Increased prominence of the cisterna magna of >10 mm should raise concern for complete vermian aplasia (Dandy-Walker Malformation). For this diagnosis to be made, there must be no vermian tissue present. There is thus a trapezoid-shaped gap between the cerebellar hemispheres. 

If possible, the fetal brain should be interrogated thoroughly in the axial, coronal and sagittal planes to confirm no vermis.

In this case, apart from the hypertelorism, there was no other fetal anomaly.

As there was a significant fetal intracranial abnormality, amniocentesis was performed. The initial report was normal, but microarray analysis revealed a 6p25 microdeletion, which has been described in the literature as being a cause for Dandy-Walker Malformation.

Case co-contributed by Dr Emmeline Lee.