Pitfalls of the duplex system: the mystery of the missing stone.

A duplex ureter constitutes about 1% of the renal tract anomalies.A 39-year-old man presented with a 4-week history of left loin pain and microscopic haematuria. Investigation with a non-contrast CT KUB revealed a 6 mm non-obstructing calculus in the left distal ureter.Left ureteroscopy and lithotripsy was planned. However, ureteroscopy failed to identify the calculus. A double J ureteric stent was left in situ and the procedure abandoned in favour of further assessment with a CT urogram. Imaging surprisingly showed a left duplex ureter with the calculus in the non-stented ureter.Repeat ureteroscopy noted the second ureter opening within the distal intramural part of the stented ureter. The calculus was identified and laser lithotripsy performed. A double J stent was appropriately reinserted and removed 2 weeks later.Our case highlights the importance of contrasted imaging prior to performing ureteroscopy for calculus disease.