Enlarged Cisterna Magna and the Dandy- Walker Malformation: Factors Associated With Chromosome Abnormalities

Thirty-three fetuses with an enlarged cisterna magna (10 mm or more) were evaluated to determine factors that might be associated with an underlying chromosome abnormality. Eighteen fetuses (55%) proved to have a chromosome abnormality, including trisomy 18 or trisomy 18 variant (12), trisomy 13 (three), Turner syndrome (one), or other rearrangements (two). Among various risk factors analyzed, the absence of ventricular dilatation correlated most strongly with a chromosome abnormality. Chromosome abnormalities were found in 17 of 22 fetuses (77%) lacking ventricular dilatation, compared with only one of 11 fetuses (9%) with ventricular dilatation (P