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Figure 6b. Dandy-Walker malformation in a fetus at 34 weeks gestation. (a) Axial and (b) sagittal RARE MR images (single shot/60) show a Dandy-Walker malformation (M), with a large posterior fossa and key-hole deformity (arrows in a). The additional information provided by MR imaging, beyond that available with US, was that the corpus callosum (arrows in b) appeared to be normal and the aqueduct (not shown) was not grossly enlarged. It is hoped that, in the future, performing MR examinations in the late third trimester will obviate MR imaging immediately after birth, which requires sedation of the neonate.