Diagnosis
Dandy-Walker malformation.
Findings
Sagittal, axial, and coronal T2-weighted imaged demonstrate marked
enlargement of the posterior fossa with cerebellar (particularly
vermian) hypoplasia and a large posterior fossa cyst that
communicates with the fouth ventricle. Associated hypogenesis of
the corpus callosum and hydrocephalus of the lateral ventricles are
also present.
Discussion
Dandy-walker malformation represents a developmental abnormality of
ventral induction, resulting in hypoplasia of the cerebellar
vermis. The diagnosis can be made by fetal or neonatal ultrasound
or MRI, with findings includinig cerebellar hypoplasia and a large
posterior fossa that communicates with the fourth ventricle. The
term "torcular-lamdoid inversion" has been used as a buzzword to
describe the abnormal elevation of the straight sinus and torcular
associated with Dandy-Walker malformation. Other abnormalities are
common, including other CNS abnormalities (hydrocephalus,
proliferation and migrational abnormalities, and agenesis of the
corpus callosum), chromosomal anomolies, and varoius congenital
sydromes. Note hydrocephalus and dysgenesis of the corpus callosum
in this case. The differential diagnosis for a posterior fossa cyst
includes Dandy-Walker malformation, Dandy-Walker variant, mega
cisterna magna, and arachnoid cyst. Dandy-Walker variant represents
a milder form of vermian hypoplasia with no significant enlargement
of the fourth ventricle or torcular-lamdoid inversion. This disease
is less commonly associated with other abnormalities, with a
minority possessing concomitant hydrocephalus, heterotopia, or
dysgenesis of the corpus callosum. Mega cysterna magna represents a
normal variant in which there is prominence of the retrocerebellar
space in the setting of a normal cerebellar vermis and fourth
vetricle, with minimal or no enlargement of the posterior fossa.
Associated hydrocephalus or other supratentorial anomoly is
uncommon. Note that it can be difficult to distiguish a mega
cisterna magna from an arachnoid cyst.
Grossman, Robert I. Yousem, David M. The Requisites:
Neuroradiology. Mosby, Philadelphia, 2003.