1 hour prone excretory CT urography showing right sided hydronephrosis and dilatation with medial displacement of the proximal ureter to the level of the transverse process of L4. The ureter is medial to the pedicle of the vertebral body. The axial CT shows the proximal right ureter being compressed as it passes behind the inferior vena cava. After passing behind the IVC, the right ureter is of normal caliber. More caudal images demonstrate the left ureter normally coursing along the surface of the left psoas muscle. Note the anterior and medial course of the right ureter, which continues along the anterior surface of the IVC, rather than lying on the psoas muscle as does the normal left ureter. Normal right renal cortical thickness. Nothing to report on the left side.