Neonatal hydronephrosis detected on routine health check-up

Prenatal dilatation of the urinary tract may be caused by obstructive defects, and it is known that 20% of normal fetuses have some degree of renal pelvic or calyceal dilatation, determined by sonographic examination. We analyzed the clinical course of patients found to have dilatation of the renal pelvis by ultrasound 1 month after birth, and compared prenatal and postnatal sonograms of each patient.

Between January 1996 and December 1998, renal ultrasounds were performed on 2,071 children at their 1 month routine health checks in our hospital. We found dilatation of the renal pelvis in 92 kidneys in 84 children and then compared these neonatal sonograms with the prenatal ultrasounds for each child. Ultrasound examinations were performed at 28 weeks of gestational age and 1 month after birth. Our criterion for diagnosis of hydronephrosis at 1 month of age was a renal pelvis measuring greater than 7 mm at the central echo complex. The medical records of patients found to have hydronephrosis were then reviewed.

Eight patients had bilateral hydronephrosis, 2 had dilatation only in the right kidney and 74 had this finding only in the left kidney. Examination of 36 (39%) of these 92 kidneys revealed renal pelvic dilatation to be present both prenatally and neonatally. The dilatation ranged from 7 to 43 mm. No dilatation of the renal pelvis was seen on the other 56 fetal examinations. During the follow-up period, 2 patients (1 with bilateral and the other with right-sided hydronephrosis) were diagnosed with vesicoureteral reflux, the 1 patient with bilateral pelvic dilatation was found to have a vesico-ureteral junction obstruction. After full evaluation, the other children were found to have no anatomic abnormalities.

We found 84 of 2,071 children showed dilatation of the renal pelvis on ultrasound examination performed at 1 month of age. Three (3.3%) of the 84 children required surgery to correct the neonatal hydronephrosis detected via this imaging modality. Interestingly, 88% of the children had only left-sided hydronephrosis, which did not predict an adverse outcome during the follow-up period. We conclude that neonatal hydronephrosis appears to be a relatively benign condition and the requirement of surgery is relatively slight.