Fetal Hippocampal Development: Analysis by Magnetic Resonance Imaging Volumetry

The hippocampal formation plays an important role in learning and memory, however data on its development in utero in humans is limited. This study was performed to evaluate hippocampal development in healthy fetuses using 3D reconstructed magnetic resonance imaging (MRI). A cohort of 20 healthy pregnant women underwent prenatal MRI at a median gestational age of 24.9 weeks (range 21.3-31.9 weeks); 6 of the women also had a second fetal MRI performed at a 6 week interval. Routine 2D ultrafast T2-weighted images were used to reconstruct a 3D volume image, which was then used to manually segment the right and left hippocampi. Total hippocampal volume was calculated for each subject and compared against gestational age. There was a linear increase in total hippocampal volume with increasing gestational age (P<0.001). For subjects scanned twice, there was an increase in hippocampal size on the second fetal MRI (P=0.0004). This represents the first volumetric study of fetal hippocampal development in vivo. This normative volumetric data will be helpful for future comparison studies of suspected developmental abnormalities of hippocampal structure and function.