Crossed fused renal ectopia complicated by a renal stone: endoscopic management with retrograde intrarenal surgery.

Crossed fused renal ectopia (CFRE) is an uncommon and congenital anomaly in which both kidneys are fused and located on one side of the body, often going undetected due to its asymptomatic nature. When symptomatic, it can present unique challenges in the management of nephrolithiasis due to altered anatomy and impaired drainage. We report a rare case of a young adult male with a large renal calculus in a left-to-right crossed-fused ectopic kidney-an anatomical variant seldom encountered in clinical practice. The patient was successfully treated with retrograde intrarenal surgery (RIRS) using a flexible ureteroscope and Holmium: YAG laser. This minimally invasive approach resulted in complete stone clearance, a rapid recovery and no recurrence at follow-up. Intrarenal surgery using flexible scopes can be considered a first-line approach for stone management in patients with CFRE, offering excellent outcomes with minimal morbidity. To our knowledge, this is the first documented case from Pakistan demonstrating the successful use of RIRS in a CFRE patient.