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Dandy-Walker Continuum

• Dandy-Walker (DW) spectrum (DWS), DW complex (DWC), "classic" DW malformation (DWM)
• Hypoplastic vermis with rotation (HVR), formerly DW variant (DWV)
• Persistent Blake pouch cyst (BPC), mega cisterna magna (MCM)

• DWS represents heterogeneous spectrum of cystic posterior fossa (PF) malformations

Diagnostic criteria
• "Classic" dandy-walker malformation 
○ Cystic dilatation of 4th ventricle → enlarged posterior fossa
○ Vermis hypoplastic, rotated superiorly

• Hypoplastic vermis with rotation (HVR)
○ Variable vermian hypoplasia
○ posterior fossa /brainstem normal-sized
○ No or small cyst, "keyhole" vallecula

• Persistent Blake pouch cyst (BPC)
○ "Open" 4th ventricle communicates with cyst
○ Fastigial recess, primary fissure, PF/brainstem normal

•  mega cisterna magna (MCM)
○ Enlarged pericerebellar cisterns communicate with basal subarachnoid spaces

Occipital bone may appear scalloped/remodeled with all DWS types (including MCM)

Routine MR imaging (thin sagittal views crucial)
DWM: Large PF with small, counterclockwise (CCW) rotated vermis
HVR, BPC: Failure of "closure" of 4th ventricle
DWS (from most to least severe) – 4th ventriculocele (10-15% of cases)

Best imaging tool
○ MR best characterizes severity, associated anomalies

Protocol advice
○ Routine MR imaging (thin sagittal views crucial)

• Many associated syndromes, mimics

Image Interpretation Pearls
• Presence of fastigium/vermian lobulation predicts cognitive outcome
• Thin sagittal views crucial for delineation, diagnosis

Reporting Tips
• Is fastigium/vermian lobulation normal?

• Most severe to mildest: DWM with 4th ventriculocele → classic DWM → HVR → BPC → MCM
• Numerous syndromes associated with DWS

• Marked heterogeneity in genetic, clinical findings
• DWM: 80% diagnosed by 1 year

Imaging gallery

Sagittal graphic of classic Dandy-Walker malformation shows an enlarged posterior fossa, elevated torcular herophili , superior rotation of hypoplastic cerebellar vermis , an overexpanded 4th ventricle with a thin wall , and a dilated ventricle (hydrocephalus). 

Sagittal T2WI MR DWS shows a hypoplastic, rotated vermis , lack of fastigial crease, and incomplete vermian lobulation of the posterior lobules beyond the primary fissure . The cyst wall is faintly seen .

Sagittal MRV demonstrates torcular lambdoid inversion. The transverse sinuses st angle upward toward the torcular  as the cyst has prevented normal fetal torcular descent. Note the persistent fetal occipital sinus . 

Coronal T2WI MR demonstrates a huge, fluid filled posterior fossa. Again, notice that the transverse sinuses  are angled upward toward the torcular herophili .

 Sagittal T2WI MR in a patient with DWM demonstrates hydrocephalus, a large posterior fossa, cephalad rotation of a small, incompletely lobulated vermis with a very shallow fastigial crease , and a very thin cyst wall . 

Sagittal T2WI MR in HVR shows ventriculomegaly , patent aqueduct with prominent flow void , and a large posterior fossa. There is no torcularlambdoid inversion.

Sagittal bSSFP demonstrates ventriculomegaly in a patient with open inferior 4th ventricle. There is cyst wall visualization inferiorly. The posteriorly displaced choroid plexus suggests Blake pouch cyst. Fastigial recess, primary fissure, and vermian lobulation are intact. 

Sagittal bSSFP shows a closed inferior 4th ventricle with acquired Chiari 1 . The primary fissure  and the vermis are compressed by the wall of the retrocerebellar cyst.

Axial T2WI MR in a patient with DWM reveals relative hypoplasia of the cerebellar hemispheres and nonvisualization of the vermis at its usual location. There is a focal calvarial  defect at the site of a prior occipital encephalocele. 

Coronal 3D surface reconstruction of the brain (viewed from the inferoposterior aspect) from T1 gradient-echo sequence shows the typical elevation of the tentorium and separation of the cerebellar hemispheres  without intervening vermis.

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