Myelination is a dynamic process that occurs during fetal life and goes on after birth in a well-defined, predetermined manner. On T1-weighted images, the pattern of myelination reaches the adult aspect at 1 year of age; on T2-weighted images, at about 2 years of age. On MR images, the last associative area to mature is considered to be the peritrigonal zone—a triangular region posterior and superior to the trigones of the lateral ventricles characterized by a persistent high signal intensity on T2-weighted images . Our MRI image of 5 year old child shows peritrigonal linear areas of hyperintensity that can be referred to perivascular spaces. According to Paper entitled "Terminal Zones of Myelination: MR Evaluation of Children Aged 20–40 Months" -- American Journal of Neuroradiology 23:1669-1673, November-December 2002, the so-called terminal zones are most likely subcortical areas rather than the peritrigonal area.
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