Periventricular leukomalacia. a. Axial T1 MRI demonstrating mild to moderate white matter volume loss (left greater than right), ex vacuo dilatation of the ventricular system, and an undulated appearance of the ventricular margin with gliosis, all consistent with periventricular leukomalacia. b. Saggital T1 MRI reveals a thin corpus callosum (arrow), another feature of periventricular leukomalacia