Overview of Ureteropelvic Junction Obstruction
The organ that produces urine (kidney) and the tube that carries urine from the kidney to the bladder (ureter) join at the ureteropelvic junction (UPJ). Narrowing (stricture) at this junction reduces the flow of urine from the kidney and can result in enlargement of the kidney caused by the backup of urine into the renal pelvis (hydronephrosis) and kidney damage. UPJ obstruction can be severe, minimal, or intermittent and is often diagnosed during prenatal ultrasound. It is the most common cause of hydronephrosis in utero and in newborns.
Incidence and Prevalence of Ureteropelvic Junction Obstruction
Approximately 1% of prenatal ultrasounds detect hydronephrosis in the fetus. In 50% of these cases, UPJ obstruction causes the condition. UPJ obstruction is more common in males and affects the left kidney more often than the right. About 20–30% of cases occur in both kidneys (bilaterally).