Antenatal Hydronephrosis
- With the introduction of routine ultrasound in pregnancy, antenatal hydronephrosis is being increasingly detected and is currently found in 1-5% of pregnancies. 1 However, this finding does not necessarily imply obstruction or impaired renal function and many cases improve spontaneously. Therefore, this is a controversial area in paediatrics and there is a lack of consensus on optimum management. The following are general guidelines only based on best available evidence.
- Antenatal hydronephrosis is defined as a renal pelvis anteroposterior diameter of >4mm less than 33 weeks gestation and >7mm less than 40 weeks on ultrasound. 2
- The most widely accepted grading system for hydronephrosis is the Society of Fetal Urology hydronephrosis system: 3,4
| Grade 0 | No or minimal collecting system visible - considered normal |
| Grade I |
Just the renal pelvis visible with an axial diameter <5-7 mm - usually considered normal |
| Grade II |
Axial renal pelvis diameter 5/7-10 mm; some calices with normal forniceal shape visible |
| Grade III |
Marked dilatation of the renal calices and pelvis >10 mm with reduced forniceal and papillary differentiation without parenchymal narrowing |
| Grade IV |
Gross dilatation of the collecting system with narrowing of the parenchyma |
- The risk of postnatal pathology is 12% for mild, 45% for moderate and 88% for severe antenatal hydronephrosis. 1 Overall, only a minority of neonates will require surgical intervention. 5 Mild hydronephrosis is more likely to stabilise or improve compared to higher grades. 6
- Common causes of antenatal hydronephrosis include pelviureteric junction (PUJ) obstruction, vesicoureteric reflux (VUR), posterior urethral valves, duplication anomalies (ureterocoele/ectopic ureter), megaureter and multicystic dysplastic kidney.
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