Correction of congenital hydronephrosis in utero. I. The model: fetal urethral obstruction produces hydronephrosis and pulmonary hypoplasia in fetal lambs.

In an attempt to simulate congenital hydronephrosis secondary to urethral obstruction, we evaluated the consequences of obstructing the urethra in fetal lambs by several techniques. When the urethra was ligated before 108 days gestation, the bladder decompressed through the urachus and the upper-urinary tract developed normally. Ligation of both the urethra and urachus produced gross bilateral hydronephrosis, hydroureter, and megacystis, as well as severe pulmonary hypoplasia, and was associated with a high perinatal mortality. Intermittent urethral obstruction produced with a balloon constrictor or by diverting urine externally and pressure-limited obstruction produced with a Pudenz valve both proved unsatisfactory for producing congenital hydronephrosis. Finally, ligation of the urachus and progressive gradual obstruction of the urethra with an ameroid constrictor produced hydronephrosis and pulmonary hypoplasia. This model simulates urethral obstruction in the human fetus and produces a clinical and pathologic picture similar to that seen in infants born with congenital hydronephrosis.