Normal urinary tract anatomy is shown in the figure. As nephrons come together in the kidney, the tubules join into a central collecting system, the pelvis. This space is continuous with the ureter, the tube that leads from the kidney to the bladder. One of the most common abnormalities on prenatal ultrasound is dilatation of these urine collecting structures. The area where the pelvis becomes the ureter (the ureteropelvic junction or UPJ) is a common site of narrowing and obstruction in children.
The natural history and treatment of urinary tract dilatation remains unclear, even as our ability to detect subtle abnormalities increases. Prospective urinary tract screening in Messina, Italy, may help answer these questions.
The authors performed a prospective screening study of healthy 2-month-old infants from January 1, 2001, through December 31, 2005. Over the 5 years, 11,801 infants were screened with ultrasound (US) for hip dysplasia and renal abnormalities. 46 infants had severe renal pelvis dilatation (RPD; pelvis diameter 15-20 mm) without other abnormalities of the urinary tract and became the study group. In addition, 240 healthy infants with normal US were enrolled as a control group.
All infants in both groups had prospective follow-up US every 3-4 months for 1 year. No prophylactic antibiotics were given to prevent urinary tract infections (UTIs). If a UTI was diagnosed and/or RPD persisted after 1 year of age, voiding cystourethrogram and nuclear scans were performed to assess vesicoureteroreflux and functional obstruction, respectively.
RPD on one or both sides occurred in 0.4% of screened infants with approximately twice as many males as females affected. When only one side showed RPD, the left kidney was twice as likely as the right to be affected. Over 12 months of follow-up, one-third of infants demonstrated resolution of RPD. Of the children with persistent abnormalities, 2/3 had UPJ obstruction (see figure) and the others had vesicoureteral reflux.
Only 5 of 46 infants (14%) developed UTIs during the study, with 3 of the 5 having reflux. In contrast, the normal control group showed 2.5% of participants having UTIs in the same time period.
Our current practice following abnormal prenatal US of the urinary tract is to obtain an US 7-14 days after birth. If the tract still appears dilated, we see the baby at 1-2 months of age with voiding cystourethrogram and nuclear scan.
Obviously, we are doing a lot more imaging on a lot more infants.
This study suggests that it is safe to wait for "invasive" imaging studies until RPD has persisted for a year or the child suffers a UTI. Since at least a third of these infants will resolve their RPD, they would not have to undergo catheterization with radiation exposure for the cystogram or nuclear scan.
The authors also discuss the relevant literature; the incidence of RPD and UTI was similar to previously published work. They also touch briefly on some of the controversies surrounding UTI prophylaxis. Current practice favors such treatment in infants with reflux, and many babies with RPD would receive such treatment until imaging studies were completed. The present study suggests a less aggressive approach is safe.
The study is a well-done prospective single-center endeavor. Based on these results, plus others discussed in the paper, we can safely reduce the studies and antibiotics we use in children with RPD.