Vascular imaging in renal donors

Radiologic evaluation of the kidney transplant donor and recipient

The kidney is the most common solid organ transplant globally and rates continue to climb, driven by the increasing prevalence of end stage renal disease (ESRD). Compounded by advancements in surgical techniques and immunosuppression leading to longer graft survival, radiologists evermore commonly evaluate kidney transplant patients and candidates, underscoring their role along the transplant process. Multiphase computed tomography (CT) with multiplanar and 3D reformatting is the primary method for evaluating renal donor candidates, detailing renal size, vascular/collecting system anatomy, and identifying significant pathologies such as renal vascular diseases and nephrolithiasis. Ultrasound is the preferred initial postoperative imaging modality for graft evaluation due to its low cost, accessibility, noninvasiveness, and lack of radiation. CT and magnetic resonance imaging (MRI) may be useful adjunctive imaging techniques in diagnosing transplant pathology when ultrasound alone is not diagnostic. Kidney transplant complications are categorized by an approximate timeline framework, aiding in differential diagnosis based on onset, duration, and severity and include perinephric fluid collections, graft compression, iatrogenic injuries, vascular compromise, graft rejection, and neoplastic processes. This review discusses imaging strategies and important findings along the transplant timeline, from donor assessment to long-term recipient complications.

Value of Non-Contrast-Enhanced Vessel Wall MR Imaging in Assessing Vascular Invasion of Retroperitoneal Tumors

BACKGROUND

Due to their location and growth patterns, retroperitoneal tumors often involve the surrounding blood vessels. Clinical decisions on a proper treatment depend on the information on this condition. Evaluation of blood vessels using non-contrast-enhanced vessel wall MRI may provide noninvasive assessment of the extent of tumor invasion to assist clinical decision-making.

PURPOSE

To investigate the performance and potential of non-contrast-enhanced vessel wall MRI in evaluating the degree of vessel wall invasion of retroperitoneal tumors.

STUDY TYPE

Prospective.

POPULATION

Thirty-seven participants (mean age: 60.59 ± 11.77 years, 59% male) with retroperitoneal tumors close to vessels based on their diagnostic computer tomography.

FIELD STRENGTH/SEQUENCES

3 T; vessel wall MRI sequences: two-dimensional T2-weighted MultiVane XD turbo spin-echo (2D-T2-MVXD-TSE) and three-dimensional T1-weighted motion sensitized driven equilibrium fat suppression turbo spin-echo (3D-T1-MSDE-TSE) sequences; conventional MRI sequences: T2-weighted fat suppression turbo spin-echo (T2-FS-TSE), T2-weighted turbo spin-echo (T2-TSE), modified Dixon T1-weighted fast field echo (T1-mDixon-FFE), and diffusion-weighted echo planar imaging (DWI-EPI) sequences.

ASSESSMENT

All patients underwent preoperative imaging using both non-contrast conventional and vessel wall MRI sequences. Images obtained from conventional and vessel wall MRI sequences were evaluated independently by three junior radiologists (3 and 2 years of experience in reading MRI) and reviewed by one senior radiologist (25 years of experience in reading MRI) to assess the degree of vessel wall invasion. MRI were validated results from the clinical standard diagnosis based on surgical confirmation or histopathological reports. Interobserver agreement was determined based on the reports from three readers with similar years of experiences. Intraobserver variability was assessed based on categorizing and recategorizing the vessels of 37 patients 1 month apart.

STATISTICAL TESTS

Intra-class correlation efficient (ICC), Chi-square test, McNemar test, area under the receiver-operating characteristic curve (AUC), Delong test, P < 0.05 was considered significant.

RESULTS

The accuracy of vessel wall MRI (91.96%, 95% CI: 85.43-95.71; 103 of 112) in detecting the degree of vessel wall invasion was significantly higher than that of conventional MRI (75%, 95% CI: 66.24-82.10; 84 of 112). The interobserver variability or reproducibility in categorization of the degree of vascular wall invasion was good in evaluating images from conventional and vessel wall MRI sequences (ICC = 0.821, 95% CI: 0.765-0.867 and ICC = 0.881, 95% CI: 0.842-0.913, respectively).

DATA CONCLUSION

Diagnosis of vessel wall invasion of retroperitoneal tumors and assessment of its severity can be improved by using non-contrast-enhanced vessel wall MRI.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 3.

An evaluation of the contribution of routine ultrasound when performed with multiphase CT in renal donor imaging assessment

OBJECTIVES

We sought to examine the contribution of routine ultrasound when performed with computed tomography in identifying exclusion criteria in potential living kidney donors.

METHODS

We performed a 10-year retrospective cohort study including all cases of potential renal donors at our center. For each case, the donor workup ultrasound (US) and multiphase computed tomography (MPCT) original reports and imaging were reviewed by a fellowship-trained abdominal radiologist in consultation with a transplant urologist and placed into one of 3 groups: (1) no significant US contribution, (2) US was useful to characterize an incidental finding (either US exclusive or US aided in CT interpretation) but did not impact donor eligibility, and (3) an US exclusive finding contributed to donor exclusion.

RESULTS

A total of 432 potential live renal donors were evaluated (mean age 41, 263 women). In total, 340 (78.7%, group 1) cases had no significant US contribution. In 90 cases (20.8%, group 2), US helped to characterize one or more incidental findings but did not contribute to donor exclusion. In 1 (0.2%, group 3) case, an US exclusive finding (suspected medullary nephrocalcinosis) contributed towards donor exclusion.

CONCLUSION

US provided limited contribution to renal donor eligibility decisions when performed routinely with MPCT.

CLINICAL RELEVANCE

Routine ultrasound could potentially be omitted in the live renal donor workup, with alternative strategies including a selective approach to incorporating ultrasound and an expanded role of dual-energy CT.

KEY POINTS

• Ultrasound is performed routinely with CT for renal donor assessment in some jurisdictions; however, this practice has come into question particularly with advances in dual-energy CT. • Our study found that routine use of ultrasound provided limited contribution, primarily assisting CT in characterization of benign findings with only 1/432 (0.2%) potential donors in a 10-year period excluded based in part on an ultrasound exclusive finding. • The role of ultrasound can be narrowed to a targeted approach for certain at-risk patients, and can be further reduced if dual-energy CT is utilized.

Renal Transplantation: Pretransplant Workup, Surgical Techniques, and Surgical Anatomy

End-stage renal disease continues to grow worldwide, and renal transplantation remains the primary and most effective treatment to handle this burden. Living-donor transplantation is the ideal mechanism for transplant recipients to have a successful allograft but carries both medical and surgical risks. Cadaveric kidneys have their own risks and can have a high rate of success as well. Multimodality imaging is crucial and has improved greatly during the last 20 years. Finally, a robust understanding of current surgical techniques can facilitate better postoperative imaging when early complications are a consideration.

Studying the effect of donor kidney volume ratios to recipients' body surface area, body mass index, and total body weight on post-transplant graft function

OBJECTIVES

The goal of this study was to retrospectively investigate the relationship between renal transplanted volume indexes (Total kidney volume (TKV)/Body surface area (BSA), Renal parenchymal volume (RPV)/BSA, Renal cortical volume (RCV)/BSA, RPV/Body mass index (BMI), RCV/BMI, RPV/Weight, RCV/Weight), and short- and long-term function of the graft.

METHODS

One-hundred and twelve live donor-recipient pairs from 2017 to 2018, whose donors underwent preoperative renal computed tomography angiography and recipients survived during 12 months of follow-up, were included in this study.

RESULTS

The crude and adjusted linear regressions for the effect of volume measurements by voxel and ellipsoid methods on the estimated glomerular filtration rate (eGFR) at different post-transplantation times demonstrated that the RPV/weight ratio had the most substantial crude effect on the eGFR 12 months and 4 years after renal transplant. Receiver operating characteristic (ROC) curves for six different renal volume ratios demonstrated no significant difference between these ratios in terms of discriminative ability (p value < 0.05). A strong direct correlation between TKV calculated by the ellipsoid formula with RPV and RCV measured using OsiriX software was noted. Analysis of ROC curves for renal volume indices has demonstrated fair to good discriminative ability of our cut-off points to estimate 4-year post-transplantation eGFR > 60 mL/min.

CONCLUSION

Renal transplant recipients' volume indices, such as RPV/weight, had strong correlations with eGFR at different points in time, and renal transplant recipients with the volume ratios higher than our cut-off points had a good chance of having a 4-year post-transplantation eGFR higher than 60 mL/min.

Vascular Variations and Incidental Pathologies in Potential Living Renal Donors Using 160-Slice Multidetector Computed Tomography Angiography

INTRODUCTION

The aim of the study is to evaluate the vascular variations and incidental pathologies in potential living renal donors using 160-slice multidetector computed tomography (MDCT) angiography.

METHODS

This is an observational study conducted at the Department of Radiology from January 2017 to May 2022. In this study, we performed retrospective data analysis of 61 CT renal angiograms, totaling 122 kidneys of potential renal donors, using a Toshiba 160 slice MDCT scanner with a four-phase CT image acquisition protocol, performed for pre-transplant workup. All patients had normal renal functions.

RESULTS

Of our 61 patients, 34 (55.7%) were male and 27 (44.3%) were female, and their mean age was 31.2 ± 9.4 years. We have found 31 (50.8%) variations in the right renal arteries and 21 (34.4%) in the left renal arteries. Of these patients, 13 had bilateral renal arterial variations. The late confluence of the renal vein was found in 3.3% of males, multiple right renal veins in 7 (11.5%), and left renal veins in 2 (3.3%). By distributing the data according to gender, we noticed more diversity in the renal vessels of male patients. Left renal artery variations were more frequent in males (16, 76.2%) than in females (5, 23.8%), and they were statistically significant (p=0.02). Likewise, variations in the right renal arteries were also more frequently found in males (19, 61.3%) as compared to females (12, 38.7%). Right renal vein variations were more common in males (9, 81.8%) as compared to females (2, 18.2%) (p=0.05).

CONCLUSION

Frequent renal vascular variations and incidental pathologies in potential living donors were found by MDCT examination, and these vascular variations should be analyzed before renal transplant.

A Cadaveric Study on the Anomalous Origin of Renal and Gonadal Vasculature: An Observational Study

Background: Due to the increasing prevalence of kidney transplantation, a greater awareness of variations in the surrounding vasculature is of surgical importance. During embryological development, both the renal and gonadal arteries arise from lateral mesonephric branches of the dorsal aorta. In adults, gonadal arteries are paired vessels that normally arise from the aorta at the level of the second lumbar vertebra. Methods: Routine cadaveric dissection completed by first-year medical students and dental students incidentally revealed anatomical anomalies. Results: We describe two cadaveric findings in male cases which demonstrate unilateral and bilateral variations of testicular arteries originating from an aberrant renal artery in one case and an accessory renal artery in the other. Conclusion: By increasing awareness of anomalous testicular arteries we hope to encourage the standardization of preoperative vasculature exploration to both minimize intra-operative risk to living male kidney donors and increase patients’ understanding of potential risks and complications prior to consenting to the procedure providing more accurate information prior to surgery.

One-stop preoperative assessment of renal vessels for living donors with 3.0 T non-contrast-enhanced magnetic resonance angiography: compared with computerized tomography angiography and surgical results

OBJECTIVE

The study was to investigate the feasibility and accuracy of assessment for living renal donors before transplantation by using 3.0 T non-contrast-enhanced magnetic resonance angiography (NCE-MRA).

METHODS

30 renal donors were investigated and underwent computed tomography angiography (CTA) and 3.0 T NCE-MRA before nephrectomy. Two radiologists independently assessed arterial and venous anatomy and potential kidney lesions. The image quality score, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), diameters and lengths of renal arteries and veins were compared between CTA and NCE-MRA. Imaging findings were compared with the surgical results served as reference standard. Agreement was assessed using κ test. The Wilcoxon test and paired sample t test were used for statistically significant differences.

RESULTS

The results of image quality score for renal arteries and veins were highly consistent between the two radiologists in NCE-MRA (p < 0.001). There was no significant difference in the scores of renal arterial and venous branches between NCE-MRA and CTA (p > 0.05). The SNR and CNR of renal vessels were higher than CTA (p < 0.001). There were no statistically significant differences in the length of renal vessels measured by the two methods (p > 0.05), and the diameter was smaller than that of CTA (p < 0.05). The detection of normal renal arteries and early branches by both examination techniques was consistent with intraoperative findings. Both methods showed good consistency between the anatomical variation of renal vein and the intraoperative diagnosis (p < 0.001).

CONCLUSION

3.0 T NCE-MRA can be used for evaluation of main renal arteries and veins with high accuracy for anatomy and variation classification, and can be used for pre-operative vascular evaluation of living donor kidney transplantation.

ADVANCES IN KNOWLEDGE

3.0 T NCE-MRA can be used for evaluation of main renal arteries and veins with high accuracy for anatomy and variation classification, and can be used for pre-operative vascular evaluation of living donor kidney transplantation.