Ureterovascular hydronephrosis and the "aberrant" renal vessels.

The pelvis, an angulated upper segment of the ureter and the lower anterior renal segmental vessels entangle to produce hydronephrosis. However, which of the 3 structures provokes obstruction is conjectural. The structural relations in this anomaly were compared to those of normal kidneys, hydronephroses from other causes and nonrotated kidneys. This anomaly was unique in that the pelvis and ureteropelvic junction bulged over the lower hilar segmental vessels instead of under as in other forms of hydronephrosis. Transient or permanent defects of medial rotation of the renal pelvis may account for the vulnerability of the ureteropelvic junction to obstruction by the lower anterior segmental branch of the renal artery, which was not aberrant in all the examples studied.