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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 ...