A 2-year-old child with delayed developmental milestones.
FINDINGS: Axial CECT sections of the brain reveal absence of cerebellar vermis with the 4th ventricle communicating with a large CSF-attenuation cyst in the posterior fossa (arrow in B) with features of hydrocephalus.
DIAGNOSIS: Dandy-Walker malformation.
7Dandy-Walker complex consists of a spectrum of malformation ranging from mega cisterna magna to atresia of the outlet foramina of fourth ventricle.
In the complete syndrome the fourth ventricle is markedly dilated. The inferior vermis is hypoplastic or agenetic. Residual vermis rotates up because of compression by the fourth ventricle.
The posterior fossa is large and the occipital bones balloon out. The tentorium inserts high (lambdoid– torcular inversion). The aqueduct of sylvius may be stenotic resulting in hydrocephalus.
The Dandy-Walker variant represents the mid point with mild hypoplasia of vermis producing key hole appearance
The mildest form of Dandy-Walker complex is the mega cisterna magna. In these cases the vermis and fourth ventricle are normal. It is usually crossed by linear veins.
MRI Features of Dandy-Walker Malformation
FINDINGS: Axial T2W and mid saggital T1W images showing the large posterior fossa (arrow in A) with elevated trocular (arrow in B). Typical features of Dandy-Walker malformation.