Hydronephrosis in children: your comprehensive overview

Written by: Diane De Caluwe
Published: | Updated: 31/12/2019
Edited by: Emma McLeod

Hydronephrosis means water in the kidney. Children with this condition experience swelling in one or both of the kidneys because the kidneys can’t drain the urine away. Sometimes causes are unexplained, other times there is a clear condition. Mrs Diane De Caluwe has a great deal of experience in dealing with hydronephrosis at her London clinic and here, she gives a comprehensive overview to parents.

Baby laughing

How the kidneys work

Urine is a mixture of waste from your blood and water. It’s processed in the kidneys, flows down a thin tube (called a ureter) and deposits into the bladder. You have two ureters and each one leads from each kidney into each side of the bladder. Hydronephrosis is when this system doesn’t work properly and urine builds up in the kidney, causing it to swell.


Initial diagnosis of hydronephrosis

Hydronephrosis is often diagnosed antenatally, meaning during pregnancy. Pregnant women receive an anomaly scan (mid-pregnancy scan) around 20 to 22 weeks into their pregnancy. This is when most of the foetus’ organs have developed and the most important abnormalities can be picked up. If the medical specialist conducting the scan finds a kidney abnormality such as hydronephrosis, they will continue monitoring it with additional scans during pregnancy.


We have an antenatal clinic for pregnant mums and in this clinic, we go over all the potential causes of kidney dilation (swelling).


After being monitored in the womb, the baby’s kidneys will be investigated after birth. The baby will have a post-natal scan to check if the swelling has improved or gotten worse.


Regardless of if the baby has one or both kidneys enlarged, they will be referred to a paediatric urology clinic. When, exactly, depends on two basic factors: the gender and if one or both kidneys are affected.

  • A newborn girl with swelling in one or both kidneys will get an ultrasound scan within 1 month 
  • A newborn boy with swelling in one kidney will get an ultrasound scan within 1 month 
  • A newborn boy with swelling in both kidneys will be admitted and get a scan within 48 hours to rule out a bladder outlet obstruction.


Common causes and diagnosis

1) Physiological (also known as transient) hydronephrosis

This is the most common cause of hydronephrosis in children. One kidney (or both) is dilated but there is no particular cause. It gets better on its own and no treatment is needed. This is why many babies only need extra monitoring during pregnancy and after birth to ensure that the condition is resolving.


2) Vesicoureteral reflux (VUR)

Vesicoureteral reflux (VUR) is another cause of hydronephrosis. In babies and children with VUR, urine flows in the wrong direction. Rather than flowing from the kidneys down the ureters into the bladder as it should, urine flows back up the ureter and possibly into the kidneys. VUR is classified from grade one (very mild) to grade five (very significant). VUR can cause scarring of the kidney.


There is a test called MCUG (micturating cysto-urethrogram) that confirms or rules out VUR. This test also confirms or rules out the existence of posterior urethral valves ( PUV), which can be found in baby boys with swelling in both kidneys. This makes the MCUG test a very important one because it can rule out or confirm two big problems.


3) Obstruction

The third group involves an obstruction that prevents urine from draining out the body as it should. This can happen on two levels:

  • The connection between the kidney and the ureter is too narrow for sufficient drainage. This is called pelvic ureteric junction (PUJ) obstruction.
  • The connection between the ureter and the bladder is too narrow for sufficient drainage. This is called vesico‐ureteric junction (VUJ) obstruction. Sometimes it’s referred to as an “obstructive megaureter”.

There is a test called MAG 3 scan to confirm or rule out obstruction. Sometimes if the MAG 3 scan is not conclusive, we perform an MRU (a special type of MRI) to diagnose or rule out obstruction.


Another test often used is called DMSA scan. It is a test to identify how much both kidneys contributing to total kidney function and if there is any scarring in either of the kidneys.


This test is very useful in helping to decide if and what type of treatment is required.


What symptoms should I look out for in a child?

Symptoms depend on the age of the child and the cause of urine build up in the kidneys.



A febrile urinary tract infection (febrile UTI) is the most common presentation in babies with hydronephrosis.

Any or a combination of the following symptoms in babies with hydronephrosis requires a urine test to rule out a UTI.

  • High fever
  • Generally looking unwell
  • Loss of appetite/vomiting

Babies with an obstruction in their kidneys can present with a UTI as well, but often look well and have no symptoms.


Older children (potty trained)

  • Children with reflux as the cause of their swollen kidneys can have a fever caused by a UTI.
  • Children with obstruction as the cause may have flank and /or back pain. The pain can be intermittent and can become so strong that the child vomits.


What treatments are usually offered?

Physiological (transient) hydronephrosis

Most cases of physiological hydronephrosis resolve in infancy. In this case, the most common plan of action is simply to perform a follow-up ultrasound and monitor the kidneys. Depending on how enlarged the kidneys are, an MCUG and or an MAG 3 test may be performed.


Vesicoureteral reflux (VUR)

Babies with VUR are initially started on prophylactic antibiotics (a small dose of antibiotics given once a day in the evening) until we know the cause and the severity of the hydronephrosis. The aim of the antibiotics is to reduce the chance of acquiring a UTI (called a breakthrough infection).


Further treatment depends on if the reflux has caused scarring on the kidney and if a UTI occurs despite the child being on prophylaxis. If we can, we avoid operating on children with reflux. Some will grow out of it (more common in those with low-grade VUR). Surgery may be worrisome but is sometimes necessary to avoid loss of kidney function or preserve existing function in a scarred kidney. Surgery is necessary when a child gets a UTI despite being on prophylactic antibiotics. In these children, medical treatment isn’t working and surgery is the only option. 


The endoscopic procedure is the most common surgical method due to its minimally invasive nature. During the surgery, we look into the bladder through a small camera and check where the ureters are. In children with high-grade reflux, the ureteric opening is wide open and we inject Deflux to make it smaller to avoid urine from going up. Deflux injection is very successful and if sometimes necessary, can be repeated.

 If unsuccessful, open-surgery or robotic surgery is the next step, depending on the age of the child.  



There is no possibility that an obstruction will heal itself and it will always need surgical treatment. This can be performed at any age and as soon as the diagnosis is made. In small babies, open surgery is the main type of surgery offered due to the baby’s size. For older children, keyhole surgery or robotic surgery is preferred, and the type offered will depend on the child’s age. 


Regardless of the type of hydronephrosis and the severity, it’s important to remember that paediatric urologists will always choose the safest method of treatment possible and guide you through your child’s treatment.


Hydronephrosis is just one Mrs Diane De Caluwe’s many paediatric and urology specialties. Visit Mrs De Caluwe’s profile to learn more and to book a consultation.  

By Diane De Caluwe
Paediatric urology

Mrs Diane de Caluwe is a leading paediatric surgeon and urologist based in London. She specialises in treating hydronephrosis, hypospadias, hernias and urinary tract infections, and offers a wide range of urological treatments, including circumcision. She is also an expert in managing both daytime and nighttime wetting in children.

After gaining her MD from the University of Antwerp, Belgium, she trained extensively in paediatric surgery, neo-natal surgery, and paediatric urology in the UK, Ireland and Belgium. She is now an examiner for the European Board of Paediatric Surgery and reviewer for the Journal of Paediatric Surgery and is one of only a few paediatric urology surgeons in the UK who performs robotic- assisted surgery.

Her work is widely published, with over 28 peer-reviewed articles and several book chapters to her name. She has recently been asked to write three chapters for a paediatric surgical and urology handbook to be published next year. and has also been offered an associate editorship for a new journal, 'Frontiers in Urology, Paediatric Urology.'

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