Prenatal diagnosis of arachnoid cysts.

Arachnoid cysts are a rare central nervous system malformation, representing only 1% of all intracranial masses in newborns. Primary (congenital) arachnoid cysts are benign accumulation of clear fluid between the dura and the brain substance throughout the cerebrospinal axis in relation to the arachnoid membrane and do not communicate with the subarachnoid space. Secondary (acquired) arachnoid cysts result from hemorrhage, trauma, and infection and usually communicate with the subarachnoid space. The common locations of arachnoid cysts are the surface of the brain at the level of main brain fissures, such as sylvian, rolandic and interhemispheric fissures, sella turcica, the anterior cranial fossa, and the middle cranial fossa. Arachnoid cysts may be associated with ventriculomegaly and dysgenesis of corpus callosum. Prenatal ultrasound and magnetic resonance imaging have led to the increased diagnosis of fetal arachnoid cysts. This article provides a thorough review of fetal arachnoid cysts, including prenatal diagnosis, differential diagnosis and associated chromosomal abnormalities, as well as comprehensive illustrations of perinatal imaging findings of fetal arachnoid cysts. Prenatal diagnosis of intracranial hypoechoic lesions should include a differential diagnosis of arachnoid cysts and prompt genetic investigations.