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UPJ Obstruction • By age, and special situations

Bilateral UPJ Obstruction: Which Side First, Follow-Up and Surgical Order

A share of newborn UPJ obstruction cases are bilateral, and this raises extra questions in both diagnosis and decision-making. This page explains what gets investigated quickly in bilateral hydronephrosis, why split function can be misleading, and how the order of surgery is decided.

Who this is forFamilies of infants and children with hydronephrosis in both kidneys, or diagnosed with bilateral UPJ obstruction
Reading≈5 min
ByProf. Dr. Ali AvanoğluUpdated
This page is part of UPJ obstruction.Read the full treatment overview on the hub page
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kidney–ureter–bladder: SFU 3 hydronephrosis, narrowing at the UPJ (red ring) · both sides
01 · How common is bilateral hydronephrosis, and why it matters02 · What's investigated first: PUV, reflux and the bladder03 · The trap in split function04 · Which side is operated on first05 · Follow-up and after surgery
In brief5 madde
  • How common is bilateral hydronephrosis, and why it matters: UPJ obstruction (ureteropelvic junction obstruction; informally, kidney outlet narrowing) is bilateral in roughly 10–30% of newborn cases in the literature; it's more…
  • What's investigated first: PUV, reflux and the bladder: In bilateral hydronephrosis, the first ultrasound looks not only at the kidneys but at the bladder too: a thickened bladder wall, widened ureters, and a…
  • The trap in split function: MAG3 gives each kidney's share of total function — split (renal) function.
  • Which side is operated on first: In bilateral UPJ obstruction, the decision for surgery is made with the same criteria as for one-sided narrowing: course, drainage, function and symptoms.
  • Follow-up and after surgery: Follow-up is more frequent in bilateral cases and covers total kidney function: ultrasound assesses each side separately, and blood creatinine and blood pressure are…
01

How common is bilateral hydronephrosis, and why it matters

UPJ obstruction (ureteropelvic junction obstruction; informally, kidney outlet narrowing) is bilateral in roughly 10–30% of newborn cases in the literature; it's more common in male infants, and some case series report a more severe course and a higher need for repeat surgery.

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  • When both kidneys are affected, there's less backup to lose; this is why guidelines call for the post-birth ultrasound to be done without delay in severe bilateral hydronephrosis (kidney swelling). The usual "wait until day 3–7" rule for mild, one-sided widening doesn't apply here.
  • Hydronephrosis is a finding, not a diagnosis; bilateral widening can also be due to causes other than UPJ obstruction. In male infants especially, bilateral widening raises suspicion of posterior urethral valves (PUV — a membrane in the urethra blocking urine flow), and this possibility should be ruled out in the first days.
02

What's investigated first: PUV, reflux and the bladder

In bilateral hydronephrosis, the first ultrasound looks not only at the kidneys but at the bladder too: a thickened bladder wall, widened ureters, and a widened-looking posterior urethra in a male infant all favor PUV. In that situation, the path diverges from UPJ evaluation.

  • Severe bilateral hydronephrosis, a thickened bladder wall, a male infant: ultrasound and VCUG are not delayed.
  • A history of oligohydramnios (low amniotic fluid): rapid evaluation after birth.
  • Low urine output, not feeding, sleepiness in a newborn: same day.
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  • Guidelines recommend VCUG (a voiding cystourethrogram, informally the "catheter study") in male infants with bilateral hydronephrosis, so that both PUV and kidney reflux (vesicoureteral reflux, VUR) can be seen.
  • If the bladder and ureters are normal, and the widening in both kidneys is limited to the renal pelvis, bilateral UPJ obstruction becomes more likely, and evaluation continues with MAG3 diuretic renography (a kidney scan).
03

The trap in split function

MAG3 gives each kidney's share of total function — split (renal) function. In bilateral narrowing, since both kidneys are affected, this ratio can be misleading: if both kidneys are equally damaged, the result comes out around 50–50 and can look "normal," even though total function may in fact be reduced.

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  • This is why, in bilateral narrowing, attention isn't paid to the percentage alone but to each kidney's own drainage curve, its drainage after furosemide (a diuretic), parenchyma (kidney tissue) thickness on ultrasound, and blood creatinine level. Creatinine is a direct marker of total function and is part of follow-up in bilateral cases.
  • Even so, split function is still useful: if there's a marked asymmetry between the two kidneys (say, one side at 30% and the other at 70%), the side with the lower share and worse drainage is usually the one that needs to be addressed first.
04

Which side is operated on first

In bilateral UPJ obstruction, the decision for surgery is made with the same criteria as for one-sided narrowing: course, drainage, function and symptoms. If both sides remain within the limits for follow-up, both are followed; like one-sided cases, most bilateral cases can improve or stay stable without surgery.

  • Priority: worse drainage, more widening, thinning of the parenchyma, a lower function share, symptoms.
  • The other side: followed with serial ultrasound; repaired in a second session if needed.
  • Both sides in one session: a selected case, depending on center experience.
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  • If repair is needed, the general approach is to repair the side with worse drainage, more pronounced widening, and function under greater threat first; if one side has symptoms, that side takes priority. The other side stays under follow-up — sometimes it improves on its own, sometimes a second operation follows in a separate session.
  • Repairing both sides in the same session can be done in selected cases, particularly with a laparoscopic or robotic approach, depending on center experience; in infants, most centers prefer two separate sessions. The choice between open, laparoscopic or robotic approach is made through the joint assessment of two pediatric urology specialists.
05

Follow-up and after surgery

Follow-up is more frequent in bilateral cases and covers total kidney function: ultrasound assesses each side separately, and blood creatinine and blood pressure are tracked. If one side has been repaired, that side is followed on ultrasound around month 3 and then every 6–12 months; the other side continues on its own schedule.

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  • Because the need for repeat surgery in bilateral narrowing in male infants has been reported slightly higher in the literature than in one-sided cases, follow-up is kept longer. The widening isn't expected to disappear completely; success means stable or decreased widening on both sides, preserved total function, and a symptom-free course.
  • Flank pain with fever, a drop in urine output, or swelling is a more important warning sign in bilateral cases than in one-sided ones; seek same-day evaluation in these situations.
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Frequently asked questions
Both kidneys show widening — does that mean it's UPJ obstruction in both?
Not always. Bilateral widening can also be due to bladder outlet obstruction (PUV in a male infant), kidney reflux, or transient widening. This is why the bladder and ureters are checked with ultrasound first, VCUG is recommended in male infants, and UPJ obstruction is evaluated with MAG3 once these are ruled out.
MAG3 came back 50–50 for the two kidneys — does that mean there's no problem?
In bilateral narrowing, an equal share can be misleading: if both kidneys are equally affected, the percentage can look normal while total function has actually dropped. This is why drainage curves, parenchyma thickness and blood creatinine are evaluated together.
Can both sides be corrected in the same operation?
It's possible in selected cases at experienced centers, especially with a laparoscopic or robotic approach. In infants, most centers prefer to repair the worse side first and follow the other, or repair it in a second session. The decision depends on the infant's size, the state of both sides, and center experience.
Is the chance of surgery higher with bilateral narrowing?
Most bilateral cases can also improve or stay stable with follow-up; but in male infants, the course has been reported more severe and the need for repeat surgery slightly higher in some case series. This is why follow-up is kept more frequent and longer.
←Previous • By age, and special situationsUPJ Obstruction in a Solitary Kidney
Related pagesFull index →
By age, and special situationsUPJ Obstruction in a Solitary KidneyIn a child with a single kidney, UPJ obstruction calls for a more careful, earlier decision, because there's no backup kidney to fall back on. This page explains where evaluation differs in a solitary kidney, which findings aren't left waiting, and how follow-up proceeds.Follow-up or surgery?Split (Differential) Kidney Function and What the 40% Threshold MeansSplit (differential) kidney function is the percentage share each kidney contributes to total function on MAG3 diuretic renography (a kidney scan). In UPJ obstruction, 40% is the most frequently cited threshold for the surgical decision; but interpreting this number without knowing how reliable it is can be misleading.Follow-up or surgery?UPJ Obstruction: Follow-Up or Surgery? How the Decision Is MadeNot every child with UPJ obstruction (ureteropelvic junction obstruction; informally, kidney outlet narrowing) needs surgery. The decision is made from the combination of the kidney's share of function, its emptying speed, the course of the hydronephrosis over time, and any symptoms. This page explains what goes on each side of that scale.BasicsKidney Swelling Seen Before BirthKidney swelling seen on a pregnancy ultrasound (prenatal hydronephrosis) occurs in roughly 1–5% of pregnancies, and most cases are temporary. After birth, the cause is investigated with a planned ultrasound schedule; UPJ obstruction is the most common of the lasting causes. This page walks through the post-birth path step by step.
UPJ Obstruction topic clustersMain treatment page →
Basics 7Diagnosis and evaluation 6Follow-up or surgery? 7Conservative follow-up 5Pyeloplasty and approaches 7After surgery and follow-up 6By age, and special situations 7
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