Nephrolithiasis in "back-to-back" kidneys.

A 57-year-old woman presented with a 1-week history of left lower quadrant pain and nausea and vomiting. Computed tomography without contrast demonstrated a left 2.3-cm calculus at the ureteropelvic junction and a 6-mm lower pole calculus. The kidneys were in the pelvis and oriented "back-to-back," with the lateral portions of the kidneys fused in the midline. To our knowledge, this is the first description of this renal fusion anomaly. The patient underwent robotic pyelolithotomy of the ureteropelvic junction calculus and subsequent flexible ureteroscopic laser lithotripsy of the lower pole calculus and ureteral stent placement through the assistant working port.