Ultrasound Appearance of Fetal Posterior Fossa and a Case Report of Prenatal Diagnosis of Dandy-Walker Malformation.

Prenatal sonographic assessment of the posterior fossa in the mid-sagittal plane at 11-14 weeks' gestation has been highlighted as an essential diagnostic step by the current literature. This approach is used for the early detection of open spina bifida during the first trimester by analyzing the three spaces of the posterior fossa: brain stem, the fourth ventricle and cisterna magna. Abnormal size of fetal posterior fossa spaces is an important sign in the diagnosis of fetuses with central nervous system malformation and needs to be submitted for differential diagnosis when any alterations are observed. Among them, Dandy-Walker malformation is one of the major causes of congenital hydrocephalus, being a rare condition, with poor-prognosis, manifested by enlarged posterior fossa. On the basis of available evidence, the assessment of the fetal posterior cranial fossa is feasible from 11 to 14 weeks gestational age and it is believed that abnormal appearance of the posterior fossa at this stage of pregnancy could improve early detection of Dandy-Walker malformation by prompting an early second trimester ultrasound evaluation.