Ureteropelvic junction (UPJ) obstruction is a partial or total blockage of the flow of urine that occurs where the ureter enters the kidney. The etiology of UPJ obstruction includes both congenital and acquired conditions. UPJ obstruction is the most common pathologic cause of antenatally detected hydronephrosis.
The epidemiology, pathophysiology, clinical features, and management of congenital UPJ obstruction will be reviewed here.
The reported incidence of ureteropelvic junction (UPJ) obstruction is 1 in 500 live births screened by routine antenatal ultrasound; however, not all cases require surgical intervention [1,2]. UPJ obstruction is the most common anatomical cause of antenatal hydronephrosis. In one retrospective study, functionally significant UPJ obstruction was noted in 1 in 1500 fetuses screened by antenatal ultrasound .
Boys are affected with UPJ obstruction more commonly than are girls . Lesions are found more frequently on the left than on the right side. The reported rate of bilateral involvement ranges from 10 to 40 percent .
Congenital ureteropelvic junction (UPJ) obstruction is caused by anatomic lesions or functional disturbances that restrict urinary flow across the UPJ, resulting in hydronephrosis (figure 1 and picture 1) . Most cases are thought to be due to partial obstruction, because complete obstruction results in rapid destruction of the kidney. In some cases, partial obstruction may also lead to progressive deterioration of renal function. However, in many infants, an equilibrium state may develop in which renal function remains stable.