[Focus on Dandy-Walker malformation].

The aim of this review is to summarize our knowledge about Dandy-Walker malformation (DWM) and introduce recent notions about its prognosis. DWM is a malformation associating hypoplasia of the vermis, pseudocystic fourth ventricle, upward displacement of the tentorium, torcular and lateral sinuses and anterio-posterior enlargement of the posterior fossa. It is frequently associated with genetic anomalies, brain malformations (anomalies of gyration, grey matter heterotopias, meningoceles, corpus callosum agenesis...) or systemic malformations (heart, orthopedic, intestinal, urogenital and facial anomalies). It is also part of many syndromes. Its rarity, the difficulty of its diagnosis, the fact that the malformation is mainly known through hospitalized patients, mainly from neurosurgical departments, have made its definition variable and prevents us from having an accurate knowledge of its natural history and prognosis. Hydrocephalus, so frequent in neurosurgical series that some have included it in the definition, is actually rare as has been seen in prenatal series. Treatment, when necessary, is still controversial, the main options remaining cyst fenestration, ventriculo- and/or cystoperitoneal shunts and more recently endoscopic third ventriculostomy. The prognosis, commonly said to be unpredictable, is actually foreseeable after scrutinous observation of the brain anatomy, and mainly of the vermis. A cerebellar vermis with three groups of lobes and two main fissures, as identified on MRI T2 sagittal views, not only has the greatest chance to not be associated with other malformation but also to have a favorable neurocognitive outcome. On the contrary, a deeply dysgenetic vermis with only two or one recognizable lobes is not only constantly associated with other brain malformation but also with poor prognosis. This is a recent advance that may be important for those involved in prenatal counselling.