Myelinated brain versus nonmyelinated brain on MRI
How does myelinated brain differ from nonmyelinated brain on an infant magnetic resonance imaging (MRI) examination? Where does one expect to see myelinization occur first?
Myelinated brain white matter, as in adults, appears hyperintense relative to gray matter on T1-weighted MR images and hypointense on T2-weighted images. In nonmyelinated brain, this pattern is reversed. Myelinization of the infant brain occurs in a predictable pattern, beginning in the brainstem and cerebellum and progressing to the posterior limb of the internal capsule, optic pathways, and parietal lobes. This pattern of change occurs from caudal to cephalad, dorsal to ventral, and central to peripheral. Myelinization should appear complete on MRI by 24 months but may be incomplete in the terminal zones up to approximately 4 to 5 years of age and in rare cases until the first decade of life.