Аннотация
Retrocaval ureter is an uncommon congenital abnormality in which the Inferior Vena Cava locates anterior to the ureter and causes its obstruction and hydronephrosis, as a result, and it is also considered one of the rare causes of hydronephrosis. The abnormality almost always occurs on the right because of the physiological position of the Inferior Vena Cava. It is a congenital abnormality, but the patients usually attend to the hospital due to hydronephrosis and right flank pain in the third and fourth decade of live. The abnormality needs surgical intervention and anastomosis of the ureter anterior to the Inferior Vena Cava.A 40-year-old woman complaining from right flank pain and occasional nausea, vomiting and dys- uria, was hospitalized in urology service of Aliabad Teaching Hospital on May 18, 2019. Renal ultraso- nography and Intravenous Urography showed moderate hydronephrosis on the right, which was mistak- enly diagnosed as uretero-pelvic junction obstruction. Consequently, after further exploration, retrocaval ureter was diagnosed and the retrocaval segment of the ureter was removed followed by end-to-end anastomosis of ureter on ureteral catheter.The case implies that, clinically, retrocaval ureter seldom causes pain in the right flank and/or hydro- nephrosis, which can be mistaken for uretero-pelvic junction obstruction in IVU.