RIRS vs. mini-PCNL: choosing the right approach for kidney stones between 1.5 and 2 cm

Kidney stones between 1.5 and 2 cm present one of the most frequent decision-making challenges in endoscopic urology. Two techniques compete for the gold standard role in this size range: RIRS (Retrograde IntraRenal Surgery, flexible ureteroscopy with laser) and mini-PCNL (miniaturised percutaneous nephrolithotomy). The choice is never automatic: it depends on anatomical and metabolic variables and the surgical team's learning curve.

What is RIRS

RIRS provides retrograde access to the renal pelvis — through the urethra, bladder and ureter — using a flexible ureteroscope with a diameter below 8 Fr. The stone is fragmented with a holmium laser (Ho:YAG) or, in more recent installations, a thulium laser in MOSES or TFL (Thulium Fiber Laser) mode, which allows low-energy fragmentation with 200 µm fibres and reduced thermal dispersion.

Main advantages: no percutaneous access, often day-surgery, rapid recovery. Main limitation: for dense stones (> 1000 HU on CT) or inferior calyceal location with an acute infundibulopelvic angle, the single-session stone-free rate drops significantly.

What is mini-PCNL

Mini-PCNL accesses the collecting system via posterolateral percutaneous access, using reduced-diameter sheaths (14–20 Fr, vs. 24–30 Fr for standard PCNL). Fragmentation is achieved with an ultrasonic, pneumatic or laser lithotripter. The technique can also treat high-density stones and aspirate fragments in real time, improving the single-session stone-free rate.

The risk profile includes percutaneous bleeding (although reduced compared to standard PCNL), possible pleural injury for supracostal access, and a mean hospital stay of 2–3 days.

Selection criteria: our protocol

Based on the literature and a series of over 400 procedures, the protocol of the Robotic Urology Unit at San Carlo di Nancy is as follows:

Favour RIRS when:

• CT density < 900 HU
• Pyelon or upper/middle calyceal location
• Patient on anticoagulation therapy that cannot be suspended
• Patient preference for day surgery

Favour mini-PCNL when:

• CT density ≥ 1000 HU (calcium oxalate monohydrate or cystine stones)
• Lower calyx with infundibulopelvic angle < 45° or infundibular length > 3 cm
• Multiple concurrent kidney stones
• Horseshoe kidney or anatomical anomalies limiting retrograde access

Data from our series

In 412 patients treated between 2020 and 2025 for 1.5–2 cm stones:

• RIRS (n=241): 3-month stone-free rate 82%, second intervention required in 17%, Clavien ≥ II complications 4.1%
• mini-PCNL (n=171): 3-month stone-free rate 91%, transfusion rate 2.3%, mean hospital stay 2.4 days