Radiology, Vol 193, 761-763, Copyright © 1994 by Radiological Society of North America
Closure of the cerebellar vermis: evaluation with second trimester US
B Bromley, AS Nadel, S Pauker, JA Estroff and BR Benacerraf
Department of Obstetrics and Gynecology, Massachusetts General Hospital, Boston.
PURPOSE: To evaluate with sonography the normal development of the fetal
cerebellum in the second trimester. MATERIALS AND METHODS: The study
included all patients undergoing second trimester genetic amniocentesis who
had structurally normal fetuses, in whom the posterior fossa was adequately
seen and in whom the karyotype was later determined to be normal. Views of
the cerebellum were obtained prospectively, and the inferior vermis was
determined to be open or closed at the time of the initial scan. Follow-up
was obtained by means of subsequent scans and review of the pediatric
record. RESULTS: Of 897 fetuses that met the inclusion criteria, 147 had an
open vermis at initial scanning. At 14 weeks gestation, 56% of fetuses had
an open vermis, decreasing to 23% at 15 weeks and 6% at 17 weeks. In utero
follow-up sonograms were obtained in 79% of fetuses with an initially open
vermis and demonstrated closure in all but one fetus. The remaining 21%,
without sonographic follow-up, were normal as newborns. CONCLUSION: The
prenatal diagnosis of Dandy-Walker variant should not be made before 18
weeks gestation because the development of the cerebellar vermis may be
incomplete at that time.
