The retroperitoneal Ureter is a slightly flattened tube (diameter 4-7 mm and 30 cm length). The ureter begins as the most posterior structure of the renal hilum as a continuation of the renal pelvis. It is primarily an abdominal structure, with a lesser course in the lesser pelvis.
In its course, the ureter crosses vessels at three sites:
On the psoas - it lies posterior to the testicular (ovarian) vessels
At the pelvic inlet - it lies anterior to the common iliac artery
In the lesser pelvis - it lies posterior to the ductus deferens and inferior to the uterine artery