This is one of several overgrowth syndromes. It is a generally a benign disease of bone that is characterised by the replacement of normal bone with tissue similar to scar (fibrous) tissue. It can involve one or more sites and is typically noted at around 10 years of age. It can present as simple facial swelling, and can progress to gross asymmetry with overgrowth of the craniofacial skeleton. Surgery can be performed to remodel this overgrowth or even to prevent blindness.