Determining the Stone Free Rate of Retrograde Intrarenal Surgery. Which Radiological Technique? RIRSearch Study Group

Area of Science:

• Urology
• Medical Imaging
• Nephrology

Background:

• Retrograde intrarenal surgery (RIRS) is a common procedure for kidney stones.
• Accurate determination of stone-free status post-RIRS is crucial for patient management.
• Current imaging modalities for assessing stone-free status include ultrasonography (USG) and kidney ureter bladder radiography (KUB).

Purpose of the Study:

• To evaluate the diagnostic performance of USG and KUB in determining stone-free status after RIRS.
• To compare the sensitivity and specificity of USG and KUB based on varying definitions of stone-free status.
• To assess the added value of KUB when combined with USG for evaluating residual stones.

Main Methods:

• Prospective study of 178 patients undergoing RIRS between September 2021 and September 2022.
• Postoperative assessment at one month included KUB radiography, USG, and noncontrast abdominal tomography.
• Analysis of sensitivity, specificity, and predictive factors for USG and KUB based on residual stone definitions (<4 mm, <2 mm, no residual stone).

Main Results:

• Stone-free rates varied from 56.7% to 79.2% depending on the definition used.
• USG demonstrated high specificity (84.3%) but low sensitivity (64.9%) for residual stones <4 mm.
• Sensitivity of USG decreased further for smaller residual stones (<2 mm: 57.1%; no residual stone: 52.5%).
• Adding KUB to USG slightly improved sensitivity but did not significantly alter specificity.

Conclusions:

• USG is a specific but insensitive tool for assessing stone-free status post-RIRS.
• Combining USG with KUB does not enhance diagnostic efficacy for stone-free determination.
• Noncontrast abdominal tomography is recommended for accurate assessment of stone-free rates in clinical trials following RIRS.