Altered hippocampal morphometry in infants born very preterm

Preliminary evidence suggests individuals born very-premature have smaller hippocampi on MRI when compared to term-born controls. Moreover, these volumetric reductions have been associated with various cognitive deficits. The hippocampus undergoes an intense period of postnatal volumetric growth during the first year of life. However, this period of development has only been characterized in post-mortem studies. Although volume gain has been previously delineated, changes in hippocampal shape remain undescribed during this unique period. The objective of this study was to characterize and compare morphometric development between very-preterm born infant and healthy controls throughout the first year of life using multivariate tensor-based morphometry (mTBM). We segmented left and right hippocampi from 133 T1-weighted images acquired from 20 very-preterm infants and 67 term-born controls between at birth or term-equivalent age and 12 months of age. MRI were performed on a 3 Tesla scanner at 3-month intervals (i.e., term-equivalence, 3, 6, 9, 12 months) We used mTBM to compare shape between groups at each time-point. We found that subregions of the hippocampus including the dentate gyms, CA2, CA3 and subiculum were morphometrically different, especially at term-equivalence age. Morphometric differences were less prominent at 3 and 6 months but reappeared at 9 and 12 months, particularly in the left hippocampus. Although hippocampal shape differences between very-preterm and healthy term-born infants seem to decrease during the first 6 months of life, atypical shape development reappeared at 9-12 months which likely highlights altered periods of morphologic development. Future long-term studies will inform if these developmental differences continue to increase or disappear in subsequent years.