Choroid plexus cysts in fetuses with trisomy 18.

An association between fetal choroid plexus cysts and trisomy 18 has been suggested. However, the prevalence of such cysts in aneuploid fetuses is unknown. To determine this frequency, we studied 14 fetuses with trisomy 18 examined at the Central Laboratory for Human Embryology. Five fetuses were found to have choroid plexus cysts on postmortem ultrasound examination. All those with cysts were earlier than 26 weeks in gestation, and the prevalence among second-trimester fetuses was 71.4%. In contrast, such cysts are reported in less than 1% of the general population of second-trimester fetuses. Thus, choroid plexus cysts are common in trisomy 18, and the finding of such cysts on a second-trimester ultrasound examination should suggest further evaluation, including chromosome analysis.