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Congenital anomaly of the cerebellum and fourth ventricle characterized by hypoplasia of the cerebellum and hydrocephalus caused by cystic expansion of the fourth ventricle in the posterior fossa.

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Approximately 1:25,000 newborns is affected. Accounts for less than 5% of hydrocephalus patients. Frequency is higher in females than in males.

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Heterogenous. Some autosomal recessive cases with a possible genetic defect on the long arm of chromosome 9. Recurrence risk is considered low (1-5%) if it is not associated with a mendelian disorder. Exposure to isotretinoin in the first trimester was associated with the malformation but now is uncommon.

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Unknown. Syndrome initially thought to result from atresia of the fourth ventricle's foramina during embryologic differentiation, resulting in cystic transformation of the roof of the fourth ventricle. Cerebellar malformation now is considered to be independent of this atresia. The cyst arises from compromised cerebrospinal fluid absorption.

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In approximately 80% of cases, the diagnosis is made in the first year of life, and in approximately 25% of cases it is made in the neonatal period. Affected children present with hydrocephalus associated with bulging fontanelles and occiput. Transillumination of the skull is positive. MRI or CT scans confirm enlargement of the posterior fossa, fourth ventricle (grossly), aqueduct of Sylvius, and third and lateral ventricles. The posterior fossa cyst may extend through the foramen magnum into the spinal canal. Partial or complete absence of the cerebellar vermis and elevated imprints of the transverse sinuses are additional features. The bones forming the posterior fossa are thinned. This malformation has been reported to occur in combination with other genetic syndromes.

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Obstructive hydrocephalus is present in approximately 90% of patients and is often associated with cranial nerve palsies. Most children have cerebellar signs (ataxia, nystagmus) and evidence of long-tract signs (spasticity). Signs of raised intracranial pressure (irritability, vomiting, convulsions), infantile hypotonia, developmental delay, and mental retardation (in up to 70%). Associated anomalies occur in almost 50% of cases. Agenesis of the corpus callosum with associated mental retardation and interference with medullary control of respiration leads to medullary failure. Pontine lesions involving the apneustic center result in abnormal respiratory control (e.g.: apneas). The clinical picture in older children involves delayed motor development with poor coordination and gait control. Intellectual development is delayed, and learning problems are frequently reported. Seizures have been reported in up to 30% of patients. Extracerebral anomalies are present in approximately one third of patients and include cleft palate, micrognathia, eye abnormalities (increased intraocular pressure), skeletal abnormalities of lumbar vertebrae, and polydactyly. Congenital cardiac defects have been reported in approximately 15% (ventriculoseptal defect) of patients. Renal abnormalities have been reported. Infundibular hematomas, posterior fossa lymphomas, and syringomyelia are reported features that complicate Dandy-Walker syndrome. The reported mortality rates vary from 26 to 50%.

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Assess the airway for associated abnormalities such as cleft palate or micrognathia and be prepared for difficult laryngoscopy and tracheal intubation. Positioning of ...

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