Antenatal hydronephrosis and postnatal evaluation: Case

This infant has the increased-risk UTD A2-3 antenatal hydronephrosis from the ureteropelvic junction obstruction on the right. The anteroposterior diameter of 16 mm at 32 weeks exceeds the 10 mm threshold and places the fetus in the increased-risk category, and the postnatal confirmation at day 5 with the diameter of 22 mm and the dilated renal pelvis and the major and the minor calyces is consistent with the Society for Fetal Urology grade 3. The MAG3 renogram confirms the impaired drainage and the reduced split function on the right. ^[6]

Clinical findings

The key findings are the increased-risk antenatal category with the progressive dilatation from 8 mm at 24 weeks to 16 mm at 32 weeks, the correctly timed postnatal ultrasound at day 5 that confirmed the severe right hydronephrosis, the normal-calibre ureter that points to the ureteropelvic junction obstruction rather than the reflux, and the MAG3 renogram that showed the impaired drainage with the split function of 42 percent on the affected side. The normal blood pressure, the normal growth, and the normal creatinine are reassuring for the overall renal function. ^[1]

The progression of the anteroposterior diameter across the serial antenatal scans is an important finding, because the worsening dilatation suggests the progressive obstruction rather than the transient physiologic dilatation. The Nakane study showed that the antenatal grade 1 and grade 2 hydronephrosis resolves in the majority of the cases, but the progressive and the high-grade dilatation carries a higher probability of the pathology, which is why the postnatal evaluation was correctly initiated. ^[12]