Pre-operative assessment of living renal transplant donors with state-of-the-art imaging modalities: computed tomography angiography versus magnetic resonance angiography in 118 patients

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.

Retrospective analysis of the perioperative outcome in living donor kidney transplantation with multiple renal arteries: does accessory vessel ligation affect the outcome?

PURPOSE

Accurate surgical reconstruction of arterial vascular supply is a crucial part of living kidney transplantation (LDKT). The presence of multiple renal arteries (MRA) in grafts can be challenging. In the present study, we investigated the impact of ligation versus anastomosis of small accessory graft arteries on the perioperative outcome.

METHODS

Clinical and radiological outcomes of 51 patients with MRA out of a total of 308 patients who underwent LDKT with MRA between 2011 and 2020 were stratified in two groups and analyzed. In group 1 (20 patients), ligation of accessory arteries (ARAs) and group 2 (31 patients) anastomosis of ARAs was performed.

RESULTS

Significant differences were observed in the anastomosis-, surgery-, and warm ischemia time (WIT) in favor of group 1. Students t-test showed comparable serum creatinine levels of 2.33 (± 1.75) to 1.68 (± 0.83) mg/dL in group 1 and 2.63 (± 2.47) to 1.50 (± 0.41) mg/dL in group 2, were seen from 1 week to 1 year after transplant. No increased rates of Delayed graft function (DGF), primary transplant dysfunction and transplant rejection were seen, but graft loss and revision rates were slightly higher when the ARAs were ligated. Analysis of Doppler sonography revealed that segmental perfusion deficits tend to regenerate during the clinical course.

CONCLUSION

Ligation of smaller accessory renal arteries may not affect the outcome of living kidney transplantation, except for a minor increase in the reoperation rate. Segmental perfusion deficits of the graft seem to regenerate in most cases as seen in Doppler sonography.

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.

Does the Side Matter? A Retrospective Cohort Study Comparing Left and Right Pure Laparoscopic Donor Nephrectomies

OBJECTIVES

Right laparoscopic donor nephrectomy (RLDN) is no longer regarded inferior to left LDN (LLDN). However, this knowledge is based on many studies suffering from inherent learning curves, center-specific imbalances, and different laparoscopic techniques.

METHODS

Pure LDNs at a high-volume referral center from 2011 to 2016 were retrospectively analyzed. Patient, graft characteristics, outcomes of LDNs, and corresponding open kidney transplantations were compared between LLDN and RLDN including a follow-up.

RESULTS

160 (78.4%) LLDNs and 44 (21.6%) RLDNs only differed regarding graft characteristics, as more right grafts had multiple veins (34.1 vs. 6.9%, p < 0.001) and worse scintigraphic function (44 vs. 51%, p < 0.001). RLDNs were shorter (201 vs. 220 min, p = 0.032) with longer warm ischemia time (165 vs. 140 s, p < 0.001), but left grafts were transplanted faster (160 vs. 171 min, p = 0.048). Recipients of right kidneys had more postoperative complications (grade 3: 25.6 vs. 11.3%, p = 0.020). At a follow-up of 45 (range 6-79) months, neither the kidney function, nor death-censored graft (5-year: LLDN 89 vs. 92%, p = 0.969) and patient survival (5-year: LLDN 95 vs. 98%, p = 0.747) differed.

CONCLUSIONS

Pure LLDN and RLDN can have different outcomes at high-volume centers, especially higher complications for recipients of right grafts. However, long-term function and graft survival are the same irrespective of the chosen side.

Is Bigger Better? Living Donor Kidney Volume as Measured by the Donor CT Angiogram in Predicting Donor and Recipient eGFR after Living Donor Kidney Transplantation

BACKGROUND

The role of kidney volume measurement in predicting the donor and recipient kidney function is not clear.

METHODS

We measured kidney volume bilaterally in living kidney donors using CT angiography and assessed the association with the donor remaining kidney and recipient kidney (donated kidney) function at 1 year after kidney transplantation. Donor volume was categorized into tertiles based on lowest, middle, and highest volume.

RESULTS

There were 166 living donor and recipient pairs. The mean donor age was 44.8 years (SD ± 10.8), and donor mean BMI was 25.5 (SD ± 2.9). The recipients of living donor kidneys were 64% male and had a mean age of 43.5 years (SD ± 13.3). Six percent of patients experienced an episode of cellular rejection and were maintained on dialysis for a mean of 18 months (13-32) prior to transplant. Kidney volume was divided into tertiles based on lowest, middle, and highest volume. Kidney volume median (range) in tertiles 1, 2, and 3 was 124 (89-135 ml), 155 (136-164 ml), and 184 (165-240 ml) with donor eGFR ml/min (adjusted for body surface area expressed as ml/min/1.73 m2) at the time of donation in each tertile, 109 (93-129), 110 (92-132), and 101 ml/min (84-117). The median (IQR) eGFR in tertiles 1 to 3 in kidney recipients at 1 year after donation was 54 (44-67), 62 (50-75), and 63 ml/min (58-79), respectively. The median (IQR) eGFR in tertiles 1 to 3 in the remaining kidney of donors at 1 year after donation was 59 (53-66), 65 (57-72), and 65 ml/min (56-73), respectively.

CONCLUSION

Bigger kidney volume was associated with better eGFR at 1 year after transplant in the recipient and marginally in the donor remaining kidney.

Unenhanced magnetic resonance angiography as an accurate alternative in the preoperative assessment of potential living kidney donors with contraindications to computed tomography angiography and to contrast-enhanced magnetic resonance angiography

Objective

To evaluate the accuracy of steady-state free precession (SSFP) unenhanced magnetic resonance angiography (MRA) at 1.5 T for the identification of multiple renal arteries, using computed tomography angiography (CTA) as the reference standard.

Materials and Methods

This was a prospective study involving 39 patients (26 males; mean age, 62.6 years) who underwent CTA and unenhanced MRA to evaluate the proximal and middle segments of the renal arteries. The analysis was performed in two phases: the quality of unenhanced MRA images was classified as diagnostic or nondiagnostic for the presence of multiple renal arteries by two independent readers; two other independent readers then evaluated the images previously classified as being of diagnostic quality. The sensitivity, specificity, and overall accuracy of unenhanced MRA were calculated, CTA being used as the reference standard. The kappa statistic was used in order to calculate interobserver agreement.

Results

The image quality of unenhanced MRA was considered diagnostic in 70-90% of the extrarenal arterial segments. The CTA examination revealed 19 multiple renal arteries (8 on the right and 11 on the left). The accuracy of unenhanced MRA for the identification of multiple renal arteries was greater than 90%, with a sensitivity of 72.7-100% and a specificity of 96.3-100%.

Conclusion

Unenhanced MRA provides high quality imaging of the extrarenal segments of renal arteries. This method may be used as an alternative for the evaluation of the renal arteries, given that it has an accuracy comparable to that of CTA.

Dynamic CTA in Native Kidneys Using a Multiphase CT Protocol-Potential of Significant Reduction of Contrast Medium

RATIONALE AND OBJECTIVE

The objective of this study was to assess an optimized renal multiphase computed tomography angiography (MP-CTA) protocol regarding reduction of contrast volume.

MATERIALS AND METHODS

Thirty patients underwent MP-CTA (12 phases, every 3.5 seconds, 80 kV/120 mAs) using 30 mL of contrast medium. The quality of MP-CTA was assessed quantitatively measuring vessel attenuation, image noise, and contrast-to-noise ratio. MP-CTA was evaluated qualitatively regarding depiction of vessels, cortex differentiation, and motion artifacts (grades 1-4, 1 = best). Mean effective radiation dose was registered. Results were compared to standard renal computed tomography angiography (CTA) (80 mL). Student t test was applied, if variables followed normal distribution. For other variables, nonparametric Mann-Whitney U test was used.

RESULTS

All acquisitions were successfully performed, and no patient had to be excluded from the study. MP-CTA enabled high attenuation (aorta: 503 ± 91 HU, renal arteries: 450 ± 73 HU/456 ± 72 HU) at adequate image noise (13.7 ± 1.5) and good contrast-to-noise ratio (34.2 ± 10.2). Good attenuation of renal veins was observed (286 ± 43 HU/282 ± 42 HU). Arterial enhancement was significantly higher compared to renal CTA (aorta: 396 ± 90 HU, renal arteries: 331 ± 74 HU/333 ± 80 HU; P < .001). MP-CTA protocol enabled good image quality of renal arteries (1.5 ± 0.6) and veins (1.7 ± 0.6). Cortex differentiation and motion artifacts were ranked 1.8 ± 0.8 and 1.6 ± 0.8. The mean effective radiation dose was 9 mSv (MP-CTA).

CONCLUSIONS

Compared to standard renal CTA, the renal MP-CTA enabled the significant reduction of contrast volume and simultaneously provided a significantly higher arterial attenuation.

Renal volume assessed by magnetic resonance imaging volumetry correlates with renal function in living kidney donors pre- and postdonation: a retrospective cohort study

Renal function of potential living kidney donors is routinely assessed with scintigraphy. Kidney anatomy is evaluated by imaging techniques such as magnetic resonance imaging (MRI). We evaluated if a MRI-based renal volumetry is a good predictor of kidney function pre- and postdonation. We retrospectively analyzed the renal volume (RV) in a MRI of 100 living kidney donors. RV was correlated with the tubular excretion rate (TER) of MAG3-scintigraphy, a measured creatinine clearance (CrCl), and the estimated glomerular filtration rate (eGFR) by Cockcroft-Gault (CG), CKD-EPI, and modification of diet in renal disease (MDRD) formula pre- and postdonation during a follow-up of 3 years. RV correlated significantly with the TER (total: r = 0.6735, P < 0.0001). Correlation between RV and renal function was the highest for eGFR by CG (r = 0.5595, P < 0.0001), in comparison with CrCl, MDRD-GFR, and CKD-EPI-GFR predonation. RV significantly correlated with CG-GFR postdonation and predicted CG-GFR until 3 years after donation. MRI renal volumetry might be an alternative technique for the evaluation of split renal function and prediction of renal function postdonation in living kidney donors.

Preoperative Computed Tomography Parameters and Deterioration of Remaining Kidney Function in Living Donors

INTRODUCTION

After living kidney donation, a decrease of kidney function (described as estimated glomerular filtration rate [eGFR]) is observed in majority of donors. However, the loss is more significant in some patients without an explicable reason. The aim of this study was to identify quantitative parameters in computed tomography (CT) of the abdomen that would predict greater eGFR reduction after kidney removal.

MATERIAL AND METHODS

One hundred and ten preoperative multiphase CT examinations of the abdomen of kidney donors were analyzed for the following renal parameters: cortex, parenchyma and pyramids volume, scarring thickness (low grade: <1 cm, high grade: >1 cm), cortical gaps, vascularisation, and cortex-to-aorta enhancement index (CAEI). The radiologic and biometric (eg, donor weight) parameters were correlated with eGFR (CKD-EPI formula) change between baseline and at discharge.

RESULTS

Donor weight was correlated with a loss of eGFR (P < .001). Kidney volumetric parameters including renal cortex and parenchyma volume, as well as renal artery cross-section area were associated with donor weight (r = 0.50 P < .001 and r = 0.39 P < .001). CAEI was correlated with a loss of eGFR (P = .003) and was related to the donor's sex in favor of men. Forty-one (37%) donors had an additional renal artery, which did not influence kidney function. No influence of cortical gaps or scarring on eGFR was observed.

CONCLUSIONS

CAEI may be a helpful tool in predicting greater short-term kidney function decrease after living kidney donation. Male sex is the strongest risk factor of greater eGFR loss after kidney donation.

Influence of CT-based depth correction of renal scintigraphy in evaluation of living kidney donors on side selection and postoperative renal function: is it necessary to know the relative renal function?

PURPOSE

To analyse the influence of CT-based depth correction in the assessment of split renal function in potential living kidney donors.

METHODS

In 116 consecutive living kidney donors preoperative split renal function was assessed using the CT-based depth correction. Influence on donor side selection and postoperative renal function of the living kidney donors were analyzed. Linear regression analysis was performed to identify predictors of postoperative renal function.

RESULTS

A left versus right kidney depth variation of more than 1 cm was found in 40/114 donors (35%). 11 patients (10%) had a difference of more than 5% in relative renal function after depth correction. Kidney depth variation and changes in relative renal function after depth correction would have had influence on side selection in 30 of 114 living kidney donors. CT depth correction did not improve the predictability of postoperative renal function of the living kidney donor. In general, it was not possible to predict the postoperative renal function from preoperative total and relative renal function. In multivariate linear regression analysis, age and BMI were identified as most important predictors for postoperative renal function of the living kidney donors.

CONCLUSIONS

Our results clearly indicate that concerning the postoperative renal function of living kidney donors, the relative renal function of the donated kidney seems to be less important than other factors. A multimodal assessment with consideration of all available results including kidney size, location of the kidney and split renal function remains necessary.

Vascular CT and MRI: a practical guide to imaging protocols

Non-invasive cross-sectional imaging techniques play a crucial role in the assessment of the varied manifestations of vascular disease. Vascular imaging encompasses a wide variety of pathology. Designing vascular imaging protocols can be challenging owing to the non-uniform velocity of blood in the aorta, differences in cardiac output between patients, and the effect of different disease states on blood flow. In this review, we provide the rationale behind—and a practical guide to—designing and implementing straightforward vascular computed tomography (CT) and magnetic resonance imaging (MRI) protocols.

Teaching Points

• There is a wide range of vascular pathologies requiring bespoke imaging protocols.

• Variations in cardiac output and non-uniform blood velocity complicate vascular imaging.

• Contrast media dose, injection rate and duration affect arterial enhancement in CTA.

• Iterative CT reconstruction can improve image quality and reduce radiation dose.

• MRA is of particular value when imaging small arteries and venous studies.

Does size matter? Kidney transplant donor size determines kidney function among living donors

BACKGROUND

Kidney donor outcomes are gaining attention, particularly as donor eligibility criteria continue to expand. Kidney size, a useful predictor of recipient kidney function, also likely correlates with donor outcomes. Although donor evaluation includes donor kidney size measurements, the association between kidney size and outcomes are poorly defined.

METHODS

We examined the relationship between kidney size (body surface area-adjusted total volume, cortical volume and length) and renal outcomes (post-operative recovery and longer-term kidney function) among 85 kidney donors using general linear models and time-to-chronic kidney disease data.

RESULTS

Donors with the largest adjusted cortical volume were more likely to achieve an estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m2 over a median 24-month follow-up than those with smaller cortical volumes (P <0.001), had a shorter duration of renal recovery (1.3-2.2 versus 32.5 days) and started with a higher eGFR at pre-donation (107-110 versus 91 mL/min/1.73 m2) and immediately post-nephrectomy (∼63 versus 50-51 mL/min/1.73 m2). Similar findings were seen with adjusted total volume and length.

CONCLUSIONS

Larger kidney donors were more likely to achieve an eGFR ≥60 mL/min/1.73 m2 with renal recovery over a shorter duration due to higher pre-donation and initial post-nephrectomy eGFRs.

Renal Collecting System Anatomy in Living Kidney Donors by Computed Tomographic Urography: Protocol Accuracy Compared to Intravenous Pyelographic and Surgical Findings

OBJECTIVES

To evaluate the accuracy of triple-bolus computed tomography urography (CTU) as a surrogate of intravenous pyelography (IVP) for determining the anatomy of the urinary collecting system in living kidney donors.

MATERIALS AND METHODS

In an analytic descriptive cross-sectional study, 36 healthy kidney donors were recruited during 12 months. Preoperative IVP and CTU were utilized to evaluate kidneys' anatomy; major and minor calyces and variation were used as anatomical indices to compare the accuracy of CTU and IVP; the images were then compared to surgical findings.

RESULTS

Thirty-six kidney donors (92% male; mean age: 28 ± 6 years) were enrolled in this study. The kappa coefficient value was significant and almost perfect for the CTU and IVP findings in detecting the pattern of calyces (kappa coefficient 0.92, asymptotic 95% confidence interval 0.86-0.97). Anatomic variations or anomalies of the urinary collecting system included the bifid pelvis (5.6%), duplication (8.3%), and extra-renal pelvis (2.8%). Both the sensitivity and specificity of CTU in the detection of the anatomy and variations were 100%; the sensitivity and specificity of IVP were 83.3% and 100%, respectively.

CONCLUSIONS

The triple-bolus preoperative CTU can be considered an alternative to IVP for assessing the anatomy of the urinary collecting system.

Urologic considerations and complications in kidney transplant recipients

Urologic considerations during the kidney transplantation process, starting with initial recipient evaluation and continuing through the post-transplant, long-term follow-up, are critical for minimizing urologic complications and improving graft survival. Appropriate, targeted, preoperative urologic evaluation of the recipient allows for an optimized urinary tract to accept the graft, whereas post-transplant urologic follow-up and monitoring decrease the risk of graft lost secondary to a urologic cause, particularly in patients with a urologic reason for their kidney failure and in those patients with concomitant urologic diagnoses. Urologic complications comprise the second most common adverse post-transplant event, occurring in 2.5% to 14% of patients and are associated with high morbidity, graft loss, and mortality. Early and late urologic complications, including hematuria, hematoma, lymphocele, urine leak, ureteral stricture, nephrolithiasis, and vesicoureteral reflux, and their causes and treatment options are explored. A multidisciplinary team approach to kidney transplantation, including transplant surgery, urology, and nephrology, optimizes outcomes and graft survival. Although the current role of the urologist in kidney transplantation varies greatly by institution, appropriate consultation, participation, and monitoring in select patients is essential.

Experiences with the use of iteratively reconstructed dose-modified MDCT angiography examinations of living renal donors

PURPOSE

To evaluate the performance of iteratively reconstructed (IR) dose-modified (DM) multidetector computed tomography (MDCT) angiography (CTA) examinations of renal donors in comparison to standard dose filtered back projection (FBP) images.

MATERIALS AND METHODS

Eighty-five potential donors who underwent dual-phase CTA on 16-/64-MDCT scanners were retrospectively reviewed. Images from a 16-MDCT scanner were reconstructed with filtered back projection (group A, 47) and examinations from 64-MDCT with IR (group B, 38). Scan parameters were constant for both groups except for higher noise index (× 1.3) in group B. Images were interpreted for the relevant anatomy and IQ by 2 readers. Surgical report served as reference standard for operated kidneys, whereas for nonoperated kidneys, interobserver agreement was evaluated.

RESULTS

Radiation dose was 36% lower in group B compared to group A. All CTA examinations were rated for diagnostic quality with comparable IQ scores. In 48 operated kidneys, 10 surgically confirmed vascular anomalies were correctly identified by both readers. In the remaining 122 nonoperated kidneys, there was an excellent interobserver agreement.

CONCLUSIONS

Iteratively reconstructed technique preserves high image quality and diagnostic performance at significantly lower radiation doses in DM kidney donor CTA examinations.