Prenatal diagnosis of Dandy-Walker malformation: report of a case.

Dandy-Walker malformation is one of the major causes of congenital hydrocephalus. We report on a case that was diagnosed by sonography in a fetus at 34 weeks' gestation. The diagnosis was confirmed by postnatal computed tomographic (CT) brain scan and magnetic resonance imaging (MRI). The prenatal sonographic findings were a large posterior fossa in communication with the fourth ventricle, a small and splayed cerebellar hemisphere and marked degrees of ventriculomegaly. The postnatal CT scan images were similar to the prenatal sonography. The hypoplasia of the cerebellar vermis and the associated hypogenesis of the corpus callosum can only be clearly delineated by MRI. Dandy-Walker malformation is one form of the Dandy-Walker complex and cystic malformations of the posterior fossa. It should be differentiated from Dandy-Walker variant, or mega-cisterna magna, and arachnoid cyst. Dandy-Walker complex may be associated with chromosomal, intracranial and extracranial abnormalities. Early in utero detection is useful for detailed evaluation of associated anomalies. Obstetric management depends on gestational age, karyotype abnormality and associated intracranial and extracranial anomalies. In the present report, the infant presented no progressive ventriculomegaly and no surgery was required. The infant developed normally.