Beyond Open Neural Tube Defects: Sagittal Landmarks at 11–14 Weeks in the Prediction of Second Trimester Posterior Fossa Abnormalities

Abstract

Abstract Background Objective assessment of posterior fossa landmarks such as the measurement of brain stem width or intracranial translucency have not been consistently shown to be predictive of future posterior fossa abnormalities, other than the Arnold–Chiari II malformation. Objective To study the association between the objective and subjective assessments of the posterior fossa landmarks at the 11–14 weeks’ scan and the posterior fossa abnormalities detected at the second-trimester anomaly scan. Methods Design—Blinded retrospective case–control study. Setting—Tertiary level multioperator fetal medicine center. Cases-fetuses with one of the second trimester diagnoses of posterior fossa abnormalities (Blake’s pouch cyst, mega cisterna magna, vermian agenesis, Dandy–Walker malformation, cerebellar hypoplasia) that had a 11–14 weeks’ examination at our center; Controls-fetuses with normal second trimester anatomy that had a 11–14 weeks’ examination at our center. Main outcome measures: measurements of the posterior fossa landmarks and subjective assessment of the landmarks. Results Significant inter-rater agreement existed for three out of four measurements of posterior fossa landmarks. No significant difference was noted in the measurements between cases and controls, in fetuses with measurable landmarks. Abnormal landmarks were more in cases than controls (brainstem OR 4.2 (95% CI 1.5–11.8); intracranial translucency OR 3.7 (95% CI 1.3–10.1); any landmark OR 3.1 (95% CI 1.2–7.9). Conclusion Abnormal posterior fossa landmarks at the 11–14 weeks’ examination is associated with threefold risk of posterior fossa malformation.