Intravesical Aminophylline to Facilitate Ureteroscopic Access in Children With Distal Ureteral Stones.

Inclusion Criteria: * Children older than 2 years and younger than 18 years. * Single unilateral lower/distal ureteral stone confirmed by low-dose non-contrast computed tomography according to local policy. * Stone size 5 to 15 mm. * Candidate for definitive treatment by semi-rigid ureteroscopy. * Sterile urine culture before surgery, or previously positive urine culture that has been properly treated before intervention. * Intraoperative failed initial gentle negotiation of the ureteric orifice/intramural ureter according to the study definition. * Written informed consent from the parent or legal guardian, with child assent when appropriate. Exclusion Criteria: * Known hypersensitivity to aminophylline, theophylline, or ethylenediamine. * Use of oral or intravenous aminophylline or theophylline within the previous 24 hours. * Pre-existing ipsilateral JJ ureteral stent. * Stone peeping at the ureteric orifice. * Congenital or acquired abnormality that may affect distal ureteric access, such as ureterocele, obstructive megaureter, distal ureteric stricture, previous ureteric reimplantation, or previous ipsilateral ureteral reconstruction. * Known bladder dysfunction or conditions likely to affect normal bladder capacity. * Multiple ipsilateral ureteral stones or associated renal stones requiring flexible ureteroscopy or a ureteral access sheath strategy. * Febrile urinary tract infection, pyonephrosis, sepsis, or any case requiring urgent decompression instead of definitive ureteroscopy. * Cardiac disease, arrhythmia, uncontrolled hypertension, hyperthyroidism, epilepsy or seizure disorder, or significant hepatic impairment. * Inability to complete follow-up.