Usually diagnosed between 2 and 30 years of age

Most commonly an asymptomatic, incidental finding

Sometimes activity-related pain with larger lesions in weight-bearing bones

Diaphyseal or metadiaphyseal, central

Elongated lesion, aligned with longitudinal axis of long bones

Distribution: femur, 35% to 40%; tibia, 20%; skull and facial bones, 10% to 25%; ribs, 10%; uncommon sites—hands and feet, spine, clavicle

Typically geographic lysis, may have sclerotic rim (monostotic lesions)

Expansile remodeling in some cases

Broad endosteal scalloping and diffuse cortical thinning

Fibrous or fibro-osseous

Woven bone in marrow creates a “ground glass” appearance

Fibrous dysplasia in distal ulna demonstrating central, diaphyseal location and ground glass matrix ( left ).

Expansile remodeling and cortical thinning are seen in a humerus lesion ( right ).

In this tibial lesion, fibrous dysplasia extends from the metaphysis into diaphysis ( left ). Note also the long extent of cortical thinning.

The margin can have a prominent rind of sclerosis (type IA margin), as seen on this tomogram of a lesion in the intertrochanteric femur ( right ).

Fibrous dysplasia in a rib typically appears elongated ( arrows ), as seen in this expansile lesion with ground glass matrix ( left ).

Increased radionuclide uptake on bone scan reflects increased matrix turnover ( right ). The elongated shape of fibrous dysplasia is a pattern not typically seen in neoplasms or fractures ( arrows ).