Dandy Walker Variant

  • Etiology: Abnormality of ventral induction
  • Imaging:
    — Smaller retrocerebellar cyst
    — Milder fourth ventricle dilation
    — Milder inferior vermian agenesis or hypogenesis
    — Normal size or mildly enlarged posterior fossa
    — Associations: Corpus callosum agenesis, migrational (polymicrogyria, heterotopia), cephaloceles (occipital), hydrocephalus, hypoplasia or atrophy of cerebellum or brainstem
  • DDX: Dandy Walker Continuum
  • Dandy Walker malformation
    — Retrocerebellar cyst connecting to dilated fourth ventricle
    — Inferior vermian agenesis
    — Mass effect: cerebellar hemispheres splayed out and rotated up
    — Enlarged posterior fossa
    — High tentorium and sinuses (lambdoid torcular inversion)
    — Associations: Corpus callosum agenesis, migrational (polymicrogyria, heterotopia), cephaloceles (occipital), hydrocephalus, hypoplasia or atrophy of cerebellum or brainstem
  • Dandy Walker variant
    — Smaller retrocerebellar cyst
    — Milder fourth ventricle dilation
    — Milder inferior vermian agenesis or hypogenesis
    — Normal size or mildly enlarged posterior fossa
    — Associations: Corpus callosum agenesis, migrational (polymicrogyria, heterotopia), cephaloceles (occipital), hydrocephalus, hypoplasia or atrophy of cerebellum or brainstem
  • Mega cisterna magna
    — Enlarged cisterna magna (subarachnoid space)
    — Normal fourth ventricle
    — Intact with or without atrophic vermis
    — Normal sized or mildly enlarged posterior fossa
  • Blake pouch cyst
    — Cystic dilation of fourth ventricle
  • Complications:
  • Treatment:
  • Clinical:

Radiology Cases of Dandy Walker Variant

MRI of Dandy Walker variant
Sagittal T1 MRI with contrast of the brain (upper left) shows an normal size posterior fossa containing a dilated fourth ventricle resulting in a small midline cyst. Axial (upper right) and coronal (below) T1 MRI with contrast of the brain show hypoplasia of the cerebellar vermis. No hydrocephalus is present.
MRI of Dandy Walker variant
Sagittal T1 MRI without contrast of the brain (above left) shows a cystic lesion in the inferior posterior fossa which is not causing any mass effect in a normally sized posterior fossa. Coronal T2 MRI (above right) and axial T1 MRI without contrast (below) show a mildly enlarged fourth ventricle which is connecting to the cystic lesion due to mild agenesis of the cerebellar vermis.