Dandy-Walker Malformation

Dandy-Walker malformation is a congenital posterior fossa anomaly with agenesis or hypoplasia of the cerebellar vermis, cystic dilatation of the fourth ventricle, and an enlarged posterior fossa with elevation of the tentorium and torcular.

Incidence is about 1 in 25,000 to 1 in 35,000 live births. It accounts for 1 to 4% of paediatric hydrocephalus.

Associations. Hydrocephalus (70 to 90%, often developing in the first months), agenesis of the corpus callosum, occipital encephalocele, heart disease, polydactyly, cleft palate and chromosomal anomalies. Deletions at 3q24 involving ZIC1 and ZIC4, and FOXC1 changes, are linked.

Pathophysiology. Disruption of cerebellar and fourth ventricle roof development, with failure of foramina of Luschka and Magendie to open, leads to cyst expansion.

Presentation in infancy is macrocephaly, bulging fontanelle, irritability, vomiting, developmental delay, hypotonia, truncal ataxia and later cognitive impairment. Prenatal diagnosis is by ultrasound or MRI. Some adults present with headache and mild ataxia. About half have normal intelligence, and outcome depends on associated anomalies.

Red flags.

• Rapid head growth, sunsetting eyes, vomiting or falling consciousness (acute hydrocephalus).
• Apnoea or bradycardia in infants.
• Shunt blockage or infection in a child with a shunt.

Foetal ultrasound and MRI. Postnatal MRI shows vermian hypoplasia with upward rotation, cystic fourth ventricle communicating with the cisterna magna, and associated anomalies. Chromosomal microarray or exome sequencing. Echocardiography, ophthalmology and hearing assessment.

Differential diagnosis.

• Blake pouch cyst, mega cisterna magna and isolated vermian hypoplasia.
• Posterior fossa arachnoid cyst and Joubert syndrome.

Hydrocephalus. Cerebrospinal fluid diversion is the main treatment: ventriculoperitoneal shunt, cystoperitoneal shunt, or both, or endoscopic third ventriculostomy with aqueductoplasty in selected children. Monitor for shunt malfunction (headache, vomiting, drowsiness) and infection.

Development. Physiotherapy, occupational therapy, speech therapy and educational support, and treatment of epilepsy (levetiracetam 10 mg/kg twice daily increased to 30 mg/kg twice daily).

Associated anomalies. Cardiac, ophthalmic and hearing care, and genetic counselling.

Prenatal. Counselling with foetal medicine and paediatric neurosurgery.

Monitoring. Head circumference, development, ventricular size and shunt function.

Referral and escalation. Refer to paediatric neurosurgery and neurology. Refer as an emergency for signs of raised intracranial pressure.

Special groups. In adults with a shunt, treat headache and drowsiness as shunt failure until proven otherwise.