Correction of congenital hydronephrosis in utero II. Decompression reverses the effects of obstruction on the fetal lung and urinary tract.

Urethral obstruction and urachal ligation at 93-107 days gestation produced severe hydronephrosis, hydroureter, megacystis, and urinary ascites as well as significant pulmonary hypoplasia in 17 fetal lambs. Obstructions in 9 fetuses subsequently were relieved in utero by suprapubic cutaneous cystostomy. At birth, all 4 liveborn obstructed lambs had respiratory insufficiency, and only 1 survived. Four others were stillborn. The lungs were significantly hypoplastic by weight and volume (p less than 0.025). All 8 had advanced megacystis, hydroureter, and hydronephrosis but no cystic or dysplastic renal changes. In contrast, 7 liveborn lambs diverted in utero had far less respiratory difficulty and all survived (p = 0.002). Two were stillborn. The lung weight was significantly increased (p less than 0.05). All lambs undergoing in utero decompression showed significant resolution of the severe urinary tract dilatation seen in the obstructed lambs. In utero decompression of the obstructed fetal urinary tract allows the abnormally small lungs to grow and develop and hydronephrosis to resolve.