Dandy-Walker Malformation

On the sagittal T1 weighted image, there is absence of the inferior vermis with a large cystlike structure communicating between the cisterna magna and fourth ventricle. A keyhole configuration is demonstrated on the axial FLAIR weighted images. The absence of the inferior vermis and organization of the paramedian folia of the right and left cerebellar hemispheres is nicely demonstrated on the axial T2 weighted image. There is absence of the traversing pontine fibers from the middle cerebellar peduncles on the color coded fractional anisotropy maps. A more superior axial image extending through both the posterior cranial fossa and temporal horns of the lateral ventricles demonstrates at least moderate supratentorial hydrocephalus. This is a case a Dandy-Walker malformation which is the most common posterior fossa malformation. Features include hypoplasia of the vermis with cephalic rotation of the vermian remnant, cystic dilatation of the fourth ventricle extending posteriorly, and an enlarged posterior cranial fossa with torcular lambdoid inversion. There are numerous associations in both the nonsyndromic and syndromic setting. Some of the CNS associations include cortical migration anomalies and dysgenesis of the corpus callosum. Non-CNS anomalies include cleft palate, low set ears, and cardiac anomalies.