If a scan has shown that your child's kidney is swollen because of a possible PUJ obstruction, you probably have many questions. Will the kidney be damaged? Does my child need an operation? This guide explains what the condition is, how doctors confirm it, why many babies are simply watched, when surgery is recommended, and the warning signs that need prompt care.
What PUJ obstruction is
Urine collects in a funnel inside the kidney called the renal pelvis, then drains down a tube (the ureter) to the bladder. The pelviureteric junction (PUJ), also called the ureteropelvic junction (UPJ), is where the funnel meets the tube. In PUJ obstruction this junction drains poorly, so urine backs up and the kidney swells. Doctors call this swelling hydronephrosis.
Most often the junction is narrow from before birth. Sometimes a blood vessel crosses the ureter and presses on it; StatPearls notes that crossing vessels account for almost 50% of surgically treated cases in children and teenagers with symptoms. According to the European Association of Urology (EAU) paediatric guidelines, PUJ obstruction affects about 1 in 1,500 children, is about twice as common in boys among newborns, and affects the left side more often.
How it is found: scan or symptoms
Many babies are first noticed because a pregnancy scan shows a swollen kidney. Our page on antenatal hydronephrosis explains those scan findings; PUJ obstruction is the most common disease-related cause, according to the EAU. Most of these babies have no symptoms at all.
Older children may come to attention differently. KidsHealth and StatPearls list:
- Pain in the tummy or side that comes and goes, often worse after drinking a lot.
- Vomiting, sometimes with the pain.
- A urine infection with fever (see urine infection in children).
- Blood in the urine (see blood in urine in children).
- Less often, a lump in the tummy.
How PUJ obstruction is diagnosed
Swelling on a scan does not by itself prove a blockage. Doctors check how well the kidney works and how well it drains.
| Test | What it shows |
|---|---|
| Ultrasound | How swollen the kidney is, often measured as the width of the renal pelvis, and how this changes over time. |
| MAG3 diuretic renogram | A nuclear medicine scan showing each kidney’s share of total function (split function) and how fast urine drains out. |
| Bladder X-ray test (MCUG or VCUG) | Whether urine flows backwards from the bladder, needed only in some children. |
| Urine and blood tests | Infection and overall kidney function. |
The EAU advises that the first ultrasound after birth is usually delayed for about 48 hours, because newborns are naturally a little dry, unless the case is severe, for example swelling of both kidneys, a single kidney or low amniotic fluid in pregnancy. It recommends the MAG3 renogram after 4 to 6 weeks of life. The bladder test is considered mainly after a urine infection, if the ureter is also widened, or in boys with swelling on both sides; the EAU reports reflux in up to 25% of affected children (see vesicoureteral reflux).
Watchful follow-up: why many babies do not need surgery
In many babies the drainage improves by itself. KidsHealth says many newborns improve within the first 18 months of life. StatPearls reports that the chance of spontaneous improvement depends on the grade of swelling, from about 50% for grade I to about 3% for grade IV.
During this period your child has repeated scans. StatPearls describes renal scans at 3, 6 and 12 months when the kidney’s split function is above 40%. The EAU does not recommend preventive antibiotics for babies with no symptoms, though doctors may offer them to some higher-risk infants. That decision belongs to your child’s doctor.
When pyeloplasty is advised
According to the EAU guidelines, an operation is considered when there is:
- Recurrent pain or urine infections with fever.
- Split function of the affected kidney below 40%.
- A fall in split function of more than 10 percentage points on follow-up scans.
- Poor drainage on the renogram.
- Increasing swelling on ultrasound.
When a kidney does very little work (the EAU uses below 20% of total function), the EAU says management is debated and recovery appears limited, so doctors discuss options with the family.
What pyeloplasty involves
Pyeloplasty is reconstructive surgery under general anaesthetic. The surgeon removes the narrow segment and rejoins the ureter to the renal pelvis so urine drains freely. It can be done as open surgery through a small cut in the side or tummy, or by keyhole (laparoscopic or robotic) surgery. The EAU reports that keyhole and open approaches give similar results, with shorter hospital stays after keyhole surgery.
A temporary tube (stent or drain) is often left to protect the join while it heals and is removed later. NHS information for families explains that the operation aims to protect remaining kidney function, and that a kidney that has already lost function is unlikely to return to normal. According to the EAU, the standard repair works in about 95% of children.
When to seek urgent care
Whether or not your child has had surgery, contact a doctor the same day or go to an emergency department if your child has:
- A fever, especially a baby who is feeding poorly or is unusually sleepy.
- Severe tummy or side pain, particularly with vomiting.
- Very little urine, or blood clots in the urine.
- After surgery: increasing pain, redness, swelling or discharge at the wound, cloudy or smelly urine, or a drain that stops draining or leaks.
Outlook and long-term follow-up
The outlook is generally very good. KidsHealth says surgery, when needed, is almost always successful and most children have no long-term complications. After pyeloplasty, children have further ultrasound and renogram scans to check drainage and kidney function. Because children born with urinary tract differences can have kidney problems later, StatPearls recommends regular monitoring into adulthood. The centre’s urologists see children and can assess a baby or child with suspected PUJ obstruction; see our paediatric urology page.
Frequently asked questions
Is PUJ obstruction serious?
It can be, if a blocked kidney is left without follow-up, because back pressure can reduce its function. With regular scans, problems are usually picked up early. Many babies improve without surgery, and when an operation is needed the outlook is generally very good.
Can PUJ obstruction go away on its own?
Yes, often. Many newborns with mild or moderate swelling improve during the first months or years of life. This is why doctors usually watch with repeated ultrasound and renogram scans rather than operate straight away, unless function or drainage worsens or symptoms appear.
What is split renal function?
Split function is each kidney's share of the work done by both kidneys, measured on a renogram. In a child with two healthy kidneys each does roughly half. A low or falling share in the affected kidney is one of the main reasons doctors recommend surgery.
How long does a child stay in hospital after pyeloplasty?
It varies with the child, the surgical approach and whether a drain is used. Many children stay a few days, and keyhole surgery is linked to shorter stays. Your child's surgical team will explain the expected stay, stent or drain removal and activity limits.
Can PUJ obstruction come back after surgery?
It is uncommon. NHS information for families says about 1 in 20 children need further surgery because drainage has not improved. That is why follow-up ultrasound and renogram scans are arranged after surgery. Return of pain, infections or increasing swelling should be reported to your child's doctor.
References
- EAU Guidelines on Paediatric Urology: Dilatation of the Upper Urinary Tract (PUJ Obstruction)
- Ureteropelvic Junction Obstruction – StatPearls
- A to Z: Ureteropelvic (UP) Junction Obstruction (for Parents) – KidsHealth
- Pyeloplasty in children – Cambridge University Hospitals NHS
- Pyeloplasty surgery – Evelina London Children's Hospital
Book a consultation
Prof. Samir Al-Samarrai and Dr. Amer Mousa assess urological conditions at Prof. Al-Samarrai Medical Center, Dubai Healthcare City, and discuss the options that suit your case. Medical consultations are confidential.
Read more: Urologist in Dubai: doctors, services, insurance and booking
This information is for health education and does not replace a medical examination. See our medical content policy.
Medically reviewed by: Prof. Dr. Samir Ahmed Al-Samarrai, consultant urologist. Review date: .
About the doctor
Prof. Dr. Samir Ahmed Al-Samarrai, consultant urologist. He studied medicine at the universities of Heidelberg and Johannes Gutenberg in Germany and graduated with distinction, earned his doctorate (PhD) with a research thesis in 1980, and on 23 August 1978 received his specialist certificate in the treatment and surgery of male urological diseases from the Free University of Berlin, at its medical school hospital, under the specialist regulations of the Berlin Chamber of Physicians.
Clinic: Prof. Al-Samarrai Medical Center, Al Razi Medical Complex 64, Building D, 2nd floor, No. 2018, Dubai Healthcare City, Dubai. MOHAP licence: ZGU3I12X-291225.
This article is for health education and does not replace a consultation with a doctor. Last updated: 6 November 2026.
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