title: Systematic review and meta-analysis of isolated posterior fossa malformations on prenatal ultrasound imaging (part 1): nomenclature, diagnostic accuracy and associated anomalies.
abstract: OBJECTIVE
  To explore the outcome in fetuses with prenatal diagnosis of posterior fossa anomalies apparently isolated on ultrasound imaging.
  
  
  METHODS
  MEDLINE and EMBASE were searched electronically utilizing combinations of relevant medical subject headings for 'posterior fossa' and 'outcome'. The posterior fossa anomalies analyzed were Dandy-Walker malformation (DWM), mega cisterna magna (MCM), Blake's pouch cyst (BPC) and vermian hypoplasia (VH). The outcomes observed were rate of chromosomal abnormalities, additional anomalies detected at prenatal magnetic resonance imaging (MRI), additional anomalies detected at postnatal imaging and concordance between prenatal and postnatal diagnoses. Only isolated cases of posterior fossa anomalies - defined as having no cerebral or extracerebral additional anomalies detected on ultrasound examination - were included in the analysis. Quality assessment of the included studies was performed using the Newcastle-Ottawa Scale for cohort studies. We used meta-analyses of proportions to combine data and fixed- or random-effects models according to the heterogeneity of the results.
  
  
  RESULTS
  Twenty-two studies including 531 fetuses with posterior fossa anomalies were included in this systematic review. The prevalence of chromosomal abnormalities in fetuses with isolated DWM was 16.3% (95% CI, 8.7-25.7%). The prevalence of additional central nervous system (CNS) abnormalities that were missed at ultrasound examination and detected only at prenatal MRI was 13.7% (95% CI, 0.2-42.6%), and the prevalence of additional CNS anomalies that were missed at prenatal imaging and detected only after birth was 18.2% (95% CI, 6.2-34.6%). Prenatal diagnosis was not confirmed after birth in 28.2% (95% CI, 8.5-53.9%) of cases. MCM was not significantly associated with additional anomalies detected at prenatal MRI or detected after birth. Prenatal diagnosis was not confirmed postnatally in 7.1% (95% CI, 2.3-14.5%) of cases. The rate of chromosomal anomalies in fetuses with isolated BPC was 5.2% (95% CI, 0.9-12.7%) and there was no associated CNS anomaly detected at prenatal MRI or only after birth. Prenatal diagnosis of BPC was not confirmed after birth in 9.8% (95% CI, 2.9-20.1%) of cases. The rate of chromosomal anomalies in fetuses with isolated VH was 6.5% (95% CI, 0.8-17.1%) and there were no additional anomalies detected at prenatal MRI (0% (95% CI, 0.0-45.9%)). The proportions of cerebral anomalies detected only after birth was 14.2% (95% CI, 2.9-31.9%). Prenatal diagnosis was not confirmed after birth in 32.4% (95% CI, 18.3-48.4%) of cases.
  
  
  CONCLUSIONS
  DWM apparently isolated on ultrasound imaging is a condition with a high risk for chromosomal and associated structural anomalies. Isolated MCM and BPC have a low risk for aneuploidy or associated structural anomalies. The small number of cases with isolated VH prevents robust conclusions regarding their management from being drawn. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
authors.affiliation: Fetal Medicine Unit, Division of Developmental Sciences, St George's University of London, London, UK.
authors.forename: F
authors.initials: F
authors.lastname: D'Antonio
authors.affiliation: Fetal Medicine Unit, Division of Developmental Sciences, St George's University of London, London, UK.
authors.forename: A
authors.initials: A
authors.lastname: Khalil
authors.affiliation: Hôpital d'Enfants Armand-Trousseau - Service de Radiologie, Cedex 12, Paris, France.
authors.forename: C
authors.initials: C
authors.lastname: Garel
authors.affiliation: Department of Obstetrics and Gynecology, Sant'Orsola-Malpighi Hospital, University of Bologna, Bologna, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Pilu
authors.affiliation: Department of Obstetrics and Gynecology, Università di Roma, Tor Vergata, Rome, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Rizzo
authors.affiliation: Fetal Neurology Clinic and Paediatric Neurology Unit, Wolfson Medical Center, Holon, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: T
authors.initials: T
authors.lastname: Lerman-Sagie
authors.affiliation: Fetal Medicine Unit, Division of Developmental Sciences, St George's University of London, London, UK.
authors.forename: A
authors.initials: A
authors.lastname: Bhide
authors.affiliation: Fetal Medicine Unit, Division of Developmental Sciences, St George's University of London, London, UK.
authors.forename: B
authors.initials: B
authors.lastname: Thilaganathan
authors.affiliation: Department of Medicine and Aging Sciences, University of Chieti-Pescara, and EMISAC, CeSI Biotech, Chieti, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Manzoli
authors.affiliation: Fetal Medicine Unit, Division of Developmental Sciences, St George's University of London, London, UK.
authors.forename: A T
authors.initials: AT
authors.lastname: Papageorghiou
mesh_terms: D002869:Chromosome Aberrations; D003388:Cranial Fossa, Posterior / Q000002:abnormalities* / Q000000981:diagnostic imaging*; D003616:Dandy-Walker Syndrome / Q000000981:diagnostic imaging / Q000235:genetics; D005260:Female; D005865:Gestational Age; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D009421:Nervous System Malformations / Q000000981:diagnostic imaging* / Q000235:genetics / Q000473:pathology; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods; D016216:Ultrasonography, Prenatal / Q000379:methods*
keywords: Blake's pouch cyst; Dandy-Walker malformation; mega cisterna magna; posterior fossa; vermian hypoplasia