One of the most difficult aspects of pediatric neuroimaging is the dynamic appearance of the infant brain because of its ongoing maturation. Therefore, it is critical to be familiar with the normal patterns of sulcation and myelination of a developing child's brain before attempting to interpret the neuroimaging study of a newborn or infant (Table 7). Children suffering from developmental delay and congenital malformations may display abnormally shallow and underdeveloped cortical sulci and an immature pattern of myelination. A term infant, at approximately 38 to 40 weeks gestational age, should have a nearly normal adult sulcal pattern. Myelination of a child's brain is best assessed using both T1- and T2-weighted transaxial images. T1-WI are more useful in the first 6 months of life, whereas T2-WI are more informative between 6 and 18 months of age. Maturation of white matter is reflected by T1 hyperintensity and T2 hypointensity relative to gray matter. By approximately 2 years of age, maturation of white matter is essentially complete except for that in the "terminal zones" (centrum semiovale, subcortical frontal and parietal white matter). When evaluating premature infants, it is important to have an accurate record of the postconceptional age at birth. For example, a 4-week-old neonate born at 30 weeks gestational age has a corrected age of 34 weeks, and is still expected to have a premature pattern of myelination and sulcation compared to that of a term infant.
Table 7. Milestones for normal myelination on MRI
Age for Term Infant fT1 SI (Myelin formation) JT2 SI (Myelin compaction)
Birth-2 months Posterior limb of internal Posterior portion of PLIC
capsule (PLIC) Middle cerebellar peduncle Middle cerebellar peduncle
2-4 months Anterior limb of internal capsule (ALIC) Splenium of corpus callosum Cerebral white matter Centrum semiovale
4-6 months Genu of corpus callosum
Central frontal and occipital white matter
Splenium of corpus callosum Anterior portion of PLIC
Genu of corpus callosum ALIC
Central frontal white matter Peripheral occipital white matter
Peripheral frontal white matter f = increased; J = decreased; SI = signal intensity
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