MR-IMAGING OF THE DEVELOPING HUMAN BRAIN .2. POSTNATAL-DEVELOPMENT

In vivo magnetic resonance (MR) images of the brain in neonates and in fants up to 24 months of age were retrospectively studied to evaluate normal maturation patterns in the brain. Sequential changes in myelina tion of various brain structures and development of the corpus callosu m were noted. At birth and for the first 4-6 months of life, signal in tensities of gray and white matter are the reverse of those seen in an adult brain, with the signal intensity of white matter being lower th an that of gray matter on T1-weighted images and higher than that of g ray matter on T2-weighted images. With advancing age, white matter sho ws a progressive increase in signal intensity on T1-weighted images. O n T2-weighted images, high-signal-intensity unmyelinated white matter progressively changes to myelinated white matter of a signal intensity lower than that of gray matter. At birth, the corpus callosum is isoi ntense relative to white matter and progressively increases in signal intensity, so that at age 8 months the corpus callosum has an appearan ce identical to that of an adult. Familiarity with the temporal sequen ce of normal myelination as seen with MR imaging is helpful in the dia gnosis of pathologic processes involving white matter.