Transient cysts of the fetal choroid plexus: morphology and histogenesis.

In this report, we correlate the clinical and morphologic features of bilateral choroid plexus cysts in three fetuses. These cysts were detected as incidental findings during sonography at 18 to 20 weeks gestation before elective abortion. Two fetuses were normal; the third had trisomy 18. All cysts were present bilaterally in the posterior horns of the lateral ventricles and ranged from 0.5 cm to 1.0 cm in diameter. The walls were translucent, and the cavities were filled with clear serous fluid, except for the left cyst in the third fetus, which was hemorrhagic. The cysts were surrounded by the loose stroma of the choroid plexus. We believe that the formation of these cysts is related to the histogenesis of the choroid plexus. Although such cysts have now been described by sonographers in several fetuses with chromosomal anomalies, this association may reflect ascertainment bias. At this time, we therefore advise caution in interpreting sonographic evidence of isolated choroid plexus cysts as anomalous.