Neonate hippocampal volumes: prematurity, perinatal predictors, and 2-year outcome.

OBJECTIVE To compare preterm (PT) and full-term (FT) infant hippocampal volumes and to investigate the relations among PT hippocampal volume, perinatal risk factors, and neurodevelopmental outcome. METHODS A total of 184 PT and 32 full-term infants underwent magnetic resonance imaging at term equivalent age with manual segmentation of the hippocampi on coronal slices. Perinatal data were collected and 2-year neurodevelopment was evaluated with the Mental Development Index and Psychomotor Development Index on the Bayley Scales of Infant Development. RESULTS PT and FT infant hippocampi did not significantly differ after controlling for head size, and percentage reductions in PT hippocampi (3.4%) were less than for cortical (7%) and deep nuclear gray matter (13%), and total brain tissue volume (4.7%). PT hippocampal volumes were significantly lower in infants with moderate-to-severe white matter injury (p < 0.001), exposure to postnatal steroids (right, p = 0.001; left, p = 0.008), and indomethacin treatment (right, p = 0.01; left, p = 0.03). PT infant hippocampal volumes correlated with the Mental (p < 0.001) and Psychomotor Development Indices (right, p = 0.001; left, p = 0.002) after correcting for head size and sex, but remained significant only for the Mental Development Index and left hippocampi (p = 0.04) after additionally adjusting for white matter injury and steroids. INTERPRETATION Hippocampal volumes were reduced in PT infants exposed to several perinatal events but were preserved in PT infants without these exposures. Smaller PT hippocampal volumes were indirectly associated with delayed development at 2 years.