Metachromatic leukodystrophy - bilateral symmetrical confluent areas of periventricular deep white matter signal change, in particular around the atria and frontal horns with sparing of subcortical U fibers leading to a "butterfly pattern". Progression can lead to cortical and subcortical atrophy.
Fibrous dysplasia (FD) is a non-neoplastic tumour-like congenital process, manifested as a localised defect in osteoblastic differentiation and maturation, with replacement of normal bone with large fibrous stroma and islands of immature woven bone. Fibrous dysplasia is found predominantly in children and young adults, with ~75% of patients presenting before the age of 30 years. Upto 25% occurs in the face and skull. http://radiopaedia.org/articles/fibrous-dysplasia