Background The growing incidence of prematurely born children and the improvement of survival rates have been associated with highly problematic long term neurodevelopmental outcomes. Brain structural alterations associated with these mainly cognitive difficulties most likely involve cortical organization. This study presents new ways of assessing structural organization of the cortex through thickness measurements.

Subjects/methods Preterm infants (N=42, GA 28.7±3.1 wks) were scanned at 6 years of age using the 3T MRI scanner. High-resolution 3D T1 MRI images were analyzed using MNI tools (http://www.bic.mni.mcgill.ca/~alan/lab.html). IUGR preterm subjects (N=14) were identified by abnormal antenatal Doppler measurements and mean birth weights below10^th percentile. Cortical thickness was computed between extracted cortical surfaces and analyzed using the SurfStat tools (http://www.math.mcgill.ca/keith/surfstat/).

Results GA at birth within all subjects showed positive correlation with cortical thickness measurements (bilateral precuneus, right medial temporal gyrus, right cuneus, left inferior parietal lobule and left parieto-occipital arcus) at 6 years. The effect of preterm birth in the right junction of paracentral lobule and the precuneus and in the right transverse temporal gyrus shows statistically significant differences between groups (p=0.001, positively correlated with thickness at 6 years in the IUGR group and negatively correlated in the non-IUGR group).

Discussion/conclusion Our results indicate that the regional structural reorganization of cerebral cortex after preterm birth differs in IUGR and non-IUGR subjects. Preterm birth affects the higher order association areas with increased thickness or less thinning in IUGR than non-IUGR born children. These cortical changes might underlay the specific functional deficits observed in these children.