thrombosis (HAT). Graft survival was compared between groups.

RESULTS

Overall, 338 patients were included. HAT occurred in 23 patients (6.8%), of which 7 were partial and 16, complete. Biliary complications were more common in patients with HAT (10 [43.5%]) vs. 38 [12.1%] [p < 0.001]). Graft survival was lower for patients with HAT (p = 0.047). Also, RI < 0.55 was associated with increased incidence of HAT (p < 0.001). Additionally, patients with RI < 0.55 on post-operative day 1 had decreased graft survival as compared to patients with RI > 0.55 (p = 0.041). RI on post-operative day 3 and 5 was not predictive of inferior graft outcomes.

CONCLUSIONS

Intensive use of DUS in the early post-LT period offers the possibility of early diagnosis of vascular complications, guiding medical and surgical management of HAT. Additionally, according to our data, low RI (< 0.55) on the first postoperative day also is a predictor of HAT and decreased graft-survival.

Importance of Anatomical Variation of the Hepatic Artery for Complicated Liver and Pancreatic Surgeries: A Review Emphasizing Origin and Branching

Knowledge of anatomical variations of the hepatic artery from its origin to intrahepatic segmentation is of utmost importance for planning upper abdominal surgeries including liver transplantation, pancreatoduodenectomy, and biliary reconstruction. The origin and branching pattern of the hepatic artery was thoroughly described by the classification of Michels and Hiatt. Some rare variations of the hepatic artery were classified by Kobayashi and Koops. By the use of the multidetector computed tomography (MDCT) technique, the branching pattern of the hepatic artery can be visualized quite accurately. Unawareness of these arterial variations may lead to intraoperative injuries such as necrosis, abscess, and failure of the liver and pancreas. The origin and course of the aberrant hepatic arteries are crucial in the surgical planning of carcinoma of the head of the pancreas and hepatobiliary surgeries. In liver transplant surgeries, to minimize intraoperative bleeding complications and postoperative thrombosis, exact anatomy of the branching of the hepatic artery, its variations and intrahepatic course is of utmost importance. This review discusses variations in the anatomy of the hepatic artery from its origin to branching by the use of advanced imaging techniques and its effect on the liver, pancreatic, biliary and gastric surgeries.

Indocyanine green fluorescence imaging: A novel technique in liver transplantation

Indocyanine green (ICG) is a fluorescent dye that is widely used in hepatobiliary surgery for fluorescence contrast. ICG is selectively absorbed by the liver after intravenous injection and then secreted into the bile. ICG's unique catabolism and fluorescence characteristics allow for multiple applications in liver transplantation. We have divided the applications of ICG fluorescence imaging in liver transplantation into: (i) cholangiography, (ii) evaluation of liver transplantation vessels, (iii) liver mapping, and (iv) evaluation of donor liver quality. In this review, we summarize the current status of applications of ICG fluorescence imaging in liver transplantation.

Portal Vein Stent Placement in Anastomotic Stenosis After Deceased Donor Liver Transplantation: A Case Report

Vascular complications (VCs) after liver transplantation (LT) frequently result in graft and patient loss. The smaller vessels and the insufficient length for reconstruction in living donor LT and pediatric transplantation predispose patients to a higher incidence of VCs. Herein we present a case of portal vein stenosis (PVS) in an adult deceased donor LT recipient with portal vein thrombosis requiring extended thrombectomy at the time of LT. He presented with ascites 4 months after LT, was diagnosed with PVS, and was successfully treated with percutaneous transhepatic venoplasty and placement of a portal stent. This case highlights the importance of Doppler ultrasound as a screening modality for detection of VCs after LT and the pivotal role of endovascular repair as a first-line treatment for PVS.

Magnetic Resonance Imaging of Liver Transplant

MR imaging increasingly has been adopted for follow-up imaging post-liver transplantation and for diagnosis of its complications. These include vascular and biliary complications as well as post-transplant malignancies. Interpretation of postoperative MR imaging should take into account the surgical technique and expected post-transplant changes. Contrast-enhanced MR imaging has high sensitivity for identification of vascular complications. MR cholangiopancreatography on the other hand is the most accurate noninvasive method for evaluation of biliary complications.

An Orthotopic Liver Transplantation Patient Survived Without Hepatic Artery Flow Due to Thrombosis: A Case Report

BACKGROUND

Hepatic artery thrombosis (HAT), a serious complication after orthotopic liver transplantation, almost always leads to morbidity and mortality without urgent revascularization or retransplantation, especially if HAT occurs within a few days after transplantation.

CASE PRESENTATION

Herein we describe a case report of an orthotopic liver transplantation patient surviving without hepatic artery flow due to HAT on postoperative day 1. Reanastomosis, thrombectomy, and intra-arterial thrombolysis were performed, but only retrograde arterial flow by Doppler ultrasound, not by angiography, could be demonstrated in the hepatic artery. This case report is in compliance with the Declaration of Helsinki and the Declaration of Istanbul.

CONCLUSION

Based on the evidence from this patient, we believe that patients with failed revascularization can experience a long-term survival with conservative treatment. Retransplantation should be evaluated based on laboratory findings because graft function in individual patients can recover.

Complications of liver transplant

Liver transplantation has become a definitive treatment for patients with end-stage liver disease and those meeting Milan criteria for hepatocellular carcinoma. The morbidity and mortality associated with liver transplantation continues to decrease thanks to refinements in surgical technique, immunosuppression, and imaging. In particular, imaging plays a vital role by facilitating early detection of post-operative complications and enabling prompt treatment. Post-operative complications that lead to graft failure and patient morbidity/mortality can be generally categorized as vascular, biliary, parenchymal, and malignant. Vascular complications include stenosis and thrombosis of the hepatic artery, portal vein, and inferior vena cava; hepatic artery pseudoaneurysm; arteriovenous fistula; and celiac stenosis. Biliary abnormalities include strictures, bile leak, obstruction, recurrent disease, and infection. While imaging is not primarily utilized to diagnose allograft rejection, it plays an important role in excluding mechanical causes of graft dysfunction that can mimic rejection. Ultrasound is routinely performed as the first-line imaging evaluation for the detection and follow-up of early and delayed complications. Cholangiography and magnetic resonance cholangiopancreatography are useful in detecting and characterizing biliary complications. Computed tomography is often used to further evaluate abnormal findings on ultrasound or for the characterization of post-operative fluid collections. The aim of this review is to discuss and illustrate the imaging findings of complications associated with liver transplantation and their role in facilitating treatment.

Portal Vein Stenosis Following Liver Transplantation Hemodynamically Assessed with 4D-flow MRI before and after Portal Vein Stenting

We present a case of a patient who underwent portal vein (PV) stenting for PV stenosis after a living-donor liver transplantation. A pretreatment 3D cine phase-contrast (4D-flow) MRI showed decreased, though hepatopetal, blood flow in the PV. After stenting, 4D-flow MRI confirmed an improvement in PV flow, with a more homogeneous flow distribution to each hepatic segment. 4D-flow MRI are valuable for understanding the hemodynamics of this area, planning for treatments, and evaluating the outcome of the interventions.

Investigation on revascularization time and initial damage after transplantation of fresh and cryopreserved ovarian tissue in domestic cats

The present study evaluated revascularization time of fresh and cryopreserved cat ovarian tissue after transplantation to subcutaneous tissue. Ovaries of five cats were used and eight pieces of ovarian tissue were taken from each pair of ovaries. Immediately after removal, three pieces were transplanted and one fixed for fresh control. The remaining four pieces were cryopreserved and, after thawing, one was fixed for cryopreservation control and three were transplanted. Grafts were recovered on days 2 (D2), 4 (D4) and 6 (D6) post-transplantation. Blood vessels were identified by immunohistochemistry and doppler ultrasound. Immunohistochemistry showed that the percentages of total tissue area occupied by blood vessels were similar (P > 0.05) in fresh and cryopreserved tissues. In both cases, blood vessel area was significantly higher (P < 0.05) on D4 and D6 compared to D0. Ultrasound analysis showed vascularization improvement on the periphery of grafts from D2 to D4 and from D4 to D6, both in fresh and cryopreserved tissue samples. Nonetheless, there was a significant decrease (P < 0.05) in the percentage of morphologically normal follicles (MNF) after transplantation compared to non-transplanted tissue (D0), both for fresh and cryopreserved samples. Moreover, the number of follicles found in samples was considerably smaller after grafting. In conclusion, revascularization of ovarian tissue autotransplanted to subcutaneous tissue in domestic cats occurs within 4 days after transplantation, both for fresh and cryopreserved tissue. However, large follicular loss has been observed in the first days post-transplantation, especially in cryopreserved tissues.