Terminal Zones of Myelination

Myelination progresses in an orderly fashion in the brain, from caudal to rostral, from dorsal to ventral, and from central to peripheral. Normal children between under 2 years of age have areas of persistent T2 hyperintensity in the peritrigonal region, "a triangular region posterior and superior to the trigones of the lateral ventricles." This peritrigonal region is also known as the "terminal" zone of myelination, with the thought that these are the last to myelinate. However, it seems that subcortical T2 hyperintensity in the frontotemporal lobes persists even longer, with myelination in these areas complete by 3 years of age.

References

Parazzini C, Baldoli C, Scotti G, Triulzi F. Terminal zones of myelination: MR evaluation of children aged 20-40 months. AJNR Am J Neuroradiol. 2002 Nov-Dec;23(10):1669-73.