Congenital Hydrocephalus, Infratentorial Arachnoid Cyst vs. Dandy Walker Variant
Left picture: The diagnosis is a large infratentorial arachnoid cyst spreading in a supratentorial direction on the left side, and leading to an obstructive hydrocephalus due to a displacement of the aqueduct. Right picture: In this case, too, an obstructive hydrocephalus is present which is not combined with a Dandy Walker cyst, but a Dandy Walker variant in which the brain structures of the posterior fossa are less malformed.
CT in a newborn and in an infant with macrocephaly. In both cases the content of the depicted part of the posterior fossa is striking. Left picture: The depicted part of the supratentorial ventricular system is dilated, the left occipital horn is not visible. Right picture: Here, the depicted part of the supratentorial ventricular system is symmetrical and dilated. Left picture: Here, there is no boundary of the left posterior fossa in the cranial direction. The latter is occupied by a CSF-isodense cavity which assumes the shape of the posterior fossa and assumes only cranially and laterally a round boundary on the left side. Right picture: Here, no cerebellar hemispheres are recognizable, and in the center a non-dilated IVth ventricle is visible which communicates with a semilunar CSF-isodense cavity.