Antenatal Hydronephrosis
Antenatally detected hydronephrosis is a finding, not a diagnosis — it is confirmed and graded on a postnatal ultrasound (timed after the first days to avoid underestimation) and worked up for UPJ obstruction, reflux, PUV or megaureter, with most mild cases simply observed.
The big picture
Routine antenatal ultrasound frequently detects renal pelvic dilation. Many cases are transient or physiological and resolve, but some reflect significant pathology — pelviureteric junction (UPJ) obstruction, vesicoureteric reflux (VUR), posterior urethral valves (PUV, in males), or megaureter. Severity and bilaterality, and features like a thick-walled bladder or oligohydramnios, raise concern.
Confirm and grade on a postnatal ultrasound timed after the first days (early scans underestimate); build the UPJ/VUR/PUV/megaureter differential; observe mild cases and investigate significant ones with VCUG/renogram as indicated.
Symptom sorter
What causes it.
Diagnostic algorithm
Each step answers one question. Tap to expand.
Treatment ladder
Match action to severity and cause: observe mild isolated dilation and investigate/treat significant, obstructive or refluxing disease along its specific pathway.
Complications
- Renal damage from missed obstruction/PUV
- Recurrent UTI, scarring
- Over-investigation/radiation if not targeted
- Procedure-specific risks of treating the cause
- Time the postnatal scan correctly; investigate selectively
- Identify PUV early in males
- Treat the specific diagnosis; monitor function/growth
Follow-up
- Resolution/progression of dilation on serial ultrasound
- Renal function and growth
- UTI
- Serial ultrasound at age-appropriate intervals; functional studies if progressing
- Resolving/stable mild dilation; preserved renal function
- Progressive dilation, declining function, recurrent infection
- Scheduled surveillance and on clinical change
- Underlying obstruction/reflux/PUV sequelae, renal scarring/impairment
Memory hooks
A finding, not a diagnosis.
Time the postnatal scan after the first days.
Differential: UPJ, VUR, PUV, megaureter.
Mild → observe; significant → investigate.
Male + thick bladder → think PUV.
Board traps
Very early neonatal ultrasound underestimates dilation — repeat after the first days.
Bilateral dilation + thick bladder in a male → PUV.
Labelling transient dilation as needing surgery.
Clinical cases
A neonate had antenatal renal pelvic dilation. An ultrasound on day 1 shows only mild dilation and the team plans to discharge with reassurance.
What is the pitfall and the correct approach?