CT-based renal volume and graft function after living-donor kidney transplantation: Is there a volume threshold to avoid?

Impact of donating the larger kidney by CT volumetry on the kidney function, 5-years after living donation

PURPOSE

Removing the smaller kidney for donor nephrectomy has been advocated if there is a size difference of ≥ 10% after other anatomical considerations. This study reports the difference in long-term renal function in patients who have their larger kidney removed for donor nephrectomy.

METHODS

Data of 104 donors were prospectively collected. They were divided into 2 groups depending on donated kidney being ≥ 10% larger (Group-1) or < 10% larger (Group-2) than the remaining kidney. Baseline characteristics (age, gender, BMI, surgical details, co-morbidities), estimated Glomerular Filtration Rate (eGFR, calculated using CKD-EPI formula) before and up to 5-years after surgery were collected.

RESULTS

Group 1 (n = 28) and Group 2 (n = 76) had similar baseline characteristics. The split renal volume (SRV) of donated kidney was 53.4% (52.5-58.7%) for Group 1 and 49.9% (44.3-52.5%) for Group 2 eGFR between 2 groups were similar (110.7 ± 20.8 vs 103.4 ± 22.5, p = 0.14). eGFR was not different at 6-months, 1-, 3- and 5-year post-operation. Patients with eGFR < 60 was also not significantly different between the 2 groups 23.1% vs 31.4% (p = 0.42). Group-1 had significantly greater absolute reduction in eGFR than Group-2 (45.5 ± 17.8 vs 37.6 ± 14.5, p = 0.02) at 6-months post op. After which, there was a steady improvement in eGFR up to 5-years; which was most significant from the 6-months to 1-year (p = 0.02, 0.001). The absolute and relative recovery in eGFR beyond 6-months does not differ significantly.

CONCLUSION

Despite an initial greater decrease in eGFR at 6 months, removing the larger kidney (> 10% absolute difference within the SRV limits of this study) for donor nephrectomy did not result in a significant difference in kidney function at 5 years due to similar rates of eGFR recovery after nadir levels at 6 months.

Outcomes of kidneys used for transplantation: an analysis of survival and function

Introduction

Kidney transplant recipients expect to survive the procedure with sufficient renal function for reliable dialysis freedom.

Methods

Transplant outcomes (survival and estimated renal function) were assessed after live and deceased donor transplantation from the US national database. Outcomes were stratified by age (donor and recipient) and donor type.

Results

Aggregate recipient outcomes were better transplanting living vs deceased donated kidneys. However, when stratified by the one-year renal function (within KDIGO CKD stage stratifications), surviving recipients had clinically similar dialysis-freedom, irrespective of donor type or age. The major outcome differences for recipients of age-stratified live and deceased kidneys was 1) the increasing frequency of one-year graft failures and 2) the increasing likelihood of severely limited renal function (CKD 4/5) with advancing donor age. Over 30% of recipients of deceased kidneys >65 years had either one-year graft failure or severely limited renal function contrasted to less than 15% of recipients of live kidneys aged >65 years.

Conclusions

Evolving techniques to reduce adverse events after urgent vs elective procedures, plus improved transplant outcome predictability with increased-age deceased donor kidneys using advanced predictive analytics (using age-stratified live kidney transplantation outcomes as a relevant reference point) should facilitate similar kidney transplant outcomes, irrespective of donor type.

Choosing the larger kidney on CT volumetry: a study on the early post-donation kidney function of living donors

BACKGROUND

Selecting the smaller kidney for donation has been advocated if there is a size difference of > 10% between the 2 kidneys but has never been prospectively evaluated. With increase in donor nephrectomies, it is important to evaluate this to minimize loss of renal function to donors.

METHODS

75 consecutive donor nephrectomy patients were included in our longitudinal study. The Split Renal Volume (SRV) of bilateral kidneys were measured using contrasted computer tomography scans and patients segregated into 2 groups depending on donated kidney having more (Group 1) or less than (Group 2) 52.5% of SRV.

RESULTS

Patients in Group 1 (n = 19) and 2 (n = 56) were of similar age (43.8 vs. 48.3), BMI (22.4 vs. 25.2), sex (57.9 vs. 55.4% women), respectively. Although total kidney volumes were similar in both groups, Group 1 had significantly smaller right kidney volumes (120.4 ± 24.9 vs. 142.7 ± 28.4 mls, p = 0.003). EGFR pre-operatively (116.3 ± 20.8 vs. 106.3 ± 23.8 mL/min/1.73 m2) and at 6-months (65.7 ± 13.3 vs. 66.9 ± 15.5 mL/min/1.73 m2) were not different between groups. However, patients in Group 1 had significantly greater absolute (50.6 ± 14.9 vs. 39.5 ± 14.7 mL/min/1.73 m2) and relative decline (43.0 ± 8.6 vs. 36.3 ± 10.6%) in eGFR at 6 months (p = 0.06, 0.009).

CONCLUSION

With a SRV difference of 5% between the 2 sides, removal of the larger kidney for living kidney donation resulted in greater early decline of renal function than kidney donors whose larger or equivalent kidney is preserved.

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.

Comparison of tomographic kidney volumes measured by semi-automatic segmentation method with scintigraphic split renal function in predicting posttransplant kidney functions

INTRODUCTION

In this study, it was aimed to compare scintigraphic split renal function (SRF) and computed tomographic (CT) kidney volumes by semi-automatic segmentation method in predicting graft functions after kidney transplantation.

METHODS

112 patients (77 males, 35 females) who had a living donor kidney transplant between 2015 and 2017 in our center were included in the study. While SRF was calculated with technetium-99m-diethylenetriaminepentaacetic acid (^99m Tc-DTPA) scintigraphy, CT angiography was used for volumetric calculations.

RESULTS

CT-volumetric measurements, especially renal cortical volume (RCV:103.8 ± 20 mL) and ratio to body mass index (RCV/BMI:4.45±1.3) were found to be more significant than ^99m Tc-DTPA-SRF in predicting graft functions. The correlations between SRF and RCV with 6th month eGFR (rSRF:0.052, rRCV:0.317, p=0.041) and 1st year eGFR (rSRF:0.104, rRCV:0.374, p=0.033) were found to be more significant in favor of RCV. The correlation between SRF/BMI and RCV/BMI with 1st, 6th and 12th month eGFR (respectively, p=0.02/0.048/0.024) were found to be more significant in favor of RCV/BMI. Although univariate analysis showed a significant relationship between most volumetric measurements and 1st year graft functions, in multivariate analysis only RCV (OR: 1.04(1.01-1.07), p=0.023) and RCV/BMI (OR: 2.5(1.27-5.39), p=0.013) showed a significant relationship between graft functions.

CONCLUSION

In our study, it was shown that CT-based renal volumetric measurements, especially RCV and RCV/BMI, predicted graft functions more strongly than scintigraphic ^99m Tc-DTPA-SRF. This article is protected by copyright. All rights reserved.

Automated Segmentation of Kidney Cortex and Medulla in CT Images: A Multisite Evaluation Study

BACKGROUND

In kidney transplantation, a contrast CT scan is obtained in the donor candidate to detect subclinical pathology in the kidney. Recent work from the Aging Kidney Anatomy study has characterized kidney, cortex, and medulla volumes using a manual image-processing tool. However, this technique is time consuming and impractical for clinical care, and thus, these measurements are not obtained during donor evaluations. This study proposes a fully automated segmentation approach for measuring kidney, cortex, and medulla volumes.

METHODS

A total of 1930 contrast-enhanced CT exams with reference standard manual segmentations from one institution were used to develop the algorithm. A convolutional neural network model was trained (n=1238) and validated (n=306), and then evaluated in a hold-out test set of reference standard segmentations (n=386). After the initial evaluation, the algorithm was further tested on datasets originating from two external sites (n=1226).

RESULTS

The automated model was found to perform on par with manual segmentation, with errors similar to interobserver variability with manual segmentation. Compared with the reference standard, the automated approach achieved a Dice similarity metric of 0.94 (right cortex), 0.90 (right medulla), 0.94 (left cortex), and 0.90 (left medulla) in the test set. Similar performance was observed when the algorithm was applied on the two external datasets.

CONCLUSIONS

A fully automated approach for measuring cortex and medullary volumes in CT images of the kidneys has been established. This method may prove useful for a wide range of clinical applications.

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.

Remaining kidney volume indexed to weight as a strong predictor of estimated glomerular filtration rate at 1 year and mid-term renal function after living-donor nephrectomy - a retrospective observational study

The donors' estimated glomerular filtration rate (eGFR) after living nephrectomy has been a concern, particularly in donors with smaller kindeys. Therefore, we developed this retrospective observational study in 195 donors to determine the ability remaining kidney volume indexed to weight (RKV/W) to predict eGFR at 1 year through multivariate linear regression and to explore this relationship between annual eGFR change from 1 to 4 years postdonation evaluated by a linear mixed model. Comparing RKV/W tertiles (T1, T2, T3), RKV/W was a good predictor of 1-year eGFR which was significantly better in T3 donors. Gender, predonation eGFR, and RKV/W were independent predictors of eGFR at 1-year. In a subgroup with predonation eGFR < 90mL/min/1.73 m² , a significant prediction of eGFR < 60mL/min/1.73 m² was detected in males with RKV/W ≤ 2.51cm³ /kg. Annual eGFR (ml/min/year) change from 1 to 4 years was + 0.77. RKV/W divided by tertiles (T1-T3) was the only significant predictor: T2 and T3 donors had an annual eGFR improvement opposing to T1. RKV/W was a good predictor of eGFR at 1 year, independently from predonation eGFR. A higher RKV/W was associated with improved eGFR at 1 year. A decline in eGFR on the four years after surgery was only noticeable in donors with RKV/W ≤ 2.13cm³ /kg.

Correlation and Prediction of Living-Donor Remaining Function by Using Predonation Computed Tomography-Based Volumetric Measurements: Role of Remaining Kidney Volume

OBJECTIVES

Kidney volume in healthy living donors may serve as a surrogate marker of renal function. Here, we evaluated whether preserved kidney volume correlated with and could predict donor renal function at 2 years postdonation using the CKD-EPI estimated glomerular filtration rate equation.

MATERIALS AND METHODS

Healthy living donors (n = 208) with computed tomography volume measurements were evaluated for renal function before and after donation. Preserved kidney volume was adjusted to body surface area. Demographic characteristics (including race/ethnicity and sex) and renal function variables of donors were analyzed for postdonation renal function.

RESULTS

Donor mean age was 39.4 ± 10.7 years (36.2% males, 91.9% white). Median adjusted preserved kidney volume was 180.6 mL. At 2 years postdonation, median estimated glomerular filtration rate was 62.4 mL/min (interquartile range, 54.8-73.2 mL/min). Predonation estimated glomerular filtration rate, age, and adjusted preserved kidney volume were found to be inde-pendent predictors of 2-year estimated glomerular filtration rate (P < .001). We further analyzed data by stratifying preserved kidney volumes into tertiles. Mean 2-year estimated glomerular filtration rates were 57.9 ± 12, 65 ± 16, and 73 ± 17 mL/min for lowest to highest tertile groups, respectively (P < .05). The odds ratio of having a 2-year postdonation estimated glomerular filtration rate of < 60 mL/min for donors in the lowest tertile group was 3.51 (95% confidence interval, 1.9-6.4; P < .001), whereas the risk for donors in the highest tertile group was 0.23 (95% confidence interval, 0.12-0.44; P< .001). Sensitivity analysis result was 0.764 (95% confidence interval, 0.69-0.82; P = .005) for adjusted preserved kidney volume and estimated glomerular filtration rate of < 60 mL/min.

CONCLUSIONS

Remaining kidney volume before donation correlated with and predicted estimated glomerular filtration rate after donation. Remaining kidney volume should be assessed when selecting kidneys from healthy donors.

CT evaluation of the renal donor and recipient

Proper pre- and post-transplant diagnostic imaging work-up is fundamental in ensuring a successful outcome for renal transplantation. Despite exposure to ionizing radiation, CT has high spatial resolution and is a widely available and fast imaging technique. CT is performed routinely to delineate the anatomy of the kidney, relevant vasculature, and urinary collecting system in the living donor, to assess the iliac vessels in potential recipients prior to surgery, and to assess early and late-term post-transplant complications. The purpose of this article is to outline the optimal CT protocol and the main reportable findings for both the donor and the recipient diagnostic imaging work-up as well as to point out the main issues regarding ionizing radiation exposure and contrast medium injection in these subjects.

Influence of Various Living Donor Kidney Measurements in Relation to Recipient Body Measurements on Posttransplant Allograft Functional Outcomes

OBJECTIVES

Donor kidney measurements may affect outcomes of transplanted allografts. We tested allograft and recipient measurements on kidney allograft outcomes. In this study, we compared the effects of kidney allograft volumes, which were measured using computed tomographic angiography before transplant, and allograft weight, which was measured during surgery, in relation to the recipient's body weight and body mass index on kidney function at 6 and 12 months after transplant.

MATERIAL AND METHODS

We included 74 patients (40 female and 34 male patients, mean age of 50.42 ± 9.75 y) in this study.

RESULTS

Intraoperative allograft weight was 182.68 ± 40.33 g (range, 104-266 g). The allograft volume measured using computed tomographic angiography scanning was 123.34 ± 24.26 mL (range, 78-181 mL). The estimated glomerular filtration rates of the recipients at 6 and 12 months after transplant correlated negatively with age and recipient body mass index but correlated positively with allograft volume/recipient body weight, allograft volume/recipient body mass index, allograft weight, allograft weight/recipient body weight, and allograft weight/recipient body mass index values, as concluded by univariate analyses. From multivariate analyses, we found variables of interest presumed to significantly affect the 12-month estimated glomerular filtration rates, including recipient age, allograft volume/recipient body weight, allograft volume/recipient body mass index, allograft weight, allograft weight/recipient body weight, and allograft weight/recipient body mass index.

CONCLUSIONS

Transplanted allograft and recipient body values may be used as predictors of estimated glomerular filtration rates 6 and 12 months after transplant.