[Analysis of fetal posterior fossa during the first trimester ultrasound scan]

The diagnosis of an abnormal fetal posterior fossa is usually done during the second trimester scan. However, some forms of open spina bifida with Arnold-Chiari malformation can be detected from the first trimester ultrasound with a precise examination of the posterior fossa and intracranial translucency. Furthermore, other abnormalities of the posterior fossa such as cystic malformations also seem to be accessible to early detection. This work detailed the possible usual and unusual aspects of the posterior fossa individualized during the first trimester ultrasound scan. Identifying an unusual appearance may identify high-risk fetus to present an abnormality of the posterior fossa. Then, thorough analysis of the fetal brain from 18 weeks will often differentiate a normal variant of a real brain malformation.