Fibrous Dysplasia

• Etiology unknown

• Most common 3-15 years

• Fundamental abnormality is replacement of medullary bone by fibrous tissue

• Clinically

• Deformities

• Shepherd’s crook deformity of femur

• Bone pain

• Most commonly involved bones are pelvis, femora

• In widespread disease, the skull and jaw are almost always involved

• Imaging

• Endosteal scalloping

• Cortical thinning

• Ground-glass appearance

• May have matrix calcification

• Prone to fracture

• Growth of lesions usually stops when epiphyses close

• DDX:

• Brown tumor

• Unicameral bone cyst

• Albright’s Syndrome

• Polyostotic

• Sexual precocity

• Skin pigmentation

• Almost always in a female

• Polyostotic form is usually bilateral

Fibrous Dysplasia. There are expansile, geographic, lytic lesions in the shafts of the 3rd metacarpal and proximal phalanx of the middle finger (red arrows). They have a characteristic "ground-glass" appearance to their internal matrices. Enchondromas can have a similar appearance though their internal matrix would be more coarse, resembling rings and arcs.

Fibrous Dysplasia. There are expansile, geographic, lytic lesions in the shaft of the humerus (white arrows) with endosteal scalloping and cortical thinning. The arm is bowed (red arrow). The matrix has a ground-glass appearance to it.