Fetal bilateral obstructive uropathy: a series of nine cases.

Bilateral obstructive uropathy is increasingly diagnosed in early pregnancy by ultrasound examination. Termination of pregnancy presented an opportunity to study uropathy in nine cases between 18 and 24 weeks of gestation. En bloc dissection of the urinary tract and subserial sectioning of the urethra revealed obstruction at the level of the membraneous urethra in all cases. No structural obstruction could be demonstrated in three cases, and urethral valves caused partial obstruction in two cases. The urethra was distorted by a fibrous band in one case. In three cases overriding urethral lumens appeared to represent incomplete or faulty canalization at the angled junction of the developing posterior and anterior urethra. Urethral obstruction is considered the major etiologic factor in the development of bilateral fetal uropathy and presumably the prune-belly phenotype.