Dandy-Walker syndrome

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Dandy-Walker syndrome
ICD-10 Q03.1
ICD-9 742.3
OMIM 220200
DiseasesDB 3449
MeSH D003616

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Dandy-Walker syndrome (DWS), or Dandy-Walker complex, is a congenital brain malformation involving the cerebellum and the fluid filled spaces around it.

Historical Perspective and Eponym

It is named for Walter Dandy and Arthur Earl Walker.[1]


The term Dandy-Walker represents not a single entity, but several abnormalities of brain development which coexist. There are, at present, three types of Dandy-Walker complexes.

They are divided into three closely associated forms: DWS malformation, DWS mega cisterna magna and DWS variant.


The DWS malformation is the most severe presentation of the syndrome. The posterior fossa is enlarged and the tentorium is in high position. There is partial or complete agenesis of the cerebellar vermis. There is also cystic dilation of the fourth ventricle, which fills the posterior fossa. This often involves hydrocephaly and complications due to associated genetic conditions, such as Spina Bifida.

Mega cisterna magna

The second type is a mega cisterna magna. The posterior fossa is enlarged but it is secondary to an enlarged cisterna. This form is represented by a large accumulation of CSF in the cisterna magna in the posterior fossa. The cerebellar vermis and the fourth ventricle are normal.

  • The term mega cisterna magna has been loosely applied to a large retrocerebellar cerebrospinal fluid (CSF)–appearing space with a normal vermis and normal cerebellar hemispheres.
  • More recently, the concept that a cisterna magna should enlarge only in response to volume loss of a damaged cerebellum has been revised. It is believed that when such large spaces manifest with mass effect on the cerebellum, enlargement of the posterior fossa and/or splitting of the falx, and supratentorial extension, they can be attributed not to an enlarged subarachnoid cistern but to a space-occupying lesion.
  • Mega cisterna magna occurs in approximately 1% of all brains imaged postnatally.
  • Mega cisterna magna has been associated with infarction, inflammation, and infection, particularly cytomegalovirus, as well as with chromosomal abnormalities, especially trisomy 18.
  • In the absence of other findings to suggest a posterior fossa lesion, a mega cisterna magna is unlikely to be clinically significant.
  • On imaging, prominent retrocerebellar cerebrospinal fluid (CSF)–appearing space with a normal vermis and normal cerebellar hemispheres is seen.


The third type is the variant, which is less severe than the malformation. This form (or forms) represents the most wide-ranging set of symptoms and outcomes of DWS. Many patients who do not fit into the two other categories of DWS are often labeled as variant. The fourth ventricle is only mildly enlarged and there is mild enlargement of the posterior fossa. The cerebellar vermis is hypoplastic and has a variably sized cyst space. This is caused by open communication of the posteroinferior fourth ventricle and the cisterna magna through the enlarged vallecula. Patients exhibit hydrocephalus in 25% of cases and supratentorial CNS variances are uncommon, only present in 20% of cases. There is no torcular-lambdoid inversion, as usually seen in patients with the malformation. The third and lateral ventricles as well as the brain stem are normal.

Epidemiology and Demographics

The Dandy-Walker complex is a genetically sporadic disorder that occurs one in every 25,000 live births, mostly in females.

Natural History, Complications and Prognosis

The spectrum of outcomes for Dandy-Walker syndrome are diverse. Mortality statistics are often compiled by neurologists who deal with worst case outcomes, which thus reflect a high mortality rate, or grim prognosis – both pre and post natal – in DWS infants.

Children with Dandy-Walker syndrome may never have normal intellectual development, even when the hydrocephalus is treated early and correctly. Longevity depends on the severity of the syndrome and associated malformations. The presence of multiple congenital defects may shorten life span.



Symptoms, which often occur in early infancy, include slow motor development and progressive enlargement of the skull. In older children, symptoms of increased intracranial pressure such as irritability, vomiting and convulsions and signs of cerebellar dysfunction such as unsteadiness, lack of muscle coordination or jerky movements of the eyes may occur.

Physical Examination

Other symptoms include increased head circumference, bulging at the back of the skull, problems with the nerves that control the eyes, face and neck, and abnormal breathing patterns.

Imaging Findings

The key features of this syndrome are an enlargement of the fourth ventricle, the space containing cerebrospinal fluid between the medulla and the cerebellum, a partial or complete absence of the cerebellar vermis, the posterior midline area of cerebellar cortex responsible for coordination of the axial musculature, and cyst formation near the internal base of the skull. An increase in the size of the fluid spaces surrounding the brain as well as an increase in pressure may also be present. The syndrome can appear dramatically or develop unnoticed.

Dandy-Walker syndrome is frequently associated with disorders of other areas of the central nervous system including absence of the corpus callosum, the bundle of axons connecting the two cerebral hemispheres, and malformations of the heart, face, limbs, fingers and toes.

Sonographic diagnosis in the first trimester on routine antenatal study is the most common presentation in healthcare systems where screening antenatal studies are carried out regularly. MRI is used in almost all cases in larger institutions in the late second trimester (after 18 weeks) to look for associated anomalies and plan further management at an early stage. The classic malformation is characterized by the presence of large cistern magna, communicating with the fourth ventricle through a defect in the cerebellar vermis going from the hypoplasia of the inferior part to the complete agenesis. The cerebellum is small. As a consequence of the larger cistern magna, the posterior fossa expands and the tentorium is lifted up. In the beginning of the second trimester, the inferior portion of the cerebellar vermis cannot be totally developed, and false positive diagnosis is a possibility at this stage. A combination of MRI and ultrasound at 18 weeks or later is recommended, if there is the suspicion of agenesis of the vermis, especially if the inferior portion is not seen. Hydrocephalus was originally considered as an element of the diagnosis, but recent studies suggest that it is not always present in fetal life, but usually appear in the first months of post-natal period.

The differential diagnosis includes arachnoid cysts and large intraventricular bleeds, which can be usually differentiated by the size and appearance of the cerebellum. Fetal MRI scans are now used more frequently to confirm and clarify sonographic findings


Treatment for individuals with Dandy-Walker syndrome generally consists of treating the associated problems, if needed. A special tube (shunt) to reduce intracranial pressure may be placed inside the skull to control swelling. Parents of children with Dandy-Walker syndrome may benefit from genetic counseling if they intend to have more children.