The varied sonographic appearance of the urinary tract in the fetus and newborn with urethral obstruction.

The urinary tract in the fetus responds to chronic obstruction differently than in adults. This difference leads to sonographic findings which are unique and occasionally misleading when urinary tract obstruction occurs in utero. These findings include development of macroscopic cysts and relative lack of dilatation of the intrarenal collecting system. Seven cases are presented to illustrate the spectrum of findings in fetal urinary tract obstruction at the urethral level, and criteria for distinguishing atypical renal obstructive disease with cysts from other forms of renal cystic disease in the newborn are offered.