title: Anatomical subgroup analysis of the MERIDIAN cohort: posterior fossa abnormalities.
abstract: OBJECTIVE
  To assess the diagnostic and clinical contribution of fetal magnetic resonance imaging (MRI) in fetuses of the MERIDIAN cohort diagnosed with abnormalities of the posterior fossa as the only intracranial abnormality recognized on antenatal ultrasound.
  
  
  METHODS
  This was a subgroup analysis of the MERIDIAN study of fetuses with abnormalities of the posterior fossa (with or without ventriculomegaly) diagnosed on antenatal ultrasound in women who had MRI within 2 weeks of ultrasound and for whom outcome reference data were available. The diagnostic accuracy of ultrasound and MRI is reported, as well as indicators of diagnostic confidence and effects on prognosis and clinical management. Appropriate diagnostic confidence was assessed by the score-based weighted average method, which combines diagnostic accuracy with diagnostic confidence data.
  
  
  RESULTS
  Abnormalities confined to the posterior fossa according to ultrasound were found in 81 fetuses (67 with parenchymal and 14 with cerebrospinal fluid-containing lesions). The overall diagnostic accuracy for detecting an isolated posterior fossa abnormality was 65.4% for ultrasound and 87.7% for MRI (difference, 22.3% (95% CI, 14.0-30.5%); P < 0.0001). There was an improvement in 'appropriate' diagnostic confidence, as assessed by the score-based weighted average method (P < 0.0001), and a three-fold reduction in 'high confidence but incorrect diagnosis' was achieved using MRI. Prognostic information given to the women changed after MRI in 44% of cases, and the overall effect of MRI on clinical management was considered to be 'significant', 'major' or 'decisive' in 35% of cases.
  
  
  CONCLUSIONS
  Our data suggest that any woman whose fetus has a posterior fossa abnormality as the only intracranial finding on ultrasound should have MRI for further evaluation. This is on the basis of improved diagnostic accuracy and confidence, which impacts substantially on the prognostic information given to women as well as their clinical management. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.
authors.affiliation: Academic Unit of Radiology, University of Sheffield and INSIGNEO Institute for in silico Medicine, University of Sheffield, Sheffield, UK.
authors.forename: P D
authors.initials: PD
authors.lastname: Griffiths
authors.affiliation: University Hospital Southampton NHS Foundation Trust, Southampton, UK.
authors.forename: K
authors.initials: K
authors.lastname: Brackley
authors.affiliation: Clinical Trials Research Unit, School of Health and Related Research, University of Sheffield, Sheffield, UK.
authors.forename: M
authors.initials: M
authors.lastname: Bradburn
authors.affiliation: Department of Radiology, Sheffield Children's Hospital and the Royal Hallamshire Hospital, Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, UK.
authors.forename: D J A
authors.initials: DJA
authors.lastname: Connolly
authors.affiliation: University Hospital Southampton NHS Foundation Trust, Southampton, UK.
authors.forename: M L
authors.initials: ML
authors.lastname: Gawne-Cain
authors.affiliation: Centre for Women's & Newborn Health, Institute of Metabolism & Systems Research, University of Birmingham and Fetal Medicine Centre, Birmingham Women's Foundation Trust (Birmingham Health Partners), Birmingham, UK.
authors.forename: M D
authors.initials: MD
authors.lastname: Kilby
authors.affiliation: Clinical Trials Research Unit, School of Health and Related Research, University of Sheffield, Sheffield, UK.
authors.forename: L
authors.initials: L
authors.lastname: Mandefield
authors.affiliation: Clinical Trials Research Unit, School of Health and Related Research, University of Sheffield, Sheffield, UK.
authors.forename: C
authors.identifier: http://orcid.org/0000-0002-3086-7348
authors.initials: C
authors.lastname: Mooney
authors.affiliation: Newcastle University, Newcastle upon Tyne, UK.
authors.forename: S C
authors.initials: SC
authors.lastname: Robson
authors.affiliation: Clinical and Experimental Sciences University of Southampton and Southampton Children's Hospital, University Hospital Southampton NHS Foundation Trust, Southampton, UK.
authors.forename: B
authors.initials: B
authors.lastname: Vollmer
authors.affiliation: Leeds Teaching Hospitals NHS Trust, Leeds, UK.
authors.forename: G
authors.initials: G
authors.lastname: Mason
mesh_terms: D000328:Adult; D003388:Cranial Fossa, Posterior / Q000002:abnormalities* / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D005260:Female; D005865:Gestational Age; D006801:Humans; D006849:Hydrocephalus / Q000175:diagnosis* / Q000473:pathology; D008279:Magnetic Resonance Imaging; D009421:Nervous System Malformations / Q000000981:diagnostic imaging* / Q000473:pathology; D011247:Pregnancy; D011379:Prognosis; D011446:Prospective Studies; D015203:Reproducibility of Results; D016216:Ultrasonography, Prenatal
keywords: Chiari II malformation; Dandy-Walker; cisterna magna; diagnostic accuracy; fetus; magnetic resonance imaging