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.