• brain development
• fetal brain
• white matter

The advent of diffusion tensor imaging (DTI) in addition to cadaveric brain dissection allowed a comprehensive description of an adult human brain. Nonetheless, the knowledge of the development of the internal architecture of the brain is mostly incomplete. Our study aimed to provide a description of the anatomical variations of the major associational bundles, among fetal and early post-natal periods with the aid of Klingler’s dissection, DWI-DTI MRI, and histological Nissl staining. Seventeen formalin-fixed fetal human brains were enrolled for sulci analysis and MRI anaylsis, and thirteen specimens were dissected under the operating microscope, using Klinger’s technique. Furthermore, ten additional brains were used for histological staining. Although fronto-temporal connections could be observed in all stages of development, a distinction between the uncinate fascicle, and the inferior fronto-occipital fascicle was clear starting from the early preterm period (25-35 post conceptional week). Similarly, we were consistently able to isolate the periatrial white matter that forms the sagittal stratum (SS) in the adults, with no clear distinction among SS layers. Arcuate fascicle and superior longitudinal fascicle were isolated only at the late stage of development without a reliable description of their entire course. The results of our study demonstrated that, although white matter is mostly unmyelinated among fetal human brains, cadaveric dissection can be performed with consistent results. On the other hand, MRI analysis could not be performed with standard 3T MRI machine, underlying the importance of customized MRI coils to obtain reliable results with fetal brains. Furthermore, the stepwise development of the associational fiber tracts strengthens the hypothesis that anatomy and function run in parallel, and higher is the cognitive functions subserved by an anatomical structure, later the development of the fascicle