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.