[Evaluation of stone size before flexible ureteroscopy: Which measurement is best?]

Purpose: To retrospectively assess the clinical utility in ureteroscopy (URS) planning of radiological parameters as predictor of stone-free status after a single flexible ureteroscopy.

Material: Sixty-seven patients with renal stones treated by flexible URS were retrospectively evaluated. To assess the clinical utility of radiological parameters, relationships between stone-free (SF) status and stone burden (maximal diameter, calculated area, calculated volume, cumulative diameter, and tridimentionnal volume [V3D]) were analyzed using the area under the receiver operating characteristics curve and logistic regression.

Results: Maximal diameter (AUC=0.75), calculated area (AUC 0.79), calculated volume (AUC=0.79), cumulative diameter (AUC=0.80) and tridimensional volume (AUC=0.82) revealed ability to predict SF status after URS.

Conclusion: Stone burden evaluation is critical in predicting SF status after a single URS. Planar and volumetric measurements showed equal ability to predict SF status. V3D is more accurate but diameter measurement remains easier in clinical practice.

Level of evidence: 4.