Amin Afrasiabi, MDPediatric Urology
Pediatric urology

Ureteropelvic Junction Obstruction (UPJO) in Children

A concise evidence-based overview of pediatric hydronephrosis, renal function, surveillance, and indications for intervention.

Educational overview. This page does not provide medical advice for an individual child.

Clinical overview

Ureteropelvic junction obstruction (UPJO) is obstruction to urine drainage at the junction between the renal pelvis and the ureter. Hydronephrosis, seen on antenatal or postnatal ultrasound, is a common way UPJO comes to attention, but dilation alone does not establish clinically significant obstruction.

Many children with suspected or confirmed UPJO are initially managed with surveillance rather than immediate surgery. Management depends on anatomy, symptoms, infection, drainage and function, and change over time, rather than on any single measurement or a simple choice between operating and observing.

What clinicians follow over time

Ultrasound
Serial ultrasound shows the kidney and the degree of dilation across time.
AP diameter and hydronephrosis severity
Renal pelvic anteroposterior (AP) diameter and graded severity describe the degree of dilation. This page does not propose numerical thresholds.
Parenchymal appearance
The appearance of the renal parenchyma is considered alongside dilation.
Differential renal function
Each kidney's share of total function, and whether it changes between studies.
Drainage studies and MAG3
Renography, including MAG3, is used to assess drainage and function. Its appropriate use in pediatric UPJO is a question discussed in the Academy (“Is MAG3 Overused in Pediatric UPJO?”). Renography is interpreted together with ultrasound, renal function, symptoms, and longitudinal change, not as a stand-alone diagnosis of obstruction.
Symptoms
Symptoms attributed to obstruction are part of the clinical picture.
Febrile urinary tract infection (UTI)
Febrile UTI may influence management when interpreted alongside anatomy, renal function, and longitudinal imaging.
Interval change
Change between studies is weighed together with any single result.

The central clinical question: which kidneys will deteriorate if observed?

Predictors of surgery are not necessarily the same as predictors of untreated renal deterioration. Factors associated with the decision to operate reflect treatment selection; they do not by themselves show which kidneys would have deteriorated if observed.

This distinction is important when interpreting studies. Uncertainty remains in unilateral UPJO with preserved function.

Research focus

Amin Afrasiabi’s research focus in this area is natural history and prediction in pediatric hydronephrosis and UPJO, with emphasis on anatomy, function, timing, and outcomes. This describes the focus of the work and does not report study results. See the Research page for the other focus areas.

Pediatric Urology Academy

The Pediatric Urology Academy includes a dedicated season on ureteropelvic junction obstruction (Season 3, 12 episodes). Topics include:

  • operating or observing
  • whether ultrasound can predict which kidney will deteriorate
  • use of MAG3
  • crossing vessels
  • poor function
  • hydronephrosis after pyeloplasty
  • stents after pyeloplasty
  • redo pyeloplasty
  • open, laparoscopic, or robotic approach
  • bilateral UPJO
  • the Whitaker test
  • double obstruction

When surgery may be considered

Intervention may be considered when the overall clinical picture suggests clinically significant obstruction or risk to renal function. Factors considered include:

  • symptoms
  • recurrent febrile UTI in the context of the affected system and overall obstruction risk
  • worsening dilation
  • decline in differential renal function
  • concerning drainage or function trends
  • complex anatomy

No single threshold is proposed here. How these factors are weighed depends on the individual child and is a decision for the treating team.

What remains uncertain

  • predicting untreated deterioration in kidneys with preserved function
  • distinguishing treatment selection from natural history
  • interpreting crossing vessels
  • integrating ultrasound and renography
  • identifying which children are most likely to benefit from earlier intervention