Abbreviations
• 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)
Definitions
• 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)
Consider
• 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?
PATHOLOGY
• Most severe to mildest: DWM with 4th ventriculocele → classic DWM → HVR → BPC → MCM
• Numerous syndromes associated with DWS
CLINICAL ISSUES
• Marked heterogeneity in genetic, clinical findings
• DWM: 80% diagnosed by 1 year
Imaging gallery
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 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.