Neuroimaging Characteristics of Dandy-Walker Syndrome and Variant
Dandy-Walker syndrome (DWS) is characterized on neuroimaging by three classic features: hypoplasia or agenesis of the cerebellar vermis, cystic dilatation of the fourth ventricle, and enlargement of the posterior fossa with upward displacement of the torcula and transverse sinuses, while Dandy-Walker variant (DWV) shows milder abnormalities with partial vermian hypoplasia (particularly the posterior portion), less pronounced fourth ventricular dilatation, and minimal or absent posterior fossa enlargement. 1, 2
Classic Dandy-Walker Syndrome: Key Imaging Features
Primary Anatomic Hallmarks
- Complete or near-complete cerebellar vermian hypoplasia/agenesis with upward rotation of the remnant vermis 1, 3, 4
- Marked cystic dilatation of the fourth ventricle that communicates with a large posterior fossa cyst 1, 5
- Anterior-posterior enlargement of the posterior fossa with characteristic upward displacement of the torcula, transverse sinuses, and tentorium 4, 2
- Hydrocephalus is commonly present, with dilatation of the lateral and third ventricles, often showing trans-ependymal cerebrospinal fluid permeation 5
Associated Structural Abnormalities
- Compression and anterior displacement of the brainstem due to the enlarged posterior fossa cyst 5
- The cyst wall demonstrates a characteristic three-layer structure on pathological examination: external arachnoid layer, middle loose connective tissue layer, and internal ependymal cell layer 2
Additional Neurodevelopmental Anomalies
- Agenesis of the corpus callosum may be present as an associated malformation 2
- Cortical dysplasia can occur in some cases 2
- Lissencephaly has been reported in association with DWS 2
Dandy-Walker Variant: Distinguishing Features
Primary Differences from Classic DWS
- Partial hypoplasia of the cerebellar vermis, predominantly affecting the posterior portion rather than complete absence 2
- Mild to moderate fourth ventricular dilatation without the massive cystic expansion seen in classic DWS 2
- Minimal or no posterior fossa enlargement, distinguishing it from the marked expansion characteristic of classic syndrome 2
- Preservation of more normal cerebellar hemisphere architecture with less severe hypoplasia 2
Clinical-Radiological Correlation
- Milder brain abnormalities on imaging correlate with better clinical outcomes and may even be asymptomatic in some cases 2
- Absence of significant hydrocephalus is more common in DWV compared to classic DWS 2
- Fewer additional neurodevelopmental changes such as cortical dysplasia or corpus callosum abnormalities 2
Optimal Imaging Modality
MRI as Gold Standard
- MRI is the definitive imaging modality for diagnosing and distinguishing DWS from DWV, providing superior anatomic detail of posterior fossa structures 6, 1, 3
- CT imaging can identify the major structural abnormalities but is less sensitive for detailed assessment of cerebellar architecture and associated malformations 1, 5
Specific MRI Sequences
- T1 and T2-weighted sequences are essential for evaluating cerebellar vermian hypoplasia and cyst characteristics 3
- Sagittal views are particularly useful for assessing the degree of vermian hypoplasia and the relationship between the fourth ventricle and posterior fossa cyst 3
Critical Clinical Pitfalls
Timing of Diagnosis
- Prenatal or early infancy diagnosis is typical for classic DWS, while DWV may present later or remain asymptomatic 1, 2
- Delayed presentations can occur with atypical symptoms such as persistent vomiting, abdominal pain, and abnormal posturing rather than classic hydrocephalus symptoms 5
Associated Cardiac Anomalies
- Cardiac evaluation is essential at diagnosis, as cardiac defects occur in approximately 40% of DWS cases and require comprehensive assessment including echocardiography 7