Initial Drainage Method and Flexible Ureteroscopy Outcomes in Calculous Anuria

Inclusion Criteria: * Adults aged 18 years or older. * Calculous anuria secondary to a single upper ureteral stone. * Solitary functioning kidney, whether anatomical or functional. * Single upper ureteral stone confirmed by non-contrast computed tomography. * Stone size from 6 mm to 20 mm in maximum diameter. * Patient considered suitable for either initial JJ ureteral stent drainage or percutaneous nephrostomy drainage. * Candidate for definitive treatment by flexible ureteroscopy/retrograde intrarenal surgery. * Documented renal functional improvement and clinical stabilization before definitive RIRS. * Negative or appropriately treated urine culture before definitive RIRS. * Ability and willingness to provide written informed consent. Exclusion Criteria: * Multiple stones or bilateral stones not fitting the solitary-kidney study design. * Renal pelvic, distal ureteral, or multiple ipsilateral stones. * Stone burden greater than 20 mm. * Septic shock, hemodynamic instability, or need for emergency dialysis at presentation. * Pyonephrosis requiring a non-randomized drainage decision. * Anatomical abnormalities affecting endoscopic access, such as horseshoe kidney, pelvic kidney, ureterocele, or ureteral stricture. * Previous ipsilateral ureteral reconstructive surgery. * Uncorrected coagulopathy. * Pregnancy. * Genitourinary malignancy. * Inability to complete follow-up.