Dandy-Walker Complex

Dandy Walker Complex
Dandy Walker complex includes a continuum of Dandy Walker malformation, Dandy Walker variant and mega cisterna magna [8].
Dandy Walker Malformation
Most important imaging features of Dandy Walker malformation are large posterior fossa with a large cerebrospinal fluid (CSF) cyst and absence of normal fourth ventricle (Figure 6). Occipital bone appears scalloped and remodeled. There is torcular-lambdoid inversion that is, transverse sinuses and the confluence of sinuses lie above the lambdoid suture 1, 8, 9.
Sagittal MRI (Figure 6B) reveals that the floor of fourth ventricle is normal, but dorsally fourth ventricle opens into a large CSF filled cyst. Vermis is hypoplastic and is elevated over the cyst. Cerebellar hemispheres may be hypoplastic and anterolaterally displaced. Brainstem may be hypoplastic and compressed as well. Hydrocephalus is common, corpus callosum agenesis, heterotopias, schizencephaly, cerebellar dysplasias are also associated.
Main differential diagnosis of a posterior fossa cyst includes Dandy Walker continuum, posterior fossa arachnoid cyst, cystic neoplasms, dermoid, epidermoid and enterogenous cyst.
Figure : Dandy Walker Malformation: A, Axial CT image. Fourth ventricle (Arrow) dorsally opens into a large CSF filled cyst. Subtle remodeling of occipital bone is noted. Gross hydrocephalus is present (White dots). B, Sagittal T1 weighted image. The floor of fourth ventricle (Arrow) is normal, but dorsally fourth ventricle opens into a large CSF filled cyst (Arrowheads). Vermis (Curved arrow) is hypoplastic and is elevated over the cyst. Brainstem (Black dot) is hypoplastic and compressed. C, Axial T2 weighted MR image shows a large posterior fossa CSF intensity cyst with hypoplastic vermis and cerebellar hemispheres.

Dandy Walker Variant
In this anomaly, there is mild vermian hypoplasia with communication of posteroinferior fourth ventricle and cisterna magna through enlarged vallecula, causing a variable size cystic space (Figure 7). Posterior fossa is of normal size.
Figure : Dandy Walker Variant. A, Axial CT image. B, Axial T1 weighted MR image (Different cases). There is communication (Arrows) between posteroinferior fourth ventricle and cisterna magna through enlarged vallecula, with a posterior fossa cyst. Severe hydrocephalus is present in Figure 7A.






Mega Cisterna Magna
In this variant, fourth ventricle, vermis and cerebellar hemispheres are normal. Large cisterna magna is present. Occasionally scalloping of occipital bone is seen (Figure 8).
Figure : Axial CT image showing mega cisterna magna (Arrows). Fourth ventricle, vermis and cerebellar hemispheres are normal. Scalloping of occipital bone is seen (Arrowheads).



Reference:The Internet Journal of Radiology™ ISSN: 1528-8404