Fibrous dysplasia (FD) is a non-neoplastic tumor-like congenital process, manifested as a localized 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.

Typical CT features ( as shown in this case ) are:

• ground-glass appearance to bone
• homogeneously sclerotic bone
• well-defined borders ( abrupt transition )
• expansion of the bone, with overlying cortical bone intact

It may be a mono-ostotic or poly-ostotic disease and in some cases is part of a syndrome such as McCune-Albright.