The atria of the fetal lateral ventricles: a sonographic study of normal atrial size and choroid plexus volume.

OBJECTIVE: Evaluation of the cerebral ventricular system is a routine part of all fetal sonographic examinations. Ventriculomegaly and decreased choroid volume are indicators of poor fetal outcome, so it is important to know the normal variation of these parameters. The present study describes the normal size of the fetal lateral ventricular atrium and the normal amount of choroid plexus within the atrium during the second and third trimesters. SUBJECTS AND METHODS: Six hundred eight consecutive, healthy, singleton fetuses from 13 to 42 weeks' menstrual age were examined prospectively. The atrium of the lateral ventricle was measured in the axial and coronal planes. For each axial measurement, the width of the choroid plexus was determined. RESULTS: An axial atrial measurement was obtained in 88% of the fetuses, and a coronal atrial measurement was obtained in 84%. The mean measurement and one standard deviation are 6.5 +/- 1.5 mm in the axial plane and 6.6 +/- 1.5 mm in the coronal plane. Ninety-eight percent of all measured atria were at least 60% filled by choroid plexus, and in all cases the atria were at least 50% filled. Complete filling by choroid plexus occurred in 58% of cases. CONCLUSION: This large prospective study confirms previous observations of mean atrial size. However, four standard deviations above the mean is 12 mm, suggesting currently used cutoffs for normal atrial size are too low. Other parameters, such as choroid plexus filling, may be helpful markers of normalcy in fetuses with atrial measurements between 8 and 12 mm.