The word hydronephrosis derives from “hydro” meaning water and “nephrosis” meaning
within the kidney. It’s only a description of an increased amount of fluids or urine
seen inside the kidney on a renal tract ultrasound scan. It is most commonly picked up on ultrasound
scans performed on pregnant women with an incidence of 1:500 foetuses, and occasionally,
it is picked up on renal tract ultrasound scans performed on babies and children who
have had urinary tract infections. When diagnosed pre-natally, it is usually
self-limiting and harmless and is thought to be due to the fact that the foetus produced
an increased amount of urine in the third trimester of pregnancy. In a minority of cases
however, the baby will require further investigation once it’s born.
In up to 80% of cases, hydronephrosis is harmless and self-limiting and does not require further
investigation. In the remainder of the 20%, it can be due to a blockage anywhere along the
urinary tract and this would include something called a pelvi-ureteric junction obstruction
which is a blockage at the level of the kidney. A vesicoureteric junction obstruction which
is a blockage of the level of the urether where it meets the bladder or rarely, a condition
found in boys, called posterior urethral valves which is a blockage of the bladder. In other
cases, it can also be due to vesicoureteric reflux which is kidney reflux or reflux of
urine up into the kidney in a backwards fashion. Other causes of hydronephrosis could include
double kidneys or duplex systems which can have associated cysts which cause blockage
or reflux. These cases will require investigation when the baby is born.
Hydronephrosis in pregnancy or in the foetus is completely asymptomatic. It does not cause
any symptoms. We only monitor it with repeat ultrasound scans during the pregnancy. Hydronephrosis
on the newborn baby is also usually completely asymptomatic and does not give the babies
any symptoms especially the type of hydronephrosis that is due to get better on its own over
the first few months of life. However, hydronephrosis that is due to a blockage
or reflux can cause bad urinary tract infections with fever. Sometimes, it can cause flank
pain or difficulty voiding or a poor urinary stream. Once again in the majority of cases,
kidney function is completely normal. In the minority of cases with blockage or reflux
or posterior urethral valves, then yes, the affected kidney could have reduced kidney
function. That is why it is important to pick up hydronephrosis and investigate it if necessary
as it is possible to preserve kidney function and avoid the deteriorating further.
Hydronephrosis picked up during the pregnancy does not require any treatment. We usually
perform serial ultrasound scans just to check for any progression.
Very rarely, in a condition called posterior urethral valves, the condition progresses during
the pregnancy and may require in utero intervention. This is however very unusual and will require
in depth counselling with myself and your fetal medicine team
In the rest of the cases, investigations are performed once the baby is born. We usually
start the baby on a very small dose of antibiotic given to the baby every evening just to protect
the kidney from getting infection until the investigations are organised.
The first investigation will be a renal tract ultrasound scan performed on the baby within
the first four weeks of life. I will then review you and the baby with the ultrasound
scan and decide whether the antibiotics can be stopped. If the hydronephrosis is still
there, I may decide to perform further investigations and these will enable us to carry out a diagnosis.
It is therefore important for us to pick up hydronephrosis and investigate it appropriately
by an experienced paediatric urologist.