Propensity Score-Matched Analysis Comparing Retrograde Intrarenal Surgery with Percutaneous Nephrolithotomy in Anomalous Kidneys - Beyond the Abstract

Introduction: Endourological intervention for urolithiasis in patients with anomalous kidneys can be challenging and outcomes of different interventions are reported but not well studied. Three main factors govern the success of lithiasis intervention in anomalous kidneys namely: Surgeon's Expertise for safe access to the kidney, Availability of Equipment to assess the different parts of the kidney, and Safe Exit strategy to minimise reintervention and complications. Whilst, these are both independently well established options for renal lithiasis intervention in normal kidneys with guidelines available from EAU2 and AUA3 there is no consensus on which is a better modality to successfully achieve access to the stone volume and a high Stone free rate (SFR) with least morbidity. Hence we aim to, for the first time compare the safety, outcomes, and complications of retrograde intrarenal surgery (RIRS) versus percutaneous nephrolithotomy (PCNL) in patients with urolithiasis in anomalous kidneys as the incidence of urolithiasis in anomalous kidneys ranges from 3-40%.1

Methods: To our knowledge, this is the first study to provide a head on propensity scored matched comparison and paired analysis (PSM) of stone free outcomes and complications of RIRS and PCNL in anomalous kidneys. The multicentric data of 569 patients were pooled retrospectively from 20 high volume international centers involving expert endo urologists, where 261 patients underwent PCNL and 308 patients underwent RIRS. After PSM, a homogenous cohort of 127 pairs was available for comparison. Patients were matched based on calculated propensity scores by a regression model using age, sex, comorbidities, stone size, and renal anomaly type as co-variates. Multivariate logistic regression of factors (mode of treatment [PCNL or RIRS], comorbidities, stone size) and their effects on outcomes of SFR, need to abandon surgery due to intraoperative difficulty, postoperative hematuria, and sepsis and were analyzed when applicable for 3 anomalies namely horseshoe kidneys (HSK), malrotated kidneys and ectopic kidneys.

Results: PCNL is technically challenging in anomalous kidneys due to an abnormal pelvicalyceal system orientation, vascular aberrations, and the abnormal anatomical relation of the kidney to its surrounding viscera resulting in the need for expertise and planning for a difficult access. Horseshoe kidneys (HSK) are the most common renal fusion anomaly and are found in 0.25% of the general population with a male preponderance.4 This anomaly also constitutes the largest group with a similar male gender proportion in our study. Overall, PCNL conferred a higher SFR compared to RIRS (OR=3.69, 95%-CI=1.91-7.46, p<0.001), particularly in HSK (OR=3.33, 95%-CI=1.22-9.99, p=0.023), and ectopic kidneys (OR=18.10, 95%-CI=3.62-147.63, p=0.002), with no significant difference in malrotated kidneys. There was no significant difference in post-operative sepsis observed. Interestingly, on multivariate analysis, an independent factor for sepsis was presence of hypertension, with presence of diabetes mellitus approaching statistical significance. Surgery was abandoned more often in RIRS than PCNL (6.3% vs 0%, p=0.014) and operative time was generally longer for HSK and malrotated kidney compared to other anomaly types.

The presence of multiple stones was a predictive factor for a lower stone free rate compared to single stone <2cm (OR=0.39, 95%-CI: 0.18-0.81, p=0.013).

We aim to propose a framework that can aid urologists in making an informed choice in choosing between these two modalities in the management of urolithiasis in anomalous kidneys. Our study hopes to aid clinicians in making an informed choice in a tailored surgical approach5 using either modality based on the contextual details of a patient in optimizing outcomes.

Summary Points: Choosing PCNL vs RIRS in anomalous kidneys: Our study had experts in Endourological intervention from high volume centers which remains the cornerstone for a safe outcome in such complex cases:

  • PCNL is still the modality of choice compared to RIRS, with greater stone free rate and less operation abandonment. 
  • RIRS and PCNL are both comparable in terms of operative time in anomalous kidneys.
  • Post-operative hematuria and operation abandonment are commoner in RIRS than PCNL.
  • Multiple stones lead to lower stone free rates and higher chance of sepsis.
  • Younger age and hypertension are risk factors for sepsis
  • Inolved surgeon experts were asked to subjectively assess if Endoscopic Combined Intrarenal Surgery (ECIRS) might have been a better choice vis a vis PCNL or RIRS and a overwhelming majority responded in the affirmative. This might be a good research option in the future.
We encourage and invite urologists who are keen to learn the pros and cons of intervention to read the full article so that this can help their surgical expertise.

Written by: Vineet Gauhar,1 Ee Jean Lim,2 Khi Yung Fong,3 Daniele Castellani,4 Jeremy Yuen-Chun Teoh5

  1. Ng Teng Fong General Hospital, NUHS, Singapore
  2. Singapore General Hospital, Department of Urology
  3. Yong Loo Lin School of Medicine, National University of Singapore, Singapore
  4. Urology Unit, Azienda Ospedaliero-Universitaria Ospedali Riuniti di Ancona, Università Politecnica delle Marche, Ancona, Italy
  5. S.H. Ho Urology Centre, Department of Surgery,The Chinese University of Hong Kong, Hong Kong, China
We are also ever grateful to the rest of the authors who have painstakingly contributed to this article being successfully published:

Esteban Emiliani, Nariman Gadzhiev, Dmitry Gorelov, Yiloren Tanidir, Fabio Sepulveda, Abdullatif Al-Terki, Sanjay Khadgi, Abhay Mahajan, Deepak Ragoori, Govindarajan Ramalingam, Vaddi C Mohan, Arvind Prakash Ganpule, Santosh Kumar, Daniele Castellani, Manoj Monga, Scoffone Cesare, Fabio C Vicentini, Olivier Traxer, Bhaskar K. Somani.


  1. A. S. Pawar, C. Thongprayoon, W. Cheungpasitporn, A. Sakhuja, M. A. Mao, and S. B. Erickson, "Incidence and characteristics of kidney stones in patients with horseshoe kidney: A systematic review and meta-analysis," (in eng), Urology annals, vol. 10, no. 1, pp. 87-93, Jan-Mar 2018
  2. C. Türk (Chair), A. Neisius, A. Petřík, C. Seitz, A. Skolarikos (Vice-chair), B. Somani, K. Thomas, G. Gambaro (Consultant nephrologist) Guidelines Associates: N.F. Davis, J.F. Donaldson, R. Lombardo, L. Tzelves
  3. Assimos D, Krambeck A, Miller NL et al: Surgical management of stones: American Urological Association/Endourological Society Guideline, part II. J Urol 2016; 196: 1161.
  4. H. Basar, R. Basar, M. M. Basar, and M. Erbil, "The comparison of the incidence of horseshoe kidney in autopsy cases versus urologic patient population," (in eng), Okajimas Folia Anat Jpn, vol. 76, no. 2-3, pp. 137-9, Aug 1999.
  5. E. J. Lim et al., "Personalized Stone Approach (PSA): can Endoscopic Combined IntraRenal Surgery (ECIRS) pave the way to tailored management of urolithiasis?," (in eng), Minerva Urol Nephrol, May 5 2021. 
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