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Embryology · Nervous system and senses

Dandy–Walker malformation !

  • Malformation

The middle of the cerebellum (the vermis) is missing or very small and the fourth ventricle becomes a big cyst at the back of the skull.

Updated 2026-11-01

See it in 3D: Vermis · Fourth ventricle · Cerebellum · Cerebellar tonsils

What it is

Dandy–Walker malformation is a posterior fossa anomaly with three features: an absent or hypoplastic cerebellar vermis, cystic dilation of the fourth ventricle and an enlarged posterior fossa. Many children develop hydrocephalus. It is linked to chromosomal disorders, especially trisomy 18, and must be told apart from Chiari, where the fossa is small.

Key facts

  • Triad: hypoplastic or absent vermis, cystic fourth ventricle, large posterior fossa.
  • Hydrocephalus in many cases; it is the main source of complications.
  • Frequency: about 1 in 10,000 to 30,000 newborns.
  • Associations: trisomy 18 (most common), trisomies 13 and 21, FOXC1 variants, maternal diabetes.
  • Contrast with Chiari: in Dandy–Walker the posterior fossa is large; in Chiari, small.

Embryological cause

  • Development of the dorsal hindbrain fails: the roof of the fourth ventricle and the vermis that forms from the rhombic lips.
  • The roof of the fourth ventricle does not open properly to the subarachnoid space and balloons into a cyst.
  • The cyst pushes the tentorium and torcula upward, enlarging the posterior fossa.
  • It arises in the embryonic period, while the cerebellum and fourth-ventricle outlets form.

Markers

  • FOXC1
  • ZIC1
  • ZIC4

How it presents

  • Macrocephaly or an occipital bulge in the infant, from hydrocephalus.
  • Motor delay, hypotonia, ataxia and coordination problems.
  • Intellectual disability in up to half; seizures in some.
  • A smaller group presents late with headache or unsteady gait; some have no symptoms.

Diagnosis

  • Prenatal ultrasound: a posterior fossa cyst communicating with the fourth ventricle and a small vermis.
  • MRI (fetal or postnatal) confirms the triad.
  • Karyotype or microarray, given the link with trisomies.

Test yourself

Think of the answer, then tap the question to see it.

What are the three features of Dandy–Walker malformation?

An absent or hypoplastic vermis, cystic dilation of the fourth ventricle and an enlarged posterior fossa.

Which trisomy is it most often associated with?

Trisomy 18.

How does posterior fossa size distinguish it from Chiari II?

In Dandy–Walker the posterior fossa is large; in Chiari II it is small and the cerebellum herniates downward.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

← All of embryology

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Dandy-Walker malformation: MedlinePlus Genetics (U.S. National Library of Medicine, 2024); Hydrocephalus (National Institute of Neurological Disorders and Stroke, 2024).

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