Patterns of Detection of Fetal Posterior Fossa Anomalies: Analysis of 81 Cases in the Second Half of Gestation.

ABSTRACT

OBJECTIVE: To establish which characteristics of fetal ultrasound screening lead to the diagnosis of posterior fossa (PF) anomalies. METHODS: A total of 81 fetuses with PF anomalies diagnosed after dedicated neuroimaging between July 1, 2007, and January 1, 2013, were included. The ultrasound characteristics of the fetal cerebellum categorized according to an anatomical approach to the PF, associated fetal anomalies, gestational age at diagnosis, and the potential benefits from systematic measurement of the transverse cerebellar diameter (TCD) were analyzed. RESULTS: Fifty fetuses (61.7%) presented with a PF malformation responsible for an increased "fluid-filled" space of the PF, 24 fetuses (29.6%) had a malformation associated with a decreased cerebellar biometry, 23 fetuses (28.4%) had an abnormal cerebellar anatomy and/or echogenicity, and 2 fetuses (2.4%) showed an isolated malformation of the brainstem. Forty-seven cases (58%) showed additional cerebral or extracerebral anomalies, which led to the diagnosis of PF anomaly in 55.3% of the cases. Isolated PF anomalies were associated with an increased "fluid-filled" space of the PF in 91.2% of the cases. Twenty-eight fetuses had a TCD measurement considered as pathological. DISCUSSION: Examination of the transcerebellar plane during 2nd- and 3rd-trimester ultrasound screening combined with systematic measurement of the TCD would allow improving the detection of PF anomalies.