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Key Points

  • Dandy–Walker malformation refers to the combination of hypoplasia of the cerebellar vermis, cystic dilation of the fourth ventricle communicating with the cisterna magna, and increase in size of the posterior fossa.

  • Related conditions include Dandy–Walker variant (varying hypoplasia of the inferior vermis without enlargement of fourth ventricle or cisterna magna), mega cisterna magna (enlarged cisterna magna in the setting of normal vermis), and Blake’s pouch cyst (extension of the fourth ventricle into the cisterna magna, represented by septae within the cisterna magna).

  • Some authors feel that there is no role in differentiating Dandy–Walker malformation and variant, as both can be associated with CNS and non-CNS malformations, aneuploidy, and adverse neurological outcome.

  • False-positive diagnoses of Dandy–Walker malformation are possible, especially if noted before 18 weeks, or if the abnormality is confined to the cerebellar vermis alone.

  • Following diagnosis, a detailed search for other CNS and non-CNS malformations is required, including prenatal MRI, and karyotype analysis.

  • Other than multidisciplinary counseling, no other alterations to standard obstetric care are indicated.


The Dandy–Walker malformation is a nonspecific congenital brain malformation that results from a number of diverse causes. There are two principal features of the Dandy–Walker malformation: aplasia or hypoplasia of the cerebellar vermis and posterior fossa cysts that represent cystic dilatation of the fourth ventricle (Nyberg et al., 1988).

The first case of Dandy–Walker malformation was reported in 1887 (Murray et al., 1985). In 1914, Blackfan and Dandy described a hindbrain abnormality in a patient with cystic dilatation of the fourth ventricle, hypoplasia of the cerebellar vermis, separation of the cerebellar hemispheres, and absence of the lateral and median apertures of the fourth ventricle (cited in Chang et al., 1994). The term Dandy–Walker malformation was first used in 1954, combining case reports of Blackfan and Dandy, and a subsequent report of Taggart and Walker (Chen and Chu, 1994).

The Dandy–Walker malformation originates before the 6th or 7th week of embryonic development (Russ et al., 1989). The malformation may occur in single-gene disorders, in chromosomal abnormalities, in environmentally induced malformation syndromes, or in conjunction with other multifactorial anomalies (Cornford and Twining, 1992).

The full Dandy–Walker malformation consists of complete vermian agenesis, cystic dilatation of the fourth ventricle that communicates with an enlarged cisterna magna, and an enlarged posterior cranial fossa. While obstructive hydrocephalus is nearly always an associated finding postnatally, it is usually not present prenatally (Niesen, 2002). It is unclear if such hydrocephalus is due to failure of the foramina of Lushka and Magendie to open, or to some other embryological disruption.

The full Dandy–Walker malformation is sometimes distinguished from the Dandy–Walker variant and mega cisterna magna (Chen and Chu, 1994). The Dandy–Walker variant consists of variable hypoplasia of the cerebellar vermis, without enlargement of ...

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