Dandy-Walker Malformation (DWM)
Diagnostic Criteria
- Classic DWM diagnosis requires:
- Vermian hypoplasia (underdeveloped cerebellar vermis).
- Enlarged posterior fossa.
- Elevation of tentorium cerebelli and torcular Herophili.
- Cystic dilation of the fourth ventricle.
- Hydrocephalus is common (~85% by 1 year):
- Considered a complication, not essential for diagnosis.
- May have delayed presentation.
Pathogenesis
- Fundamental defect in rhombencephalic roof development.
- Mechanism:
- Failure of anterior membranous area (AMA) integration into developing vermis.
- Possible delayed or failed opening of posterior membranous area (PMA) foramina.
- Redundant AMA expands due to CSF pulsations → posterior fossa cyst formation and enlargement.
Neuropathology
- Vermis lobules present but significantly hypoplastic or dysplastic, especially inferior lobules.
- Vermian development arrests around 12 weeks post-conception (p/c).
- Hypo/dysplasia severity gradient (superior → inferior) due to decreased influence of the isthmic organiser with increasing distance.
- Affected structures originate from the rhombic lip (rhombomere 1).
- Relatively normal development of primary ventricular neuroepithelium derivatives:
- Purkinje cells
- Deep cerebellar nuclei
Clinical Prognosis
- Highly variable outcomes, largely dependent on:
- Extent of vermian hypo/dysplasia.
- Presence of associated cerebral or extracerebral anomalies.
- When anomaly confined to posterior fossa:
- Primary prognostic factor: integrity of vermian lobulation.
- Size of cyst or posterior fossa enlargement is not prognostic.
- Intellectual impairment:
- Seen in approximately 50% of patients.
- Directly correlated with disturbances in vermis lobulation.
Management Approaches
- Generally conservative unless complicated by:
- Significant hydrocephalus.
- Compression from posterior fossa cyst.
- Traditional treatment for hydrocephalus:
- Ventriculoperitoneal shunt (VP shunt).
- Alternative approaches:
- Endoscopic third ventriculostomy + choroid plexus cauterisation (ETV+CPC).
- Cyst-peritoneal shunts.
- Placement of stents connecting third ventricle and posterior fossa cyst.