Selection criteria for minimally invasive endoscopic treatment of urolithiasis depending on stone characteristics

Introduction. According to the guidelines, the stone maximum diameter is one of the main criteria for choosing the method of nephrolithotripsy. When planning an operation, the surgeon focuses not only on the diameter, but also on the renal pelvis anatomy, stone density and number of it, the presence of hydronephrosis, a history of surgery, etc. The maximum diameter is not an exhaustive characteristic that allows you to choose the optimal treatment.Objective. To evaluate the effect of stone volume (compared to its maximum diameter) on the duration of minimally invasive endoscopic nephrolithotripsy.Materials & methods. The study was retrospective. The study included 55 patients (22 women, 33 men), the average age was 47.0 ± 1.9 years. All patients underwent minimally invasive thulium fiber laser nephrolithotripsy for stones up to 20 mm (mean maximum diameter — 13.3 ± 0.6 mm, mean density — 1041.0 ± 48.0 HU). Minimally invasive endoscopic interventions such as retrograde intrarenal surgery (RIRS, n = 30), minipercutaneous and micropercutaneous nephrolithotripsy (miniPNL, n = 16 and microPNL, n = 9, respectively) were performed. Patients with urinary system abnormalities, acute urinary tract infections and patients without stone-free status were excluded from the study. In addition to evaluating standard indicators, the stone volume was calculated in all patients using the formula of a scalene ellipsoid (median volume — 287 [144; 538] mm3). Spearman's rank correlation coefficient (r) with an assessment of the significance level was calculated for the stone maximum diameter and volume for the total sample of patients and for each surgical intervention method separately.Results. The analysis of the total sample of patients reliably revealed a weak correlation (r = 0.39) between the stone maximum diameter and surgery time. And a moderate correlation was found between the stone volume and surgery time (r = 0.53). A similar relationship with the linear distribution was also observed in the analysis in all groups.Conclusion. When choosing minimally invasive laser nephrolithotripsy, it is advisable to focus not only on the stone maximum diameter, density, and localisation, but also on the stone volume, which has a great correlation with the surgery time.