Dandy Walker malformation

Findings

There is a large fourth ventricle which appears to be in continuation with a large posterior fossa cyst which follows CSF signal.

Differential Diagnosis:
- Arachnoid cyst
- Dandy walker variant
- Dandy walker malformation


Diagnosis: Dandy Walker malformation


Key points

Classic triad makes up the Dandy-Walker malformation
- Vermian agenesis
- Communicating with an enlarged 4th ventricle
- Posterior fossa enlargement

Dandy-Walker malformation may be isolated or can occur with other malformations of the brain.

Associated CNS abnormalities include
- Agenesis of the corpus callosum
- Lipomas
- Aqueductal stenosis
- Microcephaly
- Encephalocele

The Dandy Walker Spectrum represents a broad spectrum of cystic posterior fossa malformations.

These include (from most severe to least severe):
- 4th ventriculocele: DWM in which large posterior fossa cyst erodes occipital bone causing posterior outpouching of the cyst (encephalocele) through the occipital bone
- "Classic" Dandy Walker Malformation: Cystic dilatation of the 4th ventricle which opens dorsally to a variable sized CSF cyst which causes an enlarged posterior fossa and superiorly rotated hypoplastic vermian remnant; hydrocephalus is common
- Dandy Walker Variant: 4th ventricle opens to a smaller posterior cyst with partial rotation of the vermis, variable vermian hypoplasia; normal sized posterior fossa
- Persistent Blake Pouch Cyst: Open 4th ventricle communicates with persistent cyst that fails to regress and obliterates basal cisterns; normal vermis
- Mega Cisterna Magna: Enlarged cisterna magna, 4th ventricle is closed; normal vermis

DWM commonly presents with macrocephaly and bulging fontanel, 80% are diagnosed by 1 year of age. Early death is common.
Etiology is from hindbrain development arrest. No 4th ventricle outlet foramina are formed.
Associated with other CNS/extracranial abnormalities two-thirds of the time, such as craniofacial, cardiac and urinary tract abnormalities, polydactyly, orthopedic, and respiratory abnormalities
Treatment includes CSF diversion of hydrocephalus with VP shunt