dandy – walker malformation

dandy – walker malformation

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dandy walker malformation
dandy walker malformation note the ventriculomegaly, the absence of a cerebellar vermis, the splaying of the cerebellar hemispheres and the dilatation of the third ventricle seen in these transverse views.
dandy-walker malformation
dandy-walker malformation note the complete absence of the cerebellar vermis with splaying of the cerebellar hemispheres and an enlarged cisterna magna; bilateral ventriculomegaly is clearly shown with a dangling choroid plexus in the inferior lateral ventricle.

description

normal development of the rhombencephalon (hindbrain) is essential for the emergence of the pons, cerebellum (via the metencephalon) and medulla (via the myelencephalon) and their related cavity, the fourth ventricle. arrest of this process has been proposed to result in a spectrum of abnormalities; consequences include persistence of the area membranacea superior, interruption of vermian development, and atresia of the foramina of luschke and magendie, which have all been implicated in the pathogenesis of the dandy-walker malformation. this malformation is characterised by: – hypoplasia or agenesis of the cerebellar vermis – dilatation and herniation of the fourth ventricle through this defect, seen as a large posterior fossa cyst, which displaces the adjoining falx, torcular and lateral sinuses. – hydrocephalus, which frequently accompanies the malformation. the dandy-walker variant has recently been defined; there are similar sonographic features, but there is both vermian and hemispheric hypoplasia in association with a less pronounced enlargement of the cisterna magna; in addition, hydrocephaly is not usually seen. both conditions require differentiation from isolated enlargement of the cisterna magna (megacisterna magna) and from cerebellar dysgenesis.

diagnosis

the dandy-walker malformation can be diagnosed accurately with prenatal sonography by demonstrating a prominent posterior fossa cyst communicating with the fourth ventricle through a defect in the cerebellar vermis. splaying and separation of the cerebellar hemispheres is thus always seen. the transcerebellar view provides an optimal view of the posterior fossa, allowing for assessment of the cisterna magna; measurements exceeding 10 mm are abnormal, and require further evaluation. the classic dandy-walker malformation is commonly associated with varying degrees of hydrocephalus, which may be evident prenatally but will be apparent by three months of age in approximately 75% of patients. approximately 70% of patients with dandy-walker malformation will have associated cns anomalies, principally agenesis of the corpus callosum; other conditions include subependymal neuronal heterotopia, polymicrogyria, agyria, schizencephaly, lipoma of the corpus callosum, occipital encephalocele, lumbosacral meningocele, aqueductal stenosis, and holoprosencephaly. these have also been reported in association with the dandy-walker variant. associated non-cns anomalies are present in at least 25% of infants with classic dandy-walker malformation. these anomalies include congenital heart disease, renal malformations, low-set ears, polydactyly, syndactyly, klippel-feil syndrome, cornelia de lange syndrome, cleft palate, and facial angiomas. in dandy-walker variant the list may also include duodenal atresia, intrahepatic calcification, and two-vessel cord. the sonographic examination should thus be directed towards identifying additional supratentorial and extracranial anomalies, and should include fetal echocardiography, and follow-up sonograms are useful for monitoring cyst size and ventriculomegaly. genetic syndromes associated with dandy-walker malformation include autosomal recessive disorders such as meckel-gruber, walker-warburg, and joubert syndromes; the x-linked aicardi syndrome; and other karyotypic anomalies such as duplications of 5p, 8p, and 8q, trisomies 9, 13, and 18, and triploidy. trisomy 21 and partial trisomy 11q+ have also been noted with the dandy-walker variant. fetal karyotyping is therefore recommended. rubella, cytomegalovirus, toxoplasmosis, warfarin, isotretinoin and alcohol have all been associated with the dandy-walker malformation. in both the classic malformation and the variant, prognosis is usually dependent on the associated structural and chromosomal anomalies; in the absence of either, normal postnatal development is possible.

differential diagnosis

the main presenting feature is that of an enlarged cisterna magna. other diagnoses to be considered therefore include the following conditions. arachnoid cysts, which may also present in the posterior fossa. they tend to be extra-axial, and the lesion is usually asymmetrical with no connection between the cyst and the small fourth ventricle. the prognosis is better than that in patients with dandy-walker malformation. cerebellar dysgenesis is typified by a small and misshaped cerebellum. the cisterna magna may be prominent, but the fourth ventricle is contained within the small cerebellum. megacisterna magna is not associated with hypoplasia of the cerebellar vermis, and no splaying of the hemispheres is evident. a normal fourth ventricle is usually present. there are no adverse clinical sequelae and no specific treatment is necessary.

sonographic features

complete or partial agenesis of cerebellar vermis.

midline posterior fossa cyst (fourth ventricular enlargement).

splaying of cerebellar hemispheres.

hydrocephaly is common.

associated syndromes

  • aase-smith
  • aicardi
  • atkin
  • bowen-conradi
  • buttiens
  • cerebro-oculo muscular (walker-warburg)
  • chitayat
  • chromosomal
  • coffin-siris
  • cranio-cerebello-cardiac
  • cryptophthalmos
  • cytomegalovirus infection
  • de lange
  • edwards
  • ellis-van creveld
  • fronto nasal dysplasia-polydactyly
  • frontonasal dysplasia
  • fryns
  • goldenhar
  • hydrolethalus
  • isotretinoin
  • jones
  • kallmann
  • kudo
  • maternal diabetes
  • meckel-gruber
  • moerman
  • mohr (ofd ii)
  • nasopharyngeal teratoma
  • orofaciodigital type iii
  • pallister-hall
  • postaxial polydactyly
  • renal-hepatic-pancreatic dysplasia
  • rubella-prenatal
  • rubinstein-taybi
  • ruvalcaba
  • spastic paraplegia, cerebellar hypoplasia
  • warfarin, prenatal
  • x-linked dandy-walker

references

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