Vascular complications in kidney transplant recipients

Contrast-enhanced US in Renal Transplant Complications: Overview and Imaging Features

Renal transplant is the first-line treatment of end-stage renal disease. The increasing number of transplants performed every year has led to a larger population of transplant patients. Complications may arise during the perioperative and postoperative periods, and imaging plays a key role in this scenario. Contrast-enhanced US (CEUS) is a safe tool that adds additional value to US. Contrast agents are usually administered intravenously, but urinary tract anatomy and complications such as stenosis or leak can be studied using intracavitary administration of contrast agents. Assessment of the graft and iliac vessels with CEUS is particularly helpful in identifying vascular and parenchymal complications, such as arterial or venous thrombosis and stenosis, acute tubular injury, or cortical necrosis, which can lead to graft loss. Furthermore, infectious and malignant graft involvement can be accurately studied with CEUS, which can help in detection of renal abscesses and in the differentiation between benign and malignant disease. CEUS is also useful in interventional procedures, helping to guide percutaneous aspiration of collections with better delimitation of the graft boundaries and to guide renal graft biopsies by avoiding avascular areas. Potential postprocedural vascular complications, such as pseudoaneurysm, arteriovenous fistula, or active bleeding, are identified with CEUS. In addition, newer quantification tools such as CEUS perfusion are promising, but further studies are needed to approve its use for clinical purposes. ©RSNA, 2024 Supplemental material is available for this article.

The use of ferumoxytol for high-resolution vascular imaging and troubleshooting for abdominal allografts

Ferumoxytol is an ultrasmall superparamagnetic iron oxide which has been used as an off-label intravenous contrast agent for MRI. Unlike gadolinium-based contrast agents, ferumoxytol remains in the intravascular space with a long half-life of 14-21 h. During the first several hours, it acts as a blood-pool agent and has minimal parenchymal enhancement. Studies have shown adequate intravascular signal for up to 72 h after initial contrast bolus. Ferumoxytol has been shown to be safe, even in patients with renal failure. Ferumoxytol has shown promise in a variety of clinical settings. The exquisite resolution enabled by the long intravascular times and lack of background parenchymal enhancement is of particular interest in the vascular imaging of solid organ allografts. Ferumoxytol magnetic resonance angiography (MRA) may identify clinically actionable findings months before ultrasound, CT angiography, or Gadolinium-enhanced MRA. Ferumoxytol MRA is of particular benefit as a troubleshooting tool in the setting of equivocal ultrasound and CT imaging. In the following review, we highlight the use of ferumoxytol for high-resolution MR vascular imaging for abdominal solid organ allografts, with representative cases.

Graft survival and postoperative complications following orthotopic renal transplantation

The iliac fossa is the most commonly used site to place the graft in renal transplantation in adults. However, iliac fossa may not be used in various conditions. Thus, orthotopic renal transplantation becomes a viable alternative for these selected patients. Given the technically challenging surgery and limited number of patients, data on the long-term outcomes on this regard are scarce. This narrative review serves as an update on the clinical outcomes after orthotopic renal transplantation, focusing on overall recipient survival and renal graft survival, as well as postoperative complications. We found that studies to date showed a comparable survival rate in both recipients and renal grafts in the postoperative follow-up period after orthotopic renal transplantation with a lower complication rate compared to the published data on heterotopic renal transplantation. The results of our review may encourage transplant centers to reevaluate their policies to consider orthotopic renal transplantation as an alternative technique in cases where heterotopic kidney transplantation is not possible.

Renal Transplantation: Immediate and Late Complications

Kidney grafts are the most common transplanted solid organ. To optimize graft survival, radiologists should be familiar with the anatomy and potential complications unique to transplanted kidneys. In addition to being able to recognize the imaging characteristics to diagnose etiologies of kidney graft dysfunction, an understanding of the pathophysiology is a key to narrowing the differential diagnosis. This article provides a summary of the most common complications based on broad categories of type of complication and posttransplant timing.

Risk factors of transplant renal artery stenosis in kidney transplant recipients

BACKGROUND

Transplant Renal Artery Stenosis (TRAS) is a recognized vascular complication after kidney transplantation. The overall risk predictors of TRAS are poorly understood.

METHODS

Retrospective analysis of patients with suspected TRAS (Doppler ultrasound PSV > 200 cm/s) who underwent angiographic study in a single center between 2007 and 2014. All patients with stenosis > 50% were considered with TRAS. Stenosis restricted in the body of the artery was also analyzed in a subgroup.

RESULTS

274 patients were submitted to a renal angiography and 166 confirmed TRAS. TRAS group featured an older population (46.3 ± 11.0 vs. 40.9 ±14.2 years; p = 0.001), more frequent hypertensive nephropathy (30.1% vs. 15.7%; p = 0.01), higher incidence of Delayed Graft Function (DGF) (52.0% vs. 25.6%; p < 0.001) and longer Cold Ischemia Time (CIT) (21.5 ± 10.6 vs. 15.7 ± 12.9h; p < 0.001). In multivariable analyses, DGF (OR = 3.31; 95% CI 1.78‒6.30; p < 0.0001) was independent risk factors for TRAS. DM and CIT showed a tendency towards TRAS. The compound discriminatory capacity of the multivariable model (AUC = 0.775; 95% CI 0.718‒0.831) is significantly higher than systolic blood pressure and creatinine alone (AUC = 0.62; 95% CI 0.558-0.661). In body artery stenosis subgroup, DGF (OR = 1.86; 95% CI 1.04‒3.36; p = 0.03) and Diabetes Mellitus (DM) (OR = 2.44; 95% CI 1.31‒4.60; p = 0.005) were independent risk factors for TRAS.

CONCLUSION

In our transplant population, DGF increased more than 3-fold the risk of TRAS. In the subgroup analysis, both DGF and DM increases the risk of body artery stenosis. The addition of other factors to hypertension and renal dysfunction may increase diagnostic accuracy. TRAS TRIAL REGISTRED: clinicaltrials.gov (n° NCT04225338).

Recurrent Renal Allograft Torsion After Simultaneous Kidney and Pancreas Transplantation: Is it Still Possible to Salvage the Graft? A Case Report

BACKGROUND

Kidney allograft torsion (KAT) is defined as a rotation of the renal allograft around its vascular pedicle. It is a rare complication with high rate of graft loss. The nonspecific presentation and inability to provide a definitive diagnosis by imaging, mainly in cases of partial torsion, often delay the diagnosis and treatment. We report a case of recurrent complete torsion of the renal allograft after simultaneous kidney and pancreas transplantation, requiring 2 emergency exploratory laparotomies.

CASE REPORT

A 38-year-old woman with a history of intraperitoneal simultaneous kidney and pancreas transplantation underwent 2 separate emergency exploratory laparotomies secondary to complete renal allograft torsion, respectively, 7 and 11 months after the transplant. In both episodes, no adhesions were encountered. During the first operation, nephropexy was performed. During the second operation, an abdominal wall mesh was placed and fixed to the abdominal wall. Acute kidney injury related to KAT recovered in both occasions with a creatinine of 1.3 mg/dL at 4 months follow-up.

CONCLUSIONS

Renal torsion always should be suspected in intraperitoneally placed kidneys presenting with nonspecific symptoms, abdominal pain, oliguria, and worsening kidney function. Surgical exploration should be considered to salvage the renal graft. This case illustrates the reversibility of a severe injury related to this vascular complication with an adequate return to baseline kidney function even when diagnosis and surgical treatment of KAT might be delayed secondary to its misleading clinical presentation.

Intraoperative assessment of ureteral and graft reperfusion during robotic kidney transplantation with indocyanine green fluorescence videography

BACKGROUND

The aim of this paper is to report the first preliminary experience with intraoperative indocyanine green (ICG) fluorescence videography (IFV) to assess graft and ureteral reperfusion during robot-assisted kidney transplantation (RAKT).

METHODS

We prospectively collected data from consecutive patients undergoing RAKT and IFV from living-donors at our Institution between January 2017 and April 2018. RAKT was performed following the principles of the Vattikuti-Medanta technique. ICG was injected intravenously after vascular anastomoses to quantitate graft and ureteral fluorescence signal. The signal intensity within selected intraoperative snapshots was evaluated for renal parenchyma, ureter and vascular anastomoses. A systematic review of the English-language literature about the topic was performed according to the PRISMA statement recommendations.

RESULTS

Six patients were included. Neither conversions to open surgery nor major intra- or postoperative complications were recorded. At a median follow-up of 12 months (IQR 8-13), median estimated glomerular filtration rate was 64.2 mL/min/1.73 m2 (IQR 45.3-98.4). Intraoperative quantitative assessment of ICG fluorescence was successful in all patients. Of the five studies selected by our review, mostly prospective studies, all including open KT series. Yet, most studies were limited by lack of quantitative measures of IFV fluorescence.

CONCLUSIONS

IFV during RAKT is feasible and safe and provides a reliable assessment of graft reperfusion. Larger studies are needed to standardize the technique and to evaluate the association between fluorescence signal, ultrasound parameters and postoperative kidney function.