ABSTRACT
True brain cysts have a capsule, regular margins, and may have a pressure effect. In contrast, pseudocysts have no capsule, irregular margins, and no compression effect. Choroid plexus cysts are collections of the cerebrospinal fluid due to blockage of the glands in the choroid plexus and seen in 1%–3% of fetuses at the time of the anomaly scan. Arachnoid cysts are rare cysts arising from the arachnoid and contain cerebrospinal fluid. Porencephalic cysts are destructive lesions—they commonly communicate with the ventricle due to destruction of white matter. The association of choroid plexus cysts with trisomy 18 loses significance in women with previous low-risk screening. If the brain appears otherwise entirely normal, and if the cysts are not very large, they are harmless and almost always disappear later in the pregnancy. Reassurance can be offered and no further follow-up is necessary.
