Dear Editor, Renal transplantation is the gold standard treatment for end-stage renal disease and offers superior outcomes compared with dialysis. Preemptive transplantation performed before dialysis initiation is associated with better outcomes; however, limited donor availability often necessitates placement on a waitlist and the start of dialysis.1 Marginal kidneys are increasingly accepted to expand the donor pool, including those with conditions that once were considered as relative contraindications, such as nephrolithiasis, and sometimes are managed with back-table stone removal before transplantation.2 This remains an off-label practice as the current guidelines are not well defined. We report our center’s experience with back-table stone removal from both living and deceased donors, aiming to provide data to help standardize this approach. This study received IRB approval (approval no. STUDY-25-01494), and informed consent was obtained from all participants. We retrospectively reviewed the electronic medical records of 7 patients. Surgical data were recorded in real time and analyzed postoperatively to assess the procedural outcomes. Continuous variables are reported as mean (range). Herein, we present 4 cases of ex vivo stone removal from donor kidneys: 3 from living donors (LDs) and 1 from a donor after circulatory death (DCD). These procedures added approximately 20 minutes to the ischemia time in each case. 1. Living donor cases All LDs were healthy adults (mean age, 51 years; range, 44–64 years) who underwent an evaluation for potential kidney donation. Preoperative screening included an abdominal computed tomography scan, which revealed renal calculi in all donors, with a mean largest diameter of 3.33 mm (range, 3–4 mm). None of the patients had any history of kidney stones. The decision was made to proceed with donation, with plans for back-table ureteroscopy for stone removal. Kidney procurement was performed robotically via the single-port approach in 2 cases and laparoscopically in the third. Flexible ureteroscopy was performed through the distal ureter to identify stones in the upper or interpolar poles. Intact stones were extracted using a zero-tip basket to achieve complete clearance in all cases. Subsequently, kidneys were successfully transplanted into the recipients. Ureteral stenting was performed in all patients (Table 1). Table 1 - Case summary. Case #1 Case #2 Case #3 Case #4 Stone characteristics Maximum diameter, mm 4 3 3 10 Hounsfield units 250–300 100–150 100–150 N/A Location Left Interpolar pole Left Interpolar to lower pole Left Upper Pole Right Ureter Stone number 1 1 1 1 Main component Calcium Oxalate Calcium Oxalate N/A Calcium Phosphate Procedure characteristics Ureteroscope used 7.5-Fr Pusen flexible ureteroscope 8.5-Fr Olympus flexible ureteroscope 7.5-Fr Pusen flexible ureteroscope 8.5-Fr Olympus flexible ureteroscope Techniques for stone extraction Stone basketing Stone basketing Stone basketing Ureterolithotomy and basketing Residual fragments No No No Yes Ureteral stent placement Yes Yes Yes Yes Period of ureteral stent indwelling 25 days 38 days 31 days 55 days Cold Ischemia time, min 70 53 38 1149 Warm Ischemia time, min 3.6 2.6 4.3 43 Donor characteristics Age, yr 44 64 44 35 Sex Female Female Male Male BMI, kg/m2 31.6 27.3 22.3 29.5 Condition Live unrelated Live unrelated Live related DCD Recipient characteristics Age, yr 47 75 42 58 Sex Female Male Male Male BMI, kg/m2 25.3 29.1 24.4 23.3 Perioperative complications 0 0 0 ATN and Urosepsis Stone events 0 0 0 1 Time to event, mo - - - 15 ATN = acute tubular necrosis; BMI = body mass index; Fr = French; N/A = not available. Indwelling ureteral stents were removed from the recipients after a mean of 31.3 days (range, 15–38 days). None of the LDs or recipients developed complications. Their creatinine was in normal range (0.7–1.3 mg/dL) after one year of follow-up, except for one of the donors who had a serum creatinine of 1.54 mg/dL (Fig. 1). Overall, after a mean follow-up period of 21 months (range, 13–40 months), no donor or recipient experienced stone recurrence or ureteral complications.Figure 1.: (A) Trends of Donor creatinine over time. (B) Trends of recipient creatinine over time.2. Donor after circulatory death case The DCD donor was a 35-year-old man who died from anoxic brain injury. The presence of renal calculus was unknown before transplantation. Following reperfusion, attempts to pass a stent through the ureter were unsuccessful because of proximal obstruction. Flexible ureteroscopy with a basket failed to remove the stone, necessitating ureterotomy. The stone was fragmented; the largest piece was removed through the incision, and the 2 smaller renal pelvic fragments were retrieved ureteroscopically. The ureter was closed, a double-J stent was placed, and the ureteroneocystostomy was completed. The transplantation was performed without further complications (Table 1). On postoperative day (POD) 9, the patient was readmitted with acute tubular necrosis requiring transient dialysis and on POD 21 with urosepsis. Imaging revealed a lower pole calculus in the transplanted kidney. After antibiotic treatment, transplant ureteroscopy showed a dense ureteral stricture, which was dilated, and a 3-mm stone, which was fragmented and extracted. The kidney was rendered stone-free, and the ureteral stent was replaced with a thicker double-J stent and removed on POD 55 (Table 1). Stone analysis matched the original transplanted stone, indicating a residual fragment. The patient remained free of further complications over 74 months, with serum creatinine between 1.72 and 2.23 mg/dL (Fig. 1). A 3-mm nonobstructing stone at the ureterovesical junction, detected on a 15-month computed tomography scan, remained stable until 66-month posttransplant. Our series demonstrated that back-table procedures on allograft kidneys can be performed safely before implantation, as all recipients and LDs maintained adequate renal function with minimal complications during follow-up. These findings are consistent with the existing literature supporting the safety and feasibility of ex vivo ureteroscopic stone removal and pyelo- or ureterolithotomy.3,4 We further demonstrated that these approaches are feasible for both LDs and DCDs. Donor type did not appear to influence overall outcomes, consistent with previous reports describing comparable results across donor categories.3 However, in our cohort, recipients of LD kidneys experienced fewer postoperative complications and better graft function than recipients of DCD kidneys. This difference may reflect limited preoperative preparation, as allograft stones were not identified before surgery in the DCD case. Concerns have been raised that performing stone removal before vascular anastomosis may prolong ischemia time and adversely affect transplant outcomes.5 Consequently, treating allograft nephrolithiasis after reperfusion but before ureteral anastomosis was suggested.5 Comparative data on these approaches are limited. In our study, the DCD allograft underwent stone removal after reperfusion; however, the recipient experienced more complications and worse long-term graft function. These findings must be interpreted cautiously, as the DCD case involved a larger stone burden and occurred under emergency conditions, which may have influenced the outcomes. Taken together, our observations highlight the importance of preoperative stone identification and careful procedural planning to optimize outcomes, as well as the safety and feasibility of ex vivo stone management, which appears to have a minimal impact on renal function over time in both donors and recipients. Nonetheless, our sample was small with a relatively short follow-up period, which represents the main limitation of this study. In summary, back-table management of allograft nephrolithiasis seems to be a viable strategy for safely expanding the donor pool. Continued research, particularly prospective studies, is essential to refine protocols, confirm long-term safety, clarify the optimal timing, and minimize ischemia-related risks. Acknowledgments None. Statement of ethics This study received Icahn School of Medicine at Mount Sinai Institutional Review Board approval (Approval no. STUDY-25-01494), and informed consent was obtained from all participants. All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Conflict of interest statement The authors declare that they have no conflicts of interest. Funding source None. Author contributions IG: Participated in research design, writing of the paper, performance of the research, contributed new reagents or analytic tools, data analysis; SJDT: Participated in the writing of the paper, contributed new reagents or analytic tools; AIB: Participated in research design, contributed new reagents or analytic tools; RS: Participated in the writing of the paper, research design, contributed new reagents or analytic tools; SSF: Participated in research design, contributed new reagents or analytic tools; MAP: Participated in research design, writing of the paper, performance of the research, contributed new reagents or analytic tools, data analysis. Data availability The datasets generated during and/or analyzed during the current study are available from the corresponding author upon reasonable request.
Gondolesi et al. (Mon,) studied this question.