Hydronephrosis: what does water in the kidney mean for babies?

Written by: Miss Marie-Klaire Farrugia
Edited by: Jay Staniland


The term “hydronephrosis” derives from “hydro” (water) and “nephro” (kidney) and in medical terms, means “water in the kidney”. It is a term used to describe the appearance of the kidney on an ultrasound scan, but is not a diagnosis. Hydronephrosis is most commonly seen on antenatal scans in pregnancy, affecting around 1 in 500 pregnancies, or on kidney scans done when babies or children are investigated following a urine infection.



What causes hydronephrosis?


The most common causes of prenatally-diagnosed renal tract abnormalities are:

  • A transient, self-limiting swelling due to the increased fetal urine output in the third trimester of gestation.
  • A blockage at the level of the kidney (pelvi-ureteric junction obstruction) or bladder (vesico-ureteric junction obstruction).
  • A blockage to the outflow of the bladder (posterior urethral valves).
  • A backflow of urine up into the kidney (vesicoureteral reflux).

Occasionally hydronephrosis is seen in “duplex” systems, where the kidney has two parts to it and two ureters, and may also drain into a bladder cyst (ureterocoele). Hydronephrosis discovered following a urine infection may also be caused by these conditions.


Does it cause symptoms?


Mild, self-limiting hydronephrosis is not an infection risk and does not cause symptoms. Hydronephrosis caused by a blockage or reflux may result in urine infections, pain in the flank, or a poor urinary stream.


How is it treated?


In cases which are prenatally-diagnosed, the newborn babies are usually started on a very low dose of prophylactic (preventative) antibiotic every evening. The antibiotic protects the baby against urinary tract infections (UTI) until necessary investigations are carried out. It is not a treatment, and the dose given will not harm the baby, affect its immunity, or give it any side effects.

On the other hand, a urine infection in a newborn, when the kidneys are still developing, can be very serious. The timing and type of scans organised will depend on whether the swelling affects one or both kidneys, and whether it affects the ureters (tubes leading from the kidneys to the bladder) and the bladder itself.

In the majority of cases, the babies are discharged home and brought back for their scans at 1-2 weeks of age. In a few cases, in particular in boys with swelling of both kidneys and bladder, the baby will require admission for a few days until the scans are done.

The most common investigations requested are a cystogram (to look for kidney reflux or a blockage) or a nuclear medicine scan to check the function of the affected kidney. Once a diagnosis is made, your doctor will advise what happens next. Most cases will not require surgery, however, the minority that do will be discussed with you in detail and the surgery is usually straight-forward when carried out by an experienced paediatric urologist.


Does it affect kidney function?


In the majority of cases, the child’s kidney function is completely normal. Occasionally, the affected kidney has reduced function, and this can usually be preserved with appropriate treatment. If the condition affects both kidneys, or a solitary kidney, then the kidney function may be reduced and will require long-term follow-up: this is commonly seen in boys with posterior urethral valves.

If you're worried about hydronephrosis, make an appointment with a consultant paediatric urologist.


By Miss Marie-Klaire Farrugia
Paediatric urology

Miss Marie-Klaire Farrugia is a consultant paediatric urologist and paediatric and neonatal surgeon based at Chelsea and Westminster Hospital NHS Foundation Trust and the Cromwell Hospital in central London. She specialises in all areas of kidney, bladder and genital anomalies that babies are born with or develop later in childhood. In particular, she counsels pregnant mothers whose babies are prenatally-diagnosed with a kidney condition, so that the best postnatal plan can be made for the newborn.

Miss Marie-Klaire Farrugia is the clinical lead for paediatric surgery in Chelsea and Westminster and Imperial College Hospitals; an honorary senior lecturer at Imperial College; an assistant editor for the Journal of Pediatric Urology. Her research interests include the long-term outcome of prenatally-diagnosed urological problems such as hydronephrosis, megaureter, posterior urethral valves and vesicoureteric reflux (VUR). She is an experienced open, laparoscopic and robotic surgeon and performs neonatal and childhood circumcision; repair of simple and complex hypospadias including staged graft repairs; hernia and hydrocoele repairs; surgery for undescended testes; pyeloplasty; ureteric reimplantation; surgery on duplex kidneys and ureterocoeles; posterior urethral valves; nephrectomy and hemi-nephrectomy; Deflux injection for kidney reflux with urine infections; amongst others.

Miss Farrugia is an executive member of the Society for Fetal Urology and a member of the British Association of Paediatric Urologists, the European Society for Paediatric Urology, the European Paediatric Surgery Association, the American Association of Pediatric Urologists and the Societies for Pediatric Urology.

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