Natural history of fetal simple renal cysts detected in early pregnancy

Purpose: In this 12-year prospective, longitudinal study we investigated th e natural history of fetal simple renal cysts identified by ultrasonography in early pregnancy. Materials and Method: A detailed sonographic examination of the fetus was p erformed between January 1987 and June 1998 in 29,984 consecutive pregnanci es at 14 to 16 weeks of gestation. Amniocenteses and chromosomal investigat ions were done in all cases in which a simple renal cyst was detected in th e fetus. Followup sonography was done in all cases of renal cyst during pre gnancy, infancy and, when indicated, childhood. Results: Simple renal cysts were diagnosed at 14 to 16 weeks of gestation i n 28 fetuses (1/1,100 pregnancies, 0.09%). In 25 fetuses the cysts resolved during pregnancy. In 2 fetuses the cysts remained benign but persisted pos tnatally and in 1 a renal cyst that was initially defined as simple was the first sign of unilateral multicystic dysplastic kidney. Except for nonsept ated cystic hygroma in 1 fetus, none of the others had associated anomalies of the urinary or other organ systems and no chromosomal anomalies. Postna tal followup in all cases revealed healthy children. Conclusions: A fetal simple renal cyst can be identified by ultrasonography in early pregnancy. In the absence of associated anatomical or chromosomal abnormalities, the majority of cysts will resolve during pregnancy without any sequelae. Given the transient nature of most fetal simple renal cysts detected in early pregnancy, it is possible that these cysts represent a di stinct entity within the spectrum of cystic kidney diseases.