The fate of infant kidneys with fetal hydronephrosis but initially normal postnatal sonography.

Antenatal hydronephrosis involving 49 renal units in 35 infants seen since 1984 was studied. Postnatal sonography performed in the first few days after birth confirmed upper tract dilatation in 39 kidneys (80 per cent) in 29 neonates and it was normal in 10 kidneys (20 per cent) in 6 neonates. Of the 6 neonates with a normal postnatal sonogram 5 underwent repeat renal sonography at an average of 2 months after birth, all showing moderate hydronephrosis (7 kidneys). Furosemide-enhanced diethylenetriaminepentaacetic acid renography was performed in 4 infants (5 kidneys) with ureteropelvic junction or megaureter obstruction, of whom 2 had persistent unilateral obstruction and underwent successful reconstructive surgery (1 pyeloplasty and 1 megaureter reimplantation). Two infants (3 kidneys) with nonobstructive dilatation are being followed while 1 infant with bilateral vesicoureteral reflux is being managed medically on long-term antimicrobial prophylaxis. Thus, 50 per cent of neonates with antenatal hydronephrosis and a normal postnatal sonogram performed during the first few days of life subsequently were found to have either significant obstruction (2 requiring surgery) or reflux. This study underscores the absolute necessity of followup sonography in all newborns with antenatal hydronephrosis that is not confirmed on the initial postnatal ultrasound.