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Dandy-Walker Malformation

Vermian-Cerebellar hypoplasia

Posterior Fossa Arachnoid cyst

Mega Cisterna Magna.

Triad

Complete or Partial Agenesis of the Cerebellar Vermis

Cystic Dilation of the Fourth Ventricle

Enlarged Posterior Fossa.

Skull and Dura

Large posterior fossa

High tentorial insertion with upward displacement of torcula and lateral sinuses

Enlarged skull with thinning and bulging of the occiput.

Ventricles and CSF spaces:

4th ventricle open dorsally in continuity with a large posterior fossa cyst

hydrocephalus (80-90%).

Cerebellum, Vermis and Brain Stem

Hypogenesis or agenesis of the cerebellar vermis

Hypoplastic cerebellar hemispheres (variable).

Associated Anomalies

Complete or partial callosal agenesis (20-32%)

Heterotopias or polymicrogyria (5-10%)

Occipital encephalocele

Prognosis related to presence/absence of supratentorial. anomalies