Axial T2 (A-D), midsagittal T1 (E-H), and right parasagittal T1 (I-L) sequences obtained at 3 months (A, E, I), 13 months (B,F, J), 26 months (C,G, K), and 6 years (D, H, L) of age. The initial MRI at 3 months demonstrates mild lateral ventriculomegaly and delayed myelination for age, best appreciated as absence of posterior limb of the internal capsule myelination despite presence of optic radiation myelination (A). Mild cerebellar fissure widening is also appreciated in I. By 13 months, rudimentary white matter myelination has occurred centrally on T1 weighted imaging in the corpus callosum (F) and periventricular white matter (J). However, myelination remains profoundly delayed, and the corpus callosum has not thickened as expected, now falling below the third percentile for age. By 26 months of age, the myelination within the optic radiations on T2 weighted imaging (C) and the central white matter on T1 weighted imaging (G,K) has become more robust. However, there is no appreciable progression in anatomic extent and the overall myelination remains markedly delayed. On the subsequent MRIs, no further myelination has occurred allowing differences in MRI field strength as shown on the MRI performed at 6 years of age (D, H, L). Hypoplasia of the corpus callosum, widening of the cerebellar fissures, and lateral ventriculomegaly persist without change though the foramen Magendie has grown more patulous over time potentially indicating subtle volume loss (E-H). Posterior limb of the internal capsule (A-D): white arrow (solid stem). Corpus callosum (E-H): white arrow (dashed stem). Periventricular white matter (I-L): white arrowheads. Widened cerebellar fissures (I-L): dashed circle. Widened foramen Magendie (H): asterisk.