Children's Hospital Colorado

Ureteropelvic Junction Obstruction (UPJO)

What is ureteropelvic junction obstruction (UPJO)?

A ureteropelvic junction obstruction (UPJO) is an obstruction or blockage at the junction of the kidney and ureter. Under normal conditions, the kidneys filter the blood and remove waste in the form of urine. The urine then drains from the kidneys down through the ureters into the bladder. When a UPJO occurs, the amount of urine produced is more than the amount that can be drained through the ureter causing a 'backup' of urine. This in turn creates a collection of urine in the kidney, called hydronephrosis.

This illustration shows a kidney affected by ureteropelvic junction obstruction, which leads to hydronephrosis.

What causes UPJO?

The cause of UPJO is not well known, but abnormal tethering of the ureter or a narrowing of the ureter occurs during fetal development. The most common cause of an obstruction or blockage occurs while the child is still in the womb. UPJO is considered a congenital obstruction, meaning it is a condition that occurs at or before birth.

Who gets UPJO?

The cause of a UPJO is not well known, and therefore there is no known prevention for this condition.

Get to know our pediatric experts.

Vijaya Vemulakonda, MD

Vijaya Vemulakonda, MD

Urology - Pediatric, Urology

Ty Higuchi, MD, PhD

Ty Higuchi, MD, PhD


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Marguerite Korber, NP

Marguerite Korber, NP

Certified Pediatric Nurse Practitioner