Dandy Walker complex is the term used to describe a variety of similar developmental abnormalities characterized by an enlarged posterior fossa, high position of the tentorium cerebelli and torcula Herophili, inferior vermian agenisis or hypoplasia of the cerebellar vermis and hypoplastic cerebellar hemispheres, and a cystic dilatation of the fourth ventricle that nearly fills the posterior fossa (1). Hydrocephalus seen in upto 80% of cases. Within the specrum of disorders are: Dandy Walker malformation(DWM), Dandy Walker variant, mega cysterna magna, and posterior fossa arachnoid cyst.
Dandy Walker Malformation is distinguished by triad of dysgenesis of the cerebellar vermis, cystic dilatation of the fourth ventricle, and enlargement of the posterior fossa (1). As a result, the enlarged fourth ventricle expands posteriorly as a membrane-wrapped cyst into the foramen magnum. Other occasional concomitant factors commonly associated with the malformation include: supratentorial hydrocephalus, atresia of the foramen of Magendie and of the foramina of Luschka.
Dandy Walker variant is a less severe form of the Dandy Walker malformation and is characterised by anormal or slightly enlargedposterior fossa, amild to moderately dilated 4th ventricle, normal cerebellar hemispheres and a hypoplastic cerebellar vermis without vermian agenisis. Hydrocephalus is uncommon.
Associated CNS congenital anomalies are seen in approximately 70% of cases. These include polymicogyria, grey matter heterotopias, callosal agenisis, occipital encephaloceles and holoprosencephaly and neural tube defects.
Other non-CNS congenital anomalies include heart disease, cleft palate and skeletal anomalies such as polydactyly and syndactyly.
The malformation occurs as a result of an uncharacterized insult to the developing cerebellar hemispheres and the fourth ventricle during embryogenesis. Several theories exist regarding the etiology of the malformation. One theory proposes a blockage of the foramina of Magendie or Luschka during embryogenesis. Another describes developmental arrest of the hindbrain between the 7 and 10th weeks of gestation (1). Predisposing factors include exposure to rubella, cytomegalovirus, toxoplasmosis, warfarin, alcohol, and isotreinoin during the first trimester of gestation (1). Dandy Walker malformation may also occur in association with Mendelian disorders and genetic errors such as partial deletion of chromosome 13, trisomy 13,18 and 21 (3). It is also seen with increased frequency in Klippel-Feil syndrome, Goldston's syndrome (DWM and cystic renal disease).
Dandy Walker malformation can often be diagnosed during mid-gestation ultrasound, though minor variants or slight anomalies may be less easily identified any may require follow-up scan at 18 weeks of gestation or later (2). The recurrence rate in subsequent pregnancies is estimated at 1-2% (4).
The condition occurs more frequently in females than males with an overall incidence of Dandy Walker malformation is 1: 25,000-30,000 live births (1). The mortality rates range from 12-50% with associated congenital anomalies attributing for 83% of deaths (1). Those that do survive are born with normal ventricles and subsequently develop ventriculomegaly (80%) with hydrocephalus (90%) (1). They present with developmental delay, macrocrania, or signs and symptoms of hydrocephalus.
Dandy Walker Malformation is distinguished by triad of dysgenesis of the cerebellar vermis, cystic dilatation of the fourth ventricle, and enlargement of the posterior fossa (1). As a result, the enlarged fourth ventricle expands posteriorly as a membrane-wrapped cyst into the foramen magnum. Other occasional concomitant factors commonly associated with the malformation include: supratentorial hydrocephalus, atresia of the foramen of Magendie and of the foramina of Luschka.
Dandy Walker variant is a less severe form of the Dandy Walker malformation and is characterised by anormal or slightly enlargedposterior fossa, amild to moderately dilated 4th ventricle, normal cerebellar hemispheres and a hypoplastic cerebellar vermis without vermian agenisis. Hydrocephalus is uncommon.
Associated CNS congenital anomalies are seen in approximately 70% of cases. These include polymicogyria, grey matter heterotopias, callosal agenisis, occipital encephaloceles and holoprosencephaly and neural tube defects.
Other non-CNS congenital anomalies include heart disease, cleft palate and skeletal anomalies such as polydactyly and syndactyly.
The malformation occurs as a result of an uncharacterized insult to the developing cerebellar hemispheres and the fourth ventricle during embryogenesis. Several theories exist regarding the etiology of the malformation. One theory proposes a blockage of the foramina of Magendie or Luschka during embryogenesis. Another describes developmental arrest of the hindbrain between the 7 and 10th weeks of gestation (1). Predisposing factors include exposure to rubella, cytomegalovirus, toxoplasmosis, warfarin, alcohol, and isotreinoin during the first trimester of gestation (1). Dandy Walker malformation may also occur in association with Mendelian disorders and genetic errors such as partial deletion of chromosome 13, trisomy 13,18 and 21 (3). It is also seen with increased frequency in Klippel-Feil syndrome, Goldston's syndrome (DWM and cystic renal disease).
Dandy Walker malformation can often be diagnosed during mid-gestation ultrasound, though minor variants or slight anomalies may be less easily identified any may require follow-up scan at 18 weeks of gestation or later (2). The recurrence rate in subsequent pregnancies is estimated at 1-2% (4).
The condition occurs more frequently in females than males with an overall incidence of Dandy Walker malformation is 1: 25,000-30,000 live births (1). The mortality rates range from 12-50% with associated congenital anomalies attributing for 83% of deaths (1). Those that do survive are born with normal ventricles and subsequently develop ventriculomegaly (80%) with hydrocephalus (90%) (1). They present with developmental delay, macrocrania, or signs and symptoms of hydrocephalus.
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