# Effectiveness and safety of ultra-slow full power shockwave lithotripsy compared to mini–percutaneous nephrolithotomy and retrograde intrarenal surgery for treatment of lower calyceal stone between 1 and 2 cm with high attenuation value

## TL;DR

This study compares three treatments for kidney stones and finds mini-PNL most effective, though SWL may be suitable for some patients.

## Contribution

The study introduces a comparison of ultraslow SWL with mini-PNL and RIRS for high-density lower calyceal stones.

## Key findings

- Mini-PNL achieved the highest stone-free rate (95%) compared to RIRS (85.8%) and ultraslow SWL (76.7%).
- Ultraslow SWL had the highest residual stone rates, while mini-PNL had the lowest.
- All techniques had similar minor complications but no major ones.

## Abstract

This prospective randomized study compared the effectiveness and safety of ultra-slow full power shockwave lithotripsy (ultraslow SWL), mini-percutaneous nephrolithotomy (mini-PNL), and retrograde intrarenal surgery (RIRS) for 1–2 cm lower calyceal stone with HU above 1000.

360 patients were randomized with stratification according to stone size using a block randomization to: (1) Ultraslow SWL; (2) Mini-PNL; or (3) RIRS. Primary outcomes were stone-free rates (SFR) and complications with blinding of assessors. Our follow-up protocol featured a non-contrast CTUT after 3 months for Ultraslow SWL while 1 month for both mini-PNL and RIRS groups, confirming stone-free status. The SFR was stratified as follow: true stone-free (0 mm), residual fragments ≤ 2 mm, residual fragments 3–4 mm, and failure (more than 4 mm). Secondary outcomes included operative parameters and hospitalization. Multinominal logistic regression was used for significant findings to identify predictors of success or failure.

Mini-PNL showed superior SFR (95%) versus RIRS (85.8%) and SWL (76.7%) (p = 0.007). Mini-PNL showed the lowest rates of residual stones (0.8% for fragments ≤ 2 mm, 0.8% for fragments 3–4 mm, and 3.3% for failure), while SWL had the highest residual stone (5% for fragments ≤ 2 mm, 3.3% for fragments 3–4 mm, and 15% for failure), with RIRS demonstrating intermediate outcomes (3.3% for fragments ≤ 2 mm, 3.3% for fragments 3–4 mm, and 7.5% for failure). All techniques had comparable (p = 0.110) Clavien Dindo I-II complications (pain, vomiting, colic, hematuria, skin ecchymosis, and fever/UTI) and managed conservatively with analgesics, hydration, or antibiotics, with no major complications (Grade III–V). However, interpretation of comparative outcomes must be cautious due to methodological limitations such as differing follow-up timing.

Mini-PNL achieved higher SFR, its invasiveness and radiation exposure warrant consideration. However, the comparison between RIRS and ultraslow SWL success suggests ultraslow SWL may benefit patients with moderately sized lower pole stones with high attenuation values, especially who wish to avoid invasive surgery or are considered unfit for anesthesia. The results are encouraging but preliminary and require confirmation. However, some limitations were heterogeneous follow-up imaging intervals, absence of anatomical data, lack of stone composition analysis, and baseline stone volume imbalance. Therefore, future studies should evaluate long-term outcomes and cost-effectiveness, and consider our limitations.