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.
Keywords
Intracranial translucency - Posterior fossa - 11–14 weeks - First-trimester anatomy
- Early pregnancy anomaly scan
