Aim. To determine the possibility of performing minimally invasive percutaneous nephrolithotomy (PCNL) under ultrasound guidance with the use of X-ray during the access tract formation.
Materials and methods. The results of 102 mini-PСNL procedures, performed by a single surgeon during the period 2018-2019, were analyzed retrospectively. In the beginning, ureteral catheter Ch5 was put into an ipsilateral ureter. Further, a puncture of the collecting system was performed with an advancement of the guidewire. At the next stage, a dilation of tract was done using X-ray guidance for the safe formation of the working channel, followed by holmium lithotripsy. At the end a nephrostomy or JJ-stent was left.
Results. The mean age of the patients was 53.13±12.9, while average BMI was 29.3±6.5. In total, there were 44.1% of women. The average stone size was 20.7±10.9 mm; 45.1% of stones were left-sided. Staghorn stones accounted for 15.7% of cases and hydronephrosis was found in 18.6% of patients. The time for creating renal access, dilation of the nephrostomy tract, total operative time and fluoroscopy time were: 19.6±13.1, 7.7±4.2, 107.7±49.9, 57.1±41.2 minutes, respectively. In the Group I there were 32 (31.4%) patients undergoing to PCNL under X-ray guidance, while in Group II (n=70, 68.6%) combined US±X-ray control was used. The patients age (52.2±12.6 vs 53.6±13.2, p<0.05) and the stone size (20.6±8.9 vs 20.7±10.4, p=0.30) were comparable in both groups. There were slightly shorter access time and the total operative time in group II compared with group I (20.6±12.3 vs 19.2±13.5, p=0.27; 108.1±43.3 vs 106.9±53.2, p=0.25 respectively). In total, hematocrit level decreased by 4.5% and blood transfusions was done in 3 patients. Postoperative complications developed in 9 cases in both groups (according to the Clavien-Dindo classification, all complications were grade I-II). The stone-free rate (SFR) was 87.2%, and a second-stage was required in 2 cases.
Discussion. The use of ultrasound guidance improves visualization of the collecting system and contributes to the creation of an optimal renal access. It significantly reduces the radiation exposure to the patient and the operating team. We were able to puncture the collecting system in all cases. SFR after PCNL under ultrasound guidance was 88.6%, which is comparable to the results of conventional PCNL with X-ray navigation.
Conclusion. PCNL can be performed effectively and safely under ultrasound guidance, which reduces the number of renal punctures and lowers the complication rate. However, this technique also has disadvantages, including longer puncture time in morbidly obese patients without hydronephrosis. With growing experience, the number of unsuccessful kidney punctures decreases, as well as operative time. The use of fluoroscopy during dilatation of the nephrostomy tract allows for preventing additional injuries of the collecting system.

Keywords: Ultrasound-guided nephrolithotripsy, percutaneous nephrolithotripsy, x-ray guided nephrolithotripsy, navigation in percutaneous nephrolithotripsy