Definition & classification
> 4 mm AP renal pelvis diameter in 2nd trimester
> 7 mm AP renal pelvis diameter in 3rd trimester
> 10 mm AP renal diameter post-natally
The challenge is to distinguish between children at risk of long term renal damage who need intervention vs those who can be safely surveilled without overtreating and overinvestigating
Think clinically significant or insignificant.
- If significant – obstruction or reflux
Epidemiology
1 – 3 % of all live births
2 x more common in boys
20 – 40 % bilateral
Associations with Down syndrome, chromosomal abnormalities
Causes
- Transient physiological state
- Obstructive
- PUJ obstruction (30 – 50 % antenatal hydro)
- Megaureter (VUJ obstruction)
- Ureterocele
- Ectopic ureter
- Posterior urethral valve
- Non obstructive
- VUR
- Prune-belly syndrome
- Neuropathic bladder / spina bifida
- Multicystic dysplastic kidney
Things to consider
- Unilateral or bilateral
- Male or female
- Degree of hydronephrosis / diameter
- Calyceal dilation
- Renal parenchyma – thickness and appearance
- Bladder and ureters appearance
- Amniotic fluid volume (for respiratory function)
Classification systems
Society Fetal Urology (SFU)
(https://www.nature.com/articles/nrurol.2013.172)
Upper tract dilation (UTD) classification system – consensus group which has both antenatal and post natal groups
https://link.springer.com/article/10.1007/s00247-015-3305-0
Who is at risk?
Low risk
- SFU grade 1 or 2 ; < 15 mm
- Approx. 10 % risk of needing intervention
Intermediate risk
- SFU grade 3 or bilateral grade 2, 15 – 30 mm
- Approx. 25 % risk of needing intervention
- Think about antibiotics, serial US, MCUG
High risk
- SFU grade 4 or > 30 mm
- > 60 % risk of surgical intervention
- Prophylactic antibiotics + complete evaluation – MCUG, renogram
What to do after delivery
Physical examination:
- Abdominal mass / palpable bladder / prune belly syndrome
- Spinal cord abnormalities
- Other stigmata of congenital disease
- Respiratory status (pulmonary hypoplasia due to oligohydramnios)
Ultrasound
- Early ultrasound can give false negatives due to relative oliguria and dehydration in first couple days of life
Within first 24 – 48 hours if:
- Severe hydronephrosis with suspicion of bladder outlet obstruction
- Oligohydramnios
- Solitary kidney
Around first week for other cases, say day 7.
Repeat at 4 – 6 weeks, even if first ultrasound normal.
- If normal post-natal and week 4-6 ultrasound, and mild antenatally, most significant pathology excluded.
- Continue serial ultrasounds – 3 months, then 6 – 12 monthly until 4 – 5 years old
If abnormal ultrasounds – consider further investigation with MCUG or MAG3
MCUG
Recommended for:
- SFU grade 3 – 4, renal pelvis > 15 mm
- Abnormal parenchyma or ureters/bladder
- Antenatal hydro plus postnatal UTI.
About 6 weeks of age, unless suspecting PUV (boys with bilateral HUN) in which case do within 24 – 72 hours.
Downsides are radiation exposure and risk of introducing UTI. Consider antibiotic cover for 72 hours, starting 24 hours prior.
MAG3
Recommended for:
- SFU grade 3 – 4, with MCUG negative for reflux (aim approx. 6- 8 weeks)
- Hydronephrosis and dilated ureter, with MCUG negative for reflux
- Worsening pelvicalyceal dilation on serial US
Prophylactic antibiotics
Practice is variable and somewhat controversial.
Definite reduction in UTI and febrile UTI with antibiotic prophylaxis in higher grade hydronephrosis, e.g. SFU grade 3 – 4 or > 15 mm
Probably only marginal benefit in lower grade e.g. SFU 1 – 2 or < 15 mm
Consider circumcision in boys.
Consider antibiotic prophylaxis in lower risk groups if concern will not be able to be assessed expeditiously for UTIs (i.e. rural/remote)
In summary:
Define risk – high risk (SFU 3-4 or > 15mm ; bilateral involvement; solitary kidney) or low risk.
Exclude PUV in boys early.
Otherwise, ultrasound at day 7 – 10 then again at 6 weeks, then 3 months, then 6 monthly.
If concerns – exclude VUR with MCUG.
Then exclude obstruction with MAG3.