The exact origin of the Dandy walker malformation is unknown. Insults of varying severity to both the developing cerebellar hemispheres & 4th ventricle ae currently thought tobe the causative factor.
Posterior fossa cyst malformation have been divided in to
- Dandy walker malformation
- Dandy Walker variant
- Mega cisterna magna
- Posterior fossa arachnoid cysts.
Clinical issues related to Dandy walker malformation.
- Antenatal ultrasound must detect this malformation if clearly evident.
- Patient presents with postnatal progressive enlargement of head.
- Postnatal investigation & diagnosis is important to relieve patient from progressive hydrocephalus & asses cognitive ,motor function by detecting the degree of involvement of cerebellum & associated anomalies like corpus callosal agenesis or dysgenesis with or without migrational anomalies with grey matter hetertopias,clefts ,polymicrogiria, agyria,occipital encephalocele.
IMAGING-
Ultrsound is the earliest screening investigation .Antenatal ultrasound can detect vermian , cerebellar hypoplasia & posterior fossa cystic dilation.
Postnatal ultrasound will detect degree of hydrcephalus & associated anomalies.
NECT-
-Large posterior fossa.
-High tentorial insertion s/o Lambdoid torucular inversion.
- high transverse sinuses.
MRI- Best modality
- To detect vermian, cerebellar hypoplasia
- Brainstem hypoplasia
- Heterotopias & cerebellar dysplasias
- Colpocephaly & corpus callosalagenesis & other abnormalities of brain.
D/D-
Mega cysterna magna .
posterior fossa arachnoid cyst.
Rx
VP shunting of hydrocephalus.