PROGRESSION OF MYELINATION
Proximal pathways before distal (e.g., brainstem before supratentorial brain)
Sensory (visual and auditory) before motor
Central white matter before peripheral
Posterior before anterior
MYELINATED REGIONS AT BIRTH (OR SHORTLY AFTER BIRTH)
Inferior, superior cerebellar peduncles
Central portion of centrum semiovale
Posterior limb of internal capsule to cerebral peduncle
Optic nerve, chiasm, tract
|MYELINATION MILESTONES AFTER BIRTH (MONTHS)|
|T1-Weighted Image||T2-Weighted Image|
|3 months cerebellar white matter||6 months corpus callosum (splenium)|
|4 months corpus callosum (splenium)||8 months corpus callosum (genu)|
|6 months corpus callosum (genu)||11 months anterior limb internal capsule|
|14 months frontal white matter|
|Adapted from Barkovich AJ, Kjos BO, Jackson DE Jr, et al. Normal maturation of the brain in the neonatal and infant brain: MR imaging at 1.5T. Radiology 1988;166:173.|
- During the first 6 months of life, T1-weighted images are most useful for evaluating the progression of myelination . Inversion recovery images also provide improved T1-weighted contrast differences between tissues. The inherent tissue contrast depends on the inversion time selected. In the first year of life, inversion recovery images using an inversion time of 700 to 800 ms with a repetition time (TR) of 2,000 to 2,500 ms and an echo time (TE) of 15 ms can be substituted for the T1-weighted images. Myelinated regions will appear hyperintense to gray matter on these inversion recovery images.
- After 6 months of age, most cerebral white matter appears high in signal intensity on the T1-weighted images, and beyond this time the T2-weighted images are generally relied on to further evaluate myelin progression .
- By 24 months of age, the process of myelination is essentially complete except for the terminal zones of myelination found in the occipital-parietal periventricular white matter. These regions appear as subtle ill-defined areas of hyperintensity on the long TR images and should not be confused with periventricular leukomalacia and may persist into the fourth decade.