The normal right ureter runs lateral to the inferior vena cava (IVC). A retrocaval (also known as circumcaval) ureter is a congenital anomaly in which the right ureter passes posterior to the IVC, emerges between the IVC and aorta, and then recrosses the iliac vessels anteriorly before inserting into the bladder. The portion of the ureter lying posterior to the IVC becomes obstructed, leading to dilation of the more proximal parts of the urine collecting system. This obstruction can become symptomatic during childhood or, more commonly, adulthood. The exact incidence of retrocaval ureter is uncertain but is likely 1 : 1000 to 1 : 1500, with males affected more often than females.
A retrocaval ureter reﬂects abnormal development not of the ureter, but rather of the IVC. In the fourth week of gestation, the cardinal system of veins drains the body of the developing embryo. This system is divided into the two major branches: the anterior cardinal veins, which drain the superior portion of the embryo; and the posterior cardinal veins, which drain the inferior portion of the embryo. These join to form a common cardinal vein, which drains into the sinus venosus. Meanwhile, the vitelline veins, the precursors of the portal system, drain blood from the yolk sac to the sinus venosus. Finally, the umbilical veins carry oxygenated blood from the placenta to the embryo.