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 hospital stay of usually 1–2 nights.

Selection criteria

The choice follows the EAU guidelines on urolithiasis and is tailored to stone density, location and number and to the anatomy.

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