Hippocampal rotation is associated with ventricular atrial size.

Background: Fetal ventriculomegaly is a source of apprehension for expectant parents and may present prognostic uncertainty for physicians. Accurate prenatal counseling requires knowledge of its cause and associated findings as the differential diagnosis is broad. We have observed an association between ventriculomegaly and incomplete hippocampal inversion.

Objective: To determine whether ventricular size is related to incomplete hippocampal inversion.

Materials And Methods: We retrospectively evaluated pre- and postnatal brain MRIs in normal subjects (mean GA, 31 weeks; mean postnatal age, 27 days) and patients with isolated ventriculomegaly (mean GA, 31 weeks; mean postnatal age, 68 days) at a single academic medical center. Lateral ventricular diameter, multiple qualitative and quantitative markers of hippocampal inversion, and evidence of intraventricular hemorrhage were documented.

Results: Incomplete hippocampal inversion and ventricular size were associated in both normal subjects (n=51) and patients with ventriculomegaly (n=32) (P<0.05). Severe ventriculomegaly was significantly associated with adverse clinical outcome in postnatal (P=0.02) but not prenatal (P=0.43) groups. In all additional cases of isolated ventriculomegaly, clinical outcome was normal over the time of assessment (mean 1±1.9 years; range 0.01 to 10 years).

Conclusion: Lateral ventricular atrial diameter and incomplete hippocampal inversion are associated. Less hippocampal inversion correlates with larger atria. For every 1-mm increase in fetal ventricular size, the odds of incomplete hippocampal inversion occurring increases by a factor of 1.6 in normal controls and 1.4 in patients with ventriculomegaly.