Abstract 1942

Renal cystic diseases, which comprise a heterogeneous group of disorders with highly variable pathogenesis, clinical course and prognosis, may be detected at any age including the neonatal and fetal period. The significance and outcome of simple renal cysts detected in the fetus during routine prenatal ultrasound screening is unknown. The purpose of this 12 year, prospective, longitudinal study was to investigate the natural history of fetal simple renal cysts identified in early pregnancy. A detailed sonographic examination of the fetus was performed between January 1987 and June 1998 in 29,984 low and high risk consecutive pregnancies at 14-16 weeks of gestation. The diagnosis of a simple renal cyst was based on the presence of a solitary, nonseptated cyst, with well defined borders, with no communication between the cavity of the cyst and the renal pelvis, in an otherwise normal appearing kidney. Aminocenteses and chromosomal investigations were done in all cases in which a simple renal cyst was detected in the fetus. Sonographic follow-up studies were performed in all these fetuses during pregnancy and infancy. In fetuses with persistent cysts, follow-up was continued during childhood. Simple renal cysts were diagnosed at 14-16 weeks' gestation in 28 fetuses - a frequency of 1 in 1100 pregnancies (0.09%). The cysts measured 2.1 to 4.0 mm (mean 3.2 mm) in maximum diameter. In 25 fetuses the cysts disappeared during pregnancy. In two cases, the cysts, which were larger at 22 weeks' gestation, were still present without further change in size, at the age of 3 years and 6 years, respectively. In one fetus, a renal cyst that was defined as "simple cyst" at 14 weeks of gestation, signaled the diagnosis of unilateral multicystic dysplastic kidney at 18 weeks' gestation. Except for nonseptated cystic hygroma in one fetus all other fetuses had no associated anomalies of the urinary system or other organ systems and no chromosomal anomalies. Postnatal follow-up in all cases revealed healthy children.

In conclusion, a fetal simple renal cyst is not a rare ultrasonographic finding in early pregnancy. Each fetus with such a finding should be followed up closely, thoroughly evaluated for anatomic abnormalities of the urinary tract and other organ systems and investigated for chromosomal aberrations. In the absence of associated abnormalities, the vast majority of cysts will disappear 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 distinct entity within the spectrum of cystic kidney diseases.