Abstracts of poster sessions
Special morning lecture Normal pre-and postnatal brain development J. Barkovich, San Francisco, USA The central nervous system derives from the dorsal epiblast of the vertebrate embryo, and is induced by a combination of signals originating in the region of Hensen's node in the posterior margin of the early embryo 1 . After many steps, a neural tube is formed that subsequently develops a series of vesicles at its anterior (rostral) end. These three vesicles are designated the prosencephalon or
... orebrain (which soon divides into diencephalon and telencephalon), the mesencephalon (midbrain), and the rhombencephalon (hindbrain), which divides into the rostral metencephalon (pons and cerebellum) and caudal myelencephalon (medulla oblongata). This differentiation along the anteroposterior (AP) axis (also called the rostral-caudal axis) is called patterning, a name given to the early differentiation of the neural tube 2 . Patterning similarly occurs in the dorsal-ventral axis; these two orthogonal process result in the development of the protomap of the developing brain 3, 4 . From this point onward, the brain develops as a result of the establishment of germinal zones, where cells are generated, cell migration, development and navigation of neurites through the developing brain, establishment of synaptic connections among neurites, the development of sulci, and, finally, refinement of synaptic connections; this latter process continues throughout life. From an MRI perspective, we are most interested in brain development beginning at the middle of the second trimester, the time at which fetal MRI becomes diagnostic. The processes that can be evaluated by magnetic resonance techniques are 1 sulcation and myelination, which can be evaluated by MRI 5; 2 development of the cerebral microstructure (which loosely corresponds to development of white matter tracts, maturation of synapses, and organization of the cortex, best evaluated by diffusion tensor imaging 6-12; 3 maturation of cerebral chemistry (which is grossly evaluated by magnetic resonance proton spectroscopy 13-20; 4 maturation of cerebral blood flow (evaluated by perfusion CT and MR imaging, single photon emission computed tomography, and positron emission tomography 21, 22; and 5 maturation of glucose metabolism (best evaluated by fluorodeoxyglucose positron emission tomography 23, 24 . These processes, and their evaluation by various imaging techniques, will be discussed in this lecture, along with general concepts of brain maturation.