Assessment of the corpus callosum at 20-24 weeks' gestation by three-dimensional ultrasound examination.

OBJECTIVES To determine the range of positions of the fetal head in which a three-dimensional (3D) volume is acquired for subsequent successful imaging of the corpus callosum. METHODS We used 3D volumes of the fetal head obtained from singleton pregnancies at 20 to 23 + 6 weeks' gestation. The volumes, which had been acquired with the head in different positions, were then reconstructed with the objective of obtaining a mid-sagittal section of the brain to demonstrate the presence of the corpus callosum. RESULTS In the reconstructed mid-sagittal sections it was possible to demonstrate the corpus callosum in at least 90% of cases when the 3D volume acquisition plane was (1) mid-sagittal with the angle between the transducer and the direction of the fetal nose ranging from 0 degrees to 179 degrees and from 330 degrees to 359 degrees , (2) oblique around the crown-rump axis with an angle from the mid-sagittal plane of less than 30 degrees , (3) oblique around the anteroposterior axis from the axial plane at the level of the biparietal diameter to the mid-sagittal plane or (4) axial at the level of the biparietal diameter with an angle between the transducer and the midline echo of the brain of 60-119 degrees . In the mid-sagittal sections either the translucent corpus callosum or a comma-shaped echogenic structure was seen depending on whether the plane of volume acquisition was sagittal or axial. CONCLUSIONS In 3D ultrasound examination the extent to which the corpus callosum can be demonstrated to be present is entirely dependent on the plane of volume acquisition.