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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. [ABSTRACT FROM AUTHOR]

Objective: To assess the contribution of fetal magnetic resonance imaging (MRI) in fetuses of the MERIDIAN cohort diagnosed with ventriculomegaly (VM) as the only abnormal intracranial finding on antenatal ultrasound.Methods: This was a subgroup analysis of the MERIDIAN study of fetuses with only VM diagnosed on ultrasound in women who had a subsequent MRI examination within 2 weeks and for whom outcome reference data were available. The diagnostic accuracy of ultrasound and MRI was reported in relation to the severity of VM. The difference in measurements of trigone size on the two imaging methods and the clinical impact of adding MRI to the diagnostic pathway were also studied.Results: In 306 fetuses with VM, ultrasound failed to detect 31 additional brain abnormalities, having an overall diagnostic accuracy of 89.9% for ultrasound, whilst MRI correctly detected 27 of the additional brain abnormalities, having a diagnostic accuracy of 98.7% (P < 0.0001). There were other brain abnormalities in 14/244 fetuses with mild VM on ultrasound (diagnostic accuracy, 94.3%) and MRI correctly diagnosed 12 of these (diagnostic accuracy, 99.2%; P = 0.0005). There was a close agreement between the size of trigones measured on ultrasound and on MRI, with categorical differences in only 16% of cases, showing that MRI did not systematically overestimate or underestimate trigone size. Complete prognostic data were available in 295/306 fetuses and the prognosis category changed after MRI in 69/295 (23.4%) cases. The overall effect of MRI on clinical management was considered to be 'significant', 'major' or 'decisive' in 76/295 (25.8%) cases.Conclusion: Our data suggest that a woman carrying a fetus with VM as the only intracranial finding on ultrasound should be offered an adjuvant investigation by MRI for further evaluation. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]