Fetal Dandy-Walker malformation complicated by late third-trimester unilateral intraventricular hemorrahage

Dandy-Walker malformation accounts for approximately 5% to 10% of congenital hydrocephalus cases and consists of 3 major abnormalities: cystic dilatation of the fourth ventricle, complete or partial agenesis of the cerebellar vermis, and hydrocephalus. It appears that the development of this condition is primarily a delay or total failure of the foramen of Magendie to open, allowing a buildup of cerebrospinal fluid with development of the cystic dilatation of the fourth ventricle. Dandy-Walker malformation has been reported in a wide variety of syndromes, including various mendelian disorders, chromosome abnormalities (trisomies 9, 13, 18, and 21, triploidy, and others), and antenatal exposure to teratogens (rubella, cytomegalovirus, toxoplasmosis, warfarin sodium, alcohol, isotretinoin, and maternal diabetes). Associated structural anomalies, which may occur in between 69% and 75% of cases, include intracranial abnormalities (agenesis of the corpus callosum and defects of neuronal migration), congenital cardiac disease (atrial and ventricular septal defects, atrioventricular canal defect, and pulmonary stenosis), renal anomalies, facial clefts, and syndactyly. We present an unusual case in which Dandy-Walker malformation was diagnosed ultrasonographically in a fetus at 34 weeks' gestation, who subsequently had a large unilateral intraventricular hemorrhage and marked neonatal thrombocytopenia after cesarean delivery. The association of an antepartum intraventricular hemorrhage in a fetus with Dandy-Walker malformation is unusual and may be worthy of further investigation.