(957) Ventriculomegaly and choroid plexus asymmetry as first trimester markers of absent cavum septi pellucidi

We performed a retrospective review in a single consultative MFM practice to identify patients with absent cavum septi pellucidi for years 2018 through 2022. Patients with the Dandy-Walker continuum or holoprosencephaly were excluded. Patients with first trimester exams were evaluated for midbrain and falx diameter in the midsagittal plane, choroid plexus to lateral ventricular length in the axial plane, and choroid plexus symmetry in the axial plane.

Results:

Forty-one patients were identified with absent cavum septi pellucidi. Of these, twenty-eight had first trimester scans.  Eleven were excluded for holoprosencephaly or the Dandy-Walker continuum.  For the remaining seventeen, 6/17 (35.3%) had normal first-trimester imaging, 6/17 (35.3%) had abnormal axial views with normal mid-sagittal views, and 5/17 (29.4%) had an abnormal sagittal view or combined abnormal sagittal and axial views.  A novel finding was significant asymmetry of the choroid plexus related to frontal ventriculomegaly.

Conclusion:

This series confirms that extended mid-sagittal and axial views of the fetal brain at 11–13+6 weeks will identify abnormalities in the majority of fetuses destined to show abnormal cavum septi pellucidi.  The anatomic correlate appears to be first-trimester ventriculomegaly which will precede abnormal corpus callosal development.