Beware the stone in the duplex: Use of CT intravenous pyelogram (CT IVP) in detecting calculi in duplex ureteric systems

The current practice guidelines determine that non-contrast computed tomography kidney, ureter and bladder (CT KUB) is the gold standard for detecting urolithiasis in the setting of renal colic. However, there are a number of drawbacks of CT KUB. We present two recent cases of missed stones in complete duplex ureteric systems with inadequate preoperative imaging. Although ureteric calculi were initially confirmed on CT KUB in both patients, the presence of duplex systems was missed resulting in unremarkable ureteroscopy. Unchanged calculi were detected on follow-up imaging requiring later intraoperative diagnoses of duplex systems and successful removal of the stones. Stones seen on CT KUB with no stone on ureteroscopy should raise clinical suspicion for duplex ureteric systems. Contrast imaging can be useful in endoscopic treatment of ureteral, and renal, calculi, which could save time and prevent incorrect conclusions.