Ureteroscopy for renal allograft lithiasis: institutional experience and global insights from a systematic review
Review Article

Ureteroscopy for renal allograft lithiasis: institutional experience and global insights from a systematic review

Jun Heng Lim1#, Xinyan Yang1#, Tsung Wen Chong1, Edwin Jonathan Aslim1, Valerie H. L. Gan1,2, Lay Guat Ng1, Kazumi Taguchi3, Yadong Lu1 ORCID logo

1Department of Urology, Singapore General Hospital, Singapore, Singapore; 2SingHealth Duke-NUS Transplant Centre, Singapore, Singapore; 3Department of Nephro-Urology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan

Contributions: (I) Conception and design: JH Lim, X Yang, TW Chong, Y Lu; (II) Administrative support: EJ Aslim, VHL Gan, LG Ng; (III) Provision of study materials or patients: TW Chong, EJ Aslim, LG Ng, VHL Gan, Y Lu; (IV) Collection and assembly of data: JH Lim, X Yang, VHL Gan; (V) Data analysis and interpretation: All authors; (VI) Manuscript writing: All authors; (VII) Final approval of manuscript: All authors.

#These authors contributed equally to this work.

Correspondence to: Yadong Lu, MD. Department of Urology, Singapore General Hospital, Outram Road, Singapore 169608, Singapore. Email: yadong.lu@yahoo.com.

Background: Renal allograft lithiasis (RAL) is a rare but potentially serious complication following kidney transplantation. Traditionally, ureteroscopy (URS) has been considered a second-line treatment for stones <15 mm, typically after failed extracorporeal shock wave lithotripsy (ESWL), due to concerns over challenging ureteral access. This study reviews Singapore General Hospital (SGH)’s experience and compares outcomes with published literature to evaluate efficacy and safety.

Methods: Retrospective review was conducted on RAL cases treated with URS at SGH from January 2015 to December 2023. Data collected included demographics, end-stage renal failure etiology, preoperative biochemistry, stone characteristics, and surgical details. Stone-free status and complications were assessed. Additionally, a systematic literature review was performed using five databases (PubMed, Embase, Web of Science, SCOPUS, Cochrane Library) from inception up to August 13, 2023. We included all primary studies with no restriction on study design, published in English, including conference abstracts and excluded articles on ex-vivo or pre-transplant URS. Risk of bias assessment was performed using Joanna Briggs Institute Critical Appraisal Tools.

Results: Five URS procedures were performed at SGH for RAL during the study period, yielding a stone-free rate (SFR) of 71.4%. One case involved an encrusted double-J (DJ) stent. The systematic review included 30 studies (10 case reports, 20 case series) totaling 145 URS procedures. The overall SFR was 82.3%. Thirteen complications (9.0%) were reported, including ureteral perforation (n=3), urinary tract infections (n=3), and nephrocutaneous fistula (n=2). No graft loss was reported. These rates are comparable to those seen in non-transplant URS.

Conclusions: URS appears to be a safe and effective treatment for RAL, with outcomes comparable to non-transplant populations. Increasing evidence supports URS as a first-line option in select transplant patients. The current evidence is limited by small case numbers, retrospective study designs, and lack of standardisation in defining and assessing stone-free outcomes.

Keywords: Renal allograft lithiasis (RAL); ureteroscopy (URS); kidney transplantation; endourology; stone-free rate (SFR)

Submitted Aug 12, 2025. Accepted for publication Nov 04, 2025. Published online Dec 18, 2025.

doi: 10.21037/tau-2025-574

Highlight box

Key findings

• Evidence from both our case series and systematic review indicates that ureteroscopy (URS) is a safe and effective first-line treatment for renal allograft lithiasis (RAL).

What is known and what is new?

• Historically, URS has been considered a second-line treatment for stones <15 mm, typically only used after failed extracorporeal shock wave lithotripsy, due to concerns over challenging ureteral access.

• Our case series of five patients had a stone-free rate (SFR) of 71.4% and our systematic review of 30 studies encompassing 145 ureteroscopic procedures demonstrated an overall SFR of 82.3% for a mean stone diameter of 10.3 mm. The reported complication rate of 9.0% was comparable to that observed in non-transplant populations. Collectively, these findings support URS as a safe and efficacious option in renal transplant recipients.

What is the implication and what should change now?

• URS should be considered a first-line treatment modality for RAL. However, procedural success is influenced by several transplant-specific factors, including altered anatomy, ureteral angulation, smaller ureteric lumen, prior surgical scarring, adhesions, and the type of ureteral anastomosis. Future studies evaluating the roles of preoperative antegrade access, endoscopic combined intrarenal surgery, ureteral access sheaths, and direct in-scope suction may further refine URS techniques and improve outcomes in renal allograft patients.

Introduction

Renal allograft lithiasis (RAL) is an uncommon but potentially devastating complication in transplant patients. RAL has an incidence of 0.1–6.3% (1). If left untreated, RAL can be a cause of sepsis, obstruction and potential graft loss (2). Timely diagnosis and effective treatment of RAL is essential in preserving graft function (3).

Diagnosing RAL can be challenging as the transplant kidney is denervated and renal colic or graft tenderness is typically absent (1,2). Hence, RAL typically has a late presentation with patients presenting with graft dysfunction or sepsis. Occasionally, mild discomfort may be felt over the graft due to distention of overlying soft tissue (2), but hydronephrosis is typically significant by this point.

Anatomically, the non-native location of the kidney presents challenges for treatment. Similar to native kidneys, management options include extracorporeal shockwave lithotripsy (ESWL), ureteroscopy (URS) and percutaneous nephrolithotomy (PCNL). In particular, for stones <15 mm, URS has been less favoured compared to ESWL (4) due to difficulty in achieving retrograde access in an anteriorly sited ureteroneocystostomy, as well as ureteral tortuosity. Hence, URS has typically been used as a second-line management after failure of ESWL. With the advent of smaller flexible ureteroscopes, holmium:yttrium-aluminum-garnet (Ho:YAG) laser (4,5) and improved flexion-deflexion capabilities (3) of flexible ureteroscopes, the viability of URS in RAL has greatly improved.

In this paper, we summarized Singapore General Hospital (SGH)’s experience with treating RAL using URS and compare it with a systematic review of currently available data. We present this article in accordance with the PRISMA reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-2025-574/rc).

Methods

Clinical records review

A clinical audit was conducted on patients who underwent URS for urolithiasis between January 2015 and December 2023 at SGH, the largest renal transplant center in Singapore within the SingHealth cluster. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Institutional Review Board of SingHealth (IRB No. 2025-0907). As this was a retrospective study involving de-identified data, patient consent was waived. Data were filtered for cases involving renal allograft and the diagnosis of RAL was confirmed by computed tomography (CT) scan. Stone burden was defined as the maximum stone diameter measured on preoperative imaging. Patients’ biodata, date and type of renal transplant, etiology of end-stage renal failure (ESRF), pre-operative biochemical investigations (serum creatinine, serum calcium, serum uric acid, urinary pH), stone characteristics [size, number, location, presence of hydronephrosis, Hounsfield unit (HU)], operative techniques [usage and size of ureteral access sheath (UAS), antegrade/retrograde access, type of ureteroscope used] were collected. Patient’s stone-free rate (SFR) was assessed using ultrasound (US) or CT. All patients were maintained on standard triple immunosuppressive therapy (tacrolimus, mycophenolate mofetil, and prednisolone) according to institutional transplant protocol. All patients were followed longitudinally in our transplant program lifelong, with routine graft surveillance and serum creatinine monitoring.

Systematic review

Study selection

Five databases (PubMed, Embase, Web of Science, SCOPUS, Cochrane Library) were searched from inception to 13 August 2023. The search strategy included the following terms: renal/kidney transplant/graft, ureteroscopy, retrograde intrarenal surgery. We included all primary studies with no restriction on study design, published in English, including conference abstracts and excluded articles on ex-vivo or pre-transplant URS. While PCNL and micro-PCNL procedures were excluded, we have included procedures involving endoscopic combined intrarenal surgery (ECIRS).

Data extraction

After removal of duplicates, article title and abstracts were screened. Full texts were analysed to confirm the studies’ inclusion where available. Two independent investigators screened abstracts and full texts, with disagreements resolved by a third reviewer. Data were extracted from the SGH registry by one investigator, while another investigator performed data extraction from the selected studies. A standardised data collection form was developed to collect information such as study design, date, location, patient characteristics (age, gender, time from renal transplantation, type of renal transplant), stone characteristics (number, size, location, composition), operative technique (ureteroscope used, laser used, UAS used, antegrade/retrograde access), outcome measures (SFR, operative time, follow-up, complications). The primary outcome was SFR, while secondary outcomes included mean age, interval from transplant, size and location of stones, most common symptoms, operative techniques, and post-procedural complications. We performed backward citation search for all relevant and available secondary studies to find relevant primary studies fulfilling the above criteria. Due to heterogeneity in study design, outcomes, or reporting, results were synthesised descriptively.

Risk of bias assessment

As articles found included a combination of case reports and case series, risk of bias assessment was performed using Joanna Briggs Institute Critical Appraisal Tools checklist for case reports and case series respectively and is summarised in Tables 1,2.

Table 1

Risk of bias assessment for case reports

First author [year] (Ref.) Were patient’s demographic characteristics clearly described? Was the patient’s history clearly described and presented as a timeline? Was the current clinical condition of the patient on presentation clearly described? Were diagnostic tests or assessment methods and the results clearly described? Was the intervention(s) or treatment procedure(s) clearly described? Was the post-intervention clinical condition clearly described? Were adverse events (harms) or unanticipated events identified and described? Does the case report provide takeaway lessons?
Brafman et al. [2016] (6) + + − − + + ? +
Santillán et al. [2021] (7) + + + + + + + +
Sugino et al. [2023] (8) + + + + + + + +
Jo et al. [2016] (9) + + + + + + ? +
Singh et al. [2015] (10) − + + − + + − +
Kuroda et al. [2019] (11) + + + + + + + +
Li et al. [2020] (12) + + + + + + + +
Mitsui et al. [2017] (13) + + + + + + + +
Hadidi et al. [1995] (14) + + + + + + + +
Gupta et al. [2023] (15) + − − − + + + +

+, yes; −, no; ?, unclear.

Table 2

Risk of bias assessment for case series

First author [year] (Ref.) Were there clear criteria for inclusion in the case series? Was the condition measured in a standard, reliable way for all participants included in the case series? Were valid methods used for identification of the condition for all participants included in the case series? Did the case series have consecutive inclusion of participants? Did the case series have complete inclusion of participants? Was there clear reporting of the demographics of the participants in the study? Was there clear reporting of clinical information of the participants? Were the outcomes or follow up results of cases clearly reported? Was there clear reporting of the presenting site(s)/clinic(s) demographic information? Was statistical analysis appropriate?
Challacombe et al. [2005] (16) + + + + + + + + − +
Rhee et al. [1999] (17) + ? + ? ? + + + − +
Sevinc et al. [2015] (3) + + + + + + − + − +
Lai et al. [2017] (18) + + + + + ? ? + − +
Hyams et al. [2012] (19) + ? ? + + + + + − +
Yuan et al. [2015] (20) + + + + ? + + + − +
Del Pizzo et al. [1998] (21) + − + + + − − + − +
O’Kelly et al. [2020] (22) + + + + + + + − − NA
Patterson et al. [2022] (23) + ? ? + + − + + − +
Sarier et al. [2019] (24) + + + + ? + − + − +
Gerber et al. [2021] (5) + + + ? ? + + + − +
Swearingen et al. [2015] (25) + ? ? + + + + + − +
Hosseini et al. [2009] (26) + ? ? ? ? + − + − +
Ulker et al. [2019] (27) + ? ? ? ? − + + − +
Basiri et al. [2006] (28) + ? ? + + − − + − +
Li et al. [2011] (29) + − + ? ? + + + − +
Rifaioglu et al. [2008] (30) + ? ? ? ? + ? + − +
Friedersdorff [2017] (31) + + + + + + + + − +
Klingler et al. [2001] (32) + + + + + + − + − +
Emiliani et al. [2018] (33) + − + + + + + + − +

+, yes; −, no; ?, unclear. NA, not applicable.

Results

Clinical records review

A total of five renal transplant recipients underwent surgical treatment for RAL at SGH from January 2015 to December 2023 (Tables 3,4). One of these patients had undergone dual renal transplantation. Forty percent of the patients were male, and the mean age at the time of RAL diagnosis was 53±8 years. Eighty percent of the patients were recipients of deceased donor kidneys. Two patients received allografts from standard-criteria donors, while two patients received allografts from extended-criteria donors. One patient underwent transplant surgery at an overseas center; therefore, donor information was unavailable. All patients underwent ureterovesical (UV) anastomosis.

Table 3

Biodata of patients with RAL who underwent URS in SGH

Patient Age at time of stone surgery (years) Gender Race Symptoms at diagnosis Co-morbidities Pre-existing donor urolithiasis Previous stone surgery Interval from transplant to stone surgery (months) Living or deceased donor Single or dual transplant Type of ureteric anastomosis
1 62 F Chinese Nil ESRF from IgA nephropathy, hyperlipidemia Yes Nil 14 Deceased Dual UV
2 49 F Chinese Graft discomfort, decreased urine output ESRF from FSGS, hypertension No Nil 52 Deceased Single UV
3 66 M Malay Nil ESRF unknown cause Unknown Nil 115 Living Single UV
4 50 F Chinese Fever ESRF from chronic glomerulonephritis, hypertension, hyperlipidemia Yes Failed ESWL ×2 13 Deceased Single UV
5 53 M Malay Haematuria Not available Yes Not available Not available Deceased Single UV

ESRF, end-stage renal failure; ESWL, extracorporeal shock wave lithotripsy; F, female; FSGS, focal segmental glomerulosclerosis; IgA, immunoglobulin A; M, male; RAL, renal allograft lithiasis; SGH, Singapore General Hospital; URS, ureteroscopy; UV, ureterovesical.

Table 4

Stone characteristics, operative techniques and outcome measures for patients with RAL who underwent URS in SGH

Patient Stone number Stone burden (mm) Stone location Presence of hydronephrosis Pre-stenting Indication for pre-stenting If access sheath used Operative time (min) Stone composition Stone free status
1 2 7 Mid ureter of superior kidney Yes No NA No 57 Calcium oxalate, sodium urate Yes
4 Lower pole of inferior kidney
2 1 8 Ureter Yes Yes Anuric Yes 116 Calcium oxalate, calcium phosphate Yes
3 2 5 Distal ureter No Yes Failed first attempt at retrograde access due to tight ureter Yes 230 Calcium oxalate No (4-mm residual stone)
4 Distal ureter
4 1 7 Mid-lower pole No No NA Yes 80 Calcium oxalate, calcium phosphate No (3-mm residual stone)
5 1 11 Renal pelvis No Yes 2 failed attempts at retrograde access due to tight neo-ureteric orifice No 111 Not available Yes

NA, not applicable; RAL, renal allograft lithiasis; SGH, Singapore General Hospital; URS, ureteroscopy.

Only one patient was symptomatic at presentation, reporting graft discomfort and decreased urine output. Intervention for asymptomatic or donor-derived stones was performed either in the setting of graft dysfunction or to prevent future obstruction or infection. One asymptomatic calyceal stone was treated due to recurrent urinary tract infections (UTIs). The mean interval from transplant to stone surgery was 54 months (range, 13–115 months). A total of seven stones were identified in six allografts, with a mean ± standard deviation (SD) stone diameter of 6.6±2.5 mm. Three of the seven stones were pre-existing donor urolithiasis. Three patients had ureteric calculi, one patient had a renal calyceal calculus, and one patient had a calculus located in the renal pelvis. The renal calyceal calculus was treated due to recurrent UTIs. The mean ± SD HU for the stones was 995±534. Two patients had mixed calcium oxalate and calcium phosphate stones, one patient had a mixed calcium oxalate and sodium urate stone, and one patient had a calcium oxalate stone.

All cases were performed using flexible ureteroscope via retrograde approach. Three patients underwent pre-stenting due to indications of anuria and failed upfront retrograde access. UAS was used in three of the five patients. Additionally, three patients received post-operative antibiotics as per institutional protocol for asymptomatic bacteriuria or prophylaxis. They were not considered postoperative infections.

The SFR was 71.4% (5 of 7 stones), as defined by complete stone clearance. Patient 3 experienced failed retrograde access for URS due to acute angulation of the transplant ureteric orifice, exacerbated by a high bladder neck. The patient subsequently underwent antegrade nephroureteric stent insertion, followed by successful URS, laser lithotripsy, and double-J (DJ) stent insertion. Antegrade access facilitated the insertion of disposable flexible ureteroscope into the transplant ureter. The distal ureteric stones were fragmented and evacuated using a basket. However, the mid-to-upper transplant ureter was extremely tight, necessitating the placement of a 4.8-Fr DJ stent at the end of the procedure. Postoperatively, the patient developed persistent extended-spectrum beta-lactamase Escherichia coli UTI. During DJ stent removal 2 months later, the proximal coil was found to be encrusted and couldn’t be removed. A subsequent attempt at flexible URS was unsuccessful due to the tight proximal allograft ureter. The patient ultimately underwent successful ECIRS with mini-PCNL, DJ stent removal, and transplant ureter dilation to 12 Fr. Postoperative CT showed a 4-mm residual stone in the lower pole of the allograft. Patient 5 underwent pre-stenting (6 Fr) before ureteric dilation (up to 12 Fr). However, insertion of 11/13 Fr UAS failed, necessitating placement of a new 7-Fr stent. The patient subsequently underwent graft URS three weeks later. Despite another attempt to insert 11/13 Fr UAS, the procedure was unsuccessful. Flexible ureteroscope was advanced into the renal pelvis via a guidewire, but the 275-micron laser fiber couldn’t be inserted due to resistance at the tip of the flexed ureteroscope. The patient underwent two sessions of ESWL for complete stone clearance, which was confirmed on follow-up CT. Renal function for all patients returned to baseline post-operatively, and none required blood transfusions. No long-term ureteral strictures or graft loss were observed during follow-up.

Systematic review

A total of 30 studies were included (Figure 1), consisting of 10 case reports and 20 case series with a total of 145 ureteroscopic procedures (Table 5).

Figure 1 PRISMA diagram with inclusion and exclusion criteria. RIRS, retrograde intrarenal surgery.

Table 5

Characteristics of included studies

First author [year] (Ref.)    Study characteristics    Demographics
Country Study design Recruitment period Sample size Mean age of diagnosis (years) Gender (% male) Aetiology of ESRF Mean interval from transplant (years) No. of DDRT No. of LDRT Type of urinary anastomosis Immunosuppression
Brafman et al. [2016] (6) USA Case report NA 1 71 0 – 2 – – – –
Challacombe et al. [2005] (16) UK Case series 1977–2003 2 38 38 (I) Genitourinary TB, adenocarcinoma 6 1 1 Lich-Gregoir extravesical ureteroneocystostomy with extravesical seromuscular tunnel Cyclosporin + prednisolone
(II) Dysplastic R kidney, Hinman syndrome, neuropathic bladder
Rhee et al. [1999] (17) USA Case series January 1984–October 1995 1 34 0 – 0.5 1 – – –
Sevinc et al. [2015] (3) Turkey Case series February 2008–December 2014 6 55.3 50 – – – – – –
Lai et al. [2017] (18) China Case series January 2010–January 2015 6 54.7 – – – – – – –
Santillán et al. [2021] (7) Argentina Case report – 1 27 0 Perinatal asphyxia syndrome 10 – – Upside-down implantation with ureteric anastomosis following Lich-Gregoir technique MMF + prednisolone + tacrolimus
Hyams et al. [2012] (19) USA Case series 2006–2011 12 42 50 – 7.3 5 7 – –
Sugino et al. [2023] (8) Japan Case report – 1 66 100 Diabetic nephropathy + arteriosclerosis obliterans 10 1 – Lich-Gregoir –
Yuan et al. [2015] (20) China Case series August 2000–July 2014 6 53 33 Diabetic nephropathy (×3), obstructive uropathy (×1), hypertensive nephropathy (×1), unknown (×1) 2.0 6 – Extravesical ureteroneocystostomy MMF + prednisolone + tacrolimus/cyclosporin
Del Pizzo et al. [1998] (21) USA Case series July 1991–September 1996 4 – – – – – – – –
Jo et al. [2016] (9) South Korea Case report – 1 47 0 – – – – – –
O’Kelly et al. [2020] (22) Ireland Case series April 2019–April 2020 4 67.5 0 – 14 4 – – –
Patterson et al. [2022] (23) Ireland Case series 2019–2022 10 62 – – 12.8 – – – –
Sarier et al. [2019] (24) Turkey Case series November 2009–January 2017 18 42.5 72 – 2.2 – 18 Extravesical Lich-Gregoir MMF + prednisolone + tacrolimus/cyclosporin
Singh et al. [2015] (10) India Case report – 1 – – – 0.4 – – – –
Gerber et al. [2021] (5) USA Case series January 2009–January 2018 18 53.6 44 – – – – Lich-Gregoir technique (×15), ureteroureterostomy (×1), cutaneous ureterostomy (×1), Politano-Leadbetter technique (×1) –
Swearingen et al. [2015] (25) USA Case series June 2009–September 2013 7 60 (range, 40–72) 42.9 Obstructive uropathy (×1), T1DM (×3), T2DM (×1), reflux nephropathy (×1), polycystic kidney disease (×1) 7.4 (range, 4–10) 3 4 – –
Hosseini et al. [2009] (26) Iran Case series July 2004–March 2008 4 50.7 100 – – – – – –
Kuroda et al. [2019] (11) Japan Case report – 1 46 100 – 15 – 1 – –
Ulker et al. [2019] (27) Turkey Case series 2016–2018 3 47.6 – – 5.2 – – Ureteroureterostomy –
Li et al. [2020] (12) China Case report – 2 35.7 100 – 6.7 2 – – MMF + prednisolone + tacrolimus
Mitsui et al. [2017] (13) Japan Case report – 1 40 100 IgA nephropathy 1 – 1 End-to-end ureteroureterostomy MMF + prednisolone + tacrolimus + basiliximab
Basiri et al. [2006] (28) Iran Case series June 1989–February 2002 6 – – – – – – Leadbetter/Politano or Lich/Gregoir –
Li et al. [2011] (29) China Case series 1979–2009 2 30.5 50 – 0.3 – – – MMF/azathioprine + prednisolone + tacrolimus/cyclosporin
Rifaioglu et al. [2008] (30) USA Case series 1997–2007 8 48 50 – 0.4 7 1 – –
Friedersdorff [2017] (31) Germany Case series 2002–2014 5 61.3 0 Kidney shrinkage (×1), MPGN (×1), HSP (×1), secondary oxalosis (×1), nephrocalcinosis (×1) 2.2 5 – Leadbetter-Politano, 3-stitch, and 2-stitch techniques –
Hadidi et al. [1995] (14) Jordan Case report – 1 21 100 CGN 2 – 1 – Prednisone + azathioprine
Klingler et al. [2002] (32) Austria Case series November 1993–December 2000 1 65 42 – 2.6 – – – Cortisone + cyclosporin A
Gupta et al. [2023] (15) USA Case report – 1 72 100 – 6 – – – –
Emiliani et al. [2018] (33) Spain, Italy Case series 1982–2017 11 – – – – – – – Azathioprine + prednisolone + tacrolimus/cyclosporin

CGN, chronic glomerulonephritis; DDRT, deceased donor renal transplant; ESRF, end-stage renal failure; HSP, Henoch-Schönlein purpura; IgA, immunoglobulin A; LDRT, living donor renal transplant; MMF, mycophenolate mofetil; MPGN, membranoproliferative glomerulonephritis; NA, not applicable; T1DM, type 1 diabetes mellitus; T2DM, type 2 diabetes mellitus; TB, tuberculosis.

Demographics

The mean age at diagnosis of RAL was 50.9 years and 52.1% of patients were male. Of 69 procedures with reported symptoms at diagnosis, 27 presented with infection, 15 presented with acute kidney injury including oliguria/anuria, 16 presented with pain/discomfort and 11 presented with haematuria. Seven cases of RAL were reported to be incidental findings on routine imaging. Among the 89 cases in which the interval from transplantation to presentation was reported, the mean duration was 5.4 years. Of the patients whose transplant type was specified, 35 underwent deceased donor transplantation and 34 received living donor transplantation. Aetiology of ESRF, type of urinary anastomosis and immunosuppressive regime were inconsistently reported (6, 9, and 9 studies respectively).

Stone characteristics

The mean stone size was 10.3 mm (range, 3–21 mm). Stone location was reported as ureteral in 63 cases, renal in 24 cases, ureteropelvic junction or renal pelvis in 13 cases, and multiple sites in 15 cases. Out of 34 stones analysed, 19 were calcium oxalate stones, 6 were calcium phosphate stones, 2 were uric acid stones, 3 were struvite stones and 4 were mixed stones.

Operative technique

The mean operative time where reported was 72.9 min (range, 45–150 min) amongst 48 cases. UAS were used in 26 cases. Where reported, there were 105 retrograde, 31 antegrade and 4 combined antegrade/retrograde procedures. Laser lithotripsy was reported to be used in 71 cases and used an Ho:YAG laser where specified.

Outcomes

The average SFR is 82.3%. Imaging used to determine stone-free status post-operatively or during follow-up included US in 48 patients, CT in 21 patients, X-ray in eleven patients and nephrostogram in 11 patients. Where reported, stone-free status was defined to be complete stone-free status in 13 studies, while one study defined SFR to be fragments <3 mm. The SFR was higher in antegrade URS (23/24, 96%) than in retrograde URS (67/81, 82.7%), and was higher with the use of retrograde semirigid URS (19/21, 90.5%) than with flexible URS (28/34, 82.4%).

Out of all 145 procedures, 13 post-operative complications were reported (9.0%) (Table 6), with three cases of ureteral perforation, three cases of UTI and two cases of nephrocutaneous fistula. Ten studies reported no complications. There was no reported graft failure as a result of RAL or surgery.

Table 6

Complications of URS/RIRS for RAL

Complication N Incidence rate (%)
UTI 3 2.1
Ureteral perforation 3 2.1
Nephrocutaneous fistula 2 1.4
Ureteral stent encrustation 1 0.7
Hematuria 1 0.7
Ureteral stenosis 1 0.7
Retained stone fragments due to distal ureteral stricture 1 0.7
Not specified 1 0.7
Total 13 9.0

RAL, renal allograft lithiasis; RIRS, retrograde intrarenal surgery; URS, ureteroscopy; UTI, urinary tract infection.

Risk of bias assessment

Most case reports adequately reported the patient’s clinical status and subsequently treatment, but some were unclear on the imaging modality for diagnosis of RAL. However, as conference abstracts were included, details such as consecutive and total inclusion of participants were not clear for some studies. The overall quality of evidence is generally low in view of study design, heterogeneity and sparse reporting of relevant variables of interest.

Discussion

This is the largest reported case series to date for ureteroscopic treatment of RAL in Singapore, contributing regionally relevant data to the global evidence base. However, the sample size remained limited due to the scarcity of transplant kidneys, low incidence of RAL and stringent donor selection criteria, particularly for living donors.

Majority of symptomatic patients presented with complications of urolithiasis such as sepsis and obstructive uropathy rather than pain. Diagnosis of an obstructing urinary calculus is often reached during workup for graft failure instead (34). There is also likely a large proportion of RAL detected incidentally on routine imaging, but the exact prevalence remains unclear due to limited data reported in the included studies. Early detection of RAL through routine imaging is desirable and a high index of suspicion is important as symptoms often suggest a late diagnosis. Delayed treatment can lead to severe consequences, including graft loss and overwhelming urosepsis, particularly in immunosuppressed renal transplant patients.

Compared to non-transplant recipients, renal transplant recipients have additional risk factors for urolithiasis which can be divided into metabolic and urodynamic (20). In patients with chronic kidney disease (CKD), tertiary hyperparathyroidism and low urine output are contributing factors to urolithiasis. Specific transplant-related causes of urolithiasis include pre-existing donor urolithiasis, ureteral obstruction secondary to anastomotic stricture, immunosuppressive medications particularly cyclosporine (causing hyperuricosuria) and glucocorticoids (causing hyperuricemia, hypercalciuria), and nonabsorbable suture material (1,19,35). Position of the renal allograft can also affect urinary drainage and predispose to RAL formation (36). The vast majority of stones both in our series and in literature are composed of calcium oxalate and phosphate, which suggests that immunosuppressive medication and UTI do not contribute significantly to stone formation for renal transplant recipients. Prevention of RAL should be directed at investigating and correcting metabolic abnormalities that can contribute to the development of RAL (16,19,24,31,37). The work-up or reporting of such predisposing metabolic abnormalities is sparse—only five included studies reported such data. Prevention and treatment of ureteral obstruction with methods such as perioperative stenting can minimise urinary stasis and reduce incidence of RAL (38).

While ESWL may be considered first-line treatment for RAL <15 mm due to its non-invasive nature, it’s limited by the bony pelvis for a transplant sited in the iliac fossa, which can impair localisation of calculi and block shockwaves (3,39). Furthermore, abnormal ureteral orientation, ureteral tortuosity and non-native UV junction may impair stone clearance and increase the risk of steinstrasse (3). This necessitates close monitoring for ureteral obstruction which may be asymptomatic in the case of renal transplant recipients (39). Multiple sessions may be required, each incurring a risk of parenchymal injury or hematoma (5). Ex vivo URS of donor grafts can clear stones before implantation in a controlled setting without compromising graft function. Reports show high SFRs with low complications for small, incidental donor stones (40). Incorporating this step may reduce post-transplant lithiasis and streamline recipient care.

The SFR for URS in RAL is 82.3% among included studies for mean stone diameter of 10.3 mm. This suggests that URS is a viable choice for RAL, although it can be technically challenging. The success of URS is dependent on the interaction of multiple factors not limited to stone location and size. There are factors specific to allografts that make retrograde access challenging:

  • Altered anatomy and ureteral angulation:Retrograde ureteral access is more challenging in RAL due to a more anteriorly sited UV anastomosis (3,8), ureteral tortuosity (22) and non-native ureteral orientation as a result of pelvic location of allograft that would require a greater degree of secondary deflection of ureteroscope (41,42).
  • Smaller ureteric lumen:
    The ureters in renal allografts are often narrower in diameter and may develop strictures as a result of compromised vascular supply, recurrent infections, or prior episodes of rejection, further increasing the complexity of endoscopic access.
  • Surgical scarring and adhesions:
    Scarring and adhesions following the transplant may contribute to increased ureteral tortuosity, thereby compromising retrograde access.

A posterolateral extravesical ureterocystostomy (e.g., modified Lich-Gregoir method) has been shown to increase the success rate of retrograde ureteric access as it results in a more anatomical location for the ureteric neo-orifice (24). Preoperative antegrade access through percutaneous nephrolithotomy may facilitate subsequent ureteroscopic procedures; however, it introduces additional risk of graft parenchymal injury.

PCNL via antegrade access may facilitate the management of renal stones but offers limited advantages for distal ureteric stones and carries a higher risk of compromising graft function (20). Percutaneous access to the kidney may be impeded by overlying bowel and arrangement of hilar structures (22,41), and dilation of the tract with a balloon or Amplatz sheath may be unsuccessful due to scarring (3). Studies didn’t consistently report the approach used with the SFR to allow comparison between approaches. The use of ECIRS has been recommended to improved SFR (7,41). Mitsui et al. also proposed the use of antegrade guidewire insertion to overcome ureteral tortuosity in retrograde URS (13).

The complication rate of 9.0% for URS in RAL is comparable to that in non-renal transplant recipients of 4–25% according to the European Association of Urology (EAU) guidelines (4). The most common complications are UTI (2.2%), ureteral perforation (2.2%), the incidence rate of which are comparable to that in non-renal transplant recipients (43,44), suggesting that URS is safe in renal transplant patients. To reduce risk of post-operative UTI, international guidelines recommend treatment of asymptomatic bacteriuria in all patients including renal transplant patients (4,45) who are immunosuppressed.

The use of UAS in RAL remains a subject of debate, with reported utilisation in only 16% of cases. Limited data prevent stratification of SFRs based on UAS. In non-transplant recipients, UAS use has not been associated with improved SFRs but has been shown to reduce postoperative infectious complications, likely by lowering intrarenal pressure, and reducing operative time (4). Advances in flexible URS continue to enhance stone clearance efficiency. Notably, Direct In-Scope Suction (DISS) technology, which enables suction through 8.4-Fr or 7.5-Fr flexible ureteroscopes, presents a promising alternative. The adoption of DISS may play an increasing role in RAL management, potentially obviating the need for UAS while maintaining procedural efficacy and safety.

This study has several limitations. Firstly, owing to the low incidence of RAL and low rates of renal transplantation, the current evidence base for URS in RAL is limited to low level of evidence studies such as retrospective case series and case reports. Furthermore, data for all variables were not available or clearly reported for all studies, such as the approach used, usage of UAS, location and size of urinary calculi. There’s also no consensus on the precise definition of SFR (46) and multiple studies didn’t provide a clear definition. The imaging and timeframe used to determine stone-free status wasn’t uniform across studies, and included a combination of US, CT or nephrostography. However, this review provides insights into how advances in endourological technology and instrumentation have made URS feasible and safe in treatment of RAL, a procedure traditionally considered technically challenging. Our systematic review was conducted with a predefined search cut-off of August 2023. More recent studies published thereafter were not included in the quantitative synthesis but may provide additional insights and further inform this evolving field.

Conclusions

In conclusion, RAL is an uncommon complication of renal transplantation, but delayed treatment may result in significant morbidity. Despite concerns of difficult ureteral access, there is increasing data supports URS as safe and effective option for managing RAL.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the PRISMA reporting checklist. Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-574/rc

Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-574/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tau.amegroups.com/article/view/10.21037/tau-2025-574/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Institutional Review Board of SingHealth (IRB No. 2025-0907). As this was a retrospective study involving de-identified data, patient consent was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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Cite this article as: Lim JH, Yang X, Chong TW, Aslim EJ, Gan VHL, Ng LG, Taguchi K, Lu Y. Ureteroscopy for renal allograft lithiasis: institutional experience and global insights from a systematic review. Transl Androl Urol 2025;14(12):3988-4001. doi: 10.21037/tau-2025-574

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