Outcome of fetal cerebral posterior fossa anomalies.

Introduction: Limited data exist on the outcome of Dandy-Walker malformation (DWM), Dandy-Walker variant (DWV) and mega-cisterna magna (MCM). We report the first population-based study of posterior fossa anomalies from the northern region of England.

Methods: Cases were identified from the Northern Congenital Abnormality Survey (NorCAS) and regional Fetal Medicine Unit databases for the period 1986-2004 for DWM/V and 1995-2005 for MCM (defined as a cisterna magna > or =10 mm). Outcome data was obtained from pediatric records and/or general practitioner/health visitor questionnaires for all survivors.

Results: A prenatal diagnosis of a posterior fossa abnormality was made in 91 cases, with a further 12 cases of DWM/V diagnosed postnatally, giving incidences of DWM/V and MCM of 1/11574 and 1/8268 births respectively. In five cases where DWM/V was suspected prenatally, the diagnosis was not confirmed. Of the 47 with DWM/V, 41 (87%) had additional anomalies. There were three survivors, all with neurodevelopmental disability. Of the 39 cases of MCM, 24 (62%) had additional anomalies. There were 30 survivors; one child died at 3 months and the outcome was normal in 25 children including 12/13 (92%) with isolated MCM.

Summary: Posterior fossa anomalies are relatively common. The outcome is very poor in DWM/V owing to the high rate of associated anomalies. The outcome appears better with MCM, especially if this is an isolated finding.