The purpose of this study was to evaluate how the upper calyx–lower calyx infundibular (ULI) angle influences intrarenal stone migration during percutaneous nephrolithotomy (PCNL) in patients with a solitary renal pelvis stone and significant hydronephrosis. 50 adult patients with a solitary renal pelvis stone larger than 20 mm were considered for PCNL with a pneumatic lithotriptor for stone fragmentation. Inclusion criteria were moderate to severe hydronephrosis and upper calyx infundibular width >10 mm, and access point was the lower calyx in all cases. The ULI angle as well as stone fragment migration from the renal pelvis toward the upper calyx was noted during the operation. To determine the “critical” angle above which the probability of stone migration would be increased significantly, receiver operating characteristic curve was used. Mean stone size was 33.8 ± 13.2 mm. In 23 patients (46 %) the stone migrated toward the upper calyx during stone fragmentation. Mean ULI angle was significantly wider in patients whose stone migrated (120.2 ± 20.5 versus 102.2 ± 21.4, P = 0.004, 99 % CI = 6.04–29.9). A ULI angle of 117.5° was the critical angle, above which the rate of stone migration rose significantly (P < 0.008). One-session stone-free rate was significantly higher in patients without stone migration (P = 0.03). In patients with a solitary renal pelvis stone and significant hydronephrosis, a wider ULI angle was associated with a greater likelihood of stone scattering which could potentially affect the outcome of PCNL with pneumatic lithotriptor. A cut-off angle of 117.5° was the critical angle, above which access via a calyx other than the lower calyx (example: middle or upper calyx) seems advisable.
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