Heron Werner, MD*, Pedro Daltro, MD*, Dorothy Bulas, MD#
* Clínica de Diagnóstico por Imagem (CDPI) & Instituto Fernandes Figueira (IFF) – FIOCRUZ Rio de Janeiro – Brazil
# Professor of Radiology and Pediatrics – Children"s National Medical Center – George Washington University Medical Center – 111 Michigan Ave, NW, Washington D.C. 20010
The cystic malformation of the posterior fossa has been classically divided into Dandy-Walker deformity, Dandy-Walker variant and mega cisterna magna. The Dandy-Walker deformity is characterized by cystic dilatation of the third ventricle and enlargement of the posterior fossa together with posterior displacement of the tentorium and torcular Herophili (confluence of the venous sinuses), presenting a variable degree of aplasia or vermian hypoplasia (Table 1). The Dandy-Walker variant is characterized by a mild hypoplasia of the inferior cerebellar vermis with the connection of the posteroinferior portion of the fourth ventricle with the cistern magna. Characteristically, the posterior fossa is of normal dimension and the brain stem is preserved. In the mega cisterna magna the vermis, the cerebellar hemispheres and the fourth ventricle are normal.
|Cranium and dura
|Cerebrospinal fluid space and ventricular system
|Cerebellum, vermis and brain stem
|Associated anomalies of the central nervous system – 70% of cases
|Other associated anomalies
The study of the posterior fossa by MRI must be done within the third semester. Garel et al. (1998) describe their experience of seven cases of Dandy-Walker deformity which were evaluated by ultrasound and MRI. In all cases, ultrasound had no difficulty in making the diagnosis of the cystic dilatation of the fourth ventricle as well as the agenesis or hypoplasia of the cerebellar vermis. However, the evaluation of such fetuses by MRI may provide some additional information, such as the identification of agenesis of the corpus callosum.