Ultrasonographic evaluation of fetal paranephric pseudocysts.

Ultrasonographic evaluation of the fetus with urinary tract obstruction requires not only precise delineation of the level of obstruction but also differentiation from other nonobstructive renal entities. The authors evaluated five fetuses in which large unilocular paraspinous fluid collections were seen at ultrasonography. While these masses simulated the appearance of large hydronephrotic sacs, they actually represented paranephric pseudocysts. In four of the five cases in which a paranephric pseudocyst was seen the ipsilateral kidney was nonfunctioning.