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Inverted pediatric kidney transplantation: are there any ‘downsides' to an upside-down kidney?
Jin Kyu Kim, MD, Priyank Yadav, MD, Michael Chua, MD, MASc, Mandy Rickard, MN, NP, Armando J. Lorenzo, MD, MSc.
The Hospital for Sick Children, Toronto, ON, Canada.

Introduction
Kidney transplantation remains the preferred option for management of end-stage renal disease (ESRD etiology) in children. There are both donor factors and patient factors that may require a surgeon to consider inverting the donor kidney, such as right allograft with vascular anatomic variants or donor kidneys with a short renal vein. It has been previously shown in a small cohort of patients who had an ‘inverted' kidney that despite theoretical concerns of change in spatial orientation of the collecting system and ureter, there were no significant differences in outcomes. We aim to revisit the implications of inverted donor kidney in pediatric renal transplantation in children with at least 1 year follow up data.
Methods
Patients who underwent kidney transplantation at our institution between January 2011 to June 2021 were reviewed. We compared patients who had an inverted renal transplant with those who had traditional transplantation. Propensity-score matching (PSM) was performed in 1:2 ratio, with exact matching on sex, nature of ESRD, donor type, and prior dialysis status. Other matched variables included age, dialysis duration, height, weight, pre-operative urine output, operative time, cold ischemia time, warm ischemia time, and estimated blood loss. The outcomes assessed included delayed graft function (DGF), urine leak, lymphocele, rejection, graft calculus, ureteric stricture, and nadir creatinine. Categorical variables were compared using Fisher Exact test and continuous variables were assessed using Mann-Whitney U test.
Results
A total of 24 patients with inverted kidney orientation were identified. Following PSM, 41 patients were matched to the inverted kidneys, with some patients who could not be matched 2:1 due to incompatible propensity scores. All patients had at least 1 year follow up data. Baseline characteristics were matched appropriately by PSM and no significant differences were noted between the two groups (Table 1). In comparing outcomes, between the two groups, there were no differences in delayed graft function (0/24 vs. 3/41, p=0.290), urine leak (3/24 vs. 2/41, p=0.350), lymphocele (2/24 vs. 4/41, p=1.000), rejection (3/24 vs. 5/41, p=1.000), graft calculus (2/24 vs. 0/41, p=0.133), and ureteric stricture (0/24 vs. 2/41, p=0.527). The two cases of renal calculus seen in the inverted transplant group occurred on post-operative day 13 and 1584. There was no difference with nadir creatinine (median 34umol/L IQR23-57 vs. 35 umol/L IQR 20-50, p=0.624) or time to nadir creatinine (8 days IQR 6-12 vs. 8 days IQR 7-28, p=0.315).
Conclusion
Inverted renal allografts do not appear to significantly contribute to increased risk of post-operative outcomes. While there were two cases of renal calculus seen in the inverted calculus group, this only represents 0.8% of the cohort and without statistical significance compared to the traditional group. Even though further studies are needed, these data provide reassurance that inverted orientation of the allograft is a reasonable strategy to establish a comfortable vascular anastomosis.
Table 1. Comparison of baseline characteristics

Kidney Orientation
TraditionalInverted
Median/CountPercentile 25/%Percentile 75Median/CountPercentile 25/%Percentile 75
Age (Months)149.747.8180.1121.050.4176.7
SexMale2253.7%1354.2%
Female1946.3%1145.8%
Primary ESRD CauseNephrologic/Other3175.6%1875.0%
Urologic/Obstructive1024.4%625.0%
Type of DialysisNo dialysis/pre-emptive transplant717.1%416.7%
Hemodialysis1536.6%833.3%
Peritoneal Dialysis1639.0%1041.7%
Both types of dialysis in past37.3%28.3%
Dialysis Duration (Months)17.56.828.715.64.626.6
Height (cm)128.393.0154.0129.0100.4155.6
Weight (kg)28.016.043.828.817.543.8
Type of DonorDeceased3995.1%2395.8%
Living24.9%14.2%
Pre-operative urine output (mL/kg/hr).3.01.8.6.12.0
Cold ischemia time (minutes)540.0408.0705.0536.0308.5720.0
Warm ischemia time (minutes)42.032.049.045.042.057.0
Operative time (minutes)276.0226.0350.0213.0100.0231.5
Estimated blood loss (mL)150.070.0213.011.510.312.0
Donor kidney length (cm)10.910.311.6536.0308.5720.0


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