title: Enlarged posterior fossa on prenatal imaging: differential diagnosis, associated anomalies and postnatal outcome.
abstract: BACKGROUND
  The primary aim of this study was to ascertain the prevalence of the individual conditions and of associated anomalies in fetuses with the prenatal diagnosis of enlarged posterior fossa (PF) and to explore the diagnostic accuracy of ultrasound in these anomalies. The secondary aim was to evaluate the postnatal outcome of children affected by PF anomalies.
  
  
  METHODS
  All fetuses with enlarged PF detected by prenatal sonography at a referral center from 2001 to 2015 were analyzed retrospectively. Some were also studied by fetal magnetic resonance imaging (MRI) or volume ultrasound examinations. Fetal sonographic and MRI were compared using following classification: Dandy-Walker malformation (DWM); megacisterna magna (MCM); Blake's pouch cyst; isolated vermian hypoplasia; vermian agenesis; PF arachnoid cyst (AC); and cerebellar hypoplasia (CH).
  
  
  RESULTS
  The ultrasound diagnoses of the 69 fetuses were as follows: MCM (n = 29; of these isolated n = 15), DWM (n = 28, isolated n = 4), vermian hypoplasia (n = 5, isolated n = 4), Blake's pouch cyst (n = 4, isolated n = 1), CH (n = 2; none isolated) and AC in the PF (n = 1, isolated). Thirteen of the 41 karyotyped fetuses were aneuploid, including seven with DWM. Associated malformations were found in 37/69 cases. There were 39 live births, including 11 with confirmed DWM, six of whom show a normal development. Twelve infants with isolated MCM show normal development. There were eight false-positive prenatal diagnoses (or resolution until birth) of "enlarged PF": three with Blake's pouch cyst, two with MCM and one with vermian hypoplasia.
  
  
  CONCLUSIONS
  An enlarged PF requires specific diagnoses for the best possible counseling. The term "Dandy-Walker variant" should not be used anymore. Isolated MCM and Blake's pouch cyst can either resolve or be normal variants, but may also indicate the presence of a more severe anomaly or associated malformations.
authors.affiliation: Department of Obstetrics and Gynecology, Inselspital, University of Bern, Bern, Switzerland.
authors.forename: Anja
authors.initials: A
authors.lastname: Wüest
authors.affiliation: Department of Obstetrics and Gynecology, Inselspital, University of Bern, Bern, Switzerland.
authors.forename: Daniel
authors.identifier: http://orcid.org/0000-0001-7705-1584
authors.initials: D
authors.lastname: Surbek
authors.affiliation: Institute of Diagnostic and Interventional Neuroradiology, Inselspital, University of Bern, Bern, Switzerland.
authors.forename: Roland
authors.initials: R
authors.lastname: Wiest
authors.affiliation: Institute of Diagnostic and Interventional Neuroradiology, Inselspital, University of Bern, Bern, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Weisstanner
authors.affiliation: Institute of Diagnostic and Interventional Neuroradiology, Inselspital, University of Bern, Bern, Switzerland.
authors.forename: Harald
authors.initials: H
authors.lastname: Bonel
authors.affiliation: Division of Pediatric Neurology, Inselspital, University of Bern, Bern, Switzerland.
authors.forename: Maja
authors.initials: M
authors.lastname: Steinlin
authors.affiliation: Department of Obstetrics and Gynecology, Inselspital, University of Bern, Bern, Switzerland.
authors.forename: Luigi
authors.identifier: http://orcid.org/0000-0003-3957-3810
authors.initials: L
authors.lastname: Raio
authors.affiliation: Prenatal Zürich, Zürich, Switzerland.|Medical Faculty, Heinrich Heine University, Düsseldorf, Germany.
authors.forename: Boris
authors.identifier: http://orcid.org/0000-0002-8442-3865
authors.initials: B
authors.lastname: Tutschek
mesh_terms: D016080:Arachnoid Cysts / Q000000981:diagnostic imaging / Q000196:embryology / Q000453:epidemiology*; D003388:Cranial Fossa, Posterior / Q000002:abnormalities / Q000000981:diagnostic imaging* / Q000196:embryology; D003616:Dandy-Walker Syndrome / Q000000981:diagnostic imaging / Q000196:embryology / Q000453:epidemiology*; D003937:Diagnosis, Differential; D005260:Female; D005865:Gestational Age; D006801:Humans; D008279:Magnetic Resonance Imaging; D011247:Pregnancy; D011256:Pregnancy Outcome; D011296:Prenatal Diagnosis; D012189:Retrospective Studies; D013557:Switzerland / Q000453:epidemiology
keywords: Dandy-Walker malformation; Ultrasound; magnetic resonance imaging; megacisterna magna; prenatal diagnosis