Brain MRI and DTI at 2 years of age. (A) Axial T1-weighted images reveal microcephaly with simplified cortical gyration and underdevelopment of the frontal lobes. Note the inward deformation of the lateral walls of the trigones (arrows). (B) Sagittal T2-weighted image shows pontine hypoplasia and dysmorphic corpus callosum with enlarged splenium (arrowheads). (C) Corresponding axial fractional anisotropy (FA)-weighted colour directional maps confirm the disproportion between the genu (arrow) and the splenium (empty arrow) of the corpus callosum. Note the presence of abnormally thickened fiber bundles with superior-to-inferior direction, located between the optic radiations and the lateral ventricles (arrowheads). The fibers are color-coded by direction: red is left-to-right (and vice versa), green is anterior-to-posterior (and vice versa), blue is superior-to-inferior (and vice versa). (D) DTT, oblique view, shows the course of the splenium of the corpus callosum superimposed on sagittal and axial T1-weighted images fused with FA-weighted colour directional map. The inward deformation of the lateral walls of the trigones is due to an abnormally thick tapetum. The tapetum is made of fibers of the corpus callosum connecting the inferior temporal lobes.