Dandy-Walker Malformation
The imaging findings of a retrocerebellar cyst with flattening or hypoplasia of the inferior vermis are diagnostic of Dandy-Walker malformation (DWM), and management centers on treating hydrocephalus through combined shunting of both the lateral ventricles and posterior fossa cyst, with comprehensive genetic evaluation and multidisciplinary developmental monitoring. 1, 2
Diagnostic Confirmation
Obtain postnatal brain MRI with multiplanar imaging including sagittal T2-weighted sequences to definitively characterize vermian anatomy and identify associated brain malformations. 1, 3 The key diagnostic features that must be present include:
- Large median posterior fossa cyst communicating freely with the fourth ventricle 4, 5
- Small, rotated, upwardly displaced cerebellar vermis 4, 5
- Upwardly displaced tentorium and enlarged posterior fossa 4, 5
- Anterolaterally displaced but structurally normal cerebellar hemispheres 5
Morphometric analysis of the vermis is essential, as visual assessment alone may miss critical anatomic details that determine prognosis. 1, 3 On sagittal T2 sequences, assess whether the vermis shows normal lobulation (two fissures, three lobes, fastigium) versus severe dysplasia (one or no fissures), as this distinction strongly predicts neurodevelopmental outcome. 5
Prognostic Assessment
The vermian anatomy directly correlates with neurological outcome and guides counseling. 5
Favorable prognosis indicators:
- Vermis with preserved lobulation (two fissures, three lobes) despite being small and rotated 5
- Absence of additional brain malformations 5
- Normal intellectual development occurs in approximately 90% of these cases 5
Poor prognosis indicators:
- Severely dysplastic vermis with absent or single fissure only 5
- Associated brain malformations including corpus callosum agenesis, lissencephaly, polymicrogyria, or cortical dysplasia 3, 6, 5
- Mental retardation occurs in 100% of cases with severe vermian dysplasia and associated brain anomalies 5
Comprehensive Evaluation Protocol
Screen for associated brain malformations on MRI with diffusion-weighted imaging: 1, 3
- Corpus callosum dysgenesis or agenesis 4, 6
- Lissencephaly (particularly with TUBA1A mutations showing dysmorphic basal ganglia and brainstem) 7, 3
- Polymicrogyria 3
- Cobblestone malformations (Walker-Warburg syndrome, muscle-eye-brain disease) 7, 3
Initiate genetic evaluation immediately: 1, 3
- Chromosomal microarray analysis as first-tier testing 3
- If lissencephaly pattern present, test for chromosome 17p13.3 microdeletion (LIS1 locus) 8, 3
- Consider TUBA1A, DYNC1H1 mutations based on imaging patterns 3
- Karyotype analysis to exclude chromosomal abnormalities 1
Assess for systemic malformations: 3, 4
- Cardiology evaluation before any surgical intervention, as congenital heart disease occurs in multiple associated syndromes (22q11.2 deletion, Down syndrome, Noonan syndrome, Turner syndrome) 8, 3
- Renal ultrasound for structural anomalies 8, 3
- Ophthalmologic examination for ptosis, amblyopia, refractive errors, strabismus 8, 3
- Audiologic assessment for sensorineural hearing loss (up to 40% in syndromic cases) 8, 3
Surgical Management
Hydrocephalus is present in 91% of DWM patients at diagnosis and requires definitive treatment. 2, 9
Combined shunting of both the lateral ventricles and posterior fossa cyst is the superior initial surgical approach, achieving successful resolution of hydrocephalus and posterior fossa symptoms in 92% of cases. 2 This outperforms isolated lateral ventricle shunting, isolated cyst shunting, or posterior fossa craniectomy with membrane excision. 2
- Expect 96% of survivors to remain shunt-dependent long-term 2
- Monitor for shunt complications including infection, obstruction, and overdrainage 9
- CSF diversion improves symptoms of increased intracranial pressure, irritability, and allows for developmental progress 9
Developmental Management Framework
Establish a designated primary care medical home to coordinate preventive care, immunizations, and acute illness management, while neurology manages malformation-specific complications. 8, 3
Perform baseline developmental assessment in all children with DWM regardless of additional anomalies, with reassessment at regular intervals using standardized screening tools. 8, 1, 3 Developmental delay occurs in approximately one-third of children, with seizure risk significantly increased when additional brain abnormalities are present. 8, 2
Initiate early intervention services immediately upon identification of any developmental delays, as early treatment may improve outcomes. 8
Create a portable medical summary including diagnosis, current medications, emergency management plan, and all provider contact information. 8
Critical Pitfalls to Avoid
Do not confuse DWM with other posterior fossa cystic lesions: 4
- Mega cisterna magna shows intact cerebellum with extraaxial fluid collection posteroinferiorly 4
- Blake's pouch cyst demonstrates retrocerebellar fluid with midline communication to fourth ventricle but normal vermis 4
- Retrocerebellar arachnoid cysts compress cerebellar hemispheres and fourth ventricle rather than communicating with it 4
Do not rely on axial imaging alone—sagittal views are mandatory to accurately assess vermian anatomy and distinguish true DWM from mimics. 1, 5
Do not assume poor prognosis without detailed vermian morphology assessment and evaluation for associated brain malformations, as isolated DWM with preserved vermian lobulation has excellent neurodevelopmental outcomes. 5