Infratentorial Cyst

Example of a congenital infratentorial cyst. CT with a liquid zone in the posterior fossa of the same density as CSF which has a shape of a crescent moon; no structure of a fourth ventricle is recognizable. Additional pictures show a dilatation of the supratentorial ventricles.:<:br:> Diagnosis: Dandy Walker cyst as one type of different Dandy Walker malformations. In Dandy Walker cyst the foramina of the fourth ventricle are often closed; there are defects of the cerebellum, and the fourth ventricle is part of a large cyst. The Dandy Walker cyst is usually combined with a supratentorial hydrocephalus. The cyst as well as one of the lateral ventricles must be shunted by a communicating drainage because a primary aqueductal stenosis may be present, or a secondary aqueductal insufficiency may occur. In general, congenital intracranial cysts in the newborn may have large CSF volumina depending on the type of cyst (up to 200-300 ml), a supra- and/or infratentorial extension and a space-occupying effect.