Correction of congenital hydronephrosis in utero III. Early mid-trimester ureteral obstruction produces renal dysplasia.

Is the renal dysplasia (RD) commonly seen in babies with urinary tract obstruction a developmental consequence of the obstruction or is it an associated embryologic malformation? We produced complete unilateral ureteral obstruction in six 58- to 66-day old lamb fetuses by clipping a silastic ring on the ureter. Three fetuses survived to term. All obstructed kidneys were not only grossly hydronephrotic but dysplastic by histologic criteria; ie, parenchymal disorganization, primitive epithelial structures, and marked fibrosis. The contralateral unobstructed control kidneys were normal. The changes were similar to those seen in the human neonate with obstruction and RD, suggesting that in this model RD was caused by obstruction to the flow of urine early in fetal development.