Development of fetal cerebral cortex: assessment of the folding conditions with post-mortem magnetic resonance imaging.

Quantitative data of fetal cortical folding and its developmental changes supply important information in the estimation of fetal age and assessment of brain maturation, so the increasing tendencies of cortical growth and its folding conditions at the beginning of the second and third trimesters with post-mortem Magnetic Resonance Imaging (MRI) were analyzed. 131 fetal specimens of 14-40 weeks gestational age (GA) were selected and scanned with 3.0 T MR. Then the length of folded cortical margin (LFCM) and length of unfolded cortical margin (LUCM) were measured by Photoshop and ZoomMagic software. Degrees of cortical folding (DCF) were calculated by means of (LFCM-LUCM)/LFCM. Growth curves were obtained between the 3 above values and GA, and significant differences in age stages, hemispheres and genders were analyzed. The relationship between LFCM in centimeters, DCF and GA in weeks was described by two exponential growth curves [LFCM=5.325 exp(0.079GA); DCF=11.890 exp(0.043GA)]. The curves increased rapidly after 26 weeks GA, which could be recognized as a cut-off point of fetal cortical and sulcal development. LUCM and GA were described by a logarithmic growth curve which slowed down after 26 weeks GA [LUCM=30.580 Ln(GA)-72.490]. Significant differences of the 3 values before and after 26 weeks GA (p<0.01), but not any in hemispheres and genders were noticed. These results, which may be valuable in assessing normal brain development and can serve as a model in clinical settings, indicate that the cerebral volume first increases and is then followed by increases of the surface area.