During the past 10-15 years, important advancements have been witnessed in percutaneous nephrolithotomy (PCNL) techniques and instrumentation. The development of miniaturized PCNL techniques and modern laser technologies has contributed to lower complication rates, alongside changes in exiting strategies and postoperative drainage protocols. Ultrasound is increasingly utilized to create percutaneous access, and many medical centers have transitioned to the supine position for PCNL or perform Endoscopic Combined Intrarenal Surgery (ECIRS). All these developments have helped to individualize treatment strategies and to improve clinical outcomes for patients. However, there remains an ongoing discussion regarding the optimal indications and limitations of the different miniaturized PCNL techniques compared to standard PCNL and retrograde intrarenal surgery (RIRS).

This prospective observational study is organized under the auspices of the International Alliance of Urolithiasis (IAU) and focuses on the contemporary indications, surgical techniques, instrumentation, exiting strategies, efficacy, and risk factors for intraoperative and postoperative complications of PCNL. Participating investigators will collect data on the PCNL procedures performed in their respective clinical centers prospectively for a period of 12-18 months. The study will be initiated in each clinical center following formal approval from the IAU Scientific Committee, which will also announce the conclusion of the study.

OBJECTIVES

Primary Study Objective:

To evaluate the contemporary indications, clinical efficacy, and safety profile of percutaneous nephrolithotomy (PCNL) for the treatment of renal stones.

Secondary Study Objectives:

To systematically assess intraoperative and postoperative complications of PCNL utilizing the standardized Clavien-Dindo classification system.

To identify and define specific independent risk factors contributing to intraoperative and postoperative complications following PCNL.

To execute a comparative efficacy analysis between miniaturized PCNL techniques and standard PCNL stratified by stone size and complexity.

The captured variables will undergo comprehensive statistical analysis to determine their respective effects on final procedural outcomes, stone-free rates, and perioperative complications. These parameters are categorized as follows:

Patient Preoperative Variables: Age, comorbidities, Body Mass Index (BMI), active anticoagulant/antiplatelet medications, stone configuration, presence of a solitary functioning kidney, and congenital musculoskeletal or anatomical renal abnormalities.

Preoperative Imaging and Diagnostics: Modalities utilized for surgical planning, stone density (Hounsfield units), cumulative stone size/burden, and stone number/location.

Preoperative Urinary Tract Status: Documented frequency of urinary tract infections (UTIs), identification of isolated bacterial strains, and protocols for preoperative antibiotic treatment (including specific drug types and duration).

Intraoperative Variables and Technical Access: Patient positioning (prone vs. supine variations), imaging modalities utilized for renal access puncture, definitive tract size, and the specific method of tract dilatation (balloon, metal telescopic, sequential fascial, or single-step/one-shot dilators).

Instrumentation and Efficacy Metrics: Type and size of the percutaneous access sheath, specific surgical instrumentation utilized (micro, mini, super-mini, ultra-mini, or standard PCNL), energy modalities used for lithotripsy fragmentation, and methods deployed for stone fragment extraction or evacuation.

Exiting Strategies and Postoperative Care: Choice of post-procedural drainage protocols (totally tubeless, tubeless, or standard nephrostomy tube placement, including tube type and size), time to drainage extraction, and total postoperative length of hospital stay.

Morbidity and Follow-Up: Documentation of procedural morbidity, with all adverse events classified according to the Clavien-Dindo system, alongside the subsequent management and treatment of any recorded complications.

DATA COLLECTION AND PROTOCOL MANAGEMENT Patients will be enrolled prospectively and consecutively across participating international sites, targeting a cumulative registry sample of up to 10,000 participants.

The International Alliance of Urolithiasis (IAU) Scientific Committee oversees and provides formal institutional approval for the initiation of data collection at each participating clinical center. Institutions participating in the registry must submit a formal application and cover letter to the IAU Scientific Committee.

Data collection is conducted via a secure, web-based data management system, with each approved clinical center utilizing a unique, personal username and password for system access. Every participating clinical site designates a local study coordinator responsible for ensuring accurate data entry and compliance.

To maintain data integrity, completeness, and quality control across all international centers, the IAU Scientific Committee has established a dedicated Audit Committee for continuous monitoring. Final data analysis and scientific reporting will be guided and coordinated directly by the IAU Scientific Committee.

Inclusion Criteria:

• Patient age 18 years or older at the time of enrollment.
• Diagnosed with single or multiple renal calculi (including complex and staghorn calculi) or proximal ureteral stones.
• Scheduled to undergo any primary or secondary percutaneous surgical stone intervention, including standard percutaneous nephrolithotomy (PCNL) or any of its miniaturized variations (Mini-PCNL, Ultra-mini PCNL, Super-mini PCNL, or Micro-PCNL).
• Voluntarily provided written informed consent for participation and data utilization.

Exclusion Criteria:

• Patient age under 18 years.
• Patients scheduled to undergo alternative primary treatment modalities for the targeted stone burden as a standalone procedure (e.g., retrograde intrarenal surgery [RIRS] or shockwave lithotripsy [SWL]).
• Presence of an active, untreated urinary tract infection (UTI) or clinical urosepsis at the time of the scheduled surgical procedure.
• Uncorrected severe coagulopathy or uncorrectable bleeding diathesis.
• Missing, incomplete, or unavailable medical charts or follow-up records rendering outcome assessment impossible.

The study population consists of consecutive adult patients (18 years or older) diagnosed with renal or proximal ureteral calculi who are candidates for percutaneous stone surgery and are treated in real-world clinical practice settings. Participants are enrolled across 21 participating secondary and tertiary referral academic medical centers and hospitals globally, capturing a highly diverse and heterogeneous international population across multiple geographic regions

De-identified individual participant data collected during the study, including data dictionaries, will be made available to researchers whose proposed use of the data has been approved by the IAU Scientific Committee. This is intended for the purpose of further academic research and meta-analyses to improve patient care in endourology

6 months after publication of the primary manuscript 36 months after publication.

Qualified academic researchers and clinicians with a methodologically sound research proposal that aims to advance the field of endourology and stone disease management." What: De-identified individual participant data (IPD) that underlie the results reported in the published articles, including the study protocol, statistical analysis plan (SAP), and data dictionary.

How: Proposals should be submitted directly to the corresponding author (Prof. Iliya Saltirov, saltirov@vma.bg). All requests will be reviewed by the IAU Scientific Committee to ensure ethical standards and scientific validity. To gain access, requesters must sign a formal Data Access Agreement (DAA) to protect participant confidentiality and ensure data security.