Enlarged posterior fossa with torcular-lambdoid inversion (torcular lying above the level of the lambdoid due to abnormally high tentorium).
The overall size of the skull is increased.
A large fluid attenuating cystic mass occupies the posterior fossa which is communicating directly with the fourth ventricle.
Cerebellum and vermian hypoplasia with bilateral rudimentary remnant of cerebellum which are pushed anterolaterally by the cystic mass.
The aqueduct of Sylvius appears narrowed and prominent obstructive hydrocephalus.
Dysgenesis of corpus callosum as it appears smaller in size.